6.1 Degradation of marine environments

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Priority Rating: 2

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Description

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Degradation of the marine environment refers to damage caused to marine ecosystems and species. Direct effects of humans on marine habitats and biota includes dredging and dumping (reclamation), removal of biota (through fishing), and construction of marinas, port facilities or breakwaters. Indirect effects include introduction of foreign diseases or species, and discharge of nutrients (accelerating the growth of some organisms) and other pollutants that can adversely affect marine biota and habitats (see 'Introduced marine species' and 'Marine contamination').

Direct impacts are caused by a variety of pressures, mainly due to an increasing population, urbanisation and industry and tourism development. Dredging refers to excavation of sediments from the sea bed to make the water deeper, or as a part of an extractive process. Dumping (or reclamation) refers to the deposition of sediments in the marine environment to create new land. Both of these processes (whether they are conducted during extractive operations, construction of pipeline trenches, port expansions, shipping activities, or construction of marinas and canals) are destructive to many marine ecosystems. Introducing soil and mud into the water column increases turbidity and sedimentation, leading to smothering and shading of benthic flora and fauna. Reclamation results in complete physical loss of the natural environment.

Over-fishing and some fishing activities (e.g. trawling, aquaculture) can have severe impacts on species and degrade marine habitat (see 'Fisheries'). Over-fishing of a target species removes predator or prey animals and affects the ecological food chain. Trawling (the dragging of a weighted net behind a boat) can include catch of non-target species, such as seals, dolphins, sharks, sea snakes, fish, turtles, crocodiles, birds and invertebrates (known collectively as by-catch), and has the potential to devastate benthic habitats. Recently, poaching has been recognised as a significant problem in the North West and has the potential to negatively affect sensitive ecosystems and species. Aquaculture (farming of marine flora and fauna) can contribute to degradation of habitat (for ponds, access and infrastructure) and change the ecology of an area by contributing nutrient waste, and potentially transmitting disease or reducing genetic variability.

Objectives

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To protect the marine environment and ensure there is no significant further loss and degradation of marine habitats, biota and functionality by:

• Defining and protecting environmental values in order to protect and improve the condition of the marine environment;
• Reducing and eliminating (where practical) the major environmental pressures that degrade, or threaten to degrade, the marine environment and it's associated values;
• Conserving the marine environment and associated values identified as most important; and
• Managing and using marine resources in a sustainable manner and rehabilitating degraded marine areas where practical.

Condition

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Marine habitats vary enormously throughout the State due to the varied nature of the geology, coastal energy, currents and species. Protecting marine environments depends on understanding their type and processes. Marine habitat mapping generally falls into one of two categories - relatively detailed for a small area, or very large scale and course for large areas.

Ten of WA's 16 marine bioregions have had some benthic habitat mapping done. This is limited to areas of high conservation value (e.g. Pilbara coast, Dampier Archipelago, Ningaloo Reef, Jurien Marine Park, Mandurah to Geographe Bay and the Recherche Archipelago), areas important for the fishing industry (such as nursery areas), areas subject to oil and gas exploration or development proposals, areas containing species which have been used as biological indicators (e.g. seagrasses), and. Surveys of marine biodiversity, including some habitats, have been published for Albany, Rottnest Island, the Houtman Abrolhos Islands, Dampier and Esperance to date (eds Wells et al., 1991; eds Wells et al., 1993; ed. Wells, 1997; eds Walker & Wells, 1999; eds Wells, Walker & Jones, 2003; eds Wells, Walker & Kendrick, 2005). While there may be information available about other marine habitats, accessing and interpreting this information is difficult. Survey data may be owned by different organisations, subject to commercial in confidence considerations or otherwise not be publicly available.

Indicator M3: Areas and locations of marine habitat which have been lost or seriously degraded by human activities.

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It is not possible to report the total area of loss or serious degradation of marine habitats as it is not recorded in any central database. Some local areas of marine and coastal habitat loss have been quantified.

The EPA has established guidelines for development proponents to protect benthic primary producer habitats from direct and indirect impacts of development proposals (Environmental Protection Authority, 2004). Six categories have been established for ecological protection, each with different allowable 'cumulative loss thresholds' (ranging from 0-10%) depending on the ecological and conservation significance of the area (Environmental Protection Authority, 2004).

