Teleost and elasmobranch eye lenses as a target for life-history stable isotope analyses.

Incrementally grown, metabolically inert tissues such as fish otoliths provide biochemical records that can used to infer behavior and physiology throughout the lifetime of the individual. Organic tissues are particularly useful as the stable isotope composition of the organic component can provide information about diet, trophic level and location. Unfortunately, inert, incrementally grown organic tissues are relatively uncommon. The vertebrate eye lens, however, is formed via sequential deposition of protein-filled fiber cells, which are subsequently metabolically inert. Lenses therefore have the potential to serve as biochemical data recorders capturing life-long variations in dietary and spatial ecology. Here we review the state of knowledge regarding the structure and formation of fish eye lenses in the context of using lens tissue for retrospective isotopic analysis. We discuss the relationship between eye lens diameter and body size, describe the successful recovery of expected isotopic gradients throughout ontogeny and between species, and quantify the isotopic offset between lens protein and white muscle tissue. We show that fish eye lens protein is an attractive host for recovery of stable isotope life histories, particularly for juvenile life stages, and especially in elasmobranchs lacking otoliths, but interpretation of lens-based records is complicated by species-specific uncertainties associated with lens growth rates.

Concentrations of mercury and other trace elements in porbeagle shark Lamna nasus.

Concentrations of 11 trace elements in three tissues of porbeagle shark Lamna nasus (n=33) were determined. The maximum observed concentrations of Cd and Pb in muscle were 0.04 and 0.01mgkg-1, respectively, and all muscle samples were below European seafood limits for these metals. Hg concentrations in either the red or white muscle that exceeded European regulations for seafood were observed in one-third of specimens. Hg concentration, however, increased with length, and all fish >195cm had concentrations >1.0mgkg-1, with a maximum observed value of 2.0mgkg-1. Concentrations of Fe and Cu were, on average, 9.7 and 10 times higher in red muscle than in nearby white muscle, respectively. Mn, Zn, As and Se were also found in significantly higher concentrations in red muscle than in white muscle.

Organohalogen contaminants and trace metals in North-East Atlantic porbeagle shark (Lamna nasus).

The North-East Atlantic porbeagle (Lamna nasus) population has declined dramatically over the last few decades and is currently classified as 'Critically Endangered'. As long-lived, apex predators, they may be vulnerable to bioaccumulation of contaminants. In this study organohalogen compounds and trace elements were analysed in 12 specimens caught as incidental bycatch in commercial gillnet fisheries in the Celtic Sea in 2011. Levels of organohalogen contaminants were low or undetectable (summed CB and BDE concentrations 0.04-0.85 mg kg(-1)wet weight). A notably high Cd concentration (7.2 mg kg(-1)wet weight) was observed in one mature male, whereas the range observed in the other samples was much lower (0.04-0.26 mg kg(-1)wet weight). Hg and Pb concentrations were detected only in single animals, at 0.34 and 0.08 mg kg(-1)wet weight, respectively. These contaminant levels were low in comparison to other published studies for shark species.