It sounds like an episode of a marine crime show: In late January 2024, federal regulators learned that a dead female North Atlantic right whale had been sighted near Martha's Vineyard, Massachusetts. The whale was towed to shore, where more than twenty American and Canadian scientists gathered to perform a necropsy, or animal autopsy.
On February 14, the US National Oceanic and Atmospheric Administration announced that the whale was number 5120 in a catalog that keeps track of individual whales. Furthermore, the agency said that rope embedded deeply in the whale's tail likely came from lobster fishing gear in Maine.
Entanglement in fishing gear is a deadly threat to these critically endangered animals. Scientists estimate that before commercial whaling expanded in the 18th and 19th centuries, there may have been as many as 10,000 North Atlantic right whales. Today, fewer than 360 individuals remain. Nearly 90% of them have been entangled at least once.
When whales become entangled in fishing gear, they expend extra energy dragging it along as they swim. If the rope gets stuck around their mouth, they may have trouble eating and slowly starve. Ropes wrapped around the bodies, fins or tails of whales can cut the animals' skin and go deep into their flesh, as happened to whale No. 5120. This can cause infections, chronic emaciation and damage to the whales' muscles. , bones and baleen - the bristly structures in their mouths that they use to filter prey from the water.
North Atlantic right whales are protected by law both internationally and in U.S. waters, including policies aimed at reducing the number of deaths or serious injuries caused by entanglements. But even if entanglement doesn't kill a whale, it can affect the reproductive potential of individuals, which is critical for a species with such low numbers.
In a recently published study, we show that even complications that scientists consider minor have devastating consequences for female whales and that, surprisingly, potential mothers who experience 'minor' complications have the lowest chance of reproducing. As researchers with expertise in marine biology, ecology and statistics, we believe that our findings underscore the urgent need for ropeless fishing gear that can reduce threats to the survival of this species.
Smaller females have fewer young
Understanding reproductive patterns is essential for supporting species that are critically endangered. Historically, North Atlantic right whales began breeding around age nine and then gave birth to a single calf every three to four years for decades.
Today, however, many females have yet to reproduce at all. Furthermore, those who have successfully produced calves now only produce another calf on average after seven years.
As we showed in a 2022 study, after an encouraging recovery of the North Atlantic right whale population from the 1970s to the early 2000s, the number of reproductively mature female whales has declined as of 2014. In 2018, there were only about 73 breeding females left, representing about half of all females and one-sixth of the entire species.
Other research has shown that poor health and physical condition make it more difficult for these females to even begin breeding. Since the early 1980s, North Atlantic right whales have literally shrunk, with adults having shorter bodies than they did a few decades ago. This trend is related to entanglements in fishing gear. As is the case with all mammals, decreasing female body size reduces the chance of reproduction. Smaller whales have fewer calves.
Low calving rates are a major factor in the decline of the North Atlantic right whale, so it is important to understand what is causing this. Many organizations are involved in tracking North Atlantic right whales, including government agencies, aquariums and conservation groups. Photos taken from the air allow researchers to identify individuals to monitor whale population trends, births and deaths, ocean habitat use patterns, health and the number of scars from entanglements and ship strikes.
Our new research shows that female whales that experience even minor entanglement before reaching sexual maturity may never breed. Even females that have reproduced previously are less likely to reproduce again after an entanglement.
We determined this by using a mathematical model that incorporated information about the identities of individual whales, derived from photographs of natural markings known as calluses on the whales' heads. By identifying and photographing whales repeatedly over time, scientists can estimate different stages of their lives, such as when females give birth.
Weakness of current regulations
Researchers categorize the severity of injuries resulting from entanglements as mild, moderate or severe. The scientists who manage the whale catalog classify scars or wounds on the skin as minor if they are smaller than 2 centimeters without getting into the blubber. If they are larger and get into the blubber, they are classified as moderate. Injuries that extend deep into the muscle or bone are categorized as severe.
Our research makes clear that such value-laden terms are potentially misleading, as even minor complications can threaten the successful reproduction of whales.
Several laws purportedly protect the North Atlantic right whale, including the US Endangered Species Act and Marine Mammal Protection Act, and Canada's Species at Risk Act. In our opinion, these measures do not give enough weight to preventing all types of complications, regardless of their severity.
Under the Marine Mammal Protection Act, NOAA develops and implements conservation plans and Take Reduction Plans, which are designed to minimize wildlife deaths and serious injuries from commercial fishing gear.
The Atlantic Large Whale Take Reduction Plan, developed in 1997, requires fishermen to use weak links, with a maximum breaking strength of 771 kilograms, to connect lobster and crab pots to surface buoys. These links are meant to break when whales swim into them, so the whales don't get entangled and weighed down by ropes and traps.
The plan also requires fishermen to use heavy ground lines to connect multiple traps or pots. These lines are designed to sink to the bottom rather than float in the water column. And the plan closes fishing areas seasonally if whales are known to be present in those areas.
Coming back from the edge
Current population estimates suggest that the number of North Atlantic right whales could be stabilizing, meaning the number of deaths is approximately equal to the number born. While these estimates seem promising, females must begin and continue producing calves to increase whale numbers.
Our work clearly shows that both the lethal and sublethal consequences of entanglements are of great concern to these whales. As we see it, eliminating entanglement, not mitigating it, is the only way to prevent the extinction of this species. Any entanglement, no matter how serious, is bad news for the whales.
This article is republished from The Conversation, an independent nonprofit organization providing facts and trusted analysis to help you understand our complex world. It was written by: Joshua Reed, Macquarie University; Leslie New, Ursinus College; Peter Corkeron Griffith Universityand Rob Harcourt, Macquarie University Read more: Leslie New receives funding from the U.S. Office of Naval Research and the National Science Foundation. She is also a member of the Scientific Committee of the International Whaling Commission. Peter Corkeron advises Public Employees for Environmental Responsibility on whale conservation issues. He led the National Oceanic and Atmospheric Administration's major whale research program for the northeastern U.S. from 2011 to 2019, then led the New England Aquarium's right whale research program until 2022. Rob Harcourt is receiving funding from the Australian Federal Government Department of Climate Change, Environment, Energy and Water for whale research. He was a member of the National Scientific Committee on Marine Mammals Joshua Reed does not work for, consult with, own stock in, or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