An example of cumulative mangrove habitat loss can be seen in Port Hedland (Figure M1.1). The development of port and salt industries in Port Hedland began in the 1960s, and there has been progressive and considerable loss since that time of habitat areas that were occupied by dense stands of mangroves. If recently approved port projects proceed as planned, the cumulative loss of closed canopy mangrove habitat would be about 342 ha representing about 13% loss of the total extent of that habitat type (Figure M1.1). This would exceed the EPA's habitat loss threshold for this habitat type.

While environmental impact assessments are conducted for individual project proposals, data are not routinely validated to check that the areas of habitat loss arising from approved (and implemented) projects are consistent with losses predicted by proponents (unless specific environmental conditions are set). However, it is known that most marine habitat loss and degradation has been concentrated around port facilities and areas of major urban and industrial development.

Figure M1.1: Estimates of areas of mangrove loss in the Port Hedland Management Unit.

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Data source: Environmental Protection Authority (2005); Townley & Associates Pty Ltd (2005). Analysis: EPA. Note: The red line represents 10% of the estimated spatial extent of mangrove habitat present within the management unit prior to the commencement of development activities (about 267 ha).

Cockburn Sound is another example of a benthic primary producer habitat that has exceeded the EPA's cumulative loss threshold - in this case for seagrasses (Figures M1.2 and M1.3). The loss of seagrass in Cockburn Sound has been well-documented and is an example of severe decline in seagrass-dominated habitat. The ecological condition of Cockburn Sound was considered to have been at its lowest in the 1970s, with poor water quality, high chlorophyll a levels and the loss of extensive areas of seagrass from the eastern margin of Cockburn Sound (Environmental Protection Authority, 2006a). The coverage of seagrasses has declined from 2930 ha (80% coverage) in 1967 to 660 ha (18% coverage) in 1999 (DAL Science and Engineering, 2002). Decline was most significant in the Eastern Shoals (James Point to Woodman Point) (Figure M1.3). It was also significant in the Southern Flats, east of the Garden Island Causeway, but that area is showing signs of a slow recovery. It is important to recognise that substantial time and resources have been invested by the Government, industry and the community to improve the environmental quality in Cockburn Sound since the 1970s (Environmental Protection Authority, 2006). During the mid to late 1980s and early 1990s, chlorophyll a concentrations and water clarity improved and have generally stabilised since then (see 'Marine Contamination').

Anecdotal evidence indicates significant loss of marine habitat has also occurred around WA, particularly around the large port facilities of Perth, Shark Bay, Geraldton, Albany, Exmouth and Esperance. However, very few places currently have data available to show changes over time.

Figure M1.2: Change in areas of bare sand and seagrass extent over time at the Southern Flats location in Cockburn Sound.

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Data source: DAL Science and Engineering (2002).

 

Figure M1.3: Change in areas of bare sand and seagrass extent over time at the Eastern Shoals in Cockburn Sound.

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Data source: DAL Science and Engineering (2002).

Pressures

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Major shipping corridors result in direct damage to the marine environment by anchor drag and the need for dredging activities to maintain shipping channels. Activities at larger ports present a risk of introduction of species, accidental spills, potential contamination, and habitat destruction (Figures M1.4 and M1.5). Dampier has the highest number of vessel visits (Figure M1.4) and both Port Headland and Dampier had the highest tonnage transport move through the port in 2006 (Figure M1.5). Dampier, Port Hedland and Geraldton have had an increase in the number of vessel visits since 2001-02, but the number of visits to other ports has remained stable. The amount of cargo moving through ports has also been stable at most ports, but significant increases have occurred at Dampier and Port Hedland due to the export of iron ore during the resources boom (Figure M1.5). Pressure from ports, other marine facilities and related infrastructure is expected to increase. However, other coastal development (including housing, marinas, and industrial areas) can also have a negative impact on the marine environment.

Figure M1.4: Vessel visits to ports in Western Australia.

Data source: Department for Planning and Infrastructure.

 

Figure M1.5: Total tonnages moving through Western Australian ports.

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Data source: Department for Planning and Infrastructure, Government of Western Australia (2006).

