Physiological processes and gross energy budget of the longline-cultured Pacific oyster Crassostrea gigas were investigated in Geoje-Hansan Bay, Korea during two entire culturing periods. Based on ...physiological measurements of food consumption, feces production, ammonium excretion, and respiration from July 2008 to February 2009 and from July 2013 to February 2014, scope for growth appeared to be positive during most of the culturing period, except for one period with extremely high temperatures (up to 25°C). Estimates of physiological energy production matched well with tissue energy increment measured by gross biochemical composition during the culturing period, suggesting that the oysters might adjust their physiological performance to relatively low concentrations of suspended particulate matter in the bay to optimize energy acquisition. Such an adaptive adjustment includes an increased absorption of energy and a reduced loss of metabolic and excretory energy, resulting in positive production under high culturing density. Using physiological measurements, we further assessed the feedback effects of the longline aquaculture of oysters on the bay system. Ecological efficiency, estimated by a series of energetic efficiencies at the whole bay level, was low compared with Lindeman's law of trophic efficiency. Biodeposition and ammonia excretion rates in this study were relatively low compared with other intertidal plastic bag cultures. These results indicate that the cultured oysters might have only minor effects on benthic and pelagic environments of the bay. Overall, our results suggest that the adaptive physiological performance of oysters and consequently weak feedback effects on ambient habitats should facilitate sustainable longline aquaculture in the bay for a prolonged period without severe habitat deterioration.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We conducted a simulation study to evaluate performance of surplus production models (SPMs) with a time-varying intrinsic growth rate (SPMTVr) for stocks with predation-driven changes in ...productivity. Data sets were simulated using an age-structured, linked, predator–prey model of Atlantic menhaden (Brevoortia tyrannus), a forage fish native to the Northwest Atlantic, and Atlantic striped bass (Morone saxatilis), its primary predator, with differing time series of fishing mortality on both predator and prey. Simulations generated test data sets for Atlantic menhaden SPMs that included either a static or time-varying intrinsic growth rate parameter. The SPMTVr largely produced more accurate, less variable estimates of exploitation rate and biomass than models with static intrinsic growth. We also applied SPMTVr to empirical Atlantic menhaden catch and survey data for 1964–2016. The SPMTVr fit the survey data well, estimated an intrinsic growth rate time series that mirrored long-term juvenile survey trends, and produced biomass and exploitation rate trends that mirrored a statistical catch-at-age model. The SPMTVr estimated dynamic, maximum sustainable yield (MSY)-based reference points that reflected changing stock productivity.
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Moving toward ecosystem-based fisheries management requires integration of biotic and abiotic factors into our understanding of population dynamics. Using blue crab (Callinectes sapidus) in the ...Chesapeake Bay as a model system, we applied Gaussian Graphical Models (GGMs) to understand the influence of climatic, water quality, and biotic variables on estimates of key indices of blue crab recruitment for 1990–2017. Variables included the North Atlantic Oscillation (NAO), Susquehanna River discharge, wind forcing, hypoxic volume, submerged aquatic vegetation, and the catch per unit effort of striped bass (Morone saxatilis). Direct effects of age‐1+ crabs and summer salinity on recruitment were significant. Phase of the NAO in summer and spring, summer and winter discharge, and hypoxic volume indirectly affected the recruitment. A simulation study showed that GGM model selection achieved nominal coverage and outperformed structural equation modeling (SEM) and Multivariate Adaptive Regression Splines (MARS). GGMs have the potential to improve ecosystem-based management of blue crabs in Chesapeake Bay. Specifically, the approach can be used to examine ecosystem impacts on blue crab productivity and to improve forecasts of blue crab recruitment.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Management strategy evaluation (MSE) is a simulation-based approach to examine the efficacy of management options in achieving fishery-, ecosystem-, and socioeconomic-related objectives while ...integrating over system uncertainties. As a form of structured decision analysis, MSE is amenable to stakeholder involvement, which can reduce implementation barriers associated with nontransparent decision-making procedures. Based on analysis of three MSE processes (Atlantic tunas (Thunnus spp.), Atlantic herring (Clupea harengus), and eastern oysters (Crassostrea virginica)), we provide suggestions for improving stakeholder engagement in MSE. By assembling a workgroup and modeling team with diverse backgrounds, including professional facilitators, communication liaisons, and social scientists, dialogue can be improved and an atmosphere of mutual learning fostered. Communication further benefits from clearly defining roles, responsibilities, and terms of engagement for all involved; explicitly and transparently identifying goals and objectives of the MSE before modeling has begun; and, when appropriate, revisiting goals and objectives throughout the MSE process. Although MSEs are not without limitations, the participatory modeling framework, wherein stakeholders are actively engaged at each stage of MSE development, provides a useful mechanism to support fisheries management.
