DIET OF SLIMY SCULPIN IN A TRIBUTARY TO SKANEATELES LAKE M. A. CHALUPNICKI and J. H. JOHNSON USGS Great Lakes Science Center Tunison Laboratory of Aquatic Science Cortland, NY INTRODUCTIONRESULTS METHODS The feeding ecology of benthic fish in cold water streams have typically been overlooked but play an important role in supporting larger fish communities. Slimy sculpin (Cottus cognatus, Figure 1) are a native benthic fish of the Great Lakes that often dominates the benthic ecosystem of cold water streams and are very important in predator/prey interactions. Prior to the invasion of round goby (Neogobius melanostomus) and zebra/quagga mussels (Dreissena polymorpha/ Dreissena bugensis) in the Finger Lakes, slimy sculpin were the major component of the bottom community supporting the larger fish community. Although they are known to be benthic insectivores, their widespread range of cold water stream and lake habitats enables them to be specific in their diet based on local benthic invertebrate community composition. As part of understanding the ecological food web position of coldwater streams in New York, we characterized the diets of slimy sculpin in Grout Brook, the major tributary to Skaneatelas Lake over a 24-h period. DISCUSSION ABSTRACT:In the fall, we examined the diel feeding ecology of slimy sculpin (Cottus Cognatus) from Grout Brook, a tributary to Skaneateles Lake. Of the six time periods examined, slimy sculpin consumed the least during the nighttime (2400-h and 0400-h). Chironomids were consumed the most during all time periods except for 2400-h where Ephemeropterans were consumed the most. There was a moderate preference by slimy sculpin for food from the benthos (0.59 ± 0.06) with Diptera (Chironomids), Ephemeroptera (Baetidae) and Trichoptera (Brachycentridae) the major taxon groups. Slimy sculpin do not appear to select specific prey but behave opportunistically to what is available in the brook. Computed daily ration and index of fullness ranged from 0.12 to 0.22 and 1.15% across the diel cycle, respectively. Estimates of daily consumption ranged from % to 4.0% of their body weight which is in the same range of estimates from other species in the literature. Skaneateles Lake (Figure 2) is one of smaller the Finger Lakes of central New York and one of the cleanest. Grout Brook is a north flowing tributary that is the major water source that enters into southern Skaneateles Lake. The brook is a small cold water tributary that is a major spawning stream for numerous migratory species, including rainbow trout (Oncorhynchus mykiss), brown trout (Salmo trutta), Atlantic salmon (Salmo salar) and white sucker (Catostomus commersoni). Slimy sculpin are abundant in the stream, and along with juvenile rainbow trout are the dominant fish species. We conducted a systematic diel diet evaluation of slimy sculpin in the lower reaches of Grout Brook using a backpack electroshocker to collect approximately 30 Slimy sculpin within a 300-m stretch of the brook every 4-h over a 24-h period. Fish collected were placed immediately in 10% buffered formalin until diet evaluation in the laboratory. We also collected available benthic prey concurrent with fish collections at specific intervals to quantify food sources within the brook using a Surber every eight hours and consisted of a 3 minute agitation of the stream bottom to quantify bottom prey. Contents of all three nets were pooled together and preserved in 90% ethanol until identification in the laboratory. Slimy sculpin stomachs were removed and weighed prior to contents being identified. Taxa found in the diet as well as collected for available prey were generally identified to family and enumerated. Diet composition and available prey composition were quantified based on the dry weight for each taxon (105 0 C for 24-h). 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. Feeding periodicity estimates were also used in estimating the 24-h diet of slimy sculpin (i.e., specific 4-h intervals where feeding was highest contributed more to the 24-h diet). Diet overlap among the six time periods was compared by calculating overlap coefficients (Cλ). Coefficient values range from 0, when there are no similarities, to 1, when samples are identical. Values ≥0.60 are considered biologically significant. Because the Shapiro-Wilks test showed that the data were not normally distributed, we used the nonparametric Kruskal-Wallis one-way analysis of variance test to examine differences in mean length (TL, mm ± SE), weight (W, g ± SE), and feeding intensity (g ± SE) among the six time periods Statistix 8.0 statistical software (Statistix 8.0, Tallahassee, Florida). A Linear Food Selection Index was used to quantify prey selection in the diet in relation to the benthos. In order to estimate the consumptive