Research Document - 2011/053

Mortality reference points for the American Eel (Anguilla rostrata) and an application for evaluating cumulative impacts of anthropogenic activities

By G. Chaput and D. Cairns

Abstract

Canada has committed to using the Precautionary Approach (PA) in managing stocks. To be compliant with the PA, fishery management plans should include harvest strategies that incorporate a Limit Reference Point that defines the critical / cautious zones, and a Removal Reference that defines the maximum removal rate in the healthy zone. We propose that the Spawner Per Recruit (SPR) model should be the minimum default model considered to define fishing rate reference points for the American Eel (Anguilla rostrata). We discuss how the SPR approach can be extended to include complex life histories at the local scale, including those associated with the phenotypic plasticity of habitat use, stock complex dynamics, and cumulative impacts. The assumptions or estimates of natural mortality and probability of metamorphosing are relevant only for the age or size groups which are also vulnerable to the human activity being assessed. The derivation of these reference points and their use in management will benefit the species as a whole by ensuring that spawning escapement from each region would be proportional to abundance and conditioned by the life history characteristics of the region. Defining only mortality rate reference levels can be inadequate when stock biomass is low as it does not provide protection against depensatory effects which could express themselves at low biomass levels. Defining reference points is the first part of the larger assessment and management process. Assessing stock status of American Eel remains a challenge.

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