Dredging can be a one-off project (e.g. for installation of new infrastructure, known as 'capital dredging') or repeated from time to (e.g. to remove accumulated sediments from shipping channels or harbour basins, known as 'maintenance dredging') (Figure M1.6). Government managed dredging occurs at many of the maritime facilities for which it has direct management responsibility. In 2003 and 2004 the locations where the largest volumes of this type of dredging occurred were Mandurah-Dawesville, Kalbarri, Denham, Esperance, Onslow and Carnarvon (Brodie-Hall & Barr, 2004). Other regional ports are managed by separate semi-autonomous Port Authorities (Esperance, Albany, Bunbury, Fremantle, Geraldton, Dampier, Port Hedland, and Broome) and privately operated shipping facilities (e.g. Cape Cuvier, Cape Lambert) and are generally large facilities which cater for import and export trade. Maintenance and capital dredging data at these facilities is collected as part of the environmental impact assessment process, but it is not possible to provide the total dredge volume at present.

Offshore petroleum extraction and onshore industry (Figure M1.6) can place pressure on marine habitats and biota by releasing toxic compounds and nutrients, through physical disturbance and by light and noise pollution. Future increases in pressure are forecast because of expansion of the oil and gas industries, the Gorgon Venture on Barrow Island, and developments in Exmouth and areas south of Shark Bay. Pipelines that connect offshore industry to mainland transport infrastructure can impact the marine environment, especially during the construction period.

Areas where people live and stay along the coast are also often subject to degradation of the marine environment. The construction of coastal housing can impact or destroy coastal ecosystems, but also the marine environment by discharges of treated waste water to the marine environment (see 'Marine contamination'). In addition, people need infrastructure to access and use the marine environment, such as jetties, wharves, groynes, sea walls, marinas and moorings (Figure M1.6).

Figure M1.6: Locations of major infrastructure and human activities in the marine environment.

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Data source: National Oceans Office - ports [ver. 2003]; Department of Planning and Infrastructure - oil and gas facilities [ver. 2002]; Australian Maritime Safety Authority - shipping lanes [ver. 2004]; Department of Planning and Infrastructure - dredge locations [ver. 2004]; Department of Planning and Infrastructure - coastal infrastructure [ver. 2004]; Department of Industry and Resources - petroleum pipelines [ver. 2004]; Department of Planning and Infrastructure -  mooring controlled areas [ver. 2004]. Data presentation: EPA.

Fishing has a variety of environmental impacts, including targeting of particular species and size classes and potential to impact other species as either by-catch, prey or predator species. Even though the managed fisheries are relatively well managed and moving toward a whole-of-ecosystem based approach, significant pressure remains from increased recreational fishing, some non-compliance and illegal fishing. Trawling is a method of fishing that has been singled out as having a high environmental impact. Aquaculture can contribute to marine degradation from the release of waste, accidental release of introduced species, altered water regimes, and clearing of coastal native vegetation to support infrastructure (Figure M1.7).

Figure M1.7: Locations of major trawling, fishing and aquaculture activities in the marine environment.

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Data source: Department of Fisheries - all areas trawled [ver. 2005]; Department of Fisheries - aquaculture licence areas [ver. 2006]; Department of Fisheries - selected fisheries areas [ver. 2006]. Analysis: EPA. Data presentation: EPA. Note: only the top six commercial fisheries (economic value) are shown. Pearl diving and aquaculture licence areas were excluded as they are high economic value fisheries with little environmental impact.

Indicator M4: Areas impacted by trawler activity.

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Trawling is known to cause extensive loss of species (e.g. algae, seagrass and sponges) and degradation of marine environments. Trawling can be done with or without disturbance of sea floor by using equipment that either scrapes the sea floor or is suspended in the water column (depending on the type of marine animal targeted). Bottom trawling has an effect similar to that of clearing native vegetation on land, as it involves the removal of areas of marine habitat. Trawling (and especially frequent trawling) can alter the species balance and modify conditions to favour some species, while disadvantaging other species.

There are several marine environments open to trawling along the WA coastline, including the Kimberley, Pilbara (off-shore and on-shore), Shark Bay, the Abrolhos Islands and the South Coast. Management actions are in place to maintain sustainable fisheries, so trawling occurs in a defined season with a limited number of boat operators holding licences, and the area trawled in any one year is a small proportion of the total trawl ground. There are often permanent or temporary closures of common trawling areas, so the actual areas being trawled in any one year represent at most 54% of total gazetted trawled areas (Figure M1.8). In general, trawled areas in 2005 represented a decrease from previous years. Some species show natural variations in population levels so catch sizes and trawl areas are adjusted in response. There is a greater focus of effort in some trawl areas due to variation in the abundance of animals being fished, ease of operation of equipment and proximity to ports. Significant changes to marine biota are likely in these areas compared with those that are trawled infrequently.

