PAPASTAMATIOU, YP; LOWE, CG; KELLEY, KM; California State University, Long Beach; California State University Long Beach; California State University Long Beach: Gastric pH Changes Associated with Feeding in Leopard Sharks: Using pH to Study the Foraging Ecology of Sharks

Little is known about feeding periodicity or daily ration levels of sharks in the wild, due in large part to their low abundance and difficulty in observing them in the field. In vertebrates, there are marked changes in the pH of the stomach after ingesting a meal. We are investigating using gastric pH as an indicator of feeding in leopard sharks (Triakis semifasciata). Pressure-insensitive pH and temperature probes were placed in the stomachs of three captive adults. Sharks were then fed meals of squid at differing ration levels, over periods ranging from 5-14 d. The stomach remained highly acidic (pH 0.5-2) except during times of feeding when there was a rapid increase in pH by approximately 1 unit. A strong positive correlation was found between mass of food ingested and the area under the pH-time curve. In order to determine if the presence of the probe induced acid secretions, samples of gastric fluid were removed from juvenile sharks at specific time intervals after a meal. One hour after a meal the pH was 3.310.35(SD), whereas after 72hr, the pH had dropped to 1.870.29(SD). Preliminary studies using western-immuno blots of serial sampled gastric fluid, show that pepsin is present in stomach fluid at least 48 hr after a meal. Our data thus far suggests that acid secretion in the stomach of leopard sharks may be continuous and that pH may serve as an effective indicator of feeding events in these animals.