Aligning habitat use with management zoning to reduce vessel strike of sea turtles

Vessel collision is a recognised threat to sea turtles residing in coastal waters. Although management systems (i.e. Go Slow Zones) are in place in some areas to minimise vessel-turtle collisions, incidents may persist when the spatial extent of the protection and habitat use by animals do not match or when turtle populations increase. In Queensland, Australia, most incidents are recorded in the Moreton Bay region despite enforcement of the Go Slow Zones in some of the bay's shallow water zones (water depth ≤ 5 m). Our study investigated the degree to which the current Go Slow Zones provide protection to sea turtles in Moreton Bay, and the potential for improvement of current management initiatives. We tracked 18 green (Chelonia mydas) and 20 loggerhead (Caretta caretta) turtles using Argos-linked Fastloc GPS tags for periods between 22 and 999 d, and examined how they used habitat in relation to the Go Slow Zones and water depth. We found that the highest protection was provided to green turtles (39%) and loggerhead turtles (55%) residing in the eastern side of Moreton Bay, where most of the current Go Slow Zones are located. However, we also found that the current Go Slow Zones offer little or no protection to turtles using southern, western and northern Moreton Bay, or any deeper water zones (water depth > 5 m). Given the frequent use of the shallow areas by our study turtles, if all shallow zones in Moreton Bay were to be designated as Go Slow Zones, nearly a half or more of their habitats could be protected from vessel operation. Additionally shallow zones plus a 1.2 km, 2.4 km, or 3.6 km buffer could protect ≥80%, ≥90% or ≥95% of their habitats as the extra areas cover the deeper zones adjacent to the shallow zones. Our findings are highly informative to conservation managers when revising or developing Go Slow Zones in Moreton Bay, with potential application to the management of other coastal areas used by sea turtles globally.