Southern Right Whale Die-Off

Since 2005, there has been exceptionally high mortality of southern right whales (Eubalaena australis) in the region of Península Valdés, Argentina. The Southern Right Whale Health Monitoring Program (SWRHMP) established for the Península Valdés region by a consortium of local NGOs has recorded a total of 366 right whale deaths, with peaks in 2003 (31), 2005 (47), 2007 (83), 2008 (95) and 2009 (79). Most (91%) of the animals dying have been first-year calves. At its 61st annual meeting in Madeira in June 2009 the Scientific Committee of the International Whaling Commission recommended that a steering committee be formed to plan a workshop in 2011 to review possible causes and impacts of this mortality and to identify future research needs.

The workshop was held from 15-18 March 2010, at the Centro Nacional Patagónico, Puerto Madryn, Argentina and it was hosted by the Centro Nacional Patagónico (CENPAT).

Aims of the Workshop
The general aim of the workshop was to obtain a better understanding of all aspects of the recent high mortality of right whales in Argentina. Towards this end, it brought together three groups of scientists: (1) local experts with direct knowledge of the ecology and marine environment of the Península Valdés region, (2) experts studying right whales in the region and (3) international experts on whales and mortality factors such as disease and biotoxins.

Specifically, the workshop sought to determine the cause(s) of the recent high mortality and the implications of this mortality for the right whale population as well as to develop a future research and monitoring programme.

Workshop discussions

The workshop report details the following aspects of the discussions:
Historical information on the right whale population around Península Valdés, prior history of stranding events in the area, die-offs in other baleen whale populations, predation by killer whales, parasitism by kelp gulls, influence of whale watching, potential right whale food sources around the peninsula, background information on right whales elsewhere in the western south Atlantic, summer foraging areas and prey, fishery interactions, vessel strikes, exposure to chemical pollutants, infectious diseases, biotoxins, and nutritional stress caused by declines in food. The seasonal timing and location of strandings, the proportion of age and sex categories represented, the pathology, serology and histopathology reports and distribution of haplotypes and clades among stranded/living whales were also evaluated.

The workshop considered the evidence and concluded that there is reason for concern about the relatively high level of mortality, particularly of calves, experienced in recent years by the population of southern right whales that uses the Península Valdés region as a calving/nursery area. A total of 366 whales, including 333 calves, were found dead at Península Valdés between 2003 and 2009. For the vast majority of these, the cause of death is unknown.

Three leading hypotheses to explain the spikes in mortality of first-year whales (calves) in 2005, 2007, 2008 and 2009 were identified by the workshop: a decline in food availability, biotoxin exposure and infectious disease. It was not possible to determine which of these is most likely, and it was acknowledged that some combination of factors may be involved. A fourth possible contributing factor, chemical contaminants, was considered less likely, and demographic factors, killer whale attacks, disturbance from whale-watching activities, vessel strikes and fishing gear entanglement were ruled out as significant causes of what appears to be a series of acute mortality events.

In addition to the specific recommendations and questions presented for each hypothesis presented in detail in the workshop report the following research strategy (presented below in brief) was proposed to investigate the hypotheses and to guide the allocation of research effort according to the strengths and capabilities of the different research groups.

1. The work of detecting and investigating strandings and then analysing the patterns of mortality and the samples from necropsies to evaluate body condition and presence or absence of disease, toxins or other possible causes of mortality, should continue as a top priority.

2. Continued and expanded investigations of environmental factors that may be affecting the whales in the calving/nursery area should also remain a priority.

3. Besides the efforts to investigate dead whales, it is important to continue and expand the long-term research on live whales in the Península Valdés region to obtain demographic and behavioural information. A top priority should be the establishment of a reporting network to alert the research community whenever abnormal behaviour is observed that could be related to die-off causation.

4. Identification of the feeding grounds of the Península Valdés right whales and investigation of environmental factors that affect these whales’ survival and reproduction should also be a priority.

5. The long-term aerial photo-identification programme (WCI/ICB) stands out, along with the stranding network (SRWHMP), as a top priority. The 40-year datasets on the population of right whales at Península Valdés should be maintained and data collection should continue. These data are critical for monitoring population trends, describing the significance of the recent die-offs and testing causation hypotheses. The recently initiated CENPAT aerial surveys to monitor trends in abundance and the boat-based photo-identification work are important complements to the long-term research and monitoring efforts.

6. Cooperation and collaboration between research groups are essential to building the knowledge needed to answer complex questions concerning die-offs such as those observed in recent years in Argentina. Therefore, efforts to improve such cooperation and collaboration should be a high priority for governments and NGOs.

The absence of conclusive information regarding the cause of this exceptional right whale mortality should not preclude appropriate management measures.

For more information refer to the report on the Southern Right Whale die-off Workshop.

The above provides a background to the southern right whale and its conservation. The CSG regularly posts news items and updates about southern right whale conservation and these can be found on our News page or at the following links:

December 2014 – Satellite tagging southern right whales off Patagonia to help understand the reasons for recent die-offs

May 2013 – Why are so many whales dying in Argentine Patagonia?