The role of estuarine and inshore-marine environments in the life cycles of the exploited marine fish species of temperate Western Australia

Rodney Charles John Lenanton

The way in which "estuarine-dependent" fish use selected permanently open, seasonally open, and normally closed estuaries, and inshore marine waters is discussed. Attention is initially focused on the impact of reducing the connection between the sea in those estuaries in which bars tend to form at their mouths, and the effect of the resultant fluctuations in salinity on the composition and abundance of the estuarine fish community. Many of the commercially important and alleged "estuarine-dependent" marine species utilise nearshore marine habitats as an alternative to those provided by estuaries, even when a bar does not prevent access to the estuary. Many of these nearshore marine habitats, particularly the surf-zone, often harbour large accumulations of detached macrophyte detritus. Most of the fish caught in the surf-zone were represented by juveniles, and a number were important commercial species that were also abundant in estuaries. The total number of fish was strongly correlated with the amount of detached macrophytes present. The dominant species caught fell into two groups, i.e. those that were equally abundant in weeded and non-weeded surf-zones, and those that were almost exclusively found in weed. Dietary analyses of fish, allied with the large numbers of pisciverous cormorants present, show that the weed in the surf-zone provides a rich feeding site and suggests that it is a refuge from diurnal predation. The number of the commercially important Cnidoglanis macroceQhalus (mainly O+) was positively correlated with both the volume of fine red algae and dead seagrass. These respective two components of the drift have been shown to provide a habitat and food supply for the amphipod Allochestes comQressa, which is a major food item of the surf-zone populations of C.macrQQeQhalus. The contribution of the weight and value of "estuarine-dependent" finfish species to the total commercial fishery of temperate Western Australia was shown to be 20.3 and 2.4% respectively. Since many "alleged" "estuarine-dependent" species also use protected inshore marine waters as nursery areas in both south-western Australia and in other regions of temperate Western Australia where estuaries are absent, these species cannot be considered to be entirely dependent on estuaries. It is therefore preferable to regard these species as "estuarine-opportunists".

The role of estuarine and inshore-marine environments in the life cycles of the exploited marine fish species of temperate Western Australia

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