- Email: [email protected]
Association between the Catches of Round Gobies and Smallmouth Bass on the Upper Niagara River
J. Great Lakes Res. 32:672–679 Internat. Assoc. Great Lakes Res., 2006
Association between the Catches of Round Gobies and Smallmouth Bass on the Upper Niagara River Dennis J. Dunning1,*, Quentin E. Ross2, E. Terry Euston3, and Susan A. Haney3 1New
York Power Authority 123 Main Street White Plains, New York 10601 2348
County Highway 2 Mount Upton, New York 13809 3Normandeau
Associates, Inc. 1921 River Road P.O. Box 10 Drumore, Pennsylvania 17518 ABSTRACT. We wanted to confirm the presence of round gobies (Neogobius melanostomus) in the upper Niagara River and determine if there was a negative association between the catches of round gobies and smallmouth bass (Micropterus dolomieu). Our approach was to compare the catch rates of round gobies and smallmouth bass by anglers based on their method of fishing (from boat or from shore) and the fish they sought (anything or black bass). During 2003, both boat anglers and shore anglers caught round gobies in the upper Niagara River. The catch rates of round gobies and smallmouth bass for shore anglers who sought anything were positively and significantly correlated (r = 0 .081, P < 0.001). The catch rates of round gobies and smallmouth bass for shore anglers who sought black bass were negatively and significantly correlated (r = 0.141, P < 0.005). Correlations were not done using the catch rates of round gobies and smallmouth bass by boat anglers because they caught so few round gobies. Our results suggest that round gobies did not disrupt fishing for smallmouth bass on the upper Niagara River during 2003 if disruption is defined exclusively by the association between catch rates of smallmouth bass and round gobies. However, catching round gobies did lead to angler perceptions of poor fishing quality. INDEX WORDS:
Round gobies, smallmouth bass, sport fishing, catch rates, Niagara River.
INTRODUCTION The round goby (Neogobius melanostomus) is a prolific, invasive, and non-indigenous species of the Great Lakes with the potential to disrupt sport fishing because it competes aggressively with native species for bait and lures (Charlebois et al. 1997). Anglers fishing on waters of the Great Lakes near Detroit reported that, at times, they could catch only round gobies when fishing for walleye (Marsden and Jude 1995). The round goby also has the potential to disrupt sport fishing because it competes with native species that are important to sport fish (French and Jude 2001). For example, competition between round gobies and mottled sculpins (Cottus bairdi) *Corresponding
for food and spawning substrate is thought to have caused recruitment failure and local extinction of mottled sculpins in Lake Michigan (Janssen and Jude 2001). Although the potential for round gobies to disrupt sport fishing was recognized, there were no empirical data conclusively demonstrating a negative association between the catches of round gobies and sport fishes. As a result, determining the effect of round gobies on sport fishing was identified as a research priority during a roundtable discussion at the 1996 Round Goby Conference (Charlebois et al. 1997) and by attendees of the Second International Round Goby Conference (Charlebois et al. 2001). In Lake Erie, round gobies spread quickly after first being collected in the central basin during 1994
author. E-mail: [email protected]
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Catches of Round Gobies and Smallmouth Bass (LEFTG 2003). Within 2 years, the density of round gobies in the central basin increased by two orders of magnitude. They were found throughout the central and western basins and in the western part of the eastern basin by 1998 and throughout the eastern basin during 2000. During 2001, round gobies outnumbered all other fish caught in the eastern basin by trawling that was conducted to monitor the status and trends of forage fish. Although no trawling was done in the upper Niagara River, which is connected to the eastern end of Lake Erie, presumably round gobies were there after 1999. The upper Niagara River hosts important coldwater, coolwater, and warmwater sport fisheries (NYSDEC 1984). During 1996, an estimated 21,150 anglers spent 260,140 angler days and about $1.8 million fishing on the upper Niagara River (Connelly et al. 1997). Additionally, the upper Niagara River provides excellent sport fishing opportunities for nearly 0.5 million people living in the heavily urbanized area adjacent to it, including Buffalo, the second largest city in New York State (Einhouse et al. 2002). If round gobies were present in the upper Niagara River, they could disrupt important sport fisheries. Serendipitously, information about sport fisheries of the upper Niagara River was collected by angler surveys conducted during 1999 and 2003. Angler surveys have been used to monitor expansion of round goby populations in Lake Michigan because angling is a quick and efficient method for catching round gobies (Clapp et al. 2001). During 1999, no round gobies were caught in the upper Niagara River by anglers (Einhouse et al. 2002). If round gobies were caught in the upper Niagara River during 2003, their potential to disrupt sport fishing could be assessed by comparing the catch rates of sport fish during 1999 and 2003. However, a comparison between years could be confounded by changes in the abundance of sport fish unrelated to round gobies. The extent of the confounding would be impossible to assess unless estimates of sport fish abundance, independent of the angler surveys, were available. An alternative approach for assessing the potential of round gobies to disrupt sport fishing is to compare the catch rates of sport fish and round gobies by anglers during a year when round gobies were caught in the upper Niagara River. Our objectives were to confirm the presence of round gobies in the upper Niagara River during 2003 and to determine if there was a negative association between the catches of round gobies and smallmouth bass (Micropterus dolomieu). The smallmouth bass
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fishery on the upper Niagara River is large and active (Einhouse et al. 2002). Since monitoring is not done on the upper Niagara River to assess trends in the number of smallmouth bass, there are no estimates of abundance for smallmouth bass other than those from the angler surveys. Therefore, to determine if there was a negative association between the catches of round gobies and smallmouth bass on the upper Niagara River, we compared the catch rates by anglers from a survey designed to estimate catch and harvest monthly, seasonally, and annually. If there was a negative association between the catch rates of round gobies and smallmouth bass, it could be interpreted as either round gobies affecting smallmouth bass catch rates or vice versa. In the Great Lakes, the seasonal movements and preferred habitat of round gobies show some of the highest overlap with smallmouth bass, including times of the year when anglers fish for smallmouth bass. Round gobies move inshore during the spring, where they prefer cobble substrate to spawn on, remaining there until autumn, when they move offshore as water temperature declines (MacInnis and Corkum 2000a, MacInnis and Corkum 2000b, Ray and Corkum 2001, Janssen and Jude 2001). METHODS The upper Niagara River flows north from Lake Erie to Niagara Falls. It splits at the south end of Grand Island into the Chippewa and the Tonawanda channels and becomes a single channel again at the north end of Grand Island (Fig. 1). The border between Canada and the United States (U.S.) runs the length of the river. Where the river splits, the border runs near and along the east shore of the Chippewa Channel. The angler survey conducted during 2003 covered the upper Niagara River between the Peace Bridge, near Lake Erie, and an imaginary line that crosses the river 2.5 miles above Niagara Falls. The imaginary line is the start of a safety zone above Niagara Falls where boating is prohibited. The survey assessed fishing from boats and from shore between 5 April and 30 November. It was conducted on 3 weekdays per week and every weekend day and federal holiday in the U.S., with one exception. The Friday after Thanksgiving was substituted for the Thanksgiving Day holiday. Anglers who fished from shore (shore anglers) were interviewed at each of 17 public access sites in the U.S. while they were fishing or as they were leaving a site (Fig. 1). Anglers who fished from
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FIG. 1. Sites on the upper Niagara River where interviews were conducted with shore anglers (▲), boat anglers (●), and both shore and boat anglers (■) during 2003.
