Research Document - 2016/105

A Framework for the Assessment of the Status of River Herring Populations and Fisheries in DFO’s Maritimes Region

By Gibson, A.J.F., Bowlby, H.D., and Keyser, F.M.

Abstract

Alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis) are diadromous species of fish that are collectively referred to as river herring. River herring return to many of the river systems in Nova Scotia and Southwest New Brunswick and are fished together as “gaspereau”. The fishery is geographically widespread, with fishing practices and gear types that differ among rivers, and is managed primarily through effort controls. Within the Maritimes Region, the status of river herring stocks has not been regularly assessed.

Towards the goal of developing an on-going monitoring and assessment program, this framework was developed to provide an overview of the spatial scale for assessment and identification of stock units, reference points against which status could evaluated, monitoring methods, analytic methods and research recommendations, taking into account DFO’s precautionary framework for fisheries management.

River herring have a high degree of fidelity to natal rivers, the populations of each species in individual rivers are considered to be discrete. Reference points are well developed for alewife and are defined on two axes: one that identifies whether overfishing is occurring, and one that identifies whether abundance is in the critical, cautious or healthy zones. Reference points for blueback herring have not been developed. Monitoring and assessment approaches differ depending whether data are fishery dependent or independent. With fishery dependent data only, in the short term, status can only be assessed relative to fishing mortality reference levels, whereas in the longer term, statistical catch-at-age models, which are well developed for at least alewife, can be used to estimate both abundance and mortality rates enabling status evaluations on both axes. In situations where fishery independent data (escapement counts) are available, status can be evaluated on both axes in the short term, whereas in the longer term, application of statistical catch-at-age models would be expected to lead to an improved understanding of population dynamics leading to improved advice. Research that helps to apportion landings from mixed-stock fisheries to specific stocks, as well as research leading to an improved understanding of how other human activities affect stocks (e.g. efficiency of fish passage facilities, survival at dams, increased habitat in reservoirs) is anticipated to significantly improve advice within the precautionary framework.

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