a few gray whale calves are born before their mothers reach the warm,
lagoons of Mexico's Baja Peninsula. How does being born in the open ocean
during their mother's migration affect the calves? This question puzzles
After all, it's tough to study what you can't see and keep track of. Here's
what two scientists think about southbound babies:
whale and Mom, heading south along California: Jan. 2006
Photo Tony Nichols
Dave Rugh (say "Roo"), wildlife biologist with the National
Marine Mammal Laboratory (NMML) in Washington state. Dr. Rugh and
Kim Shelden of the NMML worked together to describe southbound gray whale
passing on the migration trail near Carmel, California. Naturally they
wonder about these babies' chances of survival compared to the babies
in the lagoons. It's hard to see a whale calf from shore, but shore-based
observers in central California count calves each southward migration. Dr. Rugh says
as four calves to as many as 60 have been sighted in a season during
the past two decades. Many more new calves swm past without being
told Journey North: "I wish I had an unequivocal answer to the
question about survivability of gray whales born in the Baja lagoons
born while migrating. However, we do not have data on the percentage
within the lagoons, nor can we trace the fate of those that were born
elsewhere. Adult whales have been observed leaving a lagoon and returning
with a calf, so the lagoons are not critical for birthing as much as
may be advantageous as nurseries. The relatively protected, warm waters
reduce heat loss in the calves. Many calves are born well north of the
lagoons, so we can assume they have evolved the ability to survive birth
at sea outside of the protection of the lagoons. So far we have not found
any clear evidence that it is any worse to be born en route.
that gray whale calves may encounter outside of the lagoons are high
(calves are vulnerable to drowning) and colder water (thermoenergetics
can put an increased demand on their resources). Sharks and killer
can kill gray whales both in and out of the lagoons, so it is not known
how much of an advantage it is to be inside a lagoon to avoid predation."
is a biologist and gray whale calf expert with the National
Marine Fisheries Service. Each spring he conducts the official gray
whale cow/calf census for the U.S. government. Mr. Perryman says: "If a calf
is born along the migration route, it will be required to migrate instead
of just hanging around. This, it seems, would cause it to burn
energy. Calves are born skinny, with little or no insulative blubber layer,
so they will also burn up some energy keeping warm. The water in the
is not only warm, but the salinity (saltiness) is very high. Calves can
float easily to the surface in the lagoon's high-density water, while
in the lower salinity waters along the California coast may have to swim
to the surface, and the higher waves can make them more vulnerable to
Storms may separate them from their mothers. Probably the most important disadvantage of being born along the migration
route is that killer whales can find the calves. There are normally no
in the lagoons, so it is a safer place if you are a calf."
This! Journal or Discussion Questions
- In a two-column
chart, list the facts shared by scientists in one column and their opinions
in the other. Why is it difficult to know for certain about the survival
rate of gray whale babies in each environment?
Dave Rugh's comments in your own words and tell a friend what this scientist
- What do
you think are the best conditions for a baby whale's birth and survival
in its first months of life? Make a list based on the scientists' comments
and your own ideas.
Science Education Standards
develop explanations using observations (evidence) and what they already
know about the world.
have basic needs. They can survive only in environments in which their
needs can be met.
- All organisms
must be able to obtain and use resources, grow, reproduce, and maintain
stable internal conditions in a constantly changing external environment.