Sensitivity of Lake Sturgeon population dynamics and genetics to demographic parameters [Powerpoint Slide]

Lake sturgeon Acipenser fulvescens restoration is a priority throughout the Great Lakes basin, where sturgeon have been reduced to less than 1% of historic levels due to habitat degradation, overharvest, and fragmentation of spawning populations. The population parameters most important to long-term lake sturgeon persistence are unknown

Reproductive Dynamics of Gulf Menhaden (\u3ci\u3eBrevoortia patronus\u3c/i\u3e) in the Northern Gulf of Mexico: Effects On Stock Assessments

Gulf menhaden (Brevoortia patronus) produce one of the largest U.S. fisheries, yet information on reproductive dynamics of the stock is sparse. Males and females reach 50% maturity at 140.8 and 137.2 mm fork length, respectively and recruit into the commercial fishery at this size. Analysis of fishery-dependent data from 1964 through 2014 indicated that somatic condition was lower during the late 1980s and late 2000s and that reproductively active fish from 2014 were significantly larger and had greater gonadosomatic index values than those from 1964 through 1970. Histological analysis performed on fish from 2014 through 2016 revealed spawning-capable and actively spawning fish of both sexes from early October through midMarch. Females have indeterminate fecundity, are batch spawners, and spawn every 2.1-4.3 days, although oocyte recruitment shows some characteristics of determinate fecundity. Mean relative batch fecundity was 107.8 eggs/g ovary-free body weight (standard error 17.1). Estimates from age-structured assessment models based on updated fecundity and maturity measures resulted in a 100-1000x greater production of eggs than previous estimates. Model output, including the number-at-age, age-specific fishing-induced mortality, and spawners-per-recruit are sensitive to alterations in age-specific annual fecundity. Therefore, updated estimates of Gulf menhaden reproductive dynamics can affect assessments of the stock

Combining Ecosystem and Single-Species Modeling to Provide Ecosystem-Based Fisheries Management Advice Within Current Management Systems.

Although many countries have formally committed to Ecosystem-Based Fisheries Management (EBFM), actual progress toward these goals has been slow. This paper presents two independent case studies that have combined strategic advice from ecosystem modeling with the tactical advice of single-species assessment models to provide practical ecosystem-based management advice. With this approach, stock status, reference points, and initial target F are computed from a single-species model, then an ecosystem model rescales the target F according to ecosystem indicators without crossing pre-calculated single-species precautionary limits. Finally, the single-species model computes the quota advice from the rescaled target F, termed here Feco. Such a methodology incorporates both the detailed population reconstructions of the single-species model and the broader ecosystem perspective from ecosystem-based modeling, and fits into existing management schemes. The advocated method has arisen from independent work on EBFM in two international fisheries management systems: (1) Atlantic menhaden in the United States and (2) the multi species fisheries of the Irish Sea, in the Celtic Seas ecoregion. In the Atlantic menhaden example, the objective was to develop ecological reference points (ERPs) that account for the effect of menhaden harvest on predator populations and the tradeoffs associated with forage fish management. In the Irish Sea, the objective was to account for ecosystem variability when setting quotas for the individual target species. These two exercises were aimed at different management needs, but both arrived at a process of adjusting the target F used within the current single-species management. Although the approach has limitations, it represents a practical step toward EBFM, which can be adapted to a range of ecosystem objectives and applied within current management systems.publishedVersio

Identifying trade-offs and reference points in support of ecosystem approaches to managing Gulf of Mexico menhaden

