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"Starving" right whales


Robert Kenney <[log in to unmask]>


Robert Kenney <[log in to unmask]>


Thu, 9 Mar 2000 21:32:40 -0500





TEXT/PLAIN (1 lines)

Let me begin by apologizing in advance if my initial attempt at
constructing a reply to only the last bits in a complete digest of the
last 24 hours worth of FISH-SCI traffic using unfamiliar mail software
have clogged everyone's mailboxes... While I don't necessarily feel
qualified to speak to all of the various issues raised during this
discussion, I have been part of the team working on western North Atlantic
right whales for over 20 years, so I am very familiar with this particular
population and the problems it is facing.

> Date: Thu, 9 Mar 2000 18:15:02 -0400
> From: Debbie MacKenzie <[log in to unmask]>
> Are the right whales starving?

The short answer is no. Unlike the situation with gray whales in the
North Pacific last year, we do not have a single case of a right whale
mortality where starvation has been implicated as a primary or
contributing cause. And to date, no one to my knowledge has suggested
that the increase in mortality estimated by the Caswell et al. (1999)
model is due to food limitation. There is a suspicion that food
limitation may be affecting reproductive rates (more details below).

> Andrew Remsen wrote:
> >Woods Hole Oceanographic scientists have modeled the survivorship of the
> >right whale and concluded that survival has steadily declined for
> >individual whales and population growth rate is negative.

Caswell et al.'s modeling study concluded that present mortality rates
have substantially increased over the 1980's and that the population is
declining at 2.4% per annum, however it is not quite correct to say that
there has be a steady decline in survival. In fact, their analysis
confirmed our earlier (Knowlton et al., 1994) much more simple-minded
estimate that the population was growing at 2-3% in the 1980's.

> >........ Plus, their very slow reproductive rate and
> >extremely small population size makes them extremely vunerable .....

Right whale populations may reproduce and grow faster than one might
think, with females maturing as young as 5-7 years and producing a calf
every 3 years. Some southern hemispere populations are growing at 7-9%.
Not a codfish, obviously, but perhaps not what the conventional wisdom
might predict.

> Entanglement in fishing gear and collisions with ships - these are
> consistently given as the two main reasons for the decline of the right
> whale. I've followed the reports of the EWS survey crew for a couple of
> years. Considering how few calves they see, it is not uncommon for them to
> report seeing dead ones. Causes of death in the calves are generally
> "undetermined" (fishing gear and ship strikes are very easily ruled out).

Approximately one-third of known mortalities are neonates. However, the
frequency of neonatal mortalities in the Georgia-Florida calving ground
(where the EWS surveys are flown) largely reflects the numbers of calves
born - more calves born = more dead ones. Another third (probably more in
recent years) of known mortalities can be definitely attributed to ship
collisions and fishing gear entanglements. Considering the number of
carcasses which are never recovered, human-caused mortality is a very
significant impact. Regardless of any other sources of mortality or food
stress, this is one place where active management can (and MUST) be taken.

> My "observation" is not only of a decreasing population, but of clear
> clinical signs of malnutrition. The survey crew sees sick whales -

There is yet no connection between an apparent increase in the occurrence
of skin lesions (which is being assessed primarily in northern feeding
habitats, not by the EWS surveys) and nutritional stress. And it might be
stretching a point to go from skin problems to "sick whales."

> ............ Also, why are
> whales who have had no contact with ships or fishing gear unable to
> conceive or maintain pregnancies? Something else is going on.

Now we're getting to the interesting questions (more to follow).

> "Their low numbers may have allowed competitors such as sei whales,
> mackerel or herring to move into right
> whale feeding grounds?" -- sei whales? how abundant are they?...and their
> feeding strategy is different.

The last reasonable estimate indicates a couple thousand sei whales in the
stock overlapping with right whales, but the data are over twenty years
old. One might expect a larger population today. And there is a
significant overlap in prey species between right and sei whales, as well
as a distributional overlap in some habitats/years.