boats (boat anglers) were interviewed at eight public boat launch ramps in the U.S. when they returned from fishing. Each shore fishing site was sampled during every survey day, as were three randomly selected boat ramps. Shore anglers were asked what they were trying to catch, how many fish they caught, and the time they spent fishing. Boat anglers were asked the same questions as shore anglers and one additional question; where they fished. The question about where boat anglers fished was used to determine if anglers fished on the upper Niagara River, rather than on Lake Erie or a tributary of the Niagara River or Lake Erie. We only used responses from boat anglers about their fishing on the upper Niagara River. Catch rates for each angler, whether fishing alone or with a party of anglers, were calculated by dividing the number of round gobies and the
number of smallmouth bass caught by the numbers of hours spent fishing. Before comparing catch rates of smallmouth bass with those of round gobies, we had to decide if it was appropriate to partition anglers into groups based on whether they fished from a boat or from shore (fishing method) and the fish they were trying to catch (fish sought). It was important to consider fishing method because shore anglers may have fished regions of the upper Niagara River that differed in habitat, depth, and abundance of fish from regions fished by boat anglers. It was also important to consider fish sought because the baits or lures used may have differed depending upon the type of fish an angler was trying to catch. Therefore, both fishing method and fish sought had the potential to affect catch rates for round gobies and smallmouth bass. For fish sought, we considered two groups of anglers, those who said they sought anything and those who said they sought smallmouth bass, largemouth bass (Micropterus salmoides), or bass (which we collectively refer to as black bass). Anglers who sought bass meant smallmouth bass, largemouth bass, or both; but, not rock bass. Regardless of whether an angler sought smallmouth bass, largemouth bass, or bass, we only used that angler’s catch of smallmouth bass for analyses of catch rates. No anglers sought round gobies. We used angler success and catch rates to decide if it was appropriate to partition anglers into groups. Angler success was expressed as the numbers of anglers who caught round gobies and smallmouth bass and those who did not, regardless of whether the anglers sought black bass or anything. We analyzed angler success using the FREQ procedure of SAS which computes Cochran-Mantel-Haenszel and Breslow-Day statistics and relative risk estimates based on odds ratios (SAS Institute Inc. 1999). The Cochran-Mantel-Haenszel statistics were used to test for an association between fishing method and angler success after adjusting for fish sought. Breslow-Day statistics were used to test for homogeneity of the odds ratios based on fish sought. The odds ratio (OR) for a retrospective study like ours is calculated as: OR = n11 n22 / n12 n21
where n11 is the upper left cell of a 2 × 2 table with fishing method as rows and angler success as columns, n22 is the lower right cell, n12 is the lower left cell, and n21 is the upper right cell. If the odds ratios for anglers who sought anything and those
Catches of Round Gobies and Smallmouth Bass who sought black bass were not significantly different, then a common odds ratio could be used to summarize the association between angler success and fishing method. The FREQ procedure was selected to decide if it was appropriate to partition anglers into groups rather than parametric ANOVA on the catch rates because we assumed that the catch rates would not be normally distributed (Jones et al. 1995), an important assumption of parametric ANOVA. Before running the FREQ procedure, we examined the distribution of catch rates to confirm our assumption. Unfortunately, nonparametric ANOVA would only allow us to test for main effects, not interactions. However, after testing the success of anglers, we confirmed the results with paired tests of catch rates using nonparametric ANOVA, where appropriate. Finally, we tested for an association between the catch rates of round gobies and smallmouth bass within each homogenous group of anglers (where the range in catch rates was large enough that a comparison would likely produce meaningful results) using the Spearman rank correlation coefficient. This nonparametric test does not require that the catch rates for either round gobies or smallmouth bass be bivariate normally distributed, a requirement of parametric tests that our data were unlikely to meet. RESULTS Anglers caught both round gobies and smallmouth bass starting the week of 19 April. Round gobies were caught through the week of 22 November and smallmouth bass were caught through the week of 25 October. The number of anglers who caught round gobies and smallmouth bass varied seasonally and with similar temporal patterns; less than 5% of the anglers who caught either round gobies or smallmouth bass did so during the first 5 weeks and last 6 weeks of the survey. Catch rates ranged from 0.0 to 30.8 round gobies per hour and 0.0 to 24.7 smallmouth bass per hour. The seasonal pattern of catch rates of round gobies and smallmouth bass were also similar; catch rates were lower near the beginning and the end of the survey period. The shore anglers caught 14,007 fish, of which 23.4% were round gobies and 11.9% were smallmouth bass. The catch of round goby ranked second and the catch of smallmouth bass ranked fourth among all fish caught by the shore anglers. The boat anglers caught 3,347 fish, of which 1.5% were round gobies and 45.6% were smallmouth bass. The catch of round gobies ranked eighth and the catch of
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TABLE 1. Numbers of anglers on the upper Niagara River during 2003 who caught round gobies and did not catch round gobies based on method of fishing (from a boat or from shore) and for fish sought (anything or black bass).
