Refuge Notebook • Vol. 16, No. 24 • June 20, 2014

Aquatic habitat mapping “off-the-shelf” by Mark Laker

Since I was a little boy, I’ve been interested in ex- project for invasive northern pike in Stormy Lake. ploring the underwater world. My favorite TV show The Lowrance HDS sonar works by emitting an ul- was The Undersea World of Jacques Cousteau. Though trasonic pulse directly below the boat and receiving our lakes don’t offer quite the array of colors and the echo as it bounces of the lakes bottom or vegeta- charismatic species as a coral reef, they can be rich tion. This is also referred to as a down-scanning sonar. and interesting environments to explore. Just like on The StructureScan operates at a higher frequency land, the richness of aquatic species is associated with which is better for distinguishing vegetation and un- habit availability and quality. derwater structures. In addition to down-scanning, For me, the ideal method to explore the underwa- the StructureScan utilizes side-scanning technology. ter world is putting on my mask, fins, and snorkel or As opposed to the down-scan sonar which generates a SCUBA gear and jumping in the water. On a small scale profile or side view of the bottom, the side-scan sonar this works, but for large area, we need other meth- looks off to the sides to create an actual image ofthe ods. Our current project exploring aquatic habitat in- bottom. volves the elodea infestation in Stormy, Daniels, and To collect the data we ran transects (spaced 100 Beck Lakes. Elodea is a nasty aquatic invasive plant feet apart) back and forth across the lake at a speed of that has the potential to displace native plant species about 6 mph. Typically when boating you try to avoid and choke off waterways. obstacles, but when mapping you almost intentionally We have conducted numerous “rake surveys” to run over them. On Daniels Lake we encountered some determine the presence of elodea on the Kenai Penin- glacial erratics that were about 20 feet across – those sula. This involved tethering a garden rake head toa are some big rocks! Needless to say, Daniels Lake rope and dragging it across the lake bottom to sample made a few modifications to our prop. plants. From these surveys, we learned elodea prefers Contour Innovations offers two services: Lake- shallow soft bottom areas. Therefore, we wanted to Trax for anglers, and ciBioBase for research. Before map depth, bottom hardness, and presence of vegeta- acquiring the research version, I experimented with tion across entire lakes to understand where the best the LakeTrax service by mapping the outlet of Tustu- elodea habitat exists. mena Lake down to the boat launch. Anyone who has The first step in creating our lake habitat mapto navigated that stretch of water knows there are some collect depth data for a bathymetric map. A bathymet- nice boulders covered with aluminum strips just up- ric map is the underwater equivalent of a topographic stream of the launch. With just a few hours of map- map with contours for depth instead of elevation. All ping, I was able to create a nice bathymetric map and that is needed is location and depth, and lots of it. Not identify hazards. You can save maps back on your long ago it was an expensive and complicated task to Lowrance HDS unit, and in the future avoid leaving record GPS location and depth, and then process it into any trace of your boat on the rocks. depth contours. Beyond lake depth and obstacles, we also needed Researchers are constantly looking to the con- information about vegetation and the bottom sub- sumer market for readily available equipment and so- strate to understand elodea habitat. Therefore, our lutions. These are called “off-the-shelf” solutions, and lake data (called sonar logs) were processed by the can save time and money. For this project, we used the research service, ciBioBase, to produce three lay- Lowrance HDS Charter/Sonar with StructureScan to ers: depth, bottom hardness, and percent vegeta- measure depths and locations. The recorded data was tion biomass. Bottom hardness is calculated by how then processed by Contour Innovations (http://www. well the sound signal is reflected off the lake bottom. contourinnovations.com/). This off-the-shelf solution Harder surfaces reflect well and soft surfaces tend to was recommended to me by ADF&G biologist Robert absorb sound. Percent vegetation biomass is simply Massengill who was working on another eradication the percent of the water column that is occupied by

USFWS Kenai National Wildlife Refuge 47 Refuge Notebook • Vol. 16, No. 24 • June 20, 2014 vegetation (plant height divided by water depth). mask and fins to see for myself what’s really under the From the new data layers we will produce a map water. identifying areas of the lake with suitable habitat for Mark Laker has been an Ecologist with the Kenai Na- elodea. These will be important for both treatment and tional Wildlife Refuge since 2003. monitoring efforts. Though I’ll still need to putonmy

A Lowrance HDS sonar map showing underwater vegetation in Stormy Lake.

48 USFWS Kenai National Wildlife Refuge