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AFSC Seminar Series No. 1

Scheduled Seminars

Subject: Fish Discard Mortality: Sources, Prediction, and Reduction

Speaker: Michael W. Davis, AFSC, Hatfield Marine Science Center
: Thursday, 19 January 2006 noon-1:00
Where:  NOAA Sand Point Campus, 7600 Sand Point Way NE, Seattle; Bldg 9

Dear Colleagues: We’re pleased to offer you the first installment of the new AFSC Seminar Series, which highlights center-wide research relevant to ecosystem management.  

Fish Discard Mortality: Sources, Prediction, and Reduction

Michael W. Davis
Alaska Fisheries Science Center, RACE Division
Fisheries Behavioral Ecology Program,
Hatfield Marine Science Center, Newport, Oregon 


The development of direct methods to predict discard mortality in fishing operations is essential for effective conservation of sensitive fish stocks. Currently, discard mortality rates in most fisheries are the result of educated guesses with little or no data. For a few fisheries, discard mortality data are available from fishing experiments in the field or laboratory that describe the bounds of effects from fishing stressors, but suffer from low resolution. A more direct approach to predicting discard mortality entails establishing relationships between fish condition and mortality and then measuring the condition of fish discards from a wide range of fishing operations. Prediction of discard mortality in stock assessments that uses actual fishing conditions as inputs would greatly increase the accuracy of estimates for this source of fishing mortality. Results from laboratory studies in Newport have shown that behavior impairment (decreased reflex responses) can predict total mortality with sigmoid relationships that are species-specific and related to the severity of stressors and stressor combinations. These predictive relationships incorporate the effects of wounding and environmental factors over a range of fish sizes, acting as integrative expressions of stressor effects typically present in fishing. The measurement of behavior impairment and wounding on board fishing vessels to estimate discard mortality appears feasible and would greatly increase the scope of fishing conditions that could be investigated.


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