Method Boat Shore
Numbers of anglers Anything Black bass Caught Not Caught Not 1 83 7 185 376 1,248 56 239
TABLE 2. Numbers of anglers on the upper Niagara River during 2003 who caught smallmouth bass and did not catch smallmouth bass based on method of fishing (from a boat or from shore) and for fish sought (anything or black bass).
Method Boat Shore
Numbers of anglers Anything Black bass Caught Not Caught Not 28 56 146 46 403 1,221 101 194
smallmouth bass ranked first among all fish caught by the boat anglers. There was a significant association between angler success in catching round gobies and method of fishing after controlling for fish sought (P < 0.001), i.e., boat anglers caught fewer round gobies than shore anglers (Table 1). There was no significant difference in the odds ratios of catching round gobies based on fish sought (P = 0.149). Shore anglers were about 10 times more likely to catch round gobies than boat anglers. There was a significant association between angler success for smallmouth bass and method of fishing after controlling for fish sought (P < 0.001) (Table 2). There was also a significant difference in the odds ratios of catching smallmouth bass based on fish sought (P < 0.001). The odds of catching smallmouth bass were significantly different for boat anglers who sought black bass (BAB) and shore anglers who sought black bass (SAB) (P < 0.001) but not for boat anglers who sought anything (BAA) and shore angler who sought anything (SAA) (P = 0.080). BAB were about six times more likely to catch smallmouth bass than SAB. The minimum catch rate of both round gobies and
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Dunning et al. TABLE 3. Average and maximum catch rates (number/hour) for round gobies and smallmouth bass on the upper Niagara River during 2003 by fishing method (from a boat or from shore) and fish sought (anything or black bass). Number/hour Fishing method Boat Boat Shore Shore
Fish sought Black bass Anything Black bass Anything
Smallmouth bass Average Maximum 0.8 11.1 0.3 4.0 0.4 6.4 0.3 24.7
smallmouth bass was 0.0 fish per hour regardless of fishing method and fish sought. However, average and maximum catch rates of round gobies and smallmouth bass varied by fishing method and fish sought (Table 3). BAB had a significantly lower average catch rate of round gobies than SAB (P < 0.001). BAA had a significantly lower average catch rate of round gobies than SAA (P = 0.021). BAB had a significantly higher average catch rate of smallmouth bass than SAB (P < 0.001). However, BAA did not have a significantly different average catch rate of smallmouth bass than SAA (P = 0.936). BAB and
Round gobies Average Maximum > 0.0 0.8 > 0.0 0.6 0.3 8.2 0.5 30.8
BAA had very low maximum catch rates of round gobies while SAA had the highest maximum catch rate of round gobies. SAA had the highest maximum catch rate of smallmouth bass. The catch rates of round gobies and smallmouth bass for boat anglers were not compared statistically because boat anglers had very low maximum and average catch rates of round gobies (Table 3). The catch rates of round gobies and smallmouth bass for SAA were compared separately from SAB primarily because of the large difference in the maximum catch rate of both round gobies and smallmouth bass.
FIG. 2. Comparison of catch rates, expressed as fish/hour, for smallmouth bass and round gobies by 1,624 shore anglers who sought anything on the upper Niagara River.
Catches of Round Gobies and Smallmouth Bass
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FIG. 3. Comparison of catch rates, expressed as fish/hour, for smallmouth bass and round gobies by 295 shore anglers who sought black bass on the upper Niagara River.
The distribution of catch rates for both smallmouth bass and round gobies was noticeably skewed (Figs. 2 and 3). Among SAA, 76.8% caught no round gobies and 75.1% caught no smallmouth bass. Among SAB, 81.0% caught no round gobies and 65.8% caught no smallmouth bass. The widest range in catch rates of smallmouth bass occurred when no round gobies were caught by SAA (0–24.7 per hour) or bass (0–6.4 per hour). In comparison, the range in catch rates of smallmouth bass when round gobies were caught by SAA was 0–5.1 per hour and 0–1.9 per hour for SAB. The catch rates of round gobies and smallmouth bass for SAA were positively and significantly correlated (r = 0.081, P < 0.001, df = 1,622). The catch rates of round gobies and smallmouth bass for SAB bass were negatively and significantly correlated (r = –0.141, P < 0.005, df = 293). DISCUSSION The data from our study not only confirm that round gobies were present in the upper Niagara River during 2003; they also appear to indicate that round gobies were well established. Clapp et al.
