Science Advisory Report  2016/049

Review and Evaluation of Fishing-Related Incidental Mortality for Pacific Salmon


  • Fishing-related incidental mortality (FRIM) includes all mortality associated with fishing activities, beyond the mortality accounted for in retained catch. FRIM includes estimates of mortality rates for fish that encounter fishing gear but are not captured (e.g. escape mortality), that are dead upon or die during capture (e.g. on-board mortality), or that die after release (e.g. post-release mortality).
  • FRIM rates are used by fisheries management and stock assessment programs in the accounting of total mortality estimates of Pacific salmon. Issues with the FRIM rates currently used in stock assessment analyses and fisheries management plans for Pacific salmon include the variability in the length of time mortality is monitored after a fishing encounter, the need to include fishery context-specific information (e.g. water temperature), and the current lack of a transparent, objective and reliable process to incorporate new research as it becomes available.
  • A novel, fish-centric approach was developed to better understand the factors that drive incidental mortality associated with fishing and to place the reviewed literature within the context of FRIM.  An extensive primary literature review was conducted and relevant metadata were documented in updateable, searchable tables. Using this approach, detailed written reviews were provided for more than forty factors that can influence FRIM, with each factor assessed via a biologically-based mechanistic framework.
  • An interactive catalogue was created to house empirical evidence of mortality estimates relevant to FRIM of salmonids.  The protocol used for the standardized search and data extraction of the relevant primary and grey literature was documented to facilitate the future inclusion of new information, as requested by Fisheries Management.
  • Collectively, the factor analysis and mortality data catalogues provide a scientific evidence base for making future decisions about FRIM that are rigorous, objective and transparent.
  • A synthesis of the factor analysis and the different components of FRIM was conducted to better describe and predict FRIM. Five factors (capture time, handling, injury, water temperature and predators) were selected for characterizing the risk of FRIM based on two steps: first, a review of the supporting evidence and biological mechanisms relating the factor to fish response; second, a review of the magnitude of the response and utility of the factor for generating FRIM rates. In addition, the five factors can be used to derive and compare the relative risk of FRIM across Pacific salmon fisheries, providing a measure of scalability of the factor against the likelihood of mortality risk (i.e. it is possible to measure or assess the factor in a wide range of real fisheries).
  • A risk assessment tool was developed for assessing a risk score for each factor for a given fishery, and using those factor scores to generate a combined fishery-specific mortality risk score. The cumulative impact of the factors was presented as a range of mortality risk, facilitating the ability to compare the relative risk of FRIM among Pacific salmon fisheries. High correlation between the FRIM risk scores and empirically-determined estimates of mortality rates supported the validity of the approach for describing FRIM.
  • Provision of updated FRIM estimates for direct use in fisheries management was not within the scope of this project. Instead, guidance on a process to use the mortality risk scores to derive numerical estimates of mortality rates was presented. The process is dependent on anchoring risk scores to mortality estimates from the literature, following a standardized approach to sourcing appropriate information and evaluating its reliability and relevance. To ensure the anchoring process is valid, further input from experts with expertise and knowledge of relevant Pacific salmon fisheries is required. 
  • There is inherent difficulty in inferring impacts from most FRIM-related studies due to uncertainty in the representativeness of the studies to actual fishery conditions.
  • A major knowledge gap associated with most FRIM studies is the extent to which FRIM represents an incremental level of mortality over background natural mortality. There is a need for additional research efforts to refine methods for quantifying natural mortality and FRIM, and that will subsequently refine our ability to assess causal links between individual mortality events and fisheries interactions.

This Science Advisory Report is from the June 6-7, 2016 regional peer review on the Review and Evaluation of Fishing-Related Incidental Mortality for Pacific Salmon.  Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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