Diet feeding ecology of Slimy Sculpin in a tributary to Skaneateles Lake, New York.
The feeding ecology of benthic fish in cold water streams have typically been overlooked but play an important role in fish community dynamics. Slimy Sculpin (Cottus cognatus) is a native benthic fish of the Laurentian Great Lakes that often numerically dominates the benthic ecosystem of coldwater streams and is very important in predator-prey interactions (Fratt et at, 1997; Madenjian et al., 1998; Scott and Crossman, 1998). Prior to the nonnative invasion of Dreissenid mussels and the Round Goby (Neogobius melanostomus), Slimy Sculpin comprised the majority of the benthic prey fish community in Lake Ontario (Walsh et al., 2008). After these invasions, abundances of Slimy Sculpin in the Lake Ontario food web have become severely depressed (Walsh et al., 2008). However, Slimy Sculpin are widely spread throughout the coldwater streams of New York and are one of three representatives of the Cottidae in the state (Craig and Wells, 1976; Smith, 1985). Slimy Sculpin generally have narrow home ranges and they are able to inhabit the headwaters of coldwater streams due to their preference for cold temperatures (Craig and Wells, 1976). They are considered obligate benthivores and feed primarily on benthic invertebrates (Brandt, 1986; Galloway et al., 2003; Petty and Grossman, 2007). Cuker et al. (1992) note the importance of Slimy Sculpin as a major benthic predator with the ability to control significantly chironomid densities in soft sediments.
To understand the food web role of Slimy Sculpin in New York coldwater streams, we characterized Slimy Sculpin diets in Grout Brook, a 3rd order tributary to Skaneatelas Lake. The objective of this study was to determine the feeding characteristics of Slimy Sculpin over a 24 h time period. Specifically, we sought to determine if the diet composition and food consumption of Slimy Sculpin varied over this time period and if sculpin selected specific prey from the benthos. We also wanted to determine daily ration and gut fullness estimates and see how they compare to other species.
METHODS AND MATERIALS
Skaneateles Lake (24.3 km long, 2.3 km at widest point, 84 m maximum depth) is one of the Finger Lakes of central New York. Grout Brook (42.72302[degrees]N, 76.25908[degrees]W) is a north flowing tributary (13.6 km long) that drains a relatively large watershed (24.6 [km.sup.2]) into southern Skaneateles Lake. The brook is a small (2.6 m at widest point), and shallow (2 m maximum depth) tributary that has an overall elevation change of 313 m from headwaters to the mouth. There is a manmade obstruction 4.7 km from the mouth which poses a barrier to upstream migration of non-salmonid fishes. Grout Brook is an important spawning stream for numerous migratory species, including Rainbow Trout (Oncorhynchus mykiss), Brown Trout (Salmo trutta), Atlantic Salmon (Salmo salar), and White Sucker (Catostomus commersoni) (Smith, 1985). Slimy Sculpin are abundant in the stream and along with juvenile Rainbow Trout are the dominant fish species (Smith, 1985).
We conducted a systematic diel diet evaluation of Slimy Sculpin in the lower reaches of Grout Brook. We used backpack electrofishing to collect approximately 30 Slimy Sculpin within a 300 m stretch of the brook every 4 h over a 24 h period in October. Slimy Sculpin collected were placed immediately in 10% buffered formalin until diet could be evaluated in the laboratory. We also sampled the benthic macroinvertebrate assemblage every 8 h concurrent with fish collections to quantify potential prey items in the brook using three Surber samplers (0.305 [m.sup.2] frame); sampling consisted of a 3 min agitation of the benthos. Contents of all three nets were pooled together and preserved in 90% ethanol until identification in the laboratory.
In the laboratory Slimy Sculpin were measured (total length, mm) and weighed (nearest 0.001 g). Whole stomachs were removed and weighed (nearest 0.001 g) prior to contents being identified. Taxa from diet and environmental samples were all identified to family and enumerated (Peckarsky et al., 1990; McCafferty, 1998; Merritt and Cummings, 2008). For estimating diet composition and available prey composition, prey were dried in a oven at 105 C for 24 h and quantified based on the dry weight for each taxon (Johnson et al., 2008). Diel feeding patterns during each 4 h period were evaluated by dividing the wet weight of the full stomach by the wet weight of the entire fish to provide an estimate of feeding periodicity according to Johnson et al. (2008). Feeding periodicity estimates were also used in estimating the 24 h diet of Slimy Sculpin (i.e., specific 4 h intervals when feeding was the greatest and contributed more to the 24 h diet).