(2001) considered catch rates of 1–10 round gobies/hour to be high and an indication that round gobies had become well established based on angler catch rates for ports in Lake Michigan where anglers reported the presence of round gobies. In our study, about 44% of the SAA who caught round gobies on the upper Niagara River had a catch rate greater than or equal to 1 round goby per hour, including one angler who had a catch rate of 30.8 round gobies per hour. There was no evidence of a negative association between the catch rates of round gobies and smallmouth bass in the upper Niagara River based on SAA. SAA should have provided the best measure of an association because this group included: 1) 5.5 times more anglers than the next largest group, 2) anglers with catch rates of both round gobies and smallmouth bass whose range was more than three times greater than any other group, and 3) anglers less likely to use baits and lures that would preclude catching smaller fish—like round gobies, than anglers fishing for black bass. Although the correlation between the catch rates of round gobies and smallmouth bass SAB was statistically significant
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and negative, it was small and probably of little or no biological significance. The statistical significance appears to be due to a combination of sample size and the relatively large proportion of anglers who caught no round gobies (81.0%), an artifact of using survey data. This became clear when we correlated the catch rates of round gobies and smallmouth bass based only on SAB who caught round gobies. The resulting correlation (r = –0.102, df = 54) was similar in magnitude to that based on all SAB (r = 0.141, df = 293), but not statistically significant (P > 0.05). A comparable result occurred when we correlated the catch rates of round gobies and smallmouth bass based only on SAA who caught round gobies. The resulting correlation (r = 0.022, df = 374) was similar to that based on all SAA (r = 0.081, df = 1,622), but not statistically significant (P > 0.05). The proportion of SAA who caught no round gobies, like that for SAB, was also relatively large (76.8%). The higher average catch rate of smallmouth bass by BAB compared with SAB and the lower average catch rate of round gobies by boat anglers compared with shore anglers could have been due to differences in mobility, access to habitats, or fishing techniques. If the distribution of round gobies within the upper Niagara River was patchy, changed with time, differed by depth, or a combination of these, more mobile anglers should have had an advantage in avoiding round gobies. It is reasonable to believe that the boat anglers were more mobile, i.e., they could change their location more quickly and easily than the shore anglers. However, this explanation for the difference in catch rates is based on an assumption that the boat anglers caught round gobies and then decided to move. If that happened, the probability of a boat angler catching at least one round goby during a fishing trip should not have been significantly different from that of a shore angler. The fact that boat anglers had a significantly lower probability of catching round gobies than shore anglers suggests that mobility was not the most likely reason that boat anglers had a lower average catch rate of round goby than shore anglers. An alternative explanation for: 1) the higher average catch rate of smallmouth bass by BAB compared with SAB and 2) the lower average catch rate of round gobies by boat anglers compared with shore anglers is a difference in accessible habitats. This alternative is plausible if the distribution of round gobies and smallmouth bass did not completely overlap because of differences in habitat selection and boat anglers were able to fish in areas other than where the overlap occurred but shore anglers could not, e.g., deeper water. If so,
boat anglers may have developed different fishing techniques and used them in areas where the distribution of round gobies and smallmouth bass overlapped as well as in areas where the distributions did not overlap. Unfortunately, data collected during the 2003 angler survey on the upper Niagara River did not allow us to check either explanation. Our results suggest that round gobies did not disrupt fishing for smallmouth bass on the upper Niagara River during 2003 if disruption is defined exclusively by the association between catch rates of smallmouth bass and round gobies. However, catching round gobies did lead to angler perceptions of poor fishing quality. Unsolicited comments offered by shore anglers during the 2003 angler survey on the upper Niagara River indicate that some anglers were frustrated and upset if they caught round gobies when they were trying to catch black bass. Their complaints included losing bait to round gobies and the perception that catching round gobies reduced the likelihood of catching smallmouth bass because baited hooks and lures were not in the water when round gobies were handled. Therefore, managers of sport fisheries where round gobies are incidentally caught may have to deal with angler perceptions about reduced catch rates for sport fish due to round gobies that differ from reality. ACKNOWLEDGMENTS We thank John Magee for managing the 2003 angler survey until he took a position with the New Hampshire Fish and Game Department, Alex Levy of Gomez and Sullivan for managing the 2003 angler survey after John Magee, Scott Schanke of Normandeau Associates for supervising the collection of data and noting complaints from shore anglers about catching round gobies, and Donald Einhouse and Michael Wilkinson of the New York State Department of Environmental Conservation for providing information that was important in planning the 2003 angler survey. The 2003 angler survey was funded by the New York Power Authority. REFERENCES Charlebois, P.M., Marsden, J.E., Goettel, R.G., Wolfe, R.K., Jude, D.J., and Rudnika, S. 1997. The round goby Neogobius melanostomus (Pallas), a review of European and North American literature. IllinoisIndiana Sea Grant Program and Illinois Natural History Survey. INHS Special Publication No. 20. ———, Corkum, L.D., Jude, D.J., and Knight, C. 2001. The round goby (Neogobius melanostomus) invasion:
Catches of Round Gobies and Smallmouth Bass current research and future needs. J. Great Lakes Res. 27:263–266. Clapp, D.F., Scheeberger, P.J., Jude, D.J., Madison, G., and Pistis, C. 2001. Monitoring round goby (Neogobius melanostomus) population expansion in eastern and northern Lake Michigan. J. Great Lakes Res. 27:335–341. Connelly, N.A., Brown, T.L., and Knuth, B.A. 1997. New York Statewide Angler Survey 1996, Report 1: Angler Effort and Expenditures. New York State Department of Environmental Conservation, Albany, New York. Einhouse, D.W., Haws, J., Knight, J., Sztramko, L., and Wilkinson, M.W. 2002. 1999 Angler Survey of the Upper Niagara River. New York State Department of Environmental Conservation, Albany, New York. French, J.R.P., and Jude, D.J. 2001. Diets and diet overlap of nonindiginenous gobies and small benthic native fishes co-inhabiting the St. Clair River, Michigan. J. Great Lakes Res. 27:300–311. Janssen, J. and Jude, D.J. 2001. Recruitment failure of mottled, sculpin Cottus bairdi in Calumet Harbor, southern Lake Michigan, induced by the newly introduced round goby Neogobius melanostomus. J. Great Lakes Res. 27:319–328. Jones, C.M., Robson, D.S., Lakkis, H.D., and Kressel, J. 1995. Properties of catch rates used in analysis of angler surveys. Trans. Am. Fish. Soc. 124:911–928.
