Harnessing the Sun: Testing a Novel Attachment Method to Record Fine Scale Movements in Ocean Sunfish (Mola mola)

Abstract

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.