Date of Award
Doctor of Philosophy
Natural Resource Ecology and Management
Michael J. Weber
Recreational angling for Largemouth Bass (Micropterus salmoides; herafter referred to as bass) has grown in popularity in recent decades. Bass catch and release angling has become popular, resulting in generally low harvest rates despite high angling effort. Additionally, tournament angling events and anglers have grown exponentially. While many recreational and tournament bass anglers practice catch and release angling with the belief that it is a useful measure for sustaining fish populations, fish subjected to such methods may still be vulnerable to multiple sources of mortality and sub-lethal effects. While many studies have quantified the effects of angling mortality on individual bass, few have been assessed at the population level. Although effort intensive, mark-recapture studies serve as a useful empirical tool to improve assessment and management of sources of mortality in bass populations. Thus, the objectives of this study were 1) determine if angler presence and behavior (fishing depth and movement rate), bass behavioral patterns (movement rate, home range, depth, and size), and environmental conditions affect tournament angler catch rates and bass capture probability at fishing tournaments; 2) estimate daily apparent survival rates of bass to evaluate the duration of delayed tournament mortality and to identify important covariates affecting survival; 3) quantify recreational and tournament angler capture probability and natural, recreational angling, and initial and delayed tournament mortality; and 4) estimate tournament capture probability and survival of two size classes of bass [medium (381-457 mm) and large (>457 mm)] and simulate changes in capture probability and survival to asses potential effects on population size-structure. To address these objectives, a wide-scale mark-recapture study was employed during a four-year period at Brushy Creek Lake, IA, USA. Bass were captured and tagged both at tournament events and through electrofishing and recaptures were received through electrofishing and tournament and recreational angler reporting.
For my first objective, I tracked forty-nine bass implanted with radio telemetry tags weekly and five tournament anglers at each tournament event during 2018. I then quantified bass home range, weekly movement rate, depth used, and spatial overlap with anglers, as well as angler depth use, angler movement rate, and air and water temperature. I then used these estimates as covariates in a multistate mark-recapture model in program MARK to estimate capture probability at fishing tournaments. In addition to the mark-recapture model, I also used the covariates as independent variables to predict bass tournament catch-per-unit-effort (CPUE; # bass/angler hours) in a multiple regression model. Air temperature and angler overlap were positively associated with bass capture probability, while bass movement changed across the sample period and was positively related to tournament CPUE. However, bass size, bass home range, bass and angler depth use, and angler movement rate were not successful in characterizing individual variation in capture probability or correlated with tournament CPUE. Tournament anglers in the study were successful at identifying habitats where bass reside and both bass and anglers changed patterns as a result of environmental influences. This strong overlap of bass and tournament anglers creates the potential for population level impacts of tournament angling on bass populations.
Tournament angling can have significant impacts on bass populations when anglers successfully target bass; however, assessments of tournament impacts can be difficult, as some mortality occurs after release from tournaments events. For my second objective, I used a modified Cormack-Jolly-Seber model in program MARK to evaluate the duration of delayed tournament mortality and to identify important covariates affecting survival. Multiple monotonic trends were evaluated to test acute (2, 3, 4, or 7 d) and chronic (15 or 30 d) delayed mortality hypotheses and both environmental and individual covariates were tested to assess additional factors (air and water temperature and bass length, weight, condition, and number of prior tournament captures) influencing delayed tournament mortality. The most supported models revealed a 3-day trend in survival following tournament capture but no support for chronic mortality. Bass tournament mortality ranged from 17% to 33% and increased with increases in water temperature and the number of tournament capture events experienced by an individual bass. Results of the model confirmed the potential for substantial delayed mortality in bass populations and the importance of including delayed mortality when evaluating population-level effects of tournament mortality.
Using estimates from the delayed tournament mortality model, I expanded on my assessment of bass mortality. For my third objective, I used a live-dead multistate mark-recapture model to estimate recreational and tournament angler capture probability. I also evaluated contributions of natural, recreational angling, and initial and delayed tournament mortality to total population level mortality. Average annual tournament angler effort at Brushy Creek was 25.0 hr/ha and resulted in 21% of the bass population captured whereas recreational anglers only captured on average 12% of the bass population. Average total annual mortality was 0.66, with natural mortality representing the largest component (0.57), followed by delayed tournament mortality (0.06), recreational angling mortality (0.03), and initial tournament mortality (0.004). These results showed that tournament angling results in higher mortality than recreational angling but that both angling mortality sources are low compared to natural mortality. Therefore, angling mortality likely has minimal effects on bass abundance.
Although abundance of bass was likely not influenced by tournament mortality, long-term fishing mortality can lead to changes in population size-structure. For my fourth objective, I evaluated differences in tournament capture probability and survival of medium (381 – 457 mm) and large (>457 mm) bass using a multistate mark-recapture model. I then simulated changes in capture and survival rates of each size group to determine the potential for changes in population size-structure. I found that medium bass had higher tournament capture probabilities than large bass and capture probabilities of both size groups increased with air temperature. Medium bass experienced higher survival rates than large bass at tournaments and tournament survival rates of both groups were inversely correlated with water temperature. Simulations indicated increases in tournament capture probability and reductions in survival of large bass resulted in minor reductions in population size-structure whereas changes in tournament capture probability and survival of both size classes had little effect. Thus, reducing the number of large bass weighed in at fishing tournaments may result in only minor increases in bass size-structure.
This holistic assessment of both the capture probability and mortality of a bass populations by recreational and tournament anglers adds to knowledge of population level effects of catch and release angling. Findings from this study reveal that although recreational and tournament anglers can capture large portions of the population (>20%), mortality rates of recreational angling are low compared to natural mortality, resulting in minimal population level effects.
Andrea Lynn Sylvia
Sylvia, Andrea Lynn, "An evaluation of tournament angling impacts on a Largemouth Bass population using mark-recapture data" (2019). Graduate Theses and Dissertations. 17576.