Translocation of endangered black abalone (Haliotis cracherodii) as a population restoration tool

Conservation translocations are an essential tool for species restoration but come with inherent risks that require careful consideration. However, accelerating ecological change lends urgency to minimizing delays in restoring populations, biodiversity, and ecosystem function. The endangered black abalone (Haliotis cracherodii) is a large marine gastropod in eastern Pacific rocky intertidal ecosystems ranging from California, USA to Mexico that was decimated by disease in the 1980s-1990s. Natural recovery has been hindered by density-dependent reproduction. This study presents the first planned conservation translocation of black abalone, facilitated by a broad-scale, decades-long, monitoring program (Multi-Agency Rocky Intertidal Network, MARINe). Existing MARINe partnerships facilitated collaboration among agency, academic, non-profit, and for-profit partners to move the translocation effort forward quickly and efficiently. In 2023, 246 abalone were translocated in two phases from a recovering population on The Nature Conservancy (TNC) preserve on Santa Cruz Island to TNC’s protected Jack and Laura Dangermond Preserve into areas where critical habitat was restored. Lessons learned in Phase 1 were applied to Phase 2 including refined collection protocols and injury prevention/assessment. Survivorship during the translocations (from collection to field release) was very high, with a mortality rate of just 1.6%. Monitoring of abalone indicated a retention rate of more than 80% three years post-translocation, assuming no crypsis (translocated survivors not found during monitoring). However, post-release retention was likely closer to 100% when adjusted using the most conservative crypsis rates from prior abalone translocations. Post-translocation movement of abalone was higher than expected, but a high level of fidelity was associated with areas where habitat had been restored. The presence of juvenile black abalone provides encouraging evidence of recent recruitment at the restoration site, although genetic parentage analyses are needed to determine origin of juveniles. Three years in, our results demonstrate early signs of success through high retention of translocated abalone and increased local population density to a level capable of supporting larval production. This effort underscores the importance of protected areas as living laboratories and demonstrates how cross-sector collaborations can safely accelerate the pace and scale of endangered species recovery.

Accelerating ecological change due to habitat loss and degradation, biological invasions, disease, over-harvest, and climate change has resulted in a global need for species restoration (e.g. Carlton et al., 1999; Díaz et al., 2019; Dirzo et al., 2014; Harvell et al., 2004; Nagelkerken and Connell, 2015; Seddon et al., 2014; Swan et al., 2016). Key to these efforts are conservation translocations, the human-mediated movement of organisms from one location to another for a conservation benefit (Soorae, 2018). While conservation translocations have the potential to restore populations and associated ecosystems, they come with inherent risks, including disruption of local population genetic structure, spread of disease, impact to donor populations, injury to or death of translocated individuals, and unintended ecological impacts (IUCN/SSC, 2013). Consequently, every translocation effort must include a thorough assessment of potential negative impacts, and project design should aim to reduce risk wherever possible (Pérez et al., 2012; IUCN/SSC, 2013). Despite these concerns, translocation is often the only viable approach for restoring a population, and the likelihood of a positive outcome can far outweigh the risks (Novak et al., 2021). Although successful conservation translocations have been well documented for diverse taxa (Soorae, 2025), terrestrial efforts, such as the reintroduction of gray wolves (Ripple and Beschta, 2012), are more prevalent than those in marine systems. However, accelerating impacts to marine systems has heightened the need for species restoration and translocations of marine species are becoming increasingly common as researchers apply terrestrial-vetted approaches to marine ecosystems (Swan et al., 2016).

The critically endangered black abalone (Haliotis cracherodii, Leach 1814; Figure 1) is a species for which translocation has been identified as a key (and currently only) restoration tool (NMFS, 2020). These large marine gastropods are vital components of healthy rocky intertidal and shallow subtidal systems on the west coast of North America ranging from Point Arena, California, USA to Bahia Tortugas, Baja California, Mexico (NMFS, 2020; Morris et al., 1980). As the only common abalone species in the region residing primarily in the intertidal zone (Cox, 1962), it holds deep cultural and economic significance, supporting thousands of years of subsistence harvest for California coastal Tribes and, more recently, recreational and commercial fisheries (Erlandson et al., 2009; Rick et al., 2005). Because of this importance, the black abalone is a focal species for the Multi-Agency Rocky Intertidal Network (MARINe), which has monitored populations since the early 1980’s (NMFS, 2020).

In the 1980s and 1990s mass mortality events swept across most of the species’ range, resulting in declines in excess of 95% in many areas (Lafferty and Kuris, 1993; Raimondi et al., 2002). The culprit was “withering syndrome” (WS), a disease caused by the bacterium Candidatus Xenohaliotis californiensis (Friedman et al., 2000; Neuman et al., 2010). Population crashes and ensuing recruitment failure (Miner et al., 2006) led to the listing of black abalone as endangered under the U.S. Endangered Species Act in 2009 (NMFS, 2009). In 2020, the National Marine Fisheries Service (NMFS) published the Final Black Abalone Recovery Plan, which outlines specific metrics to assess population status at local and broad scales, and identifies actions needed to recover the species, including restoring populations not meeting recovery criteria (NMFS, 2020).

The threat of WS appears to have lessened in recent years, with evidence of potential genetic resistance to the disease (Brokordt et al., 2017; Crosson et al., 2014; Friedman et al., 2014), as well as the discovery of a bacteriophage that is thought to lessen the lethality of the WS pathogen (Friedman and Crosson, 2012; Friedman et al., 2014). However, in many areas, black abalone remain locally extirpated or persist at very low densities 30–40 years post-WS decline (NMFS, 2020; Multi-Agency Rocky Intertidal Network (MARINe) et al., 2020). Several recently identified threats are further contributing to black abalone loss and inhibiting natural recovery. These threats include burial of animals and critical habitat by coastal sedimentation events (e.g., landslides, debris flows) that are becoming increasingly common with climate change (Bell and Raimondi, 2020; Bragg et al., 2026; Hapke and Green, 2006), illegal harvest (NMFS, 2020), habitat loss from sea level rise (Moritsch et al, 2026), and habitat degradation due to encroachment by other species. Loss of black abalone from the ecosystem enabled other organisms to colonize preferred habitat, consisting of intertidal rocky reef crevices dominated by bare substrate and algal crusts (Miner et al., 2006). More recently, mussels have encroached into these spaces, likely due to a decline in the mussels’ primary predator, ochre sea stars, following a sea star wasting disease outbreak in 2013-2014 (Miner et al., 2018; Moritsch and Raimondi, 2018; Gerraty et al., 2026). These community shifts reduced the amount of habitat available for black abalone, as well as for crustose coralline algae, which have been shown to induce larval settlement in other abalone species (Morse et al., 1979) and serve as a food source for juveniles (Leighton and Boolootian, 1963).

