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Patterns Emerging Despite (because of?) Rough Seas!

By Mauvis Gore, 1st December 2010

Another couple of weeks doing our best to get the main batch of shark and dolphin survey work completed. We have had persistent winds from the north-east, force 4 or 5, making it impossible to do long-line or BRUV (Baited Remote Underwater Video) sampling for sharks, except in sheltered locations, most of which we have sampled already; and it’s been equally unpleasant and unproductive to undertake boat surveys further offshore for whales and dolphins (cetaceans). Yesterday, for example, we covered over 100 km in the Department of Environment’s larger boat, Sea-Keeper, zig-zagging transects out to the further edge of 12-mile bank (12 miles west of Cayman). But with 3 and 4 metre waves occasionally breaking onto the boat, even on the flying bridge we ended up thoroughly soaked – and not a dolphin in sight.

Nevertheless the data have slowly accumulated and we have taken recent enforced time on land to bring our analyses up to date. At last some clear patterns are emerging. This was more than useful when it came this morning to a 45 minute presentation to the Department of Environment staff. Perhaps most interesting are the differences in shark densities and numbers of species between the islands. Little Cayman seems to come out top, which raises the question of why densities on Grand Cayman are so low. Also noticeable are the range of cetacean species for which we now have reliable sightings, including bother killer whales (Orca) and false killers on the one hand, and Pygmy Sperm Whales and species of rare beaked whales on the other.

Now with the general picture emerging we need to start work on a couple of more experimental studies. Back in May we made some unsuccessful efforts to catch one or more of the few tiger and giant hammerhead sharks that we think are around. Come this weekend we plan another go, in order to tag these animals with acoustic and satellite tags. And we need to study the possible effects of divers feeding sharks. We have a public talk to one of the local communities planned for next Monday, when doubtless one or two of these issues will come up. The tiger sharks sound scary, but the public meeting may be scarier!

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