'Cetacean census' continues
Texas A&M researchers aboard the R/V Gyre
spot more marine mammals in the Gulf of Mexico
by Joel G. Ortega-Ortiz
Texas A&M researchers
have been intensively studying cetaceans (whales and dolphins)
in the Gulf of Mexico since 1992, when the first cruise for the
GulfCet project went out to sea. During 15 GulfCet cruises, Texas
A&M and the National Marine Fisheries Service Southeast Fisheries
Science Center collaborated to create a database of cetacean
The GulfCet database helped us understand
the oceanographic factors, like water temperature and nutrient
levels, which influence the distribution and abundance of cetaceans
in the Gulf of Mexico. We learned that the distribution of whales
and dolphins in the gulf is not random; these animals are observed
more frequently in "ocean oases" where food availability
is higher. Some of these oases are cold core gyres or eddies
(rotating bodies of water about 100-150 kilometers wide) that
draw nutrient-rich bottom water to the sea surface, thereby increasing
the plankton production. Fish and squid feed on the plankton
and attract cetaceans to the cold core gyres (Read Quarterdeck
6.1 for information on GulfCet project and eddies in the Gulf).
Because the continental margin of the northeast
Gulf of Mexico is characterized by the temporal persistence of
cyclonic eddies, the region is of considerable biological interest.
However, only four GulfCet cruises were conducted in the northeastern
gulf. Three months after the last GulfCet survey, we welcomed
the collaboration with another oceanography project to allow
us to continue our research on cetaceans in the Gulf.
The first cruise of the "Northeast Gulf
of Mexico (NEGOM): Chemical Oceanography and Hydrography"
project went to sea in November of 1997. One of NEGOM's principal
investigators, Dr. Doug Biggs, also was a principal investigator
in GulfCet. Biggs, professor of oceanography, invited me to assemble
a team of graduate student volunteers to "piggyback"
cetacean observations on the NEGOM cruises. This was a great
opportunity to continue and expand the cetacean sightings database
that we had initiated in GulfCet.
Moreover, because the objective of NEGOM
is to study the seasonal variations in seawater properties-such
as temperature, nutrients, chlorophyll, and currents-we will
be able to use the concurrent physical data to evaluate the effects
of hydrography on marine mammal distribution.
Survey for cetaceans has been conducted during
the first five NEGOM cruises aboard the R/V Gyre, the Department
of Oceanography's research vessel. During these cruises, a team
of three observers searches for whales and dolphins using long-range,
or "Big-eye," binoculars positioned atop the flying
bridge. The visual survey is conducted during daylight, when
the ship moves between hydrographic stations. In the database,
we record the geographic position of the cetacean sightings,
species, and number of individuals.
While we are scanning the seas for cetaceans,
NEGOM scientists stop the ship at predetermined stations in the
gulf and collect water samples for later analysis of oxygen,
nutrients, and salinity. Instruments measure the water's temperature,
conductivity, downwelling irradiance, percent light transmission
During the five NEGOM cruises, a total of
334 hours of visual survey were completed for 5,418 kilometers
of transect on the ship's track across the northeastern gulf.
During this effort, 289 sightings were registered and the following
species were identified: Atlantic spotted dolphin, Bryde's whale,
bottlenose dolphin, dwarf sperm whale, false killer whale, humpback
whale, killer whale, melon headed whale, pantropical spotted
dolphin, pygmy sperm whale, Risso's dolphin, sperm whale, spinner
dolphin, and striped dolphin.
Editor's note: Read Quarterdeck 6.1 (Spring 1998) for information
on the NEGOM and GulfCet projects.
Joel G. Ortega-Ortiz is a Ph.D. student in Texas A&M's
Department of Wildlife and Fisheries Sciences. His e-mail address
View maps of
the cruise track and the splaces where cetaceans were spotted.