Incorporating experimentally derived estimates of survey trawl catchability into the stock assessment process
Original version
This report is not to be cited without prior reference to the authorsAbstract
During the course of the April, 1996, meeting of the Fishing Technology and Fish Behavior
Working Group it became clear to many that the methodology for experimentally estimating the
catchability of survey trawls might have progressed sufficiently to produce estimates useful for
stock assessment. To determine whether the formation of a formal Study Group would be
warranted to study the methodology and utility of experimentally derived estimates of trawl
catchability, Steve Walsh, chairman of the FTFB, requested David Somerton to form an ad hoc
group to consider the question and report its findings at the next FTFB meeting. The group
included four members who have conducted experiments to measure trawl performance (Godø,
Ramm, Somerton, Walsh,) and two members who have analyzed or fit stock assessment models
to trawl survey data (Ianelli, Smith). The following report, which attempts to synthesize a rather
brief e-mail discussion among the members of the ad hoc group, will consider the problem from
the perspective of three questions: 1) What does the term "catchability" really mean?, 2) Are
experimentally derived catchability estimates useful for stock assessment? and 3) Can
experimentalists now produce good estimates of catchability?