Chemical signatures in embryonic otoliths of capelin, Mallotus villosus: Influence of family and environmental conditions

Identifying the natal origin of marine fish species is important to understand the relative productivity and connectivity of local populations. Otolith chemistry can represent habitats occupied during early life history stages, thereby distinguishing individuals reared in different habitats. Maternal investment of trace elements into otoliths, however, may confound identifying an individual's natal origin. Capelin, Mallotus villosus, is a key forage fish species that spawns at both beach and deep-water ('demersal', 15-40 m) habitats along the eastern Newfoundland coast. Currently, the relative productivity of these habitats to the spawning population is unknown. Previous research demonstrated habitat-specific chemical signatures of bulk samples of embryonic capelin otoliths could be identified. It is unclear, however, whether these habitat-specific signatures would be detectable in individuals due to confounding maternal effects. To investigate maternal investment, we tested whether family-based chemical signatures could be identified from otoliths of 1-d old larvae when eggs from known families (1 male + 1 female) were reared under controlled temperature (10, 15 °C) and salinity (10, 20, 30 psu) treatments. Trace element concentrations in embryonic otoliths, particularly Ba, differed significantly among families, resulting in a high classification success of offspring into families (~ 83%). Classification success was similarly high into temperature treatments (~ 83%). A water spiking experiment, whereby enriched 137Ba was added to the water of incubating eggs, also revealed that trace elements from the ambient water are incorporated into developing otoliths during egg incubation. Together, these findings suggest that family-specific chemical signatures in embryonic capelin otoliths may be modified by ambient water chemistry and environmental conditions, particularly temperature, possibly allowing the natal origin of individual capelin to be identified.