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Stomach contents of 175 Brazilian sharpnose sharks, Rhizoprionodon lalandii, were examined to assess their feeding habits. Caught by artisanal fishers between June 2006 and July of 2007 at Ipanema Beach, on the central coast of the state of Paraná, southern Brazil, R. lalandii appears to be piscivorous (89.7% IRI), feeding mainly on families of Clupeidae (5.1% IRI) and Sciaenidae (3.7% IRI) and secondarily on squid Lolliguncula brevis (8.6% IRI). Diets were similar between sexes and seasons. However, there were ontogenetic changes in their diets. The major items for neonates were Penaeidae crustaceans (%IRI = 56.4) and Engraulidae fishes (%IRI = 29.3); for the juveniles, Sciaenidae (%IRI = 62.5) and Clupeidae (%IRI = 19.7), and for adults Clupeidae (%IRI = 45.8) and Sciaenidae (%IRI = 15.9). Only neonate sharks consumed crustaceans, whereas all size classes consumed cephalopods and teleosts. Neonates had the lowest trophic level (TR = 3.8), with the diet of juveniles and adults the highest (TR = 4.2). Given its abundance and diet, R. lalandii may be an important predator of demersal and pelagic prey in coastal waters of Brazil. [ABSTRACT FROM AUTHOR]

Both food abundance and predation risk may influence habitat use decisions. However, studies of habitat use by birds in marine environments have focused only on food abundance. I investigated the possible influences of food abundance and predation risk from tiger sharks ( Galeocerdo cuvier) on habitat use by pied cormorants ( Phalacrocorax varius) over two spatial scales and on cormorant group size. Cormorants were usually solitary, but group size was highest in shallow habitats during months when shark density was low. Regardless of season, cormorant density within shallow habitats was higher over seagrass than sand, and cormorants were distributed between these two microhabitats proportional to prey density. Therefore, cormorants appear to respond to prey abundance at a relatively narrow spatial scale (i.e., tens of meters). At the habitat-patch scale (~1 km), the density of cormorants and their prey (teleosts) was higher in shallow habitats than in deep ones, but the density of cormorants was influenced by an interaction between water temperature (i.e., season) and habitat. There was decreased use of shallow habitats as water temperature, and the density of tiger sharks, increased. When shark density was low, cormorants were distributed across habitats roughly in proportion to the abundance of fish, suggesting that cormorants respond to food abundance at the scale of habitat patches. However, as shark abundance increased, the relative density of cormorants dropped in the dangerous shallow habitats such that there was a greater density of cormorants relative to their food in deep habitats when sharks were abundant. This suggests that pied cormorants trade-off food and risk by accepting lower energetic returns to forage in safer habitats. This study provides the first evidence that marine habitat selection by birds may be influenced by such a trade-off, and provides further evidence that tiger sharks are important in determining habitat use of their prey and mediating indirect interactions within Shark Bay. [ABSTRACT FROM AUTHOR]

In dynamic fission-fusion societies, following specific individuals consistently would not be expected in the absence of benefits to followers. Followers in groups may benefit if leaders have greater knowledge about habitats that are available for foraging and how to access these areas efficiently. A small residential population of bottlenose dolphins (Tursiops truncatus) in the Lower Florida Keys (LFK) demonstrates such specific individual leadership, but why others choose to follow is unknown. To determine whether consistent leaders demonstrated greater knowledge of resources and habitat we (1) compared habitat use patterns across areas that varied in prey abundance for groups led by consistent leaders and groups led by individuals that did not consistently lead, (2) compared directness of travel along with number of lead animal switches when traveling for these same two group types and (3) compared home range size and home range complexity between animals that consistently led and those that did not. Foraging groups led by consistent leaders were sighted more frequently over habitat with higher fish biomass, while those led by non-consistent leaders were sighted most often over habitat with lower fish biomass. Groups with consistent leaders had less frequent lead animal switches and took more direct paths when traveling than groups led by those that did not consistently lead. Home ranges of consistent leaders did not differ in size from other individuals, but were more complex. Our results indicate that followers in LFK dolphin groups could potentially benefit from those that consistently lead due to use of profitable habitat, ability to navigate efficiently and potentially the number of areas consistent leaders are familiar with. [ABSTRACT FROM AUTHOR]

Stable-isotope values of a scalloped hammerhead Sphyrna lewini and blacktip shark Carcharhinus limbatus and their respective embryos were analysed. Embryos of both species were enriched in δN compared to their mothers (0·82 and 0·88‰, respectively), but fractionation of δC varied. Embryonic S. lewini were enriched (1·00‰) in δC while C. limbatus were depleted (0·27‰) relative to their mothers. [ABSTRACT FROM AUTHOR]

