Characterization of spawning rainbow smelt (Osmerus mordax) in the Mohican Canyon Creek, Otsego Lake, NY

Matthew Best1and John R. Foster2

Abstract: Rainbow smelt (Osmerus mordax), a key component of the 1980’s cold-water fish fauna of Otsego Lake, was decimated in the 1990’s by the introduction of alewives (Alosa pseudoharengus). With the recent collapse of the alewife population, the rebound of the rainbow smelt population was expected. The goal of this study was to examine the population dynamics of spawning rainbow smelt in the Mohican Canyon Creek, for evidence of that rebound. Between 15-24 April 2015, (8:35pm and 11:05pm) 152 adult smelt were sampled using a Halltech backpack electrofisher. This study found that the spawning population, average size of spawners, spawning age and sex ratios had not returned to the pre-alewife levels (1983 & 1984) in 2015.

INTRODUCTION

Rainbow smelt (Osmerus mordax) were introduced into Otsego Lake in 1979 and used many of the lakes tributary streams for spawning (Leatherstocking Creek (Foster 2002, Cornwell 2001, Cornwell 2004, Best 2014), Mohican Canyon (Breitan 2001), 3-Mile Point Creek (Cornwell 2004), 6-Mile Point Stream and Shadow Brook (Harman 2002). Smelt abundance was high in the 1980’s and a dip net fishery developed in these tributary streams during the spawning runs (McWatters 1983). Population dynamics of rainbow smelt were studied in Mohican Canyon Creek by MacWatters (1984) and Cornwell (2004) and spawning behavior there was also documented (Cornwell 2001).

Rainbow smelt became a key component of the cold-water fish fauna of Otsego Lake soon after they were introduced. By 1982 smelt were abundant enough to provide a high quality forage base for mid-water, predatory, cold-water game fish, such as Atlantic salmon (Salmo salar; Sanford 1986). However, in 1986, alewife (Alosa pseudoharengus) were introduced into Otsego Lake (Foster 1990) and quickly became the dominant planktivore, reducing the abundance of many fish species, including rainbow smelt (Harman et al. 1997). With the recent collapse of the alewife population (Waterfield and Cornwell 2013, Best 2015), the population dynamics of rainbow smelt is expected to rebound to the pre-alewife levels documented by MacWatters (1984).

The goal of this study was to characterize the population dynamics of rainbow smelt spawning in Mohican Canyon Creek. In order to meet that goal, sex ratio, growth, age & length frequency distribution and catch per unit effort were determined. Data collected here, following the extirpation of alewives from Otsego Lake, will be compared to data collected by MacWatters (1984) before the introduction of alewives and Cornwell (2004) during high alewife abundance.

1 SUNY Oneonta Biol. Field Station Intern, Fisheries & Aquaculture Student, SUNY Cobleskill, Cobleskill, NY. 2 Professor & Chair, Fisheries, Wildlife & Environmental Science Department, SUNY Cobleskill, Cobleskill, NY.

MATERIAL & METHODS

This study was conducted at Mohican Canyon Creek (Latitude 42.764851, Longitude 74.899007; Figure 1) at its confluence with Otsego Lake at 5-Mile Point. This location followed previous studies (MacWatters 1984, Cornwell 2001 & 2004, Best 2015). Mohican Canyon Creek was initially studied by MacWatters due to its high density of spawning smelt and its protection from public access (MacWatters 1984).

This study was conducted 15-24 April 2015, between 8:35pm and 11:05pm (sunset occurred at 7:45 pm). A Halltech backpack electrofisher was used to capture spawning rainbow smelt on 20, 22 and 24 April. Several electrofishing runs were conducted on those dates, at approximately 45 minutes intervals. Each run had a shock time of 350-600 seconds. Electrofishing runs began at the mouth of the stream and continued upstream for approximately 40m. Headlamps remained off until electrofishing began to avoid deterring smelt from the sampling site. Captured smelt were measured (total length), sexed, and a few scales were removed from behind the pectoral fin. Smelt were held in totes until the evening sampling was completed. Then they were released at the upstream culvert 15m above the spawning site.

