Understanding Smallmouth Bass Recruitment in Relation to Nest Fishing Along Wisconsin's Door Peninsula

Abstract

Wisconsin’s Door Peninsula, which lies between Green Bay and Lake Michigan, represents one of North America's premier smallmouth bass fisheries, and some stakeholders have expressed concerns regarding the potential effect of high angler effort during nesting on the smallmouth bass population. However, limited information exists for fishery managers to address these concerns effectively. To better understand factors influencing smallmouth bass nest success and subsequent recruitment trends, my research aimed to determine if: 1) nest success (i.e., production of fry) varied in relation to a suite of abiotic and biotic variables, including angler effort and nest disturbance rates; 2) sampling effort required to detect a 50% change in mean catch-per-effort (CPE) of age-0 smallmouth bass varied among mini-fyke nets, modified boat electrofishing, and hand-held anode boat electrofishing, and 3) location-specific estimates of age-0 CPE measured at end of summer (September through early October) were related to the frequency of successful nests, fishing pressure and angler nest disturbance rates during nesting, frequency and severity of storms, and cumulative growing degree days above 22˚C (GDD22). In 2022 and 2023, I sampled four spawning locations on both sides of the Door Peninsula that encompassed a range of angler effort. These sites included Little Sturgeon Bay and Sawyer Harbor on the Green Bay side of the peninsula and Detroit Harbor and Moonlight Bay on the Lake Michigan side. In May through July of each year, I searched for nests along shallow (<1.5 m), medium (1.5-3 m), and deep (> 3 m) water transects to describe the distribution and relative frequency of nests in each location. I selected 27-54 focal nests in each location each year and repeatedly visited those same nests at 3-10 d intervals throughout the spawning period to determine nest success and measure various factors that might be related to nest success and age-0 smallmouth bass catch-per-effort (CPE) measured at end of summer. To estimate angler effort during spawning periods, I used angler interview data from Wisconsin Department of Natural Resources creel surveys coupled with effort counts I obtained using a modified bus route creel survey design. To quantify rates of angler nest disturbance, I deployed underwater cameras on nests and watched videos to record how often each nesting bass was targeted and disturbed by anglers. At end of summer in both years, I conducted modified boat electrofishing, hand-held anode boat electrofishing, and mini-fyke nets to calculate catch-per-effort (CPE) as an index of age-0 smallmouth bass recruitment. Two-factor ANOVA was used to compare nest success among locations and years. Binomial generalized linear models were used to identify what predictor variables best explained variation in nest success. I used simple logistic regression to determine if the probability of anglers targeting nesting bass was related to nest depth and the average number of boats observed. I determined how much sampling effort would be required to detect a 50% change in mean CPE to identify which sampling gear was most efficient at capturing age-0 smallmouth bass, and Kolmogorov-Smirnov tests were used to compare total length (TL) distributions among sampling gears and locations. Lastly, generalized linear models were used to identify predictor variables that best explained variation in age-0 CPE using estimates from the most efficient gear at sampling age-0 smallmouth bass at end of summer. Nest success ranged from 12.1-54.8% and significantly differed among the four spawning locations (F = 45.56, df = 3, P = < 0.01) and years (F = 20.26, df = 1, P = 0.02), with bayside locations showing higher nest success (mean  SD = 44.1  10.4) than lakeside locations (mean  SD = 16.3  4.3) and nest success was higher in 2022 (mean  SD = 35.7  18.4) than in 2023 (mean  SD = 24.7  15.0). Generalized linear regression indicated the best model explaining nest success included the predictor variables of CV in mean daily water temperature and angler nest disturbance rate (McFadden R2 = 0.40). The probability of a nest being targeted by anglers on a given day was related to the number of boats observed during camera deployment (SE = 0.31, Z = 3.12, P = < 0.01), but not was not related to nest depth (SE = 0.29, Z = 1.07, P = 0.28). Modified boat electrofishing captured the widest TL range of smallmouth bass (54-255 mm) compared to hand-held anode boat electrofishing (59-113 mm) and mini-fyke nets (39-98 mm). Total length distributions were similar between modified boat electrofishing and hand-held anode boat electrofishing (D = 0.08, P = 0.82), but both gears captured larger fish compared to mini-fyke nets (D = 0.49, P = < 0.01 and D = 0.47, P = < 0.01, respectively). Among sampling gears, modified boat electrofishing yielded the highest CPE of age-0 smallmouth bass and required the fewest units of effort to capture at least 30 age-0 smallmouth bass. Hand-held anode boat electrofishing exhibited slightly less variability in CPE (CV = 135), and mini-fyke nets exhibited slightly more variability in CPE (CV = 159), but both consistently sampled fewer age-0 bass than modified boat electrofishing. Generalized linear regression indicated the best model explaining age-0 CPE in modified electrofishing included the predictor variables of nest success and cumulative GDD22 (McFadden R2 = 0.47). My results suggest that environmental variables are the primary driver of nest success throughout the Door Peninsula. Bayside embayments consistently had higher nest success despite experiencing higher angler effort and rates of angler nest disturbance. However, additional research is needed to better address how variation in angler effort may influence nest success at specific locations, as angler effort and environmental conditions were confounded as predictors (i.e., low effort coincided with less favorable environmental conditions). Modified boat electrofishing was the most effective gear at capturing age-0 smallmouth bass for indexing age-0 recruitment, but additional validation is needed to determine if age-0 CPE can be used to predict eventual recruitment of smallmouth bass to the fishery along the Door Peninsula.