Poor Body Condition of North Atlantic Right Whale Contributes to Population Decline

Comparison to Southern right whales using aerial photogrammetry reveals ‘thin, unhealthy’ state

New research by an international team of scientists reveals that endangered North Atlantic right whales are in much poorer body condition than their counterparts in the southern hemisphere. The alarming results from this research, led by Fredrik Christiansen, assistant professor at Aarhus University in Denmark, were published this week in the journal Marine Ecology Progress Series

Since the cessation of large-scale commercial whaling in the last century, most populations of southern right whales have recovered well. Now there are about 10,000-15,000 right whales in the southern hemisphere. 

Unfortunately, the same cannot be said for the North Atlantic right whales, found today mostly off the east coast of North America. There are now around 410 individuals left, and the species is heading to extinction. Lethal vessel strikes and entanglement in fishing gear continue to kill these whales. 

As well, individual North Atlantic right whales have to deal with the energetic and other costs that come about from frequent sub-lethal entanglements in fishing gear, in particular lobster and crab pots. These burdens, along with a change in the abundance and distribution of their main prey, copepods and krill, have left these whales thin and unhealthy, which makes them less likely to have a calf. This, in turn, contributes to the current overall decline of the species. 

“As a veterinarian, I’ve long been concerned about how entanglements affect the welfare of these whales,” says Michael Moore, senior scientist and director of the Marine Mammal Center at the Woods Hole Oceanographic Institution. Now we are starting to draw the linkages from welfare to this species’ decline. To reverse these changes, we must: redirect vessels way from, and reduce their speed in, right whale habitat; retrieve crab and lobster traps without rope in the water column using available technologies; and minimize ocean noise from its many sources.” 

To quantify ”thin and unhealthy”, Christiansen and an international team of scientists investigated the body condition of individual North Atlantic right whales, and compared their condition with individuals from three increasing populations of Southern right whales: off Argentina, Australia and New Zealand. 

How Fat are Right Whales? 

The study is the largest assessment of the body condition of baleen whales in the world, and involved researchers from 12 institutes in five countries. The international research team used drones and a method called aerial photogrammetry to measure the body length and width of individual right whales in these four regions around the world. From aerial photographs, the researchers estimated the body volume of individual whales, which they then used to derive an index of body condition or relative fatness. 

The analyses revealed that individual North Atlantic right whales: juveniles, adults and mothers; were all in poorer body condition than individual whales from the three populations of Southern right whales. This is alarming, since poor body condition for North Atlantic right whales helps explain why too many of them are dying, and why they are not giving birth to enough calves to boost the population’s recovery. It could also be affecting their growth, and delaying juveniles reaching sexual maturity. These combined impacts on individuals helps explain why the species is in decline. 

Aerial view of southern right whale followed by calf
A southern right whale mother cares for her calf at the calving ground off Peninsula Valdes in Argentina, one of the healthy populations in this study. (Fredrik Christiansen)

“We are fortunate that in the south, right whales are thriving,” says Marcela Uhart, director of the Latin America Program at the Karen C. Drayer Wildlife Health Center at the University of California, Davis, and founder of the Southern Right Whale Health Monitoring Program in Argentina. We must continue to protect and learn from these healthy populations and build knowledge that may aid in the recovery of their northern counterparts. It is encouraging to see right whale scientists around the world joining efforts to inform conservation action. The plight of the North Atlantic right whale is a strong wake up call for us all.” 

Media Contacts

Marcela Uhart, Karen C. Drayer Wildlife Health Center, +54 9280 4696332, muhart@ucdavis.edu

Fredrik Christiansen, Aarhus University, +45 3133 2367 , f.christiansen@aias.au.dk 

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