ASFB Home > The effects of spatial and temporal factors on the abundance of seven key finfish species along south-western Australia.

Recolonisation of seagrass in Exmouth Gulf following a severe tropical cyclone: A study of the seagrass community and brown tiger prawns (Penaeus esculentus)

Robert Kenyon, Mick Haywood, Neil Loneragan and Richard McCulloch

CSIRO Marine Research, CLEVELAND, AUSTRALIA

THEME: ASFB

Abstract Inshore seagrass habitats act as nurseries for the tiger prawn fishery in Exmouth Gulf. In March 1999, Cyclone Vance devastated the Gulf's seagrasses. The benthic habitats and juvenile tiger prawns in Exmouth Gulf were surveyed for 3 years following Cyclone Vance for a project on stock enhancement techniques for tiger prawns (FRDC 1999/222). In June 1999, the average seagrass cover in Exmouth Gulf was only 0.15% and 70% of 119 sites surveyed were bare. By November, the seagrass cover remained sparse (1.2%) with no sites > 20% cover. By November 2000, seagrass cover had increased to 10.3%. The dominant species in 1999/2000 were Halodule uninervis and Halophila ovalis; early recolonising seagrasses. Average seagrass cover increased markedly between 2000 and December 2001, to 41.9%. Halophila spinulosa, Cymodocea serrulata and Syringodium isoetifolium were dominant. In October/December 1999, catches of juvenile tiger prawns in small beam trawls were very low (< 1 prawn per 100 m-2). Although catch rates of juveniles were higher in 2000/2001 than 1999, they remained low i.e. < 3 prawns per 100 m-2. Commercial tiger prawn landings the year after the severe cyclone (2000) were only 82 t; well below the 10-year range of 200 to 680 t. Landings increased to 208 t in 2001 and are predicted to reach 330 t in 2002. The rapid recovery of seagrasses following the impact of Cyclone Vance contrasts with seagrass recovery rates recorded elsewhere in tropical and temperate Australia. The results also highlight the link between coastal habitats and commercial fisheries.