Cayman Sharks Go Sonic!

Strange: we have had a frustrating week in terms of weather – day after day of force 4 and 5 winds from the north-east preventing us from getting out in the boat much – yet suddenly the findings of the project have begun to take shape. We are just coming to the end of a 2 week stint on Cayman Brac, one of the two smaller islands in the group, about 90 miles NE of Grand Cayman. And because of the winds and waves we have only managed to complete our video trapping and long-lining for sharks at a portion of the sites we originally intended. But now, after this period, and an earlier stint on neighbouring Little Cayman, we have at last got enough data to show that there are real differences in the numbers and types of sharks between the three islands.

Even more pleasing, a week or so ago we managed to catch and tag 4 or 5 Caribbean Reef Sharks, the most active and striking of the local species. As well as attaching numbered tags to the dorsal fins, we were able to insert into the belly small individually identifiable acoustic tags or pingers. And – the good news – having in the past few days been restricted by the weather to the same sites, we were able to detect using our mobile acoustic receiver, 3 of these individuals still active in much the same area as where they were tagged. Their locations and movements seem to support the view that during at least this part of the year individuals restrict themselves to relatively limited home ranges covering perhaps only a few km of reef. As well as the mobile receiver there are networks of fixed acoustic receivers around each of the islands, and the expectation is that these will reveal just how far the tagged individuals are prepared to roam. Watch this space!