Bimini Dolphin Research

Report # 16

We had exceptional weather this week with winds less than 3 knots and glassy calm seas; only on Saturday and Sunday the wind speed picked up to 7-10 knots during the survey hours and produced a light chop of 1-2 foot waves. Seven afternoon survey trips were conducted this week and four of these surveys resulted in dolphin sightings. The number of dolphins in the sightings and encounters varied greatly; group sizes ranged from 4-25 individuals and all groups were found to include dolphins of all age classes. The behavior most observed during these sightings was feeding; travel towards the west and southwest (to deeper waters) was observed between feeding bouts. These behavioral states resulted in brief encounters since dolphins either kept travelling or chasing fish (feeding results in dolphins spreading out in the area and swimming in many directions). Once more, spotted dolphins were observed mouthing and tossing needlefish at the surface. On one occasion, an adult spotter tossed a needlefish in the air and it hit the bow of the boat; the fish (already dead or nearly so) drifted along the hull of the boat while the adult spotter followed it at no more than four feet. Once the fish cleared the platform, the spotter grabbed it with its jaws again and swam away. All survey trips had sightings of spotted dolphins but Tuesday's survey trip also included a sighting of bottlenose dolphins. On Tuesday's survey trip we first had a sighting of 22 bottlenose dolphins crater-feeding in a small area; 10 minutes later we spotted a group of 16 spotted dolphins swimming towards the 22 bottlenose dolphins. These two groups eventually joined and formed a mixed group of 25 dolphins (juveniles and older calves formed a subgroup and stayed away from the larger group) which showed sexual/aggressive behavior. People were able to swim with the spotted dolphins before they joined the bottlenose; two more encounters were possible when the spotters and bottlenose joined but these were shorter in duration. As a reminder, we are working with Bill and Nowdla Keefe's Bimini Undersea (their dive boats and dolphin trips) for our research vessels. We are based on Bimini and go out about five miles or so from the island to search for dolphins. Until next week, Xenia