Laura Rogers-Bennett

MODELING GROWTH AND MORTALITY OF RED ABALONE (HALIOTIS RUFESCENS) IN NORTHERN CALIFORNIA

Abstract We estimate annual growth and mortality of red abalone, Haliotis rufescens, in northern California using tag recapture data applied to multiple growth and mortality models. We investigate seven growth models of the form, L t+1 = Lt + f(Lt ) where Lt is the shell length at tagging (time t), Lt+1, is the shell length one year later, and the function f(Lt ) is a model of the change in length ΔL. Abalone are drawn from a broad range of sizes (shell lengths 5–222 mm) tagged and recaptured one year later (n = 231) in the Point Cabrillo Reserve in northern California. We present the results for seven growth models, rank the fit of the models (using the sum of the squared residuals) selecting the Richards, Gaussian, Ricker, and von Bertalanffy models (in that order) as most appropriate for these variable growth data. The von Bertalanffy model yields the shortest time to fishery (recreational legal size is 178 mm) as it slightly overestimates early growth. The Ricker model yields the longest time to enter the fishery underestimating early growth. We present a table of abalone sizes as a function of time for the Gaussian model, from which we estimate the number of years to grow into the fishery (12.0 ± 1 y). Because differences among the applicable models are not great, we use the growth parameters generated by the simple von Bertalanffy model (L∞ and K) to estimate mortality. The results are consistent among our five mortality estimates ranging from 0.11–0.23 per year. Estimates of the number of years to enter the fishery and mortality estimates, as well as knowledge of how model selection can influence these estimates, is important for fishery management. Informed fishery management for red abalone is critical because the fishery in northern California is the last open abalone fishery in the state.

Elasticity Analyses Of Size-Based Red And White Abalone Matrix Models: Management And Conservation

Prospective elasticity analyses have been used to aid in the management of fished species and the conservation of endangered species. Elasticities were examined for deterministic size-based matrix models of red abalone, Haliotis rufescens, and white abalone, H. sorenseni, to evaluate which size classes influenced population growth (lambda) the most. In the red abalone matrix, growth transitions were determined from a tag recapture study and grouped into nine size classes. In the white abalone matrix, abalone growth was determined from a laboratory study and grouped into five size classes. Survivorship was estimated from tag recapture data for red abalone using a Jolly-Seber model with size as a covariate and used for both red and white abalone. Reproduction estimates for both models used averages of the number of mature eggs produced by female red and white abalone in each size class from four-year reproduction studies. Population growth rate (lambda) was set to 1.0, and the first-year survival (larval survival through to the first size class) was estimated by iteration. Survival elasticities were higher than fecundity elasticities in both the red and white matrix models. The sizes classes with the greatest survival elasticities, and therefore the most influence on population growth in the model, were the sublegal red abalone (150-178 mm) and the largest white abalone size class (140-175 mm). For red abalone, the existing minimum legal size (178 mm) protects the size class the model suggests is critical to population growth. Implementation of education programs for novice divers coupled with renewed enforcement may serve to minimize incidental mortality of the critical size class. For white abalone, conservation efforts directed at restoring adults may have more of an impact on population growth than efforts focusing on juveniles. Our work is an example of how prospective elasticity analyses of size-structured matrix models can be used to quantitatively evaluate research priorities, fishery management strategies, and conservation options.

Response of Red Abalone Reproduction to Warm Water, Starvation, and Disease Stressors: Implications of Ocean Warming

ABSTRACT Changes in ocean temperature can have direct and indirect effects on the population dynamics of marine invertebrates. We examined the impacts of warm water, starvation, and disease on reproduction in red abalone (Haliotis rufescens). We found that sperm production was highly sensitive to warm water and starvation, suggesting there may be a dramatic temperature threshold above which sperm production fails. Wild males from northern (72%) and southern (81%) California had sperm. In contrast, only 30% of the males exposed to warm water (18°C) for 6 mo or starvation for 13 mo had sperm, with spermatogenesis dropping dramatically from 300,000 presperm cells/mm3 (wild) to 46,000 presperm cells/mm3 (warm water) and 84,000 presperm cells/mm3 (starvation). In a longer warm-water experiment (12 mo), males had total reproductive failure in temperatures greater than 16°C, irrespective of food treatment. Egg production was less sensitive to warm water, but was impacted more by starvation, especially food quantity relative to quality. Wild females from northern (97%) and southern (100%) California had mature oocytes averaging 3 million eggs and 21 million eggs, respectively. Females exposed to 18°C water for 6 mo had diminished fecundity, averaging only 400,000 mature eggs whereas females in the starvation experiment did not produce any mature eggs. Normal sperm and egg production was found in abalone testing positive for Rickettsiales-like-prokaryote (RLP), the agent of Withering Syndrome in cool water. However, abalone with RLP also exposed to warm water developed the disease withering syndrome and did not produce any mature gametes. The temperature-mediated lethal and sublethal effects on red abalone reproduction described here, combined with temperatures known impacts on abalone growth, kelp abundance, and disease status, clearly demonstrate population-level consequences. We suggest that temperature needs to be explicitly incorporated into red abalone recovery and management planning, because Californias ocean has warmed and is predicted to warm in the future.

