Here in the great state of Ohio, the Ohio Department of Natural Resources is charged with the management of nearly all the natural resources found within state borders. More specifically, the Ohio Division of Wildlife is charged with the management of Ohio’s fisheries and wildlife resources. The Ohio Division of Wildlife is responsible for creating and enforcing all hunting, trapping, and fishing laws within the state. In order to determine what the laws must be set at, fisheries and wildlife biologists carry out a number of sampling and survey methods to determine the status or health of the population under study. I am lucky enough to currently work for the Division of Wildlife as a Natural Resource Technician and have first hand insight to two of the techniques used to sample fish populations in Ohio.
The first technique is commonly known as electrofishing or “shocking”. This is the process of putting electric current into the water via two extended poles off the bow or front of the boat that have a number of wire cables draped into the water. The wire cables disperse the electric current evenly throughout the water so that it is not too strong at any one spot. The electric current is pulsed into the water which causes the fish in the immediate area to be temporarily stunned and float to the surface of the water, allowing them to be netted. This technique is very effective because it allows us to only net the species that we are targeting and doesn’t harm any of the other fish. The general rule when using this method to sample a body of water is keeping 5 fish per centimeter class of the targeted species to study their otoliths. Otoliths are used to age fish, which also tells biologists how healthy and successful a specific body of water is according to how fast a species is growing each year. Electrofishing is the method commonly used for bass sampling (Largemouth and Smallmouth) in lakes and reservoirs in Ohio.
The second method of fish sampling is through the use of nets. Most recently, we have been targeting Channel Catfish which requires a specific net called a hoop net. A hoop net involves a series of metal hoops connected by netting which is suspended in the water column, but below the surface. The hoops all lead to an end section where bait of some sort is placed that the fish collect in after becoming trapped when pursuing the bait. The specific bait we use is solid blocks of grinded up cheese which catfish love. The hoop nets are suspended via buoys on the surface and anchors on the bottom. Once the nets have been in the water 48 hours, we return to each net and pull it out of the lake. Usually having anywhere from a few, to hundreds of channel catfish in each net along with various other species of fish and sometimes even turtles. The same rule of keeping 5 fish per centimeter class is followed in this technique as well. The big difference in this technique from the first is that bycatch is almost inevitable. Various species including carp, panfish (bluegill, sunfish, crappie, etc.), and even turtles are frequently found in the nets. The only type of bycatch that is generally unable to be released is turtles because they usually will drown before we get back to the nets. The other types of fish caught in the net besides channel catfish are usually counted, measured and released. This netting method is very successful for catching bottom dwelling fish such as catfish which are less susceptible to shocking methods. Netting methods also allow for fish to be caught while biologists can do other things including lab work with fish from previous samplings.
Here is a link to a YouTube video I made showing the process we go through when removing Otoliths from Channel Catfish: https://youtu.be/jSUf7pz6h9A