Catchability of Larval and Juvenile Northern Pike in Quatrefoil Light Traps

Abstract

New approaches are needed for sampling northern pike Esox lucius in the complex habitats they use as nursery areas. We evaluated the potential of Quatrefoil light traps to measure differences in density of larval and juvenile northern pike, and we monitored changes in capture probability as the fish grew in size and their swimming capabilities improved. In hatchery raceways, light traps were effective for collecting northern pike at densities that seemed most realistic relative to natural nursery habitat (4–20 fish/m2 surface area). Light‐trap catch rates differentiated among different densities in raceways, but efficiency decreased as density increased. Light traps effectively caught all sizes of fish, ranging from the stage when larvae first became active (12–13 mm total length [TL]) until the fish became too large to fit through the trap entrance (>66 mm TL). We also tried to apply the technique for sampling managed wetlands that simulated a more natural environment than the raceways. Light‐trap catches detected both increases and decreases that were attributed to different stocking rates used over 2 years in individual wetlands. Light‐trap catches showed patchy distribution of small northern pike and illustrated growth and differential survival of the fish among wetlands. Light trapping should be considered a potential tool for sampling both temporal and spatial variation in density and growth of larval and juvenile northern pike.

Interannual variation in reproductive phenology in a riverine fish assemblage: implications for predicting the effects of climate change and altered flow regimes

“…Typically, three quatrefoil light traps with 2 mm openings (Pierce et al, 2006) were set just prior to sunset, and contents were removed the following morning. April-July was chosen because it encompasses the range of spawning onset in this portion of the Rio Grande.…”

Vegetative substrates used by larval northern pike in Rainy and Kabetogama Lakes, Minnesota

“…Previous light trapping in three southern Minnesota ponds that were also managed as northern pike rearing areas showed best survival of larval northern pike in dense beds of flooded reed canary grass (Pierce et al. ). Southern Minnesota has much heavier agricultural and urban land‐use than the northern reservoirs we studied.…”

“…Pierce et al. () reported that light‐trap catch rates discriminated between different densities of larval northern pike stocked into hatchery raceways and that light traps were capable of detecting patchy fish distributions. This study also illustrated growth rates and differential survival among managed wetlands.…”

“…They compared catches in lighted (using chemical light sticks) versus unlighted quatrefoil traps, and their results showed that catches of northern pike were 3-35 times greater in lighted traps. Pierce et al (2006) reported that light-trap catch rates discriminated between different densities of larval northern pike stocked into hatchery raceways and that light traps were capable of detecting patchy fish distributions. This study also illustrated growth rates and differential survival among managed wetlands.…”

“…This study also illustrated growth rates and differential survival among managed wetlands. Light trapping can effectively sample larval northern pike from the time their mouths form and they begin exogenous feeding (10-12 mm) through the sizes when they complete the larval stage and attain the general form of the adults (about 35-40 mm; Franklin & Smith 1960;Pierce et al 2006).…”