Gulf menhaden (Brevoortia patronus) support the largest fishery by yield in the Gulf of Mexico (GoM) and are a key forage species for many marine predators. While menhaden stock assessments indicated that overfishing was not likely to have occurred in the past, concerns have been raised regarding the possible effects of menhaden fishing on their predators. In this study, we used a US Gulfwide Ecopath with Ecosim (EwE) model to explore the predicted effects of increased menhaden harvest on the GoM ecosystem and focused our analyses on Gulf menhaden predators. Key menhaden predators identified included king mackerel (Scomberomorus cavalla), Spanish mackerel (Scomberomorus maculatus), sea trout (Cynoscion spp.), red drum (Sciaenops ocellatus), and pelagic coastal piscivores [e.g., bluefish (Pomatomus saltatrix)]. As expected, these predators exhibited reduced biomass in response to increased Gulf menhaden harvest, with a predicted 11% decrease in predator biomass at simulated fishing levels near historical highs. Our results indicate strong relationships between the effects of menhaden fishing and the predator fishing mortality for king mackerel and intermediate relationships for Spanish mackerel, blacktip shark (Carcharhinus limbatus), red drum, large coastal sharks, and pelagic coastal piscivores. Biomass of predator groups such as demersal coastal invertebrate feeders [e.g., drums and croakers (Sciaenidae)] are more affected by menhaden harvest (through trophodynamics interactions and bycatch removal) compared to the isolated effect of their fishing mortality. For almost all the groups examined in the trade-off analysis, with the exception of sea trout, current biomass (2016) was higher than their target biomass representing 75% of their biomass at maximum sustainable yield. In comparison to the time series of fishing mortality rates estimated by the most recent Gulf menhaden stock assessment, the mean ecological reference point (ERP) of 0.862 was exceeded in all but 1 year from 1977 to 2007; however, neither the target nor threshold upper ERP value has been exceeded since 2008. The observed Gulf menhaden landings from 2003 to the present were generally within the range of the projected equilibrium landings (i.e., within confidence intervals) at both the ERP target and threshold values except for three recent years

Combining Ecosystem and Single-Species Modeling to Provide Ecosystem-Based Fisheries Management Advice Within Current Management Systems

Pubication history: Accepted - 7 December 2020; Published online - 8 January 2021Although many countries have formally committed to Ecosystem-Based Fisheries Management (EBFM), actual progress toward these goals has been slow. This paper presents two independent case studies that have combined strategic advice from ecosystem modeling with the tactical advice of single-species assessment models to provide practical ecosystem-based management advice. With this approach, stock status, reference points, and initial target F are computed from a single-species model, then an ecosystem model rescales the target F according to ecosystem indicators without crossing pre-calculated single-species precautionary limits. Finally, the single-species model computes the quota advice from the rescaled target F, termed here Feco. Such a methodology incorporates both the detailed population reconstructions of the single-species model and the broader ecosystem perspective from ecosystem-based modeling, and fits into existing management schemes. The advocated method has arisen from independent work on EBFM in two international fisheries management systems: (1) Atlantic menhaden in the United States and (2) the multi species fisheries of the Irish Sea, in the Celtic Seas ecoregion. In the Atlantic menhaden example, the objective was to develop ecological reference points (ERPs) that account for the effect of menhaden harvest on predator populations and the tradeoffs associated with forage fish management. In the Irish Sea, the objective was to account for ecosystem variability when setting quotas for the individual target species. These two exercises were aimed at different management needs, but both arrived at a process of adjusting the target F used within the current single-species management. Although the approach has limitations, it represents a practical step toward EBFM, which can be adapted to a range of ecosystem objectives and applied within current management systems.The Atlantic menhaden work was supported by National Oceanic and Atmospheric Administration Award No. NA15NMF4740069 and Lenfest Ocean Program grants nos. 00025536 and 00032187, and thanks all of the members of the ASMFC Menhaden Technical Committee and the ERP WG for their critical contributions to model development and helpful discussions. We acknowledge the members of the ICES Benchmark Workshop WKIrish for their participation and collaboration, and the NWWAC and BIM for facilitating the meetings. The EwE modeling work was carried out with the support of the Marine Institute and funded under the Marine Research Sub-programme by the Irish Government (Grant-Aid Agreement No. CF/16/08). DP was supported by the Science Foundation Ireland (www.sfi.ie) Investigator Programme (grant no. 14/IA/2549), and DR by Project FishKOSM funded by the Department of Agriculture, Food and the Marine’s Competitive Research Funding programmes. DH acknowledges support from the Institute of Marine Research strategic project Reduced Uncertainty in Stock Assessment (REDUS). Open access funding was provided by the Institute of Marine Research, Norway

