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Northern Right whales have declined for two reasons, in my opinion.
First, this is a relatively slow-growing population that
was overharvested, e.g. recruitment overfishing. It takes a lot
longer to rebuild a depleted population than it does to fish it down
and depensation may be occurring in this population.
Second, now that the population is near extinction, there
are too many whales killed by injuries from entanglements with
fishing gear (longlines to hold trap gears) and by vessel collisions
for there to be any population increase.
While it is possible that food limitation is an issue for right whale
survival, I doubt it is an important effect compared to human-induced
mortality. But I would be happy to reconsider this opinion if
demographic data show otherwise. Please, show me the data.
As for the environmental forcing/trophic dynamics argument
to explain reduced survival, it would useful to avoid affirming the
consequent-type arguments, such as:
If right whales have less food, then their population will decrease.
We observe that the population has decreased, therefore they have
must have had less food.
This is a logical fallacy that reasonable people should avoid.
Jon Brodziak
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