Swim Up And Be Counted!
in ponds and lakes. Commercial fish growers often rely on them to capture fish. They also are effective in small, shallow lakes and streams.
A trawl is a funnel-shaped net towed by boat. Trawls are altered in many ways to catch different aquatic organisms. Trawls are often used in the deep water of large lakes and rivers that are difficult to sample by other methods.
More than counting
We do more than count the fish we capture. We try to get information that can tell us about the population size, structure (the percentage of fish in each size-group), mortality, growth and standing crop. Depending on what we're looking for, we might record total numbers of fish captured, sampling time, gender, length and weight of the fish.
Fish managers sometimes remove a few scales. If the census subject is a catfish, they remove a spine. Scales and spines have annual marks on them that indicate when fish growth slows during the winter. Spines are cut into thin sections to be examined under a microscope. These annual marks yield information about growth history, age and mortality. This is important because you can't determine the age of a fish from its size, but you learn a lot from its growth rate. For example, it's good if largemouth bass grow 12 inches in their first three years, but a slower growth rate of, say, 12 inches in five years indicates the need for some adjustment in managing the fishery.
We also look for tags on fish. Since the 1600s, people have been tagging and marking fish to learn about their movement patterns, growth and mortality, and to identify individuals. We have several types of tags and marks available, some are external and some are internal. The commonly used "spaghetti tag" is anchored into the fish's flesh beneath its dorsal fin.
Fish managers don't always have to capture the fish themselves to glean useful information from tags. Anglers also play an important role when they report tagged fish to the managers whose address is printed on the tag. Cash rewards are sometimes given for these reports.In general, the numbers and sizes of fish in a population determine the potential of a fishery to provide benefits to anglers. This information is used to create graphs and charts that help managers identify a balanced or unbalanced fish population. All of this information gives us knowledge needed to regulate, improve, preserve, and predict future fish communities.
In some situations it is critical to get information from anglers. Creel surveys provide valuable information concerning angler activity, numbers of fish harvested and fish species preference among anglers. Creel clerks go to recreational fishing sites and interview anglers in order to get this information. The data they collect may be used to determine or evaluate lake or river regulations. Surveys also provide an excellent opportunity for managers to meet with anglers and learn what they think about a fishery.
Fisheries managers generally get into this field because they love fishing, and because they are deeply interested in preserving and improving fish resources. Their dedication to researching, managing, regulating and preserving fish communities ensures that our grandchildren will have quality fishing.
Sometimes the work can seem tedious, but when we step back and look at how good the fishing is in Missouri, all those hours tending nets, measuring and weighing fish, and even repairing boats, is worth all the effort.