Spawning Black Bass and the Invasive Round Goby in Lake Ontario and the St. Lawrence River

Transcription

1 Spawning Black Bass and the Invasive Round Goby in Lake Ontario and the St. Lawrence River By Daniel McCarthy A thesis submitted to the Department of Biology In conformity with the requirements for the degree of Masters of Science Queen s University Kingston, Ontario, Canada (January 2017) Copyright Daniel McCarthy, 2017 i

2 Abstract: This thesis examined the relationships between the invasive Round Goby (Neogobius melanostomus) and the economically important recreational fish species, Smallmouth Bass (Micropterus dolomieu) and Largemouth Bass (Micropterus salmoides). Nesting bass were located in Lake Ontario and the St. Lawrence River prior to the opening of the angling season in Predator density, offspring development, and predation intensity during simulated catch-and-release angling were measured to determine the risk of combined negative effects from recreational angling and nest predation by Round Gobies. General linear models were used to compared the influence of habitat, temperature and species on each variable. As previously demonstrated, Round Gobies preyed on Smallmouth Bass eggs and larvae when the guarding male was absent from the nest. Largemouth Bass nests were located in areas with very low Round Goby abundance and are likely not experiencing significant predation by Round Gobies. Smallmouth Bass nesting near Lake Ontario are at the highest risk for predation because of slower offspring development in colder water, and prevalent rocky/sandy nesting habitat with high Round Goby abundance. The closed fishing season in 2015 did not protect the majority of Smallmouth Bass from recreational angling over the vulnerable stage of offspring development. Smallmouth Bass recruitment might be limited in these areas from a combination of hyper abundant predators and recreational angling. ii

3 Acknowledgements: I would like to thank my supervisor Dr. Bruce Tufts for the opportunity to complete research in fisheries biology. His guidance was critical for my development and success in scientific research. I want to express my deepest gratitude for all of his instruction, understanding, and patience throughout this project. I would also like to thank my supervising committee Dr. Yuxiang Wang and Dr. Paul Martin for their ideas and feedback throughout the course of this study. This research would not have been possible without funding from the Greenburg family Fund and Queen s University. I greatly appreciate the opportunity to complete extensive field work and pursue the questions I am passionate about. I owe great thanks to everyone involved in data collection for this project, especially Randy Lindenblatt, Eric Taylor, Mary Hanely, Sean Bridgeman and Connor Elliot. Long days and cold water have never been so much fun. Finally, I would like to thank all the members of the Tufts lab: Paul Finigan, Julia Colm, Changhai Zhu, Rachel Horsby, Kathleen Allen, Ben Labenski and Courtney Kolbe. The intellectual and moral support was invaluable. iii

4 Table of Contents: Abstract.... ii Acknowledgements.... iii List of Figures... v List of Tables. vi List of Appendices.... vii Chapter 1: Introduction Black Bass Recreational Fishery in the Eastern Great Lakes Region Black Bass Spawning Round Gobies in Lake Ontario and the St. Lawrence River Relationships between Black Bass and the Round Goby Chapter 2: Methods Snorkeling Observations Snorkeling Measurements Control Observations Temperature Recordings Simulated Catch-and-Release Angling Experiment Statistical Analysis.. 19 Chapter 3: Results Developmental Stage of Bass Offspring Round Goby Abundance Simulated Catch-and-Release Angling Chapter 4: Discussion Developmental Stage of Bass Offspring Round Goby Abundance Simulated Catch-and-Release Angling Chapter 5: Summary and Conclusions 64 Literature Cited.. 66 iv

5 List of Figures Figure 1. Study Region and Bass Nesting Locations. 29 Figure 2. Observations of Bass Offspring Developmental Stage Figure 3. Degree-Days vs. Date at Three Relevant Spawning Locations. 31 Figure 4. Ordinal Logistic Regression Predictions of Smallmouth Bass Offspring Development 32 Figure 5. Predicted Developmental Stage of Smallmouth Bass Offspring in Three Relevant Spawning Locations When Bass Angling Season Opened in Figure 6. Mean Round Goby Abundance at Bass Nests and Controls. 34 Figure 7. Mean Round Goby Abundance at Observed Substrate Types 35 Figure 8. Frequencies of Nests with Each Observed Round Goby Abundance. 36 Figure 9. Round Goby Abundance at Each Nest. 37 Figure 10. Percent of Bass Nests with Round Gobies Present.. 38 Figure 11. Round Goby Abundance at Nests vs Associated Controls. 39 Figure 12. Negative Binomial General Linear Regression Predicting Round Goby Abundance at Bass Nests Figure 13. General Linear Logistic Regression Predicting the Species of Bass at Nesting Sites Figure 14. Predation Intensity by Round Gobies During Simulated Catch-and-Release of Smallmouth Bass.. 42 v

6 List of Tables Table 1. Top General Linear Models Table 2. Top General Linear Mixed Models.. 44 Table 3. Summary of Angling Experiment Results vi

7 List of Appendices Appendix A1. AIC Table Nest vs Paired Control Models Appendix A2. Diagnostic Plots Round Goby Abundance at Nests Top Models. 75 Appendix A3. AIC Table Round Goby Abundance at Nests Models Appendix A4 Diagnostic Plots Round Goby Abundance at Controls Top Models.. 76 Appendix A5. AIC Table Round Goby Abundance at Controls Models Appendix A6. AIC Table Species Nesting Habitat Preference Models Appendix A7. AIC Table Predation Intensity During Simulated Catch-and-Release 77 vii

