Contrasting ontogenetic shifts in habitat and metabolism of three sympatric key deep-sea fishes

Abstract

Many coastal fish species undergo ontogenetic shifts, but comparable knowledge for most exploited deep-sea fishes and their habitat use is lacking. We use otolith stable isotope analysis (SIA) to hindcast experienced temperature, depth, and field metabolic rate of 3 ecologically and commercially important deep-sea fishes from the Azores, mid-north Atlantic. Otoliths of bluemouth rockfish Helicolenus dactylopterus, Atlantic wreckfish Polyprion americanus, and blackspot seabream Pagellus bogaraveo were analysed to determine the stable isotope composition of carbon and oxygen in aragonite at core, mid and edge of otoliths. Oxygen SIA thermometry was used to infer water temperatures and depths, and carbon isotopes were used to derive individual field metabolic rate at each section. We identified sharp ontogenetic and interspecific differences in temperature, depth, and metabolism: juvenile rockfish inhabited intermediate depths before shifting to deeper waters as sub-adults; wreckfish occupied shallow waters before an abrupt ontogenetic shift to deep waters at maturity; juvenile seabream recorded the warmest temperatures, before gradually shifting to deeper waters as they grow. The mass-specific metabolic rates declined expectedly across all 3 species as individuals grew and occupied deeper and colder environments. Rockfish revealed the highest metabolic rates at low temperatures while in wreckfish, allometric scaling exponents for the whole organism field metabolic rate were comparatively low, potentially associated with changes in activity levels associated with ontogenetic depth changes. The thermal and metabolic differences throughout the ontogeny between the species illustrate the diversity of life cycles in deep-sea fishes and the relevance of integrating these into multispecies fisheries management.