Field Excursions 10/8 to 10/10/2013

We visited Fidalgo, Dabob, and Oyster Bay sites on 10/8, 10/9, and 10/10 respectively to check on trays and liberate oysters from each tray.

Fidalgo Bay

Weather conditions:
Wind NE 10-25 knots
Scattered Showers
Low tide of -1 at roughly 1 am.

Wind conditions caused partial submersion of trays during low tide but executive decision was made to open the trays and liberate the oysters if needed. Trays were in good condition with no sign of disturbance by weather or vandalism.

Upon opening the trays we found that:
  • Tiles in center of trays were covered with 3-4 inches of silted mud which completely encased the adhered oysters
  • Windscreen Bags (WSB) were also covered with 1-2 inches of silted mud.
  • Oysters inside WSB ranged in size from ~10mm to over 50mm (this is based on personal observation)
  • Several oysters of large size in each bag were large enough to indicate that the bags needed to be open.
  • WSBs had stains on bottom that aligned with the wholes in the bottom of the tray.

Siltation will be the biggest problem with this set up at this site. The tiles had an effect which caused an enormous pile up of silt mud in the center of the tray. This mud touched the upper mesh on the tray and will most likely cause considerable mortalities. While there were know immediate signs of mortality, the fact that a portion of the population of each tray did not grow suggests that mortality has occurred or will likely occur over the winter. As for the larger oysters there might be an explanation of why some grew under the siltation. The stains on the bottom of the WSBs is evidence that there was bottom flow through of ambient water. This most likely allowed for bioseston to reach some of the animals and kept mortality low. Now that the animals are liberated into the tray it is expected that two things will likely occur; 1) smallest oysters may be lost to turn and water movement by washing them out of the trays and 2) larger oysters will not be protected from siltation effects and may suffer mortality.

Dabob Bay

Weather Conditions:
Wind <1 knot
Clear Skies
Low Tide of -1.2 at roughly 2 am

While the project site is good distance from the shore it was still accessible during low tide but slightly submerged. Trays were in good condition with no signs of disturbance by weather or vandalism. We decided to open 1-2 trays to determine growth and the need to open WSBs.

Upon opening 2 trays we found that:
  • There was very little siltation <1/4 inch
  • WSBs were clean and clear of siltation
  • Oysters in WSBs were very small ~10 to 25 mm.
  • Overall size of oysters in WSBs was small enough to warrant leaving the animals IN the WSBs.

This site shows very low growth of all the oysters present in the trays, likely due to low plankton productivity. This was somewhat surprising as compared to the "native" C. gigas in the tidal flat that were quite large though obviously had grown only in shell length but not in width or cup depth. The lack of siltation, relatively clean trays/tiles, and submerged nature of their position suggests that no further repositioning is needed to maintain the animals throughout the winter. Though we might revisit the issue during much lower tides. These animals will probably indicate a selection toward nutrient deficiency.

Oyster Bay

Weather Conditions:
Wind >1 knot
Partly Cloudy Skies
Low Tide of -1.4 at roughly 4 am.

The project site is actually on a raised rebar structure which was directly over a muddy substrate it was assumed that siltation would be an issue as well as the need to reposition the animals due to their raised substructure which would leave them exposed to detrimental winter conditions. Upon opening the first tray we decided to open all the trays. We were inhibited from doing so by three trays which were screwed shut under the original protocol of the project.

Upon opening the majority of the trays we found that:
  • There was a minor amount of siltation, < 1/2 inch
  • WSBs were clean and clear of significant siltation.
  • Oysters in WSBs were very large with average size being between ~30 to 50 mm.
  • Size of oysters dictated that we open the WSBs and liberate the oysters.

This site showed good growth of oysters in all trays. Their placement higher in the water column probably negated the effects of siltation from the muddy bottom while exposing them to more beneficial food sources. Though placement in water column might have affected nutrient availability the size and depth of adjacent non-native C. gigas shells also indicated that food quality is high and quite abundant. In the original plan for the night we wanted to move the trays from the rebar structures to a hard bottom for the winter, we were unable to due to lack of available bottom. We will have to reposition the trays before winter to keep the animals from sitting out of the water during very low tide (-2.25 or greater) during freeze events. These animals will be a great indicator of what high nutrient flow does for adaptation.


We had planned on viewing the Manchester samples on 10/11 but the lessened low tide of -0.7 as well as having to take a boat to the sample site made it very unlikely that we would be able to access the samples or take care of business before the tide came back in. It has also been decided that the Manchester site trays will need to be placed in a subtidal area to keep them submerged throughout winter.

We are planning to visit/revisit Manchester, Oyster Bay, and Fidalgo Bay sites to better position the animals for the winter as well as find better ways to negate the effects of siltation at Fidalgo. These trips will likely occur the week of the Oct 20th.