8 Chapter 1: Introduction Recreational fishing is one of the largest industries in North America. Recent reports estimated nearly 20% of the population of North America participates in angling (DFO 2011, USDI 2011, ASA 2013, Tufts et al. 2015). Over $50 billion is spent every year in the angling industry, which supports over jobs across North America (DFO 2011, USDI 2011). Anglers travel from around the world to fish in Canada and the United States. The socioeconomic benefits are felt across all areas of both countries, particularly in some of the more rural areas (DFO 2011). The majority of North America s Atlantic and Pacific coastal marine fisheries are currently fully exploited by commercial harvest (FAO 2012). In contrast, most inland fish stocks are predominately used by recreational anglers (Post et al. 2002). One important difference between recreational angling and commercial fishing is that fish are captured on an individual basis when angled, rather than in large numbers. This provides the opportunity to select specific fish for harvest or release. In fact, the majority of fish caught in modern recreational fisheries are released. Estimates based on Canadian fisheries projected that, of the approximately 47 billion fish angled worldwide each year, 30 billion fish are released (Cooke and Cowx, 2006). Anglers are increasingly aware that releasing fish benefits the health and quality of recreational fisheries (Bartholomew and Bohnsack 2005), and voluntary catch-andrelease is the most common reason for releasing fish in some fisheries (Gaeta et al. 2013). Additionally, more management agencies are also using catch-and-release as a conservation tool for maintaining healthy populations (Paukert et al. 2007). Catch-and-release as a 1

9 mechanism of selective harvest is the root of sustainability in modern recreational fisheries (Tufts et al. 2015). To maximize the benefit of selective harvest, it is important to reduce the impact on released fish. The physiological disturbances in angled fish are beginning to be well understood, and a large number of factors that affect the survival of released fish are well described (Cooke and Suski 2005). An important conclusion from this research is that mortality in catch-andrelease fisheries is low; the vast majority of released fish do survive (Tufts 1997, Muoneke and Childress 1994, Boyd et al. 2010). Understanding the factors contributing to physiological disturbances in angled fish has helped define the best practices for live release in many fisheries (Morrissey et al. 2005, Suski et al. 2006, Cooke and Suski 2005). Another important benefit of incorporating selective harvest into recreational fisheries is increasing total angling opportunities. At any given biomass, fisheries can support a greater amount of effort if selective harvest is incorporated (Schaefer 1954, Hunt et al. 2011, Tufts et al. 2015). Increased opportunities result in increased socio-economic benefits from the fishery while maintaining healthy and sustainable populations. In addition to the economic benefits of recreational fisheries, anglers also have many indirect benefits on conservation. For example, the American Sport Fishing Association reports that US anglers donate over $400 million annually to conservation (ASA 2013). Similarly, Trout Unlimited records over $1 million in donations every year, most of which funds aquatic habitat restoration programs, benefitting sport fish and many different aquatic organisms alike (Trout Unlimited Canada, 2015). 2

10 Anglers also fund government conservation initiatives through license fees and tax funds. In Ontario, recreational license fees are used exclusively for fish and wildlife conservation programs. Nearly every province in Canada has a similar program. In British Columbia, a part of these funds are used for recreational fishery improvements, such as stocking programs or building boat ramps. Improved angling opportunities attract more anglers, bringing in more money from license fees and angling related purchases. Additionally, high quality angling opportunities promote tourism by attracting foreign anglers. In 2010 approximately foreign anglers travelled to Canada and spent $44 million in Canada (DFO 2011). Travelling anglers spend the majority of trip expenses on travel, food, and lodging, supporting several other industries in addition to the angling industry (DFO 2011). Management agencies face several challenges between promotion of recreational fishing and conservation of the resource (DFO 2011). In some fisheries, even catch-and-release with no retention can cause significant harm. For example, it is illegal to target fish officially listed on the U.S. Endangered Species Act, or the Species at Risk Act in Canada. This protects species from any other sub-lethal impacts of catch-and-release. Other important ways recreational fisheries have achieved sustainability is through the use of angling seasons, gear restrictions and location restrictions. Reviews of catch-and-release fishing concluded that targeting fish in their extreme temperature ranges, angling fish from extreme depths, angling with certain gear types, and targeting species during their reproductive period all have evidence of negative effects on individual fitness and/or the population (Bartholemew and Bohnsack 2005, Cooke and Suski 2005, Arlinghaus et al. 2007). Furthermore, many recreational species face additional challenges from habitat degradation, pollution, and 3

11 invasive species (Dextrase and Mandrak 2006, Jelks et al. 2008, McCune et al. 2013). In some cases, catch-and-release fishing and interactions with recent invasive species have compounding effects, which pose significant threats to the health of the fishery (Steinhart et al. 2004a). One example is the Round Goby, Neogobius melanostomus, invasion in the Laurentian Great Lakes. Embryo survival and recruitment in many indigenous nest guarding species may be compromised by the combined effects of nest predation from the hyper abundant Round Goby and recreational angling. To maximize the socio-economic benefits of recreational fisheries while maintaining healthy fish stocks with high quality angling opportunities, it is important to understand the compound effects of recreational fishing and other major pressures on fish populations. 1.1: Black Bass Recreational Fishery in the Eastern Great Lakes Region Over the past few decades, bass fishing in the Eastern Great Lakes region has been growing in popularity (Funnel 2012, Kerr 2012). Smallmouth Bass (Micropterus dolomieu) and Largemouth Bass (Micropterus salmoides) are the only species of Black Bass present in this region, and are consistently among the most commonly targeted species in Ontario (Funnel 2012) and the most popular freshwater species in New York (Connelly and Brown 2009). Eastern Lake Ontario and the St. Lawrence River have world class bass fishing reputations, and the socio-economic importance of bass in these regions is significant (Kerr 2012, Perry et al. 2014). Native to the St. Lawrence River and Great Lakes (Scott & Crossman 1998), Smallmouth Bass and Largemouth Bass have been more resilient to anthropogenic change than many other 4