Natural recovery is further hindered by the black abalone’s mode of reproduction, termed “broadcast spawning”, in which gametes are released into the water column where fertilization occurs. For this to be successful, individuals must be densely aggregated, but populations decimated by disease are often too sparse to reproduce. Research suggests that when adult densities fall below 1/m 2, recruitment failure can occur (Miner et al., 2006). A compounding factor is the species’ short pelagic larval duration, with localized dispersal under typical oceanographic conditions (Chambers et al., 2006; NMFS, 2020; McShane, 1992). Consequently, natural recruitment and local population recovery has largely been limited to a few geographic regions with adult densities that exceed the critical threshold (Kenner, 2021; Whitaker, 2022; Multi-Agency Rocky Intertidal Network (MARINe) et al., 2020). Populations along the southern California mainland notably remain at densities far below that required for successful reproduction or natural recovery. To meet federal delisting requirements conservationists must manually reestablish self-sustaining, dense populations throughout the species’ historic range (NMFS, 2020).

Although the NMFS Recovery Plan (2020) identified translocation as a key restoration tool, this approach has long been hindered by significant regulatory and logistical hurdles. As noted, translocating wild animals involves risks that must be weighed against the benefit of success. However, new insights gained through research and chance opportunities have tipped the risk to benefit scale. Concern about unintentional spread of disease has been tempered by widespread presence of both the WS pathogen and its mitigating bacteriophage throughout the species’ range, even in regions where populations have been asymptomatic for the disease (Wooldridge et al., 2024). It is hypothesized that some level of disease resistance combined with the bacteriophage (Friedman et al., 2014) might explain the absence of black abalone decline during recent marine heat wave events (Multi-Agency Rocky Intertidal Network (MARINe) et al., 2020), which were historically linked to sharp population declines (Raimondi et al., 2002). Another major barrier was the lack of donor animals; because black abalone have never been successfully reared in captivity, any translocation effort must rely on sourcing individuals from wild populations. Recent recovery of black abalone populations at a handful of locations on the California Channel Islands (Kenner, 2021; Neuman et al., 2010; Whitaker, 2022) provided populations with sufficient densities to collect animals with minimal impact to donor populations. Furthermore, population genetics research revealed low genetic structure and maintenance of high genetic diversity among populations throughout California (Wooldridge et al., 2024), thus reducing concerns about disrupting local genetic structure. Finally, two coastal sedimentation events provided emergency “test cases” to refine safe removal and translocation methods, demonstrating that black abalone could be moved without substantial injury or death (Bell and Raimondi, 2020; Bragg et al., 2026).

The work above, in combination with several decades of MARINe long-term monitoring data, laid the groundwork for a black abalone conservation translocation effort, following the 2015 Refugio Beach Oil Spill (RBOS). Although oiling coverage was patchy, the spill impacted an estimated 35 km of rocky shoreline, potentially affecting dozens of black abalone and vast swaths of critical habitat (Raimondi et al., 2019; RBOS Trustees, 2021). As part of the RBOS Damage Assessment and Restoration Plan, funding was allocated to support a translocation project on The Nature Conservancy’s (TNC) Jack and Laura Dangermond Preserve (hereafter, Dangermond Preserve; TNC, 2017), just west of the spill’s footprint. This site was ideal due to its historical (pre-WS) record of a large black abalone population (Raimondi et al., 2002), high-quality habitat, restricted public access within a terrestrial Preserve (preventing habitat impact and illegal take), protection within a “no take” State Marine Reserve, and proximity to a healthy donor population on a nearby TNC Preserve on Santa Cruz Island. In addition, support from TNC in the form of site access, personnel support, and financial contributions will allow longer-term monitoring (than would be supported by RBOS funding alone) to assess lasting success metrics.

This effort marked the first planned population reinforcement for the species, aligning closely with IUCN/SSC (2013) guidelines. Gauging success for a translocation effort involving an endangered species can be measured using a hierarchy of success criteria. These include implementation success (collection, transport, and release with acceptable survival and minimal impact to donor populations), establishment success (persistent adult densities above reproductive thresholds), recruitment success (demonstrated larval recruitment and survival of juveniles), and recovery success (a self-sustaining population contributing to regional recovery). Here, we present results demonstrating successful implementation and refinement of black abalone translocation techniques, and early evidence of establishment and recruitment success, with high retention and population reinforcement to densities high enough to maintain local population viability. We also evaluate habitat quality preference by translocated animals based on retention rates. Ultimately, by maintaining densities above the critical threshold, this project aims to establish a self-sustaining population that serves as a local larval source to repopulate neighboring areas. Results will advance the pace, scale, and success of future black abalone recovery efforts, and, more broadly, inform decisions surrounding the efficacy and role of conservation translocations in restoring endangered species and ecosystems worldwide.

Site-wide population and habitat characterization of restoration site

Black abalone habitat assessment surveys

Selection of both restoration and donor sites was based on data from MARINe Abalone Habitat Assessment (AHA) surveys, which have been conducted throughout the species range from 2007 to present and are designed to characterize black abalone critical habitat and provide population density estimates. Here we describe a version of the AHA surveys used range-wide for areas with low abalone densities but note that in areas with high densities we apply a subsampling approach to estimate population size (see “Selection of Donor Sites” below and Engle et al., 2026 for full description). At each AHA survey site, a predetermined starting point was chosen by examining shoreline habitat maps for appropriate habitat and either a) randomly selecting a start point within a given section of coastline in Geographic Information System (GIS; preferred approach), or b) selecting a start point that could be accessed from land (many areas have limited access to the shoreline). From this starting point, abalone and habitat quality were surveyed within continuous segments of rocky intertidal habitat that were demarcated by natural features (e.g., channels, headlands), changes in the physical characteristics (e.g., change of wave exposure, rock type), or areas of habitat not suitable for black abalone (e.g., sandy beaches). Segments varied in length, ranging from tens to hundreds of meters alongshore depending on the morphology of the coastline and the density of black abalone. Within each segment, we recorded the following information: 1) the number of abalone found, 2) the size of each abalone (to the nearest 5 mm for animals <35 mm and to the nearest 10 mm for animals >35 mm), 3) the habitat quality of each animal’s immediate location (Good, Moderate, Poor; Table 1), and 4) the segment-wide proportion of Good, Moderate, and Poor habitat. For each segment the estimated proportions of Good, Moderate, and Poor habitat summed to one.

The start and end points of each segment were photographed, and the high and low intertidal zone boundaries were marked with a “high” and “low” Global Positioning System (GPS) waypoint (i.e., high start, low start, high end, low end). Segment waypoints were used to map polygons of each survey segment in GIS. A GPS “track” was recorded during the survey to help with mapping large survey segments. Where feasible and permitted, survey segments were also imaged and mapped using Uncrewed Aerial Vehicle (UAV, i.e. drone) flights, which complement on-the-ground surveys by providing additional documentation and more accurate mapping of habitat surveyed than the method described above. Segment polygons were used to calculate area and linear extent of the habitat surveyed.

