Cartilaginous fish face significant threats due to overfishing and slow reproductive rates, leading to rapid declines in their populations globally. Traditional capture-based surveys, while valuable ...for gathering ecological information, pose risks to the health and survival of these species. Baited Remote Underwater Video Systems (BRUVS) offer a non-invasive alternative, allowing for standardized surveys across various habitats with minimal disturbance to marine life. This study presents a comprehensive review of BRUVS applications in studying cartilaginous fish, examining 81 peer-reviewed papers spanning from 1990 to 2023. The analysis reveals a significant increase in BRUVS usage over the past three decades, particularly in Australia, South Africa, and Central America. The most common BRUVS configurations include benthic setups, mono-camera systems, and the use of fish from the Clupeidae and Scombridae families as bait. BRUVS have been instrumental in studying 195 chondrichthyan species, providing insights into up to thirteen different aspects of the life histories. Moreover, BRUVS facilitate the monitoring of endangered and data-deficient species, contributing crucial data for conservation efforts. Overall, this study underscores the value of BRUVS as a powerful tool for studying and conserving cartilaginous fish populations worldwide.
This study describes the effect of different baits on the attraction, surface behaviour and conditioning of white sharks Carcharodon carcharias during local ecotourism activities. The sightings, ...behaviours, and pictures used for photographic identification were obtained during August to November 2012-2014 onboard tourist boats in Guadalupe Island, Mexico. Four types of baits were used: (1) frozen bait; (2) frozen bait and natural chum; (3) fresh fish bait; and (4) mackerel bags. Data were analysed according to sex, maturity and the total of sharks using 6,145 sightings of 121 white sharks. The type of bait showed no significant difference on the effectiveness to attracting sharks. Ethological analysis showed that the type of bait had a significant effect on the shark's surface behaviour during its interactions with boats. Natural chum and fresh baits showed short term behavioural patterns constituted by increased number of violent interactions with the bait, while the frozen bait did not generate a defined behavioural pattern. Conditioning of white sharks was determined by the number of interactions and the consumption frequency of the bait. Fifty nine percent of sharks (n = 41) showed no conditioning, 36% (n = 25) showed a low risk and only 5% (n = 3) were found to have a high risk of conditioning. The results suggest that current ecotourism has no effect on the conditioning of the white sharks, and that all baits have a similar effectiveness for attracting the sharks. However, a different behavioural pattern was observed when fresh bait and chum were used, which could increase the potential of accidents during ecotourism.
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.
The influence of environmental factors on prey discrimination of bait-attracted white sharks was studied over a six-year period (2008-2013) at Dyer Island Nature Reserve (Gansbaai, South Africa). ...Across 240 bait-attracted feeding events observed in this period, both immature and mature white sharks were attracted by the seal-shaped decoy rather than the tuna bait, except for the years 2008 and 2011. Tide ranges, underwater visibility, water temperature, and sea conditions were, in decreasing order, the factors which drove white sharks to select the seal-shaped decoy. High tide lowered the minimum depth from which sharks could approach seals close to the shore, while extended visibility helped the sharks in making predatory choices towards the more energy-rich prey source, the odorless seal-shaped decoy. On the contrary, warmer water is associated with an increase in phytoplankton that reduces underwater visibility and increases the diversity of teleosts including tuna-a known prey of white sharks-driving the sharks to favor the tuna bait. Overall, sea conditions were almost always slightly rough, ensuring a good average underwater visibility. Recommendations for future research work at this site are presented.
Climate and land cover changes are the two most important stressors causing the decline of amphibians’ populations worldwide. Within the Mediterranean area, one of the global biodiversity hotspots, ...the endemic Italian yellow-bellied toad (Bombina pachypus) suffered the same fate, as the decreases and local extinctions proved over time. Since the need to preserve this Apennine endemic species is evident, we take advantage of a novel approach combining climate-based ecological niche models and post-modelling GIS techniques (i.e., the weighted overlay framework) to produce finer species distribution models for B. pachypus. In doing so, we coupled climate variables with topographic-, hydrologic-, and habitat-related predictors, sharpening the potential species’ distribution at its whole range scale. Our findings show a latitudinal subdivision in predicted suitability: Central Apennines populations are expected to suffer more than the Northern ones, with considerable potential future losses of genetic diversity. On the contrary, Southern Apennines’ suitability is predicted to remain stable over time, preserving the vast diversity. When assessing the coverage that protected areas offer to the locations of suitable habitats for B. pachypus, the protected sites of the Central Apennines result in slightly less suitable conservation areas than those in the Northern and Southern Apennines. The overall protected areas coverage is currently low (∼20%) and predicted in the future to narrow towards medium suitability values, except in Southern Apennines, where an increase is inferred. In light of our spatially-explicit results, we suggest that a national-scale conservation strategy should consider different management options according to the sub-territories that our analyses highlighted. Our coupled “weighted modelling – spatialised genetic inference” approach permits us to support different conservation policies at all spatial scales, capitalising on relatively few input data. Also, in-depth spatial analyses should be performed to support effective protection strategies and management for the conservation stakeholders.
