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17 pages, 9121 KiB

Open AccessArticle

A Proposed Method for Assessing the Spatio-Temporal Distribution of Carcharhinus melanopterus (Quoy and Gaimard, 1824) in Shallow Waters Using a UAV: A Study Conducted in Koh Tao, Thailand

by Andrea Di Tommaso, Sureerat Sailar, Francesco Luigi Leonetti, Emilio Sperone and Gianni Giglio

Diversity 2024, 16(10), 606; https://doi.org/10.3390/d16100606 - 1 Oct 2024

Viewed by 580

Abstract

In this study, we propose a method for assessing the temporal and spatial distribution of Carcharhinus melanopterus in shallow waters using unmanned aerial vehicles (UAVs). Aerial surveys were conducted in Tien Og Bay (Koh Tao, Thailand) thrice daily (morning, afternoon, evening) along a [...] Read more.

In this study, we propose a method for assessing the temporal and spatial distribution of Carcharhinus melanopterus in shallow waters using unmanned aerial vehicles (UAVs). Aerial surveys were conducted in Tien Og Bay (Koh Tao, Thailand) thrice daily (morning, afternoon, evening) along a 360 m transect at a 30 m altitude. Environmental factors, including cloudiness, sea conditions, wind, tide, and anthropogenic disturbance, were recorded for each time slot. We developed a Python/AppleScript application to facilitate individual counting, correlating sightings with GPS data and measuring pixel-based length. Abundance varied significantly across time slots (p < 0.001), with a strong morning preference, and was influenced by tide (p = 0.040), favoring low tide. Additionally, abundance related to anthropogenic disturbance (p = 0.048), being higher when anthropogenic activity was absent. Spatial distribution analysis indicated time-related, sector-based abundance differences (p < 0.001). Pixel-based length was converted to Total Length, identifying juveniles. They exhibited a strong sector preference (p < 0.001) irrespective of the time of day. Juvenile abundance remained relatively stable throughout the day, constituting 94.1% of afternoon observations. Between 2020 and 2022, an underwater video survey was conducted to determine the sex ratio of the individuals. Only females and juveniles were sighted in the bay. Full article

(This article belongs to the Special Issue Shark Ecology)

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15 pages, 3442 KiB

Open AccessArticle

First Use of Free-Diving Photo-Identification of Porbeagle Shark (Lamna nasus) off the Brittany Coast, France

by Armelle Jung, Arthur Ory, Paul Abaut and Lucas Zaccagnini

Diversity 2024, 16(3), 155; https://doi.org/10.3390/d16030155 - 29 Feb 2024

Cited by 2 | Viewed by 2747

Abstract

A large number of pelagic shark species have declined significantly in recent decades due to overfishing, bycatch, and habitat degradation. Whereas porbeagle sharks have become scarce due to a reduction in their populations around the world, recent stock evaluations are giving positive signals [...] Read more.

A large number of pelagic shark species have declined significantly in recent decades due to overfishing, bycatch, and habitat degradation. Whereas porbeagle sharks have become scarce due to a reduction in their populations around the world, recent stock evaluations are giving positive signals about the evolution of the North-Eastern Atlantic stock size. The porbeagle shark (Lamna nasus), an offshore pelagic species with a wide distribution, is designated by IUCN as Globally Vulnerable and Critically Endangered for Europe and subject to various international conservation conventions. An increasing number of observations are reported off the Brittany coast of Trégor. The ecological role of this area for the species is still unknown and greater knowledge is needed to develop and apply sustainable management measures on a local and international scale. This study represents the first use of photo-identification on porbeagle sharks in order to improve the ecological knowledge of the species in the Trégor area. These results confirm the effectiveness of this method, with 19 of the 131 individuals identified being re-sighted, indicating an interesting degree of site fidelity and showing a sex ratio of 100% females. Observations of individuals over several years allowed the researchers to discuss the relevance of the different types of marks. The findings suggest that the Trégor area off the Brittany coast serves as a seasonal residence for female porbeagle sharks, especially between May and October. This study represents a successful first step in the use of photo-identification for this species. It offers technical support for the sharing of the methodology and provides some biological knowledge allowing researchers to discuss potential sustainable management measures for the conservation of porbeagle sharks in the study area and their habitats while needed. Full article

(This article belongs to the Special Issue Shark Ecology)

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21 pages, 2786 KiB

Open AccessArticle

Trophic Partitioning among Three Mesopredatory Shark Species Inhabiting the Northwestern Adriatic Sea

by Licia Finotto, Daniela Berto, Federico Rampazzo, Saša Raicevich, Sara Bonanomi and Carlotta Mazzoldi

Diversity 2023, 15(12), 1163; https://doi.org/10.3390/d15121163 - 22 Nov 2023

Viewed by 1466

Abstract

While the general diet of Mediterranean elasmobranchs has been widely studied, little is known about food partitioning and competition among sympatric species, despite these being important forces structuring marine communities. Using stomach content and stable isotope analyses, we investigated diet and trophic levels [...] Read more.

