Status of rainbow smelt (Osmerus mordax) in the Mohican Canyon Tributary, May 2014 Matthew J. Best 1 INTRODUCTION Rainbow smelt (Osmerus mordax) were thought to have been introduced into Otsego Lake in 1979, and by 1982 they were abundant (Sanford 1986). While this unauthorized introduction was illegal, it was believed to have provided a high quality forage base for cold water gamefish (Sanford 1986). To take advantage of their establishment, landlocked Atlantic salmon (Salmo salar) stocking commenced. In 1986, alewives (Alosa pseudoharengus) were first documented in Otsego Lake (Foster 1990). This visually oriented, efficient planktivore quickly became the dominant forage fish, reducing the abundance of others, including smelt (Harman et al. 1997). Alewife greatly reduced zooplankton size and abundance which lead to higher algal densities and lower deep water dissolved oxygen concentrations (Haresign and Warner 1998). Though smelt abundance was notably reduced, there were reports of their spawning in Leatherstocking Creek (Foster 2002) and Mohican Canyon (Breiten 2001) periodically. Smelt have also been observed in the creek at Six Mile Point and Shadow Brook (Harman 2002) and the creek at Three Mile Point (Cornwell 2005). In 1983, McWatters (1984) documented the size, weight, and age composition of 289 smelt collected from the tributary stream in Mohican Canyon (date not specified). Smelt abundance was considered high at that time and anglers congregated at streams where smelt were known to spawn, and collected them using a simple dip net (McWatters 1984). Approximately 10 groups of smelt totaling 50 individuals were observed in spawning behavior in 2001(Cornwell 2002). Groups of 3-5 smelt gathered in riffle sections of the tributary near shore. Smaller smelt, presumably males, were located slightly downstream of larger females. Smelt were sampled in Mohican Canyon again in 2004 to further document the smelt abundance (Cornwell 2005). Walleye (Sander vitreus) stocking began in 2000 and was intended to increase angling opportunities, while taking advantage of the forage offered by the invasive alewife, with the additional intention of reducing alewife abundance so that larger crustacean zooplankton could rebound (Cornwell 2001). By the early 2010s, that strategy was realized, with practically no alewife being collected with littoral trap nets (Best 2015), gill nets (Waterfield and Cornwell 2014), or evidence through hydroacoustic surveys (Waterfield and Cornwell 2014). Concurrently, large bodied Daphnia became increasingly dominant (Tanner and Albright 2014). With the absence of the dominant planktivore, the smelt in Otsego Lake potentially have an opportunity to rebound. 1 Robert C. MacWaters Internship in the Aquatic Sciences, summer 2014. Present affiliation: Department of Fisheries and Wildlife Technology, SUNY Agriculture and Technical College, Cobleskill, NY.
The goal of this sampling effort was to evaluate smelt spawning activity in the tributary stream in Mohican Canyon and to compare the fitness of spawning smelt to previous years. MATERIAL & METHODS Adult smelt were sampled in Mohican Canyon on 21 April 2014 between 8:30pm and 9:00pm with a Halltech backpack electrofisher. Headlamps remained turned off until electrofishing began to avoid deterring smelt from the sampling site. Electrofishing began at the mouth of the stream and continued upstream approximately 100 feet lasting for 329 seconds. Smelt were measured in total length (TL) to the nearest mm with a measuring board and promptly returned to the stream. After completion of sampling effort, more smelt were observed along the lake shore. Further efforts should sample the shoreline before entering the stream. Figure 1. Map of Otsego Lake displaying sampling location from all past efforts and most recent 2014 sampling effort.
RESULTS & DISCUSSION Thirteen smelt (mean length: 130.2mm, size range: 107-179mm) were captured in 2014. These numbers are very similar to the smelt sampled in 2004. In 2001, smelt were larger than those collected in 2004 (Cornwell 2005). Smelt in 1983 had a length and weight roughly in between the 2001 and 2004 smelt (mean length: 149.5mm, mean weight: 20.6g). Table 1 summarizes the numbers of smelt collected, their mean lengths and weights, size ranges, and method of collection in each sampling effort. Table 1. Characteristics of Spawning Rainbow Smelt in the Mohican Canyon tributary in 1983, 2001, 2004, and 2014. Date Number Collected Mean Length (mm) Mean Weight 9g) Size Range (mm) Capture Method 1983 289 149.5 20.6 101-210 Dip Net 4/22/2001 17 176.8 34.2 170-231 Seine 4/15/2004 33 125 9.9 96-196 Seine 4/21/2014 13 130.2-107-179 Electrofishing The length frequency chart from the 2004 smelt shows a high abundance of smelt between 100-130mm. There could have been two-three age classes of smelt based on where their lengths were distributed (Figure 2). In 2014, 110-130mm smelt were most abundant. There was likely only two age classes displayed in 2014 (Figure 3). Figure 2. Length frequency of spawning rainbow smelt in the Mohican Canyon tributary on 15 April 2004.
Figure 3. Length frequency of spawning rainbow smelt in the Mohican Canyon tributary on 21 April 2014. For comparison, 36 Smelt collected in Pepacton Reservoir (32miles South of Otsego Lake) by DEC during routine gillnetting in 1990-1997 had an average total length of 250mm with a size range from 125-255 (Lindhart 2002). Pepacton Reservoir adults are slightly larger than Otsego Lake s spawning population (Cornwell 2004). Since 2001, sampling was limited to one night which did not necessarily coincide with peak spawning, so these efforts cannot allow for comparisons of abundance. It is also worth noting that sampling has been done using different capture methods (Table 1). Despite the negative impact from the alewife in the past, smelt continue to spawn. Spawning smelt have been anecdotally observed in several Otsego Lake tributaries by Otsego Lake residents and documented by BFS and DEC staff (Foster 2002; Harman 1997; Harman 2002; Sanford 1986). Alewives are considered significant predators on ichthyoplankton and have contributed to the decline of several Great Lakes fisheries (Brandt et al. 1987; Crowder 1980; Wells 1977). During summer stratification alewife and rainbow smelt occupy similar habitats, though smelt tend to occupy cooler, deeper water (Simonin 2011). While alewives dominated Otsego Lake, the abundance of smelt was reduced. Alewives spawn in late spring/early summer, concurrent with larval smelt hatching and returning to the lake to start feeding. While the smelt s spawning efforts were likely successful in past years, the alewife likely limited their recruitment to adulthood. After the re-introduction of walleye to Otsego Lake, the alewife population was decimated. With nothing directly competing with the smelt s resources, the smelt have an opportunity to reoccupy the lake s forage base.
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