As many as 1,434 humpback whales pass through Bermuda’s waters every year as they migrate, according to a decade-long study co-authored by Bermudian Andrew Stevenson.

The scientific paper published this month in Frontiers, said that while the number of whales seen near Bermuda varies year-to-year, there had been a slight increase between 2011 and 2020.

“These abundances are comparable with some destination feeding grounds and confirm the contemporary importance of this Marine Mammal Sanctuary as a stopover site,” the paper states.

“Given the limited protection afforded to humpback whales in Bermudian waters, these estimates should encourage the implementation of area-based management tools to mitigate risks from increasing human activities such as shipping, commercial fishing and marine wildlife tourism in the waters around Bermuda.

“Moreover, with Bermuda’s migratory connections to both feeding and breeding grounds across the entire North Atlantic, this time series may facilitate population monitoring at a basin scale.”

Mr Stevenson said that while some have claimed that far more whales pass through the island’s waters, he said the estimate lined up with what he has seen over the years.

“I would have said it was about 1,500,” he said. “The most important thing though is that it is going up.”

North Atlantic humpback whales are often seen in Bermuda’s waters between the months of December and May as they migrate between feeding grounds to the north and breeding grounds to the south.

As part of the paper, authored by Thomas Grove, Ruth King and Lea-Ann Henry of the University of Edinburgh along with Mr Stevenson, researchers logged whales seen passing near the island during their migration period.

While the whales recorded represented only a fraction of those that came through Bermuda’s waters, the researchers utilised scientific models to estimate the total number of whales that came past the island.

“Our abundance time series suggests that up to 1,434 whales visited the study area each year, with intra-seasonal sightings demonstrating stopover residency,” the paper said.

“Together, these results confirm the use and importance of Bermuda as a migratory stopover for humpback whales.

“Due to the lack of recent abundance estimates for North Atlantic feeding and breeding grounds, it is challenging to place these results in the context of the wider North Atlantic and comparisons with outdated abundance estimates should be made cautiously.”

The paper noted that researchers spotted a few repeat visitors to the island with 13 per cent of whales seen on multiple years during the course of the study.

However it noted that the migration corridor for the animals was wide, which meant individual whales might not use Bermuda for a stopover every year.

It was also suggested that some whales may not migrate every year with females taking a “break year” after giving birth and remaining in the northern feeding grounds.

The paper noted that the results were “timely” given the Government’s efforts to move forward with the Bermuda Ocean Prosperity Programme and limited protections offered to humpbacks.

“The declaration of Bermuda’s exclusive economic zone as a Marine Mammal Sanctuary in 2012 formed part of a trans-boundary network of ‘protected areas’ but provided no management measures,” the paper’s authors said.

“The inclusion of humpback whales in Bermuda’s Protected Species Act of 2003 broadly prohibits disturbance, harassment and injury and existing whale-watching guidelines are voluntary.

“Moreover, around Bermuda and the wider Sargasso Sea, anthropogenic activity, particularly large vessel traffic, has increased in recent years and this growth is forecast to continue. As a result, ocean ambient sound is now dominated by shipping in Bermudian waters.

“Combined with possible increases in commercial fishing activity and whale-watching tourism, any resulting mortality or disturbance may impact whales across the North Atlantic, particularly western feeding grounds and northern Caribbean breeding grounds.”

The paper’s authors said they hoped the paper would encourage consideration of area-based management tools to mitigate the risks caused by human activities around the island.

“Future marine spatial planning around Bermuda should consider the potential impact that growing anthropogenic pressures, such as vessel traffic and marine wildlife tourism, may have on thousands of humpback whales within potential critical habitat,” the study said.

“Furthermore, with Bermuda’s migratory connections to feeding and breeding grounds, this time series may facilitate monitoring of population-level processes across the North Atlantic.

“More generally, we encourage the investigation of whale abundance across a species’ range as a potential sentinel for basin-scale ecosystem change.

“As marine environmental change accelerates across the North Atlantic, sustained photo-identification survey effort in Bermudian waters should be supported to extend this time series.”