A comparison was made of sediments and associated macrobenthos at sites sampled within 42 fish farm leases distributed across Tasmania. Several key biotic and abiotic metrics recommended in previous studies for assessing environmental impacts of fish farm waste were investigated.
Maintenance and Update Frequency: notPlanned
Statement: Environmental and biological data were obtained in collaboration with, and in some cases by, salmonid farm operators from 42 separate farm lease locations distributed in six regions around Tasmania. Sampling primarily occurred from 1998 to 2003, although two farm leases were sampled in 1997 and a single lease in 2004. Farm leases varied in size and production capacity but were typically 20-60 ha, with 6-20 cages (26-36 m in diameter) stocked per lease. Cages were periodically moved within farm lease areas, with rotation times of 12-36 months. Depths of sites studied ranged from 7 m to 47 m, with mean of 20 m.
Triplicate macrofaunal samples were collected < 5 m apart at each site using a Van Veen grab (0.07 m2 surface area) or diver operated corer (150mm diameter) pushed into the sediment to a depth of 100mm. Samples were sieved in the field using a 1 mm mesh sieve, and retained material placed into vials and fixed with 5% buffered formalin. In the laboratory, the collected material was washed through a stacked series of sieves (1, 1.4, 2, 2.8 and 4 mm) using the methods described by Edgar (1990).
Material retained on each sieve was sorted, with animals separated into species groups and counted.
A Craib corer was used alongside the Van Veen grab at each site to collect triplicate sediment cores (43 mm in diameter) for analysis of sediment properties. Redox potential was measured in millivolts at the surface of the sediment and at 40 mm depth below the sediment surface.
After redox measurements were completed, two sub-samples were separated from each Craib core. The top 30 mm of sediment was collected in a vial for analysis of organic content, %C, %N, stable isotope ratios and particle size. The next 70 mm was used for particle size analysis only.
The two samples comprising the top 100 mm of each sediment core were combined for particle size analysis.
Adam Davey, Aquenal Pty Ltd.
Colin Shepherd, Marine Farming Branch, Department of Primary Industries and Water
Aquenal Pty Ltd.
Tassal Operations Ltd.
Huon Aquaculture Company Pty Ltd.
AMD Pty Ltd.
Aquatas Pty Ltd.
This study assessed the efficacy of a variety of physical and biological metrics in discriminating fish farm impacts at different distances from cages, with emphasis on the more distant effects.