Figure 1. Study site at Mohican Canyon Creek at its Otsego Lake confluence at 5-Mile Point. While this study and that conducted by Best (2015) used electrofishers to capture smelt on their spawning run, MacWatters (1983 & 1984) used dip nets, and Cornwell (2001 & 2004) used seines.

RESULTS

Spawning Conditions

Spawning rainbow smelt were first detected in Mohican Canyon Creek on 20 April 2015. During the spawning run, water temperature ranged from 8.4°C to 3.7 °C; water turbidity was low except 14.5 NTU, which occurred after a storm; pH ranged between 8.3 and 8.5; and dissolved oxygen ranged from 9.7 to 11.0 mg/L (Table 1).

Table 1. Water parameters in Mohican Canyon Creek during April 2015 sampling.

Date Temp pH Turbidity Conductivity Dissolved O2 (°C) (NTU) (uS/cm) (mg/L) 4/15/15 9.2 8.6 4.6 201 10.8 4/17/15 8.9 8.4 8.1 208 11.0 4/20/15 8.4 8.3 4.9 231 9.7 4/22/15 6.2 8.5 14.5 214 9.9 4/24/15 3.7 8.4 2.5 204 11.0

Length Frequency Distribution

On average spawning males had a total length of 124 mm, and females had a length of 121mm (Figure 2). The size of spawning males and females did not differ in 2015 (T-test P >05).

When measurements of the 152 smelt captured in this study were combined with 13 smelt from Best’s (2015) 2014 study, the post-alewife mean length was 124 mm. The post-alewife smelt size (124mm) did not differ from the size of spawning smelt (125mm) during high alewife abundance (Cornwell 2004). However, smelt were considerably smaller than the average length (149 mm, N=1352) collected in the pre-alewives years of 1983 and 1984.

45

40 Male Female 35 30 25 20 15 10

Number of SpawningSmelt 5 0 100 105 110 115 120 125 130 135 140 145 150 155 160 165 170 175 180 185

Total Length (mm)

Figure 2. Length frequency distribution of spawning rainbow smelt captured in Mohican Canyon Creek in April 2015.

Sex Ratio

In Mohican Canyon Creek, female smelt were significantly less abundant than male smelt in 2015 and in 1983 (Chi square test, P < .001, Figure 3). In 2015, only 7% of the smelt captured were females, while in 1983 females made up 32% of the spawning population and in 1984, females were 47% of the spawning population (Chi square test, P < .001).

100 Male 90 Female 80 70 60 50 40 30 Per Cent Spawners 20 10 0 1983 1984 2015 Date

Figure 3. Per cent of males and females spawning in Mohican Canyon Creek in 1983, 1984 and 2015.

Age Frequency Distribution

The age-frequency distribution of rainbow smelt spawning in Mohican Canyon Creek was significantly different between all three years studied (Chi square test, P < .001). In 2015 smelt captured in Mohican Canyon Creek were dominated by one year olds, which made up 75% of the spawning population (Figure 4). However, in the pre-alewife years (1983-1984) 2 year old smelt dominated the spawning population (62% & 88%, respectively). The percentage of 3 year old smelt was small in all studies (6% in 1983; 0.3% in 1984; 5% in 2015). In fact there were no smelt sampled that were over 3+ years of age in 1983, 1984 and 2015.

100 1983 90 1984 80 2015 70

60 50

Per CentPer 40 30 20 10 0 1 Year Old 2 Year Old 3 Year Old Age of Spawning Population

Figure 4. The age-frequency distribution of rainbow smelt spawning in Mohican Canyon Creek in 1983, 1984 and 2015.

Growth

One year old smelt sampled in 2015 were 124mm, growing 12-14 mm larger than in 1984 and 1983, respectively (Figure 5). However, with an average size of 142mm, 2 year old smelt in 2015 were 10-13mm smaller than in 1983-1984. On average the size of three year old smelt was very similar between the 3 years, with only 6 mm difference between the three sample years.

200 180 160 140 1983 120 1984 100 2015 80

Total Length 60 40 20 0 Age-1 Age-2 Age-3 Age

Figure 5. Size at age for rainbow smelt spawning in Mohican Canyon Creek. Spawning Run Timing

Spawning rainbow smelt were not present in Mohican Canyon Creek on 15-17 April. They were first detected on 20 April 2015.

