Smallmouth bass seasonal dynamics in northeastern South Dakota glacial lakes

Smallmouth bass Micropterus dolomieu are top predators and among the most popular sportfish in the United States. Smallmouth bass were introduced into many South Dakota lakes in the late 1980's and the introductions have resulted in many self-sustaining populations. As smallmouth bass become more popular in South Dakota there is a need to better manage these smallmouth bass populations. The objectives of this study were to (1) determine monthly sampling dynamics and size structure of smallmouth bass in four northeastern South Dakota glacial lakes, (2) determine the seasonal diets of smallmouth bass in four northeastern South Dakota glacial lakes, and (3) quantify and compare prey consumption among age-1, age-2, and age-3 smallmouth bass in Lake Oahe and Pickerel Lake, South Dakota.;For the first objective, smallmouth bass were collected monthly from May to September in Lakes Enemy Swim and Roy in 2007 and Lakes Clear and Pickerel in 2008. Smallmouth bass were collected using modified-fyke nets and night electrofishing in rocky habitats. Monthly mean catch per unit effort (CPUE) values of smallmouth bass collected with modified-fyke nets were variable, but generally low among months and lakes. Monthly mean CPUE values for smallmouth bass collected with night electrofishing were variable in all four lakes; however, CPUE of all bass collected was generally lowest in May and increased through September primarily due to the capture of age-0 bass becoming vulnerable to electrofishing. Monthly mean CPUE values of smallmouth bass longer than 180 mm were highest in May and June and then decreased in the following months. Similar to CPUE values for smallmouth bass longer than 180 mm, size structure was generally higher in May and June when compared to the other months. Smallmouth bass in all four lakes overall mean relative weight was greater than 80, but relative weight varied among lakes. Based on these results, I recommend that standardized spring (May to June) night electrofishing surveys should be conducted in northeastern South Dakota to monitor smallmouth bass population structure and dynamics.;For the second objective, smallmouth bass were collected monthly from May through September in Lakes Enemy Swim and Roy in 2007 and Lakes Clear and Pickerel in 2008 using night electrofishing. Gastric lavage was used to remove stomach contents in smallmouth bass longer than 180 mm, while bass shorter than 180 mm were sacrificed for stomach contents removal. In general, aquatic invertebrates were the dominant prey items both in percent composition by number and by weight for all smallmouth bass. For smallmouth bass shorter than 180 mm, diet composition was dominated by aquatic invertebrates in May and June then the bass switched to prey fishes through September. Consumed prey fishes were primarily yellow perch Perca flavescens and bluegills Lepomis macrochirus, although prey fish consumption varied by lake. Smallmouth bass longer than quality length (280 mm) primarily consumed decapods (crayfish) in all months and lakes. Food habits of smallmouth bass in this study were similar to other studies, but overall smallmouth bass were opportunistic predators and readily consumed available prey items.;For the final objective, bioenergetics simulations were conducted on data collected from May to October 1994 at Lake Oahe in two locations (Oahe Dam and Okobojo Bay) and from May to September 2008 in Pickerel Lake. Bioenergetics models were constructed for age-1 to -3 smallmouth bass from all locations. The energetic contribution for age-1 smallmouth bass was primarily from aquatic invertebrates in all locations. Age-2 smallmouth bass energetic contribution was diverse among different prey items at Oahe Dam, while prey fish were the dominant energy source at Okobojo Bay and Pickerel Lake. Pickerel Lake age-3 smallmouth bass diets were primarily aquatic invertebrates in May and changed to prey fishes into September, while the majority of the energy derived (57%) was from prey fishes. Growth trajectories of age-3 smallmouth bass among locations exhibited the same trend across months with a steady increase in weight. (Abstract shortened by UMI.)...