Industry monitoring has identified sizeable increases in sediment loading of copper and zinc at farm sites in the Huon and D’Entrecasteaux Channel, with Cu levels in some sites exceeding existing management trigger levels (ANZECC/ARMCANZ (2000)). This is a major concern for both farmers who are reliant on antifoulant use to ensure adequate environmental conditions within pens for fish growth and stock health. While there is some evidence to suggest that paint-associated copper may be less readily bioavailable than other forms, this information is currently insufficient to warrant changes to existing guidelines. Consequently the industry needs to better define the potential for environmental impacts associated with copper contamination, and a strategy for management and remediation of these sediments needs to be developed.

There is an urgent need to understand both the consequences of copper accumulation and the conditions that affect copper build up under cages, and to incorporate this information into management practice. Specifically, we need to
i) develop management limits for sediments,
ii) determine reliable approaches for monitoring Cu bioavailability,
iii) determine the potential for natural or assisted remediation (can it occur and can it be managed),
iv) the implications of farm management practices on sediment contamination (i.e. fallowing, in situ cleaning, sediment disturbance).
This information will enable the development and implementation of comprehensive management strategies.

The Tasmanian salmonid industry has recently been faced with several significant production issues necessitating increased use of antibiotics and antifoulants. The effects of these chemicals on the local ecology and ecosystem function are currently poorly understood and without evidence to the contrary, it is difficult for the industry to refute the perception that such chemicals have a detrimental effect on the environment.

There is a large body of literature regarding the effects of antibiotics, however the information pertaining to aquaculture is limited. Improvements in husbandry and vaccine development have now all but eliminated the use of antibiotics in aquaculture overseas, consequently there have been few recent aquaculture specific studies, with even fewer studies on ecosystem effects, the available information largely focussing on environmental persistence and antibiotic resistance. However, there is quite a lot of information in the terrestrial livestock and medical areas on the comparative effects of various antibiotics as well as quite a substantial ecotoxicological literature. In contrast there is a substantial local literature on the environmental impacts of antifoulants and heavy metals. There is a need for a targeted review to establish environmental risk factors associated with current antibiotic and antifoulant usage and to develop an appropriate strategy to research and monitor ongoing impacts.

Some data on sediment residue levels for both antibiotics and antifoulants has been collected by the salmon industry in compliance with drug/chemical licensing permit conditions authorities and by the state government in response to concerns regarding antibiotic usage. So far this data has not been collated and has only been subjected to preliminary analysis; a comprehensive evaluation of this data would markedly improve our understanding of current impacts and help to determine what additional information may be required.

There are two major aspects:

1. Importance to industry of control of precocious sexual maturation
Tasmanian salmon typically mature after only one winter at sea, in contrast to northern- hemisphere populations where the majority take two ‘sea-winters’ to mature. The Tasmanian fish still reach 3 – 5 kg during this period due to the favourable effects of higher temperature on growth, however, the less desirable outcome of early maturation is the compression of the harvest season. Strategies designed to improve seasonal production have been estimated to be worth $A 8 – 16 million per year to the Tasmanian salmon industry (confidential industry estimate prepared for CRC for Aquaculture in 1998).

2. Requirement to conduct research in Tasmania
Functional photoperiod manipulation techniques have been developed overseas so why do it in Tasmania rather than simply import solutions? Overseas protocols have been trialled by the Tasmanian industry but have given negative or unpredictable results. Confounding factors which require consideration before overseas protocols can be applied successfully and predictably in Tasmania are:

A. Light intensity.
Due to Tasmania’s low latitude and high number of sunshine hours relative to the majority of northern hemisphere salmon farming areas, it is likely that salmon farmed in Tasmania are exposed to higher daytime light intensities, particularly at the equinoxes. Relative light intensity is a critical factor for the success of photoperiod manipulation practices and it is expected that higher, yet to be determined, levels of nighttime illumination will be required under Tasmanian conditions.

B. Temperature.
Overseas scientists report increased melatonin secretion (up to approx. 30%) at summer temperatures relative to winter temperatures in Atlantic salmon maintained under identical photoperiods. Tasmania’s relatively high water temperatures suggest that a further increase in light intensity will be required to reduce plasma melatonin levels below the putative threshold required to ensure that the fish perceive any modification to photoperiod.

C. Seasonal and individual variation.
Assuming that the preceding factors can be adequately clarified, it will be necessary to account for the possible effects of differences between seasons (both within and between years) and individual variation within fish populations in relation to the response of stocks to photoperiod manipulation. Relative to overseas salmon farming areas, Tasmania tends to have a short, mild winter, an early, warm spring and a long, hot summer. Thus timing of the critical “gate-open” decision period for maturation has yet to be determined under Tasmanian conditions.

Stock enhancement strategies can be a cost-effective means of restoring or maintaining fisheries, and have proven essential in catchments with barriers to migration (Knights and White 1998). Regulation of natural river systems has obstructed eel migration in many catchments, and with the implementation of appropriate management tools such as fish passes / ladders and translocation through trapping / netting programs, restoration of stocks can be achieved. Such strategies have not only proven successful in increasing commercial fishery yields, but also contribute to enhanced spawning stocks and increased silver eel escapements.

Hydro electric operations (dams and power generating turbines) reduce the chance of successful emigration of silver eel, especially for larger female eel (Dekker 1999), and, depending on flow and turbine type and number, may represent a major source of mortality to pre-spawning adults (Ritter et al 1997).The design of downstream passage ways and the use of non-generating periods to reduce mortality have been trialled and implemented in New Zealand, the USA and Europe, but have yet to be adopted or investigated in Australia.

The sustainability of the eel resource in Tasmania and of existing (and potentially new) commercial eel fisheries in hydro-impounded catchments will ultimately depend on the implementation of appropriate and effective mitigation strategies (passage and/or translocations) specific to both upstream and downstream migrations.

This proposed program addresses the issue of sustainability by assessing both cause and effect of impacts and various mitigation options. It is envisaged that the results and recommendations arising from this proposed study will underpin the development of an integrated management strategy for managing eel fisheries in hydro-impacted catchments with direct benefits to managers and industry alike. Results from this study could be readily transferred to other States, with coordination and dissemination through the existing Australian and New Zealand Eel Reference Group (ANZERG).

REFERENCES

Dekker, W. 1999. Effects of Transfers and Restocking of Eel. Report of the EIFAC Working Group on Eels - Denmark, September 1999. Pp13-17.

Knights, B. and E. White, 1998. An appraisal of stocking strategies for the European eel, Anguilla anguilla - In Cowx, I.G. (ed): Stocking and Introduction of Fish. Fishing News Books. Pp 121-140.

Ritter, J.A., Stanfield, M. and Peterson, R.H. 1997. The American Eel in Eastern Canada - Stock Status and Management Strategies. Proceedings of Eel Workshop January 13-14 1997, Quebec City, QC. Can. Tech. Report 2196. 174p.