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Impacts in Inland Saline Aquaculture A Case Study for Trout Production from Saline Groundwater in Western Australia
by Alan Lymbery, Mark Starcevich and Rob Doupé
January 2007
RIRDC Publication No 05/166 RIRDC Project No UMU-27A
Background
There is increasing interest
among farmers affected by salinity in pursuing aquaculture opportunities
using saline groundwater. Inland saline aquaculture, however, may have
its own environmental impacts and these will need to be identified and
managed before a sustainable aquaculture industry can develop.
Objectives
The aim of this project
was to develop an environmental management system for the Saltwater Trout
Alliance, an alliance of producers who are growing rainbow trout in inland
saline water in the Wheatbelt and Great Southern regions of Western Australia.
More specifically, the project aimed to: ??identify potential environmental
impacts
??provide quantitative data
on the extent of some of these impacts
??undertake an environmental
risk assessment of the impacts
??identify and experimentally
test treatment procedures for the most important impacts
??develop a template for
an environmental management system
??test consumer acceptance
of trout produced in an environmentally friendly way.
Methods and results
Identification of environmental
impacts
To identify potential environmental
impacts we surveyed farmers from 113 properties throughout the Western
Australian wheatbelt, and interviewed representatives of resource management
agencies.
Four types of culture units have been used to grow trout: natural salt lakes, farm dams, constructed earthen ponds and tanks. An analysis of their water flow characteristics suggested that lakes, dams, ponds and tanks are likely to produce qualitatively similar environmental impacts. We classified potential environmental impacts from trout production in inland saline water into two types. First, those that occur through the consumption of resources: displacement of native vegetation; use of surface water flows or groundwater; consumption of invertebrate fauna in salt lakes; and consumption of fishmeal-based trout pellets. Second, those that occur through the production of wastes: nutrients, principally nitrogen and phosphorous from uneaten food or excretion, in the culture system; release of nutrients as effluent from the culture system to natural waterways; release of fish into natural waterways; chemicals, such as chemotherapeutics, disinfectants or anaesthetics in the culture system; release of chemicals into natural waterways; and discharge of saline water from the culture system into natural waterways. Regulatory mechanisms are in place for all of these impacts except the consumption of trout pellets, but their effectiveness may be compromised by the diversity of government agencies involved and by the fact that many of the regulations do not apply to small-scale operations. Eighty six per cent of farmers surveyed believed that environmental management guidelines are essential to the development of a sustainable inland saline aquaculture industry, and 89 per cent of farmers indicated that they would implement such guidelines if they were available.
Quantitative study of
effluent release
One of the potential environmental
impacts identified through the survey, the release of nutrient enriched
effluent into natural waterways, is generally considered a major problem
for land-based aquaculture throughout the world. To quantify the extent
of this impact from inland saline trout production in Western Australia,
we measured nitrogen, phosphorous and other water quality components of
inflow and outflow water from four different trout production systems:
floating cages in a dam; tiered earthen ponds; raceway ponds and recirculating
tanks. We found significant increases in total nitrogen, ammonia, nitrite/nitrate,
total phosphorous and orthophosphate concentrations in outflow waters,
compared to inflow waters from all four trout farms. In addition, the proportion
of biologically active nitrogen and phosphorous components (ammonia, nitrate,
nitrite, orthophosphate) was increased from inflow to outflow in the tank
production system, although not in the pond production systems. Total nitrogen
loads varied from 0.011-0.285 kilograms/day/tonne, and total phosphorous
loads from 0.038-0.065 kilograms/day/tonne. Although these loads are less
than those typically found in the effluent from overseas trout farms, the
inland saline aquaculture industry in Western Australia is at a very early
stage of development and fish stocking rates are quite low.
Risk assessment of environmental
impacts
To develop appropriate treatment
and monitoring strategies for environmental impacts from farming trout
by the Saltwater Trout Alliance, we conducted a qualitative risk assessment
of the potential impacts which were identified in the survey. From site
visits, interviews with farmers and a focus group meeting with resource
managers, we assessed both the likelihood of occurrence and the consequences
of each impact, on a scale of one to five. While most of the potential
environmental impacts were considered either unlikely to occur or to have
relatively minor environmental consequences, the release of nutrients,
the release of saline water and the consumption of fishmealbased trout
pellets all represent serious risks that cannot be avoided or retained
if a sustainable inland aquaculture industry is to develop. We therefore
need to consider ways in which either the likelihood of occurrence or the
consequences of these risks can be reduced.
Treatment of environmental
impacts
Alternatives to fishmeal-based
artificial diets for salmonids are not readily available at present.
