We recently sent out a mailer to our subscribers letting them know about the portability solutions that we have come up with. Within minutes we received photos and details from many of our customers about how some they have used a little ingenuity to mount their Lowrance units on unique water craft. Below we have a photo gallery of images that could help you design your own portable setup. Of primary importance, however, is a mount that minimizes cavitation (air bubbles) directly under the transducer (e.g., surface noise) and maintaining a correct angle on the transducer. See recent blogs on this topic. The preferable solution is to permanently mount separate transducers following DIY guidance like shown here on each survey craft and just move the Lowrance Elite or HDS display from boat to boat. But if the job calls for a fully portable mount, we can help!
Overrun by these invasive species, Lake Yankton soon looked like chocolate milk, with a water clarity of only three inches — that’s right, inches, not feet. So the cavalry was called in to assess the situation and provide a solution. Leading the effort was Nebraska Game and Parks Commission District Fisheries Manager Jeff Schuckman.
Fortunately for Nebraska anglers, this wasn’t Schuckman’s first rodeo. He knew the lake could be rehabilitated with careful application of Rotenone, a common fish-killing chemical. The challenge would be to determine just how much of the chemical was needed, and then purchase and apply just enough to do the job — no more, no less.
One of the biggest challenges to understanding aquatic resources are the optical properties of water and an inability of our human eyes to see the complex world that lurks beneath the surface. In contrast, when “aeroplanes” (that’s what they were called in the Wright Brother’s days) first took flight in the early 1900’s and pilots figured out how to fix cameras to the belly to take aerial photos, it opened up a new world of exploration for biologists and foresters studying terrestrial landscapes. The term “landscape” got a whole new meaning.
ciBioBase’s Trip Replay feature that couples bottom depth, aquatic vegetation biovolume, and bottom hardness maps with your actual Sonar Log empowers you with a verification tool that ensures an accurate map in every system you map, every time. The sonar log also provides users and our Quality Control team helpful information about signal quality and transducer placement that can help both parties diagnose issues.
A little known feature in ciBioBase allows users to reprocess their Lowrance HDS/Elite sonar log at different color and sensitivity settings (Figure 1).
Sometimes, your Sonar Log may look a little too “hot” making it difficult to distinguish between plants and bottom (Figure 2).
|Figure 2. Sonar Log showing colors that may be “too hot” to distinguish between plants and bottom.|
Try reprocessing the sonar log at a colorline of 240 (default is 220). This will bring in “cooler” colors to the sonar log and may help you better distinguish subtle bottom features and gaps in plant beds (Figure 3).
|Figure 3. Sonar Log reprocessed with a colorline of 240.|
Alternatively, Lowrance has a powerful free desktop software program called SonarViewer which allows you to replay your Sonar Log with options to dynamically control sensitivity, colorline, zoom, and range (Figure 4).
|Figure 4. SonarViewer is a free download from Lowrance and has a range of tools for enhancing the contrast of bottom features detected by your Lowrance HDS or Elite.|
Use SonarViewer to review your files prior to upload to ciBioBase if you suspect possible signal quality issues or are testing different transducer setups for optimal signal quality. Signal Quality should also be continually monitored by watching your SONAR page on your HDS or Elite while collecting data on the water. A helpful rule of thumb is that a signal that is clear and crisp to your eyes is most likely clear and crisp to ciBioBase algorithms.
At Contour Innovations we’ve long argued the importance of objectively assessing submersed aquatic vegetation (SAV) abundance to better inform management decisions. Our last blog post discussing a recent controversy over the role of herbicides in indirectly affecting fisheries declines in Wisconsin reinforces why this is so important. When we talk abundance per se, we need a metric that is quantitative, yet is intuitive. The percent of the water column taken up by vegetation growth (i.e., percent “biovolume”) represents such a metric and is the primary variable that is mapped in ciBioBase. Zero means no growth (blue). 100% represents growth all the way to the surface (red; Figure 1).
|Figure 1. SAV Biovolume map (left), boat tracks (red lines), boat location (red dot), and sonar chart of vegetation growing to the lake surface on Orchard Lake, MN.|
Zero is undesirable in lake environments where vegetation growth is natural or where an artificial lake is managed for vegetation-dependent fisheries (e.g., largemouth bass or northern pike). No vegetation growth can also cause and be an effect of water quality impairments as discussed here). In contrast, 100% is undesirable from an aquatic recreation standpoint because props get tangled up and it’s difficult to navigate your boat through surface mats of vegetation (Figure 2).
|Figure 2. Aquatic Vegetation (100% Biovolume) growing all the way to the water surface on Orchard Lake, MN and impediments to motorized recreation.|
If no plant growth is bad (0%), but plant growth all the way to the surface (100%) is bad, then good MUST be somewhere in between. Indeed! From a Fisheries standpoint, 40-60% average biovolume is good because there is habitat for vegetation-dependent species like largemouth bass, bluegill, northern pike, and indicator species like blackchin shiners that are sensitive to vegetation loss (Figure 3).
|Figure 3. Probability of sampling blackchin shiners as a function of increasing SAV % biovolume in Square Lake, MN (Adapted from Valley et al. 2010 Hydrobiologia 644:385-399)|
From a water quality standpoint, 40-60% biovolume is sufficient to anchor sediments and will promoting better water clarity than if nothing was growing. Finally, 40-60% biovolume means that most growth is below the depth of your outboard prop and thus you generally won’t encounter the situation as seen in Figure 1.
