Trace elements and isotopes analyses on historical samples of white sharks from the Mediterranean Sea

The white shark Carcharodon carcharias has been present in the Mediterranean Sea since 3.2 million years ago. Nevertheless, the current population shows a low genetic variability suggesting an endangered small population, on which there is scarce information regarding ecotoxicology or trophic ecology. Given that white shark's sightings are rare in the Mediterranean and the possibility of obtaining samples is highly limited, the aim of this research was to provide general information regarding the concentration of trace elements and stable isotopes (delta N-15 and delta C-13). Laboratory analyses were performed on 18 and 12 subsamples from two different white sharks' vertebrae obtained from two adult specimens caught in 1987, in Favignana Island, Italy. Perforations were made along the vertebrae to describe both trace elements and stable isotopes at different life stages. A total of 38 trace elements were analysed, in which the highest concentrations were found in Fe, Sr, U, Pb, and Zn. The fluctuations of these elements during the ontogeny of both individuals could have been related to changes in diet and environment, although the specific origin remains unknown. Regarding stable isotopes, the vertebrae from the male showed an isotopic range from 9.6 parts per thousand to 10.8 parts per thousand (delta N-15) and from -16.5 parts per thousand to -13.0 parts per thousand (delta C-13) with a mean +/- SD value of 10.3 +/- 0.4 parts per thousand for delta N-15 and -14.6 +/- 1.3 parts per thousand for delta C-13; whereas the female vertebrae had an isotopic range from 9.8 parts per thousand to 11.1 parts per thousand (delta N-15) and from -16.9 parts per thousand to -15.0 parts per thousand (delta C-13), with a mean +/- SD value of 10.8 +/- 0.6 parts per thousand for delta N-15 and -15.8 +/- 0.8 parts per thousand for delta C-13. There were no significant delta N-15 differences (U = 6, p = 0.07346) between the two individuals. However, there were just significant differences in delta C-13 (t = -1.8, p = 0.049256), which could suggest sexual segregation in terms of habitat use and feeding habits

Diving into the vertical dimension of elasmobranch movement ecology

Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements

Diving into the vertical dimension of elasmobranch movement ecology

Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements

Diving into the vertical dimension of elasmobranch movement ecology

This is the final version. Available on open access from the American Association for the Advancement of Science via the DOI in this recordData and materials availability: Processed data and code used in the analysis are accessible from the Zenodo Repository: 10.5281/zenodo.6885455Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements.Bertarelli FoundationResearch EnglandMoore FoundationPackard FoundationInstituto Politecnico NacionalDarwin InitiativeGeorgia AquariumRolex Awards for EnterpriseWhitley Fund for Natur

Reproductive biology of the banded guitarfish, Zapteryx exacperata, from the Gulf of California, Mexico

The banded guitarfish, Zapteryx exasperita, is a common species in the artisanal elasmobranch fisheries in the Gulf of California. Fishery-derived specimens were examined to determine critical aspects of the reproductive biology of this poorly known group of rays. Two functional testes and ovaries were found in males and females respectively. Median size at maturity (L 50161) for males was 64 cm total length (TL) and for females 69 cm TL. Average length of gravid females was 78.8 +/- 3.8 cm TL. Histological analysis showed no evidence of sperm storage in the oviducal gland. Gestation was estimated to occur over a five to six month period (February-July) and was concurrent with vitellogenesis. Mean uterine fecundity was estimated as 7 (range 2-13, SD. = 3). The sex-ratio of embryos was 1 : 1. The reproductive cycle for Z. exasperata from the Gulf of California was estimated to last one year with parturition, ovulation and copulation occurring during the summer months. Differences found in the reproductive cycle of Z. exasperata between the Gulf of California and the west coast Of Baja California could have implications in the future management plans for this fishery in the Gulf of California

Seasonal structure of fish assemblages in rocky and sandy habitats in Bahía de La Paz, Mexico

