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Abstract--We describe the food habits of the Sowerby's beaked whale (Mesoplodon bidens) from observations of 10 individuals taken as bycatch in the pelagic drift gillnet fishery for Swordfish (Xiphias gladius) [...]

Abstract--Using data collected simultaneously from a trawl and a hydrophone, we found that temporal and spatial trends in densities of juvenile Atlantic croaker (Micropogonias undulatus) in the Neuse River estuary [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2004.06.020 Byline: Damon P. Gannon, Nelio B. Barros, Douglas P. Nowacek, Andrew J. Read, Danielle M. Waples, Randall S. Wells Abstract: Bottlenose dolphins possess a sophisticated echolocation system, but evidence suggests that they use this sensory modality sparingly in the wild. Several authors have noted that soniferous fish are prevalent in the diet of bottlenose dolphins, leading to the hypothesis that these predators detect their prey by passive listening. We tested this hypothesis by performing controlled acoustic playback experiments with free-ranging dolphins in Sarasota Bay, Florida. We used recorded calls of prey fish and sounds of snapping shrimp as experimental and control treatments, respectively, and measured the dolphins' direction of travel and rate of echolocation as response variables. Dolphins changed their direction of travel significantly, turning towards the sound source when fish sounds were played. In addition, dolphins significantly increased their rate of echolocation immediately following playbacks of fish sounds. The sounds of snapping shrimp elicited neither directional nor echolocation responses. The occurrence of echolocation sounds was low, except following playback of fish sounds. We conclude that bottlenose dolphins use passive listening extensively during the search phase of the foraging process. By listening passively, dolphins may obtain useful information on the identity, number, size and location of soniferous prey. Once dolphins discover prey by passive means, they then appear to use echolocation to track the prey during the pursuit and capture phases. Such judicious use of echolocation suggests that this sensory modality incurs significant energetic or ecological costs. These findings have implications for coevolution of dolphins and their prey with regard to sound production and detection. Author Affiliation: (*) Duke University Marine Laboratory, Beaufort, North Carolina, U.S.A. (a ) Mote Marine LaboratoryU.S.A. (a ) Chicago Zoological Society, Chicago, Illinois, U.S.A. Article History: Received 23 October 2003; Revised 26 February 2004; Accepted 2 June 2004 Article Note: (miscellaneous) MS. number: A9736

We describe the food habits of the Sowerby's beaked whale (Mesoplodon bidens) from observations of 10 individuals taken as bycatch in the pelagic drift gillnet fishery for Swordfish (Xiphias gladius) in the western North Atlantic and 1 stranded individual from Kennebunk, Maine. The stomachs of 8 bycaught whales were intact and contained prey. The diet of these 8 whales was dominated by meso- and benthopelagic fishes that composed 98.5% of the prey items found in their stomachs and cephalopods that accounted for only 1.5% of the number of prey. Otoliths and jaws representing at least 31 fish taxa from 15 families were present in the stomach contents. Fishes, primarily from the families Moridae (37.9% of prey), Myctophidae (22.9%), Macrouridae (11.2%), and Phycidae (7.2%), were present in all 8 stomachs. Most prey were from 5 fish taxa: Shortbeard Codling (Laemonema barbatulum) accounted for 35.3% of otoliths, Cocco's Lanternfish (Lobianchia gemellarii) contributed 12.9%, Marlin-spike (Nezumia bairdii) composed 10.8%, lanternfishes (Lampanyctus spp.) accounted for 8.4%; and Longfin Hake (Phycis chesteri) contributed 6.7%. The mean number of otoliths per stomach was 1196 (range: 327-3452). Most of the fish prey found in the stomachs was quite small, ranging in length from 4.0 to 27.7 cm. We conclude that the Sowerby's beaked whales that we examined in this study fed on large numbers of relatively small mesoand benthopelagic fishes that are abundant along the slope and shelf break of the western North Atlantic. [ABSTRACT FROM AUTHOR]

Prey selection was investigated in wild, resident common bottlenose dolphins, Tursiops truncatus, during the summer months in Sarasota Bay, Florida, USA. Stomach content analyses of 15 dolphins with extensive sighting histories and well-documented distributions were used to determine prey use. Prey availability was assessed by purse seine surveys. We compared the relative abundances of prey available to estimates of prey use at closely matching spatial and temporal scales. G-tests determined that dolphins in this study significantly selected for prey at the species, family, and soniferous/non-soniferous prey levels ( G adj = 753.98–1,775.93, df = 1–21, p ≤ 0.01). While comprising only 6.3% of the total available prey, soniferous fishes accounted for 51.9% of the total prey consumed. Manly’s standardized forage ratios and 95% Bonferroni confidence intervals determined significant positive selection for soniferous prey and against non-soniferous prey (βS = 0.9461 vs. βNS = 0.0539). Dolphins selected against Gerridae, Clupeidae, and Sparidae ( β ≤ 0.0014), as well as against all the species within those families ( β ≤ 0.0190). It is likely that passive listening for soniferous prey provides an ecological or energetic advantage to cetaceans utilizing this specific foraging technique. [ABSTRACT FROM AUTHOR]

We recorded 31 species in the stomachs of 146 coastal bottlenose dolphins (Tursiops truncatus) from North Carolina, U.S.A. Sciaenid fishes were the most common prey (frequency of occurrence = 95%). By mass, Atlantic croaker (Micropogonias undulatus) dominated the diet of dolphins that stranded inside estuaries, whereas weakfish (Cynosicon regalis) was most important for dolphins in the ocean. Inshore squid (Loligo sp.) was eaten commonly by dolphins in the ocean, but not by those in the estuaries. There was no significant pattern in prey size associated with dolphin demography, but the proportion of the diet represented by croaker was higher for males than for females, and mature dolphins ate more croaker than did juveniles. Dietary differences between dolphins that stranded in the estuaries and those that stranded on ocean beaches support the hypothesis that some members of the population inhabit the ocean primarily while others reside principally in estuaries. The overwhelming majority of prey were soniferous species (75% of numerical abundance), which is consistent with the hypothesis that bottlenose dolphins use passive listening to locate noise-making fishes. However, spatiotemporal patterns in consumption of Sciaenid fishes did not coincide with their spawning, which is when peak sound production is thought to occur. [ABSTRACT FROM AUTHOR]

Ten prey taxa were recorded from the stomach contents of eight long-finned pilot whales (Globicephala melas) independently stranded along the U.S. mid-Atlantic coast. Relative importance of prey species was determined by methods that incorporate prey frequencies of occurrence, proportions of numerical abundance, and proportions of reconstructed mass. Separate analyses of trace (free, durable body parts representing well-digested prey items) and non-trace (relatively intact prey specimens) food material were conducted in order to address biases caused by differential rates of digestion and passage through thegastrointestinal tract. Different measures of prey importance yielded varying results, but the long-finned squid (Loligo pealei) was themost important prey species regardless of how prey importance was defined. Fishes were relatively unimportant in the diet. Our results indicate that the diets of western North Atlantic long-finned pilot whales differ substantially from what has been previously reported inthe literature and that results from food-habits studies that utilize different techniques may not be comparable. [ABSTRACT FROM AUTHOR]