Local environment affecting northern shrimp recruitment: a comparative study of Gulf of St. Lawrence stocks

Climate and density-dependent effects are important drivers of recruitment (R). In the Gulf of St. Lawrence (GSL), recent years indicated an exceptional warming of water associated with variations in plankton phenology and fish abundance. At the same time, northern shrimp (Pandalus borealis) recruitment and stock dynamics fluctuated greatly, but the underlying mechanisms remain poorly understood. We estimated recruitment from yearly fisheries independent abundance estimates for three different northern shrimp stocks in the GSL (Sept-Iles, Anticosti, and Esquiman). For 2001-2016, we quantified how northern shrimp R changed in relation to physical variables, phytoplankton bloom characteristics, zooplankton abundance and phenology, and predator biomass. Results indicated that northern shrimp R seemed related to phytoplankton bloom characteristics and resulting zooplankton phenology in addition to northern shrimp adult abundance, rather than to fish predator biomass. Importantly, the significant variables explaining the R were stock specific, implying that environmental variability and stock abundance effects depend on the area considered. In future, Esquiman area might show increasing northern shrimp R under moderate warming but northern shrimp Sept-Iles R might be impaired. These results improve our understanding of stock-specific northern shrimp recruitment dynamics in a changing environment and can ultimately improve its management in the GSL.