Potential Impacts of Global Warming on the Snow Crab

If climate change is sustained, the surface and bottom waters of the Gulf of St. Lawrence will continue to become warmer. Some species caught in the Gulf, such as Lobster,will benefit while others will suffer. This is the case with the snow crab because it is more dependent on cold water than any other species fished in the Gulf of St. Lawrence.

To understand how rising water temperatures affect the snow crab, Bernard Sainte-Marie and his team have undertaken research focused on key aspects of the bio-ecology of snow crab. This species has a complex life cycle that includes a planktonic phase, during which its larvae drift in surface waters, and a benthic phase during which juveniles established on the bottom develop until they undergo the terminal molt to adulthood. The snow crab inhabits bottoms where water temperatures range from -1.5 to 4°C. However, early benthic juvenile stages have a narrower thermal preference, primarily waters ranging from 0 to 2°C.

Research results show that rising water temperatures would have multiple and, to some extent, conflicting effects on the benthic phase of the snow crab in the Gulf of St. Lawrence. On the positive side, moderate warming (1 to 2°C) of bottom waters would increase the fertility of individual females. Females would undergo their terminal molt at a larger average size, produce more eggs per brood and reproduce annually rather than once every two years. Males also would undergo their terminal molt at a larger average size. As a result, a higher percentage of them would reach the legal catch size, and the average size of crabs caught in the fishery would be larger.

Warming would also have negative consequences, the most significant being a contraction of the area of bottom bathed by cold waters. This would concentrate crabs in a smaller area, and increase natural mortality due to competition for resources and cannibalism. (Yes! The snow crab is a cannibal species.) Additional mortality from physiological limits to survival beyond 4 to 5°C, and the possible return of natural predators such as cod could exacerbate these negative effects. With sustained warming, the negative effects would outweigh the positive ones.

The impact of warming on the snow crab will not be the same throughout the Gulf of St. Lawrence. The population will decline in areas of the Gulf of St. Lawrence currently experiencing the “warmest” temperatures before it does in the coldest areas. Limited warming in areas such as the Lower North Shore, where a recent drop in water temperatures has affected snow crab productivity, could even be beneficial for the population and the fishery.

As with any kind of climate event, there may be unexpected fluctuations. For example, cold temperatures in the Gulf of St. Lawrence in the summer of 2014 and winter of 2015 temporarily changed the warming trend, and generated one of the strongest crab year-classes recorded in 30 years.

Bernard Sainte-Marie
Science