Autonomous measurement of ingestion and digestion processes in free swimming sharks

Abstract

Summary Direct measurement of predator feeding events would represent a major advance in marine trophic ecology. To date, devices available for empirically quantifying feeding in free-swimming fishes have relied on measuring stomach temperature, pH or physical motility, each of which has major, practical limitations. We hypothesized that the considerable physical changes which occur in the stomachs of carnivorous predators during the processes of ingestion and digestion should be quantifiable using Bulk Electrical Impedance measured across paired electrodes. We used a prototype archival data logging tag (Wildlife Computers Inc. Redmond, WA) to record changes in impedance inside the stomachs of captive, free swimming tiger and sandbar sharks over multiple, successive feeding events. Feeding and digestion events produced characteristic changes in electrical impedance of the stomach contents identifiable as 5 successive phases: (1) Pre-ingestion (empty stomach), (2) Ingestion, (3) Chemical 'lag' phase, (4) Mechanical 'chyme' phase, and (5) Stomach emptying phase. The duration of the chyme phase was positively related to meal size.

A combination of gyroscope and accelerometer for identifying alternative feeding behaviours in fish

“…Over the last two decades, researchers have attempted to record the feeding behaviours of predators in nature using electronic devices, such as animal-borne video cameras (Davis et al, 1999;Watanabe and Takahashi, 2013), stomach/oesophageal temperature and impedance telemetry (Austin et al, 2006;Hanuise et al, 2010;Meyer and Holland, 2012), and accelerometers/hall sensors attached to jaws or heads (Hanuise et al, 2010;Naito et al, 2013;Watanabe and Takahashi, 2013;Wilson et al, 2002). However, very few studies have attempted to distinguish prey types (Wilson et al, 2002), except for studies using cameras.…”

Telemetry and random‐walk models reveal complex patterns of partial migration in a large marine predator

“…Genetic techniques may provide some critical validation, because we would predict that adult females show philopatry to Oahu (e.g., Mourier and Planes 2013). Finally, novel electronic tags soon will be able to identify specific behaviors such as feeding and mating so that we can investigate whether immigration to particular islands leads to increased feeding rates (Papastamatiou et al 2008, Meyer and Holland 2012, Whitney et al 2012.…”

In the belly of the beast: resolving stomach tag data to link temperature, acceleration and feeding in white sharks (Carcharodon carcharias)

“…Distinguishing foraging attempts and successful ingestion can help better inform energy budgets and foraging strategies which can be particularly relevant for species such as large predatory sharks that may forage only occasionally [35]. This approach could also be extended to ectothermic species by recording additional measurements such as impedance [28] that can reflect digestive activity when temperature alone cannot.…”

“…Furthermore, in many cases ingestion results in stomach temperature reductions attributable to the potential cooler temperature of the prey, or food item, and associated influx of ambient water. These reductions in temperature or dips can be used to mark the initiation of the feeding event [27,28].…”

“…Here we describe a novel method to deploy accelerometers in the stomachs of large free-swimming sharks and how, with the addition of stomach sensors, unique insights into feeding behavior can be achieved [28]. The system is tested on white sharks (Carcharodon carcharias) during their annual coastal residency off the California coast.…”