Is dredging killing the Gladstone fish and making us sick?

Fishing has been banned in Gladstone while authorities try to determine what’s killing marine species. robstephaustralia

Several individuals have required medical attention after a mystery disease appeared to spread to humans from fish in waters near Gladstone, Queensland.

Fishing bans are currently in place and local residents have been told not to eat local seafood.

While little is known about the disease, test results from several affected fish are due to be released in the coming days.

Environmentalists, such as Dr Andrew Jeremijenko, have suggested that the dredging of Gladstone Harbour – to accommodate the burgeoning liquified natural gas (LNG) development on nearby Curtis Island – could be to blame for the disease.

So how much of an effect does dredging have on water quality? And how does a change in water quality affect the health of fish species?

Associate Professor Dean Jerry, Head of Aquaculture at James Cook University shared his thoughts.

What do we know about the disease so far?

From my understanding, we don’t know a great deal. It appears to be a new occurrence, possibly a virus that’s just shown up suddenly at the start of the dry season here in North Queensland.

These sorts of epidemics are quite often caused by two factors. One is the introduction of a new disease which hasn’t been in the region before and which infects local fish species.

Second, from an aquaculture perspective, we often find that when disease becomes a problem some environmental stressor has occurred. These environmental stressors can lower the immune system of the fish species and their ability to combat disease or pathogens which are out in the water all the time, but are not normally a problem.

In this instance we don’t really know whether it’s the introduction of a new disease or some environmental change which has sparked an epidemic.

What sort of environmental effects could cause something like the outbreak we’ve seen?

Generally what we find is that water quality is a big environmental stressor that affects fish. If there are suddenly a lot more nutrients in the water, or toxins in the system, the fish have to work a lot harder to osmo-regulate (or process through their metabolism) their own nutrients. This places much more stress on the physiology of the fish.

If oxygen levels in the water drop, that places a lot of stress on the fish too. But in an aquaculture context it’s normally water quality in terms of nutrification that’s the main issue.

Some people have pointed the finger at the dredging of Gladstone port, suggesting it’s probably having a negative impact on marine life. What do we know about the effects of dredging on water quality?

What happens with dredging is that you stir up sediments on the ocean floor. Once you get down below the first couple of centimetres, that sediment is quite often what we call a deoxygenated environment, where there’s a lot of things such as heavy metals and hydrogen sulphide gas.

Industry is booming in Gladstone. Eddy Respondek