2023 stock status update of Eastern Scotian Shelf Northern Shrimp (SFAs 13-15)

Abstract

Advice on the status of the Eastern Scotian Shelf (ESS) Northern Shrimp (Pandalus borealis) stock is requested annually by Fisheries and Oceans Canada (DFO) Resource Management to help determine a Total Allowable Catch (TAC) that is consistent with its management plan (DFO 2011). Annual science advice is required because of the potential for rapid changes in abundance, variable recruitment to the population and fishery, and changes in the size of ESS Northern Shrimp available for harvest. This stock is also near the southern limit of the species’ distribution where it is thought to be more vulnerable to significant and rapid declines, as observed in the adjacent Gulf of Maine and Gulf of St. Lawrence (GSL) stocks (ASMFC 2018; DFO 2022a). For further comparison, the GSL stocks have declined in their survey abundance since the mid-2000’s in three out of four areas (DFO 2022a). The GSL stocks have also been moving to shallower water depths, which has similarly been observed for the ESS Northern Shrimp stock in recent years. This movement to shallower waters in the GSL has been interpreted to be the result of unfavorable environmental conditions dominated by the effect of warming water temperatures (DFO 2022a). Northern Shrimp exhibit protandrous sequential hermaphroditism, hatching as males and eventually transitioning into females; a unique biological feature linked to the reproductive success. For this reason, faster growth coupled with lower mortality in males increases reproductive success of ESS Northern Shrimp (Henshaw 2018). Under cooler environmental conditions, Northern Shrimp grow more slowly, change sex later, and live longer, reaching a larger maximum size. In contrast, faster growing shrimp under warm environmental conditions initiate an earlier transitional stage and thus reach a smaller maximum size more quickly (Hardie et al. 2018). Flexibility in this growth response, and in the onset of the transitional stage, results in the growth rate being strongly influenced by variable environmental factors throughout all life cycle stages (Koeller 2006). This Science Response Report provides information on the 2023 fishery and an assessment of considerations for its management in 2024. This report is from the regional peer review held on January 5, 2024, entitled the Stock Status Update of Northern Shrimp on the Eastern Scotian Shelf.