1 Harry and Laura Nohr Chapter of Trout Unlimited Scott Ladd Memorial Internship Report (2012-2013) Assessment of the Trout Diets in Southwest Wisconsin Steams Sarah Scott and Patrick Gellings (2012 Interns) Kris Wright (Faculty Advisor) Biology Department University of Wisconsin-Platteville
2 Introduction: The quality and quantity of prey items available to brown trout (Salmo trutta) can be important in the maintenance of their populations (Chapman 1966). Quantity and quality may be affected by allochthonous input and substrate size which in turn may affect brown trout life history Wisconsin (Young 1980, River Bilby & Bisson 1992). Juvenile brown trout tend to show a preference toward particular macroinvertebrate taxa, which differ from adult brown trout (Brynildson et al. 1973, Glova & Sagar 1991). Angling, anthropogenic, and environmental pressures may affect trout populations and therefore understanding what food items are available and consumed may provide insight into how different trout populations deal with these pressures ( Brafia et al. 1992, Marschall & Crowder 1996, Hari et al. 2005, Alexander & Hansen 2011). In Southwest Wisconsin many trout stream are located in agricultural settings, which can affect prey abundance and therefore trout populations. These changes may be brought about by excessive stream erosion from cattle traversing the stream and the lack of vegetation in the riparian zone. Increased erosion can lead to increased fine sediment load which can affect the type and number of macroinvertebrates and thus some of the food source for trout populations. Consequently, in Southwest Wisconsin what, when, and how much trout are feeding on may be different than in non-agricultural settings. The primary objectives of this study were to examine the diets of brown trout in Southwest Wisconsin and to examine factors that could influence the prey abundance. The primary hypothesis was that brown trout will prefer macroinvertebrates from the drift/surface area, which was congruent with other studies (Ringler 1979, Cada et al. 1987). The secondary hypothesis was that there will be shift in diet as adult brown trout become larger. Methods: In the summer of 2012, sampling was conducted on seven streams in Southwest Wisconsin: Harker-Lee Creek, Six-mile Creek, Blue River, Rountree Branch, Little Platte River, McPherson Branch, and Crow River (Figure 1, Table 1). All sites except Harker-Lee Creek and parts of the Rountree Branch were located near agricultural land.
3 Sampling occurred in early June through late August. At each site, 300 meters were sampled from downstream to upstream from the starting point that were then divided into twelve equal transects. Stream habitat, macro invertebrates, and fish were sampled. Habitat sampling used Wisconsin DNR standards. Habitat samples were collected at each Wisconsin of the twelve River transects along the site at four equally spaced points across the transect. Data collected consisted of river depth, embeddedness, width, substrate type present, overhead coverage, and macrophyte coverage. Substrate type was measured as a percentage present at each of the four points along the transect, and macrophyte and overhead cover were measured as percentages along the entire transect. Invertebrate sampling occurred at six random transects used during the habitat sampling. Invertebrate sampling consisted of using a 0.093 m 2 Surber sampler to collect invertebrates from the stream bed. Five of the six samples were sorted on-site for ten minutes, while the entire sixth sample was preserved in ethanol and processed in the lab within the month. Fish sampling included the use of backpack electro fisher consisting of one single pass covering the entire 300 meter site. Processing of the fish included measurements for body length (mm) and identification on site and then released back into the stream. There was a less than one percent mortality rate of fish. Fish diet sampling was done via gastric lavage with a filter basket, a filter, and a water bottle filled with the site s water. Water squirted into the mouth/stomach to flush out the stomach contents into the filter set-up. The fish was then measured, indentified, and then placed into a holding bucket for release. The stomach contents within the filter were then persevered in ethanol with an ID tag (fish species, date, stream, site, and length) to be processed at the lab within the month collected. A minimum of 15 fish per site were sampled, although this did not always happen due to low trout numbers in some sites. Data analysis included regressions and an electivity index. The regressions looked at possible influential factors includeing gravel/cobble, fines, and macrohpytes. Each of these were compared with the following 5 most abundant macroinvertebrate taxa: Diptera, Ephemeroptera, Trichoptera, Mollusca, and Arthropdoa. In addition, the total sum of
