Body size and temperature scaling of field metabolic rate in wild marine fishes

Abstract

"Time integrated Field Metabolic Rate (FMR) is arguably the most ecologically relevant measure of the energetics of wild animals, but the relative complexity of determining FMR routinely means that we have relatively few large datasets describing variation in energy use in free-living wild animals, particularly for aquatic ectotherms where double labelled water methods cannot be used. Emerging proxies based on stable isotope systematics associated with respiration allow retrospective estimation of time integrated field metabolic rate, experienced temperature and growth in any free-living marine teleost fish. Here we present FMR data obtained for 780 individuals from 10 species of fishes sampled within a one month period in the Barents Sea. The dataset includes individual Atlantic cod with a body size range over 4 orders of magnitude, dramatically increasing the body size range over which scaling of field metabolic rates have been assessed for any single species. The allometric exponent for body size scaling of FMR is 0.9 across all taxa. Within-species scaling exponents range from 0.7 – 1.2. Mass scaling exponents may be non-linearly related to body size, but these field data are confounded by size-dependent temperature preferences. In all but one species, FMR is relatively insensitive to temperature, implying that FMR is not strongly constrained by external temperatures for fish populations operating within environmental conditions to which the population is adapted/acclimated. "