Old World Fishing Technique for Modern “Big Muddy” Fish Monitoring
BY JONATHAN YONCE, COLUMBIA FWCO
Missouri River. Credit: USFWS
Each year on the lower 250 miles of the Missouri River several types of fishing gears are used by the Columbia Fish and Wildlife Conservation Office to monitor fish populations. One very successful gear that biologists use is the gill net. Many commercial fishers are familiar with gill netting; it has been a method commonly used to capture fish for thousands of years. Although banned in much of the world as a means to capture food fish, for some commercial, research and monitoring purposes it is still allowed but heavily regulated. This gill netting season began in November of 2014 and ended this April. With a season that stretches over six months we capture fish in a wide variety of environmental conditions and shifting behavioral patterns.
Archaeological findings throughout the world have shown that gill netting existed in ancient times. On the North American continent native fishers would use nets made of natural fibers such as cedar bark. Using stones as weights and wood planks as floats they fished gill nets in a similar fashion to today’s techniques. Gill nets passively fish an area and capture fish moving through over a period of time. These nets are a series of panels of mesh with a “foot rope” or lead line along the bottom, and a float line. The floats on top of the net stretch it vertically in the water column and the weights follow the contours of the waterbody’s substrate. Once deployed fish swim into the net, push their head through the mesh but the rest of their body cannot fit through. Most fish have a gill plate that keeps them from backing out of the net because it catches on the mesh. Fish that are smaller than the width of the mesh can freely swim through without being captured. The selectivity of gill netting by using different size mesh helps biologist minimize unintended catch.
Gill netting is such a productive method it has become a means of fisheries exploitation in many areas of the world; this has led to its banning for recreational and commercial fisheries in certain localities. Modern introductions of synthetic fiber, such as nylon, have made it easier to mass produce gill nets and allowed them to be fished for longer periods without repair. These modern nets are less visible to fish and capture larger numbers in the same amount of time compared to traditional nets made of natural fiber. Due to the properties of the materials used in these nets they are highly resistant to abrasion and degradation and have the potential to last many years if they are not recovered. This has led to environmental concerns, particularly in commercial fishing operations in the oceans of the world. The United Nations General Assembly has called for the cessation of all “large-scale pelagic drift-net fishing” in international waters because of the high potential for fish harvest exploitation using this type of fisheries gear and lost nets harming sea life for years after deployment.
When managed responsibly, gill nets can provide biologists with a very useful tool to capture fish in riverine habitats and return them safely. Each gill net set is always a trove of piscine treasures; employees eagerly wait to see what scaly, slimy fluvial being will arise from the depths of the murky Big Muddy. This year 4,784 fish were captured using 247 gill net sets, deployed throughout the lower 250 miles of the Missouri River. Included in this catch total were 30 different species of fish found within the Missouri River system. During the 2015 gill net season 22 pallid sturgeon, one lake sturgeon, 3,205 shovelnose sturgeon, 279 blue suckers, 27 sauger and four paddlefish were caught. Gill nets have provided important data throughout the years of biological monitoring within the Missouri River and will continue to be a staple fishing gear for years to come.