Safe distance between fish farms to be determined
In order to determine a maximum level of acceptable impact on the environment under salmon farms in British Columbia, the BC Salmon Farmers Association years ago provided some CAD$ 400,000.- (~€309,000 at today’s exchange rate) towards a study that explained the relationship between biological impact of waste discharge from fish feces and lost feed and the chemical changes in soft-bottom sediments. A clear relationship was found between changes to sediment fauna and changes in sediment sulphides. This allowed regulators to set a maximum level of allowed impact that could easily be monitored by chemical sampling rather than by expensive and time-consuming biological sampling. These levels allow for the production of some 3-4,000 tonnes of salmon during a two-year production cycle at some of the best locations.
Studies about the far-field and accumulative effects of waste discharges are still needed, and an initiative by Spanish researchers may help shed some light on this, as ScienceDaily reports;
Scientists at the Spanish Institute of Oceanography (IEO) and the University of Barcelona have developed a methodology to detect the influence of discharges from open water fish farms on marine ecosystems. With this methodology, based on the analysis of the isotopic signal of nitrogen in the tissue of marine macrophytes, coastal managers can select areas which are suitable for aquaculture under ecological criteria, in order to establish a safe distance between the farm and the sensitive ecosystem.
Researchers from the Seagrass Ecology Group at the IEO and the Department of Ecology at the University of Barcelona have collaborated in the development of macrophyte bioindicators which are sensitive to nutrient input from fish farms and its application to define their areas of influence. This new methodology could be useful to select suitable areas for aquaculture in open water under ecological criteria.
The methodology consists of the analysis of the proportion of different isotopes of nitrogen in the tissues of marine vegetation (algae and marine angiosperms), and compares it with the same isotope ratios in discharges whose impact is evaluated. This determines how much nitrogen measured in primary producers comes from aquaculture effluents and how this nitrogen vary in space from fish farm facilities. This information allows (managers) to establish, under ecological criteria, a safe distance to protect vulnerable ecosystems from the impact.
Part of this methodology, recently published in the scientific journal Marine Environmental Research, has been applied to study the influence of a large fish farm complex (with a production of 6,000 tons per year) located in San Pedro del Pinatar (Murcia), on nearby Posidonia oceanica meadows. Discharges from these farms were found to affect marine angiosperms communities located two kilometers away.
This work and some other related ones, which are in the process of publication, have been funded by the National Board of Marine Farming (JACUMAR) and form part of Maria Garcia's PhD thesis, presented on March 19 at the University of Barcelona. The thesis, entitled "Study and development of biological indicators to measure the spatial extent of discharges from fish farms," is supervised by the paper's lead author, Juan Manuel Ruiz, together with Marta Perez.
In the thesis, a wide range of bio-indicators of the impact of aquaculture on seagrass beds is discussed, especially those related to nitrogen, taking into account other case studies both from the Mediterranean (Murcia and Tarragona) and Atlantic (Canary Islands). A method to evaluate the extent of nutrients from fish farms is also proposed. This method is based on the measurement of nitrogen in several incubated individuals in pelagic bioassays located at increasing distances from marine farms. The effectiveness and reliability of this bioassay were very high and this method can be applied to determine a safe distance for installing marine farms.
