In this week’s fishing report, Regional Fisheries Biologist David Basley, of the Maine Department of Inland Fisheries and Wildlife, explains the process by which Maine biologists use trap nets to sample fish populations in regional lakes and ponds. 

With fall fast approaching, staff in the Fish River Lakes region will be setting trap nets in Long Lake to sample landlocked salmon and brook trout.  These nets are designed to capture fish that are traveling the shoreline as the water cools.  Trap nets are not effective in the summer because the shallow water is too warm for salmonids to be present.  

The nets are designed to capture fish alive and act much as a herring weir on the coast.  A lead that consists of a fine mesh net 50-100 feet in length is stretched from shore and tied to a net that somewhat resembles a minnow trap.  That is it has a funnel that the fish swim through guided by a set of “wings” into the holding box of the net that is generally 4 ft x 4 ft or larger.  All fish captured stay in the holding box until fisheries personnel arrive to process the fish.  

Processing consists of netting the fish and separating the game fish from non-game species.  Game fish are held in a tub of water and anesthetized with a sedative to prevent injury.  One anesthetized, the salmon will be checked for missing fins indicating year of stocking, measured, weighed and released into another tub of water to recover from the sedative.  Brook trout will also be checked for missing fins because although the sport fishery in Long Lake is from wild fish, an occasional hatchery trout will migrate into the lake from another water.  The trout will be measured, weighed and a scale sample removed from female and immature fish prior to being put in the recovery tub.  This scale sample will be examined under a microscope at a later date for age determination.  Scale samples are also taken from female and immature wild salmon.  Changes in the external physical character of sexually mature male brook trout and salmon make it difficult to collect a scale sample from these fish.  Prior to release into the lake, a piece of the tail is clipped to identify the fish as having been processed should it be recaptured again at a later date.  

Trap net data allow biologists to follow age and growth of stocked fish in those waters annually stocked with salmonids. These data in conjunction with any creel survey information can be used to make necessary adjustments in stocking programs.  Data from waters with wild salmonid fisheries can assist in evaluating the effectiveness of regulations in maintaining suitable growth rate and abundance of these wild populations.

-Dave Basley, Regional Fisheries Biologist

The Missouri Department of Conservation is funding a 3 year research project investigating the spawning habits and movement patterns of catfish in the Missouri River and its tributaries.  While adequate data exists for other game species, little is known about catfish spawning ecology.  This research could provide fisheries managers with essential information needed to make recommendations about season, length and bag limits, which would likely result in more and bigger catfish for Missouri anglers.  The DOC is considering a number of regulation options to provide a better fishery, but plans to wait on research results before making regulation decisions.

Read more about the catfish research going on, and the options the DOC is pursuing here. 

The Fish Ecology Lab I work in is responsible for long term population monitoring in the Logan River, Utah, which is home to an important metapopulation of Bonneville cutthroat trout.  A large part of this monitoring project involves collecting fish via electrofishing at eight different long term index sites throughout the river and its tributaries.  In the main stem of the Logan, high flows require that we use a canoe electrofishing unit and a large team of students, biologists, technicians, and volunteers. 

In order to complete the task, we rig up a canoe with a large generator, an electroshocking unit, multiple probes (anodes: +) operated by individuals, and a large cable cathode (+) hanging from the canoe.  

When the generator and shocking unit are turned on, and all probes and safety switches operating, an electric current is sent through the water between the probes and the cable hanging from the canoe.  This current causes fish nearby to turn sideways and become unable to escape the electrical field.  

A row of netters stand behind the people with probes and capture the fish that are caught in the electric current.  Fish are then transferred to the plastic tubs in the canoe, which contain cool river water oxygenated with bilge pumps. 

The individual pushing/pulling the canoe operates the master safety switch (we like to call it the ‘dead-man switch’), which has to be depressed for the unit to be shocking.  This person is responsible for watching everyone and ensuring that nobody gets zapped.  If about to stumble or reach into the water to get a fish between the rocks, a person calls out ‘off!’, upon which the switch is disabled and shocking postponed. 

