Cormorant Fact Sheet

What cormorant species are present in Tasmania?

There are four species of cormorant in Tasmania, all of which are Protected Wildlife under the Nature Conservation (Wildlife) Regulations 2021:

• Great Cormorant - Phalacrocorax carbo
• Black-faced Cormorant - Phalacrocorax fuscescens
• Little Black Cormorant - Phalacrocorax sulcirostris
• Little Pied Cormorant - Phalacrocorax varius

Why have cormorant numbers increased in Tasmania recently?

Between 2020 and 2023 Australia experienced three consecutive La Niña climate events. La Niña years bring above average rainfall to south-eastern Australia, which provides perfect conditions for cormorants to breed and to build higher population numbers. These weather events also produce excellent spawning conditions for trout and native fish, providing an abundance of food in Tasmania for cormorants. This is a natural cycle that has occurred for many years.

What is their impact on fish populations?

Although cormorants have a varied diet, they are predominately fish eaters. In Tasmanian inland waters they eat native fish, trout and pest fish. To date, there have been no formal peer reviewed studies in Tasmania looking at the impacts of cormorants on trout populations, however, studies conducted in Europe have demonstrated that cormorants were able to reduce trout populations in rivers between 30 and 70%.

There is no doubt that recent cormorant numbers have impacted trout numbers in Tasmania – particularly in rivers. The impact of cormorants was also likely compounded by the extremely low rainfall and low river levels in Tasmania throughout the latter part of summer and into early winter during 2024.

It may be hard to believe, but large numbers of cormorants are beneficial to some aspects of the fishery. Large spawning events (such as those seen in recent La Niña years) can lead to an overpopulation of small fish that outcompete the larger, older fish, causing them to lose condition. In this scenario, cormorant predation may improve the overall size and condition of fish as the population recovers.

Cormorants also actively reduce populations of pest fish like redfin perch, which will result in benefits to populations of trout and native fish.

What is their impact on trout behaviour?

Naturally, trout do everything they can to escape cormorant predation. This results in trout congregating in areas where they can escape the birds. Such areas include complex snags (under willows or in/under long thick weed beds), undercut banks, in fast flowing water or even shallow water where it is harder for cormorants to actively hunt. You may have noticed large stretches of rivers with apparently no trout, and then found areas where they are apparently schooling up. Some trout may even adopt a nocturnal feeding strategy – opting to forage for feed during the nighttime and seek refuge from predation during the daylight hours.

How many, and what size fish do they eat?

Daily feed intake of cormorants varies between the species found in Tasmania. Studies conducted in Europe have estimated the Great Cormorant (this is the same species as found in Tasmania, and the largest one present here) eats between 441 g and 1,095 g of fish per day, with an average of 672 g.

Cormorants can comfortably eat fish up to about 1,000 g in weight or 400 mm in length. The girth of the fish (as opposed to the length) is the major factor that influences the size of the fish they eat.

What has happened in the past, and what is likely to happen in Tasmania now?

It’s likely we will see the natural ecological balance return to normal over the coming years. As the cormorants begin to exhaust the available food supply, their numbers will likely begin to reduce, or they will move somewhere else in search of food. Eventually the population will reduce to more normal levels.

Once cormorant numbers decline (as we have seen in previous years) the trout numbers are able to re-bound quickly and with less competition for space and food, the growth rates and condition of trout can be exceptional.

The last cormorant population boom in Tasmania occurred around 2013. This followed a La Niña event that lasted from 2010-12. By 2016, trout populations had naturally recovered and catch rates (reflected in the annual postal surveys) in the rivers had returned to normal levels.

Prior to this, cormorant population boom events occurred in Tasmania during the 1950s, 1970s and 1980s. In each instance the trout fishery recovered over a period of 3-4 years.

Why don’t we shoot cormorants?

All species of cormorants in Tasmania are protected under the Nature Conservation (Wildlife) Regulations 2021.

Permits to shoot cormorants are occasionally granted to operators within the salmon industry, to protect very localised assets (i.e. floating pens or ponds of fish), where shooting of small numbers is used in conjunction with acoustic deterrents to disperse birds.

Case studies from around the world have shown that whilst culling of cormorants may be successful on a local scale, it generally forces the birds into other areas, thereby just moving the problem.

Moreover, the use of firearms, within public spaces is highly problematic and in general, not accepted by the public and most probably would not be permitted. On private land this may be acceptable where it is to protect a business activity, but it is unlikely to be accepted to protect a recreational activity.

A lot of anglers talk about the ‘cormorant bounty’ that was in place during the 1950s. Whilst this provided an opportunity for anglers to feel like they were doing something about the problem (and make some money in the process), there is no available evidence to suggest this culling operation was successful in significantly reducing cormorant numbers at a population level, and importantly, reducing predation of fish stocks. It is likely that the natural ecological balance simply restored.

Why don’t we stock more fish?

Stocking has been shown to be one of the worst things that can be done to counter cormorant predation. It simply causes the birds to hang around longer. The key aspect for the long-term recovery of the fishery is the presence of fry post spawning. This is the stock that will naturally repopulate the fishery after the cormorant numbers have reduced.

Studies overseas and here within Tasmania, show that the stocking of rivers provides little benefit to increasing trout numbers, with natural recruitment (from spawning and dispersal of fish from feeder streams) being the best and most productive way of returning trout stocks to pre-impact levels.

The IFS has maintained our stocking program of assisted lake fisheries this season. While some of these stocked adult fish may have fallen victim to cormorant predation, in this instance the considered benefits of providing anglers with ongoing opportunity to catch a fish outweighed the potential negatives.

What is the best thing we can do then?

Studies worldwide have found that river health and the amount of habitat available to trout as refuge areas is by far the most important factor in limiting the impact of cormorants on a fishery.

Advocating for and improving waterway health is by far the best measure to reduce the impact of cormorants on the trout fishery.

How can you improve your catch rate in waters that have been impacted by cormorants?

There are a few things you can try to improve your catch rate of trout in waterways impacted by cormorants:

• Target areas in the river or lake that have more structure – including weed beds, snags, logjams, over-hanging trees and under-cut banks.
• Don’t overlook the shallower areas in rivers which, under normal circumstances, would not be preferred habitat for trout. You may find the trout holding in the shallower water to avoid predation.
• Try fishing the areas of higher current in the river.
• If you are feeling adventurous – try fishing for trout at night. This is a technique known for producing big trout and may also help you come across any trout that have switched to a more nocturnal feeding pattern.