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Fish Counting Weir, Vaki Riverwatcher

A handy feature of the VAKI Riverwatcher system is that it allows us to record video clips of each fish that passes through our fish counting weirs. In addition to identifying the fish species, length, and passage date when we review the video, we also document the condition of each fish. We look for abrasions, lacerations, fungal infections, lamprey scars, hook scars—and in this case the actual hook! In this video you can see the shiny fishing lure dangling from a Chinook salmon’s dorsal fin. The angler is probably disappointed that he or she foul-hooked this salmon and lost not only the catch, but the lure to boot—although it does make for a flashy fish accessory.

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Field Crew, Fish Counting Weir, Research

Fish don’t take days off for bad weather, so our field work often means spending time in whatever conditions nature has to offer. Our crew powered through the deluge to install a fish counting weir on the Salinas River a few weeks ago. Unlike other rivers that get their water from snowmelt, the Salinas Basin is a rain-driven system—and sometimes requires working in the driving rain. The volatile flows on this flashy river quickly ramp up after a downpour, so we take extra care in securing the weirs to withstand the impact.

Scientists recently studied the Salinas Basin to understand the processes that cause rivers to branch. They compared Salinas to Pennsylvania’s Allegheny Plateau, and created a mathematical model that factors in two competing forces: water cutting through the soil, and the soil filling back in. Salinas has softer rocks and more runoff, so the water wins out and creates branching systems that are four times as fine as the Pennsylvania rivers. The complex river network makes an interesting and challenging site for us to monitor—whether rain or shine.

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Field Crew, Fish Counting Weir

Adding a little humor to an otherwise routine task, this crewmember shows off his dance moves after cleaning algae from the viewing window of a fish counting weir. Using high tech electronic fish counting systems, like the Vaki Riverwatcher, to record fish passage provides highly accurate results; but like most things in life (here comes the cliché), you only get out what you put into it. Field technicians regularly visit our fish counting weirs to clean the camera lens, lights and glass that monitor the fish passage chute (or in this case the dance floor).

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Fish Counting Weir

A FISHBIO crew recently installed the anchoring system for a fish counting weir in the Salinas River. Fish counting weirs are designed to withstand a substantial flow, but the Salinas River can be an especially challenging system due to rapid changes in river flows and the sandy substrate. Because of volatile flows in this flashy, rain-fed system, crews are taking extreme measures to reinforce the anchoring system (substrate rail) that holds the weir in place. Crews were driving heavy-duty rebar pins along with large, arrow-shaped anchors  8 feet into the sandy substrate at regular intervals across the width of the river. The creative minds in our FABLAB devised an ingenious way to speed up the process of hammering the stakes deep into the river substrate. They fabricated a sleeve that fits over the end of the stake and attaches to a pneumatic jackhammer driven by an air compressor positioned stream-side. We have posted a video on our YouTube page demonstrating how this system works.

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Field Crew, Fish Counting Weir

At first glance this appears to be a strange fisheries snorkel survey, but in fact this technician is doing underwater construction work. We recently installed a substrate rail that will eventually hold a fish counting weir in place. This technician was wearing a hardhat because he was operating a jackhammer above the water (YouTube video), but he didn’t remove it before plunging face first underwater to inspect the heavy rebar stakes driven into the river bottom. This installation process is different from the substrate rails we’ve anchored previously, because every site has a different river bottom substrate, providing a new challenge for our field technicians.

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Fish Counting Weir, Vaki Riverwatcher

We’re always looking for better ways to showcase the easy setup and use of the VAKI Riverwatcher fish counter. We’ve had great success over our 8 years of using it, and get asked a lot of questions about installation and how it works. So, it only made sense to put our technicians to the task of fabricating a portable display in the FABLAB to demo it.

Because the system is made up of 4 key components, they’re easy to put together and easily adaptable to various applications, such as resistance board weirs, fish traps, fish ladders, fykes, flumes and many others. Our own Scott Wucherer demonstrates how the system works.

