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Fisheries Behavioral Ecology
Research Topic 3: Determine Factors that Cause Bycatch Mortality

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The third step is to determine which fishing factors cause significant mortality or impairment in fish condition. Statistical hypothesis testing is performed with data for condition measures and mortality. The laboratory studies identify important factors for mortality but do not produce direct estimates of escapee and discard mortality. Further studies may be performed in the field based on the laboratory results to estimate bycatch mortality. Relationships between fishing conditions and bycatch mortality may be modeled from limited experimental work. Future bycatch mortality could then be predicted from knowledge of fishery conditions.

Graphs of sablefish discard mortality and fishing conditions

Graphs showing data for mortality (proportion) in sablefish resulting from laboratory exposure to simulated fishing conditions.  The fishing gear axis represents capture by pot (Pot), hooking (Longline), and towing in a net (Trawl).  The temperature axis represents 30 minute exposure to increased seawater temperature after capture which simulates the effects of passage through a thermocline.  After exposure to seawater temperature, all fish were exposed to 15 minutes air at 16 oC , except for towed fish which were exposed to increased air times indicated in parentheses.  Smaller (30-49 cm total length) and larger fish (50-70 cm total length) were tested to show the effect of fish size.

Our research has shown that fish size and species may modify the effects of potential mortality factors.  If these factors are of interest, then experiments can be conducted which use various sizes of fish and different species.  See Davis (2002) for further information on size and species effects.    

For further information on bycatch mortality factors see articles (Olla et al., 1997; Olla et al., 1998; Davis et al., 2001; Davis and Olla, 2001; Davis and Olla, 2002; Davis and Parker, 2004; Davis and Schreck, 2005; Lupes et al., 2006; Milston et al., 2006).


Steps for Studying Bycatch Mortality in the Laboratory
[ Step 1] [ Step 2 ] [ Step 3 ] [ Step 4 ] [ Step 5 ] [ Step 6 ]


Research Topic 1: Fish and Environment

Research Topic 2: Fish Habitat

Research Topic 3: Bycatch Mortality

Research Topic 4: Fishing Gear

Last updated 27 March, 2009

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