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

Abstract

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 noninstrumented 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.

Site Fidelity and Movement Patterns of Groundfish Associated with Offshore Petroleum Platforms in the Santa Barbara Channel

“…It is also possible that these fish had died and were scavenged by a predator (e.g., sealion Zalophus californianus or shark) and the predator was detected moving between these platforms. However, a predator that has consumed a transmittered fish should regurgitate the transmitter after 5-10 d (Papastamatiou and Lowe 2004).…”

Autonomous measurement of ingestion and digestion processes in free swimming sharks

“…In marine ecosystems, the advent of electronic tags has provided unprecedented new insights into movements of highly mobile sharks and fishes (Meyer et al, 2007;Meyer et al, 2010), but we still know very little about where and when these animals are feeding or how much they are eating (Papastamatiou and Lowe, 2004;Bestley et al, 2008). We need this information both to understand the ecology of individual species and to gain a broader understanding of patterns of energy flow through marine food webs.…”

“…Unfortunately, the utility of stomach temperature telemetry alone for quantifying feeding in fishes and sharks appears to be limited to a small number of endothermic species that either utilize visceral warming to aid digestion (Bestley et al, 2008) or maintain relatively warm stomach temperatures and ingest cool prey (and cool seawater) during feeding (Goldman, 1997;Papastamatiou and Lowe, 2004). However, even in endothermic fishes, interpretation of cold spikes in stomach thermal records could be confounded by fishes drinking cool seawater (Wood et A more broadly applicable and unequivocal measure of feeding is clearly needed and in recent years stomach pH tags were successfully used to identify feeding events and quantify meal size in captive poikilothermic sharks (Papastamatiou et al, 2008).…”

“…However, even in endothermic fishes, interpretation of cold spikes in stomach thermal records could be confounded by fishes drinking cool seawater (Wood et A more broadly applicable and unequivocal measure of feeding is clearly needed and in recent years stomach pH tags were successfully used to identify feeding events and quantify meal size in captive poikilothermic sharks (Papastamatiou et al, 2008). Unfortunately, these devices also proved to have major shortcomings, including a limited lifespan for measuring pH (maximum 16days), sensor drift, inherent fragility due to the incorporation of a glass electrode, and a maximum depth limit of 100m (Papastamatiou and Lowe, 2004). To substantially advance the field of marine trophic ecology we need a more robust device with solid-state sensors capable of providing long-term, quantitative feeding data from a wide variety of free-ranging sharks and fishes.…”

Tissue pH and gut ecomorphology in six freshwater teleostsoccupying different trophic levels

“…) and the other is characterized by continuous acid secretion and the maintenance of a low, acidic pH during fasting (Papastamatiou and Lowe, 2004;Bucking and Wood, 2009). Our results demonstrated that C. argus and S. chuatsi hold a closely neutral pH in the stomach mucosa through a long period of fasting, acidification perhaps only stimulated by the ingestion of food (Nikolopoulou et al, 2011).…”