1. The recent decline in the Mediterranean population of short‐beaked common dolphins Delphinus  delphis  has  been  the  subject of scientific controversy  and  political  indifference. Research on these animals has been very limited and there has been no large‐scale, systematic effort to assess and monitor their abundance and distribution. The consequent lack of data has prevented a good understanding of historical and ongoing trends. 2. Nonetheless, literature and osteological collections confirm that common dolphins were widespread and abundant in much of the Mediterranean Sea until the late 1960s and that their decline occurred relatively quickly. Today, common dolphins remain relatively abundant only in the westernmost portion of the basin (Alboràn Sea), with sparse records off Algeria and Tunisia, concentrations around the Maltese islands and in parts of the Aegean Sea, and relict groups in the south‐eastern Tyrrhenian and eastern Ionian Seas. Otherwise, these dolphins are rare in, or completely absent from, Mediterranean areas where information is available. 3. Circumstantial evidence and qualitative judgements by the authors suggest that the following factors may have contributed to the decline of common dolphins: reduced availability of prey caused by overfishing and habitat degradation; contamination by xenobiotic chemicals resulting in immunosuppression and reproductive impairment; environmental changes such as increased water temperatures affecting ecosystem dynamics; and incidental mortality in fishing gear, especially gillnets. The cumulative importance of these factors is poorly understood, and as a result, few conservation measures have been implemented. 4. This paper reviews current knowledge and suggests priorities for action aimed at identifying and mitigating the main threats to common dolphins in the Mediterranean, with the ultimate goal of restoring the species’ favourable conservation status in the region.

A bottlenose dolphin community was studied from small inflatable craft from 1987 to 1994 in a relatively large area (about 800 km2) east of the islands of Loˇsinj and Cres, northern Adriatic Sea. A total of 106 individuals were photoidentified based on natural permanent marks on their dorsal fins. Most of the dolphins were resighted on a regular basis, indicating a high level of year‐round site fidelity, although their range was evidently greater than the chosen study area. Dolphin density was highly variable and considerably lower than for most well‐known bottlenose dolphin communities. Groups averaged seven individuals, with a mode of two. Groups entirely composed of adults were the smallest, groups with calves the largest. Group fluidity was high, seasonal and yearly changes in mean group size being also considerable. Summer was the peak calving season, with a striking variation in the number of births on alternate years. Poor evidence of shark predation was found. The social organization of this dolphin community seemed to be highly flexible, possibly as an adaptation to cope with environmental changes as well as with a limited and variable availability of prey.

AESTRACTThe diurnal behavior of a bottlenose dolphin (Tursiops truncatus) community was observed from small inflatable craft between 1987 and 1994. Following a preliminary ad libitum study 11,839 3-min behavioral samples were recorded in 1991-1994. The behavioral budget showed a predominance (about 80%) of activities characterized by long (>30 sec) dives, considered to be largely related to prey search or feeding. Obvious foraging near the surface was observed rarely. The frequent following of trawlers (accounting for 4.6% of the behavioral budget) was indicative of the presence of alternative strategies for finding food. Yearly and seasonal behavioral variation-particularly in feeding-related and travel behaviors-was consistent with the hypothesis of behavioral flexibility as a response to environmental changes and fluctuating prey kind and availability. Yearly shifts in social behavior appeared to be partly influenced by breeding cycles. Groups engaged in feeding-related activities were significantly smaller than traveling or socializing groups, and dramatic interannual group-size shifts seemed to be largely affected by environmental variables, rather than being entirely determined by behavioral activity changes. The remarkable behavioral flexibility of this bottlenose dolphin community may contribute to its survival in the shifting environmental conditions of the northern Adriatic Sea. However, the high proportion of time consistently devoted to feeding-related activities, as compared to other areas, suggests that food resources in the KvarneriC were not only highly variable but also depleted.' We dedicate this work to Ken Norris, who first gave the stature of solid science to the act of observing wild dolphins: in deep appreciation for enriching us with the inspiration of his teaching, with the example of his imaginative work, and with the encouragement of his ever friendly and liberal advice.

Once one of the most common cetaceans in the Mediterranean Sea, the short-beaked common dolphin has declined throughout the region since the 1960s and in 2003 this population was classified as Endangered in the International Union for Conservation of Nature (IUCN) Red List. Here, we document the species' precipitous decline in eastern Ionian Sea coastal waters across 13 yr. While 150 animals were present in the study area (1050 km 2) in 1996, only 15 were observed in 2007. A 12 mo assessment of fishing effort and catch, together with circumstantial evidence, suggests that the decline was caused largely by prey depletion resulting from overfishing. We analyzed the impacts of various fishing gear and estimated the degree of resource overlap between common dolphins and local fisheries. The total biomass removed annually by 308 fishing boats in the study area averaged 3571 t, while that consumed by common dolphins was 17 t. Resource overlap between common dolphins and fisheries-expressed as an average Pianka index of 0.5-differed according to fishing gear, being higher for purse seiners (0.7) and beach seiners (0.4) and lower for bottom trawlers (0.1), trammel boats (0.2) and longliners (0.0). Only about 10 active purse seiners (4% of the total active fishing fleet) were responsible for 33% of the biomass removal, and likely had the greatest impact on prey of common dolphins. This study indicates a high risk of local disappearance of common dolphins in the very near future, unless fishery management measures are implemented immediately. Purse seining should be the main management target.

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