While the general diet of Mediterranean elasmobranchs has been widely studied, little is known about food partitioning and competition among sympatric species, despite these being important forces structuring marine communities. Using stomach content and stable isotope analyses, we investigated diet and trophic levels and evaluated the diet overlap and partitioning of Scyliorhinus canicula, Mustelus mustelus, and M. punctulatus in the northwestern Adriatic Sea. These shark species were confirmed as opportunistic mesopredators, but significant differences in their diets emerged. The two bentho-demersal Mustelus species had a larger trophic overlap with S. canicula than between each other. Given the pronounced morphological similarity of these two Mustelus species, this is likely a strategy to limit competition. The strictly benthic S. canicula showed a more varied diet compared to the other species. Stable isotope analysis highlighted that despite the smaller size and overlapping diets, S. canicula occupied a slightly higher trophic level. A better characterization of the trophic role of these species in the food web of the basin can be obtained from these data. At an ecosystem level, this information is essential to evaluate the possible consequences of the decline or recovery of the population of these exploited species. Full article

(This article belongs to the Special Issue Shark Ecology)

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11 pages, 1146 KiB

Open AccessArticle

Trophic Ecology during the Ontogenetic Development of the Pelagic Thresher Shark Alopias pelagicus in Baja California Sur, Mexico

by Clara Sánchez-Latorre, Felipe Galván-Magaña, Fernando R. Elorriaga-Verplancken, Arturo Tripp-Valdez, Rogelio González-Armas, Alejandra Piñón-Gimate and Antonio Delgado-Huertas

Diversity 2023, 15(10), 1057; https://doi.org/10.3390/d15101057 - 1 Oct 2023

Viewed by 1543

Abstract

The trophic ecology of the Pelagic Thresher shark (Alopias pelagicus) was evaluated based on chemical ecology using stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) in the vertebrae and muscles. Individuals were caught between August 2013 [...] Read more.

The trophic ecology of the Pelagic Thresher shark (Alopias pelagicus) was evaluated based on chemical ecology using stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) in the vertebrae and muscles. Individuals were caught between August 2013 and October 2019 on both the coasts of Baja California Sur, Mexico. In Bahía Tortugas, the mean vertebrae (n = 35) values were 12.72 ± 1.06‰ (δ¹⁵N) and −14.79 ± 0.61‰ (δ¹³C), while in muscles (n = 32) these values were 16.63 ± 0.76‰ (δ¹⁵N) and −17.18 ± 0.39‰ (δ¹³C). In Santa Rosalía, the mean vertebrae (n = 125) isotopic values were 14.4 ± 1.59‰ (δ¹⁵N) and −14.18 ± 0.51‰ (δ¹³C), while in muscles (n = 43), these values were 18.08 ± 0.96‰ (δ¹⁵N) and −16.43 ± 0.34‰ (δ¹³C). These results show higher δ¹⁵N values in Santa Rosalía as an effect of baseline isotopic differences between the two regions, whereas the δ¹³C values were lower in Bahía Tortugas, suggesting offshore ecological behavior (p < 0.05). In Santa Rosalía, there were significant differences by sex for δ¹⁵N in muscle, whereas the δ¹³C showed ontogenetic shifts, indicating that neonates feed in coastal areas more commonly than juveniles or adults (p < 0.05). Neither sex nor ontogenetic differences were observed in Bahía Tortugas (p > 0.05), suggesting a high overlap between their isotopic niches. Therefore, Alopias pelagicus uses the same ecological niche throughout its life, and there is consistency between sexes. The mean trophic position for both tissues and regions was 4.5, which corresponds to a tertiary predator, without any differences between stages or sex. Due to their higher energetic needs, juveniles and females showed the greatest isotopic niche amplitude; thus, their ecological niche is the widest. Full article

(This article belongs to the Special Issue Shark Ecology)

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16 pages, 1313 KiB

Open AccessArticle

A Cocktail of Plankton and Organochlorines for Whale Shark in the Foraging Areas of Nosy Be (Madagascar)

by Letizia Marsili, Guia Consales, Patrizia Romano, Rachele Rosai, Paolo Bava, Francesca Romana Reinero and Primo Micarelli

Diversity 2023, 15(8), 911; https://doi.org/10.3390/d15080911 - 4 Aug 2023

Viewed by 3279

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Shark Ecology)

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12 pages, 3065 KiB

Open AccessArticle

Unexpected Records of Newborn and Young Sharks in Ligurian and North Tyrrhenian Seas (North-Western Mediterranean Basin)

by Cecilia Mancusi, Fabrizio Serena, Alessandra Neri, Umberto Scacco, Romano Teodosio Baino, Alessandro Voliani and Letizia Marsili

Diversity 2023, 15(7), 806; https://doi.org/10.3390/d15070806 - 26 Jun 2023

Cited by 3 | Viewed by 2245

Abstract

Between 2007 and 2022, 112 specimens of newborn and young pelagic sharks were recorded in the waters of Tuscany Region, in the South Ligurian–North Tyrrhenian Seas (north-western Mediterranean basin). The sharks belonged to the Carcharhinus plumbeus (n = 14), Prionace glauca (n = [...] Read more.

