Postprandial response of gastric pH in leopard sharks (Triakis semifasciata)and its use to study foraging ecology

Changes in gastric pH of leopard sharks Triakis semifasciata were quantified as an indicator of feeding frequency and ration size. Continuous in situ measurements of gastric pH were made in captive adult leopard sharks using an autonomous pH/temperature probe for periods ranging from 5-16 days. Instrumented sharks were fed meals of squid at different ration sizes. Gastric fluid samples were also taken from non-instrumented juvenile leopard sharks at different time intervals after feeding, and the pH measured to quantify effects of the pH probe in the stomach. Continuous in situ measurements of pH show that empty stomachs have a low pH of 1.54+/-1.42 (mean +/- S.D.) and that feeding causes a rapid increase in pH to 3.11+/-0.71, followed by a gradual decrease back down to baseline levels. There was a positive relationship between changes in pH and meal size (r(2)=0.72, P=0.001). There were no significant differences in pH between continuous in situ and laboratory serial sample measurements. Together these findings indicate that gastric acid secretion may be continuous in leopard sharks, and that changes in gastric pH may be used to estimate feeding chronology, frequency and ration size of leopard sharks in the field.