Gyre Daily Reports - June 16, 2005

We decided to survey eastward along the 1000 meter isobath toward a region near 94^oW where it appears that productive shelf waters are being drawn into deeper water by an anticyclonic eddy (Figure 1). In the night as we surveyed southeast between approximately 27.37^oN 94.86^oW and our way point 16 at 26.79^oN 94.51^oW, we crossed an extensive Sargassum field. No sperm whales were heard during the night. Once we reached the way point 16, we turned northeastward to survey toward way point 17 at 27.54^oN 94.29^oW. Both RHIBs were deployed between approximately 14:00 to 23:00 UTC to extend our area of observation. With one RHIB off to each side of Gyre, we surveyed a swath approximately 20 miles wide. 

No sperm whales were seen or heard during the day. However, we saw several varieties of dolphins, flying fish, sea birds, and other fish in the glassy, calm seas of the morning. Three to five Risso's dolphins were identified. Mid-morning the visual team spotted a group of about 30 rough-toothed dolphins. RHIB-1 also saw these dolphins (Figure 2). Biopsy samples were obtained on three. Four members of the group came over to Gyre and rode the bow wave for about 30 minutes. We turned on the digital recorder to record the sounds these animals were making while they were at the bow. About an hour later, we diverted Gyre to investigate a large, white, floating object around which the group of rough-toothed dolphins were massed. We came across what seemed to be a floating 4x8 wooden panel beneath which there was a large school of fish. The dolphins were feeding on these. The group came over to Gyre to ride the bow wave. Two held fish in their mouths as they rode the bow wave (Figure 3). In the vicinity of the ship's bow, we counted 27-32 animals, including at least one calf and two small ones. Recordings were made of their sounds. From identifying marks on at least one individual, this group likely is the same as the earlier group. The RHIBs also saw spotted dolphins (Figure 4) and four separate whales sharks, with remoras, that were swimming with schools of fish.

We took 7 XBTs. The 15^oC isotherm depths ranged from 245 m to 261 m on the transect to way point 16. The near surface salinity increased from less than 34.5 to over 35. Near surface currents roughly were northeastward at 0.5 knots or less. These data are consistent with a transit through a region of likely anticyclonic circulation. On our transit toward way point 17, the 15^oC isotherm depths became shallower, and the salinity returned to 34.5 or less. The near surface currents were southeastward. These data are consistent with a region on the east side of an anticyclonic circulation feature that is drawing more productive and less saline shelf water into deeper water.

The 38 kHz fishery echo sounder was deployed from about 18:30 to 19:45 UTC to collect data in a region with likely anticyclonic circulation and no whales. The 38 kHz ADCP was turned off during the time this echo sounder was deployed.

Our position at 02:45 UTC on 17 June 2005 is 27 06.732'N 94 18.723'W.

Figure 1. Ocean color showing cyclonic eddy in which sperm whales were tagged and the region of shelf water being transported into deeper water.

Figure 2. Rough-toothed dolphin in the northern Gulf of Mexico taken from RHIB-1 on 16 June 2005. Photograph by Craig Hayslip, OSU, on SWSS 2005 S-tag cruise.

Figure 3. Rough-toothed dolphins riding the bow wave of the R/V Gyre on 16 June 2005. Note the fish in the mouth of two animals. Photograph by R. Iliana Ruiz-Cooley, OSU, for SWSS 2005 S-tag cruise.

Figure 4. Spotted dolphin in the northern Gulf of Mexico taken from RHIB-1 on 16 June 2005. Photograph by Craig Hayslip, OSU, on SWSS 2005 S-tag cruise.