Biodiversity assessment of the elasmobranch (shark and ray) fauna of Israel, with first insights into species ecology and distribution patterns:
Background information and significance
Globally, populations of aquatic apex and mesopredators, including elasmobranchs (sharks and rays), are declining at alarming rates (Heithaus et al., 2008; Vaudo and Heithaus, 2009). Elasmobranchs are sensitive to overfishing due to their slow growth, late maturation, low fecundity and long gestation periods (Camhi et al., 1998; Walker, 1998). As aquatic ecological communities are regulated by both ‘bottom-up’ and ‘top-down’ processes (Norse and Crowder, 2005), losses of predators and their regulatory effect on lower trophic species have been shown to influence and even change entire ecosystems (Heithaus et al., 2008; Ferretti et al., 2010; Estes et al., 2011).
Of the 70 species of elasmobranchs occurring in the Mediterranean Sea, 21 species are listed as globally critically endangered or endangered on the IUCN Red List (Cavanagh and Gibson, 2007). Some pelagic species of sharks (blue shark Prionace glauca, shortfin makos Isurus oxyrhinchus, thresher sharks Alopias spp., hammerhead sharks Sphyrna spp.) have declined in the Mediterranean Sea by up to 95% throughout their range (Ferretti et al., 2008). There are also species whose IUCN status in the Mediterranean Sea is defined as data deficient (Cavanagh and Gibson, 2007), including the dusky shark Carcharhinus obscurus which occurs in Israel’s waters (A. Barash, unpublished data).
Despite their key role within the ecosystem and their endangered status, populations of elasmobranchs are poorly studied along the Israeli Mediterranean coast. This research will be a first comprehensive study of elasmobranchs in Israel, describing their ecology, molecular taxonomy, phylogeography, and responses to anthropogenic disturbances.
This study aims to provide first insights into the species of elasmobranch fishes (sharks and rays), their distribution and ecology in Israel’s Mediterranean waters. Specifically, the following outcomes are expected:
Create an up to date list of elasmobranch species found in Israel’s Mediterranean waters
Establish a species distribution list based on presence/absence data for different seasons and locations along the coastline
Assess anthropogenic influences on species distribution
Formulating management recommendations for elasmobranchs based on the identification of endangered species, key habitats and other areas of high species diversity or density
Examine the phylogenetic origin of elasmobranch populations, to better understand migration routes, connectivity of populations and the possibility of migration through the Suez Canal.
Assessing the trophic ecology of elasmobranchs that occur in Israel's Mediterranean waters.
Proposed study methods
The whole Mediterranean coast of Israel (approx. 190 km long) will be included in the proposed study. Sampling areas will be divided into the following areas:
Areas with high anthropogenic influences (e.g. power plants in Hadera, Ashdod, Ashkelon and Tel-Aviv).
Areas with medium anthropogenic influences (e.g. marinas)
Areas with low anthropogenic influences (e.g. beaches/nature reserves)
To date, surveys yielded only limited information on species compositions, as sampling has been restricted to visual observations from the surface and inspections of catches from fishermen (A. Barash, unpublished data).
A fisheries independent survey/ tagging program: Elasmobranchs will be targeted with different fishing gear (drum lines, long lines, gill nets, seine nets), depending on the locations and the size class of animals. Biological data will be recorded from each specimen (species ID, length, weight, sex, DNA sample). Animals are then tagged and released. Species targeted in the tagging program will be based on conservation priority and abundances. An acoustic tagging program in combination with satellite tagging of selected sharks will provide information on habitat use within the distribution range. Moreover, it will allow the identification of key habitats, such as breeding and nursery areas
Fisheries survey: biological data will be recorded from animals landed by fishermen, animals sold at fish markets, and from landings confiscated by the NPA (Nature and Parks Authority). In cases where fishermen consent, stomach contents and sexual maturity will be assessed. Moreover, recaptures of tagged specimens will be recorded.
Genetic work will be done to verify species composition, and population origin. This will be accomplished by sequencing and comparing CO1 fragments, and by referencing the local populations to known markers of conspecific populations elsewhere.
Stable Isotopic composition of carbon and nitrogen will be determined at different developmental stages and geographic locations to establish food sources comparison and to take a fresh look into the local food web.
This project will be, in part, based on my own research which was conducted as part of my MS thesis and in collaboration with Ecoocean.
Camhi, M., Fowler, S., Musick, J.A., Braeutigam, A., and Fordham, S.V. (1998) Sharks and their relatives: Ecology and conservation. Occasional Paper of the IUCN Species Survival Commission No. 20 (20): 63.
Cavanagh, R.D., and Gibson, C. (2007) Overview of the conservation status of cartilaginous fishes (Chondrichthyans) in the Mediterranean Sea. 3:
Estes, J.A., Terborgh, J., Brashares, J.S., Power, M.E., Berger, J., Bond, W.J. et al. (2011) Trophic downgrading of planet Earth. Science 333: 301-306.
Ferretti, F., Myers, R.A., Serena, F., and Lotze, H.K. (2008) Loss of large predatory sharks from the Mediterranean Sea. Conserv Biol 22: 952-964.
Ferretti, F., Worm, B., Britten, G.L., Heithaus, M.R., and Lotze, H.K. (2010) Patterns and ecosystem consequences of shark declines in the ocean. Ecol Lett 13: 1055-1071.
Heithaus, M.R., Frid, A., Wirsing, A.J., and Worm, B. (2008) Predicting ecological consequences of marine top predator declines. Trends Ecol Evol 23: 202-210.
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Vaudo, J.J., and Heithaus, M.R. (2009) Spatiotemporal variability in a sandflat elasmobranch fauna in Shark Bay, Australia. Mar Biol 156: 2579-2590.
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