Physiological response of wild rainbow trout to angling: impact of angling duration, fish size, body condition, and temperature

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Abstract

This study evaluated the immediate physiological response of wild rainbow trout to catch-and-release angling in the Alagnak River, southwest Alaska. Information was recorded on individual rainbow trout (n = 415) captured by angling including landing time and the time required to remove hooks (angling duration), the time to anesthetize fish in clove oil and withdraw blood, fish length and weight, and water temperature at capture locations. Plasma cortisol, glucose, ions (sodium, potassium, chloride), and lactate were analyzed to determine the effects of angling duration, fish size, body condition, and temperature. Levels of plasma ions did not change significantly during the observed physiological response and levels of plasma glucose were sometimes influenced by length (2000, 2001), body condition (2001), or temperature (2001). Levels of plasma cortisol and lactate in extended capture fish (angling duration greater than 2 min) were significantly higher than levels in rapid capture fish (angling duration less than 2 min). Rapid capture fish were significantly smaller than extended capture fish, reflecting that fish size influenced landing and handling times. Fish size was related to cortisol and lactate in 2002, which corresponded to the year when larger fish were captured and there were longer landing times. Body condition (i.e., weight/length regression residuals index), was significantly related to lactate in 2000 and 2001. Water temperatures were higher in 2001 (mean temperature ± S.E., 13 ± 2 °C) than in 2002 (10 ± 2 °C), and fish captured in 2001 had significantly higher cortisol and lactate concentrations than fish captured in 2002. The pattern of increase in plasma cortisol and lactate was due to the amount of time fish were angled, and the upper limit of the response was due to water temperature. The results of this study indicate the importance of minimizing the duration of angling in order to reduce the sublethal physiological disturbances in wild fish subjected to catch-and-release angling, particularly during warmer water temperatures. It is also important to note that factors such as fish size may influence both the duration of angling and subsequent physiological response.

Introduction

Fish captured by catch-and-release angling are often subjected to physical exhaustion during the landing process, lethal and non-lethal hooking injuries, and handling and air exposure during the hook removal process. In addition to studies focusing on the relationship between hooking injury and mortality (e.g., Muoneke and Childress, 1994), many studies indicate the importance of the physiological disturbance during the angling process as contributing to mortality (Wydoski et al., 1976, Dotson, 1982). In general, studies documenting the physiological disturbance of wild fish from hooking stress have found minimal mortality (Wydoski et al., 1976, Gustaveson et al., 1991, Tufts et al., 1991, Pankhurst and Dedual, 1994, Booth et al., 1995, Brobbel et al., 1996). However, mortality may increase when fish are angled at warmer water temperatures (Dotson, 1982, Titus and Vanicek, 1988, Wilkie et al., 1996). There are also sublethal effects that may be induced by physiological changes provoked by a stress event including changes in reproductive behavior or function (Campbell et al., 1992, Kieffer et al., 1995, Cooke et al., 2000), disease resistance (Pickering and Pottinger, 1989), growth suppression or decrease in appetite (Gregory and Wood, 1999), post-release predation (Cooke and Philipp, 2004), and other behavioral effects such as changes in social hierarchies and migratory behavior (Lewynsky and Bjornn, 1987, Mäkinen et al., 2000). Physiological disruptions from stress events can be considered cumulative (Barton et al., 1986); therefore, it is possible that fish caught and released several times during a fishing season may be more vulnerable to these types of sublethal effects.

Increases in levels of plasma cortisol after the onset of an acute stress, as well as secondary physiological responses such as hyperglycemia, hyperlacticemia, and ionic disturbance, have been measured to assess the effects of landing time (Wydoski et al., 1976, Gustaveson et al., 1991, Pankhurst and Dedual, 1994, Thorstad et al., 2003). Recent studies have also addressed the effect of hook type on the ease of removal and handling time by comparing various hook types, such as circle versus standard “J” hooks and barbed versus barbless hooks (e.g., Cooke et al., 2001, Cooke et al., 2003), and by measuring the physiological response to air exposure, which commonly occurs during the hook removal process (Ferguson and Tufts, 1992, Cooke et al., 2001). Studies examining the physiological response or hooking mortality of angled wild fish typically hold fish after capture, which can potentially bias study results by the addition of confinement and crowding stress (Wright, 1972) and further injury from confinement (McLaughlin et al., 1997, Cooke and Hogle, 2000). While it is recognized that the most comprehensive type of study to evaluate the effects of catch-and-release fishing in wild fish includes monitoring the behavior and recovery of angled fish after release (Cooke et al., 2002), the associated injuries and potential addition of confinement stress make holding fish after capture undesirable for some fish populations and species.

