Table of Contents
High for Right Whales but Humans Hold the Dice
by Tracey Crago,
WHOI Sea Grant
They have been the subject of lawsuits, scientific research, public
outcry, and fisheries regulations, yet the plight of the North Atlantic
right whale, Eubalaena glacialis, remains grim. If conditions remain
as they are today, the northern right whale will become extinct
in approximately 200 years, say WHOI population biologist Hal Caswell
and his graduate student, Masami Fujiwara. But that doesnt
have to be the end of the story: according to their survival probability
model, extinction can be avoided.
The model and its take-home messages are big news for anyone following
the right whale saga for the last two decades. To avoid extinction,
the model shows that, at the current population level (approximately
300), two female deaths must be prevented each year. That would
increase the population growth rate to one, the critical level separating
growth from extinction. The number of female deaths that must be
prevented is directly proportional to the population level.
female right whale, identified as 1157a, and her calf in southern
waters. According to Fujiwara, at current population levels
(~300), the prevention of two female deaths per year could increase
the population growth rate to one, the critical level separating
growth from extinction. Photo courtesy of New England Aquarium.
indicates that the early-1980s population growth rate was greater
than one, or increasing, though slightly," says Fujiwara. "Since
that time, the population growth rate has declined, and populations
started declining in the early 1990s. That means that to avoid extinction,
we dont have to return to a situation [like that of] pre-whaling
years; we just need to find out what happened between 1980 and now
that is causing the whales to die," he explains.
The two leading causes of death in northern right whales are ship
collisions and fishing gear entanglements. These findings have resulted
in a flurry of research and technological developments, along with
fisheries management restrictions and shipping regulations. And
Recently, the Massachusetts Division of Marine Fisheries (MDMF)
settled a lawsuit waged by Richard "Max" Strahan, who
accused MDMF of driving the northern right whale to extinction.
In a recent Cape Cod Times article, Dan McKiernan, a MDMF lobster
scientist, credited Strahans lawsuit with accelerating the
rate at which the state and federal government were working to reduce
the impact of fishing gear and ship strikes on right whales. "Since
1996," the article states, "the state and federal governments
have embarked on a multi-faceted program to save right whales. A
critical habitat area was established in Cape Cod Bay. Survey flights
now criss-cross the bay pinpointing concentrations of right whales
and warning fishermen to move their gear. New regulations required
fishermen in areas where whales are present or migrating to alter
MIT Sea Grant has supported the development of a high-tech buoy
that can detect the distinctive right whale vocalizations at a range
of about five miles. The device can be used to supplement current
visual observation techniques, and may prove especially useful in
poor visual conditions such as fog and darkness.
With all of the attention on the northern right whale, the most
endangered species of large whales, scientists wanted to determine
whether or not the population had any hope of recovery. An initial
study, published in 1999, was conducted by Caswell, Fujiwara, and
Solange Brault of the University of Massachusetts, Boston. The model
employed rigorous statistical estimates of survival probability
and found that, not only was right whale survival probability going
down over time, but the population was declining as well.
The most recent study, supported in part by WHOI Sea Grant, attempted
to go a step further by looking at the survival probability differences
among sexes and life stages. To do this, Fujiwara and Caswell considered
the differences between males and females, and classified the population
by stages: calf, immature, mature, and mature mother with calf.
Next, they looked at the probability of each individual in the study
making a transition from stage to stage, including death as a stage.
As with the previous study, they used data gathered by the New England
Aquarium (NEAq) as part of the North Atlantic Right Whale Consortium,
to look at individual sighting history data. Their data includes
individuals sighted between 1980 and 1997, for a total of about
370 individuals. Sightings are gathered primarily in Massachusetts
and Cape Cod Bays, Bay of Fundy, Great South Channel, Browns
Bank, and off the Florida and Georgia coasts.
The model is based on mark-recapture statistical methods, some of
which were newly developed by Fujiwara with WHOI Sea Grant support.
These methods can be applied to other populations for which individual
sighting data are available. Fujiwara and Caswell use what are called
"maximum likelihood" methods to estimate survival, transition
probabilities, sighting rates, and the response of these variables
to environmental factors. This method, says Fujiwara, "lets
the data speak for itself, rather than making us guess or make assumptions."
The new study has yielded some population-specific findings. One,
says Fujiwara, is that "the survival probability of females
who reproduce is declining." Recent reports of surging birthrates
in right whales this season (December, 2000-March, 2001), could
eventually factor into the model, first as females with calves,
then the calves on their own.
As for the application of their model to management efforts, Fujiwara
acknowledges that there are many efforts underway to reduce ship
collisions and entanglements but it will be important "to assess
the effect of those management actions." This will require
continued measurement of the population growth rate, which, he admits,
is not an easy task. Any models that must contend with small population
sizesand thus a limited sample sizerequire very sophisticated
analysis, says Fujiwara. "We are dealing with very slight changes
in survival probabilities and a small number of individuals,"
As such, it means that not everyone can do this type
of model. Fujiwara is now among a relatively small circle of population
biologists with the necessary tools, resources, and know-how to
perform such sophisticated models. In fact, it was his interest
in mathematical population models, quantitative biology, and statistics
that brought him to the MIT/WHOI Joint Program in Oceanography in
1997, and to Caswells lab in particular. Fujiwara hopes to
graduate in 2002, but will spend this summer presenting results
of their latest model at professional meetings and the next year
finishing up his dissertation and beginning his search for a job.