Diet overlap among the six time periods was compared by calculating overlap coefficients (C[lambda]) using the equation of Morista (1959), later modified by Horn (1966). Co-efficient values range from 0, when there are no similarities, to +1, when samples are identical. Values [greater than or equal to] 0.60 are considered biologically important (Zaret and Rand, 1971). Because the Shapiro-Wilks test showed the data were not normally distributed, we used the nonparametric Kruskal-Wallis one-way analysis of variance to examine differences in feeding intensity (g, mean [+ or -] se) among the six time periods (Statistix 8.0 statistical software, Tallahassee, Florida). Strauss's (1979) Linear Food Selection Index was used to quantify prey selection in the diet relative to the benthos to estimate consumptive demand of Slimy Sculpin. Coefficient values range from -1, when there is an avoidance of the prey taxa, to +1, when prey taxa are preferred. We derived daily ration and index of fullness models using equations developed by Mychek-Londer and Bunnell (2013) in order to compare feeding rates and gut fullness between lake and stream populations. A slope constant (r) was set at 0.0115 to be used to derive daily ration according to Mychek-Londer and Bunnell (2013) gastric evacuation experiments. Fish dry weight was estimated as fish wet weight multiplied by 0.216 (D. B. Bunnell, pers. comm.). We then estimated specific feeding rates (g [g.sup.-1][d.sup.-1]) by dividing daily ration dry weight by fish dry weight. A linear regression was then applied to daily ration and index of fullness calculation to derive values.
We captured 27-30 Slimy Sculpin per time period (n = 205, length (mean [+ or -] SE) = 55.4 [+ or -] 0.7 mm, weight (mean [+ or -] SE) = 1.83 [+ or -] 0.08 g) to quantify the diel variation in the diet composition and food consumption intensity. We recovered 22 taxon from Slimy Sculpin examined with eight taxon contributing 94.7% of the diet (Fig. 1). Baetids (33.1%) and chironomids (33.1%) were the dominant prey items in the 24 h diet (Fig. 1). Peak consumption of baetids occurred at 2400 h and 0400-h and stayed a consistent food source throughout the rest of the time periods. Chironomid larvae were consumed the most in the early night (2000 h), early morning (0800 h) and midday hours (1600 h) and also provided a substantial food source throughout the rest of the time periods. Brachycentrid larvae were also consumed at similar levels of consumption as chironomid larvae with a peak at midafternoon (1600 h) but were more consistent in the diets throughout all time periods (14.9%-34.1%) except mid-morning (0800 h), where brachycentrid larvae were not present Slimy Sculpin preyed on other dipterans, trichopterans, and ephemeropterans throughout the day but at lower intensities. We identified 23 taxa from the benthic samples with six taxa comprising 83.7% of the macroinvertebrate assemblage (Fig. 2). Trichopteran larvae were the most abundant available prey item (32.3%). Trichopteran densities remained high through all time periods in the benthic community, while baetid and plecopteran densities peaked during mid-morning and were lower at night. Tipulid larvae were present in all benthic community samples at moderate levels (12.1%-16.3%) but did not contribute as much to the diet of Slimy Sculpin. Taxa from the diet and benthos that contributed less than 1% were combined into an "other" category. Slimy Sculpin diet contents were highly similar to the benthic community during all periods except mid-morning (0800 h) (Table 1). Diet composition was similar during all time periods (Table 2). Food consumption of Slimy Sculpin was highest during mid-morning and did not differ throughout the day and into the night until early morning (Fig. 3). Slimy Sculpin preferred 16 different taxa and avoided 17 taxa across the 24 h time period, acting opportunistically and consuming the most readily available benthic prey (Fig. 4). Daily ration for Slimy Sculpin was estimated to be y = 0.4247[e.sup.-0.606x], [r.sup.2] = 0.9188, where y is the calculated daily ration and x is the fish dry weight (g) (Fig. 5). Mean daily ration (0.172 g dry wt.) across the seven time periods sampled ranged between 0.12 to 0.22 g dry wt. for the 24 h period (Table 3). Slimy Sculpin fish consumption equation as an index of fullness was y = 1.1265[x.sup.-0.557], [r.sup.2] = 0.3703, where y is the calculated index of fullness and x is the fish dry weight (g) (Fig. 5). Mean index of fullness for Slimy Sculpin (1.15 %) across the seven time periods sampled ranged between 0.698-1.47% (Table 3). Mean specific feeding rate as a percentage of fish body weight across the 24 h time period was 0.78% and ranged 0.007-4.0%.
