Using censored regression when estimating abundance with CPUE data to account for daily catch limits

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.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

A performance evaluation of surplus production models with time-varying intrinsic growth in dynamic ecosystems

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, MSY-based reference points that reflected changing stock productivity.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Valuing Changes in Frequency of Fish Stock Assessments

Updating stock assessments frequently and ensuring that the most recent fishery dependent and independent data is included is a costly endeavor. We use a management strategy evaluation for the mid-Atlantic summer flounder fishery to determine the economic returns to increasing update frequencies and decreasing the data management lag. We simulate the annual acceptable biological catch for the period 2015-2040 under a range of update frequencies and data lags. We calculate present value net economic benefits for the commercial and recreational fisheries for each scenario. Discounting, the timing of harvest quotas, species specific price flexibilities and fishing cost response to biomass and quota differences suggest that the benefits gained from frequent updating and reduction in data lags will vary by fishery. For summer flounder, we find the cost of more frequent updating (1 year versus 5 years), and reducing the data management lag (1 year versus 2 years), are more than compensated for by societal benefits generated by the fishery.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

An Evaluation of Acceptable Biological Catch (ABC) Harvest Control Rules Designed to Limit Overfishing

In this paper we developed a simulation model to evaluate a range of acceptable biological catch (ABC) control rules to determine their relative performance at achieving common fishery management objectives. We explored a range of scenarios to determine robustness of a control rule to different situations, and found that across scenarios the control rules that used a buffer to account for scientific uncertainty when setting the ABC were able to limit the frequency of overfishing. Modest buffers when setting the ABC were generally effective at limiting overfishing, but larger buffers resulted in higher average biomass, similar long-term benefits to the fishery (high yield, low variability in yield), more rapid recovery of depleted populations, and a lower risk of the population being overfished, and these results were robust to the level of uncertainty in the assessment model estimates. In addition, fixing the ABC over the interval between assessments and having a short interval between assessments was generally more effective at meeting management objectives than using projections and having a long assessment interval.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Ranking ecosystem impacts on Chesapeake Bay blue crab (Callinectes sapidus) using empirical Gaussian Graphical Models

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.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

International Review Panel Report for the 2019 International Fisheries Stock Assessment workshop

The Panel recognised the very high quality of the research presented at the 2019 International Fisheries Stock Assessment Review Workshop. This included research on stocks of southern African hakes, sardine and rock lobster. New information and research related to an experimental spatial fishing closure near African penguin colonies was also presented.This report starts with observations from the Panel on some general issues for the species and analysis programmes reviewed, and then focuses on answering the questions posed by DEA Research, providing a more detailed technical review where necessary, and finally recommending further work concerning each topic. The recommendations are annotated by their priorities (H, M, L). Much of this report reflects responses to the questions. For ease of reading, answers to the questions that also have research components are indicated by an asterisk

International Review Panel Presentation for the 2023 International Fisheries Stock Assessment workshop

Presentation to the International Stock Assessment Workshop, University of Cape Town, 27 November - 1 December 2023: 17pp, titled: 'International Review Panel Presentation for the 2023 International Fisheries Stock Assessment workshop'</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

Trends in Relative Abundance and Early Life Survival of Atlantic Menhaden during 1977–2013 from Long-Term Ichthyoplankton Programs

<p>The Atlantic Menhaden <i>Brevoortia tyrannus</i>, a commercially important clupeid, supports one of the oldest and largest commercial fisheries on the U.S. East Coast. Despite recent increases in adult biomass, juvenile indices have declined coastwide and have remained particularly low in Chesapeake Bay. In order to understand the underlying causes of this decline, knowledge of larval recruitment is essential. We developed an index of larval abundance by using larval data collected from two large-scale ichthyoplankton sampling programs that occurred from Nova Scotia, Canada, to Cape Hatteras, North Carolina, during 1977–1987 and 1999–2013. Larval abundance data were standardized to a day-0 age by applying an age–length key from a study of larval ingress into Chesapeake Bay; a delta-lognormal model was used to account for spatial and temporal changes in sampling. We found that Atlantic Menhaden larval abundance increased from 1977 to 2013 and was highest in the winter; most individuals were detected at nearshore stations. Over our time series, larval abundance corresponded closely to adult spawning stock biomass. Due to the lack of a direct relationship between our larval abundance estimates and a coastwide juvenile index, we examined several environmental factors (temperature, Chesapeake Bay discharge, Atlantic Multidecadal Oscillation [AMO], wind speed, and wind direction) for potential effects on the relative survival of larvae. Larval abundance had a significant negative effect on relative survival. Temperature and to a lesser extent wind speed and AMO appeared to exert the greatest effects on the early life survival of Atlantic Menhaden: cooler temperatures, intermediate wind speeds, and negative-phase AMO were the most favorable for survival. Our findings suggest that the observed reduction in recruitment is not a problem of larval supply but rather is limited by survival between the larval and juvenile stages.</p> <p>Received December 17, 2015; accepted May 31, 2016 Published online August 12, 2016</p