Thank you, Mr. Chair and members of the committee.
Thank you for this opportunity to be a witness on the question of lobster and snow crab migration.
My name is Richard Wahle. I'm a research professor at the University of Maine's School of Marine Sciences. I also recently became director of the university's Lobster Institute. I have conducted research on crustacean fisheries and ecology for the past 35 years, and much of my research has focused on lobster.
The Lobster Institute serves to maximize the engagement of the University of Maine with stakeholders in the lobster fisheries in both the U.S. and Canada. I will therefore say up front that my experience really lies more with lobster than snow crab fisheries.
Without being redundant regarding previous testimony given before this committee, in this statement I would like to start by emphasizing some basic distinctions in the biology and ecology of the two species, especially with regard to their movements and size at maturity. Second, I will take the opportunity to clarify some apparent confusion between the term “migration” and “geographic range shifts” in the context of climate change. Finally, I'll close by underscoring the need for more cross-border collaboration and monitoring of the living marine resources we share. I will give you an example of one such effort I lead for the American lobster.
The centre of the American lobster abundance is currently the southern Gulf of St. Lawrence and the northeast Gulf of Maine. It ranges northward into Labrador and Newfoundland and extends into the deep waters off the U.S. mid-Atlantic states. There is scientific consensus that the upper physiological limit in temperature is around 20°C and the lower limit is around 12°C, which is the minimum temperature for larval development.
The depth distribution is largely determined by those limits. Lobsters in the Gulf of St. Lawrence are mostly limited to depths shallower than 50 metres. Those further south extend considerably deeper, into offshore banks and shelf waters.
Growth and the onset of maturity are also temperature-dependent. In warmer regimes, lobsters grow faster but mature at a smaller size. These differences in maturation size are the basis for different minimum legal size limits along the species range.
Further, the reported downward trends in the size at maturity over the past few decades have been linked to a warming climate. The optimal thermal envelope for lobsters has been shifting northward in a warming ocean. What has been described as a northward migration in response to climate change is more accurately depicted as a demographic shift in the balance of birth and death rates. I'll add that the depletion of predatory groundfish in the Gulf of Maine and the Gulf of St. Lawrence has also likely contributed to the population surge and the northward shift in the centre of lobster abundance.
The snow crab is a subarctic species distributed around the north Atlantic and Pacific. In Atlantic Canada, it is largely segregated by depth from the lobster population because of its differing thermal preference, despite some overlap in their latitudinal range. The northwest Atlantic population is centred in the Gulf of St. Lawrence and extends north along coastal Labrador and south along the Scotian Shelf.
Snow crabs prefer cold temperatures of between -1°C and about 11°C and therefore tend to be restricted to greater depths and more northern latitudes than where lobsters range off Atlantic Canada. Unlike lobster, they also tend to prefer soft mud or sand instead of the shallower, rocky habitats preferred by lobster. Furthermore, while lobster continue to grow after maturity, snow crabs reach a terminal molt and stop growing. The snow crab fishery targets only the large, reproductively mature males.
As for movements and migrations, both lobsters and snow crabs have two opportunities for movement during their lifetime. One is during the water-borne larval stages, spanning the first weeks to months after hatching, when they may be passively transported many kilometres from their point of origin. The other is by movements along the bottom, mostly as larger juveniles and adults. The smallest lobsters are cryptic and restricted to rocky habitat. Larger ones engage in seasonal inshore and offshore movements and are most prevalent coastally during the summer. Larger lobsters can move tens to hundreds of kilometres over the course of a year, which has been used by U.S. lobster stock assessment scientists as a justification for combining the Gulf of Maine and Georges Bank stocks into one.
In contrast, snow crabs settle in sand/mud environments in deeper water than the environments occupied by lobster. They then migrate to even deeper waters as they age. Tagging studies in Atlantic Canada suggest their lateral movements along the shelf are more limited than those of lobster.
Finally, I will close by underscoring the benefits of cross-border collaboration in monitoring the living marine resources we share. I founded the American lobster settlement index. It's a collaboration of U.S. and Canadian academic institutions, industry members and fishery management agencies that monitor the pulse of baby lobsters that repopulate coastal lobster nurseries each year at some 100 sites between Rhode Island and Newfoundland. For 30 years it has been an important early warning system for changes in this iconic fishery. I look forward to continued collaboration on this program with my Canadian and U.S. colleagues, and would be happy to answer questions about it.