Habitat-based densities were calculated using the following equation, where density (D) in a given habitat type i equals the number of abalone found (N) in the habitat type i divided by the product of the survey area (A) and the proportion (P) of the area estimated to be a given habitat type i:

This approach has been successfully used for over 20 years to assess black abalone densities and quality of Endangered Species Act designated critical habitat throughout the species’ range (e.g., Raimondi et al., 2012, 2019). These assessments were key for informing recovery criteria and actions in the Black Abalone Recovery Plan, such as habitat availability, habitat-based densities of abalone, and extent of historic range currently occupied (NMFS, 2020).

Restoration site characterization

The Nature Conservancy’s (TNC) Dangermond Preserve in Santa Barbara County, CA was selected as an ideal location for this first-ever conservation translocation effort because of its protection from public access, land manager support, abundant suitable habitat, and long-term (30+ year) black abalone population data showing high pre-WS densities, severe WS-induced loss, and subsequent lack of recovery (Supplementary Figure 1). In February 2022, we conducted a site-wide population and habitat characterization survey spanning 440 linear meters of shoreline (11,719 m 2 of habitat) using the AHA methods described above. Rocky reef habitat within the site was delineated into five segments and boundaries were recorded using GPS. Segment polygons were mapped in GIS and the proportion of Good, Moderate, and Poor habitat was calculated for each segment, which was then used to determine black abalone density by habitat category. Two segments containing extensive rocky reef habitat were selected for the translocation effort. We designated these the West Block (at the western edge of the site) and the East Block (eastern edge of the site).

Plot selection and habitat restoration

Within both the West and East Blocks we selected 10 distinct crevices consisting largely of Good black abalone habitat to serve as translocation or habitat restoration only (hereafter “restoration”) plots. Plot type was assigned using a stratified random approach by pairing neighboring plots and then randomly designating one as “translocation”, in which habitat restoration and translocation of abalone would occur and the other as “restoration”, in which only habitat restoration would be done, resulting in five translocation plots and five restoration plots within each of the two blocks. True control plots, where neither habitat restoration nor abalone translocation occurred were not established due to limited availability of contiguous Good crevice habitat (fragmented Good habitat was present throughout site). Plot boundaries were permanently marked with stainless steel screws drilled into the substrate, and plot locations were mapped and photographed. Plot lengths ranged from 1.45 m to 5 m (mean = 2.8, SD = 1.1) and plot areas ranged from 0.57 m 2 to 4.8 m 2 (mean = 1.45, SD = 1.16). Plot area was calculated by multiplying crevice length by mean depth; if suitable habitat occurred on both the crevice top and bottom the estimated area was doubled. The estimated total area within translocation plots was used to determine the number of translocated abalone needed to achieve densities of at least 3 abalone/m 2. This density was chosen based on the finding by Miner et al. (2006) that natural recruitment is observed only when adult black abalone densities are at least 1/m 2. Our goal was to greatly exceed this minimum density threshold to account for post-translocation movement of animals and increase the likelihood for successful reproduction.

To assess initial habitat quality, we estimated the percent cover of bare substrate, crustose and foliose algae, and sessile and mobile invertebrates present in each plot (see Supplementary Figure 2 for full list of taxa and substrate). Estimates of cover were made by visually assessing the percent of the substratum that was occupied by each taxa. Visual estimation has been shown to be quicker and provide more repeatable estimates of cover than point-sampling (e.g., Dethier, 1984; Meese and Tomich, 1992) and worked well in crevice habitat where a point-sampling method can be challenging. While we recorded percent cover data for four substrate categories and 16 species/lumped taxa, we were primarily interested in cover of rock, crustose coralline algae, mussels, and sandcastle worms (Phragmatopoma californica). Our focus on these four groups of substrate/taxa is based on decades of monitoring showing a positive association between black abalone density and cover of rock and crustose coralline algae, and a loss of Good habitat associated with increased cover of mussels and sandcastle worms (pers. obs.).

In February 2023, we restored habitat in both translocation and restoration plots to a condition suitable for black abalone occupation (i.e., mostly bare rock or crustose algae as described above) by clearing fouling organisms using hand tools including crowbars, hammers, and paint scrappers. In cases where “resident” black abalone were present (seven plots in West Block and three in East Block), no habitat clearing was done within 10 cm of the animal. Percent cover of substrate and taxa within plots was assessed again using the visual method described above immediately following habitat restoration, and then once more in the year following translocation of black abalone (in June 2024; 16 months post-habitat restoration). Restoration plots were established to test for the effect of habitat restoration only vs. restoration plus translocation (translocation plots) on population recovery success. However, the ability to make this assessment was compromised by much greater than expected post-translocation movement of black abalone from translocation plots to restoration plots (see 3.5 Post-Translocation Monitoring and Supplementary Figure 3). Thus, we examined changes in mean cover of taxa for restoration and translocation plots combined and present only qualitative patterns of habitat change over time.

An unexpected outcome of higher than anticipated abalone movement from translocation plots to restoration plots and surrounding habitat was that it allowed for qualitative comparison of retention rates within plots (habitat restored) vs. outside of plots (habitat not restored). Using our block-wide counts inside and outside plots (See Sections 2.5 and 3.5 and Supplementary Figure 3) and habitat quality data for both the West and East Blocks, we could explore patterns of abalone movement and retention (density) in areas with or without habitat restoration. For this comparison, we restricted outside plot area to that categorized as Good (approximately 4.3% of total habitat in the West Block and 2.6% in the East Block) during our site-wide AHA surveys. Plot density was calculated as total count (excluding “resident” abalone) divided by total combined plot area by plot type (Translocation, Restoration). We calculated density in Good habitat outside of the plots by assuming that 75% of the abalone counted outside of plots during block-wide surveys were found in Good habitat, which was the proportion found in Good habitat during the 2024 and 2026 site-wide AHA surveys (See Sections 2.5 and 3.5 and Figure 2). We examined patterns in the distribution of abalone, particularly after movement had largely stabilized, to determine whether habitat restoration was associated with higher abalone density.

Donor site selection and population surveys

Data from AHA surveys (see methods above) and MARINe annual monitoring surveys were used to identify several candidate donor sites with abundant black abalone populations on Santa Cruz Island, CA where black abalone have shown promising signs of natural recovery. We consulted with Channel Islands National Park, TNC, NOAA NMFS, and California Department of Fish and Wildlife (CDFW) on site selection and permitting and ultimately chose two donor sites from TNC’s Santa Cruz Island Preserve to collect black abalone for translocation to the restoration site. To protect black abalone at these locations, we do not include site names and locations, but refer to them as Site A and Site B. We collected tissue samples from abalone on both Santa Cruz Island and the Dangermond Preserve for genetic analysis to determine if these populations were genetically distinct, which was not the case (Wooldridge et al., 2024).

