The Shark Trade in Costa Rica: Genetics, Mercury Contamination and Human Dimensions and the Implications for Conservation




O'Bryhim, Jason Ray

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In the past two decades shark populations have declined as a direct result of increased demand for shark products. As a result one quarter of shark species are now listed as “vulnerable”, “endangered”, or “critically endangered” by the International Union for Conservation of Nature (IUCN). For example, in Costa Rica, two threatened and commercially valuable species, the scalloped hammerhead (Sphyrna lewini) and silky shark (Carcharhinus falciformis), have experienced declines of ~90% and 80% respectively. However, within Costa Rica there is still a lack of: species-specific catch data for elasmobranchs in both artisanal and industrial fisheries, contamination levels of elasmobranch products, and information on the type of elasmobranch conservation measures that would potentially be supported by Costa Rican fishermen. Thus, it is impossible to monitor the impacts fisheries are having on specific elasmobranch populations, determine the potential health risk to elasmobranchs and consumers of their products from contaminants, and determine the conservation measures that would prove to be most successful in protecting shark populations. Therefore, the objectives of this research were to attempt to fill some of these information gaps by determining: 1) artisanal fishermen’s knowledge of sharks, their perceptions of local fisheries impacts on shark populations, and levels of potential public support for various conservation measures (i.e. MPAs); 2) species composition and abundance in artisanal and industrial fisheries using DNA barcoding; and 3) mercury (Hg) contamination levels in shark meat being sold for human consumption at markets. Using social surveys within two artisanal fishing communities we determined that support for new shark conservation measures was high (97%). However, support declined, to between ~60 to 6%, as proposed legislation potentially obstructed the fishermen’s ability to continue their current use of their fishing grounds. This highlights the importance of fisheries managers to work with artisanal fishermen to develop regulations, which 86% of surveyed fishermen were willing to do, to develop effective legislation that has a greater chance of compliance by fishermen. Within these artisanal fisheries, we identified seven species of shark (C. falciformis, C. porosus, C. limbatus Mustelus lunulatus, Nasolamia velox, Rhizoprionodon longurio, S. lewini) and one ray (Dasyatis longa), with the scalloped hammerhead (S. lewini) accounting for ~75-80% of all sharks landed. Recorded total lengths for scalloped hammerheads in the artisanal fisheries sampled, based on observer data, suggests that each of the sharks sampled were either juveniles or neonates. The “endangered” conservation status of the scalloped hammerhead shark and its current susceptibility to artisanal fisheries methods highlights the needs for new shark conservation measures in these fisheries. We also found that at least nine species of shark (Alopias pelagicus, C. falciformis, C. obscurus, C. porosus, M. lunulatus, N. velox, R. longurio, S. lewini, S. zygaena) and one ray (D. longa) were being sold in local markets, with the silky shark representing ~80% of samples tested. Therefore, silky sharks represent the most highly exploited pelagic shark in Costa Rica, which is of concern based of recent population declines and their listing as “vulnerable” in the Eastern Tropical Pacific by the IUCN. Within the markets total Hg concentrations in the shark products being sold were highest in S. zygaena (15.75 ± 2.11 ppm dry wt, 3.50 ± 0.47 ppm wet wt) and C. limbatus (11.89 ± 3.67 ppm dry wt, 2.50 ± 0.78 ppm wet wt). However, all shark species tested exceeded US Environmental Protection Agency (EPA) Hg limits of 0.3 ppm. Using previously established equations we were able to estimate THg concentrations (ppm dry wt.) for the livers of these sharks using the known muscle concentrations. Sphyrna zygaena, which is listed as “vulnerable” by the IUCN - had the highest estimated mean THg liver concentrations (4.67 ± 1.03 ppm dry weight). Thus, the consumption of shark products being sold in the Costa Rican markets poses a potentially serious health risk to consumers. The elevated Hg levels found in the muscle tissues and internal organs (liver) of this species also have the potential to negatively impact the health and conservation status of these species. It is apparent that new conservation measures are needed to protect elasmobranchs in Costa Rica, particularly the scalloped hammerhead in artisanal fisheries and the silky shark in pelagic fisheries. Despite the potential human health risk associated with the consumption of elasmobranch products, the level of contamination could prove to be a useful tool in reducing demand for elasmobranch products, and thus aid in the conservation of threatened species. Regardless, monitoring of shark contamination, fisheries and market sales in Costa Rica is poor and further legislation will be needed to ensure the sustainability of their shark populations.



Conservation biology, Genetics, Toxicology, Conservation, Costa Rica, Genetics, Mercury, Sharks, Social Survey