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Fish Counting Weir

One of the primary advantages of using an Alaskan weir (aka fish weir, portable resistance board weir) to sample salmon and other fish populations is its ability to operate effectively at a wide range of flows, such as the 1,500 cfs shown here. For high flows we fasten plastic drums under the weir panels to increase the panel’s buoyancy and keep the weir above water. However, high flows create high turbidity levels, which makes fish counting under these conditions difficult without a little technological help. We use a Vaki Riverwater that provides infrared images of fish when the turbidity is too high for the camera and video systems to work effectively.

Photo source: FISHBIO

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Fish Counting Weir

This post is the last in a “how to” series on the basic components of building a fish counting weir. A weir can have many uses, in some cases this fence-like structure might be built to exclude fish from a certain location, but the majority of weirs are used to enumerate migrating species or to trap fish in order to collect biological data or brood stock for a hatchery programFor fish counting weirs, an opening must be created in order for fish to be counted as they pass through. This can be achieved by removing one or more resistance weir panels, but is better accomplished by modifying a panel to create a passing chute. Fish migrating upriver encounter the weir and move sideways from bank to bank until they locate the opening. For salmonid monitoring, the passing chute is located near the thalweg where there is ample flow for fish to cue in on. Passing chutes can be fitted with electronic monitoring equipment (VAKI Riverwatcher, Video recorder, PIT tag antenna, etc.) and/or a livebox fish trap.Fish traps can be as large and sophisticated, or as small and simplified as need for a particular application. A livebox fish tap typically consists of a rectangular cage fabricated from aluminum or galvanized steel to prevent corrosion. One or more fykes are located at the entrance to help guide the fish into the box, and to reduce the likelihood of fish escaping or moving back downstream. Liveboxes may also include a crowder gate that can guide trapped fish to one side of the trap or facilitate removal. Resistance board weirs are gaining recognition as a respected device in fisheries management and we hope that after reading our posts you have better understanding of the process of weir fabrication.

See the other posts from this how to series:
Fish counting weir: how to series
Fish counting weir: substrate rail
Fish counting weir: resistance weir panels
Fish counting weir: rigid weir and bulkhead

Photo source: FISHBIO

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Fish Counting Weir

welding-rigid-weir

rigid-weir-panels

Resistance board weir panels are designed for use in the main river channel and adjust to changing flow and debris conditions, but they are not intended for sloped river banks. Instead, rigid weir panels are used on either side of the resistance panels to extend the weir out to the bank. Rigid panels are simply galvanized steel pipes welded to iron cross members, held in place by A-frame supports. We usually make the panels 3 ft. wide and 5 to 10 ft. tall, depending on the expected range of channel depths. Large vertical panels (5 ft. x 20 ft.) called bulkheads serve as an interface between the stationary and movable parts of the weir, moving up and down with the resistance board panels. Bulkheads consist of a welded aluminum frame with PVC conduit pickets spaced 2 in. apart, and are fastened to long stakes driven into the substrate.

rigid-weir-bulkhead

Photo source: FISHBIO

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Fish Counting Weir, Monitoring, Salmon, Steelhead

large-woody-debris

The recent rain and snow has caused a lot of problems for holiday travelers throughout the country this past week, and the impact of the bad weather on the working schedules of fisheries biologists should not be overlooked. High flows have many impacts on stream and riparian environments, including transporting large debris downstream. In this case, FISHBIO biologists assist a tree on its downstream journey past a fish counting weir. One of the primary benefits of a collapsible fish counting weir is that large debris and high flows do not result in a blowout of the weir. Rather, the weight of debris and force of flowing water cause the weir to collapse, which often allows debris to pass downstream over the top of the panels on its own. In some cases, such as this one, biologists need to lend a helping hand.

Many years ago, fish and wildlife agency biologists often cleared streams of large woody debris thinking that it only caused a hazard for river traffic. However, the importance of woody debris to salmon and trout habitat has become well established over the last two decades. Woody debris serves many purposes for salmonids, including providing slow water refuges and cover from predators; facilitating creation of pools and spawning habitat; offering feeding stations and enhanced food production; preventing bank erosion and increasing channel stability; and generally increasing stream habitat complexity.

Photo source: FISHBIO