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Here, we describe the trophic structure of the La Paz Bay, Baja California Sur, Mexico, and evaluate the role of weak trophic interactions in the ecosystem using a suite of topological indices. We used information derived from published and unpublished stomach contents analysis studies from the region to construct an unweighted and directional trophic network (comprising 250 nodes and 1528 associated interactions) to assess the impact of predators in three scenarios. Each scenario simulated the removal of weak interactions corresponding to removal of those nodes with trophic contributions less than 5%, 10%, and 15%. In each removal scenario, the nodes phytoplankton and zooplankton exhibited the greatest betweenness and closeness centrality, suggesting that they are critical groups in the structure of the web, especially in the transference of indirect effects to the largest number of possible nodes in the network. The multiphyletic nature of the phytoplankton and zooplankton, and their ubiquity in diets served to increase their connectivity to all taxonomic groups. We note the presence of numerous weak interactions (67% of taxa have weak trophic interactions) and speculate that this characteristic confers ecological resilience in the Bay of La Paz coastal marine ecosystem.

Increased bottom water temperatures have caused a relocation and contraction of the range of the Atlantic surfclam, Spisula solidissima, in the Mid-Atlantic Bight (MAB). Consequences include declining stock abundance and landings per unit effort (LPUE) in southern portions of the range. A management strategy evaluation (MSE) assessed the potential of rotational closures to improve surfclam productivity and fishery viability under three levels of abundance. In simulations, fishing vessels harvest the stock under performance and quota constraints and captain behavioral proclivities. Management alternatives examined included the addition of area management to the current management plan using two closure location rules and three closure durations at two levels of incidental mortality. Simulations showed that area management increased stock abundance and fishery LPUE, particularly when surfclam abundance was low. Simulations suggest area management could help insulate the stock and commercial fishery from further shifts in range.

A critical issue in understanding trophic connectivity in ecological systems is the lack in quality and quantity of information about feeding habits. In this work, we present a method for integrating a diversity of feeding habits data from published studies to evaluate the impact on indices that describe characteristics of individual taxa and their connectivity. We focus our study on feeding habits of the fishes of the northern Gulf of Mexico and seek to understand the importance of the forage fish Gulf Menhaden (Brevoortia patronus) in predator diets. We created a database of diet studies from the northern Gulf of Mexico that included six diet metrics: frequency of occurrence, wet weight, dry weight, number, volume, index of relative importance, and index of caloric importance. We then used this information to construct a set of traditional networks (all prey and predators were from a single taxonomic level and trophic connections were parameterized with a single diet metric). We also constructed a “robust” network where all taxa were identified to the lowest taxonomic level and trophic connections were parameterized using a resampling approach that included all available information. Linear regression and resampling methods were used to convert data reported in other diet metrics into the frequency of occurrence diet metric. For both traditional and robust networks, we used network indices to describe topological properties. With the robust network, we conducted removal simulations where the forage fish species Gulf Menhaden, and associated Clupeidae representatives, were removed from the network and the feeding effort of the predators was reallocated among their other prey items. We found that network and node-specific indices were sensitive to the choice of taxonomy and diet metric level. In the robust network, predator species with the greatest number of identified prey had the lowest precision in their connections and prey from the Arthropoda phyla had the lowest precision for connections. From the removal and reallocation simulations, we found that Actinopterygii and Arthropoda were the most impacted prey taxa with 1.2% to 4.3% increase in predation and approximately 23 taxa would receive 50% of the reallocated predation. Overall, the resampling methods we present provide a potential means for combining disparate diet data and enables a comprehensive understanding of trophic interactions within an ecosystem.

Age and growth of early-life-stage Atlantic tarpon Megalops atlanticus collected from Mississippi coastal waters in the northcentral Gulf of Mexico (GOM) are described using otolith microstructure analysis. Tarpon leptocephali (n = 95, 16.0-27.8 mm standard length, LS ) collected from June throughOctober 2013-2018, ranged in age from 22 to 43 days (mean = 30.9 ± 0.5 days). Leptocephalus somatic growth rates ranged 0.46-1.24 mm day-1 (mean = 0.76 ± 0.02 mm day-1 ), and leptocephalus otolith growth rates ranged 1.78-3.97 μm day-1 (mean = 2.58 ± 0.04 μm day-1 ). Growth rates were inversely correlated to leptocephalus age, indicating the shrinkage phase associated with leptocephalus metamorphosis. Juvenile tarpon (n = 358, 50-359 mm fork length, LF ) were collected from August through December 2007-2018. Juveniles exhibited a positive allometric relationship (adjusted R2 = 0.99, P

