Introduction: Running a Gill Net to Collect Fish Samples
Gill netting is a widely used sampling method by the DNR and Fish and Wildlife Service. This technique allows these organizations to collect large numbers of fish for either research or hatchery use. This tutorial will provide a general overview of this sampling method and how it is conducted in the field.
Remember, not just anyone can grab a net and collect fish. Permission must be obtained by either the DNR or another government agency.
Gill netting requires time for preparation, time for setting nets, waiting time, and time for retrieving nets. The time each on of these tasks takes to complete will vary with the number of nets you will be setting and how long you leave them in the water.
Step 1: Equipment and Materials
What is needed?
- Custom gill net with lead line and float line
- Two floats that double as markers
- Two anchors
- Large net container (a trash can in this example)
- Boat (w/ motor)
- Livewell with aeration
- At least a two man crew
- Life preservers
- Pocket knife
Step 2: Preparation and Organization
A very important aspect of gill netting is preparation.
It all starts with organization. The gill nets are very long and need to be arranged in such a way that they do not tangle. This is achieved as follows.
1) Start by placing both the lead line and the float line of one end of the net into the bottom of the container.
- Feed both lines in a circular motion around the bottom of the container
- Keep both lines together but prevent them from twisting (this will help when setting the net).
2) Load the boat.
- Nets, anchors, float markers, and safety equipment should be arranged on the boat in an organized fashion. Prevent clutter!
- It works best if you place the float markers and anchors one one side and the net containers on the other, leaving a center walkway from the back to the front of the boat.
Step 3: Choosing Your Net
Select a net fit for gill netting
- Not just any net will get the job done.
- A gill net is specifically designed with a lead, a float line, and four attachment clips to hook on your anchors and float markers.
- The lead line sinks and holds the net to the bottom and the float line keeps the top of the net at the surface. This maximizes the surface area of the net.
Step 4: Determine Your Mesh Size
Gill nets have the ability to be very selective to both size and species of fish. One way this is done is by changing the size of the nets mesh holes. A gill net catches a fish when its head goes through the mesh hole and gets stuck around the widest part of their body. When trying to back out, the mesh catches the gill slit, trapping the fish.
Match mesh size with target fish girth.
- The stretched measure of mesh you choose should represent the relative girth of the fish you aim to catch.
- For example, when gill netting for walleyes during their spawn to collect eggs for hatcheries, a 4" mesh is commonly used. Only the larger, sexually mature fish will get caught in the net and the smaller individuals will pass right through.
Step 5: Net Placement: the Right Place at the Right Time
- Different fish are active at different times of the day. Selecting a time where your target species is the most active will help catch the most fish.
- The charts above are some general behaviors of fish over the course of the day. (These vary with time of year and lake system)
- Different species inhabit different habitats within a waterbody. Setting your nets in areas where your target species is most likely to be found will provide selectivity toward that species.
Putting these together:
- If walleye were your target species, the best combination would be to set your nets at night or early morning on rock piles or near the face of a rocky shoreline. The combination of high activity and selective habitat will yield much higher catch rates.
Step 6: Setting the Net
1) Approach the area where you will set the net (in this case a rock shoreline)
- The driver of the boat will get the nose of the boat up near shore. Watch your depth finder! Trim up the motor if the water gets too shallow.
2) Attach float marker and anchor.
- Another crew member will hook the anchor and float line to the two connector clips on the end of the net.
- For the shore side end, attach both the float line clip and the lead line clip to the anchor clip and the float marker clip.
3) Throw the anchor and float marker near shore.
- Aim for where the water meets the rocks. This will make retrieval easier while still covering the maximum area.
4) Reverse the boat and feed out the net.
- The driver of the boat will slowly reverse the boat out from the shoreline.
- While moving backwards, the other individual will help the net feed out as it is pulled from the container.
- Make sure the lead line and the float line do not twist, this will mess up the lie of the net and the lead line will drag the float line down.
These steps all take place in rapid succession. Use the attached video to clarify this process.
Step 7: Attach Float and Anchor
5) Attach anchor and float line.
- As the end of the net nears, attach the float marker to the float line clip and the anchor to the lead line clip. This is important to the function of the net.
6) Pull the net tight.
- Make sure there is plenty of tension.
- This is demonstrated in the image above.
7) Drop the anchor and float line.
- Keep the lines separated while keeping tension in the line.
- Drop the anchor and float in separate directions to keep them from crossing over and tangling.
Step 8: Waiting Game
Sit and wait
- Over time, fish will swim into the net and become entangled.
- The longer you wait the more fish you could potentially have in your net.
Careful not to leave the net out too long!
- Being stuck in the net is very stressful to fish and the likely hood of mortality increases as time passes.
- Most gill nets are set between 4 and 8 hours.
Step 9: Pulling in the Net
This process is basically the net setting procedure done in reverse.
1) Locate your float marker and pull it out of the water.
2) Remove the float marker and pull in the net.
- A small portion of the net will be pulled in before the anchor will surface.
3) Remove the anchor.
- Place the unattached float and anchor back near the side of the boat leaving the middle walkway open.
4) Continue to pull in the net.
Note: As you pull the net in, it is most efficient to feed it back into the container as described in the preparation step so it is ready to be reset.
Step 10: Remove Fish From the Net
As you pull in the net there will likely be fish entangled.
1) Pull the fish up onto the deck.
2) Remove the fish from the net.
- With the application of a little force, the fish can be pushed through the mesh.
- Push from their tail towards their head to get the mesh over the largest part of their back.
3) If necessary, cut the net.
- In cases where the fish cannot be pushed out of the net, a knife is used to cut the mesh.
- Starting from nose of the fish, run the blade sharp side up to cut the mesh. Repeat until the fish is free from the net.
- Be careful to not puncture the fish with the tip of the blade! Use the knife with caution!
4) Place fish in live well.
- Any fish that need to be collected for any further procedures are placed in a holding tank.
- All other fish are immediately released back into the water.
Step 11: Finishing Up
1) Continue to retrieve the net and remove fish.
- Also continue to feed the net neatly back into the container.
2) Pull in the float marker and the anchor.
3) Remove the float marker and anchor and finish feeding the net into the container.
At this point, you head back to the boat ramp, put your boat on the trailer, and drive back to the station to analyze the catch.