12 species. Often, Smallmouth Bass and Largemouth Bass are managed with the same regulations and angling seasons (Paukert et al. 2007), despite having several important differences in physiology (Furimsky et al. 2003) and ecology (Morrissey et al. 2005). To conserve the quality and health of black bass fisheries, many management agencies currently include a closed angling season during the spawning period for both species (May & early June). However, many challenges arise for management agencies when regulating bass in the Northern regions of their distribution. For example, bass fishing season opens while some fish are still spawning, and currently this has unknown implications. Since the timing of bass spawning is tightly linked with temperature (Scott and Crossman 1998, Ridgway & Friesen 1992, Shuter et al. 1980), the severity of this issue is intensified on large bodies of water that warm much slower than many of the surrounding systems. Additionally, much of the research that forms the basis for management decisions has examined bass populations on small waterbodies. Relatively little is known about populations in larger Northern lakes, such as the Great Lakes. Another challenge for management is the constant social and economic pressures to open bass fishing season. Over the past few decades there has been a growing trend to remove closed bass fishing seasons and regulate fisheries with size and creel (daily catch) limits (Quinn 2002, Paukert et al. 2007). This trend is exemplified by the opening of an early season catchand-release period in the New York waters of Lake Erie in A similar season is now being considered for the Eastern basin of Lake Ontario and the St. Lawrence River. This region is a large, slow warming water body with relatively little known about the ecology of the resident bass population. 5

13 There is a general lack of information in the literature examining bass populations on large water-bodies. Contrasted with the importance of bass fishing in this region and the influential management decisions underway, there is a clear need to understand more about Largemouth and Smallmouth Bass in Lake Ontario and the St. Lawrence River. 1.2: Black Bass Spawning In Canada, both Smallmouth and Largemouth Bass spawn between May and July. Males build circular nests and court females, who leave the nest site after deposition of the eggs. Males are left to defend the offspring for 3-5 weeks, fanning eggs to prevent accumulation of sediment and provide sufficient oxygen, as well as defending the offspring from predation. Male bass do not actively forage during this period, despite having increased energetic investment while caring for the brood (Cooke et al. 2002, Hanson et al. 2009). At their Northern ranges, as in the Great Lakes, males rarely attempt multiple spawning events per season, and abandonment of the brood results in almost certain failure of reproductive success in any given year (Philipp et al. 1997, Steinhart et al. 2008). Male basses guard their offspring over several stages of development, starting with deposition of the eggs and ending with transition into juveniles. Offspring progress to hatched embryos after approximately 4 10 days in temperatures common in most Canadian waters. Hatched embryos remain in the nest living off their yolk sac until they are able to swim-up in the water column. Swimming above the nests marks the transition to the larval stage (Steinhart et al. 2004). Larvae remain above the nest for 5 7 days before beginning to leave, but are still guarded by the male for several days (Scott and Crossman 1998). 6

14 Smallmouth Bass build nests on rocky, sandy, or gravelly substrate usually near the protection of boulders, rocks, sunken wood or, more rarely, dense vegetation (Scott and Crossman 1998). Nests are cm in diameter in cm of water. Spawning occurs over a range of temperatures, but most commonly between 12 O - 20 O C. Eggs are deposited over a period of about 6-10 days depending on water temperatures and spring warming characteristics. Largemouth Bass prefer spawning on mud, gravel, or sand substrates around dense vegetation (Scott and Crossman 1998) in cm of water. Nest building usually begins when the water temperature reaches 15 O C and spawning occurs shortly afterwards. Spawning can occur after very little nest preparation, usually depositing the eggs on rootlets, submerged wood, or other vegetation. Largemouth Bass spawn in slightly warmer temperatures than Smallmouth Bass, but in water bodies containing both species Largemouth Bass will often spawn first. This happens because the shallow bays around bulrushes and other emergent vegetation that are used by Largemouth Bass heat up more quickly in the spring, compared to the deeper, rockier spawning sites used by Smallmouth Bass (Scott and Crossman 1998). In lentic environments, spawning time is driven by temperature and spring warming characteristics (Shuter et al. 1980). Once the eggs have been deposited, rapid drop in temperature, particularly below 10 O C, can cause the guarding male to abandon the nest (Shuter et al. 1980, Scott and Crossman 1998). Changes in water level, brood predation, predator density, and wave action have all been associated with increased nest abandonment (Steinhart et al. 2004, Phillip et al. 1997, Scott and Crossman 1998). In a large Northern lake, survival on the nest is a critical life stage for Smallmouth Bass and predictive of recruitment for the year 7

