HATTIESBURG, MS / ACCESSWIRE / October 27, 2022 / Researchers with the Science Center for Marine Fisheries (SCEMFIS) have been at the forefront of investigating new ways to improve the science behind menhaden fisheries, the largest fisheries by weight on both the Atlantic and Gulf coasts. The latest effort funded by the Center looks at one of the remaining areas of uncertainty in menhaden science, and how much it potentially affects the accuracy of menhaden assessments.
Menhaden assessments rely largely on data supplied by the menhaden fishery, which, along with assessment modeling and other data collected for the assessments, is used to estimate key measures such as biomass, abundance, and fecundity. But because the data supplied by the fishery is limited to the younger menhaden that are harvested commercially, there is a comparative lack of data on older menhaden to use in the assessment. As a result, these older menhaden are grouped together for counting purposes in what is known as a "plus group."
Defining these plus groups incorrectly has the potential to introduce bias into the assessments, which can affect their accuracy and subsequently affect quota allocations for the fishery. This study looks at the composition of these plus groups to find how big an impact this potential bias has on the final assessment results.
To determine this, the study ran a series of simulations, based on the existing assessment models for both Atlantic and Gulf menhaden, and determined how assumptions made about the plus groups affect the end results. In the models currently used in the Gulf and Atlantic menhaden stock assessments, Gulf menhaden use a plus group of age 4+ menhaden, while Atlantic menhaden use a plus group of 6+. The study simulated what would happen to the assessment results if these definitions were modified by including more or fewer ages of menhaden in the group.
The study found that the definition of what is included in the plus group varies in how it affects the accuracy of the assessment. For Gulf menhaden, increasing the age of the plus group decreased the amount of bias in measurements like abundance and spawning stock biomass, while reducing the plus group age decreased the amount of bias in measurements like recruitment. For Atlantic menhaden, the composition of the plus groups had less of an impact, with the best performing plus group being the one currently used in the assessment model.
"These results show that not only are well-defined plus groups important for stock assessments, but also that the current plus groups are among the best-performing options for the current menhaden assessments," said Genny Nesslage, an Associate Research Professor at the University of Maryland Center for Environmental Science's Chesapeake Biological Laboratory, and one of the authors of the study. "We also outline ways for fisheries scientists to improve these assessments and make them even more accurate."
About SCEMFIS
SCEMFIS utilizes academic and fisheries resources to address urgent scientific problems limiting sustainable fisheries. SCEMFIS develops methods, analytical and survey tools, datasets, and analytical approaches to improve sustainability of fisheries and reduce uncertainty in biomass estimates. SCEMFIS university partners, University of Southern Mississippi (lead institution), and Virginia Institute of Marine Science, College of William and Mary, are the academic sites. Collaborating scientists who provide specific expertise in finfish, shellfish, and marine mammal research, come from a wide range of academic institutions including Old Dominion University, Rutgers University, University of Massachusetts-Dartmouth, University of Maryland, and University of Rhode Island.
The need for the diverse services that SCEMFIS can provide to industry continues to grow, which has prompted a steady increase in the number of fishing industry partners. These services include immediate access to science expertise for stock assessment issues, rapid response to research priorities, and representation on stock assessment working groups. Targeted research leads to improvements in data collection, survey design, analytical tools, assessment models, and other needs to reduce uncertainty in stock status and improve reference point goals.
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SOURCE: Science Center for Marine Fisheries