The role of social network behavior, swimming performance, and fish size in the determination of angling vulnerability in bluegill

Abstract

An individual’s behavioral and physiological characteristics can have important impacts on fitness, including during interactions with humans. For example, certain traits (metabolic rate, boldness, etc.) have been shown to impact angling vulnerability in fish targeted by recreational anglers. While prior work has focused on boldness behavior and several metrics of metabolic performance, the role of two critical traits, social behavior and swimming performance, have rarely been directly examined. To address this gap, we conducted a study utilizing bluegill Lepomis macrochirus, a highly popular sportfish species found throughout much of North America, to determine the relationship between social behavior, swimming performance, fish size, and angling vulnerability. One hundred and seven bluegill were assessed for social behavior in a laboratory setting, using scoring methods derived from social network analysis. Bluegill were then assessed for swimming performance (critical swimming speed, Ucrit) before being angled in a naturalistic pond setting over nine daily angling sessions. Following angling, a subset of fish were left uncaptured (N = 28), were captured only once (N = 68), or were captured twice (N = 11). Both fish total length and swimming performance were positively linked with vulnerability to initial capture, with fish length also being linked to vulnerability to recapture. In addition to length, social behavior (higher sociability and lower aggression) was positively linked to vulnerability to recapture. Collectively, these results indicate that the drivers of angling vulnerability shift as angled fish populations gain more experience with lures, and that for bluegill, the most vulnerable individuals are likely to be larger and highly social. Individuals within a species show several differences in their behavior and physiology. These differences may have major consequences for fitness, especially in environments impacted by humans. One example of this is freshwater fish targeted by recreational anglers, where individuals with certain behavioral or physiological traits might be more likely to be caught. In this study, we assessed the social behavior, aggression, and swimming performance of bluegill Lepomis macrochirus before angling them in a naturalistic pond setting. We found that larger size and higher swimming performance were linked to vulnerability to initial capture, while length and higher sociability caused fish to be more vulnerable to being caught a second time. Collectively, this means these traits may evolve as a result of selective harvest and also that the drivers of vulnerability may change after fish gain experience with anglers.