Density and habitat use by the round goby (Apollonia melanostoma) in the Bay of Quinte, Lake Ontario Ana Carolina Taraborelli a, 1 , Michael G. Fox b, ⁎, Ted Schaner c , Timothy B. Johnson d a Watershed Ecosystems Graduate Program, Trent University, Peterborough, Ontario, Canada K9J 7B8 b Environmental and Resource Studies Program and Department of Biology, Trent University, Peterborough, Ontario, Canada K9J 7B8 c Lake Ontario Management Unit, Ontario Ministry of Natural Resources, Glenora Fisheries Station, Picton, Ontario, Canada K0K 2T0 d Glenora Fisheries Station, Ontario Ministry of Natural Resources, Picton, Ontario, Canada K0K 2T0 abstract article info Article history: Received 28 July 2008 Accepted 31 December 2008 Communicated by John Janssen Index words: Habitat Invasive species Round goby We assessed round goby (Apollonia melanostoma) density and size structure in two sections of the Bay of Quinte (Lake Ontario) that had been invaded by this species two years apart. Round goby density was assessed with 50 m linear transects, recorded with an underwater video recording apparatus developed for this study that included a depth sounder for maintaining a fixed distance above the substrate. The highest mean round goby densities were observed in the shallowest depth zone (1.5–3 m) at both sites, but there were differences between the sites in the habitat types where the highest densities occurred and there were no significant density differences among habitat types at either site (rock with sparse vegetation, mud with sparse vegetation, sand/mud with moderate vegetation cover). In the upper bay, mean body length of round gobies declined with depth, whereas in the lower bay, mean round goby length was greatest in the deepest zone. Mean body length of round gobies did not differ significantly by habitat type in either section of the bay. © 2009 Elsevier Inc. All rights reserved. Introduction Since the first report of its presence in the Bay of Quinte, Lake Ontario in 1999, the round goby (Apollonia melanostoma) has been considered a numerically dominant component of the nearshore fish community (Hoyle and Schaner, 2002). Round gobies were regularly sampled in assessment trawls and gillnets beginning in 2002, and their contribution to the total catch was as high as 35% (gillnets) and 73% (bottom trawls) through 2007 (OMNR, 2008). Gillnetting and bottom trawling are two of the methods that have been used to estimate round goby density, but all of the methods tested are problematic when used to assess the density of this species in the range of habitats where it occurs (reviewed by Johnson et al., 2005). Passive gear (e.g., minnow and Windermere traps, tube samplers) tested on gobies under field and laboratory conditions showed low capture efficiencies and high escape rates. Electrofishing has a low capture efficiency because the round goby has no swim- bladder and it sinks when shocked. Shoreline seine netting can be effective in smooth bottom habitats, but is restricted to shallow areas, and does not provide good quantitative estimates when used in the range of habitats typically encountered in the littoral zone. Visual techniques (SCUBA, remote operated cameras) were considered by Johnson et al. (2005) to be the most effective methods for assessing round goby density; however SCUBA divers often attract round gobies and thus bias the density estimates. Remote operated vehicles (ROV) were suggested by Johnson et al. (2005) to be superior to SCUBA for round goby assessment because round gobies were attracted to divers but not to the camera. However, ROVs are costly to purchase, and their large size can scare away fish or cause them to hide (personal obser- vation, A.C. Taraborelli). Bottom trawling was considered a moderately efficient gear for estimating round goby density, but it is restricted to smooth substrates and is expensive to implement (Johnson et al., 2005). In bottom trawls, fish escapement occurs mainly under the footrope (Somerton et al., 1999) and contact varies with the nature of the substrate (rough or smooth, hard or soft), affecting trawl effi- ciency (Munro and Somerton, 2002). Changes in trawling speed can also affect footrope contact with the bottom, and thus influence density assessments of bottom dwelling fish (Weinberg, 2003). Previous studies had shown that the round goby has an affinity for several types of rocky substrates (e.g. gravel, riprap, cobble, reef) (Jude and DeBoe, 1996; Chotkowski and Marsden, 1999; Jude, 2001; Ray and Corkum, 2001; Phillips et al., 2003), but also it frequently occupies habitats with macrophytes (Jude and DeBoe, 1996; Jude, 2001) and is less common in mud substrates (Johnson et al., 2005). Round goby abundance has generally been found to be lower in soft substrates than in rocky substrates (Jude and DeBoe, 1996; Ray and Corkum, 2001; Johnson et al., 2005). While quantitative estimates of round Journal of Great Lakes Research 35 (2009) 266–271 ⁎ Corresponding author. E-mail address: mfox@trentu.ca (M.G. Fox). 1 Present address: Glenora Fisheries Station, Ontario Ministry of Natural Resources, Picton, Ontario, Canada K0K 2T0. 0380-1330/$ – see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.jglr.2008.12.004 Contents lists available at ScienceDirect Journal of Great Lakes Research journal homepage: www.elsevier.com/locate/jglr