Understanding Atlantic Menhaden Population Dynamics Through Use of Data from a Large-scale Historical Tagging Study
Principal Investigator:Michael Wilberg
Start/End Year:2014 to 2016
Institution:Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science
Co-Principal investigator:Thomas Miller, Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science; Amy Schueller, Beaufort Laboratory, National Marine Fisheries Service; Joseph Smith, Beaufort Laboratory, National Marine Fisheries Service
Rationale: Atlantic menhaden (Brevoortia tyrannus) plays an important role in linking production from lower trophic levels to diverse marine predators and supporting the largest commercial fishery on the U.S. east coast. A significant management controversy has arisen because of uncertainties over their movement into and out of Chesapeake Bay and the size or age-dependent vulnerability of fish to the commercial fishery. A landmark mark-recapture study of Atlantic menhaden was conducted during the 1960s–70s, which allows estimation of movement rates. Over one million menhaden were tagged, and over 200,000 tags were recovered, but the data were never fully analyzed. The proposed work will substantially improve our knowledge of menhaden population dynamics (migration and mortality rates), reduce uncertainty in estimates of stock status, and advance ecosystem-based management of the fishery.
Objectives: Our proposed research has four objectives: 1) estimate migration, survival, and exploitation rates from the historical adult tagging data. Substantial advances in mark-recapture methods since the 1970s have allowed for the joint estimation of migration and survival rates using a multi-state hierarchical Bayesian Cormack-Jolly-Seber model, the estimates of which will then be available for the stock assessment and our third objective; 2) estimate age-based selectivity of the commercial fishery based on age-0 tag releases; 3) compare spatial distribution of menhaden over time; and 4) conduct a simulation study to estimate the effects of the current spatial distribution of the Atlantic menhaden fishery, which is centered on Chesapeake Bay, on the spatial distribution and population dynamics of Atlantic menhaden. The simulation model will estimate the effects of the fishery on the sustainability of the menhaden resource.
Methods: Migration and survival rates will be estimated using a suite of Bayesian hierarchical mark-recapture models. We will divide the Atlantic coast into five regions and estimate the probability of survival within and movement among regions accounting for tag induced mortality, tag shedding, and probability of detection. We will separately apply this approach to the smaller age-0 (these fish are known age) data set to estimate age- based fishery selectivity in each region. We will use data from the NMFS trawl survey and food habits database to determine if menhaden's range changed over time. Finally, we will use simulation analyses to estimate the effect of the spatial distribution of the fishery on the spatial distribution of menhaden. We will simulate the population using estimates of migration and natural mortality rates from the mark-recapture study and fishing mortality rates based on stock assessment estimates.
Outcomes: We will obtain estimates of migration rates and selectivity patterns, develop maps of the menhaden's range, and obtain estimates of the impact of the spatial distribution of the fishery on menhaden. We will also develop an outreach program for managers in the Atlantic States Marine Fisheries Commission, and for the public through science and math education materials based on mark-recapture models, an interactive website and visitors center display for visualizing menhaden migration, public lectures angling groups, and press releases.
This section describes how this project has advanced scientific knowledge and/or made a difference for coastal residents, communities, and environments. Maryland Sea Grant has reported these details to the National Oceanic and Atmospheric Administration (NOAA), one of our funding sponsors.
Summary: Researchers used data from a historic, large-scale fish tagging study to produce new analyses that improved understanding of the population dynamics of Atlantic menhaden and informed sustainable management of the commercial fishery for this species.
Relevance: The commercial fishery for Atlantic menhaden (Brevoortia tyrannus) is the largest on the U.S. East Coast. Menhaden are significant in the food web of the Chesapeake Bay and coastal ocean, serving as prey for species such as striped bass that provide economic value through harvests by recreational and commercial fishers. Resource managers need improved knowledge about the effect of the fishery, which is centered on the Chesapeake Bay, on the sustainability of the menhaden resource both in the estuary and along the Atlantic coast from New England to Florida. New understanding about menhaden population dynamics, including migration and mortality rates, could reduce uncertainty in estimates of stock status and advance ecosystem-based management of the fishery.
Response: Researchers carried out new analyses and modeling using data from a mark-recapture study of Atlantic menhaden conducted during the 1960s and 1970s. More than one million menhaden were tagged and over 200,000 tags were recovered. The researchers used these data and data about the effort and catch of the commercial menhaden reduction fishery to estimate age-based selectivity of the commercial fishery, natural and fishing mortality, and the spatial distribution of menhaden. Unlike previous analyses of this tagging dataset, this project estimated migration among five Atlantic coast zones and accounted for lost tags. The project team provided an education campaign for fisheries managers and the general public. Researchers from the Chesapeake Biological Laboratory at the University of Maryland Center for Environmental Science and the Beaufort Laboratory of the National Marine Fisheries Service (NMFS) collaborated on the study.
Results: This project supported the development of new, quantitative estimates of menhaden migratory patterns, an improvement over the solely qualitative descriptions provided in previous analyses of this tagging dataset. Among the findings were that fishing mortality was highest in the southern Atlantic region, and fish movement appeared to vary by season and age. These findings informed a stock assessment of Atlantic menhaden prepared by a technical committee for the Atlantic States Marine Fisheries Commission (ASMFC), which manages the fishery. The assessment concluded that the menhaden resource is not overfished nor experiencing overfishing relative to existing biological reference points. The ASMFC subsequently decided in 2015 to increase the total allowable catch by 10 percent over the 2014 level, which was consistent with the stock assessment. The ASMFC also expressed interest in establishing ecological-based reference points for managing Atlantic menhaden that reflect its role as a forage species (prey for other species). The results of the MDSG research project will be useful for informing future spatial management of menhaden along the Atlantic coast and ultimately to help ensure that the menhaden fishery is sustainable.