RAMP and bonefish recovery from capture stress

Bonefish are typically captured in a high value capture and release sport fishery.  Released bonefish can be subjected to high rates of predation if predators are present and stress levels are high.  Recovery from capture stress is important for survival and maintenance of bonefish fishery stocks.  Recovery technology including holding bonefish in bags or live wells prior to release has been evaluated by Brownscombe et al. 2013.  They used measurements of reflex impairment (RAMP), locomotory activity, and predation to test recovery from capture stress and survival after release.

Bonefish Key West Flats Fishing

Practical application of RAMP was suggested by Brownscombe et al. 2013. "Bonefish anglers may be able to use RAMP to assess bonefish condition, and make educated decisions on whether to release the fish, or retain it for a short period to facilitate recovery. Likewise, if water temperatures and bonefish impairment scores are very high, responsible anglers can recess until conditions are more favorable."

Here are some excerpts from their paper regarding the validation of RAMP to measure capture stress and predict delayed mortality after release:

"The primary objective of this study was to evaluate the effectiveness of retaining bonefish in recovery bags for reducing short-term locomotory impairment when subjected to angling-related stressors, and whether potential improvements in swimming ability translated to increased survival.

Reflex indicators have recently been deemed effective predictors of mortality (Davis, 2010; Raby et al., 2012), and could be used by anglers to evaluate in which instances fish would benefit from recovery. We predicted that fish retained in recovery bags would exhibit lower reflex impairment, as well as higher locomotory ability and survival than those immediately released.

We validated the use of reflex action mortality predictors (RAMP) (Davis, 2005, 2010) to assess bonefish vitality after 0, 2, 4 and 6 min of air exposure. The 0-minute assessments (n = 30) occurred prior to air exposure on fish from all treatments, while bonefish in the 2-minute treatment (n = 20) were those used in recovery bag experiments (see below), and 4, 6 min treatments (n = 5) were conducted on alternate fish. Five predictors were measured; tail grab, equilibrium (orientation), body flex, head complex, and vestibular-ocular response (VOR). These predictors were chosen because Raby et al. (2012) found that they were strong predictors of coho salmon (Oncorhynchus kisutch) mortality after being caught in commercial nets, and all these predictors can be easily and quickly measured by bonefish anglers. RAMP was assessed in the same manner by Raby et al. (2012). The presence of a tail grab response was assessed by grabbing the fish's tail while it is submerged in water; it was considered impaired if the fish did not attempt to swim away from the handler. Equilibrium was assessed by rolling the fish upside down in water; impairment was indicated when the fish was unable to right itself within 3 s. Body flex was tested by holding the fish by the middle of the body in air; it was considered impaired if the fish made no attempt to struggle free. Head complex was considered impaired if while holding fish in air, a regular pattern of ventilation of the fish's operculum was not observed for at least 5 s. VOR was assessed by rolling the fish back and forth in air; it was considered impaired if its eyes did not roll to maintain the same pitch and track the angler. Higher RAMP scores indicated greater impairment.

Based on the responsiveness of bonefish to the RAMP indices, we used them to evaluate the utility of the recovery bags. After air exposure, bonefish released with accelerometers had similar RAMP scores between immediate release (2.8 ± 0.14) and recovery (2.7 ± 0.14) treatments. However, after retention in a recovery bag for 15 min, all bonefish had RAMP scores of zero (i.e., full recovery).

Our results demonstrate that retaining bonefish in recovery bags for 15 min reduced locomotory impairment upon release during the critical time period where most predation occurs, and this practice has the potential to increase survival after catch-and-release angling. Presumably, retaining bonefish in a live well with ambient oxygen levels (Shultz et al., 2011) would have a similar benefit if an angler had access to a boat.

The five impairment indicators we tested on bonefish provided a gradient in impairment scores that related to the degree of stressor (i.e., 0–6 min of air exposure). RAMP scores have been correlated with stressor duration and mortality for a number of fish species (Davis, 2005, 2007; Davis and Ottmar, 2006; Humborstad et al., 2009; Raby et al., 2012). Indeed, the duration of a stressful event increases the level of physiological disturbance in bonefish (Suski et al., 2007; Donaldson et al., 2008), while longer handling times and air exposure durations result in higher post-release predation rates (Danylchuk et al., 2007a). In this study, bonefish that were equipped with accelerometers exhibited moderate impairment scores after 2 min of air exposure, while no impairment was detected after 15 min of retention in a recovery bag, and fish from the recovery treatment exhibited significantly higher levels of activity upon release. Therefore RAMP scores appear to be a good indication of bonefish vitality. 

The impairment indicators tail grab, equilibrium, and body flex were the first to become impaired in bonefish, and impairment levels within these predictors did not vary with increased stress duration. This was likely because bonefish were all highly impaired at the lowest level of stress we inflicted. Indeed, a previous study found roughly that 50% of bonefish lose equilibrium after angling events (Danylchuk et al., 2007a), while 95% of bonefish lost equilibrium after simulated angling stress (2 min of air exposure) in this study. These three predictors may provide an indication of impairment levels with lesser degrees of stress. Head complex was the next to become impaired at 4 min of air exposure, followed by VOR at 6 min. Therefore head complex and VOR predictors are indicative of very high levels of physiological disturbance in bonefish. This predictor-specific pattern of impairment in bonefish is nearly identical to that of coho salmon (see Raby et al., 2012)."