Characterization of metal contaminants in the Critically Endangered angelshark (Squatina squatina): A first ecotoxicological insight

Abstract

Elasmobranchs are particularly susceptible to heavy metal bioaccumulation due to their apex predator status, high trophic level and limited metabolic detoxification capacity. This poses significant risks to Critically Endangered angelshark (Squatina squatina) populations in contaminated habitats. This study quantified 21 trace elements and heavy metals in liver and muscle tissues from 24 stranded S. squatina in the Canary Islands, Spain, using cold vapor atomic absorption spectrophotometry (CV-AAS) and inductively coupled plasma optical emission spectrophotometry (ICP-OES). No statistically significant correlations were found between metal concentrations and size, probably due to the limited size range (104.31 ± 18.29 cm TL). Sex also did not affect metal concentrations in the assessed tissues. Liver samples exhibited significantly higher metal concentrations than muscle, consistent with the detoxification and storage functions of this organ. Geographical comparisons revealed significantly elevated concentrations of mercury (Hg; liver: 0.997 ± 1.467 mg/kg ww, muscle: 0.835 ± 0.533 mg/kg ww) and cadmium (Cd; liver: 2.09 ± 1.76 mg/kg ww, muscle: 0.841 ± 1.54 mg/kg ww) in the Canary Islands population compared to other Squatinidae species around the world. These differences are likely driven by a combination of dietary composition, habitat characteristics, volcanic activity and anthropogenic factors. Although toxicological thresholds for elasmobranchs remain undefined, elevated pollutant levels may impair growth, reproduction, and juvenile development, threatening long-term population viability. Establishing baseline contaminant thresholds is crucial for assessing ecotoxicological risks and informing targeted conservation efforts for this species.