Population trends for northern shrimp (Pandalus borealis) and key predators off eastern Newfoundland and Labrador. The biomass series for shrimp (■, left Yaxis) is represented by the CPUE index for NAFO Division 2HJ3K. The biomass series for fish predators (♦, right Y-axis), obtained from published documents in most cases, are given as tons x 103 or kilograms per tow from annual research trawl surveys. dfo-mpo.gc.ca

Population trends for northern shrimp (Pandalus borealis) and key predators off eastern Newfoundland and Labrador. The biomass series for shrimp (■, left Yaxis) is represented by the CPUE index for NAFO Division 2HJ3K. The biomass series for fish predators (♦, right Y-axis), obtained from published documents in most cases, are given as tons x 103 or kilograms per tow from annual research trawl surveys. In the early 1990s, a major shift in species composition and community structure occurred along the entire shelf. The changes in species composition and community structure that occurred in this ecozone during the early 1990s were characterised by a decrease in target and non-target groundfish abundance (e.g., Atlantic cod, redfish, skate). In addition, a dramatic increase in the biomass of invertebrates (e.g., crab and shrimp) has occurred coupled with the loss and lack of recovery of capelin, a key forage species. Unlike changes that occurred in the adjacent Scotian Shelf ecozone, these changes were not accompanied by a decrease in zooplankton or an increase in small forage species. The harp seal population declined during the 1960s, reaching a minimum of less than 2 million in the early 1970s. Following the introduction of a quota system in the 1970s, the population tripled by the mid-1990s to a very high level (~5.5 million). Since that time, the population has continued to increase at a slower rate (likely due to large harvests in recent years) of approximately 1.5% annually up to its last assessment in 2009, where Northwest Atlantic harp seals numbers were estimated at 6.9 million (95% CI=6.0 to 7.7 million). The reasons for the aforementioned changes in community structure are still under debate, but overexploitation of groundfish, climate change (e.g., cooler water temperatures), and trophodynamics (e.g., predation release) are some of the hypotheses used to explain them. However, the scenario likely involves some combination of all these driving forces.

Canadian Science Advisory Secretariat Science Advisory Report 2010/030, 2010 Canadian Marine Ecosystem Status and Trends Report [pdf], July 2010