Right whales may never breed after runins with fishing gear
A new study has reported that even entanglements scientists classify as ‘minor’ have devastating impacts on the critically endangered right whales and that, surprisingly, potential mothers who suffer such entanglements have the lowest chance of starting t
through the early 2000s, the number of reproductively mature female right whales declined from 2014 onward. By 2018 there were only about 73 breeding females left, representing roughly half of all females and a sixth of the entire species.
Other research has shown that poor health and physical condition are making it harder for these females to even start breeding. Since the early 1980s, North Atlantic right whales have literally shrunk: Adults have shorter bodies than they did several decades ago. This trend is associated with entanglements in fishing gear. As is true for all mammals, decreasing female body size reduces the likelihood of reproducing. Smaller whales have fewer calves.
Low calving rates are a significant factor in North Atlantic right whales’ decline, so it is important to understand what causes them. Many organisations are involved in tracking North Atlantic right whales, including government agencies, aquariums and conservation groups. Photos taken from the air enable researchers to identify individuals and so monitor whale population trends, births and deaths, ocean habitat use patterns, health, and rates of scarring from entanglements and collisions with ships.
Our new study found that female right whales who have experienced even a minor entanglement before reaching sexual maturity may not ever start to breed. Even females who have previously reproduced are less likely to breed again following an entanglement event.
We determined this by using a mathematical model to incorporate information on the identity of individual whales, derived from photographs of natural markings known as callosities on the whales’ heads. By identifying and photographing whales repeatedly over time, scientists can estimate different stages of their life, such as when females give birth.
Weakness of current regulations
Researchers categorise the severity of injuries that result from entanglements as minor, moderate or severe. The scientists who manage the right whale catalogue classify scars or injuries on the skin as minor if they are smaller than 2 cm without entering the blubber. If they are larger and enter the blubber, they are classified as moderate. Injuries that extend deep into the muscle or bone are categorised as severe.
Our research makes it clear that such valueladen terms are potentially misleading because even minor entanglements can threaten whales’ successful reproduction.
Multiple laws ostensibly protect North Atlantic right whales, including the U.S. Endangered Species Act and Marine Mammal Protection Act, and Canada’s Species at Risk Act. In our view, these measures do not give enough weight to preventing all types of entanglements, regardless of severity.
Under the Marine Mammal Protection Act, the NOAA develops and implements conservation plans and socalled Take Reduction Plans, which are designed to minimise wildlife deaths and serious injury resulting from commercial fishing gear.
The Atlantic Large Whale Take Reduction Plan, developed in 1997, requires fishers to use weak links, with a maximum breaking strength of 771 kg, to connect lobster and crab pots to buoys on the surface. These links are intended to break when whales swim into them, so that the whales do not become entangled and weighed down by ropes and traps.
The plan also requires fishers to use heavy ground lines to connect multiple traps or pots. These lines are designed to sink to the bottom rather than floating in the water column. And the plan closes trap fishing areas seasonally when whales are known to be present in those zones.
The number of reproductively mature female right whales declined from 2014 onward. By 2018 there were only about 73 breeding females left, representing roughly half of all females and a sixth of the entire species
Coming back from the brink
Current population estimates suggest that the numbers of North Atlantic right whales could be stabilising, meaning that the number of deaths is approximately equal to the number being born. While these estimates seem promising, females need to start and continue producing calves to increase whales’ numbers.
From our work, it is very clear that both lethal and sublethal impacts of entanglements are of grave concern for these whales. As we see it, eliminating entanglement, not mitigating it, is the only way to avoid the extinction of this species. Every entanglement, whatever its severity, is bad news for the whales.
(Joshua Reed is a research associate in biology, Macquarie University; Leslie New is an assistant professor of statistics, Ursinus College; Peter Corkeron is an adjunct senior research fellow, Centre for Planetary Health and Food Security, Griffith University; and Rob Harcourt is a professor of marine ecology, Macquarie University. This article is republished from The Conversation.)