Oyster Bulletin No. 3 – 6 August 2011

We sampled for larvae on Tuesday 2 August (afternoon high tide) and Friday 5 August (morning high tide). Water temperatures have been steady over the past week, given the calm conditions with cloud cover. Cloud cover reduces heating of the tideflats during low tide, and calm conditions reduce the chance of cold upwelled water from the ocean. Wednesday afternoon saw a peak in water temperature associated with an incoming tide on a sunny day, but this does not seem to have triggered a mass spawning of oysters. Instead, very early stage larvae are appearing in small numbers not expected to produce a noticeable set after 2 weeks in the plankton. These early-stage larvae are 80-100 microns were spawned 2-5 days ago. The larval counts are provided below; recall that 2010 had peak counts above 5000 following the spawning event around August 18, 2010; currently the counts are a factor of 10 lower. If you’re interested in clams, please see the attached document, which summarizes some of the work we have initiated on Manilas.

Oyster larvae per 20 gallons:

EAST SIDE (Friday temperatures 65.3-68 degrees F):

Station 3: Tuesday 42, Friday 168
Long Island Slough: Tuesday 54, Friday 262
Cougar Bend: Tuesday 38, Friday 321
Naselle Bridge: Tuesday 22, Friday 6

WEST SIDE (temperatures 65-66 degrees F):

Mill Channel: Tuesday 14, Friday 510
Peterson Station: Tuesday 157, Friday 570
Smokey Hollow: Tuesday 70, Friday 255
Bear River: Tuesday 65, Friday 82

At this time, although oyster larvae are not common, they represent a sizeable fraction of plankton of their size. Clams (multiple species) are about equally abundant. Plankton samples also contain some barnacles and copepods, as well as some slipper shell larvae (or other snails) near the rivers. Conditions still seem good for survival and growth of larvae, if they should appear in larger numbers.