Bacterial infections (currently Vibrio harveyi) are emerging as mortality episodes related to stress events which are out of abalone farmers’ control. Data for appropriate antibiotic use is unavailable. Inappropriate unregulated use in shellfish including abalone has led to antibiotic resistance and residue problems in several countries. Legal antibiotic access is limited, will worsen with proposed legislative changes, and in the longer term would require at least MUP registration.

MUP would require data on a range of parameters, including tissue levels achieved with various dose rates and how this varies with size, species, temperature and physiological state, duration of residues in tissues, acute and longer term toxicity, and efficacy against the pathogens of concern under the proposed conditions. Environmental safety data requirements would limit the choice of antibiotics to those already available for other aquatic animals, that is oxytetracycline, amoxycillin, potentiated sulphonamides (trimethoprim / sulphadiazine combination), and possibly quinolones such as oxolinic acid. Each of these has major potential limitations in either stability or bioavailability under marine conditions, efficacy against current pathogens, or acceptability for aquaculture use (quinolones). Volumes required for bath treatments, leaching from feeds, and cessation of feeding in infected abalone may all limit practicality.

To address all these parameters for MUP application in not warranted unless sufficient stability, bioavailability, and tissue levels are achieved, hence this preliminary study of the practicality of administration and in vitro and in vivo bioassay of bioactivity. The techniques developed for in vitro assessment of abalone antibacterial defenses and the in vivo infection model will also indicate the role of stress and whether alternate approaches to disease control also warrant investigation. Industry appreciates avoidance is preferable to treatment, and though stress may be unavoidable, understanding its role and being able to measure the effect may assist in developing alternate strategies.

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.