Research Document - 2012/043

What is 2.4? Placing Atlantic Salmon Conservation Requirements in the Context of the Precautionary Approach to Fisheries Management in the Maritimes Region

By A.J.F. Gibson and R.R. Claytor

Abstract

The Department of Fisheries and Oceans (DFO) has adopted “A fishery decision-making framework incorporating the Precautionary Approach (PA)” that is to be used where decisions regarding commercial, recreational, or subsistence controls on harvest and all other removals are required.

For Atlantic salmon, the value of 2.4 eggs/m² of fluvial rearing habitat has a long history as a reference point in science and management advice. Here, this history is reviewed and the results of some newer population dynamics research that allows the conservation requirement to be placed in the context of the PA framework are summarized.

Although, in the past, reference points have been estimated for Atlantic salmon populations using a Ricker spawner-recruit function, this assumption was not tested. A comparison of spawner-recruit models for Atlantic salmon in the Maritimes region revealed no evidence of over-compensation and the Beverton-Holt model provided a significantly better fit when compared over all populations. Therefore, the Beverton-Holt model is the more appropriate spawner-recruit model for biomass-based reference points in the Maritimes Region. Although the value of 2.4 eggs/m² was originally proposed as a value for optimizing smolt production, it was modeled using Ricker spawner recruit functions and is not appropriate to be considered as an Upper Stock Reference in the PA framework.

In the Maritimes Region, the conservation requirement is consistent with a Limit Reference Point in the PA framework based on the empirical work defining 2.4 eggs/m² as the Atlantic salmon conservation requirement, its adoption by the Canadian Atlantic Fisheries Scientific Advisory Committee, and recent population dynamics research supporting the use of the Beverton-Holt relationship. The values for river-specific conservation requirements were estimated using consistent methods and are consistent with the framework advice on dealing with changes in productivity. Additionally, using these values as Limit Reference Points is supported by the current population dynamics work on the LaHave River (above Morgans Falls). The use of the estimated river-specific conservation requirements as Limit Reference Points for individual rivers in the Maritimes Region is recommended.

Additional research to refine Reference Points and Harvest Control Rules for fishery removals is not warranted given the current stock status and level of fish removals identified in recent Recovery Potential Assessments. Rather research on control rules guiding recovery action plans to limit mortality from other anthropocentric sources is required.

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