First ecotoxicological investigation in whale sharks of the Gulf of California (Mexico) using skin biopsy

Background The impact that pollutants have on whale sharks ( Rhincodon typus ) is a question that remains largely unexplored. Whale sharks (WSs) are known to aggregate seasonally in different areas in the Gulf of California. Although this species is protected in Mexico since 2001, habitats for most of these aggregations are not protected. Out of the 7 localities were they aggregate, 3 are protected whereas the other 4 need to have some protection. Urban and touristic developments are major threats to their habitats because they lead to mangrove and estuary damage, both being important areas for their food resources. Moreover, due to poor fishery regulations, whale sharks often die as by-catch in fishing nets. The growth of tourism in the area of La Paz and Los Cabos represents an increase in maritime traffic and, thereby an increase in the number of collisions of WSs with boats. Finally, the increasing human activity in WS grounds is the cause of chemical pollution from urban waste waters, vessels, agriculture and solid waste (it is common to see WSs feeding while surrounded by marine litter). Approach In this work, we perform the first ecotoxicological investigation, using skin biopsy, of whale sharks sampled in the Gulf of California. In order to evaluate the potential impact of anthropogenic activities on this species, 13 skin biopsy samples were collected in January 2014 from 12 males and 1 female whale shark in La Paz Bay. PCBs (twenty-one ortho PCB congeners), DDTs (six o,p '- and p,p '- DDE, DDD and DDT isomers), PBDEs (fourteen congeners from tri- to deca-substituted) and HCB were analyzed on freeze-dried blubber biopsy samples by GC-qMS. Biomarker responses (cytochrome P450 1A, CYP1A1) were detected, using western-blotting (WB) techniques, in integument biopsies (skin tissue samples) of this vulnerable (IUCN) species. Semi-quantitative analysis was performed for each WB using Quantity One software (Bio-Rad, 1-D Analysis Software). Results The average abundance pattern for the target contaminants was PCBs >DDTs > PBDEs >HCB. Mean concentration values (and ranges) of 8.42 (0.720–41.40) ng/g w.w. were found for PCBs, 1.31 (0.20–6.36) ng/g w.w. for DDTs, 0.294 (0.02–1.14) ng/g w.w. for PBDEs and finally 0.192 (0.01–0.66) for HCB. The detected values are lower than in other planktivorous shark species (e.g. basking shark) in other areas (e.g. Mediterranean Sea). Cytochrome P450 1A (CYP1A1) was also detected for the first time, using western-blotting techniques, in the skin samples of this species. The potential impact of microplastic (plastic fragments smaller than 5 mm) and related contaminants (such as plastic additives) has also been explored in this large filter feeding species. Preliminary data on the average density of microplastics in the superficial zooplankton/microplastic samples collected from the Sea of Cortez (La Paz Bay) showed that the values ranged from 0.00 items/m3 to 0.14 items/m3; furthermore, concentrations of mono-(2-ethylhexyl) phthalate (MEHP), used as a tracer of plastic additives, ranged from 13.08 ng/g to 13.69 ng/g. Conclusions Further ecotoxicological investigation on whale shark skin biopsies will be carried out in order to support the idea of the usefulness of non-lethal approaches in the worldwide ecotoxicological risk assessment of this vulnerable species.