Prior to collecting abalone from Site A and Site B for translocation, we conducted AHA surveys to estimate black abalone abundance and habitat-based densities at each site (see Supplementary Material Section 2: Supplementary Methods for details). Post-collection surveys were done at both donor sites six months after translocations occurred. Abundance and density information was needed to ensure that we met the collection criteria stipulated by our ESA collection permit. Specifically, we were required to demonstrate that: 1) collections did not exceed 10% of the total estimated population at the collection sites and, 2) that black abalone density following collections was not less than 2 abalone/m 2 in Good to Moderate habitat. To address the first criterium, we assessed whether the estimated population of black abalone at the collection sites decreased by more than 10 percent. We used a Generalized Linear Mixed Model (GLMM), where Survey period (pre, post) was considered a fixed effect and Site (A, B) was a random effect. The dependent variable was the estimated site population based on each of the spatial samples. Site population was lognormally distributed, which led to the use of a lognormal distribution in the GLMM.

To address the second criterium, we assessed whether densities of black abalone in Good or Moderate habitat were less than 2/m 2 after collection. Here we also used a Generalized Linear Mixed Model (GLMM), where survey period (pre, post) and Habitat Quality (Good, Moderate, Poor) were considered fixed effects, and Site (A, B) was a random effect. The dependent variable was the density per meter square on each of the spatial samples. Density was lognormally distributed, which led to the use of a lognormal distribution in the GLMM.

Translocations and injury and mortality assessment

Abalone collection and processing

To minimize the amount of time black abalone were held for processing and also allow time for assessment and improvement of removal and processing methods, we limited the number of abalone collected from each donor site and performed translocations in two phases: Phase 1 occurred March 17-19, 2023, and Phase 2 occurred October 27-30, 2023. In Phase 1, we collected 115 abalone from Site A and in Phase 2 we collected 135 abalone from Site B. We targeted abalone that ranged in size from 60 mm to 130 mm. We removed animals from the substrate using abalone irons and thin metal cake spatulas. Once collected, we assigned each abalone an identification number, placed it on a thin sheet of plastic to mimic substrate, prevent it from attaching to other abalone, and ease removal for processing and translocation, and enclosed it in a mesh cotton produce bag closed with a cable tie. We used soft-sided coolers to transport animals to an offshore boat. We then placed bagged abalone into several 49 L garbage bags with layers of seawater-dampened towels. Garbage bags were left open and contained in 113 L, hard-sided coolers with a layer of newspaper-wrapped ice packs on the bottom for transport to the mainland holding facility. Total transport time was 6 hours.

At the holding facility, abalone were kept in individual mesh bags and held in flow-through seawater tanks for processing. During processing, we photographed each animal (shell and foot, including any injuries incurred during removal), recorded weight and shell length, and collected tissue samples for genetic analysis. We tagged each abalone with two, 3 mm x 9 mm, numbered Floy tags (Floy Tag and Mfg., Inc., Seattle, WA) adhered to the shell with Corafix Cyanoacrylate Adhesive (Two Little Fishes, Inc., Miami Gardens, FL). Floy tags were placed at the anterior and posterior ends of the shell to enable identification and tracking of individuals during post-translocation monitoring. We also tagged each side the shell with small blobs of colored two-part epoxy (e.g., J-B Weld Clear Weld, J-B Weld Company, Sulfur Springs, TX) mixed with mica powder, which served as an additional identifier of translocated animals when Floy tags were lost or not visible (Figure 1). Adhesive and epoxy were allowed to dry before placing animals back in holding tanks to minimize exposure to chemicals. Furthermore, we had used these methods to tag abalone in prior efforts and observed no detrimental effects (e.g., Bell and Raimondi, 2020). Abalone were held for a total of 38 hours during Phase 1 and 60 hours during Phase 2.

Injuries and mortalities incurred during collection

In Phase 1, we conducted general injury assessments of abalone during processing and determined that nine required rehabilitation prior to release. Injured abalone were held for rehabilitation in a free-flowing, seawater tank at CDFW’s Marine Wildlife Veterinary Care and Research Center in Santa Cruz, CA for 26 days and were provided with fresh kelp (Macrocystis and Egregia).

During Phase 2, we modified our injury assessment procedure, carefully examining the foot of each abalone and assigning it one of four injury categories: 1) none = no injuries observed, 2) mild = superficial abrasions OR blistering OR single cuts < 1 cm deep, 3) moderate = multiple cuts < 1 cm deep OR single cuts 1–2 cm deep OR multiple abrasions with area of missing tissue < 20% foot area, 4) severe = multiple cuts 1–2 cm deep OR single cut > 2 cm deep OR area of missing tissue > 20% foot area OR tearing/separation of foot abductor muscle from shell. These categories were based on the results of previous studies on abalone foot injury (e.g., Loeher and Moore, 2020; Button and Rogers-Bennett, 2011).

Translocation to restoration site

We transported the abalone to the restoration site in hard sided coolers, as described above for collections, and released them into the pre-established translocation plots. Translocated abalone were carefully removed from the plastic sheet and gently held against the substrate until they attached. We released 112 abalone in Phase 1 into the five West Block translocation plots and the total time between collection and release was 48 hours. In Phase 2, we released 134 abalone to the five East Block translocation plots and the total time between collection and release was 70 hours.

Post-translocation monitoring

To track movement and survivorship of translocated abalone, we surveyed the translocation and restoration plots in each block and searched adjacent areas in a consistent manner to observe abalone that moved out of the plots. Monitoring was done the day after each release, two weeks post-release, then every one to three months through February 2025, and again in October 2025 and February 2026. Monitoring will continue into the future at 3–6-month intervals. We counted the number of abalone found by location and recorded size and visible tag information to determine if an individual was translocated or a resident (present prior to translocation). However, tag loss beginning as early as day 12 prevented us from consistently distinguishing residents from translocated animals. We also recorded dead abalone and empty shells. Plot density was calculated as the number of abalone in a plot divided by plot area.

To obtain post-translocation, site-scale estimates of black abalone densities by habitat type, we repeated AHA surveys of the entire Dangermond restoration site in March 2024 and February 2026. We also did extensive surveys of the West Block and East Block in March 2024, October 2024, February 2025, October 2025, and February 2026 specifically focused on juvenile abalone to document any new recruitment.

While we were not able to measure true survivorship with mark-recapture data due to tag loss, we have high confidence that “apparent survivorship” (elevated block and site-wide counts) equates to a conservative estimate of actual survivorship based on long-term monitoring data from the site pre-dating this translocation effort (Supplementary Figure 1). During this 30+ year period, no influx of animals was observed (e.g., from a shallow subtidal reservoir). Thus, post-translocation counts of adult-sized abalone that exceeded the number of known residents were by default, translocated individuals that survived.

