Why are so many whales dying in Argentine Patagonia?


The southern right whales that use Península Valdés, Argentina as a nursery ground have suffered the largest mortality event ever recorded for the species in the world. At least 605 right whales have died along the Argentine coast since 2003, including 538 newborn calves. One hundred and thirteen calves died in 2012 alone. The Southern Right Whale Health Monitoring Program is working with scientists worldwide to determine why the whales are dying, but as yet, a common cause remains to be found.

Every winter and spring, the calm bays off Península Valdés, a World Heritage Site on the Atlantic coast of Patagonia, Argentina, are filled with southern right whales which come to give birth and raise their calves. However, in recent years these remote beaches are also filled with dead whale calves. In 2008 alone, almost one hundred whales, 89 of them calves, died at Península Valdés and in surrounding areas. 2012 was a record-breaking season, with 116 whale deaths, 113 of them calves.

The difficulty of identifying the cause of this die-off has been a challenge for the researchers studying the whales at Península Valdés. Marcela Uhart, Co-Director of the Program and a Veterinarian formerly with the Wildlife Conservation Society, and Denise McAloose, the lead pathologist of the Program and also the Head of Pathology for the Wildlife Conservation Society, have not been able to determine the cause despite extensive investigations. They say that “though we collect hundreds of tissue samples to test for a variety of infectious, toxic and other diseases, to date we’ve been unable to pin down the cause of these deaths. Every year breaks previous existing patterns in terms of numbers of dead whales, time of the season of highest mortalities, location of stranded whales, etc. The only fact that remains dauntingly constant is that the majority of deaths occur in newborn calves.”

“In 2012 we lost nearly one third of all calves born at the Peninsula. Southern right whales have their first calf when they are nine years old on average,” explains Dr. Mariano Sironi, Scientific Director of the Instituto de Conservación de Ballenas in Argentina and Advisor to the Program. “This means that it won’t be until a decade from now that we will see a significant reduction in the number of calves born, as all of the female calves that died will not be contributing any new offspring to the population.”

Vicky Rowntree, Co-Director of the Program, Director of Ocean Alliance’s 43-year study of the southern right whales of Península Valdés and a research professor at the University of Utah, is concerned about the reduction in population growth rate. “The southern right-whale population is still only a small fraction of its original size, and now we have reason to worry about its recovery. Our long-term data indicate that the Península Valdés whales were increasing steadily at close to 7% per year until recently. Elevated calf mortality is reducing that growth rate substantially (by nearly a third in one estimate). If this continues, we just don’t know what will happen.”

The International Whaling Commission is the global intergovernmental body charged with the conservation of whales and the management of whaling. In 2010, the Commission organized a workshop in Puerto Madryn, Argentina to analyze the right whale die-offs at Península Valdés. Based on discussions of existing evidence, experts from around the world concluded that the three most likely causes of mortality could include malnutrition, infectious disease and biotoxins.

Last week, scientific experts met at a workshop during the 44th Annual Conference of the International Association for Aquatic Animal Medicine (IAAAM) in Sausalito, California, to analyze the new findings of this puzzling whale die-off. Dr. Peter Thomas, of the US Marine Mammal Commission and Chair of the Workshop, said that “until recently, the Valdés right whale population was considered to be healthy and growing at a steady rate after being depleted by whaling in past centuries. However, in view of the many years of high mortality, it seems that the Península Valdés whales and their western South Atlantic ecosystem may be less fit and resilient than previously thought.”

Discussions at the workshop also focused on a very unusual biological phenomenon. At Península Valdés, kelp gulls land on the backs of southern right whales to eat their skin and blubber. Rowntree and Sironi have studied the frequency of gull attacks every year since 1995. “The attacks are very painful and cause large, deep lesions, particularly on the backs of young 2-6 week-old calves. The whales flinch violently and swim away to flee from the attacking gulls”, the researchers explain. “This harassment can last for hours at a time. As a result, right whale mothers and their calves are expending much precious energy during a time-of-year when mothers are fasting and at a site where little to no food is available to replenish fat reserves. The gull harassment and the extensive wounds they make must have a very negative effect on the health and body condition of these whales and is certainly very stressful”.

Determining the cause of the calf mortality at Península Valdés is urgent for this population and in light of the critical status of other right whale populations in the northern hemisphere whose total numbers are about equal to the number of whales that have died at Península Valdés since 2003. “The current mortality of southern right whales at Península Valdés is unparalleled at a global scale. No other right whale population is losing so many calves each season”, says Dr. Frances Gulland, Senior Scientist at The Marine Mammal Center in Sausalito and Host of the IAAAM Meeting. “The populations of their northern sister species in the North Pacific and the North Atlantic are both ‘endangered’ and the more closely related southern right whale population off the coast of Chile and Peru is ‘critically endangered.’ Should these populations encounter this same crisis, they could go extinct.”

The past seven years of consistently high mortality of right whales at Península Valdés cannot be ignored. It is of critical importance to continue current research and monitoring efforts to find out why so many right whale calves are dying, and what we can do about it.

About the Program

The Southern Right Whale Health Monitoring Program was established in 2003 to document drivers of disease and mortality for the southern right whales that come to Península Valdés, Argentina to breed. It is run by a consortium of the non-governmental organizations Wildlife Conservation Society, Whale Conservation Institute/Ocean Alliance, Instituto de Conservación de Ballenas and Fundación Patagonia Natural. It began operating with support from the US National Marine Fisheries Service and the US Marine Mammal Commission, and runs with funds from foundations, private donors and the NGOs that lead the Program.

CONTACT:
Mariano Sironi – msironi@icb.org.ar;
Max Pulsinelli – mpulsinelli@wcs.org