Treatment strategies for this environmental impact therefore need to focus on reducing the amount of trout pellets used, by selecting an efficient diet, accurately calculating feed requirements from measurements of growth rate, optimising the feeding regime and, where possible, utilising natural feed sources. We compared the relative productivity and profitability of three different production systems: extensive (trout stocked in earthen ponds and totally reliant on natural feed); semi-intensive (trout stocked in earthen ponds and provided with supplementary diet); intensive (trout stocked in closed, recirculating tanks). The yield of fish increased with increasing production intensity. The mean wet weight of trout after four months of grow-out was 61.3 grams in extensive systems, 157.9 grams in semi-intensive systems and 137.9 grams in intensive systems, giving mean yields of 10.8 kilograms/pond (13.5 kilograms/hectare), 27.9 kilograms/pond (34.8 kilograms/hectare) and 54.9 kilograms/tank (21.1 kilograms/cubic metre), respectively. An economic analysis of the different production systems showed that the increases in yield were sufficient to balance the extra operating costs involved in semi-intensive systems, but not in intensive systems. Semi-intensive production systems, where trout eat both trout pellets and invertebrate prey within the pond ecosystem, appear to offer the best long-term economic prospects for an inland saline aquaculture industry. There is scope for reducing the amount of trout pellets fed in semi-intensive systems by manipulating the quality and quantity of natural invertebrate feed.
Mechanical methods for treating aquaculture effluent, such as screens and sedimentation ponds, have limited efficacy in treating dissolved nutrients and salts. We therefore investigated the ability of a subsurface-flow constructed wetland system, incorporating the estuarine sedge Juncus krausii to filter total nitrogen, total phosphorous and sodium chloride at varying concentrations from rainbow trout aquaculture effluent. After 38 days, the plant-soil ecosystem removed up to 69 per cent of total nitrogen, 88.5 per cent of total phosphorous and 54.8 per cent of sodium chloride. Nitrogen and not affected by salinity. Salinity did not affect nitrogen uptake but did reduce phosphorous removal.
Both total nitrogen and sodium chloride removal increased over time whereas total phosphorous removal remained relatively constant. Growth traits of J. kraussii were adversely affected by salinity concentration but not by nutrient level. The subsurface-flow wetland treatment system shows significant potential for incorporation into inland saline trout production, but the salt-sensitivity of J. kraussii suggests that a species displaying a higher salt-tolerance may be required.
Development of an environmental
management system
An environmental management
system is a systematic approach used by an organisation to manage its impacts
on the environment. Typically, there are five key components in a successful
environmental management system: developing an overarching policy for environmental
management; setting environmental objectives and targets to fulfil the
policy; designing and implementing procedures to achieve the targets; measuring
performance against the targets; and regularly reviewing and updating policy,
objectives, targets and procedures. Using the information collected in
this project, the Saltwater Trout Alliance has endorsed an environmental
policy which commits the organisation to producing fish products in a sustainable
fashion, and developed objectives and targets for the key environmental
impacts of the release of nutrient rich effluent, the release of saline
water and the consumption of fishmeal-based trout pellets. A range of procedures
are available for helping farmers in the Alliance to achieve environmental
targets; some of these are already in place and others need further on-farm
testing of their efficacy. A monitoring program has been established on
all farms, and recommendations have been made for annual reviews of all
components of the environmental management system.
Consumer acceptance of
environmentally sustainable production
Environmental management
systems impose costs upon an industry. Even where the social and ethical
importance of sustainable production is recognized, small profit margins
may make it difficult for producers to implement procedures to monitor
and control environmental impacts. The uptake of an environmental management
system will therefore be helped by any market advantages from branding
aquaculture products with positive environmental attributes. In a survey
of potential consumers of rainbow trout grown in inland saline water, we
found that 92 per cent of respondents considered that environmentally sustainable
production of fish was an important issue affecting their purchasing decisions,
although it was ranked as less important than food safety/quality. Over
90 per cent of respondents also indicated that they would be prepared to
pay more for fish that was labeled as either quality assured or produced
in an environmentally sustainable way.
Implications and recommendations
The key factors in developing
an environmental management system for organisations such as the Saltwater
Trout Alliance, which involve a number of cooperating enterprises, are
to ensure ownership of the system from within the organisation, rather
than have the system imposed by legislation or recommendations from outside;
to develop objectives, targets and treatment procedures on the basis of
scientifically sound, site-specific investigations of environmental impacts;
and to have in place a system for sharing of information which enables
regular reviews of performance.
For the Saltwater Trout Alliance, we recommend:
For resource management
agencies in Western Australia, we recommend:
For the inland aquaculture
industry generally, we recommend:
 
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