demand of slimy sculpin we derived a daily ration and an index of fullness using equations set by Mychek-Londer and Bunnell (2013). In order to facilitate comparison to other studies of other fish we estimated specific feeding rates (g g-1 d-1) by dividing daily ration dry weight by fish dry weight. Figure 2: Southern Skaneateles Lake Figure 1: Slimy Sculpin Figure 3: Diet of Slimy Sculpin at 4-h intervals over a 24-h period Figure 4: Benthic community composition every 8-h over a 24-h period Figure 5: Slimy sculpin diet periodicity as a function of percent body weight over a 24-h period Figure 7: Slimy sculpin daily ration as a function of fish body weight Figure 8: Slimy sculpin index of fullness as a function of fish body weight Figure 6: Slimy sculpin diet selectivity analysis of preferred prey We recovered 22 prey taxon from slimy sculpin examined with eight taxon contributing 94.7% of the diet. Baetids (33.1%) and chironomids (33.1%) were the dominate prey items in the 24-h diet (Figure 3). 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 heaviest in the early night and mid-day hours (0800-h, 1600-h, 2000-h) and also provided a substantial food source throughout the rest of the time periods as well. Brachiocentrid larvae were also present at similar levels of consumption as chironomid larvae with a peak at mid-afternoon (1600-h) but were more consistent in the diets throughout all time periods (14.9%-34.1%) except mid-morning (0800-h) where they were not present. Other dipteran, trichopteran and ephemeropteran prey were also fed upon throughout the day but at lower intensities. We recovered 23 prey taxon in the benthos with six taxon comprising 83.7% of the available prey (Figure 2). Trichopteran larvae were the most abundant available prey member (32.3%, Figure 4) and remained at high densities through all time intervals in the bottom community assemblages while baetid and plecopterian densities peaked during mid-morning and were reduced in abundance at night. Taxa from the diet and benthos that contributed less than 1% were combined into an “Other” category. Slimy sculpin diets contents had a high degree of similarity with the benthos community except during 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 (Figure 5). Slimy sculpin do not appear to select specific prey but were opportunistic, consuming the most readily available benthic prey (Figure 6). Computed daily ration and index of fullness equations were y=0.415e x and y=1.1265x (Figure 7 and 8). Mean daily ration (0.171 g dry wt.) across the seven time periods sampled ranged between 0.12 to 0.22 g dry wt. (Table 3). Mean index of fullness for slimy sculpin (1.15 %) across the seven time periods sampled ranged between % (Table 3). Computed daily consumption estimates was 0.78% over the 24-h period and ranged from 0.007% to 4.0% during the diel cycle. Table 1: Diet overlap values between fish diet and benthic community Fish Stom Fish Stom Table 2: Diet overlap values between fish diet through sampled time periods Table 3: Sample Counts, Mean Index of Fullness and Daily Ration The feeding activity of slimy sculpin was observed to shift from baetids during the day to dipteran larvae at night. This shift in activity is consistent with the literature where authors note the fullest gut contents during night hours. The primary food source of mayfly nymphs and chironomid larvae is also consistent with previous studies noting chironomids and mayfly nymphs comprising upwards of 90% of the diet. The results of this study also suggest that the high degree of similarity between slimy sculpin diet and the benthic community represents active consumption of prey peaking highest during the mid-morning when they are the most active. This is further confirmed by utilization of chironomid larvae which comprised a portion of the diet of sculpin and were abundant in the benthos. Very little information was available for daily ration comparison. In one other study where a ration value was computed for slimy sculpin, the authors reported a value that was 31% lower than our ration value, which can be related to different food web conditions between lake and stream populations. Other species such as Arctic Cod (Boreogadus saida), Bloater (Coregonus hoyi), and Arctic Charr (Salvelinus alpinus) have similar reported food consumption values ( %). However, these species are at colder temperatures in a lake environment than Grout Brook would reach. In one other study where specific feeding rates for slimy sculpin were determined our values were higher likely due to different bottom community assemblages and temperatures between lakes and streams. These data provide useful insights into the trophic ecology of slimy sculpin and allow a baseline comparison of food consumption with lake populations.