Between 2007 and 2022, 112 specimens of newborn and young pelagic sharks were recorded in the waters of Tuscany Region, in the South Ligurian–North Tyrrhenian Seas (north-western Mediterranean basin). The sharks belonged to the Carcharhinus plumbeus (n = 14), Prionace glauca (n = 66), Isurus oxyrinchus (n = 16), Mobula mobular (n = 5) Alopias vulpinus (n = 7) and Hexanchus griseus (n = 4) species. Each animal was correctly identified thanks to the photographs or videos collected. All specimens were incidentally captured with set nets in inshore shallow waters, except bluntnose six-gill sharks, which were bycatch of deep-water bottom-trawl fishery. Body mass, sex, total length and biometric measurements were recorded in 34 baby sharks following the Mediterranean Large Elasmobranches Monitoring (MEDLEM) protocol. The presence of very evident and often non-healed umbilical scar confirmed that some of the sample specimens were newborn. Further confirmation came from the comparison between the total length observed and the size at birth known for the sampled species as reported in the literature. Some baby sharks were preserved in the Museums of Natural History of Pisa and Florence University collections. The importance of the coastal area studied as a possible shark nursery is discussed. Full article

(This article belongs to the Special Issue Shark Ecology)

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15 pages, 2181 KiB

Open AccessArticle

Evidence of Non-Random Social Interactions between Pairs of Bait-Attracted White Sharks in Gansbaai (South Africa)

by Primo Micarelli, Francesca Romana Reinero, Riccardo D’Agnese, Antonio Pacifico, Gianni Giglio and Emilio Sperone

Diversity 2023, 15(3), 433; https://doi.org/10.3390/d15030433 - 15 Mar 2023

Viewed by 2952

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Shark Ecology)

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Review

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30 pages, 9713 KiB

Open AccessEditor’s ChoiceReview

A Review of the Paleobiology of Some Neogene Sharks and the Fossil Records of Extant Shark Species

by Olaf Höltke, Erin E. Maxwell and Michael W. Rasser

Diversity 2024, 16(3), 147; https://doi.org/10.3390/d16030147 - 26 Feb 2024

Viewed by 4661

Abstract

In recent years, new findings and new methods (stable isotopes of oxygen, zinc, and nitrogen; 2D and 3D modeling; and geometric morphometric analyses of the teeth) have enhanced our knowledge of the Neogene shark fauna and its paleobiology. Several papers deal with the [...] Read more.

In recent years, new findings and new methods (stable isotopes of oxygen, zinc, and nitrogen; 2D and 3D modeling; and geometric morphometric analyses of the teeth) have enhanced our knowledge of the Neogene shark fauna and its paleobiology. Several papers deal with the large Otodus (Megaselachus) species, including the construction of a 3D model, as well as insights into its lifestyle and diet. In addition, the skeletal remains of Carcharias gustrowensis, Carcharodon hastalis, and Keasius parvus and a natural tooth set of Carcharodon hubbelli have been described in the last 13 years, and the dentition of the Neogene species Carcharoides catticus, Megachasma applegatei, and Parotodus benedenii has been reconstructed. Stable isotope analyses of the teeth from the Neogene species of Araloselachus, Carcharias, Carcharodon, Galeocerdo, Hemipristris, and Mitsukurina have given insights into the trophic positions of these genera during the Neogene, and shark teeth preserved near the skeletal remains of prey animals (mammals) and shark bite traces on these remains provide direct evidence of trophic interactions. The tooth shape, fossil locality, and paleoenvironment have been used to better understand the taxa Carcharhinus dicelmai, Megalolamna paradoxodon, Pachyscyllium dachiardii, and P. distans. Among extant species, Galeorhinus galeus can be traced back to the Eocene. Alopias superciliosus, Rhincodon typus, and possibly A. vulpinus can be traced back to the Oligocene. Species present by the Miocene include Alopias vulpinus, Carcharhinus amblyrhynchoides, C. amblyrhynchos, C. albimarginatus, C. amboinensis, C. brachyurus, C. brevipinna, C. falciformis, C. glaucus, C. leucas, C. limbatus, C. longimanus, C. macloti, C. obscurus, C. perezi, C. sealei, Centrophorus granulosus, Cetorhinus maximus, Dalatias licha, Deania calcea, Galeocerdo cuvier, Glyphis glyphis, Heptranchias perlo, Isurus paucus, Lamna nasus, Negaprion brevirostris, Odontaspis ferox, Pseudocarcharias kamoharai, Sphyrna media, S. mokarran, and possibly Carcharodon carcharias. First appearing in the Pliocene are Scymnodon ringens, Somniosus rostratus, and Zameus squamulosus. For some extant species (Carcharias taurus, Hexanchus griseus, Isurus oxyrinchus, Notorynchus cepedianus, and Sphyrna zygaena), it is not clear whether the assigned Neogene teeth represent the same species. The application of new methods to more fossil shark taxa, a detailed search for shark fossils, and better knowledge of the dentition of extant species (especially those with minute-sized teeth) will further enhance our knowledge of the evolution and paleobiology of sharks. Full article

(This article belongs to the Special Issue Shark Ecology)

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