The feeding activity of Slimy Sculpin was observed to shift from chironimid larvae during the day to baetid larvae at night. The utilization of these taxa was consistent with previous work with positive selection demonstrated for both prey sources. Hondorp et al. (2011) noted the preference for certain prey, dipteran larvae and mayfly nymphs, may be a mechanism that controls Slimy Sculpin feeding activities. Ruetz et al. (2004) noted the selection of baetid nymphs as a food preference for Slimy Sculpin in a coldwater stream in Minnesota. Craig and Wells (1976) found three-quarters of the diet of Slimy Sculpin in Arctic streams were comprised of chironomid larvae while mayfly nymphs occurred infrequently. Walsh et al. (2008) and French et al. (2010) both noted chironomid larvae were the dominant prey item of Slimy Sculpin in lentic environments at depths less than 55 m. Following the introduction of dreissenid mussels into Lake Ontario, chironomid larvae declined substantially and are noted to be one of the causes of the Slimy Sculpin crash in the lake (Owens and Dittman, 2003). Conversely, Cuker et al. (1992) postulated that chironomid larvae would be a minimal food source for Slimy Sculpin due to their small size. However, they found chironomids to be a major food component for Slimy Sculpin and attributed this to their high density in the system.
There was a high degree of similarity between Slimy Sculpin diet and the composition of the benthic community with peak feeding occurring during the mid-morning. This is consistent with previous work where Slimy Sculpin were observed to be bottom dwelling feeders with peak feeding occurring during daylight hours as they are primarily visual feeders in both lake and stream environments (Van Vliet, 1964; Craig and Wells, 1975; Kohler and McPeek, 1989; Cuker el al., 1992; McDonald and Hershey, 1992; Owens and Dittman, 2003; French et al., 2010). Conversely, Brandt (1986) found peak feeding of Slimy Sculpin in Lake Ontario occurred at night and attributed this to a predator avoidance behavior. Newman and Waters (1984) also noted a nighttime feeding preference of Slimy Sulpin in streams where Gammarus was most prevalent at night and their primary food source. This is also supported by other authors noting sculpin use their lateral line to detect prey which would be more effective at night than visual recognition of prey (Hoekstra and Janssen, 1985). In Grout Brook juvenile Rainbow Trout, which descend to Skaneateles Lake by the time they reach approximately 120 mm, are likely a predation threat for small Slimy Sculpin (< 30 mm). Consequently, the lack of a predation threat for the size of Slimy Sculpins (> 50 mm) examined in Grout Brook may allow them to feed more intensively during the day.
Although there is information available on the diet and food selection of Slimy Sculpin, very little information exists on daily ration, index of fullness, and food consumption. Kraft and Kitchell (1986) and Mychek-Londer and Bunnell (2013) are the only authors to develop a feeding model for Slimy Sculpin. They stated daily ration and stomach fullness values of 0.2 to 0.8% and 1.93%, respectively, for Slimy Sculpins in Lake Michigan. Compared to Slimy Sculpin in Grout Brook, the Lake Michigan values are 31% lower for daily ration and slightly higher for stomach fullness. The computed food consumption rate is within the range reported for Slimy Sculpin in Grout Brook (0.2-0.8%). These differences in consumption rates may be related to food web conditions differences which Miyasaka et al. (2005) suggests are driven by different bottom water temperatures between lakes (4 C) and streams (Grout Brook = 10 C) because gastric evacuation rates accelerate with increased water temperatures resulting in higher food consumption. Adams and Schmetterling (2007) and Zimmerman and Krueger (2009) both note understanding ecosystem dynamics between lakes and streams is key to understanding how the niche of each species is sustained.
