Reef fish survey methods and application to population dynamics of parrotfish within the Kingdom Tonga

Abstract

With environmental and anthropogenic impacts coral reef communities worldwide are predicted to decline. This is of particular concern for the Pacific Island nations’ such as the Kingdom of Tonga. This thesis aimed to identify a method that could be applied to the collection of baseline data for shallow water coral reef fish communities, in particular to parrotfish. Parrotfish have been identified as a key ecosystem species on inshore coral reefs, and potentially indicators of reef health. A comparison of stationary and swim video Underwater Visual Census methods revealed similar results, but for both methods the stationary method overall had greater benefits. This method was then applied to the second aim of this thesis, investigating the population dynamics of parrotfish within the semi-enclosed lagoon of Tongatapu. All parrotfish were counted, and their behaviour and the size of the harem they were seen in were recorded. Terminal phase and, when possible, initial phase individuals were identified to species level for species richness. This identified 14 parrotfish species and one key species, Chlorurus spilurus (identified previously in the Pacific as Chlorurus sordidus). Very few harems contained a male, instead comprosing mainly of juveniles and initial phase individuals. Factors influencing these dynamics were identified, such as site factors; coral reef health, distance from mainland, anthropogenic and environmental influences. Through providing temporal baseline and understanding of population dynamics these results will assist in future management of inshore reef fisheries of parrotfish, with potential influence on the resilience of the coral reef health within the semi enclosed lagoon of Tongatapu.