Development of guidelines for fish health consequences of water circulation patterns in Long Pond Bay, Grand Manan

Description

The Fish Health and Oceanography Project received funding from the DFO Aquaculture Collaborative Research and Development Program (ACRDP) in late 2001. The project's main goal was to enhance understanding of the water circulation and water transport pathways within the Long Pond Bay area of southern Grand Manan and to use this to help assess the influence of the water circulation pattern on fish health and bay management concerns in the area. This report summarizes the project's findings. It also includes the presentations given at the final meeting of the project, held on 17 February 2004.

The project included collection of field data and the development of a circulation and particle transport model. Field data included the release of CAST (Convertible Accurate Surface Tracker) drifters and the deployment of InterOcean S4 and RDI Workhorse ADCP (Acoustic Doppler Current Profiling) current meters. The results from the field data were compared to the computer model results. The computer model is a three-dimensional finite element model, with resolution of 50-100 m in the southern Grand Manan area. In this model, currents are driven by the M2 lunar tide.

In general, agreement between the field data and model predictions was reasonably close. Where there were discrepancies, these could be rationalized. For example, most model runs did not include the effect of wind on the circulation and yet the winds sometimes had an effect on the trajectory of drifters. In one area, local knowledge advised of the existence of a localised magnetic disturbance which made compass readings in the area unreliable and hence could have affected S4 current meter readings gathered in the specific area of the disturbance. Minor inaccuracies in the model coastline and bathymetry and the effects of fish farms on water currents (the model did not include the presence of fish farms although the physical presence of fish cages probably affects the water flow in the vicinity of the farm) may have degraded comparisons between observed and modeled currents in a few cases.

One of the main questions addressed by the project concerned the amount of water exchange between the sole even year-class farm (site MF-303, located in northern Long Pond Bay) and its nearest neighbor (site MF-403, located about 2 km due south). The project results indicated that tidally induced water movement in the area of site MF-303 was largely in the east-west direction. This is perpendicular to the north-south axis connecting the farms. However, it was noted that under certain wind conditions, drifters were carried south into site MF-403. It also appears that, at certain phases of the tide, water from site MF-303 could be carried toward the farms in Seal Cove (to the west).

The data suggests that existing Bay Management Areas (BMAs) 20 and 21 should be considered as one BMA, but that within this area, site MF-303 is sufficiently isolated from the other sites, so that its status as the sole even year-class site in the area could be maintained. Sites in BMA 19 (White Head Island) were relatively isolated from the rest of southern Grand Manan.

The project succeeded in developing a better understanding of water circulation in the southern Grand Manan area and in establishing closer links between oceanographers and fish health specialists. In order to fully understand the links between oceanography and fish health, more knowledge is required on fish health factors, such as how long viruses can survive in seawater and movements of planktonic stages of sea lice.

Program Name

Aquaculture Collaborative Research and Development Program (ACRDP)

Year(s)

2001 - 2005

Ecoregion(s)

Atlantic: Newfoundland, Labrador Shelves

Principal Investigator(s)

Fred Page
Email: Fred.Page@dfo-mpo.gc.ca