Methodological factors affecting capture of juvenile salmon in baited “minnow” traps

Abstract

In a southcentral Alaska stream system, we conducted a study to evaluate the effect of trap type (galvanized and nylon coated), bait type (salmon roe cured with and without sodium sulfite), and soak times (1 h and 24 h) on captures of juvenile salmon using Gee‐style minnow traps. This was undertaken due to the limited research on this topic, aiming to determine how variations in methodology affected captures in juvenile salmon.We employed a three‐way fixed factorial design to sample 176 stream reaches (with a single trap in each each) from June 2021 to September 2021, capturing 296 Coho Salmon Oncorhynchus kisutch and 105 Chinook Salmon O. tshawytscha.We found an estimated 78% decrease in captures of Coho Salmon when nylon‐coated traps were used instead of galvanized traps, and we found that trap type showed no effect on number of captures for Chinook Salmon. Additionally, we did not detect effects of bait type and soak time on the number of captures for either species. Not surprisingly, there was a positive relationship between Julian date and temperature with captures for both species. Additionally, for Coho Salmon, we found a quadratic relationship between water velocity and captures.Understanding and accounting for these factors will help researchers to maximize trapping efficiency, standardize protocols, and determine the extent to which results are comparable across studies employing different methods.