Novel use of pop-up satellite archival telemetry in sawsharks: insights into the movement of the common sawshark Pristiophorus cirratus (Pristiophoridae)

Abstract

Background Understanding movement patterns of a species is vital for optimising conservation and management strategies. This information is often difficult to obtain in the marine realm for species that regularly occur at depth. The common sawshark (Pristiophorus cirratus) is a small, benthic associated elasmobranch species that occurs from shallow to deep-sea environments. No information is known regarding its movement ecology. Despite this, P. cirrata are still regularly landed as nontargeted catch in the south eastern Australian trawl fisheries. Three individuals were tagged with pop-up satellite archival tags (PSATs) off the coast of Tasmania, Australia, to test the viability of satellite tagging on these small elasmobranchs and to provide novel insights into their movement. Results Tags were successfully retained for up to three weeks, but movement results differed on an individual basis. All three individuals displayed a post-release response to tagging and limited vertical movement was observed for up to 5–7 days post-tagging. Temperature loggers on the tags suggest the animals were not stationary but moved horizontally during this time, presumably in a flight response. After this response, continuous wavelet transformations identified diel vertical movements in one individual at cyclical intervals of 12- and 24-hour periods, however, two others did not display as clear a pattern. Temperature was not significantly correlated with movement in the study period. The deepest depths recorded during the deployments for all individuals was approximately 120 meters and the shallowest was 5 meters. Conclusions This study demonstrates that sawsharks can be successfully tagged by pop-up satellite archival tags. The data presented here show that sawsharks regularly move both horizontally and vertically in the water column, which was an unexpected result for this small benthic species. Additional research aimed at resolving the trophic ecology will help identify the drivers of these movements and help to better define the ecological, behavioural and physiological roles of these sharks in their ecosystems. These data describe a substantial ability to move in the common sawshark that was previously unknown and provides the first account of movement ecology on the family of sawsharks: Pristiophoridae.

Diving into the vertical dimension of elasmobranch movement ecology

“…Many elasmobranch species showed high intraspecific variation and plasticity in DVMs, displaying various combinations of nDVM, rDVM, and neutral patterns. Variation in DVM can result from prevailing environmental conditions ( 40 ), bathymetry, spatial and temporal variation in prey distribution ( 41 ), and/or sample size limitations ( 42 ). Reef manta rays, for example, displayed nDVM patterns around the Chagos Archipelago ( 28 ), rDVM around the Seychelles ( 43 ), and both patterns off eastern Australia ( 44 ), presumably due to site-specific vertical distributions of zooplanktonic prey and baseline productivity.…”