A case study in MN, WI, NC, and FL lakes
CI is currently involved in a collaborative research project where acoustic data with Lowrance HDS was passively collected while conducting point-intercept surveys. Acoustic data (.sl2 files) were uploaded to ciBioBase and the Biovolume value for each species survey point was extracted from the exported raster grid (“Extract Value From Point” in the Spatial Analyst Toolbox in ArcGIS or see our Point-Intercept on Steroids blog). Figure 4 displays a wealth of information about the status of plant growth and management in the surveyed lakes. With on-the-fly data entry for the plant species surveys and uploading of the .sl2 file to ciBioBase, a similar graph could be produced within hours of finishing a survey, and thus facilitating informed and rapid decision making.
Specifically this graph tells us the following:
- Invasives grow closer to the surface of lakes than natives and growth seems to be highest in lakes of intermediate productivity (meso-eutrophic)
- Natives appear to grow at the 40-60% biovolume level regardless of productivity.
- Native growth can be an objective benchmark from which to judge the success of invasive management in non-eradication management regimes.
- Aquatic Plant management was successful at bringing down invasive growth to the level of natives in Gray’s Bay of Lake Minnetonka, Kissimmee, and Istokpoga
At BioBase we put Lowrance HDS to the test for GPS precision and accuracy. We know the importance of accurate maps but also recognize that “consumer-off-the-shelf” doesn’t mean it won’t provide the type of accuracy needed for accurate acoustic mapping. The question lies more in how precisely accurate we can map aquatic environments with a “survey-grade” versus consumer GPS. There are a lot of considerations when mapping from the surface of a water body. Not only the accuracy of the GPS signal itself but the movement of a survey vessel on a liquid surface, wind, number of points surveyed, survey design, depth, acoustic cone degree, etc. The list goes on because plants grow, you’re usually in a boat and water moves. But, we can still investigate the precision of the WAAS corrected GPS from Lowrance HDS. We were happy with our test results . . . but not surprised!
- Trimble GeoXH 6000 Series (post processing DGPS correction to 12” accuracy and precision)
- Lowrance HDS-5 (WAAS-Correction Enabled)
- Lowrance HDS-7 Gen2Touch (WAAS-Correction Enabled)
- Two individuals recording tracks while walking in same footprints, units held at chest level
- One individual recorded a track with the Trimble Unit while the other held the HDS
- Process repeated with the Trimble and HDS7 Touch
- Data collected in a 2-acre soccer field in Minneapolis surrounded by trees
- GPS Track lines from both units were uploaded to ArcGIS and converted to points
- Point layers from both units were spatially joined and distance from each HDS track point to the nearest Trimble GPS track point was calculated
- Conditions: Clear skies and HDOP (Horizontal Dilution of Precision) was less than 3
- Testing Completed March 14, 2013
- Pitch, Roll and Yaw – Wave action or other movements of the boat as you take a physical samples
- Tree Cover – which isn’t as common when mapping open water like lakes
- Relation of GPS antennae to transducer – Even with 12 inch DGPS accuracy, if you’re standing 3 feet from your transducer your data points will be off. If you take a core sample and enter the results into a GPS device, your boat could easily have drifted a lot more than your potential error. With Lowrance HDS we provide an external antennae that can be mounted directly above your transducer so your data collection is happening at the point spot of your GPS signal.
- Overall Survey Design – The spacing of your transects is key as it relates to the ability to confidently make predictions in unsampled locations with your geo-statistical model.
- Speed of Travel – When looking at a wide range of data collection techniques and methods, speed is always the biggest consideration for accuracy and coverage.
In an addendum to an earlier post, we continue to evaluate the accuracy and precision of BioBase depth outputs. Lowrance has been in the depth sounding business since 1957. They have tight factory calibration standards whereby depth should never be more than 2% different than the actual depth. Of course then we expect depths to be spot on on hard bottom surfaces where truth can be easily measured. But what about in mucky bottoms which are common place in many lakes, ponds, backwaters throughout the US and abroad? With this in mind, in late May of 2012, we traveled to Pool 8 of the Mississippi River near LaCrosse WI to do some testing in a mucky, moderately dense vegetated backwater (Figure 1). At some point we have to step back and ask, “what is the bottom of a body of water?”
|Figure 1. Vegetation cover and biovolume (% of water column occupied with vegetation) in Pool 8 of the Mississippi R. in LaCrosse WI on 5/29/2012. Average biovolume was 30% during the survey.|
The most difficult aspect of this testing was to get an objective estimate of the true depth. In other words, where exactly did the plants end and bottom start? Typically, investigators use a survey rod like that seen in Figure 2 to estimate actual bottom based on where they feel resistance on the survey rod. Piece of cake over sand. Not so easy over flocculant silt and muck or vegetative areas.
|Figure 2. Measuring bottom with a survey rod in a mucky Minnesota Lake. Typically, the survey rod will sink several inches into the bottom before the surveyor feels resistance and judges the depth to the bottom|
Many experienced surveyors will tell you that the rod will sink into the muck some distance before you feel resistance. There is a positive correlation in the distance it sinks and how mucky the bottom is. So, we went into this investigation expecting deeper rod depths measured than ciBioBase outputs.
Accurate and precise results in mucky, vegetated bottoms
After 30 points measured with the survey rod, we compared the results with the ciBioBase depths measured in the same location. We were pleased to see very high precision with a Coefficient of Determination (R^2) of 0.94 and a systematic difference in depth of only 4.9″ (Figure 3). The depth of 4.9″ was quite possibly the average depth where we first felt resistance of the survey rod. The upshot here is that ciBioBase depth outputs are highly precise, consistent and accurate even in mucky vegetated bottoms.
|Figure 3. Accuracy and precision of ciBioBase depths measured against depths collected with a survey rod in the mucky, vegetated backwaters of Pool 8 of the Mississippi River near LaCrosse, WI.|