Stable isotope composition of marine top predator's tissues provides insight information of its trophic ecology and migratory behavior. Previous reports have shown that dermal tissues could record longer patterns of hunting and movement. Based on this, the aim of this study was to describe the feeding and migratory habits of the white shark from Isla Guadalupe, using stable isotopic analysis of dermis. We considered a small subset of many possible prey taxa that the sharks could have eaten throughout their migration: pinnipeds, squid and tuna. We grouped the data in five focal areas: Gulf of California, Coast of California, Isla Guadalupe, SOFA and Hawaii. We performed a Bayesian mixing model to study the trophic ecology of this top predator. Average isotopic values for dermis tissue of white shark were δ
Long-distance movements of sharks within and between islands pose substantial challenges for resource managers working with highly migratory species. When no-take zones do not cover the critical areas that sharks use as part of their lifecycle, exposure to fishing activities can be significant. Shark movements between the Marine Protected Areas (MPAs) of the Eastern Tropical Pacific (ETP) have been studied for several years, however little is known about the strength of connectivity between these islands. We analyzed the extensive MigraMar ultrasonic telemetry dataset to assess how Galapagos sharks (Carcharhinus galapagensis) and silky sharks (Carcharhinus falciformis) use different islands as stepping-stones during their migrations within the Revillagigedo National Park and other ETP islands. Of the 66 sharks monitored, 63.5% moved within the same island, 25.4% between two islands or more and only 10.1% across different MPAs. A C. falciformis tagged in Roca Partida Island, Revillagigedo, travelled to Clipperton Atoll and another one tagged in Darwin Island travelled to the atoll on two different years. The largest movement of C. galapagensis was accomplished by a shark tagged at Socorro Island, Revillagigedo, later detected at Clipperton and finally recorded in Darwin Island, Galapagos. This last path was in fact, one of the longest movements ever recorded for the species. Although long-distance dispersion was not common, our results highlight the need for co-operation between different countries to ensure adequate protection for sharks in the form of swimways and other conservation tools in the ETP.
Social foraging, where animals forage in groups, takes many forms but is less studied in marine predators as measuring social associations in the wild is challenging. We used biologging (activity, cameras and telemetry receivers) sensors to measure social associations and simultaneous behaviour, in white sharks ( Carcharodon carcharias ) off Guadalupe Island, Mexico. Animal-borne telemetry receivers revealed that sharks varied in the number of associations they formed and occurred most often when sharks were swimming in straight paths or when they were turning frequently. While many associations were likely random, there was evidence of some stronger associations. Sharks varied in the depths they used and their activity, with some individuals more active in shallow water while others were more active 200–300 m deep. We propose that white sharks associate with other individuals so they can inadvertently share information on the location or remains of large prey. However, there may be a wide range of individual variability in both behaviour and sociality. Biologging now enables social associations of animals to be measured, concurrent with measures of their behaviour, so that social foraging of large marine predators can be quantified in the wild.
Cuvier’s beaked whale (Ziphius cavirostris) is the most widely distributed species of beaked whale, with a cosmopolitan distribution throughout almost all temperate, subtropical and tropical waters of the world as well as subpolar and even polar waters in some areas. Globally, it may also be the most abundant species of beaked whale within the family Ziphiidae. However, there is little information on local distribution in many areas around the world. Before 2009, no dedicated research on beaked whales occurred in Guadalupe Island. In this note, we report opportunistic sightings of Cuvier’s beaked whales recorded during a white shark research project from 2006 through 2008, and the results obtained in 2009 during a pilot study focused on the beaked whales of Guadalupe Island.
The white shark is a worldwide protected species and nevertheless coastal nursery grounds and juvenile aggregation areas have been reported, the actual information about birth or nursery areas for this species is still lacking. So, is necessary to focus research effort to identify new aggregation site, especially for young stages. During 2015 to 2017 we obtained data of 12 neonates and juveniles around Isla Cedros, in the western coast of Baja California, Mexico suggesting this island as important nursery area for white sharks. This information will help in management plans for conservation in aggregation habitats of young white sharks.
In this short note, we describe the convulsive body shuddering of a white shark as it approached two large metallic shark cages, each with multiple divers standing within them. When animals feel threatened, they experience conflicting instincts — one is to escape and another is to fight. In this situation, they do not always fight but often perform an agonistic, or aggressive display. Having arrived at the source of an olfactory corridor, this white shark was confronted with highly visible cages made with aluminium bars. The divers use hookah air hoses to breathe, and were therefore releasing bubbles, which reflect light and generate sounds as they oscillate toward the surface. The photographers may also have been taking pictures of the shark with their flash-bulb equipped cameras, which produce a sudden disruptive flash of irradiance. The shark’s behaviour is illustrated with a series of video frames as he approaches the cage. The body of the shark shutters convulsively and he opens his mouth, keeping it open for a prolonged period of 2.8 s as he passes close to the cage, while (1) depressing his pectoral fins, (2) hunching his back, (3) keeping his caudal fin held at right angle to the axis of view to increase his apparent size, and (4) shaking his body with spasmodic oscillations. The shark appears frightened, and hence may perform the display to discourage any aggression directed at him by the cage with humans emitting a panoply of frightening stimuli. Alternative explanations of the motivation behind this behaviour are also discussed. We hope that it will lead other scientists to look for this behaviour when observing the behaviour of white sharks from a cage, so they can provide further evidence shedding light upon the shark’s motivation for performing this conspicuous behaviour.
This study describes the genetic diversity and level of genetic differentiation of the scalloped hammerhead shark Sphyrna lewini from eight putative nursery areas in the Mexican Pacific Ocean, using the mtDNA control region. Genetic analyses revealed a particular spatial divergence between La Reforma and all the remaining sites, with five exclusive haplotypes and the highest genetic diversity. This pattern may be interpreted as the signature of regional female philopatry, relatively to a particular femalemediated gene flow for La Reforma, which shows a strong subdivision in the Gulf of California.
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