The Potential for Water Gun Technology to Control Invasive Northern Pike in South Central Alaska

This project tested new methods for controlling invasive northern pike populations in South Central Alaska utilizing sound pressure generated with a water gun.  A dose response to various sound energy levels on fish survival was tested. Individual fish were submerged in a mesh-lined PVC-framed cage and subjected to two pulse pressures from a 343 in³ chamber water gun at a predetermined random distance of 3, 6, or 9 meters from the water gun. Fish mortality was assessed every 24 hours for 7 days, after which all individuals were sacrificed and internal organ damage was assessed.  Damage was recorded for the swim bladder, kidney and liver condition (intact, hemorrhaged or ruptured). The same experiment was also replicated using a 120 in³ chamber water gun, at distances of 3 and 6 meters. Sound pressure levels were measured by a high pressure sensor attached to the exposure cage. Data recorded were peak pressure, peak-to-peak pressure, frequency and total pressure sound energy level (SEL) was calculated.  Peak pressure was the highest decibel level experienced by a fish, while peak-to-peak pressure was the difference between the highest and lowest pressures for a single pulse pressure. Sound energy level was the total energy from two pulse pressures experienced by the fish recorded in a seventy millisecond interval. The perceived peak pressure and peak-to-peak pressure from each pulse pressure varied significantly by treatment group for both guns tested.  Peak pressures and peak-to-peak pressure experienced by the fish exposed to the large water gun ranged from 40-200 PSI and 65-220 PSI respectively and decreased in increasing distance from the gun.  Peak pressures and peak-to-peak pressure experienced by the fish exposed to the smaller water gun were approximately half that of the larger water gun, with measures of 40-120 PSI and 60-130 PSI respectively. The general trend observed as expected was increasing mortality and greater damage with decreasing distance from the water gun. One hundred percent of fish gas bladders exposed to the large water gun were ruptured at 3 and 6m from the water gun and 86% of gas bladders were ruptured at 9m. All pike gas bladders were ruptured when exposed to pulse pressures from the smaller gun. Mortality during the experiment was only observed for fish with the highest explosion damage criteria. The utilization of water guns show promise for controlling northern pike. Future studies will evaluate pike movement in response to pulse pressure application.