Patterns of Mass Mortality among Rocky Shore Invertebrates across 100 km of Northeastern Pacific Coastline

Mass mortalities in natural populations, particularly those that leave few survivors over large spatial areas, may cause long-term ecological perturbations. Yet mass mortalities may remain undocumented or poorly described due to challenges in responding rapidly to unforeseen events, scarcity of baseline data, and difficulties in quantifying rare or patchily distributed species, especially in remote or marine systems. Better chronicling the geographic pattern and intensity of mass mortalities is especially critical in the face of global changes predicted to alter regional disturbance regimes. Here, we couple replicated post-mortality surveys with preceding long-term surveys and historical data to describe a rapid and severe mass mortality of rocky shore invertebrates along the north-central California coast of the northeastern Pacific Ocean. In late August 2011, formerly abundant intertidal populations of the purple sea urchin (Strongylocentrotus purpuratus, a well-known ecosystem engineer), and the predatory six-armed sea star (Leptasterias sp.) were functionally extirpated from ~100 km of coastline. Other invertebrates, including the gumboot chiton (Cryptochiton stelleri) the ochre sea star (Pisaster ochraceus), and subtidal populations of purple sea urchins also exhibited elevated mortality. The pattern and extent of mortality suggest the potential for long-term population, community, and ecosystem consequences, recovery from which may depend on the different dispersal abilities of the affected species.

Chapter 19 The ecology of Strongylocentrotus franciscanus and Strongylocentrotus purpuratus

Publisher Summary This chapter describes the ecology of Strongylocentrotus franciscanus (S. franciscanus) and Strongylocentrotus purpuratus (S. purpuratus). Red sea urchins, S. franciscanus, and purple sea urchins, S. purpuratus, are the most studied and well-known echinoid species in the world. Red and purple sea urchins are dominant members of near shore rocky reef communities along the North American west coast and are capable of structuring subtidal algal communities and influencing community diversity. Red and purple sea urchins are also the basis for important fisheries, with purple sea urchins making up a minor component of the fishery. Purple sea urchins are collected extensively for scientific research, including fertilization biology, embryology, genome analysis, and fertilization bioassays that are used to assess the toxicity of marine pollutants, silt, pulp-mill effluent, and ultraviolet radiation. Red sea urchins are important for fisheries, in part because of their large body size. Red and purple sea urchins reside on rocky substrates with a broad geographic and depth distribution.

Exploring the Use of a Size-Based Egg-per-Recruit Model for the Red Abalone Fishery in California

Eggs-per-recruit (EPR) models are widely used for management of invertebrate fisheries to provide guidance to managers about the magnitude of egg production for a given level of instantaneous annual fishing mortality (F). We constructed a deterministic size-based EPR model that utilizes size-specific natural mortality rates and egg production for red abalone Haliotis rufescens in California. We analyzed the sensitivity of the model to alterations in biological parameters, modeled the effect of incidental mortality of sublegal individuals on EPR, and modeled the effects of various management actions, including incorporation of a slot size limit, incorporation of a harvest refugium, and alternative legal minimum size limits. Model results were more sensitive to alterations in growth parameters and lower mortality estimates than to changes in upper mortality estimates or fecundity parameters. When F increased from 0.0 to 0.1 per year, EPR exhibited a large decline from 100% to 70%. Only the incorporation of a harvest refugium and an increase in the minimum size limit produced increases in the percent of maximum EPR. Implementing a slot limit of 152.4-203.2 mm maximum shell length (MSL) decreased the EPR value, indicating the importance of egg production by red abalone that are smaller than the current minimum size limit of 177.8 mm MSL. Because of the sensitivity of model predictions to changes in certain biological parameters, we recommend caution when applying EPR models to management, particularly for regions without spatially explicit parameter values. Despite this sensitivity, EPR models provide a heuristic framework for exploring the potential impacts of proposed fishery management strategies (e.g., harvest refugia), establishing biological reference points, examining how spatial and temporal variability in biological parameters affects egg production, and providing a guide for prioritizing research to improve data quality used for red abalone management.

Implementing a Restoration Program for the Endangered White Abalone (Haliotis sorenseni) in California

ABSTRACT A restoration program including wild population surveys, captive breeding, health monitoring, recovery site preparation, and recovery modeling has been implemented to restore white abalone (Haliotis sorenseni) populations in California. White abalone once supported a lucrative fishery and are now endangered, nearing extinction at less than 1% of baseline abundances. Recent deep water surveys indicate that populations continue to decline with no signs of recruitment, despite the closure of the fishery in 1996. Four sites with artificial reefs (n=12/site) in optimal white abalone habitat were established. No wild white abalone have been found at these sites. Captive abalone were spawned in the spring of each year from 2012 to 2015. Each year, the production of 1-y-old abalone has increased in the captive breeding program from approximately 20 in 2012, to 150 in 2013 and an estimated 2,000 in 2014. In 2015, the breeding program reached two milestones: (1) most successful spawning season to date and (2) the hatchery distributed 200 captive-reared abalone to 4 partner institutions within the White Abalone Recovery Consortium (WARC). The WARC is made up of federal and state agencies, universities, public aquaria, and aquaculture organizations, all committed to white abalone restoration. The next steps for the program include expanding the captive breeding program to increase production, monitoring abalone health and genetic diversity, and conducting stocking studies to enhance growth and survival in the ocean. The goal of the stocking program is to create a reproductive population in the wild to bring white abalone back from the brink of extinction.

