Fish and benthic biodiversity at the Point Murat Navy Pier, Exmouth Gulf, Western Australia

Fish and benthic surveys were carried out within the environs of the Navy Pier at Exmouth from 9-11 March 1996 and 2-6 April 2001. The benthic community of the pier, dolphins and surrounds was assessed using underwater video. During both surveys video footage of the same 17 pylons was taken while swimming from the surface to the bottom of each pylon on one side and while returning to the surface on the opposite side. General video footage was also taken of the surrounding habitat to help with identification of fish and benthic organisms. The video tapes were analysed using AVTAS, a quantitative benthic analysis package developed by AIMS. The same benthic categories were used for both surveys. During the 1996 survey, a comprehensive list of the fish fauna associated with the pier, dolphins, and immediate surrounds, was obtained over a period of three days, whilst using SCUBA. All adult and juvenile fish encountered were identified to species level. Juveniles were defined as the phase when the fish larvae leave the plankton and enter the adult habitat. No attempt was made to quantify fish numbers.In 2001, the survey of the fish assemblages at the pier and Bundegi Reef was conducted in two stages. During the first stage, a comprehensive fish species list was developed separately for the pier and the demarcated area of Bundegi Reef, by recording all new fish species encountered while diving. This process was followed through consecutive dives until 20 minutes of continual searching yielded no more new species.During the second stage only the pier was surveyed. Semiquantitative counts were made of those species from the major fish families. Because of the large numbers of species and individuals present at the pier and their highly mobile nature, absolute counts were considered unreliable. A more flexible technique was used whereby fish numbers were estimated using Log5 abundance categories.

The objectives of the 1996 survey were to provide a quantitative assessment of the benthic habitat including all living and non-living biota and a qualitative assessment of the fish community associated with the pier, its dolphins and the immediately adjacent habitat. In the 2001 study, a more comprehensive assessment of the marine fauna associated with the Navy Pier was undertaken, thereby providing a scientifically rigorous base for future reference. The objectives were to:- compare estimates of the percentage cover of benthic groups with that found by similar surveys conducted in 1996;- compare estimates of fish diversity with those found by similar surveys conducted in 1996; - provide fish abundance estimates for the major fish families found at the pier;- assess the uniqueness of the fish assemblage of the pier by comparing fish diversity estimates with the nearby Bundegi Reef ; and- in light of the results obtained above, outline the conservation significance of the marine fauna at the pier and recommend appropriate measures to be taken for effective, ongoing management of the area.

Built in 1964, the pier is a significant structure both above and below the water. It is constructed primarily of steel pylons and consists of the main pier head (49.7 m x 25.5 m) with two breasting dolphins each connected by a catwalk. The main pier is accessed by a walkway and has two mooring dolphins (as distinct from the breasting dolphins), which lie approximately 100 m in a north and south direction of the main pier head.