Introduction

The Northern Territory has a vast coastline which extends for around 10 000km. In contrast to many areas on the eastern coast of Australia, the ecosystems are largely intact, with only a few remote settled areas. The coastline has shallow tropical waters which support globally significant populations of threatened species, including six of the seven species of marine turtles, colonies of shorebirds, seabirds and waterbirds, sawfish, dugongs, sharks and rays.

Marine environment

Photo: © Anthony Roelofs

Issues

Limited knowledge base

One of the key issues for management of marine environments in the Northern Territory is the relative lack of knowledge about the distribution and abundance of different marine species and coral reefs. The Northern Territory Government’s Marine Biodiversity Group is in the process of undertaking systematic surveys to improve the knowledge about these ecosystems to underpin improved management strategies.

Oil spills

Oils or oil based products can be discharged in bilge water from boats, spilled down inland storm water drains or washed off land. More significant oil slicks can be caused by shipping accidents or accidents on offshore oil wells. The impacts of oil slicks on marine wildlife can be quite devastating. The affect of a spill depends on the type of oil, the location of the spill and the species in the area. Oils that stick to feathers, reduce the ability of birds to fly or even float, which can result in starvation and drowning. Ingestion of oils can affect marine mammals, including dolphins and dugongs resulting in ulcers and haemorrhage.

To date the occurrence of oil slicks in Northern Territory waters has been rare, due partly to the low level of shipping and mining activities.  While the amount of activity and therefore the risk of incident is increasing, cooperation between relevant groups has resulted in the development of oil spill prevention and contingency plans for areas most at risk. These plans have been prepared for Darwin Harbour and for the offshore oil industry in the Timor Sea and territory coastal waters.

Because even minor slicks can impact on marine species, care should be taken when refuelling boats and disposing of waste oil on land to decrease the chance of any oil entering waterways.

Marine debris

Marine debris is a significant problem in coastal areas of the Northern Territory, see the management guidelines on marine debris and ghost nets for more information.

 Aquatic pests

Introduced species may be transported accidentally or deliberately to coastal waters, through vectors such as ballast or biofouling on commercial, recreational or illegal boats; movement of marine equipment or intentional translocation. Some species have the potential to become serious marine pests that can adversely affect biodiversity and the local economy. There is a high risk of introducing invasive marine pests to Darwin, given its close proximity to Asian ports and increasing shipping traffic in the area.

The introduced black-striped mussel was detected in the Cullen Bay marina in Darwin Harbour in 1999. Black-striped mussel is capable of rapid reproduction and can foul boat and marine structures and outcompete native species. The Northern Territory Government implemented quarantine measures followed by a rapid eradication program which prevented it becoming a potentially serious threat in Northern Territory waters.

An Aquatic Biosecurity team has been established by the Northern Territory Government to undertake monitoring of areas where pests may be introduced. The team inspects vessels that have travelled in international waters and coordinates emergency responses to incursions of marine pests.

A number of marine species are listed as noxious or prohibited, including carp, mosquitofish, oscar and tiliapia. Possession or importation of these species is illegal as they are serious pests and have the potential to have major impacts on the marine environment.

Overview of marine life

Commercial fisheries and aquaculture

On a global scale, fish stocks are in serious decline. The World Bank estimates that approximately 25% of the world’s marine fish stocks are over-exploited, and a further 50% are fully exploited due to overfishing. The increasing demand for fish resources has also led to degradation of coastal, marine and freshwater environments. There is also substantial growth in the aquaculture industry, which can have significant environmental impacts.

There are 11 commercial wild catch fisheries operating in Northern Territory waters and commercial aquaculture operations for barramundi, mud crabs, pearly oysters and prawns. These operations are managed by the NT Fisheries Aquatic Resource Management group through regulations, gazettal notices and licence conditions. The Northern Territory fishery operations catch per unit effort statistics suggest that they are currently healthy. The value of fisheries production in the Northern Territory was estimated at $144.9 million in 2007, an increase of around 50% since 2003-2004. The value of fisheries production relies on environmental variables of water quality and flow as well as consumer demand.

There have been numerous changes in fisheries management in the Northern Territory in the last decade. The Northern Territory Government has implemented a number of changes aimed at sharing fishing resources between commercial and recreational interests. Changes have included voluntary and compulsory reductions in the number of commercial fishing licences, voluntary buyback of commercial coastal netting licences, gear restrictions, seasonal closures, river closures, and size limits of fish. The McArthur and Adelaide Rivers have been closed to commercial barramundi fishing operations, and commercial coastal net fishing has been banned in Darwin Harbour and Shoal Bay.