15 (Shuter et al. 1980). Consistent and stable temperature and weather patterns are ideal spawning conditions for bass (Shuter et al. 1980). Both bass species are particularly vulnerable to angling over the nest-guarding period for several reasons. First, nests are easily identifiable from the surface (especially Smallmouth Bass nests) and can be targeted by anglers in shallow areas (Philipp et al. 1997). Second, males are aggressive while guarding their brood, and will likely attack most lures presented in the vicinity of their nest (Philipp et al. 1997, Ridgway 1988). Harvest of the guarding male has obvious negative consequences for the reproductive success of the individual, but even catchand-release can result in male bass abandoning their nest and forfeiting the previous investment into their brood (Philipp et al. 1997, Zuckerman and Suski 2013, Stein and Philipp 2015). Bass are effective at defending their nests while present (Steinhart et al. 2004), but when fish are removed predators can opportunistically prey on the vulnerable offspring (Kieffer et al. 1995, Stein and Philipp 2015). The amount of predation, predator burden in the area of the nest, and the angling practices all have significant impacts on the guarding males decision to abandon his brood (Philipp et al. 1997, Zuckerman and Suski 2013, Stein and Philipp 2015). In the Great Lakes, a major predator of many benthic fish offspring is the invasive Round Goby. Offspring predation by Round Gobies has been implicated in decline of several native fish species (Kornis et al. 2012). Round Gobies are a known predator of Smallmouth Bass eggs and benthic larvae (Steinhart et al. 2004a). Although Largemouth Bass and Round Gobies exist together in the Great Lakes, but there is no information examining Round Goby predation of Largemouth Bass eggs and benthic larvae. 8

16 1.3: Round Gobies in Lake Ontario and the St. Lawrence River The Round Goby is one of the most widely distributed invasive species on earth (Kornis et al. 2012). They were first documented in North America in the St. Clair River in 1990 (Jude et al. 1992), and have since spread throughout the Laurentian Great Lakes faster than any other previous invader (Charlebois et al. 2001, Dillon & Stepien, 2001). Round Gobies are now among the most abundant species in many areas (Taraborelli et al. 2010, OMNRF 2015, NYSDEC 2015). Round Gobies are typically most abundant in rocky habitats. They spawn, feed, and hide in hard substrata (Ray and Corkum 2001, Young et al. 2010). Mud and sand substrates are still used by Round Gobies, and the abundance in these habitats can be similar to rocky habitats in some areas (Johnson et al. 2005a). In the Bay of Quinte, Round Gobies were found to be most abundant in the 1.5-3m depth range compared to 3-5m and 5-7m (Taraborelli et al. 2009). Also, there were no consistent significant differences in Round Goby abundance between habitat types (rock, mud, sand) or vegetation densities (Taraborelli et al. 2009). On other bodies of water, Round Goby abundance is correlated with depth and density of vegetation. In Lake Erie Round Gobies were most abundant in nearshore habitat (5-15m) from (Johnson et al. 2005a). Round Gobies can inhabit a wide range of depths, temperatures, salinity, and substrates, contributing to their widespread abundance. Round Gobies have become important in many food webs throughout the Great Lakes. Round Gobies have largely replaced other native benthic species throughout Lake Erie, Lake Michigan and Lake Ontario, likely due to their aggressive behavior and spawning strategies 9

17 (Dubs and Corkum 1996, Balshine et al. 2005). They can reach higher densities than previously abundant benthic species (Charlebois et al. 2001), and consequently have become an important forage item for many predators. Burbot, Yellow Perch, Smallmouth Bass (Crane et al. 2015) and some populations of Largemouth Bass (Taraborelli et al. 2010) have become heavily reliant on Round Gobies in the Great Lakes. The body condition of several native predators has improved after the introduction of Round Gobies into their diet (Crane et al. 2015). This is likely because Round Gobies facilitated a new energy pathway in the Great Lakes. In the 1980s, dressenid mussels (Dreissena polymorpha and D. bugensis) invaded the Great Lakes, causing many changes to the existing energy pathways (Johnson et al. 2005b). Dressenid mussels are efficient filter feeders, and removed much of the food potentially supporting the pelagic ecosystem. Few organisms preyed on dressenid mussels resulting in much of the previously available energy to be trapped in the benthic mussels (Johannsson et al. 2000). Invasion of Round Gobies (1990s), an efficient predator of dressenid mussels, created a vector to access the energy trapped in the benthic mussels (Johnson et al. 2005b). Newly bioavailable energy translated into increased body condition for large native piscivores. Yellow Perch, Walleye, and Smallmouth Bass condition have all improved (Crane et al. 2015). Smallmouth Bass are larger than ever recorded in Lake Erie and Lake Ontario, and both length at age and weight at age relationships have increased since introduction of Round Gobies (Steinhart et al. 2004b, Crane et al. 2015, OMNRF 2015, NYSDEC 2015, Zhu 2015). Round Gobies have also had a significant negative impact on many native predators, predominantly from consuming theirs eggs and larvae. For example, Lake Trout, Salvelinus 10

