Small pelagic fish of the south-west marine region

Legal description

The Commonwealth marine area is a matter of national environmental significance under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). As such, actions that have, will have, or are likely to have, a significant impact on it require approval.

In February 2014, the National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA) became the sole designated assessor of petroleum and greenhouse gas activities in Commonwealth waters in accordance with the Minister for the Environment’s endorsement of NOPSEMA’s environmental authorisation process under Part 10, section 146 of the EPBC Act. Under the streamlined arrangements, impacts on the Commonwealth marine area by petroleum and greenhouse gas activities will be assessed solely through NOPSEMA.

Key ecological features are not matters of national environmental significance and have no legal status in their own right. However, they may be considered as components of the Commonwealth marine area.

This KEF was identified in the South-west Marine Bioregional Plan. Under section 176 of the EPBC Act, once a bioregional plan has been made the minister responsible for the environment must have regard to it when making any decision under the Act to which the plan is relevant.

Values

Small pelagic fish are considered important for ecological functioning and integrity, providing critical links between primary production and higher predators (Freon et al. 2005). Small pelagic fish in the region collectively form the link between upwelled nutrient-rich water within the euphotic zone that supports a herbivorous, planktonic food web and a diverse range of predatory species. This includes large pelagic predatory fish (southern bluefin tuna, samson fish and kingfish), marine mammals (pygmy blue whales, southern right whales, dolphins, New Zealand fur seals and Australian sea lions), cephalopods (arrow squid) and seabirds (short-tailed shearwaters, crested terns, petrels and little penguins) (Hayes et al. 2008). Fluctuations in abundance of small pelagic fish have serious implications for the functioning of pelagic ecosystems. Some predatory species (such as southern bluefin tuna, pygmy blue whale, southern right whale, short-tailed shearwater and petrel) migrate annually during the upwelling season to take advantage of the increased prey opportunities, while others (e.g. New Zealand fur seal and crested tern) establish colonies next to these regions.

Small pelagic fish are known to occur in a number of bioregions within the South-west Marine Region, but particular interest lies in their occurrence and ecological role in the Great Australian Bight and the fisheries off Gulf St. Vincent and Spencer Gulf (Hayes et al. 2008).

National and/or regional importance

Small pelagic fish of the south-west marine region is defined as a key ecological feature for its regionally important ecological role.

Location

The spatial boundary of this KEF has not yet been defined.

Description

'Small pelagic fish' refers to shoaling, epipelagic fish that are supported by summer upwelling events in the Bonney and Eyre pelagic ecosystems. Fluctuations in abundance of small pelagic fish have serious implications for the functioning of pelagic ecosystems. In the South-west Marine Region, the small pelagic fish include 10 species: sardine, scaly mackerel, Australian anchovy, round herring, sandy sprat, blue sprat, jack mackerel, blue or slimy mackerel, red bait and saury. This group of fish also supports Australia’s largest fishery (by weight), the South Australian Sardine Fishery. This fishery suffered mass mortality events in 1995 and 1998, when more than 70% of the adult stock was thought to have perished. The distribution and abundance of anchovy expanded during these events, but this has since decreased as stocks of sardine recovered (Ward et al. 2008).

Pressure

During the development of marine bioregional plans, a regional pressure analysis was conducted to assess present and emerging pressures affecting conservation values in the Marine Regions and the effectiveness of mitigation and management arrangements that are currently in place to address these pressures. The analysis enabled pressures to be categorised in terms of their relative importance or concern and has informed the identification of regional conservation priorities. For the purpose of the plans, pressures are defined broadly as human-driven processes and events that do or can detrimentally affect the region's conservation values.

Pressures assessed as of concern for the Small pelagic fish of the south-west marine region are changes in sea temperature and change in oceanography as a result of climate change.

Pressures assessed as of potential concern are ocean acidification as a result of climate change and disease. These pressures are described in more detail below.

Changes in sea temperature (climate change)
Sea temperatures have warmed by 0.7 °C between 1910–1929 and 1989–2008, and current projections estimate ocean temperatures will be 1 °C warmer by 2030 (Lough 2009). The south-west of Western Australia in particular is one of three hotspots in the Indian Ocean where rising temperature trends exceed the Indian Ocean basin average (Feng et al. 2009). All key ecological features considered important for the region’s primary productivity and biological production are at risk from climate change. Changes in sea temperature and oceanographic processes have been implicated in the region in shifts in distribution of marine species, changes to prey variability (including positive changes for some species, such as bridled tern) and effects on reproductive time and success (Dunlop 2009; Gaughan et al. 2002; Surman & Nicholson 2009). The overall implications for ecosystem processes in the region are not known.

Change in oceanography (climate change)
The strength of the Leeuwin Current has decreased slightly since the 1970s. This weakening is expected to continue, although this prediction currently has low confidence (Feng et al. 2009). The Leeuwin Current is the basis of much of the region’s biological productivity, and its strength and seasonal/climatic variability are a primary driver for the intensity, timing and locations of productivity events in the region, from the waters off Geraldton to the Great Australian Bight (Pattiaratchi 2007). The long-term implications for the region’s ecosystems and its key ecological features are uncertain. This pressure is considered of concern for those key ecological features important for the region’s productivity and for which the Leeuwin Current is considered a primary ecological driver.

Ocean acidification (climate change)
Driven by increasing levels of atmospheric CO₂ and subsequent chemical changes in the ocean, acidification is already underway and detectible. Since pre-industrial times, acidification has lowered ocean pH by 0.1 units (Howard et al. 2009). Furthermore, climate models predict this trend will continue, with a further 0.2–0.3 unit decline by 2100 (Howard et al. 2009). Projected changes in Australian waters by 2070 include a decline in pH of 0.2 units (Lawrence et al. 2007). There is a high level of uncertainty about the effects of ocean acidification on marine life. While some organisms might be able to adapt (Orr et al. 2009), anticipated changes to phytoplankton and zooplankton have the potential to detrimentally affect ecosystem processes and the structure of ecological communities. Research on the impact of ocean acidification on Antarctic krill has found that increased levels of CO₂ kill their embryos (Kawaguchi et al. 2011). Krill are an important part of the food chain because they feed on phytoplankton and zooplankton, and are a key food source for many species that occur in Australian waters. Consequently, acidification impacts have the potential to affect species further up the food chain. The potential effects of increased acidity on the region’s biodiversity also include changes to growth and population dynamics of some shell-forming organisms, impacts on the reproductive and metabolic functions of a number of fish and invertebrate species, and sensitivity of some early-life stages to acidification (Orr et al. 2009).

Disease
Two mortality events substantially reduced pilchard stocks off South Australia and Western Australia in 1995 and 1998 (Ward et al. 2001). The two events resulted in the loss of 10–15% of the stock over an extensive area, stretching from the Great Australian Bight to the tropical coast of Western Australia. The mortality was attributed to a herpes virus, which might have been introduced, although this was not conclusively demonstrated.