- New research finds that deaths caused by human activities are not just impacting individual North Atlantic right whales and their immediate family units, but actually impeding population growth and recovery of the species, which has been declining since 2010.
- Peter Corkeron, head of a whale research initiative at NOAA’s National Marine Fisheries Service, led an international team that studied the western North Atlantic population and three populations of southern right whales, in order to determine whether or not the slow growth rate of North Atlantic right whales is attributable to humans.
- More than 80 percent of North Atlantic right whales have been entangled in fishing gear at least once in their lives, and 59 percent have been entangled two or more times, the researchers found. The increased energy demands imposed on entangled whales can reduce the likelihood that a female will successfully give birth.
On October 14, the crew of a US National Oceanic and Atmospheric Administration (NOAA) ship called the Henry B. Bigelow reported a whale carcass floating about 100 miles east of Nantucket, a small island off the coast of Cape Cod, Massachusetts. The carcass was later identified as a sub-adult North Atlantic right whale.
After reviewing data collected from the deceased whale, scientists determined the probable cause of death was “severe acute entanglement,” according to NOAA. “The whale had multiple wounds indicative of a wrapping line entanglement, including pronounced ligature impressions with related deep concave defects indicating severe constricting abrasions. Entanglement wounds were strongly suggestive of numerous transverse body wraps involving the thorax (chest) and flippers.”
This is the third North Atlantic right whale known to have died this year — one died in January and another in August — and all three appear to have been the victims of entanglement in fishing gear left behind by humans or collisions with ships. The North Atlantic right whale is listed as Endangered on the IUCN Red List.
New research finds that these deaths caused by human activities are not just impacting individuals and their immediate family units, but actually impeding population growth among North Atlantic right whales altogether.
Like many other baleen whale species, North Atlantic right whales were nearly exterminated by historical commercial whaling. Their numbers gradually increased up until around 2010, when they started to decline once again. 2018 has actually been far less deadly for the whales than 2017, when NOAA confirmed 17 North Atlantic right whale deaths, which is equivalent to about 4 percent of their total estimated population of 450 individuals. It is believed that there are only about 100 females of breeding age left in the population.
There are three species of right whales in the world, the North Atlantic right whale (Eubalaena glacialis), the North Pacific right whale (Eubalaena japonica), and the southern right whale (Eubalaena australis). Peter Corkeron, head of a whale research initiative at NOAA’s National Marine Fisheries Service, led an international team that studied the western North Atlantic population and three populations of southern right whales, which are listed as a species of Least Concern on the IUCN Red List, in order to determine whether or not the slow growth rate of North Atlantic right whales is attributable to humans.
“We studied four populations of right whales, three from the southern populations off eastern South America, southern Africa and southwest Australia plus the western North Atlantic population, that had comparable time-series data and minimum counts of calves known to be born each year,” Corkeron said in a statement. “Intensive aerial surveys of North Atlantic right whale calving habitat began in 1992, so that marked the start of our comparison.”
After comparing calf counts from 1992 to 2016 for each of those four populations, Corkeron and his co-authors found that the annual rate of increase of North Atlantic right whales was about 2 percent per year. That is a much lower growth rate than they found in the southern right whale populations they studied, which grew between 5.3 and 7.2 percent per year.
In order to examine what might be causing such low population growth, the researchers next constructed a population projection model for female North Atlantic right whales that showed an intrinsic annual rate of population increase of 4 percent, or twice what they had discovered through their own observations.
Corkeron and team conclude that “adult female mortality is the main factor influencing this rate.”
More than 80 percent of North Atlantic right whales have been entangled in fishing gear at least once in their lives, and 59 percent have been entangled two or more times, the researchers found. The increased energy demands imposed on entangled whales can reduce the likelihood that a female will successfully give birth, while recovery from entanglement or ship strike can prolong the period of time between births.
The authors note in the study that between 1970 and 2009, human activities were responsible for 70 of the 87 North Atlantic right whale mortalities for which the cause of death was determined, whereas most deaths of southern right whales that have been observed were calves in their first year of life, with “very few” being directly attributable to human activities.
“With almost no observations from any other sources of mortality, a reasonable inference is that the vast majority of non-calf female [North Atlantic right whale] mortality is anthropogenic,” the researchers write in the study. Thus, they add, “Anthropogenic mortality and morbidity has limited the recovery of [North Atlantic right whales], and baseline conditions prior to their recent decline were already jeopardizing [the species’] recovery.”
Protecting adult females of the species from injury and death is therefore crucial to the whales’ recovery. The researchers’ projections, based on their North Atlantic right whale female survival model, suggest that there could have been around 326 females in 2015, which would correlate to a total population of at least 650 individuals.
“Had that been the case, the discovery of at least 17 dead right whales in 2017 would have been cause for alarm, but relative risk to the species would have been manageable,” Corkeron and co-authors write. “Instead, the recent detection of a decrease in [North Atlantic right whale] abundance since 2010, coupled with the discoveries of mortalities in 2017, means that ‘the North Atlantic right whale is in deep trouble again.’”
• Cooke, J.G. (2018). Eubalaena glacialis. The IUCN Red List of Threatened Species 2018: e.T41712A50380891. doi:10.2305/IUCN.UK.2018-1.RLTS.T41712A50380891.en. Downloaded on 19 November 2018.
• Cooke, J.G. & Zerbini, A.N. (2018). Eubalaena australis. The IUCN Red List of Threatened Species 2018: e.T8153A50354147. doi:10.2305/IUCN.UK.2018-1.RLTS.T8153A50354147.en. Downloaded on 19 November 2018.
• Corkeron, P., Hamilton, P., Bannister, J., Best, P., Charlton, C., Groch, K. R., … & Pace, R. M. (2018). The recovery of North Atlantic right whales, Eubalaena glacialis, has been constrained by human-caused mortality. Royal Society Open Science, 5(11), 180892. doi:10.1098/rsos.180892