HOW SHARKS ARE VULNERABLE PREY: KINEMATICS OF ESCAPE RESPONSES IN PACIFIC SPINY DOGFISH (SQUALUS SUCKLEYI) DURING MECHANICAL AND ELECTRICAL STIMULI.

Abstract

The kinematics and characteristics of escape responses have been heavily studied in teleost species. With some elasmobranchs being seen as mesopredators, escape responses do occur within this category of animals, thereby making the kinematics of the particular escape responses important parameters to understand in terms of predator-prey interactions; an area that is missing empirical data. This study have been divided in to two parts, with Part A concentrating on the latency of escape responses of the Pacific spiny dogfish, Squalus suckleyi, during mechanical stimuli, and Part B containing the an analysis of how the pacific spiny dogfish react when exposed to electrical and electrochemical stimuli in the form of a by-catch reduction device (BRD) and mischmetal, respectively. Latency was found to be slower than that found for teleost species, during mechanical stimuli. As several studies has found Mauthner cells in all teleost species and connected their function to their fast latency when reacting to a potential predator threat, our results suggest that the lack of Mauthner cells in elasmobranchs is resulting in a higher latency time. The kinematics of escape responses during electrical and electrochemical stimuli showed that these types of stimuli provoked slow escape responses compared to more sudden stimuli like mechanical stimuli and attack from a predator. Additionally, the turning angles of these escape responses was found to be quite large and the response to both the BRD and the mischmetal might be categorized more as an avoidance than escape. This supports the incentive that these devices can be used in the fishery industry to reduce their bycatch of elasmobranches and increase their capture efficiency.