•Fine-tuned SDMs deepen knowledge and strongly uphold Bombina pachypus conservation.•Changes will differently affect biogeographic sectors’ suitability for B. pachypus.•Protected areas’ policy should base on predicted local responses to future changes.
is the most common Pentanchidae in the Mediterranean Sea. A scavenger and opportunistic feeder, and despite the wide distribution, little is known about its feeding habits in Italian waters. The main ...purpose of this study was to investigate the diet of the blackmouth catshark by analysing the stomach contents. The specimens analysed were obtained from five populations of the Tyrrhenian and of the Ionian Seas, collected from a depth between 40 and 700 m. A total of 259 stomachs were analysed. The stomach contents were grouped into macro-categories and identified to the lowest taxonomic level possible. Crustaceans such as
, the Cephalopods
and
, and Osteichthyes, mostly Myctophidae, were identified. Plastic debris was also found among the stomach contents and classified according to its colour and shape. Osteichthyes represent the most abundant item (44%), above all the Myctophidae family, except for the catshark population from Tuscany, in which the most frequent species were Cephalopods, such as
and
. Differences in the plastic debris contents were also observed between the Tuscany population and other populations. These could be explained as a probable consequence of the different depths at which the blackmouth catshark populations were sampled.
Our knowledge regarding the role of the microbiome in fish health has been steadily increasing in the last decade, especially for species of commercial interest. Conversely, relatively few studies ...focus on the microbiomes of wild fish, especially apex predators like sharks, due to lower economic interest and greater difficulty in obtaining samples. Studies investigating microbiome differences between diverse anatomical locations of sharks are limited, and the majority of the available studies are focused on the microbial diversity present on shark teeth, with the aim of preventing infections due to bites of these animals or evaluating the presence of certain pathogens in healthy or diseased specimens. Here, we investigated the skin, mouth, gills, and cloaca microbiomes of five individuals of two phylogenetically distant species of sharks (
and
) to obtain a better understanding of the diversity regarding the microbiomes of these animals, how they change throughout different body parts, and how much they are influenced and determined by the ecology and evolutionary relationship between host and microbiome. To confirm the taxonomy of the sharks under study, we barcoded the specimens by sequencing the mtDNA COI from a biopsy of their skin. Microbial diversity based on the 16S rRNA gene reveals that partially overlapping microbiomes inhabit different body parts of each shark species, while the communities are distinct between the two species. Our results suggest that sharks' microbiome species-specific differences are controlled by the ecology of the shark species. This is the first study comparatively analyzing the microbiome diversity of different anatomical locations in two shark species of the Mediterranean Sea.
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.
White sharks, Carcharodon carcharias, are often described as elusive, with little information available due to the logistical difficulties of studying large marine predators that make long-distance ...migrations across ocean basins. Increased understanding of aggregation patterns, combined with recent advances in technology have, however, facilitated a new breadth of studies revealing fresh insights into the biology and ecology of white sharks. Although we may no longer be able to refer to the white shark as a little-known, elusive species, there remain numerous key questions that warrant investigation and research focus. Although white sharks have separate populations, they seemingly share similar biological and ecological traits across their global distribution. Yet, white shark’s behaviour and migratory patterns can widely differ, which makes formalising similarities across its distribution challenging. Prioritisation of research questions is important to maximise limited resources because white sharks are naturally low in abundance and play important regulatory roles in the ecosystem. Here, we consulted 43 white shark experts to identify these issues. The questions listed and developed here provide a global road map for future research on white sharks to advance progress towards key goals that are informed by the needs of the research community and resource managers.
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