Walleye (Sander vitreus) Stock Assessment (2006-2007) in the Buffalo River, NY, USA

Abstract

Wall eye stock assessment The presence of a naturally occurring spawning stock of walleye (Sander vitreus) in the Buffalo River has gone undetected. This study sought to determine the extent of use of the Buffalo River by adult and juvenile walleye in 2006 and 2007 in order to assess the New York Department of Environmental Conservation' s stocking efforts. Walleye were first stocked in 2004 and stocking continued in 2005 and 2006. A total of 29 walleye, mostly juveniles, were caught during the two year study period. None of the walleye were believed to be using the river to spawn. The source of these walleye is not known but genetic analysis is pending. The Buffalo River and tributaries have limited habitat potentially suitable to support walleye spawning. No physicochemical conditions were observed that would preclude some successful walleye spawning in the Buffalo River watershed, but habitat conditions are not suitable for larval survival during movements to Lake Erie. Mean zooplankton density during the walleye larval period ranged from 4 1 .0- 86.4 individuals/L in 2006 and 2007, with rotifers being the dominant taxon in both years: 78% and 86%. Mean density of zooplankton at the river confluence with Lake Erie ranged from 2 1 . 8-25 . 1 individuals/L in 2006 and 2007. Rotifers were the dominant taxon in 2007 (73%) and cyclopoid copepods ( 40%) and rotifers (25%) were the dominant taxa in 2006. While abundance of zooplankton was adequate for walleye fry feeding, the predominance of smallbodied zooplankton was suboptimal. No ichthoplankton, including larval walleye, were caught during the study period despite intensive sampling. Fish community comparison: 2006 vs. 1981-1982 The Buffalo River, once a large industrial port for the City of Buffalo, has gone through great environmental stresses over the years. Through the development of environmental regulations and decline of industry in the City of Buffalo, the condition of the river has improved. The objective of this aspect of my thesis was to replicate a survey conducted in 1 98 1 - 1 982 (Makarewicz et al. 1982), using electro-fishing and gill netting, to determint1 the extent of change in the fish community. The fish communities of the Buffalo River exhibited similarities and differences between the surveys. Simpson's diversity was high (0.89) in 1 98 1 - 1 982 and in 2006 (0.9 1 ) but community similarity was only 48.3%. In 2006, 5 1 species from 1 4 families were caught. In 1 98 1 , 3 2 species from 1 0 families were caught. Twenty three species of fish captured in 2006 were not captured in 1 98 1 - 1 982. Four species caught in 1 98 1 - 1 982 were not caught in 2006. Centrarchidae ( 4 1 .4% ), Cyprinidae (20.7%), and Clupeidae ( 1 5 . 5 %) were the most commonly captured families in 2006. Cyprinidae (36.8%), Catostomidae ( 1 8 . 0%), and Centrarchidae ( 1 7.4%) were the most prevalent fan1ilies in 1 98 1 . Changes in the relative abundance of maj or families and the addition of many new species both indicate a change from a moderately pollution-tolerant to a less pollution-tolerant fish community during the 25 years between studies.