Site-wide population and habitat characterization of restoration site

In the pre- and post-translocation site-wide population surveys of the restoration area, we surveyed a total of 11,719 m 2 of habitat. In March 2022 (pre-translocation), we found a total of 54 abalone ranging in size from 60 mm to 210 mm (mean = 129 mm, SD = 27). Most abalone occurred in Good (68.5%) or Moderate (29.6%) habitat, with only 1.8% found in Poor habitat (Figure 2). In March 2024 (one year after Phase 1 and 5 months after Phase 2 of the translocations), we found a total of 252 abalone (75% in Good, 23.8% in Moderate, and 1.2% in Poor habitat) ranging in size from 60 mm to 210 mm (mean = 108 mm, SD = 24). High levels of tag loss meant that we could not definitively distinguish resident abalone from translocated individuals. However, as noted in Section 2.5, based on 30+ years of long-term monitoring where no immigration of adult abalone into our survey area (e.g., from shallow subtidal habitat) was observed, it is reasonable to assume that the additional 198 abalone counted in 2024 were from the translocations; thus, 80% of the 246 translocated abalone were accounted for at the time of the survey. While we do not know if the remaining, unaccounted for 20% of translocated abalone died or were simply not found, based on high crypsis rates from other studies (e.g., 28-63%, Bragg, 2026; see section 4.2 below for discussion of crypsis in black abalone), it is likely that true survivorship was higher than 80%. In February 2026, we found a total of 302 abalone (74.8% in Good, 24.5% in Moderate, and 0.6% in Poor habitat) ranging in size from 18 mm to 180 mm (mean = 114 mm, SD = 30 mm). Twelve juveniles (<50 mm) and six small adults (50 mm; a size class not observed in the 2022 or 2024 surveys) were found during this survey which accounts for some of the increase in the number of abalone. The mean sitewide density of abalone in Good habitat increased from 0.2 abalone/m 2 in 2022 to 0.76 abalone/m 2 in 2024 and to 1.0 abalone/m 2 in 2026 (Figure 2).

Effectiveness of habitat restoration within translocation and restoration plots

We qualitatively examined patterns of change in cover of substrate and organisms across all plots in each Block. Lasting effects of habitat restoration were mixed. Clearing of sessile invertebrates and foliose algae unsurprisingly resulted in substantial increase in cover of bare rock, but post-translocation rock cover (16 months post-habitat restoration) returned to pre-clearing levels as sessile invertebrates and foliose algae resettled into the plots. Cover of crustose coralline algae was similar between pre- and post-clearing surveys but was observed to be trending upwards in the post-translocation survey. Mussel cover was lower following habitat restoration and remained below pre-clearing levels in the post-translocation survey. Habitat restoration initially lowered cover of sandcastle worms, but they recruited heavily to plots and cover eventually exceeded pre-clearing levels (Figure 3, Supplementary Figure 2).

Experimental design limitations (no true control plots) coupled with higher than anticipated movement of abalone restricted our ability to examine how abalone presence might influence availability of Good habitat and ultimately long-term population recovery. However, post-translocation patterns of abalone movement were strongly associated with habitat quality, with an apparent preference for restored habitat within plots over non-restored habitat outside of plots (Figure 4). Densities of abalone were on average 30 times higher in translocation plots and 10 times higher in restoration plots compared to average densities in non-restored Good habitat adjacent to plots.

Donor site population surveys

The goals for our population surveys at donor sites were two-fold: 1) to adhere to our ESA collection permit requirements that take did not exceed 10% of the local population and densities in Good to Moderate habitat remained at or above 2 abalone/m 2, and 2) to determine whether removals had any unanticipated post-collection effects on local population size (e.g. movement of animals outside of the area), beyond the known take. Black abalone at both donor sites were extremely abundant prior to and following collections (Supplementary Figure 4). The pre-collection abundance of black abalone for Site A was estimated to be 9,991 and the post-collection abundance was estimated to be 9,760. The pre-collection abundance of black abalone for donor Site B was estimated to be 8,785 and the post-collection abundance was estimated to be 11,102. Importantly, overall densities of black abalone at both donor sites exceeded density thresholds for successful reproduction (Miner et al., 2006); density at Site A was 2.98 abalone/m 2 (but note that abalone were collected from three smaller collection plots where densities were 4.6, 9.3, and 11.3 abalone/m 2) and density at Site B was 45 abalone/m 2 (Supplementary Figure 4). Our take of abalone from each site (115 Site A, 135 Site B) was far below the maximum level allowed by our permits (999 Site A, 878 Site B) and had no detectable short-term (6 month post-collection) impact on black abalone abundance or density within the resolution of our monitoring design. The results of our GLMM analysis to assess any reduction in population size show that the effect of Survey (pre vs post) was not significant (p =.06, Table 2). In addition, the results show that the mean estimated population size grew after collection (pre-estimate = 9,087, post-estimate = 10,767). In combination, we conclude that there is no evidence for population reductions greater than 10%. The results of our analysis assessing changes in density show that while the effect of Habitat Quality was significant (p<0.0001), which is to be expected, neither Survey (pre vs post) nor Habitat Quality * Survey were significant (Table 3). The results clearly show that in both the pre and post period, density was much greater than 2 abalone/m 2 for both Good and Moderate habitat (Figure 5).

Translocations, injury, and mortality

During Phase 1, nine abalone were injured to the extent that they required rehabilitation prior to release. One abalone died on March 29, 2023, but the remaining eight were determined to be healthy and recovering and were released at the restoration site on April 14, 2023 (Supplementary Figure 5). Two additional mortalities occurred prior to release, one during collection and one during holding, resulting in an overall pre-release mortality rate of 2.6% (Supplementary Table 1). 112 abalone were released at the restoration site (104 on March 19, 2023, and 8 rehabilitated abalone on April 14, 2023). Seven of the eight rehabilitated abalone were found during monitoring on May 20, 2023. There were no confirmed mortalities, injuries, or empty shells observed during monitoring.

Abalone densities were so high at the donor site selected for Phase 2 (Supplementary Figures 4, 6), that we were able to be more selective in our collection of animals for translocation. We also chose to collect abalone near the water line as the tide was dropping, when animals were often somewhat mobile and not yet clamped down on the underlying substrate. Coincident with these refinements and differences in collection site conditions, the collection mortality rate in Phase 2 was lowered to 0.74%. In addition, we recorded detailed injury assessment information which enabled us to determine that 36% of the collected abalone had no injury, 49% had mild injury (superficial scrapes or small cuts), and 16% had moderate injury (deeper cuts or larger abrasions). No abalone were considered severely injured and no abalone were held for injury rehabilitation. 134 abalone were released at the restoration site on October 30, 2023. During monitoring of the East Block on December 12, 2023, 43 days post-release, one confirmed mortality was observed. No other mortalities, injuries, or empty shells were observed during monitoring. The number of confirmed translocated abalone declined at a similar rate regardless of injury category, suggesting that there was minimal impact of mild and moderate injuries sustained during collection on long-term survivorship (Supplementary Figure 7).

