Slots in dyke walls won’t fix mulloway fishery

Hardly a week goes by without another announcement from government that additional millions of dollars will be spent ostensibly improving the environment of the Lower Murray. Such announcements are popular with the general public in South Australia. They mostly believe the propaganda that the Lower Lakes really do represent a wetland of international importance and that government expenditure can somehow buy further improvement. In reality their dammed estuary, known as Lake Alexandrina, surrounded by rabbit-infested farmland and overpriced housing estates is brimming with invasive European carp (Cyprinus carpio) and the voracious predatory English perch, otherwise known as redfin (Perca fluviatilis). A few more fishways, as proposed in the latest $2.9 million funding announcement from the South Australian Minister for the River Murray, Ian Hunter, won’t change this dynamic. Key estuarine species, once important to the local fishery need more than distressed tepid water, they need a tide.

The Minister claims in the media release that the fishways will provide: “Greater access to breeding areas and different feeding grounds while facilitating the spread of rare native species in the Coorong and Lower Lakes area…Ultimately, it will help to ensure sustainability for more than 30 species of native fish and restore Murray-Darling Basin fish populations.”

But there is no evidence to sustain such a pronouncement, so quickly parroted by those also keen to believe the reports and papers authored by SARDI (South Australian Research and Development Institute) employees that claim the Lakes and Coorong Fishery could support a healthy mulloway (Argyrosomus japonicas) fishery if only environmental flows were restored. Indeed, these publications are exceedingly deceptive because they combine the dammed freshwater Lake Alexandrina fishery that is dominated by carp, with the salty Coorong fishery dominated by mulloway and then refer to estuarine species from the Lakes and Coorong Fishery (LCF). In reality, there are few estuarine species in the lakes and mulloway have not been recorded** from the lakes in any of the many surveys over recent decades (e.g. Bice et al. SARDI Publication No. F2010/000703-1, Table 2).

Furthermore while the popular claim, repeated in the peer-reviewed papers, often with Greg J Ferguson as senior author, claim populations of mulloway have been depleted by inadequate environmental flows, data in one of the same papers (Aquatic Living Resource, volume 21, pages 145- 52, figure 4) clearly shows that the collapse of the mulloway fishery in the 1940s occurred with completion of the barrages, which function as sea dykes. Prior to the barrages, good catches occurred even in drought years.

Ferguson et al. 2008
Click on the image for a large better view.

Indeed, the year with the highest recorded mulloway catch, exceeding 600 tonnes, was 1938. This was a drought year during a dry decade in the Murray Darling with low flow to South Australia. The following year 1939, despite the persistent drought, 595 tonnes of mulloway were harvested.

Ignoring these early records, Greg Ferguson and colleagues claim annual flow down the Murray River can explain 43 percent of the variability in the mulloway catch in the LCF. Conveniently, at least in terms of the politics, they choose to restrict their analysis to the years 1984 to 2005. But a longer record, that precedes construction of the barrages, shows that after the sealing of the Goolwa barrage in February 1940, the mulloway fishery never recovered to previous levels despite the extraordinary large flows to the Lower Lakes and Murray mouth in 1956 and 1974.

In short, it is absurd to suggest that more environmental flow will fix the mulloway fishery while the barrages remain in place. But this is the advice from Australian mulloway experts, who draw a salary from government.

Before the barrages, when the south westerly wind picked up, the sea would often pour in through the Murray’s mouth and work its way across the lake. So Lake Alexandrina was often fresh in spring and summer, but salty by autumn. In his book Poor man river: memoirs from the River Murray estuary Alastair Wood, a fisherman from Encounter Bay, tells how the mulloway would spend winter to the west amongst the mangroves of the Gulf of St Vincent. When the new season’s winds wafted up the gulf the mulloway returned to the Murray mouth.

The schools lead by large fish, forty pounders and heavier, would settle in the offshore underwater canyons. Within sight of the Murray’s mouth and smell of the river, Mr Wood describes how on a full moon and a big tide, large females would swim through the surf, in through the Murray’s mouth, and along the channels to the lake proper where they would gorge on the little bottom-dwelling fish, the congolli (Pseudaphritis urvillii).

