March 25, 2014 at 2:03 pm
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A trap net set for salmon and trout. (photo courtesy: Brian Lewis)[/caption]
Trap nets are used by MDIF&W fisheries biologists primarily in the fall to catch salmon and trout as they move into shallower water in search of spawning areas, which may include spring seeps, upwellings, and areas of flowing water (inlet/outlets). Trap nets are usually comprised of a single long net (lead) set vertically in the water trailing from shore out towards the center of the pond with two other nets (wings) branching off the center net at angles, appearing aerially like an arrow that points to the deeper part of the lake. At the point of the arrow is a large box net. The net is held vertical by a series of small floats mounted along the top of the lead, such that the installed lead spans from the top pf the water to the lake/pond bottom. The center net and the wing net off to the side work together to funnel the fish down to the holding area, the box net, as the fish swims along shore and runs along the lead further from shore seeking a way around this obstacle. In the box net the fish waits in a cool, well-oxygenated environment for the biologist to come and take measurements of the fish before giving it a temporary mark and releasing it back into the water well away from the net. Trap nets are a live capture method that need to be checked every couple of days. For more information about trap nets, check out my Trap Nets for Trout post.
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A gill net is retrieved. (Photo courtesy: Jim Pellerin)[/caption]
Gill Nets are used mostly in the summer months to sample certain species of fish located at certain depths and locations to gain information about size, growth, relative abundance and diet. Gill nets are long nets made mostly of monofilament-like material weighted down by a lead-core line on the long bottom edge and a floating line at the long top edge so that it sits in the water oriented like a volleyball net. The available mesh size of gill nets varies so that it can more specifically target certain sized fish. Gill nets are versatile nets that can be used to selectively target specific species by setting it at certain depths that coincide with specific water temperature and oxygen levels prefered by certain species of fish. For example, a net set in shallower water, perhaps close to shore in the summer is likely to catch spiny-rayed fish such as perch and largemouth bass versus a net set deeper and in the middle of the lake in the summer is more likely to catch trout. Short duration gill net sets can be used for nonlethal sampling, where targeted fish are very abundant and there are few other species present. Because the fish are in the net for a short period of time the fish can be extracted, measured, and returned to the lake with no ill effects. When lethal sampling is strategically undertaken using longer duration sets, a relatively low percentage of the population is removed with little impact to the remaining fishery. Gill nets require more frequent checking than trap nets and in cases of short sets, must be monitored.
Seine Nets A seine net is a long net that is first spread out and may span the width of the river or a small area of a pond and then dragged slowly through a section. Towards the end of the drag the person on the far end of the net loops around to the opposite shore to close the net. Some seine nets have holding boxes similar to those of trap nets so the fish cannot swim away as easily. Seine nets require multiple people to use them and are not effective when not actively manned. Seines are used to ‘sweep’ a short section water, usually in a stream-type environment. Hatcheries with natural-type raceways use seine nets to corral the fish to one end of the raceway so they can be easily netted using a dip net and loaded onto trucks for stocking. Fisheries biologists use seine nets to gather general information on fish that may be present in a water. Seines are commonly used to inventory waters where fish have not yet been surveyed. For more information about the use of seine nets, check out my Kennebago seine post.
Dip Nets are a simple net like the one used for catching fish in household fish tanks, only larger when used at hatcheries and in the fisheries field. Dip nets are predominantly used to extract fish from an area in which they are contained. Hatcheries use them to net fish into and out of the stocking trucks and to net fish for sample counts, a process to determine growth in length and weight. Fisheries biologists use them to net fish out of seine nets and the holding part of trap nets as well as to catch fish when electrofishing.
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A drop net filled with smelts is retrieved. (Photo courtesy: MDIFW Region A Fisheries Staff)[/caption]
Drop nets are used to capture small species like smelt, drop nets are dropped through a hole in the ice which is illuminated to attract plankton which attracts small fish like smelt. The net is then periodically pulled up and the fish are caught in the bag-like nets when it is pulled vertically up to the surface.
