Adrian Gleiss

Energetics is fundamentally linked to the fitness of animals and as a result is of considerable interest to many disciplines in the biological sciences, from biophysics to ecology. Despite its universal importance, our understanding of the energetics of elasmobranch fishes has been hampered by the logistical challenges of studying this taxon. This chapter reviews the state of knowledge of the energetics and metabolism of sharks and their relatives from the molecular to the ecosystem level by detailing the physiological processes related to bioenergetics and their application to biological problems. The recent advances in the field of bioenergetics of elasmobranch fishes have been underpinned by developments and improvements in methodologies both in the laboratory and in the field, offering new insight into extrinsic and intrinsic factors affecting energy demand and how energetics shape species’ ecology and evolution. Finally, this chapter highlights how a detailed understanding of bioenergetics can support the conservation and management of elasmobranchs.

Over the last several decades, advances in telemetry have greatly expanded our ability to track where sharks go and when, but are limited in their ability to provide insights into specic behaviors or reasons for using particular habitats. Until recently, the study of wild elasmobranch movements and habitat use has largely

been limited to quantifying movements via acoustic or satellite telemetry (see reviews by Nelson, 1990; Sims, 2010; Sundstrom et al., 2001); however, despite advances in these techniques, results of movement studies often remain disconnected from the behavior and physiology of the animal being tracked. Because of this, researchers have often inferred behavior from horizontal or vertical movements without the ability to test these assumptions empirically. Although brief, direct observations of

elasmobranch behaviors are possible in a few cases, we generally lack data on their daily activities even when we may have weeks or months of information about their movements. Due to technological limitations many important questions about elasmobranch behavior have gone unaddressed: When are animals most active? When do they rest? How often do they feed? How often do they mate? What is the energetic cost of different behaviors, and how does this determine where and how they spend their time?

Elucidation of the behavioural ecology of elasmobranchs is essential to further our understanding of the role of this order of vertebrates in marine ecosystems and therefore facilitate their conservation. Methodologies employed so far often rely on untested assumptions due to technological problems in resolving location, and orientation in three-dimensional space. This highlights the importance developing systems to resolve elasmobranch behaviour in the field. To that end semi-captive trials were conducted on two lemon sharks (Negaprion brevirostris) at Bimini Bahamas, where these individuals were equipped with archival-tags measuring 13 parameters (tri-axial acceleration, tri-axial magnetic field strength and a suite of environmental factors). Using tri-axial acceleration and tri-axial magnetic field strength, four behaviours and their intensities could be distinguished; resting, initiation of swimming after rest, steady-swimming, and fast-start swimming. Each behaviour could be characterised by the parameters measured (frequency and amplitude of acceleration peaks, changes in compass orientation). During steady swimming, animals displayed a wide range of tail-beat frequencies (0.4–1.2 Hz) and tail-beat acceleration amplitudes (0.002–0.16g). Overall dynamic body acceleration (ODBA), which is correlated with activity-specific metabolic-rate in terrestrial animals, showed a positive linear relationship with tail-beat frequency, indicating its potential as a proxy for energy expenditure in sharks. Comparison of ODBA for four distinct behaviours revealed it to be highest during fast-start swimming, and lowest during resting phases.

Ocean sunfish (Mola mola) are a little studied fish species which are prone to exceptionally high levels of incidental by-catch. To facilitate future studies of this species we report on a novel method for short-term deployments of high-resolution data loggers to ocean sunfish. Trials were conducted under captive (n = 1 fish) and field conditions (n = 3 fish) during 2006 and 2007 in County Kerry, Ireland. Our principal aims were: (1) to develop a low-impact harness system with an automated release mechanism; (2) retrieve the detached devices at sea; (3) to assess whether this approach enabled the collection of fine-scale behavioural data from multi-channel data loggers (daily diaries). Both the attachment and retrieval mechanisms worked well at sea with the successful relocation of all devices. The harness additionally functioned well by keeping the data logger in a fixed-position at all times (except during periods of extremely fast evasive swimming) with high resolution data retrieved for a range of variables suggesting significant potential for use on other fish species. Nonetheless, as each deployment was < 2 h it was not our objective to critically define the behaviour of ocean sunfish, but simply to obtain qualitative data upon which to base future studies. Despite the short-term deployments, provisional analysis revealed some unusual swimming behaviour suggesting that body roll, in addition to pitch and sway amplitude was intrinsically linked with vertical velocity whilst the allometric relationship between body sway and frequency (taken as a proxy for fin strokes) appeared converse to previous studies of teleost locomotion.