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1
Cetaceans on the slope of Dedicated surveys in
the Gulf of Mexico
Dedicated surveys to examine the distribution and
estimate abundance of cetaceans in U.S. waters
were conducted in oceanic and upper continental
slope waters of the Gulf of Mexico by NOAA
Southeast Fisheries Science Center (Fig 1 and Fig
2). Cetacean sightings from the surveys during
spring of 1996, 1997, 1999, 2000 and 2001 were
analysed in relation to bathymetric data using
ArcGIS9.1. Bathymetric zones were assigned to
analyse differences in numbers of sightings and
species diversity with relation to shallow areas
(lt800m depth), continental slope areas
(800m-2500m) and deep areas (gt2500m). Effort data
of surveys was overlaid onto the zones to analyse
differences with relation to effort (Fig
2.) Cetacean sightings were plotted and analysed
with relation to the zones (Fig 3.). Increased
effort would contribute to the high total
cetacean numbers in the slope area, however in
shallow areas cetacean numbers were relatively
high with low effort (Fig 4.) Slope and deep
zones showed much higher species diversity as
well as overall sighting numbers (Fig 5.) The
individual surveys were summarized per year to
highlight differences in effort, sightings and
overall cetaceans (Table 1.) Results indicate
higher numbers of sightings and species diversity
in the slope area, however this are also had the
highest amount of effort. Future studies could
include a comparison of species diversity with
biological make up of species, preferred habitats
and dynamic variables such as sea surface
temperature, productivity and prey statistics.
Fig 1. Location of survey area in relation to the
American continent also showing bathymetry
year Survey distance (km) sightings total cetaceans Average vessel speed total survey days
2001 2386.09 182 4502 10.0 43
2000 2226.38 198 8948 9.8 40
1999 2490.34 217 7099 9.2 40
1997 3443.74 268 6337 9.6 54
1996 6915.14 536 19434 9.9 53
Fig 2. Tracks of all dedicated surveys conducted
in 1996, 1997, 1999, 2000 and 2001. bathymetry is
also shown with the designated zones of shallow
(to 800m), slope (800m- 2500) and deep (gt2500m).
Table 1. Summary of the data collected in each
survey year showing effort (track distance in
km), number of sightings, total number of
cetaceans sighted, average speed of the survey
vessel and total number of survey days. Surveys
were conducted from end April to beginning of
June each year.
Fig 4. Graph showing the effort (track distance
in km) for each zone and the total number of
individual cetaceans sighted in each of these
zones. Highest numbers of cetaceans were sighted
in the slope zone and this area also had the
highest effort.
Fig 5. Graph showing the number of identified
cetacean species in each depth zone and the total
number of sightings. Species diversity was
highest in the slope zone.
Caroline Schweder MATE Center GIS Summer
Institute 2006 Geographic Coordinate System
WGS84 Data Courtesy of OBIS-SEAMAP NOAA's
National Geophysical Data Center (NGDC
Fig 3. All cetacean sightings from dedicated
surveys conducted in 1996, 1997, 1999, 2000 and
2001 with corresponding colours to the depth
zones of shallow, slope and deep.