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FISH SURVEY TECHNIQUES
 

Conducting fish surveys allows biologists and managers to understand the dynamics of a fish community in order to make proper management decisions.  During a typical survey collected fish are identified, measured, and weighed. Depending on the sampling objective the fish may also be tagged, used for aging, diet analysis, or any other type of pertinent information.  The following is a short description of fish sampling techniques used by the Arizona Game and Fish Department: 

Electrofishing
The use of electric fields in water to capture or control fish is a valuable sampling technique used by the Arizona Game and Fish Department. Electricity is passed through the water, by two types of electrodes, the anode (positive) and the cathode (negative). When applying the correct current, fish will be stunned for a few seconds, netted, and put into a holding tank for observation. The Arizona Game and Fish Department uses three different methods of electro-fishing equipment:  boat, canoe, and backpack. 

Boat
Boat electro-fishing is conducted primarily on reservoirs or larger still standing waters. The electro-fishing boat is rigged with two booms which act at anodes, extending out from the front of the boat with arrays or a metal ball that is lowered into the water.  A Smith-Root 5.0 generator is used for the power source and a control box is needed to take AC power from generator to electrodes. Two netters stand on the bow of the boat.  One operates the trolling motor and the other operates a foot pedal that applies electricity to the water.  Typically electro-fishing is conducted at night as fish tend to move into the shallows making them easier to target. Boat electro-fishing is used when targeting largemouth bass, smallmouth bass, and sunfish.

Fig 1  

Canoe
A canoe electro-shocker is used primarily for non-wadeable rivers and streams. The canoe is fixed with metal plates (cathode) on each side and a metal sphere (anode) that drops off the front of the canoe into the water.  Similar to the boat eletro-fisher a Smith-Root 5.0 generator and control box produce and control the electricity that enters the water.  Shocking sites are conducted downstream during the day alternating from bank to bank throughout a site.  The person in front of canoe operates a foot pedal that puts the electricity into the water and collects fish with a dip net.  The person in the back steers the canoe along the selected site collecting any fish missed by the person in the front.  Additionally a chase canoe follows closely behind capturing additional missed fish. Species captured varies depending on the body of water.

Fig 2

Back pack
The backpack unit is the smallest of the three types of electro-fishing devices and is used primarily in wadeable streams.  The Standard unit that Arizona Game and Fish Department used is a Smith-Root LR-24 electro-fisher mounted on a backpack frame.   Similar to the other electrofishing units, the backpack electro-shocker has both an anode and cathode.  The anode is a probe with a control switch that is placed in the water once the unit is turned.  The cathode is either another probe or a cable that drags behind the person operating the shocker.   Sites selected must begin at designated coordinates and end at a predetermine distance.  Each sample site within the stream is traversed using a sweeping motion and alternating back and forth to cover both sides of the stream.  Typically two other individuals accompany the person shocking to net  and hold fish for measurements.  All backpack shocking is done during daylight hours in an upstream direction. 

Fig 3

Gill Netting
Gill netting is a passive capture technique where a fish swims into the net and passes only part way through the mesh.  When it struggles to free itself, the twine slips behind the gill cover and prevents escape.  The Arizona Game and Fish standard for gill nets are 150 feet long and 6 feet tall.  The net consists of six panels ranging in mesh size from ½ inch to 3 inches.  The top end of the net is a float line and the bottom end is a lead line allowing the net to stay suspended in the water column. Nets are typically set during daylight hours, fished overnight, and retrieved the following day.  In most cases nets are set at the bottom oriented perpendicular to the shore. Gill nets are primarily used in Arizona to catch the following species: trout, striped bass, yellow bass, white bass, catfish, walleye, yellow perch, northern pike, and threadfin shad.  

Fig 4

Trammel Netting
This study will determine if stocking efforts in Saguaro, Canyon, and Apache Lakes are effective in improving the fishing quality in these reservoirs.  Angler catch rates will be monitored throughout to help determine the best method for future stocking efforts to establish and maintain a thriving fishing environment.  Efforts to determine water quality associated with golden algae toxin release will be helpful to predict future fish kills and to manage stocking efforts.  In addition, a monitoring program will also be established to address calls of fish kills and determine proper protocol for reported kills.

Fig 5

Seining
Seining is typically accomplished during daylight hours in waters with low visibility. A minimum of two parallel hauls will be conducted at each sample site.  A parallel haul is performed by setting the seine perpendicular to shore and pulling the net parallel to shore for a predetermined distance.  At the end of the tow, the person farthest out pulls toward shore and both wings are pulled ashore simultaneously.  The lengths of seines vary and are used to capture small fish, mostly minnows and young of year species. 

 

For more information contact:
Bill Stewart, Arizona Game and Fish Department
5000 W. Carefree Highway, Phoenix, AZ 85086-5000.
Phone: (623) 236-7368       E-mail: bstewart@azgfd.gov

Lorraine Avenetti, Arizona Game and Fish Department
5000 W. Carefree Highway, Phoenix, AZ 85086-5000.
Phone: (623) 236-7514       E-mail: lavenetti@azgfd.gov

 

 
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