18 namaycush, fry emergence was reduced to essentially zero after invasion of Round Gobies on a spawning reef in Lake Ontario (Fitzsimons et al. 2009). Round Gobies also prey on the eggs of Lake Sturgeon, Walleye (Roseman et al. 2006), Smallmouth Bass (Steinhart et al. 2004a), and likely any fish with benthic eggs. Hyperabundance of nest predators can also increase the parental care costs for nest guarding species, such as black basses. High densities of Round Gobies can increase abandonment of Smallmouth Bass broods if the energy costs of defense or the level of brood predation become too high (Steinhart et al. 2005, Steinhart et al. 2008). Although body condition of adult Smallmouth Bass has been consistently improving since introduction of Round Gobies, recruitment is potentially limiting their abundance. Population levels of Smallmouth in Eastern Lake Ontario and the St. Lawrence River have been consistently low compared to historical data, despite conditions being favorable for the production of strong year classes (NYSDEC 2015, OMNR 2015). 1.4: Relationships between Black Bass and the Round Goby Round Gobies are a known predator of Smallmouth Bass offspring (Steinhart et al. 2004a). To date, however, the only study examining this issue was carried out on Lake Erie. This study showed that when guarding Smallmouth Bass are removed from the nest, Round Gobies could completely clear an average Smallmouth Bass nest of all the offspring in approximately 17 minutes (Steinhart et al. 2004a). Furthermore, Smallmouth Bass nesting in a lake with abundant Round Gobies had increased energetic demands compared to a lake without Round Gobies (Steinhart et al. 2005). Increasing demands of defending their nest depleted guarding males 11

19 energy reserves and limited their ability to guard the brood. To date, there is no information examining the interactions between nesting Largemouth Bass and Round Gobies. A unique interaction exists between bass and Round Gobies in the Great Lakes. Adult bass condition and size at age has significantly improved following the invasion of Round Gobies, likely due to the availability of Round Gobies as a prey item (Steinhart et al. 2004b, Crane et al. 2015, Zhu 2015). However, nest predation by Round Gobies can potentially limit bass recruitment (Steinhart et al. 2004a, Steinhart et al. 2008). Additionally, catch-and-release angling of guarding male bass significantly intensifies offspring predation on nests (Kieffer et al. 1995, Stein and Philipp 2015). Therefore, for management agencies to properly manage this important resource, it is essential to understand the prevalence of Round Goby interactions with nesting bass, and whether bass are still spawning when the angling season opens. Currently, the levels of predation pressure that Smallmouth and/or Largemouth Bass offspring are receiving from Round Gobies in Eastern Lake Ontario and the St. Lawrence River is unknown. Bass nest predation by Round Gobies has only been observed on Lake Erie (Steinhart et al. 2004a). It is unclear if these results can be extrapolated to other waterbodies, or across habitat types. Furthermore, the importance of habitat in driving the interaction between nesting bass and Round Gobies has never been evaluated. It is unclear whether nest predation is an issue for all nests, or only in certain locations. Identifying the important habitat variables may be useful for predicting the prevalence of Round Goby nest predation, and identifying differences between Largemouth Bass and Smallmouth Bass. There is also little information addressing the timing of bass spawning in this region. If the angling season overlaps with the timing of the bass spawn in this region, even catch-and-release fishing could compound the 12

20 negative effects of Round Goby predation. It is important to identify what percentages of each species have completed spawning when the angling season opens. Finally, the extent of the predation that bass nests receive when guarding males are removed has not been examined in this region. All of these issues are important aspects of the relationship between Black Basses and Round Gobies, especially in light of the important management decisions currently under review. Given the importance of bass in this region, the lack of information regarding these interactions is surprising. Nest survival is a critical life stage in Northern populations of bass (Shuter et al. 1980), but currently there is a lack of information evaluating the ecology of bass in this region, and their interactions with recently invasive species. The OMNRF in Ontario, and the NYSDEC in New York both monitor adult bass populations in Lake Ontario, but it is important to understand how recruitment may be affected by compounding effects of recreational angling and Round Goby predation. This study will evaluate the influence Round Gobies might be having on nesting Largemouth Bass and Smallmouth Bass. This first part of this thesis compares the potential level of predation by Round Gobies between the species of bass present in Lake Ontario (Largemouth Bass and Smallmouth Bass). The second part will evaluate the timing of bass spawning in relation to the current angling season. Finally, relationships between Round Goby abundance and nest predation will be examined when the guarding bass is removed. Given these goals, it is hypothesized that: 1. Round Gobies will be more abundant around Smallmouth Bass nests compared to Largemouth Bass. 13

21 a. This difference will be largely because of shared habitat preferences between Smallmouth Bass and Round Gobies. 2. A large percentage of Largemouth and Smallmouth Bass nests will still be at the vulnerable stages of development when the angling season opens on Lake Ontario and the St. Lawrence River. 3. Round Gobies will prey on bass offspring when the guarding male is removed via simulated catch-and-release. 14

22 Chapter 2: Methods Active visualization methods are the most effective technique for quantifying Round Goby densities (Johnson et al. 2005a, Taraborelli et al. 2009) and are the most common technique used to assess habitat preferences and nest predation (Steinhart et al. 2004a, Taraborelli et al. 2010). Snorkeling was selected as the most practical and cost-effective technique to both locate bass nests and assess Round Goby density. Nesting locations were selected by observing suitable habitat, as described in Scott and Crossman (1998), and previous knowledge of the project supervisor, Dr. Bruce Tufts. Once bays were located, individual nests were identified by both observations from a boat and by snorkeling. A still video camera (Contour Drift HD) on a stand was positioned at the first nest located in each bay along with a floating dive flag to mark starting position and notify boaters of snorkelers in the area. After each nest and associated control was processed, snorkelers and/or the boat travelled away from the starting position, parallel to the shoreline along a similar depth contour and substrate type until locating another nest. 2.1: Snorkeling Observations Snorkelers carried polyethylene writing boards, carbon pencils, underwater cameras, a 30m rope, and a 2m PVC pipe with 0.5m markings. Each nest was given a unique observation number and snorkelers recorded depth, substrate type, vegetation type, species of bass, developmental stage of the offspring, presence of zebra mussels, and the density of Round Gobies. Snorkelers were outfitted with wetsuits for warmth, which also increased snorkeler buoyancy making observations easier and clearer. Each nest was photographed with an 15

