Forty percent of North Atlantic right whale population using Gulf of Saint Lawrence as seasonal habitat
Researchers have identified 187 individual North Atlantic right whales—about 40 percent of the catalogued population—in Canada's Gulf of St. Lawrence during the summer. They used photographs of North Atlantic right whales collected during surveys conducted between 2015 and 2019. Many of the right whales remain in the area through the summer and autumn, feeding and socializing primarily in southern parts of the Gulf. Almost all of these whales return every year—a pattern not seen elsewhere—and stay for up to 5 months.
"In order to design effective protection measures for this endangered species, we need to know when and where they are present," said Leah Crowe. Crowe is a marine mammal researcher at the Northeast Fisheries Science Center laboratory in Woods Hole, Massachusetts and lead author of the right whale study published in Endangered Species Research. "We found that the Gulf of St. Lawrence is an important habitat for a large segment of the population."
Among other study findings:
- In general, individual whales did not travel far each day while present
- Some individuals spent time in both the northern and southern parts of the Gulf of St. Lawrence
- Pregnant females were among the animals moving back and forth between northern and southern areas
The northern and southern regions of the Gulf of St. Lawrence are separated by the Laurentian Channel and Honguedo Strait. These major shipping corridors connect commercial vessel traffic from the Atlantic Ocean to the St. Lawrence Seaway and the Great Lakes.
For this study, researchers examined photographs of individuals to explore the demographics, seasonal distribution, and movement patterns of right whales in the Gulf. The whales were identified by unique patterns of rough patches of tissue, or callosities, on the top and sides of their heads.
Other researchers deployed underwater listening devices called hydrophones in the Gulf of St. Lawrence. They detected an increase in right whale presence in some areas beginning in 2015. That same year, NOAA started the first dedicated aerial surveys for right whales in the region and found them present in the Gulf. Since then, a combination of U.S and Canadian efforts have monitored whales through visual surveys and acoustic listening devices in the Gulf of St. Lawrence.
The Gulf of St. Lawrence is not the only habitat where right whales, fishing, and shipping traffic overlap. This study shows that there is a unique opportunity to protect a particular portion of the population in this region, including reproductive females and calves.
Understanding New Habitat Use by Right Whales
There were unprecedented numbers of dead right whales found in the Gulf of St. Lawrence in 2017 and 2019. They prompted swift implementation of Canadian measures to prevent further death and injury from fishing gear entanglements and vessel strikes.
In the United States, an unusual mortality event was declared for North Atlantic right whales throughout their range in 2017, which is still ongoing. Fisheries and Oceans Canada participates as a member of the North Atlantic Right Whale UME Investigation Team. This multinational effort helps to understand, respond to, and investigate UME cases.
Moira Brown, senior scientist at the Canadian Whale Institute and a co-author on the paper, emphasizes the importance of the surveys to define the location and seasonality of right whale aggregations in the Gulf of St. Lawrence. Information on the timing and distribution of right whales, such as that from this study, helps both U.S. and Canadian managers to develop protective measures.
Keeping Up With the Times
Between about 1980 and 2010, many right whales spent the spring in Cape Cod Bay and waters off Cape Cod. During the summer, they then moved north into the northern Gulf of Maine, Bay of Fundy, and Roseway Basin where they found their preferred prey—copepods, or zooplankton. Starting in 2010 this pattern began to change with many whales heading to the Gulf of St. Lawrence in late spring and using new habitats to the south of Massachusetts year-round.
"In the last decade, North Atlantic right whale distribution and habitat occupancy patterns have become less predictable," Crowe said. "Animals are spending less time in places where they have typically aggregated in the past, and we have started to observe them in places where we had not found them aggregating before."
Aerial and vessel-based surveys have been adapted to capture this new distribution and to understand when, where, and why the whales are moving, and in what numbers. Surveys have confirmed right whales in larger numbers in the Gulf of St. Lawrence during the summer. They also found an increase in the numbers of right whales using Cape Cod Bay in the late winter and spring. In addition, surveys have confirmed that right whales occur south of the islands of Martha's Vineyard and Nantucket almost year round.
"Fisheries and Oceans Canada continue their aerial surveys and monitoring of right whales including photographing individuals observed in Atlantic Canadian waters. So far, eight mother-calf pairs have been identified from photographs taken in the Gulf of St. Lawrence this year," said Angelia Vanderlaan, a research scientist at Fisheries and Oceans Canada and a co-author of the paper.
The North Atlantic right whale species population has been in decline for more than a decade. The UME that began in 2017 has highlighted the decline with 50 individuals documented over the past 4 years alone (34 dead and 16 seriously injured whales). The latest preliminary estimate suggests there are fewer than 350 North Atlantic right whales and fewer than 100 adult females. Given the urgency for the species' recovery, new habitats are being surveyed. Other important efforts are underway in both Canadian and U.S. waters to reduce deaths and injuries from vessel strikes and entanglements in fishing gear. These are the two leading causes of mortality and serious injury for right whales and the primary causes of the UME.
"This study improves our understanding of right whale use in the Gulf of St. Lawrence," said Crowe, "but it begs the question of where other individuals—the majority of the population—are during the summer. Many right whales may be using habitats that could lack protection measures."
A Group Effort
Photographic sightings used in the study were contributed by 37 organizations and individuals. Major resources were the North Atlantic Right Whale Consortium databases, and a right whale catalog maintained by the New England Aquarium. The catalog contains contributed data and photographs of 750 individual living and dead right whales identified since 1935.
More information: LM Crowe et al, In plane sight: a mark-recapture analysis of North Atlantic right whales in the Gulf of St. Lawrence, Endangered Species Research (2021). DOI: 10.3354/esr01156
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