When right whales are injured after becoming entangled in fishing gear, they are not very likely to survive.
A new study finds that most North Atlantic right whales who are hurt from being wrapped up in fishing equipment die within three years.
North Atlantic right whales (Eubalaena glacialis) are classified as critically endangered on the International Union for Conservation of Nature (IUCN) Red List of Endangered Species with their population dropping.
Threatened by fishing entanglements, ship strikes, and climate change, their numbers have been declining since 2011 when there were more than 400 whales. Today, the population numbers continue to decrease and there are believed to be between 200 and 250 of these whales alive in the wild now, according to the IUCN. The National Oceanic and Atmospheric Administration (NOAA) estimates there are fewer than 350 remaining.
In order to study how fishing gear entanglements have had an impact on the decline of the species, researchers analyzed the outcomes of these events. They tracked what happened in 1,196 entanglements involving 573 right whales between 1980 and 2011. They categorized each encounter based on how severely the whales were injured.
“Right whales are entangled frequently but understanding the sublethal effects of all entanglements is challenging. Over the years, as we have witnessed an increasing frequency of whales with both moderate and severe injuries from these entanglements, we felt it was critical to get a more quantitative understanding of both the lethal and sub-lethal impacts,” co-lead author Robert Schick, a research scientist at Duke’s Nicholas School of the Environment, tells Treehugger.
“More broadly speaking, right whales face a number of stressors, and we wanted to provide a framework for understanding stressors one at a time, as we do here, but also in combination—and that work is ongoing.”
Tracking Run-Ins
In order to analyze entanglements, researchers pored over four decades of monitoring data from research organizations in the U.S. and Canada.
North Atlantic right whales have stocky black bodies with knobby white patches of rough skin on their heads, called callosities. The patches are unique, which makes it easy for researchers to identify individual animals. They have no dorsal fins and short, broad pectoral flippers.
Right whales got their name from being the “right” whales to hunt because they moved slowly and floated when they were killed, according to the NOAA.
“They are identifiable by natural markings on their heads. With the detailed photographic catalog of individuals, we were able to look for evidence of attached fishing gear or wrapping scars from entanglements on their bodies; this allowed us to determine the number of unique entanglement events and the severity of the resulting injuries,” Schick says.
“With the same photographic evidence, we can conduct visual health assessments for each individual and then use a statistical model to estimate an underlying estimate of health over the lifespan of an individual. We then examined outcomes of survival and reproductive output in relation to these injuries.”
Entanglements often happen in fishing gear like lobster pots where the whale is caught up in the ropes that hold the equipment in the water. The injuries may be minor with the whale experiencing superficial wounds. But in more serious encounters, a fishing line can wrap tightly around the whale’s body, often causing extensive wounds and the need for the whale to expend more energy as it carries the heavy gear along with it.
Researchers found that both male and female right whales that experienced severe injuries from gear were eight times more likely to die than males with only minor injuries. Females that survived severe injuries had the lowest birth rates.
The results were published in the journal Conservation Science and Practice.
Grazing vs. Gulping
Right whales are so at risk from these injuries because they live in the coastal waters of the U.S. and Canada where there is so much fishing gear.
“They also are considered ‘grazers’ meaning that as they feed on patches of zooplankton, they swim slowly through food patches with their mouths wide open for long periods,” co-lead author Amy Knowlton, a senior scientist at the New England Aquarium, tells Treehugger.
“This presents an added vulnerability compared to other whale species that are ‘gulp’ feeders that feed on fast-moving fish. Importantly, entanglements occur in all large whale species.”
The findings are important, researchers say, because the information can be used to help protect the right whales.
“These findings highlight the fact that entanglements are causing both lethal and sublethal impacts to this critically endangered species. We have been advocating that fixed fishing gear in the U.S. and Canada be transitioned to be on-demand gear throughout their range with weaker ropes used in the interim,” Knowlton says.
“Unless gear is made to be safe for whales, there will continue to be unnecessary deaths from this industry. These deaths are illegal under the Marine Mammal Protection Act and the Endangered Species Act in the US, as well as the Species at Risk Act in Canada.”