A trap net set for salmon and trout. (photo courtesy: Brian Lewis)[/caption]
Trap nets are used by MDIF&W fisheries biologists primarily in the fall to catch salmon and trout as they move into shallower water in search of spawning areas, which may include spring seeps, upwellings, and areas of flowing water (inlet/outlets). Trap nets are usually comprised of a single long net (lead) set vertically in the water trailing from shore out towards the center of the pond with two other nets (wings) branching off the center net at angles, appearing aerially like an arrow that points to the deeper part of the lake. At the point of the arrow is a large box net. The net is held vertical by a series of small floats mounted along the top of the lead, such that the installed lead spans from the top pf the water to the lake/pond bottom. The center net and the wing net off to the side work together to funnel the fish down to the holding area, the box net, as the fish swims along shore and runs along the lead further from shore seeking a way around this obstacle. In the box net the fish waits in a cool, well-oxygenated environment for the biologist to come and take measurements of the fish before giving it a temporary mark and releasing it back into the water well away from the net. Trap nets are a live capture method that need to be checked every couple of days. For more information about trap nets, check out my Trap Nets for Trout post.
[caption id="attachment_353" align="alignleft" width="300"]
A gill net is retrieved. (Photo courtesy: Jim Pellerin)[/caption]
Gill Nets are used mostly in the summer months to sample certain species of fish located at certain depths and locations to gain information about size, growth, relative abundance and diet. Gill nets are long nets made mostly of monofilament-like material weighted down by a lead-core line on the long bottom edge and a floating line at the long top edge so that it sits in the water oriented like a volleyball net. The available mesh size of gill nets varies so that it can more specifically target certain sized fish. Gill nets are versatile nets that can be used to selectively target specific species by setting it at certain depths that coincide with specific water temperature and oxygen levels prefered by certain species of fish. For example, a net set in shallower water, perhaps close to shore in the summer is likely to catch spiny-rayed fish such as perch and largemouth bass versus a net set deeper and in the middle of the lake in the summer is more likely to catch trout. Short duration gill net sets can be used for nonlethal sampling, where targeted fish are very abundant and there are few other species present. Because the fish are in the net for a short period of time the fish can be extracted, measured, and returned to the lake with no ill effects. When lethal sampling is strategically undertaken using longer duration sets, a relatively low percentage of the population is removed with little impact to the remaining fishery. Gill nets require more frequent checking than trap nets and in cases of short sets, must be monitored.
Seine Nets A seine net is a long net that is first spread out and may span the width of the river or a small area of a pond and then dragged slowly through a section. Towards the end of the drag the person on the far end of the net loops around to the opposite shore to close the net. Some seine nets have holding boxes similar to those of trap nets so the fish cannot swim away as easily. Seine nets require multiple people to use them and are not effective when not actively manned. Seines are used to ‘sweep’ a short section water, usually in a stream-type environment. Hatcheries with natural-type raceways use seine nets to corral the fish to one end of the raceway so they can be easily netted using a dip net and loaded onto trucks for stocking. Fisheries biologists use seine nets to gather general information on fish that may be present in a water. Seines are commonly used to inventory waters where fish have not yet been surveyed. For more information about the use of seine nets, check out my Kennebago seine post.
Dip Nets are a simple net like the one used for catching fish in household fish tanks, only larger when used at hatcheries and in the fisheries field. Dip nets are predominantly used to extract fish from an area in which they are contained. Hatcheries use them to net fish into and out of the stocking trucks and to net fish for sample counts, a process to determine growth in length and weight. Fisheries biologists use them to net fish out of seine nets and the holding part of trap nets as well as to catch fish when electrofishing.
[caption id="attachment_352" align="alignleft" width="300"]
A drop net filled with smelts is retrieved. (Photo courtesy: MDIFW Region A Fisheries Staff)[/caption]
Drop nets are used to capture small species like smelt, drop nets are dropped through a hole in the ice which is illuminated to attract plankton which attracts small fish like smelt. The net is then periodically pulled up and the fish are caught in the bag-like nets when it is pulled vertically up to the surface.Categories