An extensive amount of research has been conducted to evaluate the magnitude and duration of the physiological response of rainbow trout to exhaustive exercise in hatchery or laboratory environments (Wood et al., 1983, Woodward and Strange, 1987, Pickering and Pottinger, 1989). However, little in situ research has been completed on the physiological response of wild rainbow trout to angling in their natural environment. The Alagnak Wild River, a conservation unit partially located within the Katmai National Park and Preserve of the National Park Service in southwest Alaska, supports a naturally reproducing population of wild rainbow trout (Oncorhynchus mykiss) which are targeted by a popular catch-and-release only sport fishery. Catch-and-release angling regulations were implemented due to concerns over the health of the trout population that is subjected to intense angling pressure, with reports from local guides and anglers of high incidences of hooking scars and decreasing fish size and abundance (Meka et al., 2003). Approximately 30% of Alagnak River rainbow trout have at least one scar purportedly due to previous hooking, indicating that a substantial portion of the population is subjected to multiple angling captures (Meka, 2004). The objectives of this study were to evaluate the initial stress response in Alagnak River rainbow trout in relation to landing time and handling time during the hook removal process, fish size, body condition (residual scores from regression of body mass on body size), and fluctuating seasonal water temperatures, by measuring concentrations of plasma cortisol, glucose, lactate, and ions for fish with combined landing and handling times of less than 2 min (rapid capture) and greater than 2 min (extended capture; adapted from Pankhurst and Dedual, 1994). Results on the initial physiological stress response exhibited by angled rainbow trout will be compared with results from previous investigations on the magnitude and duration of the stress response in rainbow trout.

Section snippets

Materials and methods

Adult rainbow trout were captured by hook-and-line in July and August 2000, and June–August 2000 in the Alagnak River main stem and at Nonvianuk Lake outlet within Katmai National Park and Preserve (Fig. 1). Fish were captured at the outlets of Kukaklek and Nonvianuk lakes in June 2002. There were six methods of fishing used in this study: fly barbed circle hook, fly barbless circle hook, fly barbed J hook, fly barbless J hook, spin barbed J hook, and spin barbless J hook (Meka, 2004). Each

Results

Four hundred and fifteen rainbow trout were sampled during 2000–2002, with sample sizes per physiological parameter varying among years depending on catch success (Table 1). Immediate mortality was observed in seven fish (2%, n = 7/415) that most likely died due to hooking injuries that produced significant bleeding. Levels of plasma sodium (mean, 151.8 ± 2.5 mmol/l, n = 55), potassium (3.29 ± 0.18 mmol/l, n = 52) and chloride (138.8 ± 2.0 mmol/l, n = 55) in 2000 did not vary significantly in relation to

Effects of angling duration

Alagnak River rainbow trout exhibited increases in plasma cortisol and lactate with increases in the time fish were angled and handled during the hook removal process. Capture by angling is one of the most physically demanding forms of exercise stress in fish (Booth et al., 1995) and the subsequent physiological response has been demonstrated to increase with the amount of time fish are on the hook (Wydoski et al., 1976, Pankhurst and Dedual, 1994, Thorstad et al., 2003), sometimes resulting in

Acknowledgements

The authors thank the many individuals who participated in the field aspect of this study, especially: R. Beatty, R. D’Ambruoso, B. Frampton, R. Gray, D. Parker, D. Oswald, P. Richards, D. Wilson, and C. Wall. We thank J. Nielsen and T. Hamon for creating the original study proposal and thorough reviews of this manuscript. We thank J. Margraf and N. Hughes for their guidance and critical reviews of this manuscript. Thank you to A. Moeckel, D. Lerner, and M. Monette for their assistance in the

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