Research Document 2017/010
Review and Evaluation of Fishing-Related Incidental Mortality for Pacific Salmon
By Patterson, D.A., Robinson, K.A., Lennox, R.J., Nettles, T.L., Donaldson, L.A., Eliason, E.J., Raby, G.D., Chapman, J.M., Cook, K.V., Donaldson, M.R., Bass, A.L., Drenner, S.M., Reid, A.J., Cooke, S.J., and Hinch, S.G.
Abstract
The number of fish that encounter fishing gear is greater than the number of fish retained as catch. The proportion of this difference that die from the encounter is defined as fishing-related incidental mortality (FRIM). FRIM estimates are required for improved stock assessments, but they are difficult to attain and vary across fisheries. To cope with this challenge we review and evaluate the scientific knowledge on FRIM. First, we review the different mortality components of FRIM (i.e., avoidance, escape, depredation, drop-out, on-board, short-term release, and delayed mortality) in relation to how a fish responds to different aspects of a fishery encounter (e.g., handling). To better understand how fish respond to a fishing encounter, different fishing factors (e.g. gear type) that act in consort with extrinsic (e.g., water temperature) and intrinsic (e.g., fish size) factors elicit different fish responses that can lead to the different types of mortality (e.g. acute) were examined. A fish response to a stressor (i.e., factor) is a combination of the magnitude and duration of the stressor itself. The initial fish response includes acute physiological stress and injury, followed by behaviour changes, chronic stress, and increased risk of infection. Next, a review was done to provide an up-to-date accounting of the mortality rate information available on estimates of FRIM for Pacific salmon (Oncorhynchus spp.). We created an interactive and searchable catalogue of evidence from predominantly primary literature using standardized systematic mapping protocols, with a focus on coding information to determine study reliability and relevance. Next, we synthesize the factor and mortality information to provide recommendations on the use of five major mortality risk factors that are linked to FRIM. Each factor (capture, handling, injury, water temperature, and predators) is scaled to a mortality risk to provide guidance on evaluating FRIM estimates. The recommendations from this work are focussed on addressing the current knowledge gaps and examining FRIM in broader physiological and ecological context. Ideas for future work include researching cumulative impacts, sub-lethal effects, drop-off mortality, and predation. We have chosen a fish-centric hybrid approach that focusses first on understanding factors that drive mortality, and then on mortality estimates. As such, this paper is not meant as the definitive guide on FRIM but a transparent, defensible, and rigorous evaluation of the primary evidence base for making future decisions about FRIM. Further guidance on how to use the information herein is part of an accompanying CSAS research document.
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