Donald L. Pereira

A Comparison of Bluegill Reproductive Strategies and Growth among Lakes with Different Fishing Intensities

Abstract Life history theory suggests that maturation schedules of male bluegill Lepomis macrochirus and the occurrence of alternative male reproductive strategies (i.e., parental or cuckolder) may contribute to the development and duration of undesirable bluegill population size structure (few fish larger than 150 mm). To investigate this relationship, we assessed parental male maturation schedules and relative abundance of cuckolders in six lakes subject to differing levels of fishing effort. Bluegills were collected by electrofishing shortly after the onset of the spawning season. Lakes with lower fishing effort had parental males that were older and larger at maturity than parental males in lakes with high fishing effort. Also, growth of parental males in lakes with low fishing effort was faster at older ages, and growth of immature males was faster than growth of cuckolders. Unlike other lakes, two of the three low-fishing-effort lakes had very few cuckolders. Our results indicate that intense fishin...

Development of a Fish-Based Index of Biotic Integrity for Small Inland Lakes in Central Minnesota

Abstract We developed a fish-based index of biotic integrity (IBI) for a set of Minnesota lakes having similar geophysical and chemical features. Fish data were collected by means of trap nets, gill nets, shoreline seines, and backpack electrofishing. Of 30 evaluated metrics, we identified 16 metrics of three types: species richness, community assemblage, and trophic composition. In contrast to lotic IBIs, where a single sampling gear is usually used, data from all four sampling gears were necessary for IBI development. We selected metrics based on responses to measures of human-induced stress based on watershed land use patterns and human population density. Species richness and community composition metrics describing intolerant or habitat specialist species were most sensitive to differences in human-induced stress. Because these species were found in the nearshore zone of lakes, effective sampling of the nearshore fish community was essential to the development and performance of the IBI. Trap-net- an...

Hooking Mortality of Walleyes Caught on Live and Artificial Baits

Abstract The potential benefits of catch and release or protective size limits in recreational fisheries for walleye Stizostedion vitreum can only be realized if released fish survive. In this study, hooking mortality rates were determined for adult walleyes caught on leeches and artificial lures in two Minnesota ponds. The mortality of walleyes caught and released by anglers in Klawitters Pond was 5%, though confidence intervals indicated that hooking mortality could have been as high as 23%. Mortality of walleyes caught on leeches (10%) was higher than mortality for walleyes caught on artificial lures (0%). An estimate of hooking mortality in Clubhouse Pond, unadjusted for natural mortality, was 16%. Walleyes caught on artificial lures were hooked primarily in the lips, whereas fish caught with leeches tended to be hooked more deeply in the throat and gut. Walleyes caught on leeches were smaller than those caught with artificial lures and were more likely to be males. Catch rates were similar for live ...

Effects of Vegetation Removal on Bluegill and Largemouth Bass in Two Minnesota Lakes

Abstract Abundance and growth of bluegill Lepomis macrochirus, diet and growth of largemouth bass Micropterus salmoides, and abundance of age-0 largemouth bass were evaluated in two treatment and three reference lakes in Minnesota to assess the effects of whole-lake herbicide treatments. Lakes were evaluated 1 year prior (1993), during (1994), and after (1995) treatment. In reference lakes, vegetation, fish growth, abundance, and diet remained relatively unchanged throughout the study. Herbicide applications in May 1994 decreased the percentage of sampling stations with vascular vegetation from 100% to 33% in Parkers Lake and 63% in Zumbra Lake between Aug 1993 and 1994. Vegetation returned to some areas of Parkers Lake in 1995 (77%) but continued to decline in Zumbra Lake (43%). Purse-seine catch per effort (CPE) of small bluegill (60–100 mm) decreased following treatment but returned to pretreatment levels the following year, whereas CPE of large bluegill (>100 mm) increased in 1994 in trap nets and rem...

Field Estimation of a Lethal Oxythermal Niche Boundary for Adult Ciscoes in Minnesota Lakes

Abstract Ciscoes Coregonus artedi are coldwater stenotherms that are sensitive indicators of ecological stressors, such as eutrophication and climate warming, that reduce coldwater habitat. Temperature and oxygen profile data were collected during cisco mortality events at 17 lakes during an unusually warm summer in Minnesota in 2006. Combinations of temperature and oxygen from the profiles were mapped onto a two-dimensional niche space to directly quantify an oxythermal lethal niche boundary for ciscoes. Quantile regression was used to estimate the niche boundary that described lethal combinations of oxygen and temperature for cisco. The fitted lethal oxythermal niche boundary exhibited a curvilinear interaction between lethal temperatures and lethal oxygen concentrations. The lethal temperature under normoxia (about 8 mg/L) was estimated to be 24°C. Lethal temperatures were progressively less at lower lethal oxygen concentrations (e.g., the lethal temperature was 23.0°C at 5.0 mg/L, 22.0°C at 3.0 mg/L, ...

