| Summary: | Haul-out periods in most phocids are particularly intense from a physiological point of view since they involve extended fasting periods associated with behaviours or processes resulting in considerable energy expenditure (e.g., combat, mating, lactation, moulting). The substantial tissue reorganization during these key periods can entail the mobilization of potentially associated contaminants, such as trace elements and persistent organic pollutants. The main objectives of this study were firstly to investigate the effects of fasting, lactational, and developmental phases on trace element concentrations (Cd, Cr, Cu, Fe, Hg, Ni, Pb, Se, V, and Zn) in the northern elephant seal (Mirounga angustirostris) and the grey seal (Halichoerus grypus), and on the other hand, to assess the maternal transfer of trace elements to the offspring. Changes in the diet indicators the carbon and nitrogen stable isotopes (δ13C and δ15N) were also investigated throughout lactation and post-weaning fast, and their implications were developed. Different tissue samples (blood, blubber, hair, and milk) were collected repeatedly in mother-pup pairs and weaned pups in northern elephant seals and grey seals during three longitudinal fieldworks in the breeding season. Related to the remobilization of resources during lactation and pup development, short-term variations in blood concentrations of trace elements were highlighted in this study. The results imply a careful consideration of the physiological status of marine mammals when using blood in the framework of biomonitoring of trace element contamination. Although the total body burdens of trace elements decreased over lactation in adult females, circulating concentrations of some metals, like Hg, increased significantly, drawing attention to the potential adverse effects on the immune, endocrine or nervous systems in adults. Northern elephant seals and grey seals are exposed to trace elements from the first stages of development through the placenta and through the milk. Indeed, concentrations in pup hair of both species revealed a large accumulation of all assayed trace elements during the foetal development. The maternal transfer of trace elements adds to lactational transfer of others chemicals such PCBs, PBDEs, and OCPs reported in recent studies. Immunotoxic and endocrine risks related to chemical mixtures remain unclear until now and may therefore affect phocids at a crucial period of their immune development.
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