4 macroinvertebrates were compared against total sum of fish and then total sum of trout. An electivity index (E= (R-P)/(R+P) where E was electivity, R was the number of macroinvertebrates found in nature, and P was the number of prey items found in brown trout diets) was performed based on the macroinvertebrate samples and fish diets. The electivity index was done Wisconsin with the 5 River most abundant macroinvertebrate taxa. It looked at the utilization of macroinvertrate taxa in relation to their relative abundance in nature. Results: Habitat Data showed that there was a great deal of habitat variability among the sites. Depth ranged from 0.185 ± 0.147 meters at Rountree Branch Mound View site to 0.504 ± 0.129 meters at Sixmile Branch Downstream site, while embeddedness ranged from 0.212 ± 0.147 meters at Rountree Branch Mound View site to 0.824 ± 0.278 meters at Sixmile Branch Downstream site (Figure 2). River width ranged from 3.463 ± 0.971 meters at Sixmile Branch Downstream site to 7.958 ± 1.787 meters at Blue River Wolenec site (Figure 3). Substrate composition varied greatly site to site: Sixmile Branch at the Downstream site was mostly composed of sand, while others did not show this. Most of the sites were composed of a combination of fines, sand, gravel, and cobble (Figure 4). Overhead canopy coverage ranged from 0.83% ± 2.89% at McPherson Branch Downstream site to 55.00% ± 30.60% at Rountree Branch Mound View site (Figure 5). Macrophyte coverage ranged from 12.92% ± 7.22 at Rountree Branch Campus site to 76.25% ± 18.96% at Blue River Wolenec site (Figure 6). Macroinvertebrates Macroinvertebrate totals ranged from 79 at Blue River Winker site to 2088 at McPherson Branch Downstream site (Figure 7). There were five taxa that were most abundant, which were Diptera, Ephemeroptera, Arthropoda, Trichoptera, and Mollusca (Figure 8). A series of regressions were done to test for potential influential factors to macroinvertebrate abundance. The factors tested were fines, a combination of gravel and cobble, and macrophyte cover. These were tested against the five most common taxa: Diptera, Ephemeroptera, Arthropoda, Trichoptera, and Mollusca. Most showed no significance or relationship, with the
5 exception of Ephemeroptera vs. fines, which showed significance (p < 0.05 and an almost strong negative relationship). Potential factors that could influence macroinvertebrate abundance were examined. The top five most abundant taxa were picked: Ephemeroptera, Diptera, Mollusca, Trichoptera, and Arthropoda. The factors that were examined were percent of fines, a combination of gravel and cobble, macrophyte cover, total fish, and total trout. Ephemeroptera and fines showed a negative relationship (-0.53) that was significant (p < 0.05), but not strong. No other factors appeared to influence prey abundance. Fish Communities There were an overall 18 species of fish found over the 10 sites. Several of these species were not abundant (although they were included in any calculations). The total number of fish ranged from 35 at Rountree Branch Campus site to 1082 at Blue River Wolenec site. The Blue River s large abundance of fish was the result of large numbers of Mottled Sculpin (Figure 10). The total number of fish in some sites was brought down when trout species were excluded, although the Blue River maintained high numbers of fish (Figure 11). Also, when trout were excluded, the diversity of some sites diminished (Figure 12). For example, some sites only had two species of fish when trout were excluded. Trout numbers ranged from 14 at Rountree Branch Campus site to 275 at McPherson Branch Downstream site, which included young of year trout as well (Figure 13). Most sites were composed mostly of Brown Trout, with the exception of Harker-Lee Creek, which had a comparable number of Brook Trout (Figure 14). The length of Brown Trout ranged from 136.571 ± 76.985 millimeters (mm) at Blue River Wolenec site to 258.810 ± 43.815 mm at Harker-Lee Creek Downstream site (Figure 15). Fish Diets There were five main taxa that were consumed by Brown Trout: Arthopoda with 3.612 ± 4.590 items, Mollusca with 1.977 ± 2.780 items, Empheroptera with 0.993 ± 1.313 items, Trichoptera with 0.957 ± 1.127 items, and Diptera with 0.875 ± 0.812 items (Figure 16). Other
6 items that were investigated included Coleoptera,Odonata, Hemiptera, Archanida, Pupal forms of aquatic invertebrates, crayfish, invertebrates of terrestrial origins, and fish. Total density of prey items per Brown Trout at each site ranged from 16.667 prey items at McPherson Branch Downstream site to 2.13 prey items at Rountree Branch Campus site (Figure 17). Brown Trout diets Wisconsin were mostly River composed of five taxa: Diptera, Ephemeroptera, Arthropoda, Trichoptera, and Mollusca (Figure 18). A comparison was made between brown trout sized 150-240mm and 241-300+mm. There appears to be no visible shift in diet as adult brown trout become larger (Figure 19). The electivity for Diptera was -0.455 ± 0.355, Ephemeroptera was 0.010 ±.0593, Trichoptera was 0.095 ± 0.753, Mollusca was -0.145 ± 0.714, and Arthropoda was 0.058 ± 0.382 (Figure 20). Conclusion: Brown trout predominately consumed five taxa: Ephemeroptera, Diptera, Trichoptera, Mollusca, and Arthropoda. There appeared to be little influence from fines, gravel/cobble, machrophyte cover, total fish, or total trout on the prey population, with the exception of Ephmeroptera vs. fines. This exception was not unexpected because excessive fines have been found to negatively impact Ephemeroptera (Broekhuizen et al. 2001). It was hypothesized that brown trout would consume more drift/surface prey items such as terrestrials caught on the surface or macroinvertebrate taxa in those locations, which was what was found by other studies (Ringler 1979, Cada et al. 1987 ). Instead it was found that brown trout consumed what was most available as evidenced by the larger consumption of Arthropoda, a readily available food item in most streams studied. One study found a similar thing where brown trout ate prey relative to the number present in nature (Ball 2009). There was no shift in diets as adult brown trout became larger, which was not what was hypothesized. It appeared that there might have been a shift in how many Mollusca were consumed, but that was due to an anomaly. Two small brown trout were found to have consumed upwards of 50 Mollusca, which skewed our data. Therefore, there was no evident verification of a shift in diets.