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Lake Erie Forage Task Group (LEFTG). 2003. Report of the Lake Erie Forage Task Group March 2003. New York State Department of Environmental Conservation, Albany, New York. MacInnis, A.J., and Corkum, L.D. 2000a. Age and growth of round goby Neogobius melanostomus in the upper Detroit River. Trans. Am. Fish. Soc. 129: 852–858. ———, and Corkum, L.D. 2000b. Fecundity and reproductive season of the round goby Neogobius melanostomus in the upper Detroit River. Trans. Am. Fish. Soc. 129:852–858. Marsden, J.E., and Jude, D.J. 1995. Round gobies invade North America. Illinois-Indiana Sea Grant Program. IL-IN-SG-96-10. New York State Department of Environmental Conservation (NYSDEC). 1984. 1984 New York State Great Lakes Angler Survey. NYSDEC, Albany, New York. Ray, W.J., and Corkum, L.D. 2001. Habitat and site affinity of the round goby. J. Great Lakes Res. 27:329–334. SAS Institue Inc. 1999. SAS/STAT User’s Guide, Version 8. SAS Institute Inc, Cary, North Carolina. Submitted: 3 October 2005 Accepted: 17 July 2006 Editorial handling: Marten A. Koops
Association between the Catches of Round Gobies and Smallmouth Bass on the Upper Niagara River Dennis J. Dunning1,*, Quentin E. Ross2, E. Terry Euston3, and Susan A. Haney3 1New
York Power Authority 123 Main Street White Plains, New York 10601 2348
County Highway 2 Mount Upton, New York 13809 3Normandeau
Associates, Inc. 1921 River Road P.O. Box 10 Drumore, Pennsylvania 17518 ABSTRACT. We wanted to confirm the presence of round gobies (Neogobius melanostomus) in the upper Niagara River and determine if there was a negative association between the catches of round gobies and smallmouth bass (Micropterus dolomieu). Our approach was to compare the catch rates of round gobies and smallmouth bass by anglers based on their method of fishing (from boat or from shore) and the fish they sought (anything or black bass). During 2003, both boat anglers and shore anglers caught round gobies in the upper Niagara River. The catch rates of round gobies and smallmouth bass for shore anglers who sought anything were positively and significantly correlated (r = 0 .081, P < 0.001). The catch rates of round gobies and smallmouth bass for shore anglers who sought black bass were negatively and significantly correlated (r = 0.141, P < 0.005). Correlations were not done using the catch rates of round gobies and smallmouth bass by boat anglers because they caught so few round gobies. Our results suggest that round gobies did not disrupt fishing for smallmouth bass on the upper Niagara River during 2003 if disruption is defined exclusively by the association between catch rates of smallmouth bass and round gobies. However, catching round gobies did lead to angler perceptions of poor fishing quality. INDEX WORDS:
Round gobies, smallmouth bass, sport fishing, catch rates, Niagara River.
INTRODUCTION The round goby (Neogobius melanostomus) is a prolific, invasive, and non-indigenous species of the Great Lakes with the potential to disrupt sport fishing because it competes aggressively with native species for bait and lures (Charlebois et al. 1997). Anglers fishing on waters of the Great Lakes near Detroit reported that, at times, they could catch only round gobies when fishing for walleye (Marsden and Jude 1995). The round goby also has the potential to disrupt sport fishing because it competes with native species that are important to sport fish (French and Jude 2001). For example, competition between round gobies and mottled sculpins (Cottus bairdi) *Corresponding
for food and spawning substrate is thought to have caused recruitment failure and local extinction of mottled sculpins in Lake Michigan (Janssen and Jude 2001). Although the potential for round gobies to disrupt sport fishing was recognized, there were no empirical data conclusively demonstrating a negative association between the catches of round gobies and sport fishes. As a result, determining the effect of round gobies on sport fishing was identified as a research priority during a roundtable discussion at the 1996 Round Goby Conference (Charlebois et al. 1997) and by attendees of the Second International Round Goby Conference (Charlebois et al. 2001). In Lake Erie, round gobies spread quickly after first being collected in the central basin during 1994
author. E-mail: [email protected]
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Catches of Round Gobies and Smallmouth Bass (LEFTG 2003). Within 2 years, the density of round gobies in the central basin increased by two orders of magnitude. They were found throughout the central and western basins and in the western part of the eastern basin by 1998 and throughout the eastern basin during 2000. During 2001, round gobies outnumbered all other fish caught in the eastern basin by trawling that was conducted to monitor the status and trends of forage fish. Although no trawling was done in the upper Niagara River, which is connected to the eastern end of Lake Erie, presumably round gobies were there after 1999. The upper Niagara River hosts important coldwater, coolwater, and warmwater sport fisheries (NYSDEC 1984). During 1996, an estimated 21,150 anglers spent 260,140 angler days and about $1.8 million fishing on the upper Niagara River (Connelly et al. 1997). Additionally, the upper Niagara River provides excellent sport fishing opportunities for nearly 0.5 million people living in the heavily urbanized area adjacent to it, including Buffalo, the second largest city in New York State (Einhouse et al. 2002). If round gobies were present in the upper Niagara River, they could disrupt important sport fisheries. Serendipitously, information about sport fisheries of the upper Niagara River was collected by angler surveys conducted during 1999 and 2003. Angler surveys have been used to monitor expansion of round goby populations in Lake Michigan because angling is a quick and efficient method for catching round gobies (Clapp et al. 2001). During 1999, no round gobies were caught in the upper Niagara River by anglers (Einhouse et al. 2002). If round gobies were caught in the upper Niagara River during 2003, their potential to disrupt sport fishing could be assessed by comparing the catch rates of sport fish during 1999 and 2003. However, a comparison between years could be confounded by changes in the abundance of sport fish unrelated to round gobies. The extent of the confounding would be impossible to assess unless estimates of sport fish abundance, independent of the angler surveys, were available. An alternative approach for assessing the potential of round gobies to disrupt sport fishing is to compare the catch rates of sport fish and round gobies by anglers during a year when round gobies were caught in the upper Niagara River. Our objectives were to confirm the presence of round gobies in the upper Niagara River during 2003 and to determine if there was a negative association between the catches of round gobies and smallmouth bass (Micropterus dolomieu). The smallmouth bass
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fishery on the upper Niagara River is large and active (Einhouse et al. 2002). Since monitoring is not done on the upper Niagara River to assess trends in the number of smallmouth bass, there are no estimates of abundance for smallmouth bass other than those from the angler surveys. Therefore, to determine if there was a negative association between the catches of round gobies and smallmouth bass on the upper Niagara River, we compared the catch rates by anglers from a survey designed to estimate catch and harvest monthly, seasonally, and annually. If there was a negative association between the catch rates of round gobies and smallmouth bass, it could be interpreted as either round gobies affecting smallmouth bass catch rates or vice versa. In the Great Lakes, the seasonal movements and preferred habitat of round gobies show some of the highest overlap with smallmouth bass, including times of the year when anglers fish for smallmouth bass. Round gobies move inshore during the spring, where they prefer cobble substrate to spawn on, remaining there until autumn, when they move offshore as water temperature declines (MacInnis and Corkum 2000a, MacInnis and Corkum 2000b, Ray and Corkum 2001, Janssen and Jude 2001). METHODS The upper Niagara River flows north from Lake Erie to Niagara Falls. It splits at the south end of Grand Island into the Chippewa and the Tonawanda channels and becomes a single channel again at the north end of Grand Island (Fig. 1). The border between Canada and the United States (U.S.) runs the length of the river. Where the river splits, the border runs near and along the east shore of the Chippewa Channel. The angler survey conducted during 2003 covered the upper Niagara River between the Peace Bridge, near Lake Erie, and an imaginary line that crosses the river 2.5 miles above Niagara Falls. The imaginary line is the start of a safety zone above Niagara Falls where boating is prohibited. The survey assessed fishing from boats and from shore between 5 April and 30 November. It was conducted on 3 weekdays per week and every weekend day and federal holiday in the U.S., with one exception. The Friday after Thanksgiving was substituted for the Thanksgiving Day holiday. Anglers who fished from shore (shore anglers) were interviewed at each of 17 public access sites in the U.S. while they were fishing or as they were leaving a site (Fig. 1). Anglers who fished from
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FIG. 1. Sites on the upper Niagara River where interviews were conducted with shore anglers (▲), boat anglers (●), and both shore and boat anglers (■) during 2003.
