Electro-Fishing Summary

Introduction: Electrofishing involves passing an electric current through the water to draw fish to the surface where they can be captured alive in a dip net. When conducted from a specially equipped boat, a generator causes the metal boat acts as the cathode, which discharges electrons into the water. The electric current passes through the water and is picked up by positively charged wires (anodes) dangling from booms on the front of the boat. Fish within the current are stunned and orient in the direction of the current flow, swimming toward the anodes.

On August 25, from approximately 10:45 to 4:00 PM, electrofishing sampling of the Petitcodiac River impoundment was conducted from the elecrofishing boat of the New Brunswick Co-operative Fish & Wildlife Research Unit of the University of New Brunswick. This 14-ft, heavy gauge aluminum boat is powered by a 25 hp Evinrude outboard motor, and is equipped with a portable generator that produces the electric current for electrofishing. Two anodes, called octopuses (because each is comprised of multiple dangling cables) were lowered into the water when the electro-fishing was to commence. Electro-fishing safety gear, including hip waders, rubber gloves and life jackets, were worn by the technicians at all times while they were in the boat. The two technicians that dip the fish from the water are retained within the boat by a solid steel rail. The boat motor is tiller controlled, and the boat operator also controls a foot pedal on/off switch for the electrofishing system.

The goal of the electrofishing in the Petitcodiac River impoundment was to confirm the results of the fyke-netting program, which employed fixed live traps to determine the fish species and the sizes of the fish that inhabit the Petitcodiac River impoundment. The mobile electrofishing boat was able to cover areas of the impoundment between the fyke netting sites, and to capture fish that use an ambushing rather than a mobile prey seeking strategy for capturing their food. Of particular interest was the absence in the trap netting of chain pickerel, which are reported to inhabit the impoundment. Because chain pickerel were a major target of the electrofishing, sites with emergent grass and broad-leafed aquatic plants, areas that are preferred by pickerel were heavily sampled.

The sites covered during the electrofishing exercise ranged from approximately 2.5 km downstream of the train bridge in Salisbury to 2.5 km upstream of the confluence of Turtle Creek and the Petitcodiac River. Sherry Sparks, DSS EIA Manager, Dr. Allen Curry, Fisheries Biologist at UNB, and John Bagnall and Andrew McIntyre of AMEC were present for the duration of the electrofishing activity. A map depicting the areas of concentration of the electrofishing activity is provided in Figure 1.

The results of the electrofishing exercise are summarized in the attached tables.

Conclusions: Shallow sites with emergent vegetation would have harboured chain pickerel if they were present. None were captured in the daylong electrofishing exercise. Chain pickerel are a carnivorous fish, and a notorious predator of salmonids. Pickerel are not native to the Petitcodiac River system. Their absence in the sampling is a positive result. If pickerel are present in the impoundment, they are not a dominant species.

The smallmouth bass observed were short and stocky. There is an abundance of small fish in the impoundment to serve as forage for bass, and the small size of the bass was somewhat surprising. Bass are sight feeders, and the murky conditions in the impoundment may be contributing to a lower foraging rate among bass than would occur if there were better visibility in the water. Large white suckers dominate the fish community. Suckers root in the bottom mud to obtain invertebrate forage. This activity results in conditions of high-suspended solids in waterbodies where suckers dominate. In the Petitcodiac River impoundment, an additional cause of suspended sediment is wind-generated turbulence in the shallow water.