23 underwater camera (Contour Drift HD/GoPro Hero 3; Appendix A8). Any other predators close to the nest were recorded. All nests where no guarding male was present were considered abandoned and no measurements were recorded. 2.2: Snorkeling Measurements To assess Round Goby abundance, snorkelers counted the number of Round Gobies within 2m radiuses from the center of the nest as estimated with the 2m PVC pipe. The center of the nest was chosen as the reference point so each observation would contain the same total area, regardless of the size of the nest. In addition, nests were not always completely absent of Round Gobies (previous observation; Daniel McCarthy), so the density inside the area that was cleared by the bass was important to include in the observation. Round Gobies were counted by floating over the nest for an estimated 30 seconds while positioning the pipe in a complete circle around the nest (where possible). All substrate types were recorded as a percentage of the total in the categories mud, sand, clay, cobble, boulder, and bedrock; as described in the Wentworth Sediment Scale (Wentworth 1922). All vegetation was recorded as percentage of the total in the categories emergent, submergent, floating and open; as described in the DFO habitat classifications (Robinson and Levings, 1995). Depth was measured with the PVC pipe and estimated in relationship to the half-meter markings. 16

24 Stage of the offspring were described as follows: 0 - Nest is built but no mating has occurred 1 - Eggs were present in the nest 2- Eggs have hatched and fry have not left the bottom (hatched embryos) 3 - Fry have begun to swim up the water column but are still associated with the nest (swim-up fry) 2.3: Control Observations Each nest was paired with a similar control located approximately 30m away along a similar depth contour and substrate type. After each nest was processed, snorkelers travelled 20 fin kicks (determined to be approximately 30m) parallel to the shoreline and away from the starting location to determine the associated control location. At this location, the same protocol was completed and recorded. If after 20 fin kicks the snorkeler happened to stop within a visible distance of another nest, snorkelers continued to travel until the nest was no longer visible. This observation served as a non-nesting location for a paired analysis examining a possible relationship between nest presence and Round Goby abundance. 2.4: Temperature Recordings HoboWare waterproof temperature loggers were deployed at 20 sites in typical spawning locations along the eastern basin of Lake Ontario and the St. Lawrence River. Loggers were attached to the center of 15kg cinderblocks with plastic tie wraps and deployed in depths 17

25 of 0.3-2m. Loggers recorded instantaneous temperature every hour on the hour for the duration of the spawning season. All temperature data was analyzed with HoboWare software. 2.5: Simulated Catch-and-Release Angling Experiment 40 active Smallmouth Bass nests at offspring stage 1 or 2 and spread across the study area were selected for an additional angling experiment. A permit was obtained from the OMNRF to angle Smallmouth Bass before the angling season opened (reference #GFS 15-33). After the nest protocol was complete (see above), guarding males were angled off the nest using a hook, line, rod and reel, and standardized angling tournament style lures. Fish were angled to the boat as quickly as possible, unhooked, measured for total length and immediately released. A snorkeler observed the nest for the duration of the hooking, angling and return periods, counting the total number of Round Gobies entering the nest and signaling to the angler when the fish had returned to guarding the nest. Angling, air exposure, and return time were all measured and recorded. The snorkeler photographed the offspring before and after each angling event. When guarding males were unable to be captured by angling, the nests were removed from the experiment and an additional nest was selected. Nests were selected for angling prior to each day on the water. During the angling experiment it was determined that every nest found that day that fit the experiment criteria would be included, to a maximum of 40 total nests. Nests were considered abandoned if the guarding male did not return within 45 minutes after release. 18

26 2.6: Statistical Analysis All data was imported into RStudio (V ) for analysis. General linear models and AIC information (packages: VGAM, MASS, MuMIn, bblme, lme4) was used for interpreting the data. General linear models have been used to assess Round Goby habitat preferences (Young et al. 2010) and factors influencing predation intensity during simulated catch-and-release angling (Stein and Philipp 2015). General linear models were fit with all possible combinations of predictor variables, unless otherwise noted below. A difference in AIC score of less than two was used to determine the top models. To determine the most appropriate link function (negative binomial, poisson, etc.), residual vs fitted and scale-location plots were used to determine which systematic component best captured the variation in the data and the meanvariance relationship. Top models were reported, and any conflicting conclusions between models were noted in the results Developmental Stage of Bass Offspring Ordinal logistic regression was used to predict the percent of spawning fish at each stage of development based on the cumulative daily mean temperature above 10 C (degreedays). Ordinal logistic regression is commonly used when assessing progression through discrete ordered factors (Agresti 2002). Cumulative daily mean temperature above 10 C (degree-days) is a standard measurement to predict the timing of Smallmouth Bass spawning (Shuter et al. 1980, Ridgway et al. 1991). 19