boats (boat anglers) were interviewed at eight public boat launch ramps in the U.S. when they returned from fishing. Each shore fishing site was sampled during every survey day, as were three randomly selected boat ramps. Shore anglers were asked what they were trying to catch, how many fish they caught, and the time they spent fishing. Boat anglers were asked the same questions as shore anglers and one additional question; where they fished. The question about where boat anglers fished was used to determine if anglers fished on the upper Niagara River, rather than on Lake Erie or a tributary of the Niagara River or Lake Erie. We only used responses from boat anglers about their fishing on the upper Niagara River. Catch rates for each angler, whether fishing alone or with a party of anglers, were calculated by dividing the number of round gobies and the
number of smallmouth bass caught by the numbers of hours spent fishing. Before comparing catch rates of smallmouth bass with those of round gobies, we had to decide if it was appropriate to partition anglers into groups based on whether they fished from a boat or from shore (fishing method) and the fish they were trying to catch (fish sought). It was important to consider fishing method because shore anglers may have fished regions of the upper Niagara River that differed in habitat, depth, and abundance of fish from regions fished by boat anglers. It was also important to consider fish sought because the baits or lures used may have differed depending upon the type of fish an angler was trying to catch. Therefore, both fishing method and fish sought had the potential to affect catch rates for round gobies and smallmouth bass. For fish sought, we considered two groups of anglers, those who said they sought anything and those who said they sought smallmouth bass, largemouth bass (Micropterus salmoides), or bass (which we collectively refer to as black bass). Anglers who sought bass meant smallmouth bass, largemouth bass, or both; but, not rock bass. Regardless of whether an angler sought smallmouth bass, largemouth bass, or bass, we only used that angler’s catch of smallmouth bass for analyses of catch rates. No anglers sought round gobies. We used angler success and catch rates to decide if it was appropriate to partition anglers into groups. Angler success was expressed as the numbers of anglers who caught round gobies and smallmouth bass and those who did not, regardless of whether the anglers sought black bass or anything. We analyzed angler success using the FREQ procedure of SAS which computes Cochran-Mantel-Haenszel and Breslow-Day statistics and relative risk estimates based on odds ratios (SAS Institute Inc. 1999). The Cochran-Mantel-Haenszel statistics were used to test for an association between fishing method and angler success after adjusting for fish sought. Breslow-Day statistics were used to test for homogeneity of the odds ratios based on fish sought. The odds ratio (OR) for a retrospective study like ours is calculated as: OR = n11 n22 / n12 n21
where n11 is the upper left cell of a 2 × 2 table with fishing method as rows and angler success as columns, n22 is the lower right cell, n12 is the lower left cell, and n21 is the upper right cell. If the odds ratios for anglers who sought anything and those
Catches of Round Gobies and Smallmouth Bass who sought black bass were not significantly different, then a common odds ratio could be used to summarize the association between angler success and fishing method. The FREQ procedure was selected to decide if it was appropriate to partition anglers into groups rather than parametric ANOVA on the catch rates because we assumed that the catch rates would not be normally distributed (Jones et al. 1995), an important assumption of parametric ANOVA. Before running the FREQ procedure, we examined the distribution of catch rates to confirm our assumption. Unfortunately, nonparametric ANOVA would only allow us to test for main effects, not interactions. However, after testing the success of anglers, we confirmed the results with paired tests of catch rates using nonparametric ANOVA, where appropriate. Finally, we tested for an association between the catch rates of round gobies and smallmouth bass within each homogenous group of anglers (where the range in catch rates was large enough that a comparison would likely produce meaningful results) using the Spearman rank correlation coefficient. This nonparametric test does not require that the catch rates for either round gobies or smallmouth bass be bivariate normally distributed, a requirement of parametric tests that our data were unlikely to meet. RESULTS Anglers caught both round gobies and smallmouth bass starting the week of 19 April. Round gobies were caught through the week of 22 November and smallmouth bass were caught through the week of 25 October. The number of anglers who caught round gobies and smallmouth bass varied seasonally and with similar temporal patterns; less than 5% of the anglers who caught either round gobies or smallmouth bass did so during the first 5 weeks and last 6 weeks of the survey. Catch rates ranged from 0.0 to 30.8 round gobies per hour and 0.0 to 24.7 smallmouth bass per hour. The seasonal pattern of catch rates of round gobies and smallmouth bass were also similar; catch rates were lower near the beginning and the end of the survey period. The shore anglers caught 14,007 fish, of which 23.4% were round gobies and 11.9% were smallmouth bass. The catch of round goby ranked second and the catch of smallmouth bass ranked fourth among all fish caught by the shore anglers. The boat anglers caught 3,347 fish, of which 1.5% were round gobies and 45.6% were smallmouth bass. The catch of round gobies ranked eighth and the catch of
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TABLE 1. Numbers of anglers on the upper Niagara River during 2003 who caught round gobies and did not catch round gobies based on method of fishing (from a boat or from shore) and for fish sought (anything or black bass).
