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

Transactions of the American Fisheries Society

By:
, , , , , and
DOI: 10.1577/T06-078.1

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Abstract

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 M makes it necessary to evaluate a range of estimates in assessment models. ?? Copyright by the American Fisheries Society 2007.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Direct and indirect estimates of natural mortality for Chesapeake Bay blue crab
Series title:
Transactions of the American Fisheries Society
DOI:
10.1577/T06-078.1
Volume
136
Issue:
4
Year Published:
2007
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Transactions of the American Fisheries Society
First page:
1030
Last page:
1040
Number of Pages:
11