7 The information provided by this study can be applied in similar locations. In agricultural settings, where streams have or have had higher sediment input, the brown trout appeared to not have their food preferences readily available, which would be surface and drift prey (Ringler 1979, Cada 1987). Instead, brown trout are resorting to items that are more available. Wisconsin In turn, River this may not allow adult brown trout to shift their diet preferences as they become larger, since all trout are competing for the same food items. This may affect trout populations, like in age structure dynamics, although that was not looked at in this study. Overall, brown trout appeared to be indiscriminate of what they consumed due to the lack of food preferences being available. What was near the bottom of the food chain appeared to affect these brown trout populations differently than in non-agricultural locations. Further investigation into brown trout diets and what is available to consume will be needed because there may be a link to the health of a stream if brown trout were becoming indiscriminate consumers.
8 Literature Cited Alexander, G.R. and Hansen E.A. 2011. Sand sediment in a Michigan trout stream, part II. Effects of reducing sand, bedload on a trout population. North American Journal of Fisheries Wisconsin Management River 3: 365-472. Ball, J.N. 2009. On the food of the brown trout of llyn tegid. Journal of Zoology 137:599-622. Bilby, R. E. and Bisson, P. A. 1992: Allochthonous versus autochthonous organic matter contributions to the trophic support of fish populations in clearcut and old-growth forested streams. Canadian journal of fisheries and aquatic sciences 49:540-551. Brafia, F., Nicieza, A.G., Toledo, M.M. 1992. Effects of angling on population structure of brown trout, Salmo trutta L., in mountain streams of Northern Spain. Hydrobiologia 237:61-66. Broekhuizen, N., Parkyn, S., Miller, D. 2001: Fine sediment effects on feeding and growth in the invertebrate grazers Potamopyrgus antipodarum (Gastropoda, Hydrobiidae) and Deleatidium sp. (Ephemeroptera, Leptophlebiidae). Hydrobiologia 457: 1-3. Brynildson, O.M., V.A. Hacker, and T.A. Klick. 1973. Brown Trout: Life History, Ecology, and Management. Wisconsin Department of Natural Resources, Publication 234. Cada, G.F., Loar J.M., Cox, D.K. 1987. Food and feeding preferences of rainbow trout and brown trout in southern Appalachian streams. American Midland Naturalist 117:374-385. Chapman, D. W. 1966. Food and space as regulators of salmonid populations in streams. Am. Nat., 100:345-357. Glova, G. J., and Sagar, P. M. 1991: Dietary and spatial overlap between stream populations of a native and two introduced fish species in New Zealand. Australian journal of marine and freshwater research 42:423-434. Hari, R.E., Livingstone, D.M., Siber, R., Burkhardt-Holm, P., Guttinger, H. 2005. Consequences of climatic change for water temperatures and brown trout populations in Apline rivers and streams. Global Change Biology 12: 10-26. Marschall, E.A. and Crowder, L.B. 1996: Assessing population responses to multiple anthropogenic effects: a case study with brook trout. Ecological Applications 6:152-167.
9 Ringler, N.H. 1979. Selective predation by drift-feeding brown trout (Salmo trutta). Jour. of the Fisheries Research Board of Canada 36:392-403. Young, K. 1980: Soil conservation protects the trout. Soil and water June: 7-8.