Method Boat Shore
Numbers of anglers Anything Black bass Caught Not Caught Not 1 83 7 185 376 1,248 56 239
TABLE 2. Numbers of anglers on the upper Niagara River during 2003 who caught smallmouth bass and did not catch smallmouth bass based on method of fishing (from a boat or from shore) and for fish sought (anything or black bass).
Method Boat Shore
Numbers of anglers Anything Black bass Caught Not Caught Not 28 56 146 46 403 1,221 101 194
smallmouth bass ranked first among all fish caught by the boat anglers. There was a significant association between angler success in catching round gobies and method of fishing after controlling for fish sought (P < 0.001), i.e., boat anglers caught fewer round gobies than shore anglers (Table 1). There was no significant difference in the odds ratios of catching round gobies based on fish sought (P = 0.149). Shore anglers were about 10 times more likely to catch round gobies than boat anglers. There was a significant association between angler success for smallmouth bass and method of fishing after controlling for fish sought (P < 0.001) (Table 2). There was also a significant difference in the odds ratios of catching smallmouth bass based on fish sought (P < 0.001). The odds of catching smallmouth bass were significantly different for boat anglers who sought black bass (BAB) and shore anglers who sought black bass (SAB) (P < 0.001) but not for boat anglers who sought anything (BAA) and shore angler who sought anything (SAA) (P = 0.080). BAB were about six times more likely to catch smallmouth bass than SAB. The minimum catch rate of both round gobies and
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Dunning et al. TABLE 3. Average and maximum catch rates (number/hour) for round gobies and smallmouth bass on the upper Niagara River during 2003 by fishing method (from a boat or from shore) and fish sought (anything or black bass). Number/hour Fishing method Boat Boat Shore Shore
Fish sought Black bass Anything Black bass Anything
Smallmouth bass Average Maximum 0.8 11.1 0.3 4.0 0.4 6.4 0.3 24.7
smallmouth bass was 0.0 fish per hour regardless of fishing method and fish sought. However, average and maximum catch rates of round gobies and smallmouth bass varied by fishing method and fish sought (Table 3). BAB had a significantly lower average catch rate of round gobies than SAB (P < 0.001). BAA had a significantly lower average catch rate of round gobies than SAA (P = 0.021). BAB had a significantly higher average catch rate of smallmouth bass than SAB (P < 0.001). However, BAA did not have a significantly different average catch rate of smallmouth bass than SAA (P = 0.936). BAB and
Round gobies Average Maximum > 0.0 0.8 > 0.0 0.6 0.3 8.2 0.5 30.8
BAA had very low maximum catch rates of round gobies while SAA had the highest maximum catch rate of round gobies. SAA had the highest maximum catch rate of smallmouth bass. The catch rates of round gobies and smallmouth bass for boat anglers were not compared statistically because boat anglers had very low maximum and average catch rates of round gobies (Table 3). The catch rates of round gobies and smallmouth bass for SAA were compared separately from SAB primarily because of the large difference in the maximum catch rate of both round gobies and smallmouth bass.
FIG. 2. Comparison of catch rates, expressed as fish/hour, for smallmouth bass and round gobies by 1,624 shore anglers who sought anything on the upper Niagara River.
Catches of Round Gobies and Smallmouth Bass
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FIG. 3. Comparison of catch rates, expressed as fish/hour, for smallmouth bass and round gobies by 295 shore anglers who sought black bass on the upper Niagara River.
The distribution of catch rates for both smallmouth bass and round gobies was noticeably skewed (Figs. 2 and 3). Among SAA, 76.8% caught no round gobies and 75.1% caught no smallmouth bass. Among SAB, 81.0% caught no round gobies and 65.8% caught no smallmouth bass. The widest range in catch rates of smallmouth bass occurred when no round gobies were caught by SAA (0–24.7 per hour) or bass (0–6.4 per hour). In comparison, the range in catch rates of smallmouth bass when round gobies were caught by SAA was 0–5.1 per hour and 0–1.9 per hour for SAB. The catch rates of round gobies and smallmouth bass for SAA were positively and significantly correlated (r = 0.081, P < 0.001, df = 1,622). The catch rates of round gobies and smallmouth bass for SAB bass were negatively and significantly correlated (r = –0.141, P < 0.005, df = 293). DISCUSSION The data from our study not only confirm that round gobies were present in the upper Niagara River during 2003; they also appear to indicate that round gobies were well established. Clapp et al.
