Correlates of bite force in the Atlantic sharpnose shark, Rhizoprionodon terraenovae

Abstract

Bite force is a whole-animal performance measurement that can potentially provide valuable information regarding the biology of an organism. However, there have been few studies that directly measured bite force in sharks. We examined involuntary (obtained using jaw musculature stimulation) and voluntary bite force in Atlantic sharpnose sharks, Rhizoprionodon terraenovae, and considered the effects of size, sex, season, gape, and capture method on bite force in that species. Additionally, we considered the relationship between bite force and general head measurements and the position along the jaws used to apply the bite (anterior vs. posterior). We found that there were no significant differences in voluntary or involuntary bite force and no significant differences in bite force between sexes. Atlantic sharpnose sharks, ranging between 55.1 and 105.5 cm total length, had an anterior bite force between 4.4 and 60.2 Newtons (N) and a posterior force between 20.9 and 102.8 N. Anterior bite force was found to be lowest in the summer months and highest in the spring and fall and paralleled seasonal changes in shark condition as evidenced by hepato-somatic index. As gape increased, the anterior bite force increased, with the greatest force found between 60 and 80 % of maximum gape. A best-fit multiple regression using jaw length, mouth width, head length and head width explained 80.9 % of the variation in anterior bite force. Longline-captured Atlantic sharpnose sharks produced significantly lower bite force when compared to hook-and-line-captured animals. Using published data and data from this study, we examined the body size-to-bite force relationship for nine shark species which provided a bite-force estimate of 123,876–179,219 N for the extinct megatooth shark, Carcharodon megalodon.