10 Muscoda N Dodgeville Mississippi River Platteville Site sampled Figure 1: Study area in Southwest Wisconsin showing each site sampled.
11 Table 1: Coordinates of the study sites. River Site Latitude Longitude Sixmile Branch Downstream 43 6'18.97"N 90 28'5.69"W Blue River Carpenter 43 0'23.51"N 90 26'24.99"W Blue River Wolenec 43 0'7.42"N 90 25'31.66"W Blue River Winker 43 1'10.34"N 90 27'20.26"W Little Platte River Arthur 42 50'30.45"N 90 26'50.94"W McPherson Branch Downstream 42 47'8.99"N 90 37'42.50"W Crow River Cty Rd D 42 45'47.33"N 90 30'7.04"W Rountree Branch Campus 43 43'40.15"N 90 29'42.81"W Rountree Branch Mound View Park 42 44'24.37"N 90 27'22.23"W Harker-Lee Creek Downstream 43 1'7.88"N 90 14'23.69"W
Meters 12 1.2 1 0.8 0.6 River Depth Embeddedness 0.4 0.2 0 Figure 2: Depth and embeddedness at each site.
Width (meters) 13 12 10 8 6 4 2 0 Figure 3: River width at each site.
14 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Bed Rock Boulder Large Rock Cobble Gravel Sand Fine Figure 4: Substrate composition at 10 sites collected the summer of 2012. Winker data was from 2011.
15 90.00% 80.00% 70.00% 60.00% 50.00% 40.00% 30.00% 20.00% 10.00% 0.00% Figure 5: Percent of canopy cover over sites.
16 100.00% 90.00% 80.00% 70.00% 60.00% 50.00% 40.00% 30.00% 20.00% 10.00% 0.00% Figure 6: Macrophyte coverage
17 2500 Planariidae Arachnida 2000 Nematoda Annelida 1500 Arthropoda Mullusca Hemiptera 1000 Odonata Coleoptera Trichoptera 500 0 Figure 7: Total macroinvertebrates at each site.
18 100% Planariidae 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Arachnida Nematoda Annelida Arthropoda Mullusca Hemiptera Odonata Coleoptera Trichoptera Ephemeroptera Diptera Figure 8: Relative abundance of macroinvertebrates at each site.
19 1400 1200 1000 800 600 400 200 YOY Brown Trout Brook Trout Brown Trout Brook Stickleback Johnny Darter Fantail Darter Creek Chub Northern Red Belly Dace Mottled Sculpin White Sucker 0 Figure 9: Fish totals at each site.
20 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% YOY Brown Trout Brook Trout Brown Trout Brook Stickleback Johnny Darter Fantail Darter Creek Chub Northern Red Belly Dace Mottled Sculpin White Sucker Figure 10: Relative abundance of fish at each site.
21 1000 900 800 700 600 500 400 300 200 Brook Stickleback Johnny Darter Fantail Darter Creek Chub Northern Red Belly Dace Mottled Sculpin White Sucker 100 0 Figure 11: Fish totals excluding trout numbers.
22 100% 90% 80% 70% 60% 50% 40% 30% 20% Brook Stickleback Johnny Darter Fantail Darter Creek Chub Northern Red Belly Dace Mottled Sculpin White Sucker 10% 0% Figure 12: Relative abundance of fish excluding trout numbers.
23 300 250 200 150 100 YOY Brown Trout Rainbow Trout Brook Trout Brown Trout 50 0 Figure 13: Total abundance of trout.
24 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% YOY Brown Trout Rainbow Trout Brook Trout Brown Trout 0% Figure 14: Relative abundance of trout.
Millimeters 25 350 300 250 200 150 100 50 0 Figure 15: Average size of adult brown trout at each site.
26 9 8 7 6 5 4 3 2 1 0 Figure 16: Average number of prey item per Brown Trout.
27 18 Fish 16 14 12 Terrestial Crayfish Pupae Arachnida 10 8 6 Annelida Arthropoda Mullusca Hemiptera 4 2 0 Odonata Coleoptera Trichoptera Ephemeroptera Diptera Figure 17: Brown Trout diet composition.
28 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Fish Terrestial Crayfish Pupae Arachnida Annelida Arthropoda Mullusca Hemiptera Odonata Coleoptera Trichoptera Ephemeroptera Diptera Figure 18: Relative abundance of brown trout diet prey items.
29 12 10 8 150-240 mm 241-300+ mm 6 4 2 0 Figure 19: Average number of prey item per brown trout.
30 1 0.8 0.6 0.4 0.2 0-0.2-0.4-0.6-0.8-1 Figure 20: Electivity index of Brown Trout diets.