Shark Chronicles 020- 24 hour seal survey

Shark Chronicles 020- 24 hour seal survey

Posted by Enrico Gennari on August 4, 2008

Never before has any research group attempted to observe seal movements for a 24 hour period.

SAMPLA broke that barrier with a 24 hour survey of seal movements around Seal Island twice already. It was a collective effort by all the interns, as seal movements were logged atop the Diaz Hotel during the daylight hours, and were led by SAMPLA scientists into the sunset as Cheetah was deployed and anchored in sector two on the south side of the island. Most of the seal movements occur in Sector Two, and it is also the site of the “launch pad”. This launch pad is an area where seals gather into groups before they undertake their feeding journeys out to sea.

Under a clear sky and a full moon, seals were located by the sound of their splash or the bioluminescence they set off as they swam through the water. Night vision goggles were used to determine the number of incoming or outgoing seals once a group was seen or heard. Occasionally, we tossed the omni-directional hydrophone into the water to determine if any of our tagged sharks were in the area. Pasella, the most recent shark we tagged, stayed in the area for most of the night. On several occasions the VR100 indicated that she was within 30 meters of the boat. To everyone’s disappointment, no predation occurred (at least from what we could see).

The sunset was stunning across the horizon as seals gathered around the launch pad. As if on cue, at 6pm when the last glimmer of the sun could be seen, groups of seals began shooting off to their feeding grounds. In first hour after sundown, over 200 seals were counted leaving the island. The next shift was quite anti-climatic, with only a handful of seals leaving in much smaller groups. At this time the full moon was rising and the seals were outlined in cobalt blue bioluminescence. On the third shift, SAMPLA team continued to see a few small groups leaving the island. This data is of utmost importance to SAMPLA’s research as all previous seal surveys have concluded at sundown. Being on the water at sundown and throughout the night gave a new perspective to seal behaviour.

As the night went on, the temperature dropped and everyone looked forward to their turn in the cabin to sleep and warm up. As the sun rose around 7 am (we were not sure if it ever would) the SAMPLA team had made history and collected groundbreaking research on seal movements at night.

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