Emerging conservation efforts for the world's large predators may, if successful, restore natural predator–prey interactions. Marine reserves, where large predators tend to be relatively common, offer an experimental manipulation to investigate interactions between large-bodied marine predators and their prey. We hypothesized that southern stingrays—large, long-lived and highly interactive mesopredators—would invest in anti-predator behavior in marine reserves where predatory large sharks, the primary predator of stingrays, are more abundant. Specifically, we predicted southern stingrays in marine reserves would reduce the use of deep forereef habitats in the favor of shallow flats where the risk of shark encounters is lower. Baited remote underwater video was used to survey stingrays and reef sharks in flats and forereef habitats of two reserves and two fished sites in Belize. The interaction between "protection status" and "habitat" was the most important factor determining stingray presence. As predicted, southern stingrays spent more time interacting with baited remote underwater videos in the safer flats habitats, were more likely to have predator-inflicted damage inside reserves, and were less abundant in marine reserves but only in the forereef habitat. These results are consistent with a predation-sensitive habitat shift rather than southern stingray populations being reduced by direct predation from reef sharks. Our study provides evidence that roving predators can induce pronounced habitat shifts in prey that rely on crypsis and refuging, rather than active escape, in high-visibility, heterogeneous marine habitats. Given documented impacts of stingrays on benthic communities it is possible restoration of reef shark populations with reserves could induce reef ecosystem changes through behavior-mediated trophic cascades. [ABSTRACT FROM AUTHOR]

Stable-isotope analysis supplemented with stomach contents data from published sources was used to quantify the trophic niches, trophic niche overlaps and potential trophic redundancy for the most commonly caught fish species from an East African nearshore seagrass community. This assessment is an important first step in quantifying food-web structure in a region subject to intense fishing activities. Nearshore food webs were driven by at least two isotopically distinct trophic pathways, algal and seagrass, with a greater proportion of the sampled species feeding within the seagrass food web (57%) compared with the algal food web (33%). There was considerable isotopic niche overlap among species (92% of species overlapped with at least one other species). Narrow isotopic niche widths of most (83%) species sampled, low isotopic similarity (only 23% of species exhibited no differences in δ13C and δ15N) and low predicted trophic redundancy among fishes most commonly caught by fishermen (15%), however, suggest that adjustments to resource management concerning harvesting and gear selectivity may be needed for the persistence of artisanal fishing in northern Tanzania. More detailed trophic studies paired with information on spatio-temporal variation in fish abundance, especially for heavily targeted species, will assist in the development and implementation of management strategies to maintain coastal food-web integrity. [ABSTRACT FROM AUTHOR]

Saurochory (seed dispersal by reptiles) among crocodilians has largely been ignored, probably because these reptiles are generally assumed to be obligate carnivores incapable of digesting vegetable proteins and polysaccharides. Herein we review the literature on crocodilian diet, foraging ecology, digestive physiology and movement patterns, and provide additional empirical data from recent dietary studies of Alligator mississippiensis. We found evidence of frugivory in 13 of 18 (72.2%) species for which dietary information was available, indicating this behavior is widespread among the Crocodylia. Thirty-four families and 46 genera of plants were consumed by crocodilians. Fruit types consumed by crocodilians varied widely; over half (52.1%) were fleshy fruits. Some fruits are consumed as gastroliths or ingested incidental to prey capture; however, there is little doubt that on occasion, fruit is deliberately consumed, often in large quantities. Sensory cues involved in crocodilian frugivory are poorly understood, although airborne and waterborne cues as well as surface disturbances seem important. Crocodilians likely accrue nutritional benefits from frugivory and there are no a priori reasons to assume otherwise. Ingested seeds are regurgitated, retained in the stomach for indefinite and often lengthy periods, or passed through the digestive tract and excreted in feces. Chemical and mechanical scarification of seeds probably occurs in the stomach, but what effects these processes have on seed viability remain unknown. Because crocodilians have large territories and undertake lengthy movements, seeds are likely transported well beyond the parent plant before being voided. Little is known about the ultimate fate of seeds ingested by crocodilians; however, deposition sites could prove suitable for seed germination. Although there is no evidence for a crocodilian-specific dispersal syndrome similar to that described for other reptiles, our review strongly suggests that crocodilians function as effective agents of seed dispersal. Crocodilian saurochory offers a fertile ground for future research. [ABSTRACT FROM AUTHOR]