Tracking sharks without teeth: a non-invasive rigid tag attachment for large predatory sharks

Abstract

Many marine species are difficult to study because components of their lifecycles occur solely or partially outside of the observable realm of researchers. Advances in biologging tags have begun to give us glimpses into these unobservable states. However, many of these tags require rigid attachment to animals, which normally requires catching and restraining the animals. These methods become prohibitive with large, dangerous, or rare species, such as large predatory sharks, and can have significant consequences for individual survival and behavior. Therefore, there is a need for methods and hardware to non-invasively and rigidly attach biologging tags to large predatory sharks that presents limited effects on the animals and researchers. Here we test a clamp tag and methods to non-invasively and rigidly attach biologging tags to white sharks (Carcharodon carcharias) in Gansbaai, South Africa. We developed stainless steel dorsal fin attachment clamps with abrasive pads for deployments of biologging devices on large marine organisms. We deployed 35 tags on 34 white sharks, which after modification, remained rigidly attached to the animals up to 93 h, even through significant dynamic motions, and released from the animals with little or no effect on the animals. These tags and attachments present a technique and hardware to equip large predatory sharks with biologging tags without the need to catch or restrain them, and with some additional modification, these tags may remain on the animals for long periods with potentially reduced risk for both researcher and animal.