A recently published research paper by a team of top fisheries scientists in the early 2000s has shown that a major stocking program initiated by recfishers rescued WA’s highly acclaimed Blackwood River black bream fishery from the brink of collapse due to overfishing and a declining estuary environment.
A team of top Murdoch University and Fisheries scientists put the stocking program under the microscope assessing all the data that had been collected following the release of more than 220,000 juvenile black bream into the Blackwood in Western Australia’s South West in 2002 and 2003.
The scientists’ mission was to assess whether restocking fish can be an effective way to jump-start declining estuary fish stocks to get them firing again.
Future proofing fish stocks
With decreasing rainfall, changing climate, many estuary environments and fish stocks have never been under more pressure. Finding science-driven innovative solutions to future-proof fish stocks is becoming increasingly important for the recfishing community.
The stocking project was first launched following a period of sharply falling recfishing and commercial catches of black bream from the Blackwood – surveys by Murdoch University showed that rec catches had fallen 85 per cent over three decades since the 1970s and all but one commercial black bream fisher chucking it in.
In addition, studies had shown the Blackwood River to be in a declining state of health since the ‘70s as the result of a number of factors including average rainfall falling by around a third, reduced run off and river water flow, along with impacts from agriculture and wine-making. This had all lead to reduced freshwater flows into the Blackwood, lower oxygen levels and some algal blooms leading to an increase in fish deaths. A further issue was that black bream remain residential in the estuary with limited mixing with other stocks which limits their breeding opportunities.
A team from the Challenger Institute of Technology, working closely with the Murdoch University, the Fisheries Research and Development Corporation, the West Australian Fish Foundation and supported by Recfishwest took ‘brood-stock’ black bream from the Blackwood in order to breed and rear the juvenile black bream.
The scientists stained the otoliths – the fishes’ ear bones – with a special purple dye that is still clearly visible more than 15 years later allowing them to easily identify the stocked fish when caught and scientifically examined later. This is a process called “otolith-tagging” and is crucial to restocking monitoring studies like this. An initial batch of 70,000 of the juvenile fish were released in 2002 and a further 150,000 were released a year later.
Within five years of the release of the fish, the numbers of legal-size black bream in the river had quadrupled. Critically, sampling demonstrated that half of the very strong pulse of fish spawned in 2008 came from the restocked bream.
Everything you want in a bream fishery
This shows that introducing a large batch of stocked fish into an estuary can effectively ‘turbo-boost’ the breeding output of the overall fish population and help revive and rejuvenate a struggling fishery like the Blackwood once was.
The study revealed fish coming from the 2008 class contributed between 50 and 80 per cent of the river’s commercial catch between 2015 and 2017 – but more importantly for the local community and recfishers the quality of black bream fishing in the Blackwood is being restored.
“It’s the best bream fishing river we have – it’s the jewel in the crown” says Ian Sewell, avid WA bream fisher and organizer of multiple WA bream fishing comps in the Blackwood over the years.
“It’s got everything you want in a bream fishery – varied submerged structure, deep water, steep reed banks, rock walls and rock bars – all good fish-holding terrain. It was always a good fishery but in recent years it’s just got better and better.
“In the past ‘Blind Freddy’ could see there were gaps in the sizes of fish – where you’d catch 25 cm fish and 32-35 cm fish with nothing in between – but the sign of a healthy fishery is where you see fish of all sizes small, medium large and extra large showing up in catches. It’s the progeny of that initial stocking that appears to have the biggest impact – 10 years later they were still spawning.”
Thanks to the quality of fishing being restored in the Blackwood – the river is now one of the choice locations for bream fishing comps at both a state and national level.
One of the premier bream comps run out of Augusta is the qualifying heat for the ABT Bream series, which sees around 20 boats with fishers from all over the country going toe to toe in a two-day tournament.
“It’s a lucrative catch and release tournament with zero fish mortality,” says ABT Bream Series organiser and Fishing Monthly Magazine Owner Steve Morgan. “It’s in a nice corner of WA – a ‘natural’ river flowing through some really pretty country.
“The fish look really good – dark and golden – and the river’s full of barnacle-encrusted snags, so it’s a real fishing challenge and attracts bream enthusiasts from all over. All the visiting fishers spend money on accommodation and hospitality in Augusta, so there is a really great net worth to the community.”
It’s a view shared by Augusta X-treme Outdoor Sports and Camping owner Bernice Gillam.
“I’d say 30 to 40 per cent of my business is for bream fishing gear,” she says. “We always get the out-of-towners asking what’s the best rigs for bream and all the bream competitions we get on the river are very important for the local economy. Every time someone releases a bream someone else buys a lure to catch it, so each bream provides great value time and time again.”
All of this supports the stocking program research project’s conclusion: “Restocking can be very effective in replenishing a stock of an estuarine resident species such as [black bream]… given the sporadic and infrequent recruitment events for this iconic recreational species in the Blackwood River over a 20-year period, periodic releases of cultured fish are likely to benefit the stocks and help sustain recreational fishing in the estuary.”
Here, then, is a clear example of where stocking has been dramatically successful and where the resulting economic and social value of the fishery to the local and recreational fishing community is substantial.
With increasing environmental pressures on our estuarine fisheries, fishery managers must embrace stocking as an important tool in managing estuary fish stocks especially as the climate and fish recruitment become more variable.