Science Advisory Report 2016/039

State of Knowledge of the Oceanography and Water Exchange on the South Coast of Newfoundland to Support the Development of Bay Management Areas for Finfish Aquaculture

Summary

Geography, Hydrology, Bathymetry and Oceanography in the Coast of Bays

• The Coast of Bays can be divided in three geographically distinct regions:
  • Bay d’Espoir: a long and narrow fjord subject to large runoff with an annual mean of ~252 m³/s;
  • Belle Bay: a deep and wide bay subject to significant runoff (~71 m³/s); and
  • Connaigre Peninsula: a shallower region more exposed to the open ocean and subject to a small runoff (~10 m³/s).
• Surface wind conditions in the Coast of Bays present significant seasonal as well as spatial variability. Offshore west‑northwest/northeast prevailing winds are strong (median speed of 35-45 km/h) in winter/spring while southwest prevailing winds are much weaker (median speed of 20-30 km/h) in summer.
• The tides are mainly semi-diurnal with small diurnal constituents. Tidal ranges in the whole region of interest are small (of the order of 2 m, large tides) and, consequently, associated water flushing time of the bays is large. Flushing time is significantly smaller within the Connaigre Peninsula region, ~30 days, than in both Bay d’Espoir and Belle Bay regions, ~60‑70 days.
• The whole Coast of Bays area is characterized by a strong heating and cooling seasonal cycle with annual sea-surface temperature amplitude of approximately 7°C. This seasonal amplitude of surface temperatures is large in comparison to the conditions seen in British Columbia but comparable to some regions in Nova Scotia where similar finfish aquaculture operations are currently taking place.

Water Column Structure and Seasonality

• Bay d’Espoir is a two‑to‑three layered system from spring to fall, Belle Bay is a two-layered system from spring to summer (and likely up the late fall or early winter) while the Connaigre Penninsula region is a two‑to–three layered system from spring to fall, depending on local deep water intrusion below 150 m depth.
• Due to a much larger freshwater runoff, a stronger and shallower stratification is present in the Bay d’Espoir region than in Belle Bay and the Connaigre Peninsula regions. Belle Bay presents, nevertheless, an important stratification within the depth range used by the finfish aquaculture industry (0‑20 m) while the Connaigre Peninsula was found to be more vertically homogeneous within that same depth range. Surface pycnocline depths were found to be as shallow as 3‑3.5 m in the upper part of Bay d’Espoir, from 3‑16 m in Belle Bay and generally around 20‑40 m in the Connaigre Peninsula region.
• The surface water of the Coast of Bays area was found to be generally oxygen rich (i.e., >10 mg/l in spring), although some areas such as the upper part of the Bay d’Espoir consistently showed lower concentrations in both spring and fall surveys. At depth, dissolved oxygen concentration decreased significantly in the deeper part of Bay d’Espoir and the Connaigre Peninsula subject to the intrusion of the deep Mid Slope Water (MSW). In Belle Bay, a notable decrease in dissolved oxygen concentration was found in the deeper parts of the bay; likely due to the isolation of those deep inner basins.
• While short-term (order of hours to weeks) variations in the temperature, salinity and dissolved oxygen of the water column were noted, the dataset was insufficient for determining the spatial and temporal extent of those features; precluding a good understanding of the associated dynamics. Upwelling/downwelling and internal waves were proposed as possible mechanisms explaining some of the variations observed.

Water Currents

• The median current speed observed in the Coast of Bays area ranged between 2‑14 cm/s. The maximum observed current speed at each station was 5 to 10 times larger than its median speed.
• Low median speeds are generally found in sheltered coves and high median speeds in areas around sills and within narrow channels.
• Subsurface currents measured near aquaculture sites in the Coast of Bays area show that 50% of the stations have median current speeds of 4‑6 cm/s in the upper 20 m.
• The tidal contribution to the variance of the sea level is 84% while the tidal contribution to the variance of the currents is generally less than 10% except in the upper Bay d’Espoir where the contribution is generally around 25%. Thus, a significant part of the current variability is not attributed to the tides.

The Development of a Circulation Model for the Coast of Bays and its Application to Bay Management Areas

• A Finite Volume Community Ocean Model (FVCOM) was implemented to investigate the circulation in the Coast of Bays area. The model was run in a three dimensional barotropic configuration (i.e., homogeneous water column structure) with two driving forces: tidal forcing at the open boundary and constant and quasi-uniform wind at the surface.
• The analysis of the sea level from the model showed that tidal sea surface elevation variation was well reproduced by the model with error less than 2 cm for the major constituents.
• The zones of influence defined by particle movement are variable and can reach maximum distances of 47 km in one day as observed in Bay d’Espoir.
• The regions with potential exchange of water within 24 hours can be grouped as:
  • Bay d’Espoir and Hermitage Bay;
  • Belle Bay (as a whole); and
  • Northeast Arm – Connaigre Bay.
• The model is at an early calibration stage and does not yet represent the complexity of the dynamics of the study area.

This Science Advisory Report is from the March 25‑26, 2015 Regional Peer Review on the State of the knowledge of the oceanography and water exchange on the South coast of Newfoundland to support the development of Bay Management Areas for Finfish Aquaculture. 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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