Kim W. Urian

Seasonality of Reproduction in Bottlenose Dolphins, Tursiops truncatus

We examined the seasonality of reproduction in captive and wild bottlenose dolphins, Tursiops truncatus . Stranding records of neonatal dolphins and observed births from a long-term field study were used to estimate peak periods of birth for wild populations, and information from captive-breeding colonies was used to assess the effects of latitude and origin of breeding females on timing of birth for dolphins in captivity. Bottlenose dolphins showed diffuse peaks and considerable flexibility in their seasonality of reproduction. There was no relationship between latitude and seasonality of reproduction or synchrony of births. However, there was a correlation between origin of population and seasonality of reproduction in both wild and captive dolphins. We suggest that adaptations to local environmental conditions have the strongest influence on seasonality of reproduction in these populations of bottlenose dolphins.

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.

Epidermal diseases in bottlenose dolphins: impacts of natural and anthropogenic factors

Experimental studies have highlighted the potential influence of contaminants on marine mammal immune function and anthropogenic contaminants are commonly believed to influence the development of diseases observed in the wild. However, estimates of the impact of contaminants on wild populations are constrained by uncertainty over natural variation in disease patterns under different environmental conditions. We used photographic techniques to compare levels of epidermal disease in ten coastal populations of bottlenose dolphins (Tursiops truncatus) exposed to a wide range of natural and anthropogenic conditions. Epidermal lesions were common in all populations (affecting > 60% of individuals), but both the prevalence and severity of 15 lesion categories varied between populations. No relationships were found between epidermal disease and contaminant levels across the four populations for which toxicological data were available. In contrast, there were highly significant linear relationships with oceanographic variables. In particular, populations from areas of low water temperature and low salinity exhibited higher lesion prevalence and severity. Such conditions may impact on epidermal integrity or produce more general physiological stress, potentially making animals more vulnerable to natural infections or anthropogenic factors. These results show that variations in natural environmental factors must be accounted for when investigating the importance of anthropogenic impacts on disease in wild marine mammals.

Sexual Dimorphism in Wild Bottlenose Dolphins (Tursiops truncatus) from Sarasota, Florida

We examined sexual dimorphism in external morphometric characters from 19 male and 32 female bottlenose dolphins ( Tursiops truncatus ) that were physically mature. These animals are long-term residents of the coastal waters near Sarasota, Florida, and were examined as part of an ongoing capture-release project. Males were significantly larger than females in 20 of 29 measurements; only one of eight measurements of the head showed significant absolute dimorphism. Proportional dimorphism (i.e., dimorphism corrected for body size) was less pronounced; only four linear measurements and three girth measurements exhibited significant differences between sexes. In addition, scarring of the dorsal fin occurred more frequently on males than on females. The occurrence of sexual dimorphism in this population of bottlenose dolphins is consistent with the model of a polygamous mating system.

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...