Thermal and bioenergetics of elasmobranchs: bridging the gap

Physiological telemetry is a powerful tool in studying the thermal biology and energetics of elasmobranchs in the laboratory and field. Controlled lab oratory studies have increased our understanding of the physiology and beha vior of many elasmobranchs, but have focused primarily on small, slow movin g species. Extrapolating results from these laboratory studies to free-swim ming animals in the field or to other unstudied species may be problematic, due to laboratory constraints or species specific differences. Some elasmo branchs are too large or logistically difficult to maintain in captivity, m aking them extremely difficult to study in the laboratory, and thus can onl y be studied in the field. Physiological telemetry offers a 'bridge' betwee n the laboratory and the field providing an opportunity to elucidate simila rities and differences. Previous studies have coupled a variety of sensors with ultrasonic transmitters to relay information on epaxial muscle and sto mach temperatures of free-swimming lamnid sharks. Even though these studies indicate lamnids exhibit elevated body temperatures, the degree to which t hese sharks may control body temperature is still not fully understood. Tel emetry of heart rate, swimming speed, muscle contraction rate, and tail bea t frequency has been used to estimate energy consumption of free-swimming e lasmobranchs with varying success. Based on recent advances in technology, several hypotheses regarding thermoregulation, cardiac output, and obligate ram ventilation are discussed. Although many telemetry studies have been r estricted by logistical difficulties in conducting long-term tracks, recent developments such as acoustic modems, underwater listening stations and sa tellite telemetry may significantly increase the amount and types of physio logical data that can be collected. These improvements in technology and ca ptive animal husbandry techniques will help to 'bridge the gap' between the laboratory and the field.