Society of Integrative and Comparative Biology 2008

Correlations of Bite Performance with Head and Carapace Morphometrics in Green Sea Turtles (Chelonia mydas)

Marshall, C.D.
Department of Marine Biology, Texas A&M University at Galveston, marshalc@tamug.edu

Adult green sea turtles (Chelonia mydas) are unusual relative to other sea turtles in that they are predominately herbivorous.  This herbivorous diet is reflected in the serrated morphology of their rhamphotheci, and likely in the relative morphometrics of their heads. Recent bite performance data in loggerhead turtles (Chelonia mydas), which are known for their durophagous capability, have demonstrated that bite force is correlated with head width. Therefore, the objective of this study was to characterize head and carapace morphometrics, and correlate these data with bite force performance in green sea turtles.  It was predicted that maximum bite force in green sea turtles would be less in magnitude relative to loggerheads, but would also be positively correlated with head width. Therefore, carapace & head morphometrics, and bite force performance were collected from free-ranging green sea turtles (N=63) from Punta Abreojos, Baja California Sur, Mexico. Subjects ranged from 13.6 to 149.7 kg, with a mean straight carapace length and width of 58.9 cm (S.D. ±12.5) and 46.4 ±8.0, respectively.  A bite force apparatus that incorporated a piezoelectric force transducer, with bite plates customized for sea turtles, was used to collect bite force data from subjects.  Bite force was measured at the rostral most tips of the jaws. The mean maximum bite force was 152.3±64 N and ranged from 36 to 313 N.  Mean head width, head height, and head length were 89.2±15.4, 56.1±29.2, and 118.4 ±20.5 mm, respectively.  Bite force was lower in magnitude than reported for loggerhead turtles, as predicted.  A stepwise multi-linear regression demonstrated that head width was also the best predictor of bite force (P < 0.01; R2 = 0.32).