Date of Award

2013

Degree Type

Thesis

Degree Name

Doctor of Philosophy

School

School of Natural Sciences

Faculty

Health, Engineering and Science

First Advisor

Dr Glenn Hyndes

Abstract

This thesis examines the biological and ecological aspects of members of the globally exploited Epinephilidae with reference to fisheries management and in particular the use of closures. The leopard coralgrouper Plectropomus leopardus is a common reef fish throughout the Indo-Pacific region and a major target of both commercial and recreational fisheries. There has been limited research on this species in the eastern Indian Ocean, where there are only two populations. An examination of the species found a number of significant biological differences to their eastern Australian con-specifics. Most noticeable was the strong size-related cue over their protogynous sex change. The lack of the typical social mechanisms regulating sex change for this family ultimately resulted on a spatially explicit pattern in spawning omission. After an assessment of a number of anthropogenic and environmental parameters, fishing pressure was found to be the likely cause behind spawning omission. Spawning was restricted to areas where fishing pressure was light (i.e. within protected areas), and fish were able to attain a size where they could become male. The strong link between spawning sites and males, coupled with historical samples of spawning fish at locations where current extensive sampling revealed none, re-affirms the hypothesis of fishing pressure causing spawning omission. Histology, underwater visual census and acoustic tracking were used to determine the spawning aggregation dynamics of leopard coralgrouper at some of these spawning sites. Results yielded interesting differences from the GBR population and a number of other epinephelids. At the Abrolhos Islands, spawning was not limited to the new moon, but also encompassed the full moon, with a distinct difference between male and female attendances at aggregation sites. Females only attended aggregations during these lunar phases, while males moved to the aggregations almost daily during the spawning season. The formation of aggregations in the morning and their cessation by the afternoon provided a major departure from almost all other examples of spawning aggregations in Epinephelidae, which are considered to undertake a dusk spawning. Acoustic telemetry of leopard coralgrouper at the Abrolhos Islands indicated the species is generally sedentary, which is consistent with the suite of epinephelids that were tracked at Ningaloo Reef. Twenty fish from six species of Epinephelidae were tracked for up to two years revealing highly sedentary, habitat attached movement patterns. There was limited movement between habitats, with channels bisecting the reef slope, providing a natural barrier to fish movement. The findings of the thesis are all discussed with reference to fisheries management and in particular spatial and temporal closures. They all provide evidence toward a common finding that management measures must take into account local species-specific biological and ecological characteristics.

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