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Whale births linked with climate
By Paul Rincon
BBC News Online science staff
Original article may be viewed at
http://news.bbc.co.uk/1/hi/sci/tech/3235246.stm
US scientists say monitoring the North Atlantic climate can predict the birth
rate of an endangered species of whale. There are thought to be just 300 right
whales left in the North-West Atlantic. Atmospheric conditions above the ocean
can affect zooplankton concentrations on which the whales depend for food,
impacting their reproductive success. The team developed a mathematical model to
describe the relationship which it will report in the journal Frontiers In
Ecology And The Environment. Positive phase In late winter, North Atlantic right
whales (Eubalaena glacialis) make their way to the Gulf of Maine, where they
feed on its high concentrations of copepods - crustaceans about the size of rice
grains.
The concentrations of one abundant copepod species, Calanus finmarchicus, are
linked to a pattern of atmospheric pressure called the North Atlantic
Oscillation (NAO). The NAO is said to be in either a positive or a negative
state. When the NAO has been in the positive state, the deep waters of the Gulf
of Maine become warmer and saltier. These conditions favour zooplankton,
typically leading to higher abundances of these creatures. Following a period of
negative NAO conditions, the waters become colder and fresher - conditions that
are less hospitable to zooplankton, leading to a fall in their numbers. It takes
about two years for these changes in the NAO to affect zooplankton
concentrations. Shifting pattern The researchers found that flips in NAO and
consequent fluctuations in abundances of zooplankton affected the birth rate of
right whales. Andrew Pershing of Cornell University developed the "transitional
probability" model.
"We can explain about 65% of the variability of right whale calving rates using
this model," said colleague Professor Charles Greene, of Cornell University, and
lead author on forthcoming research papers on the subject. A two-year period of
physiological stress and poor reproduction in the whales between 1999 and 2000
can be traced to a dramatic negative flip in 1996 and a decline in copepod
abundance in 1998. The NAO has been in a predominantly positive phase since the
1970s. But this may be changing. "There are tantalising indications that we may
be shifting towards a more negative phase [in the NAO]," said Professor Greene.
At the end of 2002, there was a large negative shift in the NAO. The team have
not yet analysed this data to see how it affected the zooplankton. "But if
there's anything to this hypothesis, we would expect right whale calving to be
adversely affected," said co-author Jack W Jossi of the US National Marine
Fisheries Service (NMFS). On the brink Mr Jossi added that he expected to see
adverse effects on zooplankton concentrations by winter 2004. "A female right
whale needs to put on a lot of fat to give birth. The bigger you are as a whale,
the better you can get through pregnancy," said Dr Robert D Kenney, of the
University of Rhode Island.
Dr Kenney said that drops in the concentrations of the zooplankton that right
whales feed on may affect fertility in several ways. Firstly, the whales may
need to achieve a certain level of fat in order to physiologically support a
pregnancy. Secondly, when starved of food, they may not able to produce enough
milk to support their calves - and the youngsters die. Thirdly, lack of food may
cause an increase in miscarriages. Females have a minimum three-year period
between pregnancies. The most recent figures show that the population growth
rate is -2.4% per annum. Other researchers have predicted the extinction of the
species in 200 years based on this current trend. But Professor Greene said
extinction could occur in a much shorter time if conditions worsen. The whales
have high mortality rates as well as their decreasing birth rates. They
frequently collide with ships and become entangled in fishing gear.
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