Gulf Menhaden, Brevoortia patronus, in the northern Gulf of Mexico support a large commercial fishery and are thought to play an important trophic role in the coastal ecosystem. The temporal dynamics of both fatty acid and oil content have a direct impact on the value of Gulf Menhaden to predators and to the fishery. In this work, we describe how oil content of Gulf Menhaden varies with season, sex, age, condition, and tissue and investigate how fatty acid composition of mature ( ≥ 137.5 mm FL) female tissues varies with season, month, and tissue type. We found pronounced temporal (January to October) variation in mean oil content ranging from 0.062 to 0.579 mg g−1 that exhibited a significant (p

Understanding geographic variation in growth dynamics is essential for the management of exploited fish populations because such variation can be used to define stock structure and influence perceptions of stock productivity. Sheepshead (Archosargus probatocephalus) is a species targeted by both commercial and recreational fisheries, and is distributed throughout the north and central Atlantic Ocean and Gulf of Mexico. We analyzed fishery-dependent and –independent length-at-age and weight-at-length data from Texas, Louisiana, Mississippi, Alabama, Florida, South Carolina, North Carolina, and Virginia to investigate the geographic variation in growth of Sheepshead. We constructed a series of von Bertalanffy growth functions (VBGF) and length-weight power equations using a Bayesian framework that included sex, latitudinal, and regional effects. Median posterior VBGF parameter estimates of asymptotic length (L∞) for females ranged from 561 mm fork length in the Virginia Chesapeake Bay to 418 mm in Florida Gulf coast, while the posterior median growth coefficient (k) ranged from 0.42 yr−1 in Texas to 0.20 yr−1 in the Florida Atlantic. Predicted length-at-age and weight-at-length varied considerably among States. Predicted length-at-age for age-1 and -5 individuals was greater in the Gulf of Mexico than the Atlantic. However, predicted length-at-age for older age classes was greater in the Atlantic. Predicted weight-at-length decreased along latitudinal gradients in the Atlantic and the lowest values were found in Mississippi. Given the impact of growth on fisheries reference points, such geographic variation in growth can inform the development of assessment efforts for Sheepshead in the Gulf of Mexico and Atlantic.

Network analysis is a framework that allows integration and evaluation of predator-prey interactions. In the present study, we synthesized diet composition information from 94 published studies (n = 12,335 unique predator-prey interactions) that reported food habits of teleost fishes in the northern Gulf of Mexico (nGOM). Using this information, we constructed 12 weighted trophic network models using three diet metrics and four levels of taxonomic resolution of predators and prey. We evaluated network resilience to simulated random and directed taxa loss by assessing changes in topological indices "complexity," "connectance," "efficiency," and "robustness" with respect to a priori minima. We found all networks were resilient to random removal of nodes. However, the response to directed removal varied depending on the index used to determine node importance. Directed removal simulations that targeted taxa with the greatest number of trophic interactions had the strongest impact on network topological indices. Using an additional simulation, we assessed how removal of taxa of commercial interest impacted the predation pressure on other taxa. We found a greater magnitude of predator diet shifts when Gulf menhaden (Brevoortia patronus Goode, 1878) were removed than when blue crab (Callinectes sapidus Rathbun, 1896) were removed, indicating predators of Gulf menhaden have a more limited portfolio of diet items than do predators of blue crab. Compared to previously described marine trophic networks, the network that describes the trophic dynamics in the nGOM is less connected and complex. This conclusion highlights the need for consistent reporting of stomach contents and improved understanding of the food habits of lesser-known taxa in the region.