27 2.6.2 Round Goby Abundance Negative binomial general linear models were used to evaluate relationships between Round Goby abundance at nest locations compared to control locations for Smallmouth Bass and Largemouth Bass. AIC information was compared to evaluate the support for a difference in Round Goby abundance between nest and control locations Nests General linear models with negative binomial, quasipoisson, and zero-inflated link functions were fit to the data to evaluate the most appropriate model to predict Round Goby abundance around bass nests. AIC information was compared to evaluate the support for a relationship between Round Goby abundance, dominant substrate, depth, and developmental stage of the bass offspring Controls General linear models with negative binomial, quasipoisson, and zero-inflated link functions were fit to the data to evaluate the most appropriate model to predict Round Goby abundance around control locations. AIC information was compared to evaluate the support for a relationship between Round Goby abundance, dominant substrate and depth. 20

28 2.6.5 Largemouth Bass vs. Smallmouth Bass nesting habitat preferences Logistic regression general linear models were fit to the data to evaluate nesting habitat preferences between Largemouth Bass and Smallmouth Bass. AIC information was compared to evaluate the support for a relationship between species of bass, dominant substrate and depth Simulated Catch-and-Release Angling General linear mixed models with negative binomial and quasipossion link-functions were fit to the data to evaluate the relationship between predation intensity (number of Round Gobies preying on Smallmouth Bass offspring while guarding male Smallmouth Bass was absent), predator density (initial number of Round Gobies within a 2m radius of the Smallmouth Bass nest before the guarding male Smallmouth Bass was angled), developmental stage of the Smallmouth Bass offspring, length of the guarding male Smallmouth Bass, depth, and total time the guarding male Smallmouth Bass was absent from the nest. 21

29 Chapter 3: Results 145 Smallmouth Bass nests and 61 Largemouth Bass nests were observed between May 21 and June 19, A total of 20 days within the field season were spent searching for nests. Nests were located as far West as Amherst Island and as far East as Mallorytown (Figure 1). Smallmouth Bass nesting locations were difficult to reach during high winds. Wave activity in the Eastern Basin of Lake Ontario can be significant. Boating to Smallmouth Bass nesting locations was often difficult during high winds because many nesting locations are exposed to the main basin of Lake Ontario. Large wave activity also complicated observation procedures at Smallmouth Bass nesting sites. Conversely, Largemouth Bass nesting locations often had unsuitable visibility after precipitation. In total, 5 days were spent searching exclusively for Smallmouth Bass nests, 5 days were spent searching exclusively for Largemouth Bass nests, and the remaining 10 days were split between searching for nests of either species. Smallmouth Bass nests were far easier to locate and were located in higher densities than Largemouth Bass nests, resulting in more observations of Smallmouth Bass nests. Smallmouth Bass nests were observed in 18 separate locations (average 8 nests/location) and Largemouth Bass nests were observed in 17 separate locations (average 4 nests/location). Accessibility and the number of nests that were located during each day resulted in the imbalance between the total number of Smallmouth Bass (n = 146) and Largemouth Bass (n = 61) nests that were observed. Smallmouth Bass nests were located in several different habitat types. Most commonly, Smallmouth Bass nests were located in relatively shallow (1-2m), rocky bays with little vegetation (n = 95). However, Smallmouth Bass nests were also found on mud or silt substrates 22

30 around emergent vegetation (n = 50). Largemouth Bass nests were almost exclusively located in shallow, protected, muddy bays with emergent vegetation (n = 58). Only three Largemouth Bass nests were located on sandy substrate (n = 3), and none were located on rock substrates. 3.1 Developmental Stage of Bass Offspring Largemouth Bass offspring were ahead in development compared to the Smallmouth Bass offspring (Figure 2). Additionally, bass nesting in the St. Lawrence River were ahead of bass nesting closer to the main basin of Lake Ontario (Figure 2). These trends were consistent with the temperature profiles in several important spawning locations representative of Lake Ontario bays (Dupont Bay), the St. Lawrence River (Chimney Island), and a bay approximately in the center of the study region (Howe Is.; Figure 3). Unfortunately, the researchers were not confident that the temperature recordings from Largemouth spawning locations were representative of the temperatures where Largemouth Bass were actually nesting. The Largemouth Bass temperature recordings were from depths that were not appropriate, and from locations where very few Largemouth Bass nest were located. For this reason, Largemouth Bass temperature data was not used to fit an ordinal logistic regression model. The ordinal logistic regression predicting the stage of offspring development was only fit to the Smallmouth Bass data. Cumulative daily mean temperature above 10 C (degree-days) was the only significant predictor of developmental stage (Table 1). The percentage of Smallmouth Bass nests guarding eggs is highest at 100 degree-days, and 50% of spawning Smallmouth Bass have offspring no longer vulnerable to Round Goby predation (swim-up fry) after 205 degree-days (Figure 4). Degree-days were somewhat variable across the study 23

31 locations. On opening day for bass fishing in 2015, a typical Lake Ontario bay (Dupont Bay) had accumulated 106 degree-days, and a typical St. Lawrence River nesting location (Chimney Is.) had accumulated 172 degree-days (Figure 3). Based on these values and the predictions from the ordinal regression, 4.3% of Smallmouth Bass had completed spawning in a typical Lake Ontario bay, and 30.7% of Smallmouth Bass had completed spawning in a typical St. Lawrence River location when the angling season opened in 2015 (Figure 5). 3.2 Round Goby Abundance There were more Round Gobies at Smallmouth Bass nests (mean = 5.3) and their associated control sites (mean = 6.2) than at Largemouth Bass Nests (mean = 0.31) and their associated control sites (mean = 0.56; Figure 6). Predicting Round Goby abundance using nest or control as a predictor variable was supported just as much as the null model for Smallmouth Bass ( AIC = 1.30) and Largemouth Bass ( AIC = 1.43). Bottom composition was the most consistent predictor of Round Goby abundance. Nests were located on three separate bottom substrates: rock, sand, and mud. There were more Round Gobies present on rock and sand substrates compared to mud (Figure 7). This trend was consistent across species and observation types (nests vs. controls). The differences in Round Goby abundance at rock and sand substrates were similar for nest sites and controls (Figure 7). Variability in Round Goby abundance at Smallmouth Bass nests was high; 0 Round Gobies was by far the most common observation, but over 20% of all nests had 10 or more observed Round Gobies within 2m (Figure 8; Figure 9). Percentages of nests with at least one 24