 .......Mackerel and herring in the Northwest
> Atlantic (based on DFO stock status) do not appear to be increasing in
> abundance. (Herring: landings and biomass estimates decreasing. Mackerel:
> landings in decline.) This is very speculative, with very doubtful
> evidence...I think it is "a stretch."

In fact, herring and mackerel standing stocks in the Gulf of Maine/Georges
Bank region are at or near all-time highs (at least for this century, when
people have been doing stock assessments). That being said, I think that
the evidence for competition being an important impact on right whale
foraging success is tenuous, at best. But I am becoming convinced that
food limitation is a serious concern at present.

During the 1990's the most dramatic observed change in the right whale
population has been an increase in the average interval between calves. In
1980-1992 the average was 3.7 years (the modal interval is three years -
one each for pregnancy, lactation, and replenishment of energy stores).
The average for 1993-1998 is over 5 years, with very few 3-year intervals
and with some females apparently dropping out of the reproductive pool
entirely. In a long-lived species with the expectation of multiple future
reproductive opportunities, one would expect that energy allocation
strategies would favor survival at the expense of reproduction. A decline
in food availability for right whales might be expected to manifest itself
first in reproductive effects, including an increase in the time needed to
accumulate the surplus energy needed for pregnancy and lactation.

There is no evidence for any long-term decline in productivity which might
impact right whale feeding. Their preferred prey includes the older
copepodites and adults of _Calanus finmarchicus_, which is the dominant
zooplankter in much of the North Atlantic. (Incidentally, I always make a
point of specifying zooplankton rather than simply plankton when talking
about right whale food, because I think too many people get misled into
thinking the whales eat phytoplankton). For a right whale, however, the
abundance of _Calanus_ over broad areas of ocean is unimportant. What a
right whale "cares" about is the concentration of copepods in patches the
size of its mouth opening. That concentration must be extremely high in
order to pay back the high costs of metabolism, locomotion, migration,
foraging, and reproduction. The most important factors in determining the
location and value of appropriate feeding grounds for right whales are
physical-oceanographic concentrating mechanisms rather than biological
productivity. Changes in circulation patterns are therefore more likely
to impact right whale foraging success and nutritional status than
alterations in nutrient supply.

So why haven't right whales recovered since their protection from whaling
in the mid-1930's. It's not a valid question, since there is no estimate
of abundance until around 1980. If there were only five or ten North
Atlantic right whales in 1935, they done fabulously. If there were a
thousand, they've gone down the drain. But we have zero data.

Surprisingly, some recent results of genetic studies are now suggesting
that the population has been maintained at this low level for a relatively
long period, perhaps since the episode of intensive Basque whaling in
Newfoundland in about 1530-1700. If that is true, a reasonable inference
is that the population undergoes cycles of growth and decline (which may
be more reasonable than expecting the population to have remained stable
at about 300 whales for 300 years).

In my opinion, the evidence is converging on a reasonble scenario which
fits both the long-term and recent trends. The Basque whaling in Labrador
and Newfoundland, plus American and Canadian pelagic and shore-based
whaling (the last of which continued into this century) wiped out most of
the population, leaving only a small remnant at the southern end of the
original range. (One of the most interesting questions to me is why
they've never re-occupied the original core of their range, which must
have been good habitat if the Basques could kill 20,000 of them in 170
years.) In that peripheral habitat, the population has undergone cycles
of growth and decline, possibly related to coupled atmosphere-ocean
patterns, e.g. the North Atlantic Oscillation (NAO). The short-term
switch in the early 1990's from a growing population to a declining one
corresponds to major shifts in habitat use and to a shift in phase of the
NAO. Overlaid on this is continued anthropogenic mortality, at first
opportunistic whaling and more recently ship strikes and fishery
entanglement. There's nothing we can do to change the NAO, but we can
minimize the mortality to give them a fighting chance.


Robert D. Kenney, Ph.D.
University of Rhode Island
Graduate School of Oceanography
Bay Campus Box 41
Narragansett, RI 02882-1197, USA
(410) 874-6664; ...6497 (fax)
[log in to unmask]

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