We have long understood that geography plays an important role in lake management. The ability to locate, measure, and count things like water volume, aquatic plant acreage, and location of invasive species is critical to developing plans to improve water quality. For a number of years, Aquatechnex has used the BioBase Mapping Platform to help us understand the lakes we work on. This cloud-based system uses hydroacoustic data collected during boat surveys to develop bathymetry maps, aquatic plant biovolume maps, and sediment composition maps. While we have done fisheries habitat restoration and fish stocking on a regular basis, with BioBase’s EcoFish system Aquatechnex has now added to our fisheries management practice the ability to measure and help understand the fishery in a lake.
You can’t manage what you don’t measure, and fish are notoriously hard to measure (or more accurately, to capture and count), especially non-lethally. In the Fisheries Manager’s toolbox are a range of traditional sampling gears (e.g., seines, trap or fyke nets, gill nets, electrofishing), but most of them have two major problems:
- Only a small proportion of the population is vulnerable to each type of survey gear. Often multiple gears are needed for multiple species and may only be effective at certain times of the year (e.g., during spawning).
- Most sampling gear cannot sample fish that stay in water much deeper than 6ft (2m). A fish population in a waterbody may be completely healthy, yet fish might not show up in the nets for a range of reasons.
The new EcoFish system in BioBase helps us better understand the fishery in a lake through a number of features.
Individual fish counts and school detection
Using sophisticated detection algorithms that separate fish from aquatic vegetation, structure, and other water column noise, individual fish “objects” deeper than 1m from the transducer face are identified in the sonar log and their depth and location is saved to the BioBase database and put on the BioBase map. If multiple fish cluster together so that individuals cannot be identified, the system calls the target a “school” and the location and depth of the midpoint of that school is identified (Figure 1).
Figure 1. EcoFish sonar image (echogram) of individual fish targets (blue) and a cluster of fish, i.e., school (yellow)
Relative fish size
We use the terms “large” and “small”, “short” and “long” figuratively. EcoFish cannot (yet) tell you precisely how large or long a fish is. However, we can make some confident statements about relative size. Large fish generally return more energy than small fish. More energy means the color of the fish arch is a more intense yellow or “hot” color in the raw sonar image than a small fish, which may have a more purple or “cool” color. Because BioBase processes uncalibrated single-beam sonar data, we do not know the exact length or weight of a fish from the acoustic return. But fisheries researchers and managers know the systems they are studying/managing, and generally have a rough idea of fish species and size range based on other fisheries datasets or lines of evidence (e.g., interviews from anglers, knowledge of fish behavior and habitat and where they appear on the map, or mysterious fish of the deep showing up floating dead on the surface). BioBase generates a dimensionless acoustic size or perhaps more appropriately termed “immensity” value. Users can use these immensity values and their knowledge of their system to categorize the relative size of fish targets. We publish small, medium, and large size breaks based on early feedback from a focus group of fisheries experts and test logs from a range of systems. Still, these categorizations should be viewed as experimental, and we anticipate further refining the category breaks based on new data that comes into the system.
Abundance “heat” maps
When sonar logs are processed for fish, BioBase will create an abundance “heat” map in a Viridis color palette much like it creates other interpolated maps. A purple color means no fish were detected and the brightest color yellow means 10 or more fish or a school were detected within a 5-m x 5-m area. These maps can be exported from the Tools – Export Data Export Imagery area in BioBase.
Maps of individual fish and schools along track
For users who want to see detail about where exactly individual fish were detected and what habitats they were hanging around, they can select the “Fish Targets” layer in BioBase (Figure 2).
Figure 2. Turn on the Fish Target layer to see individuals and schools overlain on any other EcoSound habitat layer.
Summary reports of fish counts, size, and depth
EcoSound Summary Reports have always been very popular, especially for aquatic vegetation summaries. Now we have added a fish section, complete with a histogram of fish counts by depth! In this great example, we see a distinct distribution of fish occupying deep depths (Figure 3). This lake in Indiana supports an endangered population of cisco that live exclusively in deep offshore waters. Until EcoFish, the only way the Indiana Department of Natural Resources (IN DNR) sampled them was through reports and collections of dead floaters. In this file, EcoFish detected 92 small- to medium-sized individuals. According to IN DNR Fisheries Biologist Matthew Linn, they’ve rarely seen individuals longer than 12 inches.
Figure 3. Automated summary reports of fish counts by size and depth. Note how clearly the cisco targets in this example are separate from other fish.
We are excited to be able to add this tool to our toolbox and look forward to helping our clients better understand their fishery.