32 observed Round Goby followed similar trends to the observed mean Round Goby abundance (Figure 10). Overall, Round Gobies were more abundant on rock and sand substrate compared to mud substrates across all observations. Between all of the nests that were observed for both Largemouth Bass and Smallmouth Bass, there were only 3 nests of either species located on exclusively sand or rock. The remaining 95 nests dominated by sand or rock had both substrate types present. Only 14 of the total 210 nests had sand as the dominant substrate type. Finally, the top models predicting Round Goby abundance at nests were improved when analyzing rock and sand substrates together ( AIC = 6.08). For these reasons, nests with sand or rock as the dominant substrate were grouped together for the remainder of the analysis. 49 of the 60 Largemouth Bass nests did not have Round Gobies present at the nesting or control location. The Largemouth Bass observations were therefore removed from the net nestcontrol difference analysis. With the remaining Smallmouth Bass nests, the difference between Round Goby abundance at the nest compared to the associated control was not well predicted by any of the habitat variables in a linear mixed model. The null model was supported just as well as any other model ( AIC = 1.73; Appendix A1). However, whether the nest had any offspring present (nest was empty or not) was in all of the other top models ( AIC < 2; Appendix A1) and was associated with more Round Gobies at the nest compared to the associated control location. 25

33 3.2.1 Nests Negative binomial General Linear Models (GLMs) were the best fitted to the data (Appendix A2). The dominant substrate type (mud vs sand/rock) at nesting locations was a better predictor of Round Goby abundance around nests than the species of bass (top models AIC = 42.9). The top models contained substrate, several orders of depth terms, the developmental stage of the offspring, and complex interactions between substrate and depth (Table 1; Figure 12; Appendix A3). Quasipoisson GLMs and zero-inflated GLMs fit the data less well, but came to the same conclusions as the more supported negative binomial models. Round Gobies were significantly more abundant around bass nests located on sand and/or rock than nests located on mud Controls Quasipoisson GLMs were the best fitted to the data (Appendix A4). The dominant substrate type (mud vs sand/rock) at control locations was the best predictor of Round Goby abundance. Species of bass associated with each control was also a significant predictor of Round Goby abundance, but not as well supported as the substrate model (top models qaic = 7.36). The top models contained substrate type and depth (Table 1; Appendix A5). Negative binomial and zero-inflated GLMs fit the data less well, but came to the same conclusions as the more supported quasipoisson models. Round Gobies were significantly more abundant on sand and/or rock substrates than mud substrates at control sites. 26

34 3.2.3 Largemouth Bass vs. Smallmouth Bass nesting habitat preferences Dominant substrate type, depth, and the interaction between substrate type and depth were the only factors in the top models (Table 1; Appendix A6). The top model was used to predict the species of bass nesting at different depths and substrate types (Figure 13). Smallmouth Bass chose deeper nesting sites, and nested in rock and sand more often than Largemouth Bass. 3.3 Simulated Catch-and-Release Angling 40 Smallmouth Bass guarding eggs (n = 31) or hatched embyos (larvae; n = 9) were angled from June 16 to June 19, Only one angled Smallmouth Bass did not return to the nest and was removed from the remaining analysis. Angling time and air exposure was typical of a conservative angling event and consistent between all groups. General linear mixed models with negative binomial link functions were the best fit to evaluate the influence of predator density, length of fish, developmental stage of the nest, and nest exposure time on the amount of Round Goby predation on offspring when guarding males were removed. Nests were grouped into site locations based on proximity (within the same bay). Including site as a random variable significantly improved the model ( AICc = 6.99; parametric Bootstrap, p = <1e -10, reps = , n = 39). Predator density and length of the guarding male were the only variables in the top models (Appendix A7). The confidence intervals for length were not significant. A non-parametric bootstrap revealed that length was not significant ([-0.253, 1.04], reps= , n = 39) and it was removed from the top model. Total time the nest was unguarded was significant in models that fit the data less well 27

35 (quasipoisson), but was not significant after a non-parametric bootstrap ([-0.692, 0.531], reps = , n = 39). Predator density (number of Round Gobies within a 2m radius before the guarding male bass was angled) was the only variable that was consistently in the top models across various model types, and the only variable that was significant during a non-parametric bootstrap (Negative Binomial [0.040, 0.348], reps = , n = 39 ; Quasipoisson [0.027, 0.403], reps = , n = 39). Therefore, predator density (Round Goby abundance) was the only variable with enough support to draw conclusions. As Round Goby abundance increased, predation intensity increased (Table 2, 3; Figure 14). 28

36 Figure 1. All locations in Lake Ontario and the St. Lawrence River where Smallmouth Bass or Largemouth Bass nests were located and/or angled. 29