GulfCet II: Visual Surveys of Cetaceans and Sea Turtles from Aircraft

The visual survey of cetaceans and sea turtles from aircraft data set is part
of the overarching GulfCet II study, Cetaceans, Sea Turtles and Seabirds in the
Northern Gulf of America: Distribution, Abundance and Habitat Associations,
which provides synoptic data and analyses on the species diversity, abundance,
and habitat characteristics for cetaceans, sea turtles and seabirds in the
northern Gulf of America. In the EPA slope, a total of 18,788 km of transects
were sampled during the four seasonal aerial surveys. All of the proposed
transect lines (84 lines) were completed during summer surveys (10,440 km).

The primary objectives of the GulfCet II visual aerial and ship surveys were as
follows: (1) obtain a minimum abundance estimate for each cetacean and sea
turtle in the northeastern Gulf to establish a baseline for monitoring trends
in abundance over time. (2) to study the seasonal abundance and distribution
patterns of cetacean and sea turtle species in the northeastern Gulf. (3)
compare spring abundance estimates of cetacean species in continental slope
waters of the north-central and northwestern Gulf (GulfCet I study area) to
those made by Hansen et al. (1996) for the same area fro 1991-94 data.

Methodology: The GulfCet II aerial surveys were a continuation of aerial
surveys reported by Hansen et al. (1996) from Gulf Cet I. Seasonal sampling
intensity in the EPA shelf and slope study areas was similar to that expended
during GulfCet I. Systemic transects with a random start that generally
crossed isobaths orthogonally were uniformly spaced throughout the aerial
survey area. This design ensured that transects were randomly situated with
respect to cetacean density and allowed examination of cetacean distribution
throughout the study area. Each season the goal was to survey 58 transect
lines (spaced every 13.5 kilometers) totaling 6,133 km of transect effort. They
included 42 transect lines (total of 5,220 km) on the continental shelf (waters
< 100 m deep). Aerial surveys were conducted during summer 1996 and 1997, and
winter 1997 and 1998. As in GulfCet I, effort was based on projected
availability of acceptable survey conditions and flight times to the study
area.

Information for this metadata was taken from the report Cetaceans, Sea Turtles
and Seabirds in the Northern Gulf of America: Distribution, Abundance and
Habitat Associations. Editors Randall W. Davis, William E. Evans and Bernd
Wursig. Prepared under the U.S. Geological Survey, Biological Resources
Division by the GulfCet Program, Department of Marine Biology, Texas A & M
University at Galveston, Galveston, Texas.