Science Advisory Report 2015/003

Carrying capacity for shellfish aquaculture with reference to mussel aquaculture in Malpeque Bay, Prince Edward Island

Summary

• This advice is provided to inform the marine spatial planning process in consideration of a request to increase suspended mussel aquaculture acreage in Malpeque Bay, Prince Edward Island. The analysis is provided relative to the concept of carrying capacity of Malpeque Bay to support current and potential increases in suspended mussel culture.
• Carrying capacity has been defined based on multiple viewpoints (physical, production, ecological, and social). This advisory report addresses mussel aquaculture in the context of production carrying capacity and ecological carrying capacity.
• In this report, production carrying capacity is assessed as the magnitude of aquaculture activity that maintains mussel growth within the range of variation in the current leases.
• Ecological carrying capacity (defined as the magnitude of aquaculture activity that can be supported without leading to unacceptable changes in ecological processes, species, populations, communities, and habitats in the aquatic environment) is partially considered by focusing on phytoplankton dynamics but cannot be fully assessed given that unacceptable changes have yet to be defined. Thresholds for unacceptable changes would be defined by management.
• Production and ecological carrying capacity are typically investigated using mathematical models that integrate complex interactions between aquaculture activities, bivalve physiology, and the environment. Due to the significant influence of local environmental conditions on ecosystem functioning, carrying capacity studies are site specific.
• Estimation of phytoplankton utilization by bivalves has been used to assess production and ecological carrying capacity, given that phytoplankton constitutes the primary step in the planktonic marine food web and is a main food source for bivalves.
• Cultured mussels are presently the dominant filter-feeders in Malpeque Bay.
• The proposed suspended mussel lease expansion in Malpeque Bay of up to 590 ha would increase the leased spatial area coverage from 7% to 10%. The placement scenario for the projected leases used in this assessment could be modified during subsequent steps of the consultation and marine spatial planning process.
• Model predictions of changes in chlorophyll a and mussel growth were used to assess the state of production carrying capacity of Malpeque Bay.
• Under current and projected levels of mussel culture and relative to the metrics of production carrying capacity used in this assessment, the production carrying capacity of Malpeque Bay would not be exceeded.
• Considerations of benthic habitat and community effects, dynamics (energy flow and nutrient cycling), and epifauna communities associated with the aquaculture infrastructure are required for a complete ecological carrying capacity assessment. The link between benthic and pelagic components and their interactions, in terms of vicinity versus bay scale effects, requires further work.
• While there are various options for production carrying capacity and ecological carrying capacity indicators, there is much uncertainty with respect to establishing thresholds that are linked to unacceptable biological and/or ecological changes.

This Science Advisory Report is from the October 8-9, 2014 Gulf Region science peer review meeting of Carrying capacity for shellfish aquaculture with reference to mussel aquaculture in Malpeque Bay, Prince Edward Island. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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