Research from the Shoalhaven estuary in NSW, where there are no obstructions to fish movement, shows that mulloway use the entire 48 km long estuary with high flow events driving fish downstream towards the mouth at Shoalhaven Heads (Matthew Taylor et al., DOI: 10.1371/journal.pone.0095680). The fish follow the shift in the location of the saltwater wedge. Of course such a wedge is absent from the lower Murray River, because the estuary was destroyed with the construction of the barrages.

Studies of mulloway in the 12 km long Great Fish Estuary in South Africa show that mulloway move up and down that estuary corresponding with the speed and direction of the falling tide or, the fish remain stationary in deeper and structured habitat within the estuary (Tor Naesje et al., Marine Ecology Progress Series, volume 460, pages 221-232). The barrages prevent the tide entering Lake Alexandrina, once the central basin of the lower Murray estuary.

Congolli rather than mulloway are now the focus of restoration efforts in the Lower Lakes. In a 2011 article by Ruchira Talukdar from the Australian Conservation Foundation, this species, common in estuaries in Tasmania, Victoria and southern NSW, is incorrectly described as being on the verge of extinction and dependent on the Goolwa Barrage boat lock for passage to the Coorong to spawn. Ms Talukdar wrote: “Upstream over-extraction of water in the Murray-Darling Basin and the prolonged drought had left the Lower Lakes disconnected from the Coorong, dealing a killing blow to congolli breeding. The females couldn’t make their downstream migration for the last four years. Fortunately for the congolli, the August 2010 floods sent enough water down the Murray-Darling to connect the Lakes to the Coorong. During a six-week rescue operation which ended in October 2010, the State Government enabled as many as 20,000 females to swim into the Coorong by using the Goolwa Barrage boat lock was used as a temporary fish passage.”

What neither the media release from the Minister, nor the article published by the Conservation Foundation, admit is that there are already fishways in the Murray Mouth barrages. They were built as part of the $60 million ‘Sea to Hume Dam’ project launched in 2003.

Monitoring of the fishways built a part of this initiative, including the Tauwitchere large vertical-slot, Tauwitchere small vertical-slot, Goolwa vertical-slot, Hunters Creek Vertical slot, and the Tauwitchere rock ramp showed 10,900 congolli moved through these structures during 2010 and 2011, with half of these fish using the rock-ramp. But the overwhelmingly dominant species using the fishways and rock-ramp were not congolli but rather the pest red fin perch and tiny ubiquitous Australian smelt (Retropinna semoni) with 442,675 and 455,089, respectively, recorded entering or leaving the fishways and rock-ramp over this period (Zampatti et al. SARDI Publication No.F2011/000186-2, see Table 3.1).

There is no shortage of money for building slots in dyke walls, and paying bureaucrats to count hundreds of thousands of insignificant tiny fish that wash between the slots, but there is a complete absence of honest reporting on the true state of the Lower Lakes fishery and what is most needed for its restoration.

What a shame.
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** This article was edited on June 3, 2014 following comment from Jimbo James (We Flick Fishing) that he had a tagged mulloway recaptured on the fresh side of the Barrages near Goolwa town. He went on to comment that, “To say ‘NOT ONE’ mulloway use the fish ways is a bit obscured as they definitely do use the fish ways. Correct that there are already fish ways there and I have had the unfortunate time of witnessing Seals sitting in these fish ways from my canoe and devouring mulloway after Mulloway and leaving the heads to just float off in the current coming from the fish way. This to me is a more immediate problem that needs to be rectified . Agreed that something really significant needs to happen to restore the mulloway population.”

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3 Responses to “Slots in dyke walls won’t fix mulloway fishery”

  1. Dennis Webb

    More interesting historical information at this website http://lakesneedwater.blogspot.com.au/2011/08/barrages-would-kill-butterfish-part-2.html .
    Chief Fisheries Inspector in 1933 was agains the barrages.

  2. Shane mulloway Evans

    Well said Jimbo. The coorong estuary is only %10 of what it was before the barrages were installed surely this has to of been the worst impact of all on the mulloway fishery.

  3. Allan Taylor

    Why not admit that the barrages have been a failure and are a liability to the restoration of a viable Lower Lakes Fishery? Also, the Coorong is not part of the MDBasin but a sea water tidal elongated estuary.

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