New findings show the severe impact of fishing gear entanglements and ship strikes on the species survival of critically endangered North Atlantic right whales, with every injury or entanglement impacting population recovery.

The study, led by Macquarie University marine science doctoral candidate Joshua Reed in collaboration with scientists at Ursinus College and Griffith University, was published in Proceedings B of the Royal Society.

Modelling of whale distribution data shows when female right whales get tangled up in ropes from lobster and crab pots, or struck by ships during their migration, they are less likely to calve, potentially leading to extinction for this species.

With only 360 North Atlantic right whales still alive, this is the world’s most endangered whale species, and its population has rapidly declined over the past decade.

“Poor calving is one of the main factors behind the decline of North Atlantic right whales, and until now, the reason for these whales’ failure to calve wasn’t clear,” Mr Reed said.

“This study makes it clear that all types of entanglement in fishing gear impact females’ ability to calve, helping address one of the big outstanding questions for saving North Atlantic right whales.”

Known as ‘the urban whale’ because they live in the waters off the heavily populated east coast of the USA and Canada, these whales pass millions of fishing ropes and hundreds of ships and boats on their migration each year.

Whales struck by ships or entangled in nets often survive, and their injuries from entanglement in fishing gear are classified as ‘minor, ‘moderate’ or ‘severe.’

The researchers analysed 40 years of data on 199 female right whales together with known fishing-gear entanglements rated by severity, to calculate the impact of these encounters on whale reproduction.

Co-author Dr Peter Corkeron from Griffith University’s Centre for Planetary Health and Food Security said the research delivered an important message: all entanglements mattered.

“Weak rope is a technology now used to try to reduce the severity of entanglements, but it doesn’t change whether whales will get entangled,” he said.

“This paper indicates rope technology won’t solve the problem of female right whales’ poor calving. We need to get all rope out of the water, urgently, for this species to start to recover.”

“This study makes clear using value-laden terms like “minor”, “moderate” and “severe” to describe the relative severity of scars from entanglements is inappropriate,” said co-author Honorary Professor Rob Harcourt, from Macquarie University’s School of Marine Science.

“These lead to an unconscious assumption that “minor” injuries aren’t important, when in fact they are.”

The research showed pre-breeding age female whales surviving entanglements classed as ‘minor’ were the least likely to transition to breeding, and whales born post-2000 were 38 per cent less likely to breed than those born earlier.

Co-author Assistant Professor Leslie New, a statistical ecologist from Ursinus College, Pennsylvania USA, said the study’s methodology showed the power of these modelling tools to inform conservation.

“Applying a standard technique in a new way, to a well-studied species, allows us to come up with a better understanding of how human impacts – in this instance, fishing entanglements – affect these female whales survival and reproduction,” she said.

The findings show management actions toward recovery of the North Atlantic right whale must address both lethal and sub-lethal impacts of entanglements, regardless of severity classification, Mr Reed said.