After finishing shocking the site, workers quickly transfer fish to the station set up for data collection.  Here, all fish are measured and weighed, and adult fish receive individually numbered floy tags for future ID.  Some fish are saved for whirling disease testing, diet sampling and aging, and the majority are returned to the river. 

This process is repeated three times within an area enclosed by blocknets.  Fish captured on the first two runs are placed outside of the blocknets so that only new fish captured on the second and third runs.  Using the numbers of fish caught in each run, we can then calculate a capture efficiency, which we use to estimate the total population of fish within the blocked-off area (usually 200 meters).  This population estimate is expanded throughout the areas adjacent to the sampling site to provide general information about the area’s fish population, and is used to monitor trends in population dynamics over time. 

We’ll be back out the next three days completing our Logan River long-term sampling.  In addition to graduate students and technicians in our lab, we are usually assisted by a number of volunteers, along with people from the Utah Division of Wildlife Resources‘ Dedicated Hunters Program, where hunters complete fish and wildlife related conservation projects and receive additional hunting priveliges in return.  A reporter from the local newspaper will be joining us during the next couple of days as well, which we hope will shed more light on what we do in the river and why we do it.

Click Here for a description of my specific research goals on the Logan River

As part of some side work for the University, I snorkeled Big Creek in northern Utah this weekend.  Big Creek is home to a population of native Bonneville cutthroat trout, which has declined due to a combination of stocking nonnative brook trout and brown trout, and habitat degradation in some areas. 

My snorkeling surveys were part of an evaluation of a stream improvement project completed by the BLM years ago.  The BLM created an exclosure that kept cattle from reaching the stream for a stretch, and constructed pools and riffles to create more diverse fish habitat. 

I snorkeled a site lower in the creek that was apparently overgrazed by cattle, which was evident by the lack of vegetation cover and undercut banks, incredibly high sediment loading, and high water temperature, near the lethal limit for trout.  I observed a number of suckers in this reach, but not a single trout.

The restoration site contained six different fish species: cutthroat trout, brown trout, brook trout, sculpin, shiner and sucker.  It was exciting to see how well trout could do in the same general area, with better habitat conditions to work under.

I snorkeled a third reach, just above the stream improvement site, which was only lightly grazed by cattle and contained even more fish.  I think the combination of better physical habitat and cooler water temperature were key in determining trout abundance and distrubution.

Another pattern I noticed was that while cutthroat numbers were the same in the two upper reaches, brook trout numbers increased significantly in the uppermost site.  This was likely a combination of the slower, meandering channel, undercut banks and pools, and colder water temperature in this reach.

Seeing those trout while snorkeling got me so excited that I decided to do some fishing after I was done.  I went above the upper reach and started casting elk hair caddis and orange grasshopper patterns in the creek.  The constant meandering S-curves in the stream made it fun to fish, and you could cover a lot of water without walking very far.  Also, there were no trees present to mess up my casts! 

I hooked into some nice Bonneville cutthroats, a mess of brook trout (which were welcomed by this native Mainer), and a nice looking brown.  Took some brookies and the brown home for dinner and sent the cutty’s back in the drink.  Made for a great weekend combo of snorkeling and fishing, and I’ll be sure to return and explore this creek even more.     

Well, it’s good to be back after a week of field work in Idaho.  I started off in eastern Idaho, working on a hooking mortality study investigating the effects of circle hooks on fish as opposed to the traditional ‘J’ hooks.  The goal of the study was to catch 300 fish with all different gear types (lures, bait and flies) with both hook types.  We placed a PIT (passive integrated transponder) tag in the body cavity of each fish caught, and made notes on hooking location and evident injuries. 