Figure M1.8: Areas trawled in Western Australian and Commonwealth waters by location, 2002-05.

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Data source: Department of Fisheries.

Indicator M5: Trend over time in environmental impacts of trawling.

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The impacts of trawling on the marine environment depend on the type of fishery (Table M1.1) and the annual impact of trawling on by-catch, protected species, food chain, and habitat for each fishery. The Shark Bay prawn fishery is of most concern for its amount of by-catch and increasing impacts on shallow sandy habitats (Table M1.1). Studies of the Pilbara dermersal finfish fishery have shown a high level of non-target fish catch in nets as well a significant shark by-catch (Table M1.1). In addition the fishery is known to capture threatened species (namely dolphins, turtles, sea snakes, pipefish and seahorses), some of which are dead by the time they reach the fishing boat. Turtle exclusion devices have been useful in preventing turtle death and injury in trawling equipment; however smaller animals such as crabs, crustaceans and fish are still caught as by-catch (non-target species). Further work to reduce the by-catch of threatened species is being undertaken. The Pilbara demersal finfish fishery also dislodges significant amounts of sessile benthic fauna (e.g. sponges). Concern has also been raised about impacts of the Abrolhos Islands scallop trawl.

The Biodiversity Trawl Project has compared conservation areas with areas of low, medium and high fishing effort in Shark Bay. Preliminary results suggest that the overall species richness and abundance of fish and larger invertebrates in trawled and untrawled sites were not significantly different. However, some individual species were present in higher numbers in untrawled areas, indicating they may be vulnerable to trawling. Some species were found in higher numbers on trawl grounds, indicating a preference for conditions in these areas (Department of Fisheries, unpublished data).

Table M1.1: Trends in various environmental impacts of trawl fisheries over time.

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Data source: Fisheries WA (1999); Fisheries Western Australia (2000 & 2001); Department of Fisheries (2002, 2003 & 2005); eds Penn, Fletcher & Head, (2005a, 2005b); eds Fletcher & Head (2006).

Indicator M6: Areas impacted by over-fishing.

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There are some areas that are of particular concern due to over-fishing (see 'Fisheries'). The Shark Bay pink snapper fishery has experienced very high fishing pressure in the past, and following a review of the inner gulf pink snapper fishery in 2002, total allowable catch-based management was introduced. This allocated approximately 75% for the commercial sector and 25% for the recreational sector for each pink snapper stock/fishery area (Fletcher & Head, 2006). The Eastern Gulf of Shark Bay was completely closed to recreational fishing between 2000 and 2003, and had short seasons in the next three year period between 2003 and 2005 (Fletcher & Head, 2006). The population of pink snapper has not recovered as expected and it is thought that wider environmental factors are playing a significant role (e.g. ocean currents affecting young fish, and perhaps water temperature). Bag limits for recreational fishers were further reduced in 2006.

The northern shark fishery is under significant pressure due to illegal fishing by international vessels that are not subject to catch and size restrictions imposed on local licensees. There was a 58% decline was recorded in the population of mature sandbar sharks in the area between northern Shark Bay and Eighty Mile Beach (south of Broome) from 2002 to 2005. In addition, a lack of juveniles indicates that there will be declining recruitment and breeding stock over the next decade (Fletcher and Head, 2006). The breeding stocks of dusky whaler and sandbar sharks on the south and west coast of WA have also been declining. While there may be some overlap of northern and southern populations of sharks (and thus some effect from illegal fishing), there has been over-fishing due to lower breeding and recruitment levels than anticipated, and also significant deaths from entanglement in plastic waste.

The south coast crustacean fisheries (especially for southern rock lobsters) have experienced significant catch declines over the last few years. There is relatively little known about the basic biology of southern rock lobsters, and recruitment may be dependant of ocean currents from South Australia. There may be significant fishing of small lobsters, leading to relatively few surviving to adulthood. The recreational crab fishery was closed in Cockburn Sound in 2006 due to concerns about depleted breeding stocks. Similar concerns have resulted in the reduction of bag limits for crabs in the Peel-Harvey Estuary and a two-month closure in 2007.