Post-translocation monitoring

Immediately post-release (1 day to two weeks post-translocation), the total number of abalone observed declined in both the East and West blocks but then stabilized after about 3 months (Figure 6). This decline can be attributed to movement from the plots and adjacent Block habitat (see section 4.2 for a full discussion on the potential causes of the observed declines). The total count of “resident” black abalone documented at the time of the translocations was 15 in the West Block and 17 in the East Block (Figure 6). The number of resident abalone did not change between day 0 and day 1 and identifiable resident abalone were consistently observed during subsequent monitoring surveys, suggesting that introduction of new animals into the area did not impact the local population. As early as 12 days post-translocation, tags were lost (or not visible) from some abalone shells, preventing accurate distinction between resident and translocated abalone. Many abalone moved out of translocation plots into restoration plots or to adjacent habitat (Supplementary Figure 3), rendering restoration plots ineffective for assessing whether habitat clearing alone might enhance larval recruitment.

Mean black abalone density within translocation plots following release of abalone (Day 0) was 15.5/m 2 for the West Block and 19.7/m 2 for the East Block (Figure 7). Mean densities declined after Day 1 and stabilized at approximately 3.5/m 2 at the West Block and 5/m 2 at the East Block (Figure 7), both exceeding our long-term target of >2/m 2. The mean black abalone density within restoration plots, into which many translocated abalone moved, stabilized at approximately 3.5/m 2 for the West Block and 3/m 2 for the East Block (Figure 7). Densities within individual plots varied. In February 2026 (1076 days post-translocation), plot densities in the West Block ranged from 0.63 to 4.0 abalone/m 2 in translocation plots and 0 to 15.6 abalone/m 2 in restoration plots. In the East Block (849 days post-translocation), densities ranged from 0 to 9.2 abalone/m 2 in translocation plots and 0 to 7.7 abalone/m 2 in the restoration plots.

During the most recent monitoring survey of the West Block (plots and surrounding habitat) in February 2026, 1076 days post-translocation, we found 100 adult abalone, equating to 79% of all abalone (resident and translocated) counted at Day 0 (Figure 6). Nine juveniles, which likely recruited post-translocation, were also counted in the West Block (Figure 6). During monitoring of the East Block in February 2026, 849 days post-translocation, a total of 102 abalone were found (all adults), which equates to 68% of all abalone (translocated and resident) counted at Day 0 (Figure 6). It is worth noting that a portion of abalone unaccounted for in these block-wide surveys likely moved outside of these regularly surveyed areas, as many of these individuals were accounted for when we conducted more extensive, site-wide AHA population surveys (see 3.1 above).

In February 2025, 694 days post-translocation, three juvenile abalone (25 mm, 30 mm, and 35 mm in length) were found outside of the plots in the West Block (Supplementary Figure 8). Assuming a juvenile growth rate of 10–20 mm/year (Leighton and Boolootian, 1963; Morris et al., 1980), it is possible that these juveniles were progeny of the translocated abalone. Genetic parentage analysis is required for determining juvenile origin and as such, genetic material was collected from two of the juveniles using a minimally invasive swab technique for later assessment. In October 2025, seven juveniles (30–40 mm) were found in the West Block, two of which were in the same locations as those found in February 2025. One juvenile (18 mm) was found in a translocation plot at the East Block. In February 2026, a total of 12 juveniles (18–40 mm) were found in the West Block (nine in the monitoring area and three in adjacent habitat), several in similar locations to those observed in prior surveys.

Conservation translocations are an increasingly common and important tool for recovering populations and reducing extinction risk, as well as for restoring the structure and function of ecosystems, but they are high-cost and potentially high-risk endeavors with no guarantee of success (IUCN/SSC, 2013; Swan et al., 2016; Bubac et al., 2019). Crucial components of successful efforts include knowledge of species’ ecology and behavior, availability of high-quality habitat, coordination among vested partners, long-term funding for adaptive management and monitoring, and support from local communities (Berger-Tal et al., 2020; Novak et al., 2021). Below, we highlight key factors that contributed to the early success of this first-ever, non-emergency conservation translocation of U.S.A. ESA-listed black abalone, which can be broadly applied to other efforts. We also describe challenges encountered and discuss how lessons learned will inform and improve future efforts.

Conservation translocation as part of a broader monitoring network

The black abalone translocation effort presented here was nested within the spatially and temporally extensive MARINe long-term monitoring program, with population data stretching back more than 30 years. This expansive data set was the basis for: 1) selecting appropriate restoration and donor sites based on documented loss and recovery, 2) knowing the critical density of black abalone adults required for successful fertilization and local production of larvae, and 3) defining high-quality habitat (Miner et al., 2006). In addition, our findings can be viewed within the broader context of ecological trends observed at scales beyond the restoration site-level. For example, Marine Heat Waves (MHW) are known stressors of rocky intertidal communities (Harley et al., 2006; Miner et al., 2021); thus, expectations for black abalone recovery rates might be tempered if a MHW event were to occur during the post-translocation monitoring period.

Among the primary challenges identified in conservation translocation efforts is an inability to conduct post-release monitoring over a period long enough to assess success (Bubac et al., 2019; Soorae, 2025). There is general agreement that evidence of survivorship, population growth, and population viability are all key metrics for evaluating translocation effectiveness. However, for most species, including black abalone, adequate assessment of these metrics requires several years to decades of post-translocation monitoring, and a substantial level of long-term funding (Bubac et al., 2019). Embedding this translocation effort within an existing long-term monitoring program offsets some of these costs.

Carrying out a conservation translocation effort within the framework of a broadscale, collaborative monitoring program has the additional benefit of leveraging existing partnerships (Gilbane et al., 2022). The team that developed and continues to support this black abalone translocation includes federal and state resource managers and scientists and non-governmental organization scientists in addition to the university scientists leading the effort. Funding from the Refugio Beach Oil Spill settlement spearheaded the effort, but additional support from this community of partners was provided in the form of permitting assistance, site access, use of facilities and research vessels, and personnel. Support from TNC allowed this translocation of black abalone to occur in a location with high-quality habitat and a documented need for recovery, on a preserve with an adjacent marine reserve providing multiple layers of protection, which is rare (Gleason et al., 2023). The translocation and donor sites, both TNC Preserves, acted as “living laboratories” providing controlled environments for this collaborative group to test novel conservation actions, study nature’s responses, and inform future recovery efforts.

