Knowledge about the social behavior of sharks is a growing research field, but not many observations are available on the social interactions between pairs of sharks in the presence of passive ...surface bait and mainly related to aggregations. Between 2009 and 2018, in Gansbaai, South Africa, 415 white sharks were sighted, and 525 surface-generated social interactions were identified, exhibited by 169 different white sharks. The mean sighting rate was 0.91 (range 0.18–1.53) white sharks per hour. Eight patterns of social interaction were exhibited: swim by, parallel swim, follow/give way, follow, give way, stand back, splash fights, and piggyback. Non-random interactions occurred when pairs of specimens approached the passive surface bait, confirming that the white sharks made a real choice, showing a dominance hierarchy during the ten years of data collection. Evidence of non-random social interactions in the surface behavior of bait-attracted white sharks Carcharodon carcharias in Gansbaai’s transient population was the goal of this research.
Seas and oceans are contaminated by persistent organic pollutants (POPs), which are released into the environment by human activities. The chemical-physical properties of POPs induce high persistence ...and toxicity in marine organisms from the lowest to the highest trophic levels. Phyto- and zooplankton are at the base of the food chain, and they can adsorb and accumulate these xenobiotic compounds. Therefore, all planktophagous species, including the whale shark (Rhincodon typus), are susceptible to ingesting these contaminants during feeding. From October to December, whale sharks migrate along the north-west coast of Madagascar in search of dense patches of plankton. During scientific expeditions to the whale sharks’ foraging areas in the waters of the island of Nosy Be (which is in the north-west of Madagascar), plankton samples were taken. In these samples, the presence and levels of some chlorinated xenobiotics (HCB, DDT and its metabolites, and PCBs) were evaluated in order to estimate the possible impact of whale shark diet on organochlorine (OC) accumulation. The fresh plankton biomass sampled from this region did not seem to be sufficient for the sustenance of the animals, which suggests that the daily contamination input of Rhincodon typus individuals, depending on their plankton diet, is minimal.
Between the years 2008 and 2013, six annual research expeditions were carried out at Dyer Island (Gansbaai, South Africa) to study the surface behaviour of white sharks in the presence of two passive ...prey: tuna bait and a seal-shaped decoy. Sightings were performed from a commercial cage-diving boat over 247 h; 250 different white sharks, with a mean total length (TL) of 308 cm, were observed. Of these, 166 performed at least one or more interactions, for a total of 240 interactions with bait and the seal-shaped decoy. In Gansbaai, there is a population of transient white sharks consisting mainly of immature specimens throughout the year. Both mature and immature sharks preferred to prey on the seal-shaped decoy, probably due to the dietary shift that occurs in white sharks whose TL varies between 200 cm and 340 cm. As it is widely confirmed that white sharks change their diet from a predominantly piscivorous juvenile diet to a mature marine mammalian diet, it is possible that Gansbaai may be a hunting training area and that sharks show a discriminate food choice, a strategy that was adopted by the majority of specimens thanks to their ability to visualize energetically richer prey, after having been attracted by the odorous source represented by the tuna bait.
The white shark (
) is a charismatic species and, consequently, one of the most studied and protected sharks. This species can be found in a wide range of temperatures and depths, showing site ...fidelity and migrating across the oceans. This offers a challenge to understanding the processes influencing their lifecycle and, more importantly, assessing anthropogenic disturbances to their populations. These predators' behaviour has been linked to diverse abiotic factors. Here, an ethological approach was used to understand the influence of environmental variables on white shark behaviour. A different environmental impact was found between the activity of females and males toward the bait. Females performed a higher number of behaviours under daylight, lower sea surface temperatures, short wavelets, clear and cloudy skies, under La Niña events, elevated moonlight and high tides. Males behaved with more complexity at dawn, medium sea surface temperatures, large wavelets, few clouds, high tides, and elevated moonlight. The world's aquatic habitats are experiencing significant physiochemical shifts due to human-induced climate change. Knowledge about how white sharks respond to environmental factors is essential to guide management and conservation actions.
Marine pollution, due to the regular discharge of contaminants by various anthropogenic sources, is a growing problem that imposes detrimental influences on natural species. Sharks, because of a diet ...based on smaller polluted animals, are exposed to the risk of water contamination and the subsequent bioaccumulation and biomagnification. Trace elements are very diffuse water pollutants and able to induce oxidative stress in a variety of marine organisms. However, to date, studies on sharks are rather scarce and often limited to mercury. In this context, the present study aimed to analyze the accumulation of trace elements and their putative correlation with the onset of an oxidative status in the muscle of the lesser spotted dogfish
, from the Central Mediterranean Sea. Ecotoxicological analysis detected the presence of Pb, As, Cd, Mn, Zn, Ni, Cu, and Fe; no significant differences were observed between sexes, while a negative correlation was found between Pb and animal length. Analysis of oxidative stress markers showed either positive or negative correlation with respect to the presence of trace elements. Lipid peroxidation (TBARS) positively correlated with Zn, Ni, and Fe; SOD enzyme activity negatively correlated with Cu and Ni; LDH was negatively correlated with Fe and positively correlated with Pb. Moreover, positive correlations between the leukocyte count and Mn and Zn, as well as with LDH activity, were also observed. The data suggested that, in sharks, trace elements accumulation may affect oxidant and antioxidant processes with important outcomes for their physiology and health.
