Population Characteristics of Black Bullhead (Ameiurus melas) in Iowa Natural Lakes

ABSTRACT

Black bullhead (Ameiurus mefas) populations in three natural lakes in northwestern Iowa were sampled to describe abundance, size structure, condition, mortality, recruitment variability, and growth in relation to a range of physical and limnological conditions. Six-hundred-and-fifty-three black bullhead were sampled with modified fyke nets during summer 2008 from Silver Lake, Lake Minnewashta, and West Okoboji Lake. Catch-per-unit-effort of black bullhead in Silver Lake (21.9 fish per net-night; fish/NN) was significantly higher than in Lake Minnewashta (P<0.0l; 10.4 fish/NN) and West Okoboji Lake (P<0.01: 5.6 fish/NN). Proportional size distribution (PSD) was similar among populations, but PSD of preferred-length fish in Silver Lake was much greater than in the other lakes. Mean relative weights were generally high across all lakes (90–92) but were highest in Silver Lake. Total annual mortality was highest in Lake Minnewashta (79%) and lowest in Silver Lake (24%). Recruitment variability of black bullhead, measured with the recruitment variability index, was 0.69 in West Okoboji Lake, 0.62 in Lake Minnewashta, and 0.47 in Silver Lake. Black bullhead length at age 3 differed (P<0.01) among lakes and was highest in Silver Lake (274 mm) followed by Lake Minnewashta (247 mm) and West Okoboji Lake (228 mm). Silver Lake is considered to have the poorest water quality of the study lakes due to high nutrient concentrations and low water clarity. The influence of black bullhead on water quality conditions is unknown, but our results suggest that these conditions are ideal for black bullhead populations in Iowa lakes.