Determination of Mercury, Methylmercury and Selenium Concentrations in Elasmobranch Meat: Fish Consumption Safety

This study measures total mercury (THg), methylmercury (MeHg) and selenium (Se) concentrations in elasmobranch fish from an Italian market with the aim of evaluating the risk-benefit associated with their consumption, using estimated weekly intake (EWI), permissible safety level (MeHgPSL), selenium health benefit value (HBVSe) and monthly consumption rate limit (CRmm) for each species. THg and Se were analysed by atomic absorption spectrometry, while MeHg was determined by HrGc/Ms. THg and MeHg concentrations ranged from 0.61 to 1.25 μg g−1 w.w. and from 0.57 to 0.97 μg g−1 w.w., respectively, whereas Se levels were 0.49–0.65 μg g−1 w.w. In most samples European Community limits for THg were surpassed, while for MeHg none of the fish had levels above the limit adopted by FAO/WHO. EWIs for THg and MeHg in many cases were above the provisional tolerable weekly intakes (PTWIs). MeHgPSL estimate showed that fish should contain approximately 50% of the concentration measured to avoid exceeding the PTWI. Nevertheless, the HBVSe index indicated that solely skates were safe for human consumption (HBVSe = 3.57–6.22). Our results highlight the importance of a constant monitoring of THg and MeHg level in fish, especially in apex predators, to avoid the risk of overexposure for consumers.

Fifty years of tagging skates (Rajidae): using mark-recapture data to evaluate stock units

Despite increased focus on ascertaining the status of elasmobranch fish, the stock units for many species are uncertain. Data from mark-recapture tagging studies undertaken from 1959–2017 were analysed for 13 batoid species. Data were most comprehensive for skates (Rajidae), with 22,374 released and 3342 (14.9%) returned. Most data related to thornback ray Raja clavata, blonde ray R. brachyura and spotted ray R. montagui. Tags were generally returned from areas less than 50 km from their release, and usually from the ICES Division in which they were released. However, straight-line distances travelled of up to 910 km (R. brachyura) and 772 km (R. clavata) were recorded, highlighting that individual skates are capable of longer-distance movements. The maximum time at liberty was 16.6 years (R. clavata). Whilst mark-recapture data indicated that the current stock units used by ICES are broadly appropriate, southward movements of several skate species tagged off Northern Ireland (Division 6.a) to the Irish Sea (Division 7.a) were observed. In contrast, skates tagged in the Irish Sea and Bristol Channel (Division 7.f) generally remained in that area, with only occasional recaptures from Division 6.a.

Transcoelomic expulsion of an ingested foreign object by a carcharhinid shark

A wild lemon shark (Negaprion brevirostris) was observed to expel an ingested foreign object through its body wall, over a minimum period of 435 days. We observed this lemon shark at a recreational diving feeding site off the coast of Juno Beach (FL, USA) on 12 occasions between 6 December 2014 and 14 December 2016. At the final observation, following expulsion, we observed this lemon shark with scar tissue and in apparent healthy condition. At minimum, this lemon shark was able to survive for over 1 year under perforation of its stomach lining, coelom and body wall. This account provides further evidence for the resilience and recovery capabilities of elasmobranch fish.