Science Advisory Report 2021/036

Modelling and Monitoring Methods Approach to Evaluate Ecological Bivalve Carrying Capacity in Baynes Sound, British Columbia

Summary

• Ecological carrying capacity assessments are typically investigated using mathematical models that integrate complex interactions including physical and biological factors. Due to the significant influence of local environmental conditions on ecosystem functioning, carrying capacity studies are site specific. These models are done on a site specific basis and are validated using observational data.
• This assessment used two numerical models to integrate these complex interactions using a 4D high-resolution model. The Finite Volume Community Ocean Model (FVCOM) was coupled with a Bivalve Culture Ecosystem Model (BiCEM) including the Dynamic Energy Budget (DEB) to simulate bivalve physiology and their interactions with the ecosystem.
• This carrying capacity model focused on the biogeochemistry and lower trophic pelagic ecosystem (plankton and organic seston) and their interaction with cultured bivalves, with a focus on the extent to which bivalves utilize these food resources. The model incorporated cultured Pacific oysters and wild and cultured Manila clams as representative of a wider diversity of the bivalve population.
• Five scenarios were considered to assess model-predicted changes in water properties outlined above: 1) No Aquaculture (leases removed); 2) Current conditions (2016-2017 aquaculture production); 3) Current conditions plus max production of all leases; 4) Expansion (new applications); and 5) Expansion plus max production of all leases.
• The scenarios provided model predictions of changes in the pelagic ecosystem (Chlorophyll-a, Net primary productivity, Particulate organic carbon, Particulate organic nitrogen, and Zooplankton) due to cultured bivalve populations in Baynes Sound based on natural variation and 1/3 of primary production. Thresholds for unacceptable changes are defined by management taking into account local setting.
• Under each scenario including Scenario 5 (Expansion plus max production), the ecological carrying capacity of Baynes Sound for bivalves would not be exceeded. Model results indicate that existing shellfish and potential future increases in shellfish aquaculture leases can be supported ecologically in Baynes Sound, but should proceed gradually and in conjunction with monitoring, focusing on areas where a high density of aquaculture already exists (Mud, Fanny, and Deep bays).
• Indicators and supporting variables to assess changes in shellfish population and the surrounding ecosystem are presented, along with monitoring methodologies for collecting field samples and carrying out congruent laboratory analyses (separate research document). These tools are intended to inform the development of future monitoring programs.
• The modelling was based on a 2016-2017 data set that reflected an anomalously warm year relative to historical data. Enhanced water-column mixing and phytoplankton production can be mitigated by 1) increasing horizontal resolution of the model grid in the areas of steep topography and 2) including additional river inputs. Additional information on bivalve densities and zooplankton data would improve model accuracy.
• The individual parameterization and subsequent coupling of FVCOM-BiCEM models was a novel approach providing a 4D high-resolution, spatially-explicit hydrodynamic-biogeochemical coupled model, resulting in an efficient approach to assessing ecological carrying capacity of shellfish aquaculture.
• This modelling approach of coupling physics and biology is recommended as a methodology to assess aquaculture management ecological carrying capacity at other potential locations considered for aquaculture applications on a site specific basis.

This Science Advisory Report is from the March 8-12, 2021 Regional Peer Review on Modeling and monitoring approaches to evaluate the ecological carrying capacity for shellfish aquaculture. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

Science Advisory Report 2021/036 (PDF, 1,733 KB)

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