Studies
Methods for a Lake Survey
Studies
Methods for a Lake Survey
We surveyed eleven lakes in the Superior National Forest between the 7-18 of July, 1998. Two different survey methods were used, quadrat and timed searches. In areas of low mussel density, timed searches were the most efficient method for surveying mussels. However, in areas of high density, a quadrat method was used to survey the populations.
Quadrat protocol: A marker buoy was placed near shore at both ends of the sampling site. Laser range-finding binoculars were then used to measure the length of the shoreline of the site. Quadrat points were determined by obtaining random numbers from the hundredths of seconds of a stopwatch, and these random numbers were multiplied by the length of the sample site to determine where the quadrats were placed. More random numbers were obtained from the stopwatch and used to determine how deep the quadrat was to be placed. Depths were divided into half meter intervals, and the depth was determined by multiplying the random number by the greatest possible depth at which mussels live and then rounding the product to the nearest half meter. A canoe was used as a work station, which went along the shore recording data measurements from the divers and determined where the quadrats were to be placed. Quadrats were placed by having the upper edge at the appropriate depth and the lower edge moving into deeper water. Divers then sampled the quadrats and removed all mussels lying completely inside the quadrat. The mussels were placed into a mesh bag, measured, and then returned to the same place and position they were originally in.
Timed Search Protocol: Divers assembled into a line perpendicular to shore with each diver assigned a specific depth to survey, depending on the gradient. If the gradient was steep (30-50°), then a two person team was sufficient to survey the area because the total viewing area in front of the two divers went from 0-3m depth, the total surveyed depth. Four person teams worked the more gradually sloped banks, because the viewing window needed to cover the same depths was much wider. Timed searches were performed for ten minutes exactly. Divers recorded each live mussel individual present and took note of the general substrate. After the ten minutes was complete, laser range-finding binoculars were used to measure the distance travelled from the divers' position at the beginning of the ten minutes to the end. For each lake, 3-9 timed searches were performed. Our approximate survey area was recorded on a map.
In both the timed search and quadrat search, we also recorded the substrate and the orientation for each mussel found. At all sites, a set of environmental parameters were measured. These included; sechhi depth, cholorphyll counts, sediment load, temperature, alkalinity, and flow rates.
We examined eight of Davis's previously searched sites in throughout July and August, 1998. After assessment of many survey techniques, we chose to use the 10 m search method for all our sites.
10 m Search Protocol: For each river site, we examined a 400 m section of river. In this 400 m section, 15 ten meter stretches were randomly chosen and searched. For each 10 m sections, divers assembled in a straight line across the rivers, with each diver assigned a particular area of stream to survey. The divers would search the entire area of a stream for 10 m, collecting shells and mussels in bags. At the end of each 10 m section, the mussels would be counted, identified, measured, then placed back into the stream where they were found. We also recorded the substrate and the orientation for each mussel found.
At all sites, a set of environmental parameters were measured. These included; sechhi depth, chlorophyll counts, sediment load, temperature, alkalinity, and flow rates.