The establishment of a defensible baseline for ecosystem productivity is important in Natural Resource Damage Assessment (NRDA) and other assessment studies so that an estimate of the ecosystem injury can be established. In order to establish the overall NRDA baseline productivity for the Deepwater Horizon Oil release (DWH), the EPA fate and effects ecosystem model AQUATOX, Release 3.1, was adapted for the Nearshore Marine Environment (NME); this version represents key estuarine habitats, especially in Mississippi Sound and Mobile Bay. These include intertidal marsh-edge and beach habitats; and subtidal oyster-reef and soft-bottom benthic habitats, characterized by generalized food webs and subject to varying salinity and energy regimes and with and without submerged aquatic vegetation (SAV). Simulation results indicate highest primary production of 2960–8181 g AFDW/m 2 /yr occurs in marsh-edge habitats where SAV’s were present. In general, highest secondary productivities were generally observed in oyster-reef habitats (719–1523 g/m 2 /yr), followed by vegetated marsh edge (141–567 g/m 2 /yr), subtidal soft-bottom habitats, including overlying water column (156–501 g/m 2 /yr) and finally beach habitats (62–1164 g/m 2 /yr). Individually, secondary productivity of each of the habitats is represented by a food web where each state variable represents a specific taxonomic or trophic group, and average trophic level is explicitly calculated by the model. Thus, secondary productivity estimates of these specific habitats can be viewed by an individual taxon or collectively by trophic-level groups or guilds such as forage fish or deposit-feeding invertebrates. The productivity, estimated by the model for each habitat, compared well with published estimates and with generally accepted ecological observations. Variations in secondary productivity across similar habitats were shown to be responsive to environmental factors such as salinity and turbidity and site characteristics such as fractal dimension of the marsh-water interface and occurrence of submerged aquatic vegetation. Simulation of these various habitat characteristics proved useful for determining the potential variation in ecological services for each habitat, and for establishing baseline productivity for NRDA purposes; it also can provide guidance for ecosystem restoration design initiatives.

The Spotted Seatrout Cynoscion nebulosus is the most popular target of recreational inshore fisheries in Mississippi coastal waters. The Gulf of Mexico (GOM) stock of Spotted Seatrout is composed of spatially distinct substocks, and each state imposes unique bag and size limits. In Mississippi, the stock is managed using minimum length limits and daily bag limits. We used two methods to evaluate the efficacy of length restrictions and fishing mortality (F) levels: (1) a per-recruit model simulation to evaluate the effects of proposed management actions on reproductive output and yield, and (2) an evaluation of how management regimes impact relative stock density (RSD). Relative stock density has been widely used as a management tool in recreational and generally freshwater fisheries but has not been widely employed in informing management of marine stocks. We used demographic information from fisheries-independent sampling and length-specific natural mortality estimates to construct both models. O...

Spotted Seatrout Cynoscion nebulosus are a highly valued recreational inshore species in Mississippi coastal waters. The accurate description of the length-at-age relationship is critical for assessment efforts of the stock. Because Spotted Seatrout exhibit small-scale movements, the stocks in the Gulf of Mexico are managed as state-specific units. Therefore, local demographic estimates of length at age are needed for assessment. We estimated the length-at-age relationship of Spotted Seatrout in Mississippi by using tag recapture records and otolith-derived age estimates. Three nonlinear length-at-age models were fit to sex-aggregated, tag recapture data and four nonlinear length-at-age models were fit to sex-specific, otolith-derived age data. For each suite of models, model support was determined using Akaike information criteria. The Francis (1988a) GROTAG method had the greatest support of the three models fit to the tag recapture data, and the resulting parameter estimates from the model were...

Large jellyfish are important consumers of plankton, fish eggs and fish larvae in heavily fished ecosystems worldwide; yet they are seldom included in fisheries production models. Here we developed a trophic network model with 41 functional groups using ECOPATH re-expressed in a donor-driven, end-to-end format to directly evaluate the efficiency of large jellyfish and forage fish at transferring energy to higher trophic levels, as well as the ecosystem-wide effects of varying jellyfish and forage fish consumption rates and fishing rates, in the Northern Humboldt Current system (NHCS) off of Peru. Large jellyfish were an energy-loss pathway for high trophic-level consumers, while forage fish channelized the production of lower trophic levels directly into production of top-level consumers. A simulated jellyfish bloom resulted in a decline in productivity of all functional groups, including forage fish (12%), with the exception of sea turtles. A modeled increase in forage fish consumption rate by 50% resulted in a decrease in large jellyfish productivity (29%). A simulated increase of 40% in forage fish harvest enhanced jellyfish productivity (24%), while closure of all fisheries caused a decline in large jellyfish productivity (26%) and productivity increases in upper level consumers. These outcomes not only suggest that jellyfish blooms and fisheries have important effects on the structure of the NHCS, but they also support the hypothesis that forage fishing provides a competitive release for large jellyfish. We recommend including jellyfish as a functional group in future ecosystem modeling efforts, including ecosystem-based approaches to fishery management of coastal ecosystems worldwide. Fil: Chiaverano, Luciano. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. University Of Southern Mississippi; Estados Unidos Fil: Robinson, Kelly L.. University of Louisiana at Lafayette; Estados Unidos Fil: Tam, Jorge. Instituto del Mar del Perú; Perú Fil: Ruzicka, James J.. Oregon State University; Estados Unidos Fil: Quiñones, Javier. Instituto del Mar del Perú; Perú Fil: Aleksa, Katrina T.. University Of Southern Mississippi; Estados Unidos Fil: Hernandez, Frank J.. University Of Southern Mississippi; Estados Unidos Fil: Brodeur, Richard D.. Northwest Fisheries Science Center; Estados Unidos Fil: Leaf, Robert. University Of Southern Mississippi; Estados Unidos Fil: Uye, Shin-ichi. Hiroshima University; Japón Fil: Decker, Mary Beth. University of Yale; Estados Unidos Fil: Acha, Eduardo Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; Argentina Fil: Mianzan, Hermes Walter. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; Argentina Fil: Graham, William M.. University Of Southern Mississippi; Estados Unidos