Early success metrics

While it is too early to assess long-term success metrics for this black abalone conservation translocation, our first few years of post-translocation monitoring data provide encouraging results. Importantly, abalone mortality was quite low during implementation, with very few fatal injuries incurred during collection and translocation. Prior to this study, a cut on a black abalone’s foot was believed to often result in the animal bleeding out and dying. Because cuts and other injuries can occur during removal, this was a primary concern inhibiting black abalone restoration via translocation. Here, we documented recovery of injured animals and post-translocation survivorship demonstrating that black abalone are more resilient to injury than previously thought. However, we emphasize that the potential for injury during removal should remain a key consideration when weighing the benefits and risks of a translocation effort. All translocations were done by researchers with extensive experience in abalone removal, and still 65% of abalone were noted as having mild to moderate injury when detailed observations were made during Phase 2. This highlights the need for experience and training. We also took steps to minimize injury including: 1) incorporating tools with a thinner profile than traditional abalone irons (e.g., metal cake spatulas), 2) timing collections with the outgoing tide to reduce the amount of time abalone were out of the water and thus less likely to be firmly attached to the substrate, 3) selecting donor sites with densely populated, easily accessible abalone. Between Phase 1 and Phase 2, we adjusted our collection approach, shifting to an extremely high-density site for increased selectivity and targeting slightly larger animals that were newly exposed by the receding tide and not yet firmly attached. These modifications coincided with a reduction in mortality rate from 2.6% to 0.74%. While several factors other than our methodological adjustments could have influenced mortality rate, including collection conditions, season, and condition of abalone, this improvement highlights the importance of taking an adaptive approach to translocation methodology, documenting and incorporating lessons learned. We also refined our post-removal injury assessments to better document the types of injuries incurred, which will help to guide future decisions about injured abalone care.

The high retention of translocated abalone at the restoration site (estimated 80% resighting rate) and stable densities following an initial post-release decline demonstrate early signs of establishment success, providing confidence in translocation as an effective tool for population recovery. While substantial movement of animals occurred among plots, within blocks, and even outside of blocks, densities in plots stabilized at 3–5 abalone/m 2, well above our long-term target of 2 abalone/m 2. Additionally, we found that site-wide density in Good habitat increased from 0.2 abalone/m 2 to 1/abalone m 2, which is considered the threshold necessary for reproduction and recruitment.

Obtaining accurate counts and density estimates for black abalone in our two translocation blocks was somewhat hindered by higher than anticipated mobility, as well as the cryptic nature of black abalone. Changes in plot counts over time can be attributed to: 1) abalone movement within a given block, which would be captured by our block-wide counts (Figure 6), 2) movement outside of a block, which would be captured by site-wide counts (Figure 2, only done two times, and would not capture movement to shallow subtidal), 3) “crypsis”, or movement to areas where they could not be seen by samplers (e.g., deep crevices), or 4) mortality. Survey conditions also influenced the accuracy of both block and site-wide counts, particularly at the West Block which is more complex and exposed to ocean conditions than the East Block. Count accuracy likely improved during good conditions where habitat could be more carefully surveyed and declined during poor conditions (e.g., large swell) where it was more difficult to survey all habitat. Crypsis rates for black abalone have been estimated to range between 28-63% (Bragg, 2026) and 69% in other abalone species (e.g., pinto abalone, Stevick, 2010) but were likely lower in our study due to comparatively lower habitat complexity. Although not specifically measured, based on the habitat at the restoration sight and our resighting rates as high as 80%, we conservatively estimate crypsis rates to be in the range of 10-20%. After accounting for crypsis, our site-wide counts suggest that mortality of translocated animals was minimal and largely occurred within the first few months, as within-block counts stabilized after initial modest declines (Figure 6). A portion of translocated animals likely moved to deep crevices where tags could not be seen, or into habitat beyond established plots. This is a noted issue in other translocation efforts (Soorae, 2018), but is in some ways, a “good problem” to have in that highly cryptic organisms may be well protected from predation. In our study, we adjusted the minimum size for translocated abalone from 60 mm to 70 mm and improved our tagging method between Phase 1 and Phase 2 to increase our odds of resighting animals. However, due to early tag loss and difficulty in detecting translocated abalone, it was not possible to conduct a mark-recapture, or similar, analysis to formally assess survivorship, nor can we accurately determine to what extent mortality, emigration, or imperfect detection (e.g., survey conditions, crypsis) resulted in our observed declines. Future black abalone translocation efforts could work to improve tagging and detection methods so that formal survivorship analyses can be conducted. Despite the hurdles encountered, our conservation translocation substantially reinforced the black abalone population at the Dangermond Preserve and allowed for refinement of our methodology to improve likelihood of success for future efforts.

High survival rates, including among injured abalone, are important for several reasons. First, it elevates the approach as a key and effective restoration tool and lessens concerns of injury when done by experienced teams. Second, it shifts the balance when making decisions about whether to remove animals in emergency response situations. If abalone threatened by a potential impact (e.g., oils spill or landslide) can be safely removed, it is likely that they will survive translocation to a safe site. Finally, in cases where abalone are recovered quickly and in good health following illegal take events, they can be returned to their habitat and will likely survive.

High survivorship of translocated individuals was coupled with minimal impact to donor populations as a whole. Assessing impacts to source populations is not regularly done yet is a critical component of translocation efforts to ensure a combined net positive effect across donor and release populations (IUCN/SSC, 2013; Mitchell et al., 2021). The donor sites we selected had extremely high abundances of black abalone, making accurate quantitative assessment of impact due to removals challenging. Our take of <1% from each donor population was well below our allowable take of 10% and our pre- and post-removal donor population estimates indicate no impact to ecological function of donor populations, as habitat-based densities were similar across surveys and well above the threshold necessary for reproduction. Future efforts might instead focus on a maximum acceptable effect size and determine whether detection of that effect size is possible given the level of error associated with the method used to estimate population size. For this project, we were fortunate to have high density donor populations from which we were taking an inconsequential fraction (relative to population size) of individuals. Future efforts in other regions or at larger scales will likely involve greater risk to source populations as the potential for lasting impact increases with an increased ratio of abalone collected to donor population size.

A final, highly encouraging finding from this study is the juvenile abalone documented within both translocation areas. Prior to this translocation effort, there had been no juveniles observed during annual monitoring or AHA surveys at this site since disease-related declines in 1993. Sizes of these juveniles are within that expected for black abalone two years post-settlement, which aligns with the post-translocation timeline. However, we will not know parentage until genetic analysis of the translocated adults and newly observed juveniles has been done. Regardless, larval recruitment and post-settlement survival and growth indicate that the translocation site provides high-quality habitat for attracting black abalone larvae and fostering population growth.

Challenges and lessons learned

Despite thorough preparation and planning, we were met with several challenges, some of which are common among translocation efforts (e.g., Soorae, 2018; Berger-Tal et al., 2020). One of our initial limitations was the availability of personnel skilled in black abalone removal. Because they live in the intertidal zone and affix tightly to the substrate when the tide is out, black abalone are more challenging to remove than subtidal abalone species. To minimize potential for injury to an animal, a researcher must be knowledgeable in quick and safe use of removal tools and must also know when to abort an effort to avoid severe injury. Because this project was divided into two phases, modest numbers of translocated abalone could be collected by the handful of trained personnel available within the MARINe network. However, any future, larger efforts will require building a broader pool of personnel trained in safe black abalone removal and handling.

