David @ Tokyo

As in various other parts of the world, the humpback whale appears to be in relatively healthy shape in the North Atlantic.

In 2002, at the IWC Scientific Committee had this to say:

In conclusion, the Committee agrees that it has greatly increased its knowledge of North Atlantic humpback whales as a result of its Comprehensive Assessment. In particular, populations are increasing in a number of areas in the North Atlantic (Gulf of Maine, Iceland, West Indies) and the rate of increase of the West Indies breeding population is estimated at 3% per annum between 1979 and 1992 (IWC, 2002l, p.236). This breeding population has an estimated population size of 10,752 in 1992 (IWC, 2002m, p.258).

However,

the Committee is unable to provide advice on the population level of North Atlantic humpback whales in relation to carrying capacity. This statement applies to past carrying capacity and to present carrying capacity.

In another document, Philip Hammond, Peter Stevick and others add that:

We estimate that this population has been increasing about 3.1% a year over the 14-year period. This growth rate is lower than we know it could be, which may mean the population is approaching the size it was before hunting began.

With that background, I was interested to see news today that the National Oceanographic and Atmospheric Administration has observed a "sharp increase in humpback deaths since last summer". Apparently scientists have been able to access one dead female whale

The dead whale is a huge find ... this is the first stranded leviathan from which they can get fresh biological samples, NOAA Fisheries spokeswoman Terri Friday said.

''We don't get a lot of opportunities to sample, so necropsies are very important,'' she told Florida Today.

Such samples can provide a life history of the animal, its food habits, illnesses and viruses that might compromise the rest of the population, the presence of biotoxins or injuries that indicate a cause of death, she said.

With only a single sample to go on I wonder whether the biological samples answer more questions than they pose.

However, in seeing this I recall the observation of an "unusual mortality event" in the essentially fully recovered eastern gray whale stock, which resides off the west coast of North America. From the discussion of the report:

Taken together, these events could be indicative of a population near carrying capacity that experienced substantial nutritional stress during poor environmental conditions, which was translated into lower reproduction and higher mortality. Although these effects have been seen only in recent years, a new analysis fitting a density-dependent model to the population-trend data suggests the Eastern North Pacific gray whale population is no longer increasing and has been relatively stable since the late 1980s or early 1990s; therefore, it may be close to or already at carrying capacity (Wade 2002).

Perhaps the North Atlantic humpback whale too has hit it's carrying capacity? I'm sure they will be a lot of scientific interest in this situation.

UPDATE 2007/01/18:
Another humpback death has been reported.

Labels: gray whale, humpbacks, unusual mortality event