Warmed waters linked to diminished food for right whales
Study says new forms of right whale protections needed.
EAST BOOTHBAY, MAINE — Overheated waters pouring into the Gulf of Maine from deep ocean reserves along the Atlantic coast appear to be diminishing the food supply on which North Atlantic right whales rely.
A new report from Oceanography says warming temperatures in the gulf are impacting densities of zooplankton, which the whales rely on for food.
The rapid pace of change near the Bay of Fundy, in particular, now indicates that traditional methods of protecting the whales, including protecting their decadeslong feeding areas, may need to be refined.
“Climate change is outdating many of our conservation and management efforts,” said the report’s lead author, Nicholas Record, a senior research scientist at the Bigelow Laboratory for Ocean Sciences in East Boothbay, Maine.
The report, published May 3 but more widely distributed May 29, aggregated existing data from ocean buoys, transects and zooplankton, and whale surveys from as far back as 2004. In that year, the Gulf of Maine was recognized as one of the fastest-warming ocean ecosystems on the planet, as measured by sea surface temperatures.
Conservation and management tools do need to change as ecosystems change, said Mike Asaro, acting assistant regional administrator for protected species at National Oceanic and Atmospheric Administration Fisheries’ Atlantic coast office.
Under the Endangered Species Act, NOAA Fisheries is required to develop and carry out recovery plans for the conservation and survival of North Atlantic right whales, which are now considered at risk of becoming extinct in coming decades because of ship strikes and fishing rope entanglement.
In April, the Atlantic Large Whale Take Reduction Team considered options for reducing threats to right whales presented by fixed-gear fisheries, Asaro said.
“The team deliberately focused on protection measures that would be resilient to the effects of climate change,” he said. “Rather than focusing on hot spots or areas of high co-occurrence, the team instead looked for broad-based solutions that would be effective even as right whale migration patterns change.”
Two primary approaches that emerged from the team meeting are reductions in vertical fishing ropes in the water, such as those found with lobstering, and modification of gear to reduce the strength at which ropes break.
The Oceanography report examines the hypothesis that right whales have been straying from historically popular feeding grounds in the Gulf of Maine since 2008. This is due to recent changes in climate and the availability of prey, specifically Calanus finmarchicus, a type of zooplankton.
The issue of whether and why the right whales are straying is considered important. Since 2010, the right whale population has declined unexpectedly to about 411. There were also 17 documented right whale deaths in 2017.
Of those 17 deaths, 12 were in Canadian waters north of the Gulf of Maine, where at the time there were fewer regulatory protections such as limits on ship speed and bans on trap fishing.
Most analyses of rapid ocean warming have focused on sea surface temperatures, but a large amount of excess heat energy is found in deeper waters, according to the report. It is anticipated that much of the climate-driven warming in the Gulf of Maine will occur in those deeper areas.
Those predicted changes in deep water temperatures matter because the Calanus finmarchicus life cycle depends on an annual dormancy in deep, cold water from late summer through the winter.
In looking first at right whale movements, and comparing data from 2004 to 2008 and 2012 to 2016, the report found that right whale sightings sharply declined in the area of the Bay of Fundy, which is considered the eastern part of the Gulf of Maine. Sightings of right whales also changed in the western part of the gulf, including marked increases within Cape Cod Bay.
The Oceanography report also found increases in Calanus finmarchicus in the western part of the Gulf of Maine in the spring, including in Cape Cod Bay. Decreases in the number of whales were noted from late summer through the winter, corresponding with the period of dormancy.
In related testing across the same time periods, scientists identified what they call two distinct oceanographic paths of water movement in the Gulf of Maine that they say are controlling the presence of Calanus finmarchicus and right whales.
One path on the surface of the sea follows along the gulf’s western coastline in the spring, where Calanus finmarchicus densities increase in the verdant coastal environment. The report describes this path as relatively stable in the spring for right whales, Calanus finmarchicus and other smaller prey, even in the face of oceanic temperature changes.
The second path in deeper waters enters the Gulf of Maine from the east during the seasonal dormancy for Calanus finmarchicus, and introduces changes from wider ocean forces affected by climate change. The northward movement of the deep and warm water toward the Bay of Fundy appears to affect the density of Calanus finmarchicus, both by bringing fewer from outside the gulf and by warming the dormant ones already in the gulf.
While the warmth of the water would likely experience an increase in metabolism and possibly emerge from dormancy early, according to the report.
Those wider ocean forces are the likely culprit in the diminishing Calanus finmarchicus population, and could be a precursor to future changes, said Daniel Pendleton of the New England Aquarium’s Anderson Cabot Center for Ocean Life, who co-authored the report.
“We typically think of warming water and of species just moving north, but here we’re seeing two different and seemingly opposite effects,” he said. “We are seeing whales apparently move north into Canadian habitats, but we’re also seeing this explosion of whales in Cape Cod Bay and south of the Islands for different reasons. This points to the fact that changes in climate may have different effects at different times of year.”
There is often an emphasis on knowing the location of animals, Pendleton said.
“However, the question of when they are in a particular place is equally important,” he said. “Our study addresses issues not only of space but also of time.”
Pendleton, Record and other collaborators developed an algorithm in 2012 that used Calanus finmarchicus data and other oceanographic conditions to rightly predict — before anyone was looking there — that areas south of Nantucket and Martha’s Vineyard would be ideal right whale habitats. Future tools used to protect right whales should be similarly predictive, Pendleton said.
In a further twist, the high density of right whales in Cape Cod Bay in the late winter and spring has continued beyond 2016 to the season that just ended. About 65 percent of the total whale population was seen at least once, according to Charles “Stormy” Mayo, a right whale expert at the Center for Coastal Studies in Provincetown who also co-authored the report. But this year there was an especially low density of Calanus finmarchicus in the bay, which led to the right whales consuming another similar species, Mayo said.
“It was a very different pattern,” Mayo said. “But it shows these animals are like, ‘We’ll take what we can get.’”
— Follow Mary Ann Bragg on Twitter: @maryannbraggCCT.