A pilot biological survey of Macquarie Harbour, western Tasmania

Supervising Scientist Report 113
O'Connor NA, Cannon F, Zampatti B, Cottingham P and Reid M
Supervising Scientist, 1996
ISSN 1325-1554
ISBN 0 642 24312 3

Download

Executive summary

Over the last century, Macquarie Harbour and the Mount Lyell region to the north-east of the harbour have been affected by mining activities at the Mount Lyell copper mine. In that time the mine has discharged large quantities of mine tailings into the Queen River. This material has been washed downstream, resulting in the deposition of over 100 million cubic metres of tailings, as well as slag and topsoil in the King River and Macquarie Harbour. In 1995 the Tasmanian and Federal Governments established a joint program, the Mount Lyell Remediation Research and Demonstration Program (MLRRDP), aimed at investigating remediation strategies for the impacted areas. As part of MLRRDP Project 13A, Water Ecoscience P/L have undertaken a pilot biological survey of Macquarie Harbour. The aims of the pilot study were to:

  • describe the vertebrate, invertebrate and floristic communities of Macquarie Harbour;
  • to report on the trace metal concentrations in tissue of edible fish species from Macquarie Harbour;
  • recommend a community (eg benthic invertebrates, macroalgae, seagrass) best suited as a monitor of the ecological health of the harbour; and
  • suggest a sampling regime to establish the present status of this community and to test for subsequent changes following the implementation of measures to reduce the level of pollutants entering the harbour from the King River.

This report presents the findings of the pilot survey. It also includes a detailed section on the recommended community for monitoring and an appropriate statistical design for an ongoing monitoring program.

A pilot biological survey of Macquarie Harbour was conducted by Water Ecoscience over 7 days from 30 August 1995 to 4 September 1995. Benthic invertebrate samples were collected from 28 sites throughout the harbour using a Smith-MacIntyre grab. Fish species were recorded from 7 sites which were seine netted and five sites which were gill netted and included samples set aside for trace metal analysis. Due to the time of year and poor water visibility, investigation of seagrass and macroalgae coverage was reduced to qualitative assessments of species present. Phytoplankton and zooplankton samples were collected from 14 sites throughout the harbour, while benthic diatoms were collected from 12 sites.

The benthic infauna recorded were less numerous and diverse than might have been expected in an estuary the size of Macquarie Harbour, although the recorded taxa were generally common to estuaries across southern and south-eastern Australia. As there had been no prior investigations of benthic fauna in Macquarie Harbour, it is difficult to asses the extent to which previous mining operations or natural conditions have affected population assemblages. However, based on the limited knowledge of the physical environment of Macquarie Harbour and comparisons with studies conducted on other south-east Australian estuaries, it is possible that 100 to 200 species of benthic invertebrates might be expected in the harbour, excluding potential mining impacts. In the present study only 49 benthic species were collected and this brings to 58 the total number of benthic invertebrate species recorded from Macquarie Harbour.

A total of thirteen fish species were collected by seine netting in Macquarie Harbour, with Tasmanian smelt Retropinna tasmanica the most widely distributed species. The highest abundances of this species were recorded in areas with low salinity. The silver fish Leptatherina presbyteroides was also common, especially in areas with high salinity. Other recorded species included the smallmouth hardyhead (Atherinosoma microstoma), shortsnout hardyhead (Kestratherina breviostris), common jollytail (Galaxias maculatus) and Tasmanian whitebait (Lovettia sealii).

Abundances and diversity of fish species captured by gill netting were relatively low. Most of the species captured were marine with the exception of brown trout (Salmo trutta) and Atlantic salmon (Salmo salar), both introduced salmonids. The greatest diversity of fish was caught at Neck Island (6 species) whilst the lowest diversity was caught at Double Cove (1 species). Red cod (Pseudophycis bachus) and greenback flounder (Rhombosolea tapirina) were the most abundant species, comprising 29% and 33% of the catch respectively. An undescribed species of skate in the Genus Raja was captured at Neck Island and Cosy Corner. This species of skate has only previously been captured in Bathurst Harbour, South-West Tasmania. Other species included juvenile blue grenadier (Macruronus novaezelandiae), and short-finned eels (Anguilla australis).