As expected, fish took baited ‘J’ hooks deeper than the circle hooks, but we’ll have to wait until sometime this winter to get the full results.  Later this fall, a crew will be in to collect all fish by electrofishing within the wiered off study site and investigate mortality rates between hook types.  They will be able to identify the individual fish that were caught using different hook and lure types by reading the code on the PIT tag implanted in each fish using an electronic tag reader.

 I then traveled to western Idaho to help my old boss’s field crew while he was away.  We obtained rainbow trout population estimates in a mountain stream via two-pass mark-recapture electrofishing.  While it sounds complicated, the mark-recapture method is quite simple.  The fish population is estimated by making two separate passes through a stream site and collecting each fish by electrofishing.  Obviously, some fish are missed, hence the need for an estimate.  This estimate is obtained by marking all fish caught in the first run, and comparing the ratio of marked to unmarked fish caught in the second run.  In other words, if you recapture a lot of marked fish and don’t catch many unmarked fish, your capture efficiency is high and the estimate is quite close to the number of fish you marked.  If you recapture few marked fish on the second run, however, the estimated number of trout will end up being much higher.

The study we worked on when electrofishing is looking at the effects of hatchery rainbow trout on wild trout in Idaho streams.  Conflicting results have emerged from previous studies, so this is a very robust attempt to explain what is truly going on.  Preliminary results show that hatchery trout survival is extremely low over the long term, so the effects may be miniscule, but this is yet to be determined.  The biologist in charge of the study is monitoring the growth of individual trout, as well as overall population survival, in areas stocked with rainbows, and in control sites where no stocking occurs.

I finished up the week by retrieving and replacing a bunch of temperature loggers I placed in different streams last year.  These loggers collect year-round water temperature data and are very valuable in modelling fish growth, as well as predicting thresholds for survival and trends related to temperature.

All in all, it was a great trip, but it’s time to get back in front of the computer and catch up on things.

Mackenzie River Reflections recently reported on an automatic fish marking system used by the Oregon Department of Fish and Wildilfe, which uses machinery to clip fins and places coded wire tags on juvenile salmon and trout before they’re stocked in the state.

These tags and other markings serve to verify the origin of the fish once they are recaptured, and are a crucial part of efforts to track stocking success.  If fisheries biologists know the time, area and condition of a fish with a specific marking, they can use this information to generate survival estimates, growth rates, and movements of the population after sampling it in the future.

Fin clipping and tagging is usually done manually, but just like in any other field, advances in technology are making it continually easier to get the job done with less human effort. 

I spent most of yesterday snorkeling in a mid-sized stream in northern Utah.  Snorkeling is oftentimes a great way to observe and count fish in streams, especially when other sampling methods prove unfeasable.  

You’d be surprised how much more can be seen by simply getting down at the fish’s level and viewing things from underwater.  You can see things much clearer, and the fish aren’t as afraid, since you’re kind of at their level. 

I had previously fished most of the same areas I snorkeled yesterday, but that didn’t prepare me for what I ended up seeing.  Almost every time I worked my way into an undercut bank with heavy vegetation cover, I found big fish.  I’d never caught a brown trout over 16 inches in that stream, so when I drifted into one undercut bank and got face to face with a 22-23 inch fish, it blew my mind.  Add to that the fact that I got within two feet of the guy, and fish tend to look bigger underwater, and you begin to get the idea. 

Aside from that big fish and the 18 incher beside it, I observed numerous holes with extensive vegetation cover that held multiple brown trout over 15 inches.  In fact, I drifted through one hole about 20 yards from a popular campsite and fishing area, that held 6 fish estimated at over 15 inches!  It makes me laugh a little, remembering average Joe complaining about how there weren’t enough fish in the river and the state needed to stock it more! 

The key reason these fish stick around, in my opinion, is that they choose to hold up in holes that are almost impossible to get a fishing line into.  Deeply undercut banks with extensive vegetation cover, right next door to fairly deep, swift water makes for conditions that would frustrate even the most experienced angler.  My friend and I tried to entice some of these big guys to get out and take the flies we drifted as close to them as possible, but only succeeded in catching fish less than 15 inches. 

