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Impairment of reflex actions was correlated with delayed and total mortality under a wide range of fishing conditions including: injury from capture or escape; environmental factors; and different fish sizes. Fish reflexes may be readily measured in the field during fishing experiments to predict bycatch mortality. Free swimming fish, such as escapees placed in sea cages after escape from fishing gear, can be tested for orientation and startle responses to light and sound stimuli. Fish that are to be discarded can be restraining and then tested for reflex actions such as body flip, operculum closure, mouth closure, gag response, and vestibular-ocular response. The proportion of reflex action impairment can be observed and is termed RAMP (reflex action mortality predictor). RAMP can then be correlated with mortality and RAMP curves calculated for mortality prediction. RAMP was related to mortality with sigmoid functions that are biphasic. As fishing stressors increased in intensity, the first phase showed increase in RAMP without concomitant mortality. In the second phase RAMP continued to increase while mortality became apparent and increased.
Injury to fish can be quantified by visual observation and by the use of fluorescein to visualize lesions under uv light. Mortality may be correlated to the extent of lesions caused by abrasion, internal injury, or hooking injury. However, because environmental factors can cause mortality without concomitant changes in physical injury, observing injury alone is not always sufficient to predict mortality. See Davis and Ottmar (2006) for further information on fluorescein. Changes in plasma constituents have been used to quantify physiological impairment in stressed fish. However, changes in cortisol, lactate, glucose, sodium, and potassium were found to generally not be correlated with mortality in laboratory studies of the effects of fishing stressors on walleye pollock, sablefish, Pacific halibut and lingcod. Plasma constituents became elevated after fish were exposed to sublethal stressors and did not increase further as fish began to show mortality. See articles for further information on plasma constituents (Davis et al., 2001; Davis, 2002; Davis and Schreck, 2005; Milston et al., 2006).
Steps for Studying Bycatch Mortality in the Laboratory
Research Topic 1: Fish and Environment Research Topic 2: Fish Habitat Research Topic 3: Bycatch Mortality Research Topic 4: Fishing Gear
Last updated
14 March, 2007
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