Publication Date

6-2008

Series Number

176

Publisher

Department of Fisheries, Western Australia

City

Perth, Western Australia

ISBN

1 921258 26 8

ISSN

1035 - 4549

Abstract

Final FRDC Report – Project 2000/135

This project produced time series of estimates of spawning biomass for pilchards in four purse seine management zones in Western Australia, three on the south coast and one on the west coast. The pilchard stocks in Western Australia have recovered strongly since the 1998/99 mass mortality.

This project has shown that the fishery independent and fishery dependent methods applied to Western Australia’s pilchard fisheries cannot provide precise estimates of the size of the pilchard spawning biomass in each management region. Although the trends indicated by the age-structured simulation model are reliable and provide good evidence for a strong recovery of pilchard stocks, the magnitude of changes in stock size from year-to-year are not known with sufficient certainty to allow high rates of exploitation.

The demonstrated increases in pilchard spawning biomass has lead to optimism for the future of the purse seine industry in southern WA, which in turn has encouraged this industry to be proactive in ensuring that exploitation rates were not set at levels that were too high to impede the recovery of the stock or put undue pressure on the long term viability of the stocks. Tracking the progress of estimating of pilchard biomass in each region over the duration of this project was a crucial factor that assisted industry members to better appreciate the need to examine factors additional to the point estimate of biomass generated in any one year.

The project also determined that the growth rates of pilchards in WA can be highly variable, sometimes changing markedly from year to year while at other times exhibiting more gradual changes over several years. The tendency for a negative relationship between annual growth rates and stock size suggests density dependence, which in turn supports the contention that that pilchard stocks in this region are limited in size by the biological and oceanographic characteristics of the continental shelf waters of southern WA. The magnitude and variability of pilchard biomass observed during this project builds on the knowledge obtained during the 1990s, providing a strong basis against which the purse seine industry can expect future quota levels to be set.

Number of Pages

82

Keywords

Pilchard (sardine), Recruitment, Age-structured model, Spawning biomass, Daily egg production method, Stock recovery, Fisheries management

Disciplines

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

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