Summary
Release of fish captured by recreational anglers is a common practice due to angler conservation ethics or compliance with fisheries regulations. As such, there is a need to understand the factors that influence mortality and sub-lethal impairments to ensure that catch-and-release angling is a sustainable practice. Longer angling times generally contribute to increased stress and mortality in fish such that reducing these times putatively reduces stress and improves survival. However, the relative importance of fight intensity (rather than simply duration) on fish condition is poorly understood. The objective of this research was to examine the effects of fight intensity on physiological stress and reflex impairment of largemouth bass (Micropterus salmoides). The largemouth bass were angled using conventional recreational fishing gear in May (water temperature ∼12°C) and June (∼22°C) of 2014 in Lake Opinicon, Ontario, Canada. Fight intensity was quantified using tri-axial accelerometer loggers mounted on the tips of fishing rods. Upon capture, reflex impairment measures were assessed, and fish were held for 1 h prior to blood sampling for measurement of physiological stress (blood glucose and lactate concentrations and pH). Physiological stress values showed a negative trend with fight duration and total fight intensity, but a positive trend with average fight intensity. Water temperature emerged as the most important predictor of the stress response in largemouth bass, while fight duration and intensity were not strong predictors. Reflex impairment was minimal, but higher reflex impairment scores were associated with elevated blood glucose. Overall, the findings of this study suggest that angling for largemouth bass at colder temperatures (<15°C) causes greater physiological stress than at warmer temperatures (>20°C). Based on our findings, we conclude that fight intensity is likely not to be a major driver of physiological stress in this species using typical largemouth bass angling gear, owing to the relatively short fight times (i.e. <2 min).
Methodology
Study site and angling experiments
This study was conducted from 1 to 7 May and from 16 to 18 June 2014 in Lake Opinicon, a mesotrophic lake located in eastern Ontario, Canada (44°33′56.0″ N, 76°19′23.6″ W). Angling was conducted using 2-m-long, medium-strength fishing rods and reels equipped with 6.8 kg break-strength, braided Dacron® fishing line, which is typical gear for anglers targeting this species. Terminal tackle included a 1/0 circle hook, baited with a 15 cm wacky-rigged plastic worm that was fished passively. In order to quantify fish fight intensity, tri-axial accelerometer loggers (model X8M, 500 mA h battery, 15 g in air, 25 Hz recording frequency; Gulf Coast Data Concepts) were mounted tightly (with electrical tape) on the fishing rods between the second and third line guides, 20 cm from the tip of the rod (Fig. 1). Accelerometer loggers have been widely used over the past several years to study the energetics and behaviour of free-living animals (for review, see Brown et al., 2013). However, the only application in recreational fisheries that we are aware of involved attaching accelerometers to fish to assess post-release behaviour (i.e. Brownscombe et al., 2013).
Reflex indicators
Once placed in the holding containers, fish were assessed for reflex impairment using methods developed under the codification of reflex action mortality predictors (RAMP; Davis, 2010). Five RAMP parameters were assessed, as follows: equilibrium, tail grab, head complex, vestibular–ocular response (VOR) and body flex. Equilibrium was assessed by flipping the fish upside down in water; a positive response was indicated by the fish righting itself within 3 s. Tail grab was measured by grabbing the fish's caudal peduncle while in water; a positive response was indicated by an attempt to escape from the handler. Head complex was assessed by observing the fish's opercula; regular opercular beats indicated a positive response. The VOR was measured by rolling the fish side to side in the longitudinal axis; a positive response was indicated by the fish's eyes moving back and forth, tracking level. Body flex was assessed by lifting the fish into the air by the centre of the body; a positive response was indicated by the flexing or movement of the body. These predictors were used because they are consistent indicators of vitality in teleost fishes (Davis, 2010; Raby et al., 2012; Brownscombe et al., 2013, 2014). Each indicator was scored as 1 = impaired and 0 = unimpaired, and overall RAMP scores were calculated as the proportion of indicators impaired.