Definition of Upper Stock Reference, Target Reference and Maximum Removal Rate Reference Points for Atlantic Salmon (Salmo salar) of DFO Gulf Region

Abstract

Fisheries and Oceans Canada (DFO) is developing a precautionary approach (PA) framework for the management of Atlantic Salmon fisheries for DFO Gulf Region rivers. DFO (2018) previously defined river-specific Limit Reference Points (LRPs) for Atlantic Salmon rivers in DFO Gulf Region. This document addresses the definition of the Upper Stock Reference (USR), the Target Reference (TR), and the maximum Removal Rate (RR) reference points in the healthy zone. The USR is defined as 80% of recruitment at maximum sustainable yield and the TR is recruitment at maximum sustainable yield. The maximum removal rate is the exploitation rate that results in maximum sustainable yield. Reconstructed time series of anadromous Atlantic Salmon returns and spawners from two rivers of DFO Gulf Region augmented by data from twelve rivers of the province of Quebec that are proximate to the rivers of the Gulf Region are analyzed. An approach using ratios is proposed to define the USR and TR values based on the defined LRP values. The ratio quantifies the spread between LRP and USR values derived from adult to adult data which is then applied to the LRP which is defined using only the freshwater phase of the salmon life cycle. The mean ratio of USR to LRP for the twelve rivers analyzed is 3.8 and the ratio of TR to LRP is 4.7. The resulting boundary of the cautious / healthy zones is approximately four times higher than the boundary of the critical and cautious zones. The maximum removal rate is taken directly from the adult to adult stock and recruitment analyses and equals 0.6. The LRP, USR, and TR are defined for each river of DFO Gulf Region known or assumed to have an anadromous salmon run. The reference points are expressed in units of eggs contributed by all anadromous sea age and size groups.