Environmental impacts of commercial operations include habitat destruction caused by trawling practices and bycatch of non-target species, including marine turtles, dugongs, sawfish, sharks and marine birds. There is also a risk of overfishing if not managed sustainably. Impacts of aquaculture include nutrient and waste discharge, fish escapes, disease and parasites, use of chemicals and fungicides, and the use of wild fish stocks for fish meal.

Recreational fishing activities

Recreational fishing is an immensely popular leisure activity in the Northern Territory, for both locals and visitors, and is estimated to be worth $35 million annually to the Northern Territory economy. Recreational fishing opportunities, particularly for the iconic barramundi, are a significant drawcard for visitors to the Northern Territory.

Recreational fishers do not require a licence, however a temporary licence is required for fishing in Aboriginal land and adjoining waters. Possession limits apply and there are also Northern Territory recreational fishing controls and a code of practice.

Environmental impacts of recreational fishing can result from boating activities. Aquatic weeds such as salvinia may be transported by boats. Boats can also pollute sensitive areas. Bycatch of species such as sharks and sawfish may also occur, and it is important to carefully remove fishing lines and hooks then release these species.

Marine overview

Photo: © NRETAS

Illegal fishing activities

With its extensive, remote and sparsely populated areas and healthy fish stocks, the northern Australian coast is a prime target for illegal fishing activity. The vast and remote areas make coastal patrols and survellience a challenge with the limited resources available across customs and indigenous sea ranger groups. There is an  extremely low and concerning rate of apprehension of illegal fishing operators - in 2005 it was estimated that there were over 13 000 vessels in Northern Territory waters, and less than 2% of these were apprehended. With the continuing decline in world fish stocks, it is likely that illegal fishing will continue to grow unless more resources are dedicated to addressing the issue.

Changes in legislation and indigenous sea country management

The Federal Court decision on the Blue Mud Bay case granted Aboriginal traditional owners freehold title to the low water mark on Aboriginal land of the Northern Territory in 2007. The High Court subsequently ruled that the NT Fisheries Act applies to all waters in the Northern Territory, with existing controls relating to fishing to still apply. However, permission is required from the relevant land councils to fish in waters overlying Aboriginal land. There is a temporary permit system in place until arrangements for a permanent permit system are finalised by the Northern Land Council and Northern Territory Government.

Around 85% of the Northern Territory coastline is Aboriginal owned and the marine environment is an integral part of coastal Aboriginal communities. There are several indigenous ranger groups which carry out activities such as marine debris monitoring, rescuing wildlife entangled in ghost nets, and monitoring marine wildlife populations. They have also played a crucial role in detecting and reporting illegal fishing activities.

Climate change

Climate change is expected to result in an increase in sea temperatures, increased cyclonic intensities and risk of storm surge events. Such changes may lead to destruction or degradation of marine habitats; alteration to the extent and functioning of mangrove communities; increased coral bleaching; and impact on marine life including skewed sex ratio in marine animals which have temperature dependent sex determination such as saltwater crocodiles and marine turtles.

Marine protected areas

The Northern Territory Government has commenced the process of establishing a system of marine parks to be part of Australia’s National Representative System of Marine Parks. Marine protected areas (or marine parks) are aimed at protecting the marine environment, and allow for multiple uses providing different levels of protection and permitted uses, from no take zones to zones allowing for fishing, commercial and other activities. The Marine Biodiversity Group is engaging with relevant stakeholders for the establishment of marine protected areas, recognising the crucial role of Traditional Owners who hold title to the majority of the coastline.

The Marine Biodiversity group is working on a range of projects aimed at improving knowledge about the Northern Territory’s marine environments. The Northern Territory and Australian Governments are also responsible for ensuring the sustainability of commercial fishing and aquaculture operations. With the continually increasing demand for fish supplies, it is likely there will be increasing pressure to expand aquaculture. It is crucial that any proposals for new or expanding aquaculture operations are comprehensively assessed through an environmental impact assessment process to ensure the Northern Territory’s unique marine environments are not affected.

Indigenous sea rangers and environmental volunteer groups continue to undertake marine debris surveys along the Northern Territory coastline. Indigenous sea ranger groups are crucial in the management of the marine environment, and should be adequately resourced to support their work.

Recreational water users should dispose of littter responsibly, keep to established tracks and boat ramps, refuel carefully, follow established water routes, and adhere to possession limits and zoning restrictions. Consumers are strongly encouraged to choose seafood which has been sustainably harvested. The Australian Marine Conservation Society has developed an informative Sustainable Seafood Guide for this purpose.

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