Response in stock size and recruitment of northern shrimp (Pandalus borealis) to changes in predator biomass and distribution in west Greenland waters

Abstract

Potential relationships between stock size of Northern shrimp (Pandalus borealis) and its main predators, Atlantic cod (Gadus morhua) and Greenland halibut (Reinhardtius hippoglossoides), in West Greenland waters were examined. Changes in spatial overlap between the species were taken into account in the analysis of the impact of predator biomass on the survival of Northern shrimp recruits. Survey estimates of total stock size of Northern shrimp were negatively correlated with Atlantic cod biomass lagged by one and two years until the beginning of the 1990s. Thereafter, the Atlantic cod stock in West Greenland offshore waters collapsed, but no immediate response of Northern shrimp to the released predation pressure was observed. Recruitment and subsequently stock biomass of Northern shrimp increased first about 10 years later following a moderate increase in the temperature conditions, which had likely enhanced plankton productivity. After a record high level in 2000, survival of juvenile Northern shrimp, i.e. the number of recruits at age 2 per unit of spawning stock biomass, decreased drastically. Statistical analysis suggests that increased predation by Greenland halibut have overruled the positive effect of favourable temperature conditions in the most recent years. In contrast, the impact of Atlantic cod on Northern shrimp was insignificant in the recent years due to low Atlantic cod biomass and a very limited spatial overlap between the two species.