Ecological surveys from several coastal environments in Bahía de La Paz were analysed to determine the seasonal changes in the fish assemblages in the largest bay of the Gulf of California. We identified 58 species from 37 genera and 23 families in seasonal gill net samples were taken over 1 yr. Using the relative abundance index (%N), the most important species were Gerres cinereus, Arius platypogon, Lutjanus guttatus, Haemulon sexfasciatus, Kyphosus elegans, Diapterus peruvianus, Chaetodipterus zonatus, and Nematistius pectoralis. By relative weight (%W) the main species were similar but in a different ranking Kyphosus elegans, L. guttatus, G. cinereus, A. platypogon, Carcharhinus porosus, H. sexfasciatus, and Scomberomorus sierra. Three seasonal species groups were determined and their abundance, richness, and diversity were analyzed. Dissimilarity analysis suggests that were closely three habitats associated with three different fish assemblages inside Bahia de La Paz: (a) an exposed coastal zone with big rocks and sandy beaches; (b) protected coastal estuarine zone with sandy and shallow bottom; and (c) an oceanic island zone with rocky bottom and sandy patches

Seasonal structure of fish assemblages in rocky and sandy habitats in Bahía de La Paz, Mexico

Ecological surveys from several coastal environments in Bahía de La Paz were analysed to determine the seasonal changes in the fish assemblages in the largest bay of the Gulf of California. We identified 58 species from 37 genera and 23 families in seasonal gill net samples were taken over 1 yr. Using the relative abundance index (%N), the most important species were Gerres cinereus, Arius platypogon, Lutjanus guttatus, Haemulon sexfasciatus, Kyphosus elegans, Diapterus peruvianus, Chaetodipterus zonatus, and Nematistius pectoralis. By relative weight (%W) the main species were similar but in a different ranking Kyphosus elegans, L. guttatus, G. cinereus, A. platypogon, Carcharhinus porosus, H. sexfasciatus, and Scomberomorus sierra. Three seasonal species groups were determined and their abundance, richness, and diversity were analyzed. Dissimilarity analysis suggests that were closely three habitats associated with three different fish assemblages inside Bahia de La Paz: (a) an exposed coastal zone with big rocks and sandy beaches; (b) protected coastal estuarine zone with sandy and shallow bottom; and (c) an oceanic island zone with rocky bottom and sandy patches

[Ichthyofauna of the Navidad Bay, Jalisco, Mexico]

A check-list and the relative abundance of the ichthyofauna from Bahia de Navidad, Jalisco, Mexico is presented. This poorly known area of the eastern Tropical Pacific ocean is characterized by its great fish diversity. A total of 245 fish species (163 genera, 72 families) were collected during the 1994-1995 annual cycle. Vouchers were deposited in Centro de Ecologia Costera, Universidad de Guadalajara. The most important families in number of species were Carangidae (20 species), Haemulidae (20), Serranidae (17), Sciaenidae (13) and Lutjanidae (8); 20 species represented 85% and 80% of relative abundance and biomass respectively. Microlepidotus brevipinnis, Caranx caninus, Caranx caballus, Kiphosus analogus and Caranx sexfasciatus, were the dominant species. Most fish species collected in Bahia de Navidad have zoogeographical affinity with the Panamic Province (65%), and in lesser proportion with the Eastern Pacific Ocean (19%), Circumtropical (7%), Mexican Province (5%), Indo-Pacific Ocean (3%) and Gulf of California (0.4%). The great ichthyological affinity between the study area and the southern Gulf of California suggests an extension of the of Gulf southern limit

[Ichthyofauna of the Navidad Bay, Jalisco, Mexico]

A check-list and the relative abundance of the ichthyofauna from Bahia de Navidad, Jalisco, Mexico is presented. This poorly known area of the eastern Tropical Pacific ocean is characterized by its great fish diversity. A total of 245 fish species (163 genera, 72 families) were collected during the 1994-1995 annual cycle. Vouchers were deposited in Centro de Ecologia Costera, Universidad de Guadalajara. The most important families in number of species were Carangidae (20 species), Haemulidae (20), Serranidae (17), Sciaenidae (13) and Lutjanidae (8); 20 species represented 85% and 80% of relative abundance and biomass respectively. Microlepidotus brevipinnis, Caranx caninus, Caranx caballus, Kiphosus analogus and Caranx sexfasciatus, were the dominant species. Most fish species collected in Bahia de Navidad have zoogeographical affinity with the Panamic Province (65%), and in lesser proportion with the Eastern Pacific Ocean (19%), Circumtropical (7%), Mexican Province (5%), Indo-Pacific Ocean (3%) and Gulf of California (0.4%). The great ichthyological affinity between the study area and the southern Gulf of California suggests an extension of the of Gulf southern limit