Atlantic halibut thrive in warming Maritime waters, study finds

Warming ocean temperatures caused by climate change will provide favourable conditions for Atlantic halibut, according to a new study, although what happens to their prey is uncertain.

A paper published in the journal FACETS links an exponential increase in Atlantic Canadian landings over the past decade to warming ocean temperatures and predicts that trend is likely to continue under low- and high-warming scenarios in coming decades.

"Under both of those scenarios, we see similar trends. Even in the higher emission scenario where it's warmer, it would appear that halibut stand to gain more habitat with these warming conditions" says co-author Ryan Stanley, a Fisheries and Oceans Canada scientist at the Bedford Institute of Oceanography.

"There's going to be winners and there's going to be losers. For halibut, it would appear, particularly for that juvenile phase, that they're gaining habitat. This seems to be somewhat of a good news story for halibut," Stanley told CBC News.

He and other researchers used 18,600 at-sea observations over 54 years to track distribution of Canada's most valuable groundfish. The most recent statistics show landings of the big flatfish in Nova Scotia were worth $60 million in 2022.

Between 2004 and 2018, warmer bottom temperatures expanded the "available thermal habitat" suitable for juvenile halibut, under 80 centimetres in length.

What happened when waters warmed

The study found the growing season got longer, juveniles matured earlier, survived better and occupied more places across the region.

"There was a pretty tight relationship with the landings that we saw, the amount of juvenile habitat and the amount of juveniles we were capturing in our surveys. With that relationship, we're able to extrapolate how continued warming in the region may influence that trend," Stanley said in a recent interview.

The models forecasts higher populations of halibut — what the paper calls the probability of occurrence — throughout the Atlantic region.

"The probability of Atlantic halibut occurrence is predicted to increase in the northern regions and remain relatively unchanged in the southern regions in all future climate scenarios. In particular, the highest increase in the probability of occurrence was predicted in the Gulf of St. Lawrence, consistent with the concept that less currently occupied northern areas are warming and consequently increasing suitable habitat with ongoing climate change," the paper says.

The assessment is based on one predictor: temperature.

Past data helps predict the future

The full impact of climate change is not known, however, on species that halibut prey upon or its predators.

The ability to make these projections reflects the importance of the surveys carried out over decades by American and Canadian scientists, Stanley says.

"It is through having those comprehensive, long-term surveys that were able to illustrate the relationship between where a species occupies, the environmental conditions associated with that habitat. And then from that robust basis we can make predictions into the future. So these long-term surveys are really incredibly valuable data sources that we can use to make very informed inferences for the influence of climate change on species like Atlantic halibut."

In recent years frequent vessel breakdowns — on new and older Coast Guard vessels — has repeatedly hampered the ability of Department of Fisheries and Oceans scientists to complete at-sea surveys in Atlantic Canada.