Macrozooplankton from the southern North West shelf, Western Australia

The distribution and abundance of macrozooplankton on the southern North West Shelf of Western Australia was investigated over two consecutive summers (October to February) of 1997-1998 and 1998-1999, using submersible light traps. Sampling was conducted over a period of 10 days centred on successive new moons. Traps were deployed at the surface and at depth along one cross-shelf transect in the first summer, and along two cross-shelf transects and one long-shore transect in the second summer.At each station, a CTD equipped with a fluorometer was deployed within a few metres of the bottom concurrently with light trap sampling. Wind speed and wind direction were obtained from the weather station at Milyering.On retrieval, catches were immediately preserved in ethanol. In the laboratory, one sample of catches from each of the paired light traps was sorted into 14 broad taxonomic groups, distinguished with the unaided eye and counted.Vertical zooplankton hauls were to a maximum depth of 60m using a 0.5 m, WP-2 net of 73 µm mesh fitted with a flowmeter. Samples were filtered through a mesh dish and frozen. This research was undertaken to describe the temporal and spatial distribution of macrozooplankton on the North West shelf, using submersible light traps. The relationship between observed distributions and environmental parameters was also investigated. The euphausiids, which are difficult to capture by other means were chosen for more detailed examination.