Bomb radiocarbon dating of the endangered white abalone (Haliotis sorenseni): investigations of age, growth and lifespan

Understanding basic life-history characteristics of white abalone (Haliotis sorenseni), such as estimated lifespan, is critical to making informed decisions regarding the recovery of this endangered species. All predictive modelling tools used to forecast the status and health of populations following restoration activities depend on a validated estimate of adult lifespan. Of the seven Haliotis species in California, white abalone is considered to have the highest extinctionrisk andwasthefirstmarineinvertebrate listedasanendangeredspeciesundertheFederalEndangeredSpecies Act (ESA). Lifespan was previously estimated from observations of early growth; however, no study has generated ages for the largest white abalone. To address questions of age and growth, bomb radiocarbon (D 14 C) dating was used on shells from large white abalone. Measured bomb D 14 C levels were compared to regional D 14 C reference records to provide estimates of age, growth and lifespan. Bomb radiocarbon dating indicated that growth was variable among individuals, with a maximum estimated age of 27 years. The findings presented here provide support for previous age and growth estimates and an estimated lifespan near 30 years. These age data support the perception of a critical need for restoringthe remnant aging and potentially senescent population. Additional keywords: age validation, carbon-14, Haliotidae, longevity, Mollusca, Southern California Bight.

Tracking Larval, Newly Settled, and Juvenile Red Abalone (Haliotis rufescens) Recruitment in Northern California

ABSTRACT Recruitment is a central question in both ecology and fisheries biology. Little is known however about early life history stages, such as the larval and newly settled stages of marine invertebrates. No one has captured wild larval or newly settled red abalone (Haliotis rufescens) in California even though this species supports a recreational fishery. A sampling program has been developed to capture larval (290 µm), newly settled (290–2,000 µm), and juvenile (2–20 mm) red abalone in northern California from 2007 to 2015. Plankton nets were used to capture larval abalone using depth integrated tows in nearshore rocky habitats. Newly settled abalone were collected on cobbles covered in crustose coralline algae. Larval and newly settled abalone were identified to species using shell morphology confirmed with genetic techniques using polymerase chain reaction restriction fragment length polymorphism with two restriction enzymes. Artificial reefs were constructed of cinder blocks and sampled each year for the presence of juvenile red abalone. Settlement and recruitment were found to vary with year and site from 2007 to 2015. In some years such as 2010 and 2013, there were many larvae and newly settled abalone, whereas in other years there were none. The two exceptionally poor years for larval and newly settled abalone were 2012 and 2015 (warm El Niño years). In 2013, there was spatial concordance between two sites 18 km apart with respect to the sizes of the newly settled individuals suggesting they were spawned and settled on the same day. The methods developed here, quantifying early life history stages, may shed light on the “black box” of recruitment and help addresswhat are the drivers of good and bad recruitment years for red abalone in northern California.

Assessing the Recovery of Pink Abalone (Haliotis corrugata) by Incorporating Aggregation into a Matrix Model

ABSTRACT Historically, Point Loma had the highest fishery landings of pink abalone (Haliotis corrugata Wood 1828) along the California coast. The current status of the population in this key location is described using population and aggregation surveys from 2004 to 2007. We developed a size-based matrix model to assess the recovery potential of this low-density population. We incorporated fecundity parameters into the model, modified by empirical nearest-neighbor distance, aggregation size, sex ratio, and size-frequency data, to evaluate their influence on the population growth rate. We found the density of the population (∼170 abalone/ha) is an order of magnitude less than the minimum spawning density (2,000 abalone/ha) used by the California Department of Fish and Wildlife for abalone management. The average aggregation size was ∼2 abalone, and more than 50% of the abalone were solitary (no neighbors within a 2.5-m distance). The average nearest-neighbor distance was greater than 5 m in all 3 y, corresponding to an estimated fertilization success rate of ∼20%. The per capita recruitment potential was 1.3–5.3 recruits per female in 2006 and 2007. Population growth rates (&lgr;) from the models including aggregation characteristics were 12%–18% less than the models with no aggregation information. A further 12% reduction in &lgr; occurred between models assuming high and low fertilization success (high, 1.04/y; low, 0.91/y), showing that inclusion of aggregation characteristics has a large impact on population viability analyses. Under the International Union for the Conservation of Nature threat categories, a population with a &lgr; of 0.91 would be classified as endangered. Based on these results, we define recovery targets for pink abalone as (1) aggregation size ≥ 5 abalone and (2) nearest-neighbor distance less than 1.6 m. We suggest aggregation characteristics will be important to include when quantifying recovery goals for depleted populations of species susceptible to reproductive Allee effects.