Impact of cyclones and aquatic macrophytes on recruitment and landings of tiger prawns Penaeus esculentus in Exmouth Gulf, Western Australia

N.R Loneragan,M Kangas,M.D.E Haywood,R.A Kenyon,N Caputi,E Sporer

doi:10.1016/j.ecss.2013.03.024

Abstract

The cover of seagrasses and macroalgae, landings and fishery-independent measures of spawning stock and recruitment for brown tiger prawns, were monitored immediately following a major cyclone in Exmouth Gulf, Western Australia in March 1999. Anecdotal evidence on the extent of seagrass from 1990 to 1998 suggests that the cyclone caused a major, immediate disruption and loss of the seagrass/macroalgal beds (to ≤2% cover), the critical prawn nursery habitat, and mangroves in the shallow inshore waters of the system. Prawn landings and recruitment to the fishery were not affected in the year of the cyclone, but were markedly lower in the two years immediately afterwards and then increased as the cover of macrophytes increased to over 40% in 2003. Tiger prawn landings and catch rates were not affected in Shark Bay, a system 500 km south of Exmouth Gulf that did not experience cyclonic disturbance. Seagrasses in Exmouth Gulf showed a succession of species from small colonising species (Halophila ovalis and Halodule uninervis) to larger, broad-leaved species (Cymodocea serrulata, Syringodium isoetifolium) only two years after the cyclone. The recruitment and landings of tiger prawns were correlated significantly with the total cover of macroalgae and seagrass. The large loss of seagrass and macroalgae reduced the settling habitat for postlarvae and the nursery habitat for juvenile tiger prawns, probably leading to the lower recruitment to the fishery. These findings suggest that the extent of seagrass and macroalgae are some of the factors defining the productivity of the tiger prawn fishery in Exmouth Gulf.

Highlights

Coastal habitats, vegetated habitats such as seagrass, mangroves and salt marsh are important habitats supporting fisheries production and biodiversity (e.g. Manson et al, 2005; Gillanders, 2006; Lotze et al, 2006; Waycroft et al, 2009)
The intertidal mudflats are lined with dense stands of mangroves, mainly Avicennia and Rhizophora species, that make up one of the largest mangrove areas in Western Australia (Paling et al, 2008)
Cyclone Vance has been the only major cyclone in the last 40 years to pass through the centre of Exmouth Gulf, travelling from north to south and running parallel to the western and eastern coastlines of the Gulf, before crossing the coast in the south (Fig. 2)

Summary

Introduction

Vegetated habitats such as seagrass, mangroves and salt marsh are important habitats supporting fisheries production and biodiversity (e.g. Manson et al, 2005; Gillanders, 2006; Lotze et al, 2006; Waycroft et al, 2009). Vegetated habitats such as seagrass, mangroves and salt marsh are important habitats supporting fisheries production and biodiversity Manson et al, 2005; Gillanders, 2006; Lotze et al, 2006; Waycroft et al, 2009). Seagrasses and algae provide important feeding habitats for species of conservation significance, such as dugongs and turtles (Gales et al, 2004). These coastal habitats are facing increasing threats from anthropogenic influences These coastal habitats are facing increasing threats from anthropogenic influences (e.g. Costanzo et al, 2001; Jackson et al, 2001; Gillanders, 2006) and since 1990, the loss rates of seagrass ecosystems have been similar to those for mangroves, coral reefs and tropical rainforests, making them among the most threatened ecosystems on earth (Waycroft et al, 2009).

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Results

Conclusion