Sharks are a diverse group of mobile predators that forage across varied spatial scales and have the potential to influence food web dynamics. The ecological consequences of recent declines in shark biomass may extend across broader geographic ranges if shark taxa display common behavioural traits. By tracking the original site of photosynthetic fixation of carbon atoms that were ultimately assimilated into muscle tissues of 5,394 sharks from 114 species, we identify globally consistent biogeographic traits in trophic interactions between sharks found in different habitats. We show that populations of shelf-dwelling sharks derive a substantial proportion of their carbon from regional pelagic sources, but contain individuals that forage within additional isotopically diverse local food webs, such as those supported by terrestrial plant sources, benthic production and macrophytes. In contrast, oceanic sharks seem to use carbon derived from between 30° and 50° of latitude. Global-scale compilations of stable isotope data combined with biogeochemical modelling generate hypotheses regarding animal behaviours that can be tested with other methodological approaches., This research was conducted as part of C.S.B.’s Ph.D dissertation, which was funded by the University of Southampton and NERC (NE/L50161X/1), and through a NERC Grant-in-Kind from the Life Sciences Mass Spectrometry Facility (LSMSF; EK267-03/16). We thank A. Bates, D. Sims, F. Neat, R. McGill and J. Newton for their analytical contributions and comments on the manuscripts.

We used remote sensing chlorophyll a concentration data, spring copepod abundance, and individual fish condition information to understand the annual recruitment variability of two neighboring haddock (Melanogrammus aeglefinus) stocks in the Gulf of Maine region. When we considered the full range of recruitment variability, the abundance of the copepods Calanus finmarchicus and Pseudocalanus spp. failed to explain the variation in survivor ratio in either stock. However, when we examined this relationship with subsets of the data, we found that Pseudocalanus spp. appears to have had an effect on survivor ratio. The full range of recruitment variability of the Georges Bank stock was found to correlate with the timing and size of the fall bloom the year before recruitment, which has been termed the parental condition hypothesis, suggesting that the fall bloom affects the condition of spawning adults and thus recruitment. The absence of a correlation between fall bloom and recruitment in the Gulf of Maine stock can be attributed to the difference in fall bloom frequency between the two stock areas. It appears that both parental condition and larval survival affect haddock recruitment; however, the relative impact of these effects depends on the contrasting nature of ecosystem environmental drivers.

The spring phytoplankton bloom on the US Northeast Continental Shelf is a feature of the ecosystem production cycle that varies annually in timing, spatial extent, and magnitude. To quantify this variability, we analyzed remotely-sensed ocean color data at two spatial scales, one based on ecologically defined sub-units of the ecosystem (production units) and the other on a regular grid (0.5°). Five units were defined: Gulf of Maine East and West, Georges Bank, and Middle Atlantic Bight North and South. The units averaged 47×103 km2 in size. The initiation and termination of the spring bloom were determined using change-point analysis with constraints on what was identified as a bloom based on climatological bloom patterns. A discrete spring bloom was detected in most years over much of the western Gulf of Maine production unit. However, bloom frequency declined in the eastern Gulf of Maine and transitioned to frequencies as low as 50% along the southern flank of the Georges Bank production unit. Detectable spring blooms were episodic in the Middle Atlantic Bight production units. In the western Gulf of Maine, bloom duration was inversely related to bloom start day; thus, early blooms tended to be longer lasting and larger magnitude blooms. We view this as a phenological mismatch between bloom timing and the “top-down” grazing pressure that terminates a bloom. Estimates of secondary production were available from plankton surveys that provided spring indices of zooplankton biovolume. Winter chlorophyll biomass had little effect on spring zooplankton biovolume, whereas spring chlorophyll biomass had mixed effects on biovolume. There was evidence of a “bottom up” response seen on Georges Bank where spring zooplankton biovolume was positively correlated with the concentration of chlorophyll. However, in the western Gulf of Maine, biovolume was uncorrelated with chlorophyll concentration, but was positively correlated with bloom start and negatively correlated with magnitude. This observation is consistent with both a “top-down” mechanism of control of the bloom and a “bottom-up” effect of bloom timing on zooplankton grazing. Our inability to form a consistent model of these relationships across adjacent systems underscores the need for further research.

