Energetics of Grenadier Fishes
Jeffrey C. Drazen
Abstract.—Energetic parameters such as metabolism, growth, and reproduction represent investments by an animal in maintenance and production. The available literature was reviewed to examine trends in these parameters for grenadiers to better understand their biology in relationship to shallow living species. Grenadiers are adapted to deep-sea habitats that have fundamentally different environmental conditions than the continental shelves where most exploited fishes live. Grenadiers have very low metabolic rates, similar to other deep-sea demersal and pelagic fishes. This appears to be the result of a relaxation in the selective pressure for locomotory capacity in dim or totally dark waters. Longevities are variable and dependant, in part, on body size. Regardless of longevity, low rates of mass-specific growth are typical and may be limited by its relationship to metabolism. Finally, reproductive outputs may be much lower than originally anticipated from gross measures of fecundity, and at least some species may reproduce less often than annually. Energetic data are sparse but until more are available for diverse species, we must assume that with a similar body form, phylogeny, and habitat, that all grenadiers have low rates of metabolism, growth, and reproduction. Grenadiers are exceptionally diverse and certainly variation exists, some of which can be explained by individual ecologies. Nevertheless it is clear that models based on the energetics of shallow living fishes cannot be used for grenadiers. Their energetic characteristics are different and make them extremely vulnerable to overexploitation. Grenadiers have become targets or major components of the bycatch in slope fisheries, so it is especially important that this basic fact be understood.