Several ecologically and commercially important
fish species spend the winter in a state of minimum
feeding activity and at lower risk of predation. To enable
this overwintering behaviour, energetic reserves are generated
prior to winter to support winter metabolism.
Maintenance metabolism in fish scales with body size and
increases with temperature, and the two factors together
determine a critical threshold size for passive overwintering
below which the organism is unlikely to survive
without feeding. This is because the energetic cost of
metabolism exceeds maximum energy reserves. In the
present study, we estimated the energetic cost of overwintering
from a bioenergetic model. The model was
parameterised using respirometry-based measurements of
standard metabolic rate in buried A. tobianus (a close relative
to A. marinus) at temperatures from 5.3 to 18.3C and
validated with two independent long-term overwintering
experiments. Maximum attainable energy reserves were
estimated from published data on A. marinus in the North
Sea. The critical threshold size in terms of length (Lth) for
A. marinus in the North Sea was estimated to be 9.5 cm.
We then investigated two general predictions: (1) Fish
smaller than Lth display winter feeding activity, and (2) size
at maturation of iteroparous species is larger than Lth to
ensure sufficient energy reserves to accommodate both the
metabolic cost of passive overwintering and reproductive
investments. Both predictions were found to be consistent
with data on size at maturation and total body energy in
December and February.