The bite force-gape relationship as an avenue of biomechanical adaptation to trophic niche in two salmonid fishes

All skeletal muscles produce their largest forces at a single optimal
length, losing force when stretched or shortened. In vertebrate feeding
systems, this fundamental force-length relationship translates to
variation in bite force across gape, which affects the food types that can
be eaten effectively. We measured the bite force-gape curves of two
sympatric species: king salmon (Oncorhynchus tshawytscha) and pink salmon
(O. gorbuscha). Cranial anatomical measurements are not significantly
different between species, however, peak bite forces are produced at
significantly different gapes. Maximum bite force is achieved at 67% of
maximum gape for king salmon and 43% of maximum gape for pink salmon. This
may allow king salmon to use greater force when eating large or elusive
prey. In contrast, pink salmon do not require high forces at extreme gapes
for filter feeding. Our results illustrate that the bite force-gape
relationship is an important ecophysiological axis of variation.