Danielle M. Waples

Behavioral responses of bottlenose dolphins, Tursiops truncatus, to gillnets and acoustic alarms

Along the east coast of the United States, by-catches of bottlenose dolphins, Tursiops truncatus, in gillnet fisheries exceed removal levels set under the US Marine Mammal Protection Act. One measure proposed to reduce this mortality is the use of acoustic alarms, or pingers, which have proven effective in reducing by-catches of other small cetaceans, but have not been tested with bottlenose dolphins. We examined the responses of bottlenose dolphins to a commercial gillnet equipped with functional (active) and non-functional (control) Dukane NetMark 1 1000 alarms near Fort Macon, NC. Between 5 April and 10 May 2001 we used a theodolite to track 59 groups of dolphins around the net. Choice of treatment was random each day and the two shore-based observers were unaware of whether alarms were active (13 days) or controls (9 days). There were no significant differences in the number of groups observed (P=0.315; 1� � =0.835) or in the closest observed approach to the net (P=0.307; 1� � =0.828) between treatments. However, dolphins entered a circular buffer approximately 100 m around the net more frequently with control than active alarms (P=0.015). We conclude that some dolphins responded to the alarms by avoiding the net, but caution that the potential efficacy of alarms is confounded by dolphin behavior. Most dolphins were aware of the net, regardless of the status of alarms, and some dolphins fed on fish in the net or discarded by the fishing vessel. We believe that it would be unwise to use pingers in these fisheries because of the limited behavioral responses we observed in our experiment. Furthermore, the responses we observed are likely to diminish or change over time as dolphins habituate or sensitize to these alarms. Further research is required to understand the behavior responsible for entanglement. # 2003 Elsevier Ltd. All rights reserved.

Fine-scale behaviour of bottlenose dolphins around gillnets.

We studied the fine-scale behaviour of bottlenose dolphins Tursiops truncatus around gillnets in North Carolina, USA, during May and June 2002. We made observations from an overhead digital video camera, suspended from a helium-filled aerostat, tethered 70 m above a fishing vessel. We positioned the camera above a gillnet set for Spanish mackerel Scomberomorus maculatus. We observed frequent encounters (n = 36) and interactions (n = 27) between dolphins and the net, but no dolphins became entangled. Most dolphins diverted their course around the net, but on nine occasions we observed dolphins engaging in depredation. We conclude that interactions between dolphins and these gillnets are common, but that entanglement is rare.

ABUNDANCE OF BOTTLENOSE DOLPHINS (Tursiops truncatus) IN ESTUARINE AND NEAR-SHORE WATERS OF NORTH CAROLINA, USA

Abstract A capture-recapture survey of bottlenose dolphins (Tursiops truncatus) was conducted in the sounds, estuaries and near-shore waters of North Carolina during July 2006, using photographic identification techniques; 291 dolphins were identified from distinctive nicks and notches on their dorsal fins. The results of our photographic analyses were applied to several capture-recapture models. The best estimate of the number of bottlenose dolphins present in estuarine waters of North Carolina during July 2006 was 813 with a 95% Confidence Interval of 483–1,142. Previously in July 2000, 1,033 (95% CI: 860-1,266) dolphins were estimated to be present in the estuaries of North Carolina. When the analysis from the 2006 surveys was expanded to include adjacent coastal waters, then the estimate of abundance increased to 1,138. Therefore, the abundance of dolphins in this area remained relatively stable between the two studies. Most dolphins were found in the northern part of the study area and there was very...