Smallmouth Bass Population Dynamics in an Urban Iowa River

Smallmouth bass are an important sportfish in highly modified rivers and streams throughout Iowa.  Smallmouth bass were collected from the South Skunk River using barge electrofishing and angling and fish >150mm were tagged to better understand temporal variation in population dynamics.  Electrofishing catch rates were higher in 2013 (30 fish/hr) compared to 2014 and 2015 (8 fish/hr) when sampling was limited due to high flows.  Conversely, angling catch rates remained static (5 fish/hr) suggesting declines in electrofishing catch rates resulted from reduced sampling efficiency associated with higher flows rather than a decline in abundance.  Due to high water the past two years, angling captured more and larger fish compared to electrofishing.  The population displayed consistent recruitment (RCD = 0.97, RVI = 0.90), slow growth (K = 0.24, L_∞ = 438), but good condition (W_r = 80-100). Size structure was small in 2013 (PSD =15) but increased in 2014 (PSD=34) and 2015 (PSD=23). Eight fish (2% of individuals) have been reported by anglers and no harvest has been reported.  Annual survival was 38% and similar between years.  Sampling will continue in future years to assess effects of environmental conditions on population dynamics.