Depth-dependent dive kinematics suggest cost-efficient foraging strategies by tiger sharks

Tiger sharks, Galeocerdo cuvier , are a keystone, top-order predator that are assumed to engage in cost-efficient movement and foraging patterns. To investigate the extent to which oscillatory diving by tiger sharks conform to these patterns, we used a biologging approach to model their cost of transport. High-resolution biologging tags with tri-axial sensors were deployed on 21 tiger sharks at Ningaloo Reef for durations of 5–48 h. Using overall dynamic body acceleration as a proxy for energy expenditure, we modelled the cost of transport of oscillatory movements of varying geometries in both horizontal and vertical planes for tiger sharks. The cost of horizontal transport was minimized by descending at the smallest possible angle and ascending at an angle of 5–14°, meaning that vertical oscillations conserved energy compared to swimming at a level depth. The reduction of vertical travel costs occurred at steeper angles. The absolute dive angles of tiger sharks increased between inshore and offshore zones, presumably to reduce the cost of transport while continuously hunting for prey in both benthic and surface habitats. Oscillatory movements of tiger sharks conform to strategies of cost-efficient foraging, and shallow inshore habitats appear to be an important habitat for both hunting prey and conserving energy while travelling.

Vertical Travel, Listing and the Enumeration of the Everyday

Drawing on the work of Georges Perec, and focusing on other authors such as Julio Cortazar and François Maspero, the chapter begins with an analysis of the phenomenon of vertical travel. It explores the ways in which the disruption of the traditional (horizontal) axis of the journey provides access to often unseen aspects of the everyday. In discerning a poetics of such a practice, the chapter privileges processes of listing and enumeration. Perec's use of observational catalogues is seen in particular as a challenge to any understanding of the list as a ‘subsumptive’ form that identifies a thing by subordinating it under a particular category. Instead, he demonstrates how lists may articulate what is observed in very different ways: arranging, combining, and ordering words, observations and things sequentially not only subverts categorical hierarchies, but also has positively generative qualities in creating new epistemological orderings. The chapter concludes with a discussion of the power of the list to subvert established orders of knowledge and to suggest alternative means of making sense of the everyday.