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Direct and indirect estimates of natural mortality for Chesapeake Bay blue crab

January 1, 2007

Analyses of the population dynamics of blue crab Callinectes sapidus have been complicated by a lack of estimates of the instantaneous natural mortality rate (M). We developed the first direct estimates of M for this species by solving Baranov's catch equation for M given estimates of annual survival rate and exploitation rate. Annual survival rates were estimated from a tagging study on adult female blue crabs in Chesapeake Bay, and female-specific exploitation rates for the same stock were estimated by comparing commercial catches with abundances estimated from a dredge survey. We also used eight published methods based on life history parameters to calculate indirect estimates of M for blue crab. Direct estimates of M for adult females in Chesapeake Bay for the years 2002–2004 ranged from 0.42 to 0.87 per year and averaged 0.71 per year. Indirect estimates of M varied considerably depending on life history parameter inputs and the method used. All eight methods yielded values for M between 0.99 and 1.08 per year, and six of the eight methods yielded values between 0.82 and 1.35 per year. Our results indicate that natural mortality of blue crab is higher than previously believed, and we consider M values between 0.7 and 1.1 per year to be reasonable for the exploitable stock in Chesapeake Bay. Remaining uncertainty about Mmakes it necessary to evaluate a range of estimates in assessment models.

Publication Year 2007
Title Direct and indirect estimates of natural mortality for Chesapeake Bay blue crab
DOI 10.1577/T06-078.1
Authors D.A. Hewitt, D.M. Lambert, J.M. Hoenig, Romuald N. Lipcius, D.B. Bunnell, T.J. Miller
Publication Type Article
Publication Subtype Journal Article
Series Title Transactions of the American Fisheries Society
Index ID 70030732
Record Source USGS Publications Warehouse
USGS Organization Great Lakes Science Center