Recruitment synchrony in spatially structured Newfoundland and Labrador populations of American plaice (Hippoglossoides platessoides)

Abstract

Appropriate stock delineation is one of the fundamentals for reliable stock assessment. Investigating stock delineation is not a common practice on regularly assessed stocks, yet it is highly desirable prior to extensive investment into new assessment approaches for a stock. Recruitment correlations are an important determinant of stock boundaries, and in this paper, we investigate these correlations between American plaice stocks/components in the Northwest Atlantic Fisheries Organization (NAFO) Divisions 2J3KLMNOPs. Currently, American plaice in 2J3K are managed as part of the Labrador and the northeast coast of Newfoundland stock, 3LNO as the Grand Bank stock, and sub-Division 3Ps as the St Pierre Bank stock. We estimated mixed-effect cohort-strength models using abundance indices from Canadian Research Vessel (RV) surveys conducted every year in the spring (3LNOPs) and fall (2J3KLMNO) and investigated the correlation in the recruitment patterns of American plaice in these NAFO divisions. We performed cluster analysis to assess if the estimated correlations are consistent with the current stock delineations. We further explored causative/correlative relationships between spawning stock biomass (SSB), temperature, and recruitment. Our analyses supported the separation of the 2J3K northeast coast stock from the Grand Bank (3LNO) and St Pierre (3Ps) stocks. Our analysis showed strong synchrony in recruitment patterns between the 3LNO and 3Ps regions indicating either interactions in American plaice populations between the Grand Bank and St Pierre stocks, or strong environmental influences on recruitment success that affect both stocks similarly. Our analyses of recruitment correlations with SSB and temperature did not indicate strong associations except for significant correlations between recruitment and SSB between 3L and 3Ps.