Current responses

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Environmental impact assessment: is undertaken by developers with projects that are likely to significantly impact the environment (including the marine environment). EPA Guidance Statement 29 outlines measures proponents can take to prevent the cumulative loss of benthic primary producer habitats (Environmental Protection Authority, 2004). Impacts have to be considered collectively, such as dredging, nutrient enrichment and the input of contaminants, and cumulatively where impacts from multiple developments contribute to significant, cumulative loss or disturbance of habitats.

Marine and coastal habitat mapping: There are many projects underway by the Coastal Cooperative Research Centre, environmental consultants, government departments and individual companies to map marine and coastal habitats. Examples include seagrass mapping in Cockburn Sound; marine habitat surveys in the vicinity of Dampier, Esperance and Geraldton ports; in fish habitat and nurseries at the Recherche Archipelago and Abrolhos Islands; and in high conservation areas. The capacity for mapping the sea floor has been enhanced dramatically by improved hydro-acoustic techniques. The Natural Heritage Trust has recently provided funding for marine habitat mapping in the South West, and hydro-acoustic surveys and underwater video footage has been used to generate state-of-the-art maps of the marine environment from Kalbarri to Eucla. As of December 2006, 900 km² of sea floor mapping had been completed in the Cape Naturaliste, Geographe Bay, Rottnest Island, Jurien Bay and the Abrolhos Islands.

Regional marine planning: The State government is preparing a framework for regional marine planning in WA and simultaneously is developing a regional marine strategic plan for State waters of the South Coast (Cape Leeuwin to the South Australian border). This aims to integrate the planning and management of the South Coast Marine environment across all sectors. 

Western Australian mangrove assessment project: A project is being undertaken by Murdoch University to identify, document and assess information about mangroves, in order to assist in their management and conservation.

Recherche Archipelago project: The Fisheries Research and Development Corporation, in partnership with universities, government departments, industries, the CRC Reef Research Centre and the Australian Institute of Marine Science, is undertaking a project to describe the habitats of the Recherche Archipelago. The project will identify, classify and map benthic habitats in the Recherche Archipelago; provide detailed ecological information to ensure the responsible management of aquaculture and fisheries in the region; and increase community awareness of fish habitats through community involvement with monitoring programs.

Strategic Research Fund for the Marine Environment: is a joint venture between the Government of WA and CSIRO that aims to enhance marine science capacity in WA, to facilitate strong collaboration among marine researchers from government, universities and the private sector, and to provide strategic marine research outcomes to inform the State's management of its marine environment.

Western Australian Marine Science Institution: was established in 2005 through the State Government's Major Research Facility Program. The institution will deliver scientific research to underpin sustainable utilisation of the State's marine natural resources and includes over 12 major collaborating partners. The Ningaloo Coast Research Program, which was established by the Premier's Office of Science and Innovation in 2003, will be incorporated into the Western Australian Marine Science Institution.

By-catch action plans: The Department of Fisheries requires implementation of by-catch action plans for ten WA fisheries; including the Shark Bay prawn and scallop trawl fisheries.

Biodiversity Trawl Project: aims to gain an understanding of the impacts of trawling on the marine environment, especially with reference to long-term ecological changes. The report from this project will be released in 2007.

Implications

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There are major implications for the marine environment if degradation pressures are allowed to continue unabated. Marine ecosystems will become more fragmented and less equipped to adapt to changing conditions, such as the effects of climate change. Natural embayments along WA's extensive coastline make ideal locations for human settlements, ports and marinas; but this places pressure on shallow water marine habitats that need to be dredged or modified. Trawling and overfishing are also impacting on marine ecosystems in some areas and many of the ecological or species changes associated with these issues have not yet been scientifically addressed. Future challenges for protecting the marine environment will hinge on addressing collective pressures and cumulative impacts.

Suggested responses

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6.4 Implement the State Water Quality Management Strategy No. 6: for Perth coastal waters, the Pilbara, Mid West and Kimberley near shore waters as a matter of priority within the next five years.

6.5 Establish a baseline condition of the marine environment and develop a consistent monitoring network in priority areas.

6.6 Update and implement environmentally sound industry codes of practice and guidelines for trawling.

6.7 Enhance marine research, planning and conservation in WA. Although some actions are underway, there are many areas requiring further progress.