(2001) considered catch rates of 1–10 round gobies/hour to be high and an indication that round gobies had become well established based on angler catch rates for ports in Lake Michigan where anglers reported the presence of round gobies. In our study, about 44% of the SAA who caught round gobies on the upper Niagara River had a catch rate greater than or equal to 1 round goby per hour, including one angler who had a catch rate of 30.8 round gobies per hour. There was no evidence of a negative association between the catch rates of round gobies and smallmouth bass in the upper Niagara River based on SAA. SAA should have provided the best measure of an association because this group included: 1) 5.5 times more anglers than the next largest group, 2) anglers with catch rates of both round gobies and smallmouth bass whose range was more than three times greater than any other group, and 3) anglers less likely to use baits and lures that would preclude catching smaller fish—like round gobies, than anglers fishing for black bass. Although the correlation between the catch rates of round gobies and smallmouth bass SAB was statistically significant
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and negative, it was small and probably of little or no biological significance. The statistical significance appears to be due to a combination of sample size and the relatively large proportion of anglers who caught no round gobies (81.0%), an artifact of using survey data. This became clear when we correlated the catch rates of round gobies and smallmouth bass based only on SAB who caught round gobies. The resulting correlation (r = –0.102, df = 54) was similar in magnitude to that based on all SAB (r = 0.141, df = 293), but not statistically significant (P > 0.05). A comparable result occurred when we correlated the catch rates of round gobies and smallmouth bass based only on SAA who caught round gobies. The resulting correlation (r = 0.022, df = 374) was similar to that based on all SAA (r = 0.081, df = 1,622), but not statistically significant (P > 0.05). The proportion of SAA who caught no round gobies, like that for SAB, was also relatively large (76.8%). The higher average catch rate of smallmouth bass by BAB compared with SAB and the lower average catch rate of round gobies by boat anglers compared with shore anglers could have been due to differences in mobility, access to habitats, or fishing techniques. If the distribution of round gobies within the upper Niagara River was patchy, changed with time, differed by depth, or a combination of these, more mobile anglers should have had an advantage in avoiding round gobies. It is reasonable to believe that the boat anglers were more mobile, i.e., they could change their location more quickly and easily than the shore anglers. However, this explanation for the difference in catch rates is based on an assumption that the boat anglers caught round gobies and then decided to move. If that happened, the probability of a boat angler catching at least one round goby during a fishing trip should not have been significantly different from that of a shore angler. The fact that boat anglers had a significantly lower probability of catching round gobies than shore anglers suggests that mobility was not the most likely reason that boat anglers had a lower average catch rate of round goby than shore anglers. An alternative explanation for: 1) the higher average catch rate of smallmouth bass by BAB compared with SAB and 2) the lower average catch rate of round gobies by boat anglers compared with shore anglers is a difference in accessible habitats. This alternative is plausible if the distribution of round gobies and smallmouth bass did not completely overlap because of differences in habitat selection and boat anglers were able to fish in areas other than where the overlap occurred but shore anglers could not, e.g., deeper water. If so,
boat anglers may have developed different fishing techniques and used them in areas where the distribution of round gobies and smallmouth bass overlapped as well as in areas where the distributions did not overlap. Unfortunately, data collected during the 2003 angler survey on the upper Niagara River did not allow us to check either explanation. Our results suggest that round gobies did not disrupt fishing for smallmouth bass on the upper Niagara River during 2003 if disruption is defined exclusively by the association between catch rates of smallmouth bass and round gobies. However, catching round gobies did lead to angler perceptions of poor fishing quality. Unsolicited comments offered by shore anglers during the 2003 angler survey on the upper Niagara River indicate that some anglers were frustrated and upset if they caught round gobies when they were trying to catch black bass. Their complaints included losing bait to round gobies and the perception that catching round gobies reduced the likelihood of catching smallmouth bass because baited hooks and lures were not in the water when round gobies were handled. Therefore, managers of sport fisheries where round gobies are incidentally caught may have to deal with angler perceptions about reduced catch rates for sport fish due to round gobies that differ from reality. ACKNOWLEDGMENTS We thank John Magee for managing the 2003 angler survey until he took a position with the New Hampshire Fish and Game Department, Alex Levy of Gomez and Sullivan for managing the 2003 angler survey after John Magee, Scott Schanke of Normandeau Associates for supervising the collection of data and noting complaints from shore anglers about catching round gobies, and Donald Einhouse and Michael Wilkinson of the New York State Department of Environmental Conservation for providing information that was important in planning the 2003 angler survey. The 2003 angler survey was funded by the New York Power Authority. REFERENCES Charlebois, P.M., Marsden, J.E., Goettel, R.G., Wolfe, R.K., Jude, D.J., and Rudnika, S. 1997. The round goby Neogobius melanostomus (Pallas), a review of European and North American literature. IllinoisIndiana Sea Grant Program and Illinois Natural History Survey. INHS Special Publication No. 20. ———, Corkum, L.D., Jude, D.J., and Knight, C. 2001. The round goby (Neogobius melanostomus) invasion:
Catches of Round Gobies and Smallmouth Bass current research and future needs. J. Great Lakes Res. 27:263–266. Clapp, D.F., Scheeberger, P.J., Jude, D.J., Madison, G., and Pistis, C. 2001. Monitoring round goby (Neogobius melanostomus) population expansion in eastern and northern Lake Michigan. J. Great Lakes Res. 27:335–341. Connelly, N.A., Brown, T.L., and Knuth, B.A. 1997. New York Statewide Angler Survey 1996, Report 1: Angler Effort and Expenditures. New York State Department of Environmental Conservation, Albany, New York. Einhouse, D.W., Haws, J., Knight, J., Sztramko, L., and Wilkinson, M.W. 2002. 1999 Angler Survey of the Upper Niagara River. New York State Department of Environmental Conservation, Albany, New York. French, J.R.P., and Jude, D.J. 2001. Diets and diet overlap of nonindiginenous gobies and small benthic native fishes co-inhabiting the St. Clair River, Michigan. J. Great Lakes Res. 27:300–311. Janssen, J. and Jude, D.J. 2001. Recruitment failure of mottled, sculpin Cottus bairdi in Calumet Harbor, southern Lake Michigan, induced by the newly introduced round goby Neogobius melanostomus. J. Great Lakes Res. 27:319–328. Jones, C.M., Robson, D.S., Lakkis, H.D., and Kressel, J. 1995. Properties of catch rates used in analysis of angler surveys. Trans. Am. Fish. Soc. 124:911–928.
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Lake Erie Forage Task Group (LEFTG). 2003. Report of the Lake Erie Forage Task Group March 2003. New York State Department of Environmental Conservation, Albany, New York. MacInnis, A.J., and Corkum, L.D. 2000a. Age and growth of round goby Neogobius melanostomus in the upper Detroit River. Trans. Am. Fish. Soc. 129: 852–858. ———, and Corkum, L.D. 2000b. Fecundity and reproductive season of the round goby Neogobius melanostomus in the upper Detroit River. Trans. Am. Fish. Soc. 129:852–858. Marsden, J.E., and Jude, D.J. 1995. Round gobies invade North America. Illinois-Indiana Sea Grant Program. IL-IN-SG-96-10. New York State Department of Environmental Conservation (NYSDEC). 1984. 1984 New York State Great Lakes Angler Survey. NYSDEC, Albany, New York. Ray, W.J., and Corkum, L.D. 2001. Habitat and site affinity of the round goby. J. Great Lakes Res. 27:329–334. SAS Institue Inc. 1999. SAS/STAT User’s Guide, Version 8. SAS Institute Inc, Cary, North Carolina. Submitted: 3 October 2005 Accepted: 17 July 2006 Editorial handling: Marten A. Koops