Migration dynamics of juvenile southern bluefin tuna

Toby A Patterson,Karen Evans,Campbell R Davies,Matt Lansdell,Alistair J Hobday,Jason R Hartog,Scott Cooper,J Paige Eveson

doi:10.1038/s41598-018-32949-3

Toby A Patterson, Karen Evans + Show 6 more

Open Access

https://doi.org/10.1038/s41598-018-32949-3

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Journal: Scientific Reports	Publication Date: Sep 28, 2018
Citations: 10	License type: open-access

Affiliation: CSIRO Oceans and Atmosphere

Abstract

Large scale migrations are a key component of the life history of many marine species. We quantified the annual migration cycle of juvenile southern bluefin tuna (Thunnus maccoyii; SBT) and spatiotemporal variability in this cycle, based on a multi-decadal electronic tagging dataset. Behaviour-switching models allowed for the identification of cohesive areas of residency and classified the temporal sequence of movements within a migration cycle from austral summer foraging grounds in the Great Australian Bight (GAB) to winter foraging grounds in the Indian Ocean and Tasman Sea and back to the GAB. Although specific regions within the Indian Ocean were frequented, individuals did not always return to the same area in consecutive years. Outward migrations from the GAB were typically longer than return migrations back to the GAB. The timing of individual arrivals to the GAB, which may be driven by seasonality in prey availability, was more cohesive than the timing of departures from the GAB, which may be subject to the physiological condition of SBT. A valuable fishery for SBT operates in the GAB, as do a number of scientific research programs designed to monitor SBT for management purposes; thus, understanding SBT migration to and from the area is of high importance to a number of stakeholders.

Highlights

Annual migrations allow animals to exploit spatially varying resources such as food or breeding habitat[1,2]
For temperate species living in seasonal environments, have been associated with seasonal shifts in the abundance of lower trophic level prey species and juvenile SBT migrations are presumed to represent a strategy for maximizing growth[16]
The migratory dynamics of SBT over a number of years have been generalized by pooling data from many individuals across a number of years[15], the degree of synchronicity in departure from and return to the Great Australian Bight (GAB) and understanding of the environmental drivers associated with migrations to and from the GAB is limited

Summary

Introduction

Annual migrations allow animals to exploit spatially varying resources such as food or breeding habitat[1,2]. Juvenile (ages 1–4) SBT aggregate in southern Australian waters throughout the austral summer from south of Western Australia across to eastern parts of the Great Australian Bight (GAB)[14]. From here they disperse westwards into the Indian Ocean or eastwards into the Tasman Sea during the autumn, before returning to the GAB in the following summer[15]. Resident Outward Inward GAB region juvenile SBT to: characterize movement rates conditional on behavioural state (resident or migrating); quantify the extent and synchronicity of the migrations of individuals to and from the GAB; and determine key areas of residency and, by association, potentially important habitat. Understanding SBT migration to and from the area is of high importance to an international fishery, and more broadly, it contributes to a better understanding of the entire region, which is one of Australia’s most valuable marine ecosystems[19]

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