Another challenge we encountered was related to the design of our translocation approach. We were interested in testing whether recovery could occur within habitat that was restored to “Good” quality, or whether the presence of adult abalone was necessary for habitat maintenance and larval settlement. Thus, our design included restoration plots, where habitat was restored but no abalone were added, and translocation plots where habitat restoration was coupled with addition of abalone. Immediately following translocation, animals began moving from translocation plots to restoration plots and surrounding areas (Figure 7, Supplementary Figure 3), rendering our restoration plots ineffective for testing the effect of habitat clearing alone as a facilitator of larval recruitment and survivorship. Predicting and accounting for animal behavior is often a primary source of complexity in conservation translocations (Berger-Tal et al., 2020; Bubac et al., 2019). Post-translocation dispersal is one factor that can contribute to translocation failure, and a high incidence of dispersal has been observed following many translocation efforts (Bilby and Moseby, 2024). While less mobile than many animals for which long-distance dispersal has hindered the success of some translocation efforts (e.g., sea otters, Jameson et al., 1982; Rathbun et al., 2000), translocated black abalone moved more than anticipated. Following the translocations, several abalone were documented moving 20–30 m from their release location in a single day, with many others moving several meters. Experimental approaches are rarely used in species restoration but have the potential to substantially improve understanding of factors affecting translocation outcomes (Armstrong et al., 1994).

Although higher than expected movement of translocated abalone rendered our intended plot treatments ineffective, an unanticipated outcome was the ability to track patterns of movement associated with habitat quality. Through our site-wide monitoring, we documented an apparent preference by abalone for restored habitat as densities within plots where habitat was restored far exceeded those outside of plots, in non-restored Good habitat. This pattern had largely stabilized 3 years post-translocation, lending support for the idea that habitat restoration should be incorporated into future black abalone translocation efforts, particularly where substantial influx of sessile invertebrates (e.g., mussels and sandcastle worms) into Good habitat followed loss of black abalone. Further, experimental investigation of the effect of habitat clearing alone as a restoration tool would be a valuable contribution to black abalone recovery efforts but might be best tested in areas where extensive habitat change has occurred, and abalone are still present in densities sufficient for local larval supply and recruitment without need for translocation.

Future efforts involving habitat restoration should incorporate ongoing maintenance until abalone densities are high enough to limit settlement of sessile invertebrates (through grazing and/or occupation of space). In our study, sandcastle worms (Phragmatopoma californica) quickly recolonized plots where they had been cleared, in abundances at or above initial levels (Figure 3, Supplementary Figure 2). There is some prior evidence that sandcastle worms increase reproductive output and recruitment following disturbance (Barry, 1988), suggesting that this species may be difficult to remove and maintain at low levels. Maintaining habitat after abalone are present can be challenging, as clearing efforts need to be done at the fine scale (i.e., no crowbars) to avoid disturbing abalone. Despite decades of monitoring black abalone and their associated habitat, we are still learning and refining the definition of “Good” quality habitat. In some instances, we overestimated the quality of restored crevice habitat, or the number of abalone a given crevice could support. Movement of translocated abalone out of crevices we deemed “Good” was likely due to our focus on substrate quality (i.e., deep crevices with high cover of bare rock and crustose algae) without considering other important factors such as wave exposure and propensity to collect kelp, a preferred food, or to balance intraspecific competition. It is important to highlight though, that densities in both restoration and translocation plots stabilized at values above that required for successful fertilization, indicating sufficient availability of suitable habitat.

Looking forward: evaluating long-term success and expanding geographic extent

Estimates of failure rates for conservation translocation efforts range from 50-70% (Bubac et al., 2019; Novak et al., 2021), often due to the same factor(s) responsible for a species’ initial decline. For this black abalone translocation, the threat of failure resulting from withering syndrome, the primary cause of decline, was thought to be low due to disease resistance and presence of a bacteriophage that lessens disease lethality (Brokordt et al., 2017; Crosson et al., 2014; Friedman et al., 2014). Indeed, more than three years in, with resighting rates near 80%, we have shown translocation to be an effective method for reinforcing black abalone populations in areas where natural recovery is not occurring. Sarrazin (2007) proposed a framework for evaluating the success of a translocation effort that separates population demographics into three stages: 1) establishment, 2) growth, and 3) regulation. We have accomplished stage 1, with high retention of translocated black abalone, and mean site-wide densities within “Good” quality habitat at the threshold required for successful fertilization/larval production. It is too soon to know if this effort will result in local population growth, but observations of juveniles are good sign. The final stage, regulation, is centered around the carrying capacity of the habitat, and might not be an appropriate metric for assessing success of large mollusks capable of attaining densities as high as 100/m 2 in the absence of natural predators (Davis, 1993).

Sarrazin’s framework can be used to evaluate translocation success at the local scale, but the key determiner of long-term success for this and future black abalone translocation efforts will be their contribution toward meeting the population recovery metrics outlined in the Recovery Plan for Black Abalone (NMFS, 2020). These metrics include attaining particular habitat-based density thresholds, successful larval production, recruitment and juvenile survivorship, and population size structure that reflects a range of ages and fecundity within each of five geographic regions making up the historic range of black abalone. To this end, we will consider this effort a future success if the population at our translocation site is bolstered sufficiently to enable “spillover” of larvae to neighboring areas, thereby enhancing regional viability.

While encouraging, one successful translocation effort is only a drop in the bucket for a species that has experienced catastrophic population loss throughout most of its historic range. Full recovery of black abalone will require additional translocations, including in areas that do not have the protection and conservation measures afforded by the Dangermond Preserve, which certainly contributed to this effort’s success (Gleason et al., 2023). Nevertheless, these pioneering efforts provide lessons learned to increase the pace and scale of translocations to recover endangered black abalone. For sites along mainland southern California that have maintained critically low numbers of abalone 30–40 years post WS-declines (NMFS, 2020; Multi-Agency Rocky Intertidal Network (MARINe) et al., 2020), it is crucial we act swiftly to bolster remnant populations to densities high enough to support reproduction before they disappear completely. Expanding translocations to this densely human-populated region of coastline is of high priority because black abalone were once abundant here and “Good” quality habitat is still present, but this effort will require substantial public education, engagement, and support to be successful. Geographic placement of future translocation efforts should be informed by historic records, both recent and archaeological (Braje et al., 2016). Areas that have supported stable, high-density populations of black abalone (as evidenced by archaeologic records or more recent long-term monitoring data or catch records) likely contain key features that enable populations to thrive (e.g., high quality habitat, consistent food source, favorable recruitment and juvenile survivorship) and have the best chance for success. Seddon et al. (2014) states that “conservation translocation projects provide a powerful means to reconnect people with their natural heritage, to engage them as conservation partners, and to make them stewards of the wild animals and habitats around them”. We look forward to engaging community members in the next phase of black abalone restoration to support, learn from, and assist with coast-wide rebuilding of populations of this ecologically and culturally important species.