Relationships Between Shoreline Development and Nest Site Selection by Black Crappie and Largemouth Bass

To evaluate potential effects of lakeshore development on nest site selection, we compared locations of black crappie Pomoxis nigromaculatus and largemouth bass Micropterus salmoides nests in three Minnesota lakes with available habitat in the littoral and riparian zones and the presence or absence of developed shoreline. We used binomial logistic regression to determine how the frequency of nest sites varied among lakes and with the presence or absence of five habitat variables. Black crappies in all three lakes were more likely to nest adjacent to undeveloped shoreline. Black crappies were also more likely to nest in stands of emergent vegetation, particularly hardstem bulrush Scirpus acutus. Largemouth bass were more likely to nest near undeveloped shoreline but were less dependent on hardstem bulrush. Shoreline development has the potential to alter nest site selection by largemouth bass and, particularly, by black crappies.

Timing of Walleye Spawning as an Indicator of Climate Change

Abstract We obtained Minnesota Department of Natural Resources historical records describing the egg-take from walleyes Sander vitreus at 12 spawning locations to determine whether the timing of walleye spawning runs could be used as an indicator of climate change. We used ice-out data instead of temperature for our analyses because walleyes often spawn soon after ice-out, and ice-out has been previously related to climate change. We used linear regressions to determine (1) the relationship between the start of spawning (based on first egg-take) or peak of the spawning run (greatest egg-take) and ice-out date and (2) whether long-term trends existed in ice-out and date of spawning over time. Linear regressions of the date of first walleye egg-take versus ice-out date showed that walleye spawning begins 0.5–1.0 d earlier for each 1.0-d decrease in ice-out date. All but two regressions had slopes less than 1.0. Similar results were found for peak of spawning runs. Regressions of egg-take and ice-out date ve...

Biological Performance Indicators for Evaluating Exploitation of Minnesota's Large-Lake Walleye Fisheries

Abstract We examined the potential for using biological performance indicators (BPIs) to detect the overexploitation of populations of walleye Sander vitreus (formerly Stizostedion vitreum) in Minnesotas large lakes. We developed equations to predict growth (i.e., the von Bertalanffy growth parameter and total length at age 3) and female age at 50% maturity from growing season length and female total length at 50% maturity from growth. Indices of spawning stock age diversity and the variation of population abundance were characterized by means of summary statistics. Thresholds for BPIs were determined by adding a measure of variability to the predicted and mean values. We evaluated the sensitivity of each BPI by comparing observed values with the thresholds for an overexploited population in Upper Red Lake. All six BPIs for Upper Red Lake exceeded the thresholds, demonstrating their potential use for monitoring walleye exploitation. However, the magnitude by which each threshold was exceeded differed by ...

Food resource effects on diel movements and body size of cisco in north‑temperate lakes

The movement patterns and body size of fishes are influenced by a host of physical and biological conditions, including temperature and oxygen, prey densities and foraging potential, growth optimization, and predation risk. Our objectives were to (1) investigate variability in vertical movement patterns of cisco (Coregonus artedi) in a variety of inland lakes using hydroacoustics, (2) explore the causal mechanisms influencing movements through the use of temperature/oxygen, foraging, growth, and predation risk models, and (3) examine factors that may contribute to variations in cisco body size by considering all available information. Our results show that cisco vertical movements vary substantially, with different populations performing normal diel vertical migrations (DVM), no DVM, and reverse DVM in lakes throughout Minnesota and northern Wisconsin, USA. Cisco populations with the smallest body size were found in lakes with lower zooplankton densities. These smaller fish showed movements to areas of highest foraging or growth potential during the day and night, despite moving out of preferred temperature and oxygen conditions and into areas of highest predation risk. In lakes with higher zooplankton densities, cisco grew larger and had movements more consistent with behavioral thermoregulation and predator avoidance, while remaining in areas with less than maximum foraging and growth potential. Furthermore, the composition of potential prey items present in each lake was also important. Cisco that performed reverse DVM consumed mostly copepods and cladocerans, while cisco that exhibited normal DVM or no migration consumed proportionally more macro-zooplankton species. Overall, our results show previously undocumented variation in migration patterns of a fish species, the mechanisms underlying those movements, and the potential impact on their growth potential.

Differing Catchability among Lakes: Influences of Lake Basin Morphology and other Factors on Gill-Net Catchability of Northern Pike

Abstract Understanding factors that affect catchability is important for interpreting fish catches from research index netting and comparing fish populations from different habitats. Population density estimates and gill-net catch rates were compared for age-2 and older northern pike Esox lucius in 16 north-central Minnesota lakes that varied in physical characteristics and northern pike populations. When northern pike density was calculated using total surface area of the lakes, numerous factors appeared to influence gill-net catchability. Those factors included several lake basin shape metrics, northern pike size structure, and northern pike density, with density dependence in catchability being especially problematic for interpreting gill-net catches. The critical finding in this study was that calculating density using littoral area rather than total surface area caused evidence of density-dependent catchability and all other relationships with catchability to completely disappear. Catchability became...