|
Click on images to see larger
Sampling in 2008 was conducted on the lower half of Coos Bay, from South Slough to the Airport. Our study sites are located in six major regions in Coos Bay (see map). We created a grid of points over each region: Airport, North Spit, Clam Island, Empire, Pigeon Point and South Slough. The points were distributed every 200 meters (m) (656 feet) along the shoreline, and every 50 m (164 feet) away from the shoreline. The sampling was, like clamming, governed by the tides and the light. This means that we surveyed on low tides, usually in the early morning, and worked quickly to gather data before the tide pushed us back onto land. In general we needed at least a -0.5 foot tide (below MLLW) to have enough time and space to sample.
Methods for Tillamook are similar to Coos Bay but we added a new method called megacoring. Stay tuned for pictures and further descriptions.
In each region, we have sampled using three different methods:
 |
 |
| The SEACOR team spread out over the mudflat, scouting terrain at Clam Island. |
Bathymetry |
Our first objective was simply to get a lay of the land. It was important for us to understand the composition and diverse terrain of the many mudflats that make up Oregon estuaries. As anyone who has been clamming knows, some places are packed with clams and others do not have any clams at all. For this reason we scouted all six regions, taking data on terrain and presence/absence of clams and other species, every 50 meters as we walked towards the water. It was remarkable to see how much the habitat could change over a short distance. Gathering this information was crucial to helping us design and carry out the rest of our study.
Bathymetry
In addition to surveying the mudflats at low tide, we also wanted to know the water depth over each of our sites during high tide. Water depth is an indicator of how long the mudflat (and subsequently the clams buried within it) is exposed as the tide recedes. To examine depth, we surveyed the regions at high tide by kayak and took soundings over each of our waypoints to obtain tidal height. Tidal heights were then used to divide each region into tidal strata based on discrete tidal groupings. The strata we outlined were used as a factor to describe clam distribution.
 |
 |
| Surveying the mudflat |
An example of a 1m² quadrat – note the butter and gaper holes inside |
After scouting was completed, we took a more in-depth approach to our evaluation. For the Rapid Assessment Method (RAM), we visited each point on our grid and laid out a 1 m² quadrat, which is a square that we designated as the area to sample in (see picture below). Based on the previous study and our observations, a 1 m² area is sufficient to study the distribution of littlenecks, cockles, and butters, but not large enough for gapers. Therefore, we looked for gaper holes in a 4 m² area. At each site, we surveyed the eelgrass and algae cover, substrate type, number and type of burrow holes, salinity, temperature, and anoxic (low oxygen) layer. Then we raked down to approximately 15 centimeters (six inches) for cockles and littlenecks.
 |
 |
| DAM sampling – searching for gaper clams in a 9m² quadrat |
Each flag represents an individual gaper clam. The SEACOR team pauses to appreciate the high density of gapers. |
 |
 |
| Raking and Measuring Clams |
 |
 |
| A 1m² area dug down to one foot (35 cm)
|
This was our most intensive sampling regime, when we finally got to dig up some clams! For this method, we started with a 9 m² quadrat to count gaper clam burrows. Of the gaper clam burrows we found, we randomly dug 10 animals and measured and weighed each one. Then, within the 9 m² quadrat, we dug out a 1m² sub-sample to a depth of just over one foot to create a core of sediment. This core told us how many clams are actually in that area, not just the ones for which we could see burrows at the surface. We measured and weighed each clam we found. We used these data to learn more about the structure and distribution of the clam populations. Because this sampling method is very time consuming, we could not sample as many sites as when conducting RAM sampling. Using the DAM sampling method, we obtained more detailed data on clams that we then used, in combination with RAM data, to estimate the abundance of clams throughout our study regions. |
