Angling is a popular recreational activity across the globe and a large proportion of fish captured by anglers are released due to voluntary or mandatory catch-and-release practices. The handling associated with hook removal and return of the fish to their environment can cause physical damage to the epidermal layer of the fish which may affect the condition and survival of released fish. This study investigated possible sources of epithelial damage associated with several different handling methods (i.e., landing net types, interactions with different boat floor surfaces, tournament procedures) commonly used in recreational angling for two popular freshwater sport fish species, largemouth bass (Micropterus salmoides) and northern pike (Esox lucius). Epithelial damage was examined using fluorescein, a non-toxic dye, which has been shown to detect latent epithelial damage. Northern pike exhibited extensive epithelial damage after exposure to several of the induced treatments (i.e., interaction with a carpeted surface, knotted nylon net, and line rolling) but relatively little epithelial damage when exposed to others (i.e., knotless rubber nets, smooth boat surfaces, or lip gripping devices). Largemouth bass did not show significant epithelial damage for any of the treatments, with the exception of fish caught in a semi-professional live release tournament. The detection of latent injuries using fluorescein can be an important management tool as it provides visual examples of potential damage that can be caused by different handling methods. Such visualizations can be used to encourage fish-friendly angler behaviour and enhance the survival and welfare of released fish. It can also be used to test new products that are intended to or claim to reduce injury to fish that are to be released. Future research should evaluate the relationship between different levels of epithelial damage and mortality across a range of environmental conditions.
All fish were angled from Lake Opinicon, located in southeastern Ontario, Canada, via standard angling practices as described below, with the exception of tournament captured largemouth bass. Tournament captured largemouth bass were caught from Big Rideau Lake, also located in southeastern Ontario, Canada, as part of a semi-professional live-release bass fishing tournament.
All experiments took place in late June and early July (2008) at water temperatures of 23–26 °C.
To avoid inflicting non-experimental epithelial damage following capture, largemouth bass were landed by firmly grasping the lower lip with the thumb and forefinger unless otherwise stated. Northern pike cannot be handled this way because of their dentition and all were landed using a wetted rubber mesh net unless otherwise stated. Once each fish was successfully landed, it was randomly assigned to a treatment group. The bass captured in the tournament were an exception (see below), as they were sampled just prior to release. To avoid any contamination of our results, fish with existing visible signs of injury at time of capture (e.g., old bird wounds or any injury that was partially healed) were excluded from the study.
In total, 87 northern pike (size range: 375–660 mm) and 72 largemouth bass (size range: 240–484 mm) (Table 1) were used in the study. When each fish was successfully landed, it was randomly assigned into one of the treatment groups listed below recognizing that both species were not exposed to all treatments (summarized in Table 1).