Habitat-based reference points for Saint John River Alewife, upstream of the Mactaquac dam

Abstract

Reference points were developed for the Saint John River Alewife stock subunit upstream of the Mactaquac Dam, in accordance with a previously peer-reviewed framework for the development of reference points for Alewife based on estimated nursery area and the median habitat carrying capacity per unit area. A nursery area of 58,676 acres, the sum of all habitat characterized as accessible or potentially accessible, was used to calculate reference points. This nursery area includes all accessible or potentially accessible nursery area above Beechwood, Tobique, and Tinker dams in New Brunswick. At 195 kg/acre, the spawning stock biomass in the absence of anthropogenic mortality (SSB0) was calculated to be 11,400,000 kg. The corresponding limit reference point (LRP) and proposed upper stock reference (USR) are 1,140,000 kg and 1,690,000 kg, respectively. If the 13,783 acres of nursery area upstream of anthropogenic barriers were accessible, the total nursery area would be 72,459 acres. For this amount of nursery area, the SSB0 is 14,100,000 kg. The corresponding LRP and proposed USR are 1,410,000 kg and 2,090,000 kg, respectively. Biomass reference point recalculation may be considered following new information on habitat accessibility and/or changes to the amount of available habitat resulting from modifications to passage efficiency or barrier removal.