Comparative organochlorine accumulation in two ecologically similar shark species (Carcharodon carcharias and Carcharhinus obscurus) with divergent uptake based on different life history

Abstract

Trophic position and body mass are traits commonly used to predict organochlorine burdens. Sharks, however, have a variety of feeding and life history strategies and metabolize lipid uniquely. Because of this diversity, and the lipid-association of organochlorines, the dynamics of organochlorine accumulation in sharks may be predicted ineffectively by stable isotope-derived trophic position and body mass, as is typical for other taxa. The present study compared ontogenetic organochlorine profiles in the dusky shark (Carcharhinus obscurus) and white shark (Carcharodon carcharias), which differ in metabolic thermoregulation and trophic position throughout their ontogeny. Although greater organochlorine concentrations were observed in the larger bodied and higher trophic position white shark (e.g., p,p'-dichlorodiphenyldichloroethylene: 20.2 ± 2.7 ng/g vs 9.3 ± 2.2 ng/g in the dusky shark), slopes of growth-dilution corrected concentrations with age were equal to those of the dusky shark. Similar ontogenetic trophic position increases in both species, less frequent white shark seal predation than previously assumed, or inaccurate species-specific growth parameters are possible explanations. Inshore habitat use (indicated by δ(13)C values) and mass were important predictors in white and dusky sharks, respectively, of both overall compound profiles and select organochlorine concentrations. The present study clarified understanding of trophic position and body mass as reliable predictors of interspecific organochlorine accumulation in sharks, whereas regional endothermy and diet shifting were shown to have less impact on overall rates of accumulation.

Profiling and Spatial Variation Analysis of Persistent Organic Pollutants in South African Delphinids

“…International and intergovernmental cooperation in monitoring the spatial and temporal trends of POPs is therefore essential in tracing the source and fate of these contaminants, especially for developing countries such as South Africa (SA), where certain legacy POPs continue to be detected at concentrations that are among the highest globally (e.g., dichlorodiphenyltrichloroethane (DDT) and hexachlorocyclohexanes (HCHs)) and where new POPs (e.g., PFOS, dechlorane, PBDEs, etc.) have emerged due to recent industrialization. − Although there are indications that the concentrations of PCBs, DDTs, and HCHs in the SA environment have decreased or been constant since the mid-1980s, , the high POP levels found in the SA human population − and other biota − still raise serious concerns.…”

Future Research Directions on the “Elusive” White Shark

“…Furthermore, combining data from various ecological tracers including established (nitrogen and carbon) and less commonly used isotopes (oxygen and hydrogen in Vennemann et al, 2001), cutting edge ecological tracers such as amino-acid compound-specific isotope analysis (AA-CSIA), fatty acids (Pethybridge et al, 2014;Meyer et al, 2017), and trace elements (Mull et al, 2012) will complement these data streams and generate novel insights into white shark trophic roles (Hussey et al, 2015;Munroe et al, 2018). For example, integrating stable isotope profiles derived from vertebrae (Kim et al, 2012;Christiansen et al, 2015) with contaminant profiles at the point of capture (Lyons et al, 2013;Beaudry et al, 2015;McKinney et al, 2016) or sampling consecutive teeth from jaws held in private collections/museums (Polo-Silva et al, 2012) can be used to reveal ontogenetic shifts in an individual white shark's trophic ecology. Concomitantly, retrospective analyses of archived samples will permit reconstruction of historic baselines and an understanding of how white shark populations are changing and adapting to human impacts in our oceans.…”

Per/Polyfluoroalkyl Substances (PFASs) in a Marine Apex Predator (White Shark, Carcharodon carcharias) in the Northwest Atlantic Ocean

“…36−40 The shark's lipid-rich liver is a major site of contaminant accumulation 38 but many biomonitoring studies evaluate accumulation in muscle tissue because it is not as responsive to short-term changes in lipid content and is thus more representative of long-term exposures. 40 Differences in bioaccumulation between white sharks and other species have been ascribed primarily to differences in diet, some of which may stem from different degrees of usage of inshore habitats and differences in metabolism and growth rate. 37,40 Diet is considered the primary source of bioaccumulation of organic pollutants in sharks 37,38 and concentrations have been observed to increase with size/age, though this relationship may be disrupted by growth dilution effects.…”