After talking it over with a friend, I think I’ll try drifting weighted streamers as near the holes as possible, just before dark, and hope I can get one to come out and take a bite.  One thing’s for sure: actually seeing the fish and knowing big ones are there gets me pretty motivated to work hard at catching ‘em.  And believe me, If I do hook on to the big one, you’ll know it!

Think about those days where you just can’t seem to get the fish to bite.  Wouldn’t it be nice to send a good ol’ shock through the water and get ‘em.  That’s just what the Maine Dept. of Inland Fisheries and Wildlife was doing recently on the Kennebec River.  Join writer Travis Barrett of Central Maine Newspapers as he experiences the rush of electrofishing first hand.

     Electrofishing is arguably one of the most important techniques used in fisheries research and management today.  The method is just as it sounds….electricity is used to stun and capture fish, which are then netted into buckets for specific data collection.  Electricity is passed through the water between two elements, an anode (positive end) and a cathode (negative).   Shocking is done with backpack units, boats, canoes and barges. 

     Backpack units are used most often in streams.  The shocking unit is mounted on a backpack and is powered by rechargeable batteries, or sometimes a small generator.  The operator holds a probe, which serves as the anode, and a tail (uncoated wire cable) hangs from the unit and drags along in the stream.  When the shocker is turned on, a pulsed direct current moves from the cathode to the anode.  Field workers avoid shock by wearing waders which insulate them from the electric current, and keeping their bare hands out of the water.  Nets are constructed of wood, fiberglass or plastic to avoid electric conductance.   Fish try to avoid the current, but exhibit a muscle response reaction termed ‘taxis’ when they are caught in it, and swim toward the anode in a sideways manner, at which point they are netted up and placed in buckets.  This method is extremely effective in capturing fish, and because of this, it is most often used to generate population estimates in streams.  Larger fish are more easily caught by electrofishing because they have more body surface for the electric current to pass through.  Stream habitat features that change the effectiveness of electrofishing include conductivity (dissolved particles), water depth and clarity, water current, temperature, and habitat complexity.      

     Canoe electrofishing is used in large streams and rivers, and man is it a blast!  A generator is mounted in a canoe and powers an electrofishing unit attached to multiple probes, usually 3.  The canoe serves as the ground, or cathode.  One person stands upstream of the canoe and guides it through the river with a lead rope.  This person also holds the ‘dead man switch’, which he or she constantly has to hold on for the unit to circulate electricity.  When the operator sees someone stumbling or falling into the water, they let up on the switch to avoid shocking the person.  Each of the probes is operated by an individual who either sweeps it down the current or throws it out and retrieves it through the area targeted for shocking.  Finally, people are lined up with nets below the probes to collect stunned fish.  This often consists of walking backwards in fast, deep water and trying to net fish, all the while hoping you don’t trip over or slip on the next rock you come across.  Fish are bucketed and data is collected between shocking runs.      

     Barge shocking is similar to the canoe method, except that it is usually done in lower gradient, slower moving rivers and streams.      

     Boat electrofishing is used in lakes and reservoirs to collect fish.  Because of lake size, it is usually not possible to generate a population estimate in lakes, but the method is very effective in collecting large numbers of fish.  The boat serves as a ground, and a shocking unit is wired to the boat’s battery or a separate power source.  This type of shocking is usually done on shorelines and shallow areas for warm water species because of the depth limitation of the current.  Multiple probes are mounted to the front of the boat and multiple people stand at the bow with long handled nets to collect fish.  The boat operator positions the bow in the desired area and the method is repeated until the sample is collected.               

     Overall, electrofishing is a very effective method, and when done correctly, exhibits minimal injury to fish and provides managers and researchers with valuable data that would otherwise be very difficult or impossible to obtain.