Modeling the Sustainability of Walleye Populations in Northern Wisconsin Lakes

Walleye populations in northern Wisconsin face exploitation from angling and spearing fisheries that are regulated using a total annual exploitation rate of 35%. However, the sustainability of the 35% exploitation rate has never been evaluated, so my primary objective was to evaluate the sustainability of walleye populations across a range of lake sizes ( abundance varies with lake size) that are then subjected to ranges of exploitation rates and allocations of angling and spearing harvest (the fisheries differ greatly in size selectivity). I also sought to determine if age at maturity and length-specific fecundity were density dependent for walleyes in Big Crooked Lake, Wisconsin, during 1997-2003, where walleye were purposely subjected to high exploitation as part of a field evaluation of walleye population sustainability under exploitation stress. I completed my secondary objective first to incorporate the results into my primary objective. To complete my secondary objective, I evaluated the effect of adult walleye Sander vitreus population density on age at 50% maturity and length-specific fecundity in Big Crooked Lake, Wisconsin, during 1997-2003. Abundance of adult walleye from mark-recapture surveys ranged from 2,046 fish (3 walleye/acre) to 4,901 fish (7 walleye/acre). Age at 50% maturity ranged from 3.89 years to 4.88 years, length of walleye sampled for fecundity ranged from 13.0 in to 24.7 in, and average fecundity of a 17-in walleye ranged from 41,061 eggs to 53,009 eggs. Age at 50% maturity increased significantly as adult walleye population density increased, whereas average fecundity of a 17-in walleye did not change significantly with density. Therefore, age at 50% maturity could be used as an indicator of population density and exploitation stress and thus could be used to set desired levels of harvest. To complete my primary objective, I developed an age-structured population model for estimating extinction risk and time to extinction for a hypothetical walleye population at a specified exploitation rate, fishery allocation, and initial abundance. The age-structured population model was parameterized from intensive surveys of walleye populations in Escanaba Lake and extensive surveys of walleye populations in northern Wisconsin lakes. Simulations covered a range of annual exploitation rates that included the currently-accepted rate of 3 5% and a range of population sizes that are presently included in regression models that relate walleye abundance to lake surface area. The risk of extinction began to increase above zero at an exploitation rate of 56-61% for an unregulated angling fishery, 73-76% for an angling fishery with a 15 in minimum length limit, and 75-80% for a spearing fishery. The probability of decline began to increase above zero at an exploitation rate of 47% for an unregulated angling fishery, 60% for an angling fishery with a 15 in minimum length limit, and 60% for a spearing fishery. As the exploitation rate increased, the average adult abundance decreased and the time to extinction decreased for all lake sizes and initial population sizes. I conclude that the current maximum exploitation rate of 35% is sustainable for all lake sizes and initial population sizes and that angler daily bag limits and spearing quotas could be increased while still ensuring the sustainability of walleye populations. However, steps should be taken to implement a field experiment to verify the results of the simulation model before the results are used for management.Wisconsin Department of Natural Resources and by the U. S. Forest Service, Federal Aid in Sport Fish Restoration (grant F-95-P)

A Simulation-Based Evaluation of Commercial Port Sampling Programs for the Gulf and Atlantic Menhaden Fisheries

© 2020 American Fisheries Society. Biological data that are collected in commercial port sampling programs are a critical component of the assessment and management of Gulf Menhaden Brevoortia patronus and Atlantic Menhaden Brevoortia tyrannus. The menhaden port sampling program represents one of the longest continuous commercial sampling efforts in the United States; however, this sampling program has not been evaluated recently to determine whether the program adequately characterizes the size and age structure of the catch despite significant changes in the spatial extent and magnitude of the fisheries in the last three decades. We conducted a simulation study to evaluate current menhaden fishery sampling targets and to examine the relative performance of a suite of alternative targets. To simulate data collection, we conducted a bootstrap analysis of the observed port sampling data. These observations were resampled with replacement across a range of current and alternative combinations of number of trips and fish sampled per trip. At the current target for sampling intensity and allocation, the mean sample weight and proportions at age for ages 2 and 3 are well characterized in both the Gulf and Atlantic menhaden fisheries. The proportions of age‐1 fish in the catch differed by stock and region, with samples from the northern Atlantic regions displaying the greatest uncertainty overall. The proportions of age‐4 and older fish were poorly characterized in both fisheries, which is likely due to their rarity in the population (Gulf) and lack of spatial overlap between the fishery and the stratified distribution of menhaden by age along the coast (Atlantic). Our results indicate that reducing the number of fish that is sampled per trip from the current target of 10 to as few as four would have a minimal effect on estimates of mean size and proportions at age in the catch. Increasing the number of sampled trips will not greatly improve the characterization of catch size or age composition