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Government of Western Australia - Department of Fisheries

Herring science

​Research by our scientists has revealed that a combination of environmental factors and fishing pressure has diminished the Australian herring (Arripis georgianus) stock in southern Australian waters.

Our 2013 report on the status of the herring stock was part of the most rigorous assessment of nearshore finfish species ever carried out in the West Coast Bioregion (from Black Point, east of Augusta, to the Zuytdorp Cliffs, north of Kalbarri).

This independently reviewed assessment considered past and present levels of fishing mortality, catch composition and trends in catch rates and recruitment (addition of young fish to a population). It also considered the vulnerability of the stock to depletion due to biological characteristics such as growth rate and fecundity (potential reproductive capacity).

Environmental factors including a steady rise in ocean temperatures and unusual flow patterns in the Leeuwin Current are thought to have contributed to a drop in herring recruitment over the past decade.

While Australian herring are part of a single stock that stretches from the west coast of Western Australia along our south coast to South Australia and into Victoria, WA waters have a special part to play in the herring life cycle. This is because adult herring , which spawn from late May to early June, are only known to spawn on WA’s lower west coast, and mainly in the metropolitan area and south to Geographe Bay.

In years when the south-flowing Leeuwin Current is strong, eggs and larvae are carried from WA’s lower west coast all along the south coast, and as far east as Victoria. But in years of a weak current, more eggs and larvae stay on WA’s west coast. Herring stay wherever they settle until reaching maturity, when they migrate along the south coast back to our west coast to spawn. The herring then stay on WA’s west coast – there is no return migration.

Herring life cycle


In some years a strong Leeuwin Current carries most herring eggs and larvae south and as far east as Victoria. On reaching maturity, the herring migrate back to WA's lower west coast to spawn. The herring then remain on WA's west coast – there is no return migration eastward.

 

Each year our researchers examine hundreds of fish skeletons donated by fishers to obtain information about the herring population, including its age structure (the number of fish of different ages). The 2013 assessment revealed that just two adult age classes – two and three-year-olds – formed most of the population. For a healthy population, there need to be more fish in the older age classes.

Herring can live for 12 years but most caught are aged one to four years. As herring mature sexually at two to three years, most are caught before they spawn or after only breeding once. So just two or three consecutive years of recruitment failure can create a serious problem.

The level of fishing mortality has increased over the past 10-15 years and is now well above the sustainable level for herring. Commercial and recreational catches from South Australia and WA’s south coast add up to about 75 per cent of the annual catch – so high numbers of herring are removed before having a chance to spawn.

Breeding females vulnerable

In addition, fishers on WA’s west coast are targeting the remaining fish that have made it into the adult breeding stock. West coast fishers usually target herring during autumn when they aggregate (gather) before spawning. These pre-spawning groups include young fish spawning for the first time as well as older fish.

For reasons that are not clear, breeding females are particularly vulnerable to being caught by line at this time. The west coast recreational catch during the spawning season is dominated by females – roughly 80 per cent of the total catch.

Fishers may catch many herring in one particular area, which may give the impression of a thriving stock. And the fact herring travel in schools can add to this perception. But this is deceptive. Herring prefer cooler water and many have failed to migrate to the west coast to spawn in recent years due to exceptionally warm ocean conditions, which have disrupted their migration and spawning patterns.

This has meant plenty of herring on WA's south coast, but very low numbers on our west coast. The unfavourable ocean conditions have also resulted in low spawning success.

While the status of the herring stock is a concern, we have successfully tackled similar challenges in recent times. For example, management measures taken to reduce fishing pressure on demersal fish stocks have begun to reverse a decline. And in WA’s rock lobster fishery, action taken in response to environmental impacts has led to a significant recovery.

Herring is a much shorter-lived, faster-growing species than demersal species such as West Australian dhufish or pink snapper. So if fishing pressure is reduced to allow more herring to grow to maturity and spawn, some evidence of recovery would be expected after five or six years with a fuller recovery expected in about 10 years.  

For more information, see frequently asked questions about herring.

Last modified: 20/02/2015 2:07 PM

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