PARR Fact Sheets

Production from suspended bivalve aquaculture has increased significantly over the past two decades, but recently has been impacted negatively by significant fouling from invasive tunicate species. Although invasive tunicates can represent a substantial biomass on suspended culture gear, there are no direct data available regarding biodeposition from these fouling communities. Research has suggested that sedimentation from suspended bivalves in culture and the associated fauna may contribute considerably to the total amount of material that settles to the bottom. The following research was done under field conditions to establish the extent to which fouling organisms contribute to biodeposition from mussel culture. The biodeposition dynamics associated with mussels and two fouling tunicates, Ciona intestinalis and Styela clava, in mussel aquaculture in Prince Edward Island (PEI) were examined in this study. The presence of C. intestinalis on mussel socks doubled the amount of biodeposition relative to mussel socks without tunicates. Although S. clava, used in the experiment, were small and had a negligible effect on total biodeposition from mussel socks, they increased sedimentation rates from mussel socks relative to that of abiotic control socks. Sinking rates of faecal pellets from large C. intestinalis varied between 1.4 and 6.5 cm s-1. Using rates of biodeposit production and sinking, and hydrological data obtained from the present study, footprints of benthic loading due to mussel and tunicate biodeposition for a typical mussel farm in PEI were modeled using Shellfish-DEPOMOD. This model predicted benthic loading below mussel socks fouled with C. intestinalis to be approximately two times greater than that from lines containing only mussels − rates of up to 15.2 g m-2 d-1− which is in agreement with the research study results. However, the extent of the biodeposition footprint (≥ 1 g m-2 d-1) below C. intestinalis-fouled mussel socks is similar to or more confined compared to mussel only socks due the greater settling rate of C. intestinalis biodeposits. Results from this research will increase our understanding of aquaculture-environmental interactions and help improve overall environmental management of benthic impacts of shellfish aquaculture in Canadian waters.

To regulate and manage the environmental effects of net pen fish farming operations, it is important to accurately predict the depositional footprint of waste materials beneath and around cages. In many areas, waste depositional models such as DEPOMOD are used to assess sites for licence attribution and site monitoring for license conditions compliance (Cromey et al. 2002 a, b). The predictive capacity of depositional models is dependant on input data based on the nature of waste materials, for example, settling speeds and re-suspension thresholds. The current DEPOMOD re-suspension module may have some practical limitations, since the onset of sediment erosion is derived from a small-sized, slow-settling, synthetic-tracer particle within a low-energy oceanographic setting. To support the development of adjusted model inputs for use along our coastlines, this study examined the settling and re-suspension parameters of Canadian commercial fish feed pellets and the associated faeces. For model refinement, future research is required to enhance these waste transport estimates based on a range of oceanographic (dispersive, quiescent) and benthic (consolidation, roughness, substrate) conditions to provide a predictive tool for industry and regulators.

Coupled biological-physical models were used to simulate the spatial and temporal concentrations of the infective copepodid stage of sea lice in the Broughton Archipelago and surrounding regions of British Columbia. To simulate 3-D circulation, temperature and salinity fields, the Finite Volume Coastal Ocean Model (FVCOM) was implemented and validated with observations. A separate biological model used the FVCOM fields to simulate the transport, development and behaviour of the planktonic larval stages. The model-computed copepodid concentrations for the critical March – April 2008 period showed generally low infective pressure around the important Knight-Tribune migratory region. Comparison of the model results with plankton sampling data and sea lice infestation data on wild juvenile salmon showed qualitative agreement and spatial associations. These coupled bio-physical models were used to assist with the development of the aquaculture industry's Coordinated Area Management Production (CAMP) plan and are an operational tool available to assist regulators in establishing sea lice control strategies.