Environmental cues that are associated with individual movement of threatened Gulf Sturgeon from upriver areas to nearshore and offshore winter feeding areas have been described throughout much of their range in the Gulf of Mexico. In this study, we focus on small-scale movement of Gulf Sturgeon between summer 'holding' areas and the fall staging area in the Pascagoula River system (Mississippi, USA). We evaluated a set of logistic regression models using Akaike's Information Criterion (AICc) and found that relative changes in barometric pressure, time of day, and water temperature were cues for small-scale Gulf Sturgeon movements during fall outmigration. Numerous environmental cues appear to drive the activity of Gulf Sturgeon in staging areas, indicating the complexity of abiotic factors affecting the observed staging patterns during emigration. The identification of the environmental drivers that are associated with Gulf Sturgeon movement is particularly important if these known saline transition zones change spatially annually with variable rainfall or due to water withdrawals and are used by Gulf Sturgeon making osmotic adjustments while moving downriver.

The haddock (Melanogrammus aeglefinus) stock on Georges Bank in the Northwest Atlantic is characterized by extremely large recruitment events relative to spawning-stock biomass. Recent work has indicated that the dynamics of the preceding autumn bloom may have explanatory power to describe these events. In this paper, we examine the hypothesis that autumn phytoplankton dynamics affect the recruitment of haddock, examine the temporal and spatial characteristics of the autumn phytoplankton bloom on Georges Bank, and correlate individual sex-specific condition measurements of haddock made in spring to recruitment patterns. Autumn bloom characteristics vary considerably across Georges Bank with earlier-occurring and larger-integral blooms occurring on the northern flank. On average, autumn blooms start on day 273 (29 September) and persist ∼50 days. There was a significant negative correlation detected between bloom start date and recruitment and a significant positive correlation of bloom integral and recruitment. The survivor ratio loge(R/SSB) was positively and significantly correlated with individual condition of females in spring. The analysis of autumn bloom on Georges Bank provides a predictive index for recruitment strength of haddock and has utility for the assessment of this stock.

The North Atlantic Ocean contains diverse patterns of seasonal phytoplankton blooms with distinct internal dynamics. We analyzed blooms using remotely-sensed chlorophyll a concentration data and change point statistics. The first bloom of the year began during spring at low latitudes and later in summer at higher latitudes. In regions where spring blooms occurred at high frequency (i.e., proportion of years that a bloom was detected), there was a negative correlation between bloom timing and duration, indicating that early blooms last longer. In much of the Northeast Atlantic, bloom development extended over multiple seasons resulting in peak chlorophyll concentrations in summer. Spring bloom start day was found to be positively correlated with a spring phenology index and showed both positive and negative correlations to sea surface temperature and the North Atlantic Oscillation in different regions. Based on the characteristics of spring and summer blooms, the North Atlantic can be classified into two regions: a seasonal bloom region, with a well-defined bloom limited to a single season; and a multi-seasonal bloom region, with blooms extending over multiple seasons. These regions differed in the correlation between bloom start and duration with only the seasonal bloom region showing a significant, negative correlation. We tested the hypothesis that the near-surface springtime distribution of copepods that undergo diapause (Calanus finmarchicus, C. helgolandicus, C. glacialis, and C. hyperboreus) may contribute to the contrast in bloom development between the two regions. Peak near-surface spring abundance of the late stages of these Calanoid copepods was generally associated with areas having a well-defined seasonal bloom, implying a link between bloom shape and their abundance. We suggest that either grazing is a factor in shaping the seasonal bloom or bloom shape determines whether a habitat is conducive to diapause, while recognizing that both factors can re-enforce each other.

proportion of eggs that hatched was 73% (95% confidence interval: 53 to 93%). We observed that 50% of larvae emerge from eggs at 3.5 days and 99% of larvae emerge at 7.5 days in incubation. Daily egg production increased to a maximum number (range: 8 to 48) of eggs at 92 days post hatch. Total egg production by individual females ranged from 38 to 141 eggs. We found a significant negative linear relationship (F = 34.7, P , 0.001, R 2 = 0.28) between the number of eggs collected from an individual during a single egg deposition event (n = 91) and mean egg volume. However, there were large variations in the sizes of individual eggs within a clutch (median CV = 14.8). Our work provides previously unreported life-history information that can be used to effectively develop experiments in the laboratory and field, and increased understanding of this species.