This study provides useful insights into the trophic ecology of Slimy Sculpin in a cold water stream ecosystem and allows a baseline comparison of food consumption with lentic populations of Slimy Sculpin. Moreover, these findings have application in gauging the relative niche that Slimy Sculpin often share in streams with highly valued salmonid species.
Acknowledgments.--We thank all technicians involved for their help in the field gathering samples and processing at the lab. This article is Contribution 1978 of the USGS Great Lakes Science Center. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
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Submitted 28 March 2014
Accepted 11 June 2015
MARC A. CHALUPNICKI (1) and JAMES H. JOHNSON (2)
Tunison Laboratory of Aquatic Science, USGS--Great Lakes Science Center, 3075 Grade Road, Cortland, New York
(1) Corresponding author: Phone: (607)-753-9391; Fax: (607)-753-0259; e-mail: firstname.lastname@example.org
(2) e-mail: email@example.com
TABLE 1.--Diet overlap coefficients comparing the invertebrate compositions in the fish stomachs and the benthos Benthos Time 1200 2000 2400 0400 -- -- 0.66 0800 -- -- 0.31 Fish 1200 0.61 -- -- Stomach 1600 0.64 -- -- 2000 -- 0.69 -- 2400 -- -- 0.69 TABLE 2.--Diet overlap coefficients between the six time periods Fish Stomach Time 800 1200 1600 2000 2400 400 0.74 0.94 0.69 0.93 0.98 800 -- 0.88 0.72 0.86 0.65 Fish 1200 -- -- 0.86 0.99 0.89 Stomach 1600 -- -- -- 0.85 0.69 2000 -- -- -- -- 0.89 TABLE 3.--Slimy Sculpin mean index of fullness (IF, %, mean [+ or -] SE) and daily ration (DR, g, mean [+ or -] SE) estimates at 4 h intervals during a 24 h using equations set by Mychek-Londer and Bunnell (2013) to estimate their consumptive demand Time Mean IF Mean DR 1200 1.26 0.17 1600 1.05 0.22 2000 1.16 0.18 2400 1.04 0.11 400 0.70 0.11 800 1.35 0.20 1200 1.47 0.18 FIG. 1.--Percent dry weight of prey items in the diet of Slimy Sculpin at 4 h intervals over a 24 h period from Grout Brook. Prey items are depicted in a clockwise order 0400 Chironomid 23.08 Baetidae 45.45 Brachycentridae 14.70 Chloroperlidae 4.43 Other 12.33 0800 Chironomid 41.1 Baetidae 21.3 Heptageniidae 14.3 Simulidae 8.6 Coleoptera 5.1 Other 9.6 1200 Chironomid 37.3 Baetidae 34.2 Brachycentridae 15.6 Simulidae 3.1 Other 9.9 1600 Chironomid 40.9 Baetidae 13.6 Brachycentridae 34.1 Limnephilidae 3.3 Annelidae 5.5 Other 2.6 2000 Chironomid 37.6 Baetidae 34.7 Brachycentridae 14.9 Ephemeroptera 5.6 Other 7.3 2400 Chironomid 18.6 Baetidae 49.2 Brachycentridae 21.5 Other 10.6 24 H Chironomid 33.1 Leuctridae 1.1 Baetidae 33.1 Brachycentridae 16.8 Heptageniidae 3.4 Chloroperlidae 1.6 Tipulidae 1.2 Ephemeroptera 1.1 Other 5.3 Note: Table made from pie chart. FIG. 2.--Percent dry weight composition of the benthic community sampled concurrently with Slimy Sculpin from Grout Brook at 8 h intervals over a 24 h period. Prey items are depicted in a clockwise order 1200 Chironomid 6.0 Tipulidae 10.2 Brachycentridae 31.6 Baetidae 19.2 Chloroperlidae 18.4 Other 14.6 2000 Tipulidae 6.9 Brachycentridae 30.1 Baetidae 36.9 Chloroperlidae 13.4 Other 12.1 2400 Chironomid 4.8 Tipulidae 4.9 Brachycentridae 32.3 Rhyacophilidae 3.9 Baetidae 18.9 Chloroperlidae 16.7 Other 16.3 Note: Table made from pie chart.
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|Author:||Chalupnicki, Marc A.; Johnson, James H.|
|Publication:||The American Midland Naturalist|
|Date:||Jan 1, 2016|
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