Assessing trace-element indicators of benthic organic enrichment associated with aquaculture activities

Description

Aquaculture wastes, such as faeces or uneaten food, can accumulate beneath and near farm sites. In the near-field (i.e., sites located near to the farms where the wastes are released), this accumulation is predictable using depositional modelling tools such as DEPOMOD. The organic enrichment effects associated with this deposition are well known and managed to ensure environmental sustainability. However, the far-field effects (i.e., the effect at a distance from the farms) that may be associated with the release of aquaculture waste material are poorly understood, partly because it is difficult to accurately predict where wastes will be ultimately dispersed. Additionally, once wastes are moved from the immediate vicinity of a farm site it is difficult to distinguish between deposits coming from farm activities, other industrial sources and naturally occurring organic materials. To monitor, and if necessary, regulate, the far-field effects of aquaculture wastes, it is necessary to be able to identify where wastes are transported and what material originates from farm sources.

A limited number of sensitive detection tools (sediment free sulfides and geonormalized trace-metals or "standarised" trace elements) are available to environmental monitoring programs for making such identifications. Research at the time, focused on trace-metal assessments at a variety of aquaculture sites, has shown that aquaculture waste material (fish feed and faeces) has a trace-metal signature that can be distinguished from that of naturally-occurring trace-metals. It was proposed that the geonormalization of trace-elements may identify depositional "hot spots" and track transport pathways to determine the fate of farm waste material. This approach could help to identify areas where wastes would accumulate in the far-field and ultimately, inform aquaculture management in the spatial design of monitoring programs.

As a first step towards conducting a robust regional impact assessment (longer-term research goal), this PARR project focused on obtaining, formatting, and running a preliminary analysis on archived benthic data sets previously collected by the British Columbia Ministry of the Environment and Fisheries and Oceans Canada. These datasets support a region-wide assessment of aquaculture-derived trace-metal signature under various oceanographic, bathymetric and operational settings. This geonormalization approach may be adopted to assess the fate of aquaculture wastes in the far-field and across a range of environmental settings.

Findings

Sediment trace-elements functioned as direct tracers of aquaculture waste material (i. e., zinc and copper) and may complement existing monitoring variables (i.e., sulfides) that serve as an indicator of benthic organic enrichment events. These metrics combined may be used together in a triage approach for defining benthic faunal health. Given their conservative nature, trace-elements can be used to complement existing benthic organic enrichment indicators in environmental monitoring programs of active sites as well as fallowing periods.

Results suggested that the conservative and stable nature of trace-elements does not allow for significant decreases in elemental concentrations between fish peak-production and fish pre-stock conditions.

Program Name

Program for Aquaculture Regulatory Research (PARR)

Year(s)

2012 to 2014

Principal Investigator(s)

Terri Sutherland
Research Scientist, Fisheries and Oceans Canada, DFO-UBC Centre for Aquaculture and Environmental Research (CAER), Pacific Region
Email: Terri.Sutherland@dfo-mpo.gc.ca

Team Member(s)

Bernie Taekema, Aquaculture Management Division, Fisheries and Oceans Canada, Pacific Region

Kerra Hoyseth, Aquaculture Management Division, Fisheries and Oceans Canada, Pacific Region

March Klaver, Aquaculture Management Division, Fisheries and Oceans Canada, Pacific Region