Parasitological, hematological, and ecotoxicological analyses were carried out on a population of lesser spotted dogfish
from the central Mediterranean Sea. Parasitological analyses highlighted a ...poor helminthic community, highly dominated by a single taxon represented by the cestode
sp. No differences in the parasitic load between females and males were observed. Hematological analyses showed that the number of leukocytes was significantly lower in the sharks that resulted in parasitism, and this could be due to the ability of some trace elements, such as arsenic, weakening the immune system and exposing animals to a higher risk of parasite infection, although further hematological and parasitological analyses are required on a larger number of samples. Trace elements analyses in the vertebrae, skin, and liver highlighted that the most abundant and potentially toxic elements were lead (Pb), arsenic (As), and cadmium (Cd). Other trace elements were also abundant, such as manganese (Mn), zinc (Zn), nickel (Ni), copper (Cu), and iron (Fe). Pb, As, and Mn showed the highest concentrations in vertebrae, while Cd, Cu, and Zn were the highest in the liver, probably due to their concentration in the prey items of the sharks; Fe and Ni showed the highest concentrations in the skin, due to their presence in the water column, especially along the coast where animals were collected. The concentration of some trace elements analyzed in the vertebrae decreased with the growth of the sharks. These results confirm that elasmobranchs, being predators at the apex of the marine food chain, act as final receptors for a series of polluting elements regularly discharged into the sea.
Despite the growing interest in human-made noise effects on marine wildlife, few studies have investigated the potential role of underwater noise on elasmobranch species. In this study, twelve ...specimens of small-spotted catshark (
) were exposed to biological and anthropogenic sounds in order to assess their behavioural changes in response to prey acoustic stimuli and to different amplitude levels of shipping noise. The sharks, individually held in aquariums, were exposed to four experimental acoustic conditions characterized by different spectral (Hz) components and amplitude (dB re 1 µPa) levels. The swimming behaviour and spatial distribution of sharks were observed. The results highlighted significant differences in swimming time and in the spatial use of the aquarium among the experimental conditions. When the amplitude levels of biological sources were higher than those of anthropogenic sources, the sharks' swimming behaviour was concentrated in the bottom sections of the aquarium; when the amplitude levels of anthropogenic sources were higher than biological ones, the specimens increased the time spent swimming. Moreover, their spatial distribution highlighted a tendency to occupy the least noisy sections of the aquarium. In conclusion, this study highlighted that anthropogenic noise is able to affect behaviour of catshark specimens and the impact depends on acoustic amplitude levels.
The study aims to identify antibacterial properties in unfertilized eggs of Scyliorhinus canicula and Scyliorhinus stellaris. Despite challenging marine conditions, these eggs retain their integrity ...for extended periods and remain unaffected by pathogens. The antibacterial activity was measured using minimum inhibitory and minimum bactericidal concentration analysis. The eggs of S. stellaris exhibited a slight inhibitory effect against Staphylococcus aureus and Listeria monocytogenes, whereas both species' eggs showed no activity against gram‐negative microorganisms.
Described in the present report are documented attempts to tag and sample the white shark,
Carcharodon carcharias
(Linnaeus, 1758), along Italian coasts in the Mediterranean Sea, which took place ...near the Lampedusa Island in the lower Tyrrhenian Channel of Sicily, off the coast of Rimini in the Adriatic Sea, and of Civitavecchia in the central Tyrrhenian Sea. The project, activated in 2015, was aimed at tagging and sampling specimens of the white shark in order to collect data useful to implement conservation strategies in the Mediterranean Sea. Despite four tagging attempts made in 2017, 2018, 2021, and 2022 with 288 total hours of baiting activity and the use of 1030 kg of chum, no white sharks or any other shark species were sighted.
U radu su dokumentirani pokušaji označavanja i uzorkovanja velike bijele psine
Carcharodon carcharias
(Linnaeus, 1758) uz talijansku obalu u Sredozemnom moru. Istraživanje je obavljeno na području oko otoka Lampeduze, u sicilijanskom kanalu u južnom Tirenskom moru, ispred Riminija u Jadranskom moru te kod Civitavecchije u centralnom Tirenskom moru. Projekt, koji je započeo 2015. godine, bio je usmjeren na označavanje i uzorkovanje primjeraka velike bijele psine s ciljem prikupljanja podataka važnih za implementaciju mjera za očuvanje populacije ove vrste u Sredozemnom moru. Unatoč četiri pokušaja označavanja obavljena 2017., 2018., 2021. i 2022. godine, u ukupnom trajanju od 288 sati primamljivanja uz pomoć mamca te 1030 kg mamca, ni jedan primjerak velike bijele psine, ni drugih vrsta morskih pasa, nije primijećen.
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