Estimating Early Mortality and Implications for Reference points for the Atlantic Menhaden Stock

Hongsheng Bi and Michael Wilberg, Chesapeake Biological Laboratory, UMCES,


Atlantic menhaden, Brevoortia tyrannus, constitute the largest landings, by volume,
along the Atlantic Coast with distributions from Florida to Maine. This Species spawns in coastal waters and uses estuaries as its juvenile nursery habitat. Based on the stock assessment in 2009, overfishing of Atlantic menhaden is occurring. Meanwhile, coastal environments have changed rapidly including changes in temperature, circulations, and lower trophic levels. Understanding how environmental factors affect early life survival, and incorporation into fishery management reference points, is important for improving fisheries management and stock assessment. In the past year, we have developed a coast wide menhaden larvae index using NEFSC ichthyoplankton survey data and estimated relative larval survival rates in 1977-2010. In year 2, we will focus on
examining how environmental conditions affect larval survival. Specifically, we will: 1)
identify critical time periods for menhaden, 2) examine potential sub lethal conditions during winter time, and 3) investigate how menhaden larval mortality relates to environmental conditions. Our ultimate goal is to incorporate changes in larval mortality into stock-recruitment models and development of time-varying reference points. This work brings together oceanographers and stock assessment scientists from agencies and academia to develop processbased indices, and provides a unique opportunity for scientists to work at the boundary between oceanography and population dynamics to directly contribute to the stock assessment process.