Snow Crab and lobster in hot water!
Fond of Snow crab? Hurry up! You may see less of this crustacean on your plate by 2070. The increasing water temperature in the southern Gulf of St. Lawrence is to blame. According to a discovery by three scientists at Fisheries and Oceans Canada, the variation is enough to potentially disrupt the life cycle and habitat of two emblematic tenants: the Snow Crab and lobster.
With the Snow Crab and Lobster Thermal Habitat Changes in the Southern Gulf of St. Lawrence project, funded for one year starting in April 2012, “we wanted to use modelling to study thermal habitat changes in relation to climate change for these two species of commercial importance to Eastern Canada,” according to Mikio Moriyasu, head of the Snow Crab Section of the Gulf Fisheries Centre, based in Moncton.
And, given the gradual increase in water temperature, the two crustaceans are not competing on a level playing field. Unlike the lobster, which can live at a depth of up to 25 metres in temperate waters of between -1.5° and 22°C, the Snow Crab resides in the southern Gulf of St. Lawrence at a depth of 40 to 250 metres in a much narrower temperature range, preferably between -1° and 3°C.
According to Mr. Moriyasu: “If the temperature changes drastically, the long-term survival of the Snow Crab will be threatened.”
A major undertaking
This is a real threat according to data on historical temperatures measured at the surface by satellite or at a depth during species sampling campaigns.
“Since the mid-1990s, the average water temperature in the southern Gulf of St. Lawrence has increased by 1.5°C. We have also found that the volume and surface area of the intermediate layer of cold water, which provides suitable habitat for the Snow Crab, has decreased since that period. In the last six years, the volume of cold water has even dropped below the average for the last 30 years,” according to Joël Chassé, Research Scientist at the Gulf Fisheries Centre, based at the Maurice Lamontagne Institute.
With the help of his colleagues—Mikio Moriyasu and Michel Comeau, Head of the Lobster Section at the Gulf Fisheries Centre—Mr. Chassé modelled the thermal habitat of the Snow Crab and lobster for this project. “As we knew that crustacean population movements depend on masses of cold water, we created a digital model capable of predicting the extent of suitable habitat for the two species between now and 2070,” Mr. Chassé indicated.
However, to determine the regional distribution of the two species in this way, they had to develop and customize the predictive tool based on atmospheric and hydrological models (precipitation, fresh water), while integrating regional ocean conditions. A tedious process that is still in its early stages, although it represents significant progress, the researcher pointed out.
“We are still refining the model by including parameters such as oxygen concentration and water acidity,” Mr. Comeau indicated. “How will areas of acid water affect shell calcification and growth of these two crustaceans? Will hypoxic water (with a low oxygen concentration) affect larval development or species biology?” These are all questions that demand answers.
According to the model’s current predictions, it seems that the extent of suitable Snow Crab habitat is decreasing, while lobster habitat area seems to be expanding.
“The raw information needs to be qualified,” Michel Comeau explained, adding: “An increase in the geographic area where the temperature is acceptable for a lobster’s life cycle does not automatically imply that it provides the rocky bottom habitat conducive to the species settling there.”
As it tolerates a wider temperature range than the Snow Crab, the lobster has already expanded its habitat in the last 20 years. These population movements benefit certain fishing areas, such as those north of Prince Edward Island. However, the lobster population in Northumberland Strait has decreased because the summer temperature already exceeds 22°C, which is close to the lethal level for the lobster. “In 2011-2012, we noted, in all areas of the Gulf except Northumberland Strait, record landings since the first surveys in 1892,” Mr. Comeau said.
A decrease in the Snow Crab’s living area would lead to a decrease in the abundance of the species. As Mikio Moriyasu pointed out, the repercussions of the gradual increase in water temperature could include impacts on the female’s breeding cycle and larval growth and survival, and increased moulting frequency. According to Michel Comeau, the lobster would be affected less: the higher water temperature would mainly result in an increase in spawning frequency in females, potentially every year instead of every two years.
As these two species of crustaceans are of great economic importance to Eastern Canada, their evolution in response to climate change is being closely monitored by Fisheries and Oceans Canada scientists.
And for good reason: “An increase in Snow Crab moulting frequency would increase mortality due to handling during the fishing season as the Snow Crab is vulnerable after moulting (soft shell). Crabs with soft shells have no commercial value and so harvesters dispose of them at sea,” Mr. Moriyasu explained. Crab that does not survive this handling does not contribute to the reproduction of the species.
A major problem because, "if the females lay their eggs once a year instead of every two years as they currently do in the very cold temperatures, they may need more adult males to mate with," the researcher added.
To preserve the resource for coming decades, scientists will have to continue to provide fisheries managers with reliable advice, hence the importance of constructing a predictive model that is as realistic as possible.