An Evaluation of Fish Assemblages of the Saw Mill River, New York: An Urban Stream

Abstract

Presence/absence data of 11 species of fish collected during 2008, 2009, and 2010 from five selected stations along the freshwater reach of the Saw Mill River, Westchester County, NY were examined using correspondence and parsimony analysis. The length of the river sampled extended from its northern source in Chappaqua (river km 36.9) south to Executive Boulevard (river km 6.4) in Yonkers, a distance of approximately 30.5 km. Correspondence analysis showed the distribution of stations in “species space” and indicated that two stations (Chappaqua and Hawthorne Cinema) aligned to the left of the origin of Axis #1 but in different quadrants, while the other three stations (Rumbrook, Lawrence Street, and Executive Boulevard) aligned to the right of the origin of Axis #1, with Rumbrook in a different quadrant than the Lawrence Street and Executive Boulevard stations. However, the analysis does not indicate specifically which fish assemblages are associated with each station. Parsimony analysis, which treats each collection site as if it were a “taxon” and the presence/absence of the fish as “character states” of those “taxa”, addressed this problem and aggregated the stations into two main groups, one containing two stations (Lawrence Street and Rumbrook) united by the presence of Rhinichthys cataractae (Longnose Dace) and the other consisting of three stations (Chappaqua, Hawthorne Cinema, and Executive Boulevard) united by the presence of Micropterus salmoides (Largemouth Bass). Within this larger group is a sub-group consisting of two stations (Chappaqua and Hawthorne Cinema) united by the presence of Lepomis gibbosus (Pumpkinseed). In addition, the analysis allows one to readily visualize aspects of the fish distributions along the length of the river. For example, Catostomus commersonii (White Sucker), Lepomis auritus (Redbreast Sunfish), and Rhinichthys atratulus (Blacknose Dace) were found at all sites, while Semotilus atromaculatus (Creek Chub) was found at both Chappaqua, the northernmost station, and also at Rumbrook, the approximate mid-point station of the section of the river sampled. The Longnose Dace was only found in the southern reaches of the river from Rumbrook south to Lawrence Street, and Etheostoma olmstedi (Tessellated Darter) was found at Executive Boulevard and Lawrence Street, our two southernmost stations. The analysis also readily identifies species that are endemic to a particular section of the river: Ambloplites rupestris (Rock Bass) at the Lawrence Street station, Salmo trutta (Brown Trout) at the Hawthorne Cinema site, and Pimephales promelas (Fathead Minnow) at Chappaqua.