SEPULVEDA, C. A.*; WEGNER, N. C.; AALBERS, S. A.; BERNAL, D.; Pfleger Institute of Environmental Research; Scripps Institution of Oceanography; Scripps Institution of Oceanography; University of Massachusets, Dartmouth: Gut evacuation rates in free-swimming juvenile mako sharks Isurus oxyrinchus

The mako shark Isurus oxyrinchus belongs to the Family Lamnidae, a highly specialized group that is capable of regional endothermy (warming of the eye and brain region, the stomach and the red muscle). Because of the difficulty in working with large pelagic predators, the effects of increased stomach temperature on the digestion rates of warm-bodied sharks have not been directly tested. In the present study we have developed techniques that modify traditional acoustic telemetry methods such that they address questions related to mako shark digestion rates. Wild mako sharks are fed a depth/temperature acoustic transmitter that is concealed within a prey item (chub mackerel, Scomber japonicus) of known mass and manually tracked. At 2hr intervals the tracked mako is subsequently re-fed rations of known mass. After 8hrs of manual tracking, the mako is recaptured and the gut contents sampled. Preliminary findings suggest that juvenile mako sharks are capable of clearing a 200g chub mackerel ration within an 8hr period. We will present data on gut clearance rates (digestion), stomach temperatures and gastric pH for juvenile mako sharks swimming in the wild.