Numbers of males were present in the stream throughout the evening sampling period (8:35-11:05 pm; Table 2). Female smelt were consistently sampled in the stream between 9:40 and 11:05 pm, similar to MacWatters (1983) observation that the peak time for females to enter the stream was approximately 10:30 pm.

Table 2. The number of male and female rainbow smelt captured along a 40m spawning reach of Mohican Canyon Creek in 2015.

Date Time (PM) Run Males Females 1 9 8:35 4/20/2015 2 19 9:15 9:45 3 27 3 1 3 8:50 9:40 2 13 2 4/22/2015 10:20 3 15 1 11:05 4 8 1 9:40 1 35 2 4/24/2015 10:05 2 7 1 3 6 10:30

In 2015, several walleye and lake trout were observed around the mouth of the Mohican Canyon Creek during the smelt spawning run.

DISCUSSION

The population of rainbow smelt became large enough to support a smelt fishery, and to support the forage base for the introduction of a new mid-water game fish Atlantic salmon shortly after their introduction into Otsego Lake in 1979 (Sanford 1986). When the planktivorous alewife was introduced into Otsego Lake a significant decline in the smelt population occurred. Alewife have significant spatial and diet overlap with smelt, so smelt population dynamics could have been altered through competition and/or predation on their fry (Simonin et al. 2012). In Otsego Lake, alewives had a severe reduction on the size and abundance of large bodied zooplankton (Harman 1997, Warner 1997, Tanner and Albright 2014), which are a significant part of the diet of smelt (Johnson et al. 2004). Smelt population decline may have also been due to alewife predation on their fry (Brandt et al. 1987; Crowder 1980; Wells 1977). By 2011, the alewife population collapsed to zero (Waterfield & Cornwell 2014) and has not rebounded to date. Since the smelt forage base of large bodied zooplankton has rebounded (Tanner and Albright 2014) and alewife predation on larval smelt has been eliminated in recent years, population dynamics of smelt should be showing a rebound to the pre- alewife years.

Data collected in this study shows no evidence of a rebound in smelt population dynamics. The size of smelt sampled in 2015 were virtually the same, 124mm, as the smelt sampled when alewives were abundant, 125 mm (Cornwell 2004) and were considerably smaller that the 149mm observed in the pre-alewife samples (MacWatters 1984). Further, the spawning population was significantly younger in 2015 (age-1) compared to the pre-alewife samples dominated by 2 year olds (MacWatters 1984). Growth was initially better in 2015 to age-1, but growth to age-2 was slower than in the pre-alewife samples (MacWatters 1984). The smelt spawning population was overwhelmingly dominated by males in 2015, while there was a more even distribution between males and females to the pre-alewife samples (MacWatters 1984). Possibly more time is needed for the smelt population to adjust to the post-alewife ecology of Otsego Lake. Therefore, the spawning population of smelt should continue to be monitored at Mohican Canyon Creek to document changes in population dynamics.

It was clear in conducting this study that the abundance of rainbow smelt has not returned to the 1983-1984 pre-alewife levels. What is different about the ecology of Otsego Lake between pre-alewife and post-alewife years? The 2015 age frequency distribution (Figure 4) shows good survival of smelt between age-1 and age-2 in the pre-alewife years, but poor survival in post- alewife years. In the pre-alewife years, 1983-1984, there were no mid-water predators in Otsego Lake. In the post-alewife years (2015) there were populations of piscivorous walleye, Atlantic salmon and brown trout, feeding in the preferred smelt habitat around the thermocline. The presence of these mid-water predators may be preventing the rebound of rainbow smelt in Otsego Lake. Perhaps the reason we can’t catch smelt like we did in the good old days is because hungry populations of lake trout, walleye, Atlantic salmon and brown trout have caught them first!

ACKNOWLEDGEMENTS

SUNY Cobleskill’s Fisheries, Wildlife and Environmental Sciences Department provided equipment, volunteers, transportation and guidance in this research. Tom Breiten generously allowed us to use his property in Mohican Canyon Creek. Mark Cornwell, Brent Lehman and Ben German provided assistance in prepping gear and carrying out the field work.

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