The artificial reef fish case

Yellowtail cod is an example of a baitfish found in abundance around artificial reefs studied by UNSW researchers. Credit: John Turnbull

Scientists at UNSW have discovered why artificial reefs attract more small foraging fish, or baitfish, than natural reefs.

This is an important discovery that could lead to the construction of more efficient artificial reefs to help recreational fishermen.

Using a high-tech fish finder called a multibeam echo sounder, researchers at the School of Biological, Earth and Environmental Sciences obtained a 3D image of five natural reefs and three artificial reefs at the off Sydney during the day and night and in different conditions.

They found that the high vertical habitats provided by the 9-meter-high artificial reef allowed baitfish such as yellowtail amberjack and mado to spread out and feed much higher above the seabed. while remaining close to the security offered by physical structures.

Because they had a higher structure to protect them, these lower food chain fish also had more access to food – drifting plankton – than they would get on a low-lying natural reef. altitude.

And thanks to the “meal delivery service” – the Eastern Australian Current – consistently delivering a conveyor belt of plankton as food, these baitfish eat more, with subsequent benefits for their predators, including the spotted flathead. blues, one of New South Wales’ most iconic businesses. and recreational fish.

Their study, published in Series on Advances in Marine Ecology, has implications for the eight man-made reefs of New South Wales.

“Zooplankton and these small fish support about half of the biomass of fish,” said one of the study’s authors, Professor Iain Suthers of the School of Biological, Earth and Environmental Sciences.

“Schools of these small fish are sometimes referred to as ‘mouth walls’ because they persist above a reef and peck zooplankton from the tidal flow.

“They link plankton to fishing and underpin the durability of the blue-spotted flathead, which has implications for the sustainability of inshore fisheries near highly urbanized areas, as the flathead ambushes these. small baitfish. “

The study describes the so-called “pinch point” of the coastal food web and helps explain why the reefs around Sydney can be such a productive habitat for forage fish, despite a 50 percent drop in kelp, which has left it behind. – even supports coastal food webs and subsequently offshore fishing. the NSW coast.

Lead author Matthew Holland, who conducted the research when he held a PhD. A UNSW Science candidate and now a researcher at Plymouth University in the UK, says artificial reefs allow fish to use space differently than they do in nearby natural habitats.

“In temperate and subtropical coastal areas, like the Sydney coast, much of the seabed is relatively flat and featureless,” says Dr Holland.

“But rocky reefs or any form of hard structure on the seabed are rare overall, and fish tend to congregate on structures such as artificial reefs.

“By building artificial reefs as ‘skyscrapers’ rather than ‘single story buildings’, we can provide more usable space for fish, which can move up and down the water column while staying close. of these structures to protect themselves from predators. “

Dr Holland says they were surprised at the huge amount of plankton actually drifting over Sydney’s natural and man-made reefs.

“We collected zooplankton samples by towing nets behind the boat during our surveys,” he says.

“Based on the speed of the current, we calculated that 43 grams of zooplankton were being delivered to each square meter of reef every hour during the day.

“Based on the energy requirements of the fish we studied, each square meter of reef could potentially support up to 25 kilograms of fish feeding only on these tiny organisms. ”

The eight artificial reefs of New South Wales are located at South Head in Sydney, Port Hacking in South Sydney, Shoalhaven, Port Macquarie, Merimbula, Newcastle, Wollongong and Tweed Heads.

Like artificial reefs, oil rigs off the coast of California have proven to be some of the most productive reef habitats.

Professor Suthers says the study justifies the decommissioning of old oil and gas pipelines or platforms in the Bass Strait and the Northwest Plateau for use as artificial reefs.

But Dr Holland says that while scientists have demonstrated why artificial reefs can be more productive than natural reefs, they don’t necessarily replace natural reefs.

“Natural reefs often have higher biodiversity because they contain a greater variety of habitats which can therefore support a greater variety of organisms,” he says.

“It is important that we also preserve natural reefs to maintain this biodiversity. “

Now, scientists want to see their findings shape the design and location of future artificial reefs in hopes of improving coastal environments and improving opportunities for recreational fishermen.


Reef domes are a boon to the environment and recreational fishing


More information:
MM Holland et al, Small-scale spatial and daily dynamics of zooplanktivorous fish on temperate rocky and artificial reefs, Series on Advances in Marine Ecology (2021). DOI: 10.3354 / meps13831

Provided by the University of New South Wales

Quote: The fishy business of artificial reefs (2021, October 5) retrieved October 5, 2021 from https://phys.org/news/2021-10-fishy-business-artificial-reefs.html

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