Complete life history information is essential for effective population management, but little is known about the demographic characteristics of the southern stingray Dasyatis americana. We describe life history characteristics of southern stingrays maintained in captivity from birth to 13 years. Size (disc width [DW]) at maturity ranged from 48 to 52 cm in males and from 75 to 80 cm in females; age at maturity was 3–4 years in males and 5–6 years in females. Individual growth was described using three models: the Gompertz function, von Bertalanffy growth function (VBGF), and logistic function. Analyses of DW at age and weight at age indicated that females were significantly larger at birth and reached larger maximum sizes than males. Because of the ability of the VBGF to fit the observed growth and that of previously reported maximum sizes, we favor its use to describe individual growth dynamics for this species. Using this model, we estimated that for males (n = 20), the asymptotic DW (DW∞) was...

Analysis of bomb generated radiocarbon ( 14 C) changes in a red abalone, Haliotis rufescens Swainson shell was used to evaluate age-at-length relationships derived from data from a previous multiyear, multisite tag-recapture study. Shell carbonate was extracted from four successive growth trajectory locations in a single shell with a maximum shell length of 251 mm. Extraction locations were based on Von Bertalanffy growth function (VBGF) predictions and chosen to span the initial rise of the 14 C-bomb pulse that is known to have occurred in surface ocean waters during 1958 ±1 y in the northeast Pacific. The close temporal correspondence of the red abalone sample series to regional D 14 C records demonstrated the utility of the technique for validating age-at-length relationships for the red abalone. The findings provided support for a mean VBGF derived age of 32 y (range 30-33 y) for the specimen; however, the analysis of 14 C data indicated that the specimen could be older.

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.

Estimates of size-specific mortality were made for red abalone, Haliotis rufescens, from mark-recapture data for three size classes at six sites in California. Instantaneous mortality for the smallest size class (≤100 mm) was 0.67 y−1 (0.52–0.84 y−1, mean ± S.E.) to 1.02 y−1 (0.84–1.24 y−1, mean ± S.E.) and decreased with increasing size in both northern and southern California. Mortality was spatially variable for legal size abalone (>178 mm), 0.05 y−1 (0.0–0.14 y−1, mean ± S.E.) to 1.35 y−1 (1.17–1.56 y−1, mean ± S.E.) in northern California and varied temporally in southern California, 0.27 y−1 (0.15–0.42 y−1, mean ± S.E.) to 0.89 y−1 (0.73–1.08 y−1, mean ± S.E.). Estimates of fishing mortality were 0.97 y−1 (±0.21S.E.) and 1.29 y−1 (±0.17S.E.) at two sites in northern California. Understanding the spatial and temporal dynamics of mortality estimates is critical for fishery 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.

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.

The shift in marine resource management from a compartmentalized approach of dealing with resources on a species basis to an approach based on management of spatially defined ecosystems requires an accurate accounting of energy flow. The flow of energy from primary production through the food web will ultimately limit upper trophic-level fishery yields. In this work, we examine the relationship between yield and several metrics including net primary production, chlorophyll concentration, particle-export ratio, and the ratio of secondary to primary production. We also evaluate the relationship between yield and two additional rate measures that describe the export of energy from the pelagic food web, particle export flux and mesozooplankton productivity. We found primary production is a poor predictor of global fishery yields for a sample of 52 large marine ecosystems. However, chlorophyll concentration, particle-export ratio, and the ratio of secondary to primary production were positively associated with yields. The latter two measures provide greater mechanistic insight into factors controlling fishery production than chlorophyll concentration alone. Particle export flux and mesozooplankton productivity were also significantly related to yield on a global basis. Collectively, our analyses suggest that factors related to the export of energy from pelagic food webs are critical to defining patterns of fishery yields. Such trophic patterns are associated with temperature and latitude and hence greater yields are associated with colder, high latitude ecosystems.