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Coastal sharks are challenging to manage in the United States due to their slow life history, limited data availability, history of overexploitation, and competing stakeholder interests. Furthermore, ...species like the sandbar shark (Carcharhinus plumbeus) are subjected to international exploitation unmanaged by the US. We conducted a management strategy evaluation using Stock Synthesis on the sandbar shark to test the performance of various configurations of a threshold harvest control rule. In addition to uncertainties addressed in the operating model (OM), we built multiple implementation models to address uncertainties related to future levels of a partially unmanaged source of removals, the combined Mexican and US recreational (MexRec) fleet. We found that the presence of unregulated removals had the potential to significantly influence the success of the various management procedures (MPs) tested. Notably, if MexRec catches continue to increase with total stock abundance following historical trends, the rate of MexRec removals will be too large to allow the sandbar shark to recover across OMs. We present trade-offs between performance metrics across a range of 24 MPs and three implementation models.
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Harvests from recreational fishing are increasingly as important as commercial harvest to populations of popularly fished marine recreational species. However, it has yet to be determined whether the ...increasing importance of recreational fishing is a general trend of marine fisheries in the US or whether such a trend is limited to only those species recognized as popular recreational fishes. 71% of marine species in the US have experienced an increase in the proportion of total harvest from the recreational sector during the time harvest data are available for both sectors. Species demonstrating an increase in the proportion of harvests by the recreational sector included those generally regarded as commercial, bait, and bycatch species, as well as those considered recreational species. Marine species categorized as overfished could not be predicted from either fishery characteristics or life history characteristics in a PCA analysis of available data for fished species in the US. Consequently, there appears to be little to predict vulnerability of populations to fishing efforts save that all fished species can be made vulnerable to overexploitation. Well-developed yield-based strategies, designed for commercial fisheries, are not likely to be effective in managing populations as the diverse recreational fishing sector continues to increase in its importance. Thus, new management strategies for US marine fisheries are needed. Some possible alternative strategies are discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Sperm limitation, where the reproductive output of a population is restricted by its sperm production, is a concern for several crustacean species around the world. We used a simulation study to ...evaluate the effects of different fishing pressures and regulations on the male to female sex ratio and the average number of sperm received per female for the blue crab Callinectes sapidus population in Chesapeake Bay. We created an individual-based model that tracked a cohort of immature females on a daily step over a 2 yr period as the cohort grew, matured, and mated with mature males. The model included sex-specific growth, maturity, and mating of a closed population. We ran the model under multiple scenarios of mate choice behavior to quantify the patterns in sperm counts and sex ratios across a broad range of simulated fishing pressures and regulations. Average sperm counts in mated females and male to female sex ratios of the modeled population varied among scenarios, but were not related to each other. Fishing pressure had a significant negative effect on average sperm per female only in scenarios with unfished females and the exploitation rate for males at 5 times that currently estimated in Chesapeake Bay. Our results suggested that sperm per female is not linearly related to mature male to female sex ratios and that sperm limitation does not appear to be a concern for the blue crab population of Chesapeake Bay under current regulations.
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Abstract
Stock-wide trends in fish relative abundance are challenging to obtain when a single, comprehensive survey is unavailable, and multiple, spatially, and/or temporally fragmented surveys must ...be relied upon instead. Indices of abundance from multiple surveys frequently have differing trends, resulting in obscured true abundance patterns of the resource. We use an age-structured simulation model of two coastal shark species in the southeast United States to explore the performance of dynamic factor analysis (DFA) for reconciling multiple indices of abundance that are in conflict. Survey-specific time-variation in catchability was induced to generate conflicting indices of abundance. Key simulation sensitivities included survey variability, abundance pattern in the resource, and missing years of survey data. We caution against using DFA when there is no contrast in the underlying stock abundance or when trends in catchability in all surveys result in no survey that is representative of stock abundance. When multiple representative surveys were available, DFA proved useful across species in estimating stock-wide trends from conflicting survey indices with different selectivities, catchabilities, variances, and, to a lesser extent, with missing data. Our results suggest that resolving contrasting patterns among multiple time-series of relative abundance can improve understanding of the temporal trend in stock abundance.
In fisheries where there is a limit on total catch in a given period, catch-per-unit-effort (CPUE) data may not be proportional to abundance because catches may be censored at the limit. Commonly ...used depletion estimators (e.g., Leslie method) could be biased when ordinary least squares (OLS) regression is used to estimate abundance with censored CPUE data. We used simulations to examine the performance of OLS regression and a censored regression approach when estimating abundance and exploitation using censored CPUE data over a range of known exploitation rates. We also applied the censored regression approach to data from a commercial fishery for the eastern oyster (Crassostrea virginica). The censored regression approach always performed better than the OLS regression when estimating abundance and exploitation in our simulations. Harvest and abundance of oysters in Fishing Bay, Maryland, increased during 2009 to 2013 and then decreased through 2016, while exploitation rates had no substantial trend over time. The censored regression approach is useful for estimating abundance and exploitation when the distribution of CPUE is affected by daily catch limits.
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