Commercial fish and shellfish in the Barents Sea: Have introduced crab species affected the population trajectories of commercial fish?

The Barents Sea shelf system, particularly the southwestern, western and southern parts, is one of the most productive ocean regions in the world due to the influence of warm Atlantic water. We conducted an analysis of long-term data based on original and published sources focused on the trends in abundance of key commercial species in the Barents Sea. We specifically examined the patterns and characteristics of both invasive species and invasion processes, using the example of two introduced crabs: the red king crab (Paralithodes camtschaticus) and the snow crab (Chionoecetes opilio), which in polar ecosystems may provide an important case study for improving our ability to predict the impact of new invaders. Warm temperature anomalies were observed in the Barents Sea in the 20th century and in the early twenty-first century, with peaks from 2001 to 2007 and in 2012, associated with a pronounced decrease in total ice cover since 1999. Since their introduction, the stock biomass of red king crabs has varied widely. These fluctuations were associated with high levels of illegal fishing of red king crab. The total biomass of commercial snow crabs increased exponentially in the last decade. Since the late 1990s the stock of northern shrimp has varied with an overall rising trend, although landings in more recent years were relatively stable. Cod, haddock, and saithe stocks remained at relatively high levels. Capelin stock size is characterized by large fluctuations that are likely to reflect natural processes. Cross-correlation analysis suggests that neither crab species had negative effects on the stocks of important fish. However, a potential negative impact of snow crab on the northern shrimp population could not be rejected due to their overlapping distribution and predator-prey interactions. The high overall productivity of the Barents Sea in recent years, as evidenced by high abundances of major fish stocks, is more likely associated with warming in the Arctic region, and the introduction of both crab species has had no apparent detrimental effects on fish stocks while resulting in positive economic benefits.