Mussel stock structure and density in longline culture

Description

With the 2015 proposed increase in mussel production in Malpeque Bay, PEI, there was a need to determine the amount of aquaculture production that can be supported by the aquatic environment without causing permanent changes in ecosystem function, species populations, communities, or habitats; this is also known as the Ecological Carrying Capacity (ECC). ECC is typically estimated using mathematical models which combine and describe complex interactions among shellfish aquaculture, natural shellfish populations, and the environment (e.g., currents, water exchange, nutrient dynamics, etc.). For example, the size and density of cultured mussels will determine the amount of phytoplankton being removed from the water column which, in turn, influences the overall ability of the system to sustainably support both cultured and natural shellfish populations. In PEI, leaseholders provide stock information to the Department on an annual basis, which is useful for assessing whether or not leases are used, but has little value in informing the estimate of Ecological Carrying Capacity. To address this gap, a survey of the PEI Blue Mussel (Mytilus edulis) longline system was carried out to generate information on mussel lease use. Specifically, the survey focused on seasonal trends in stock composition, densities, and the degree of fouling by invasive tunicates. Characteristics such as size and weight was also recorded and used to calculate rates of filtration and waste production (i.e., biodeposition). This information contributes to improving the accuracy of model simulations and predictions of the overall capacity of an area to support changes in shellfish aquaculture production.

Findings

Naturally-collected mussel larvae developed into commercial-size individuals (i.e., shell length over 55 mm) over a 25 month period. Stocks were composed of two mussel size classes (i.e., two year classes) from October to May. Clearance rate (i.e., the volume of water cleared or filtered of suspended particles per unit time) was modelled as a function of mussel shell length and abundance on collector ropes or polyethylene socks. For collectors, clearance rate rapidly increased and peaked at a shell length of 23.3 mm. Thereafter, rates declined due to self-thinning processes (i.e., mussels falling off the collectors), which exceeded individual mussel growth. For socks, clearance rate was similar but peaked at a shell length of 60.5 mm. A few mussel samples (≤ 11.9 %) were colonized by invasive tunicates. During the production cycle, the demand by mussels for suspended food particles (e.g., phytoplankton) fell significantly in September compared to other times in the year. These data inform ecological carrying capacity models for longline mussel culture.

Publications

Comeau, L., R. Filgueira, J.D.P. Davidson, A. Nadeau, T. Guyondet, R. Sonier, A. Ramsay, and J. Davidson. 2017. Population structure and grazing capacity of cultivated mussels in Prince Edward Island, Canada. Canadian Technical Report of Fisheries and Aquatic Sciences. Vol. 3228. Fisheries and Oceans, Moncton, NB. 138.

Program Name

Program for Aquaculture Regulatory Research (PARR)

Year(s)

2015 to 2017

Principal Investigator(s)

Luc Comeau
Research Scientist, Aquaculture and Coastal Ecosystems, Gulf Fisheries Centre
343 Université Ave., Moncton, New Brunswick
Email: Luc.Comeau@dfo-mpo.gc.ca

Team Member(s)

Peter Warris

André Nadeau

John Davidson

Jonathan Hill

Jeffrey Davidson, Aquatic and Ecosystem Health, University of Prince Edward Island, PEI