Seagrass and macrophyte assemblages were difficult to locate and sparse at the visited sites. This was most likely due to the survey occurring during the senescencing phase of the seagrass life cycle and low light penetration in the harbour waters. Senesced blades of the seagrass Zostera muelleri were found at Yellow Bluff and Swan Basin, the brown algae Ectocarpus fasciculatus was collected from the fish farm nets near Liberty Point, while the stonewort Nitella sp. was found at Farm Cove and Kelly Basin.

The phytoplankton in Macquarie Harbour were characterised by low species abundance and the presence of freshwater taxa in most samples, primarily reflecting the freshwater layer occupying the euphotic zone. Dinoflagellate species characterised the sites located in the southern area of the harbour, while diatoms characterised the sites influenced by marine inputs near the harbour mouth. This distribution pattern may be due to light availability in the water column (the environmental variable measured as significantly affecting phytoplankton distribution), and/or increased copper complexing capacity in fresher waters together with the greater copper tolerance of diatoms than other algal groups.

Zooplankton may be loosely placed into two groups within the harbour. The 'northern' group at the harbour mouth and the outlet of the King River had a lower species abundance and diversity, while having a majority of truly marine taxa. The 'southern' group occurred in areas receiving inflow from four rivers and contained the majority of freshwater taxa recorded in the survey.

Six species of fish were analysed for trace metal concentrations, including the short-finned eel (Anguilla australis), brown trout (Salmo trutta), Atlantic salmon (Salmo salar), red cod (Pseudophycis bachus), longsnout flounder (Ammotretis rostratus) and greenback flounder (Rhombosolea tapirina). Tissue metal concentrations for individual fish were generally below the maximum permitted concentrations of the Food Standards Code (FSC) of the National Food Authority and Tasmanian regulations. The exception was for selenium in fish collected from four of the five sampling sites (mainly greenback flounder and red cod), which in many instances was above the recommended levels of 1 mg/kg. In addition one of the two short-finned eels caught had a mercury concentration above the FSC recommended limits, although still within Tasmanian regulations. As the sample sizes for determination of metal concentrations was small, some further investigation is required to evaluate whether selenium levels in fish pose a risk to public health with consumption.

For the purposes of developing a biological monitoring program, the Macquarie Harbour ecosystem can be divided into the following component communities (with some overlap):

  • zooplankton;
  • phytoplankton;
  • fish;
  • seagrass; and
  • benthic macroinvertebrates.

Although all these components are important parts of the Macquarie Harbour ecosystem, logistic and financial constraints decree that only one such community can be sampled as part of a monitoring program. The community chosen needs to meet the following criteria:

  • life histories of constituent taxa need to be in the order of several months to a few years so that they do not exhibit marked short term fluctuations in response to seasonal climatic changes;
  • the taxa need to be reasonably persistent in a spatial sense (ie do not undergo great seasonal fluctuations in distribution and abundance due to factors such as migration);
  • the taxa need to be relatively sedentary, rather than migratory, so that it is clear they can tolerate conditions at the sampling site;
  • the taxa need to be in close association with potentially contaminated sediments on the bottom of the harbour rather than isolated from sediments, high in the water column;
  • the costs of sampling the community and the identification of the constituent taxa need to be feasibly born by a monitoring agency and need to be competitive with other types of environmental monitoring; and
  • the community chosen needs to be an important part of the Macquarie Harbour ecosystem with extensive links to other components so that observed changes will reflect changes in the health of the whole harbour.

Benthic macroinvertebrate communities fit these criteria more closely than the other ecosystem components listed above. As a result, benthic macroinvertebrates are the most commonly used ecosystem components in most marine impact assessment and monitoring programs and are the recommended community for the Macquarie Harbour biological monitoring program. The effectiveness of the monitoring program may be greatly increased if data on a range of physical and chemical variables is simultaneously collected along with each sample. Additional parameters recommended for sampling include:

  • sediment copper concentration;
  • depth of sample site;
  • sediment particle size;
  • sediment organic matter content;
  • salinity at the sample site; and
  • temperature.

As recovery of the harbour is expected to proceed over a number of decades, it is recommended that future monitoring occur on an annual basis as little additional information is likely to be gained with seasonal monitoring.