Production rates of walleye and their relationship to exploitation in Escanaba Lake, Wisconsin, 1965–2009

Understanding variability in fish production, biomass, production/biomass (P/B) ratios, and their relationship to exploitation is central to fisheries sustainability. At Escanaba Lake, Wisconsin, USA, data from a compulsory creel census (1965–2009) were combined with survey data on fish populations to test for empirical relationships between annual production and exploitation rates of walleye (Sander vitreus). Empirical estimates of walleye production were relatively high and temporally variable in Escanaba Lake. Annual production, biomass, and P/B ratios ranges were 2.4–11.3 kg·ha−1·year−1, 9.1–49.4 kg·ha−1, and 0.15–0.30 year−1, respectively. Walleye production rates were significantly and positively correlated with adult (i.e., age 3+) walleye density — the core metric used to manage walleye populations in the Ceded Territory of Wisconsin. However, adult walleye density correlated best with ages 4–6 production. Annual exploitation based on the percentage of individuals removed from the population was linearly related to annual exploitation based on the percentage of production removed. On average, 100% of annual production was harvested at ∼20% annual exploitation of individuals; thus, higher sustained exploitation rates would deplete walleye biomass in Escanaba Lake over time. A sustainable annual exploitation rate of 20% annually is lower than the 35% limit reference point currently used for walleye management in the Ceded Territory of Wisconsin. Nevertheless, our estimate is strongly concordant with two recent and independent modeling efforts addressing this same topic. We suggest empirical estimates of fish production are a vastly underutilized tool for better understanding sustainable exploitation rates in walleye populations and, likely, fisheries in general.

Comparative Recoveries of Planted Yearling and Fall-Fingerling Brook Trout (Salvelinus fontinalis) from Ontario Lakes

Yearling and fall-fingerling brook trout (Salvelinus fontinalis) were planted in two lakes with few or no resident fish species and in three lakes with resident populations. The comparative recoveries of the two size-groups of trout planted were assessed by creel census and/or intensive gillnetting. Recoveries of planted yearling brook trout were greater from lakes supporting few or no resident fish species (15.9–35.9%) and less in lakes supporting suckers, minnows, and sticklebacks (5.9–14.8%). Experience was similar with fall fingerlings planted in the same set of lakes though comparative recoveries were less. Lakes with few fish competitors yielded 3.5–4.8 kg of trout for each kilogram of fall fingerlings planted compared with 2.9–3.0 kg for each kilogram of yearlings planted. The returns of trout from lakes also supporting resident species were only 0.3–0.8 kg for each kilogram of yearlings or fall fingerlings planted. Key words: Salvelinus fontinalis, planting, survival, growth, yield

Creel census of amateur line fishermen in the Blackwood River estuary, Western Australia, during 1974-75

A creel census was carried out from May 1974 to April 1975 on the amateur line fishermen of Blackwood River estuary, from the Swan Lakes and Deadwater to Alexandra Bridge. The estimated total fishing pressure was 76 149 fisherman hours which was mainly concentrated in the summer and autumn months. The rate of success averaged 3.86 fish per fisherman per hour fishing. The estimated harvest of fish was 287 300. In the Hardy Inlet and Swan Lake region, western sand whiting (Sillago schomburgkii) was the main species caught for most of the year, except for the autumn months when Australian herring (Arripis georgianus) was the major species. In the Blackwood River, black bream (Mylio butcheri) dominated the catch throughout the year.