El Niño Events Affect Southern Right Whale Breeding Success

CAMBRIDGE, UK, January 24, 2006 (ENS) - Global climate processes are affecting the number of calves produced by southern right whales in the South Atlantic, according to a newly published 30 year study by an international team of scientists.

Southern right whales, Eubalaena australis, migrate from the South Atlantic to the Southern Ocean to feed. Following an El Niño event, changes in sea temperatures affect the availability of krill, a shrimp-like crustacean, which is the main diet of these whales.

El Niño is a disruption of the ocean-atmosphere system in the tropical Pacific that has consequences for weather around the globe. El Niño events happen periodically every two to seven years when tropical Pacific trade winds die out and ocean temperatures become unusually warm.

It is known that these changes affect penguins and seals in the Antarctic, but this is the first time the link has been made with southern right whales as they return to their calving grounds in the South Atlantic off Peninsula Valdes, Argentina.

Researchers study a southern right whale off the coast of Patagonia, Argentina. (Photo by Iain Kerr courtesy Ocean Alliance)

Reid is one of the six scientists from the United States, Great Britain and Germany who contributed to this study. Reid and co-authors Russell Leaper, Justin Cooke, Phil Trathan, Keith Reid, Victoria Rowntree, and Roger Payne found a strong relationship between breeding success of whales in the South Atlantic and El Niño events in the western Pacific. The results are published this week in the online journal "Biology Letters," a peer-reviewed publication of The Royal Society.

Contributing author Dr. Roger Payne of the Massachusetts based Ocean Alliance and the Whale Conservation Institute has studied the world's largest population of southern right whales on their Argentine calving grounds for the past 32 years. This program, focused on 2,000 individuals, is the longest continuous study of any baleen whale species based on known individuals.

Dr. Roger Payne of the Massachusetts based Ocean Alliance and the Whale Conservation Institute (Photo courtesy Ocean Alliance)

For this study, 1,828 southern right whales were individually identified by photographs taken from 1971–2000 on their breeding grounds off Peninsula Valdes. Of those whales, 564 have been seen calving at least once.

Leaper, of the International Fund for Animal Welfare, and Cooke, of the Centre for Ecosystem Management Studies in Germany, originated the idea that that there might be a connection between calving success and sea surface temperature time series.

To test this theory, Leaper, Cooke and their colleagues compared sea surface temperature time series from the southwest Atlantic and the El Niño 4 region in the western Pacific with an index of annual calving success of the southern right whale breeding in Argentina.

They found there was a strong relationship between right whale calving output and sea surface temperature deviations, or anomalies, at South Georgia in the autumn of the previous year and also with mean El Niño 4 sea surface temperature anomalies delayed by six years.

Southern right whales in the South Atlantic Ocean (Photo by Iain Kerr courtesy Ocean Alliance)

"The warmer water causes a reduction in the abundance of krill, which are shrimp-like crustaceans eaten by large whales and other predators," Rowntree said.

Southern right whales were some of the first species to be heavily depleted by whaling and have been given international protection since 1935. But illegal catches by the USSR continued with several thousand being taken in the South Atlantic in the 1960s.

Since the 1970s the population of southern right whales in the SW Atlantic has been increasing at an average of seven percent a year but is still only at a small fraction of its pre-exploitation size.

There are few long-term analyses of conditions in the Southern Ocean, making temperature trends difficult to monitor. Scientists at British Antarctic Survey combined several sets of satellite data, historical records and measurements taken from ships to reconstruct the temperature in the upper layer of the sea over the past few decades. They found the average sea temperature off the Antarctic Peninsula during the summer rose by 1.2 degrees Celsius during the period 1955-1994.

The findings of this study extend similar observations from other krill predators, the researchers say, and show clear linkages between global climate signals and the biological processes affecting whale population dynamics.

If sea surface temperatures continue to rise this could threaten the recovery of the southern right whale, the researchers predict.