Sperm Whale Seismic Study (SWSS) Chronicle 4

Special Reports from the SWSS Scientists

SWSS Program Manager and
Associate Research Scientist
Department of Oceanography
Texas A&M University
College Station, Texas

Acoustics stayed with whales throughout the night, at one point monitoring whales from 7 separate beam directions. Because the 38 kHz fishery echosounder had been deployed shortly after contact, we had another night of 3-D tracking data with concurrent 38 kHz and 70 kHz echosounder data.

By dawn (about 11:00 UTC), ship traffic had entered the vicinity, with up to 3 ships in the vicinity at one time. The ship sounds are at similar frequencies to those of the sperm whale clicks that are monitored by acoustics (see Figure 1 for an example of sperm whale clicks on the monitoring screen). So, the sounds of the ships mask those of the sperm whales, making it difficult for acoustics to track whales. Once the ships had left the area, the whales were no longer heard.
 

At approximately 13:15 UTC, the 38 kHz fishery echosounder was pulled in, and at 13:30 UTC the 38 kHz ADCP was turned on. With the visual team in place on the flying bridge and the acoustics team in the "Bat Cave", we then proceeded to survey southward. Near-surface currents were directed to the northwest at about 1 knot or less. An XBT taken at 14:31 indicated the 15C isotherm was at 210 m.

At about 15:00 UTC acoustics re-acquired sperm whales. With the rising sun, however, came rising winds and diminishing opportunity to launch the tag boats. We stayed in acoustic contact throughout the day. Acoustics tracked up to 7-8 individuals. Then about 23:00 UTC, the seas calmed enough to launch the tag boat and attempt to tag. RHIB-1 was deployed in an area with about 5 whales (see Figure showing RHIB-1 and the tag team as they depart GYRE).

The tag team made approaches to two whales. They got within about 10 m of one, but it made shallow dives and then fluked up before the team was able to get a tag on. The tag team got within about 30-40 m of a second whale but it fluked up. Photo-identification shots were made of both whales. The tag boat was recovered by 01:00 UTC on 10 June 2005 and secured to tag another day. The 38 kHz ADCP was turned off and the 38 kHz fishery echosounder was deployed as we are still with whales.

Our position at 02:33 UTC on 10 June 2005 was 27^o11.5210'N 95^o22.7442'W. We are closely monitoring progress of Tropical Storm Arlene; if it enters into and crosses the eastern Gulf of Mexico as expected, we should be able to continue to work in the western Gulf with seas similar to those we have been experiencing the past few days.