Publication Date

10-1996

Series Number

Fisheries Research Report No 108

Publisher

Fisheries Department of Western Australia

City

Perth

ISBN

0 7309 1920 X

ISSN

1035 - 4549

Abstract

The biology, distribution and stock size of whitebait along the lower west coast of Western Australia were studied between 1991 and 1994. Age, growth and reproductive biology of whitebait were investigated using samples collected from the commercial fishery. The distribution of adult whitebait and their main spawning times were determined using data on eggs that were caught in plankton samples. Aspects of the population dynamics of whitebait were investigated by examining the relationships of historical catch data with fishing effort and some environmental parameters.

Whitebait are a small species with most growth occurring in the first year (K = I. 52, T0 = 0. 042 and L00 = I 00). They are also a short-lived species, having a maximum age of three or four years, and an estimated natural mortality rate of 1.5. The catch of whitebait from the Swan Estuary, Warnbro D Sound and Bunbury predominantly consists of fish less than two years old, while the catch from' Mandurah is mainly fish less than one year old. First spawning by whitebait occurs when they are 65-80mm in length and at an age of about one year. Whitebait are batch spawners, with females producing 750- 3500 eggs every three to five days during the peak of the spawning season.

Plankton samples indicated that whitebait predominantly spawn from May to August (i.e. winter) with a peak in June and July. The distribution of eggs showed that populations of adults occur along the entire coast coast between Fremantle and Bunbury and that whitebait do not normally extend very far offshore, with the bulk of eggs occurring within JO km of the coast. Even within this region, the numbers of eggs found were not usually large and were highly variable, indicative of a small, patchy stock. The plankton data obtained in July 1994 indicated that the spawning biomass was likely to be less than I 000 t. Since populations of whitebait in the study region are not large, are apparently restricted to the nearshore waters, and the bulk of the population consists of only two year classes, they are likely to have little resilience to increases in fishing pressure.

Annual catches of whitebait have been strongly influenced by environmental factors. In particular, there was a strong, positive relationship between the annual catch of whitebait and the strength of the Leeuwin Current in the previous year. There was also a relationship between annual catch in some regions and the strength of the Leeuwin Current in the previous 2 years. Although a direct effect of the Leeuwin Current on whitebait has not been established, the lag period in the relationship suggests that it is likely that this current influences recruitment success. Interannual variations in the strength of the Leeuwin Current may also affect the behaviour of whitebait (e.g. movements within an area) and, therefore, their catchability. Recommendations for the sustainability of the whitebait resource along the lower west coast of Western Australia are provided.

Number of Pages

136

Keywords

Whitebait (Hyperlophus vitttatus), south western Australia, Western Australia, Recreational fishing

Disciplines

Aquaculture and Fisheries | Marine Biology | Natural Resources and Conservation | Natural Resources Management and Policy | Sustainability

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