A study by
Cooke et al. 2013 reviewed the physiological consequences of C&R (catch and release) fishing. They concluded that:
"An underlying tenet of catch-and-release studies that incorporate physiological tools is that a link exists between physiological status and fitness. In reality, finding such relationships has been elusive, with further extensions of individual-level impacts to fish populations even more dubious."
They presented a conceptual scheme for the development of physiological stress in C&R fishes:
Cooke et al. 2013, Figure 1. "Schematic of the general stress response to fisheries capture. The thick black solid line labelled ‘general response’ provides an example of a typical response of a physiological indicator of stress, such as plasma cortisol, to a fisheries capture event. Following the initial response, a negative feedback occurs and recovery is initiated. The stressors connected by a bracket to the general response line exemplify the multiple, interactive and potentially cumulative stressors involved in a fisheries capture event, all of which contribute to the general stress response and are dependent on environmental conditions and the initial condition of the individual fish. The thick black broken line represents a disrupted recovery pattern, where recovery to routine physiological condition does not occur and there are life history consequences. The grey broken line represents an example recovery profile for individuals held in facilitated recovery gear, where the general physiological response is muted and recovery to routine condition is accelerated."
Observations of physiological stress in fishes have measured short-term changes associated with C&R angling. However Cooke et al. 2013 conclude that:
"Beyond the problems noted previously, there is mounting evidence that, taken alone, conventional blood chemistry measures may not be definitive enough to forecast long-term survival following fisheries-related injuries and stressors (see Skomal & Bernal 2010; Pankhurst 2011; Renshaw et al. 2012), although another possible explanation is that researchers are failing to use the appropriate physiological indices (Renshaw et al. 2012; see section below on use of a limited set of metrics). Although now technically feasible to attempt to link physiological condition to fate, it has thus far failed to enhance C&R science with respect to long-term outcomes. However, with shorter-term outcomes (e.g. behavioural endpoints) and when used for conducting mechanistic laboratory studies to complement field studies, physiology has yielded valuable insight."
Prediction of delayed mortality has been successful with observations of reflex impairment (RAMP) in fishes from C&R fisheries. Cooke et al. 2013 note:
“Unlike traditional physiological tools, there has been considerable success in using a simple reflex impairment index [reflex assessment mortality predictors (RAMP) score] to predict delayed mortality for fish released from commercial fishing gears and subsequently monitored in large tanks (summarised in Davis 2010) or released into the wild with telemetry tags (Raby et al. 2012). The success of RAMP for predicting mortality is likely attributed to its holistic nature: underlying physiological impairments are integrated into whole-animal responses that can easily be assessed in a quantitative way. In the context of C&R, Campbell et al. (2010) developed a condition index for red snapper, Lutjanus campechanus Poey, that combined reflex impairment with indicators of barotrauma and was associated with immediate mortality and proxy indicators of post-release predation risk (post-release mortality was not assessed directly).
Additional research is needed to develop predictors of fate in C&R science and the logical focus should be on fisheries for which significant mortality is observed that seems to be independent of physical injury (e.g. deep hooking). Reflex assessment mortality predictors will not replace traditional physiological metrics, but it is a valid and inexpensive complement and could be incorporated into any study of C&R mortality even if the project team has little or no experience in physiological research.”
In communicating the results of C&R fishing to management and fishing communities, Cooke et al. 2013 found:
“Although physiological tools can play an important role in understanding and mitigating the sublethal consequences of C&R on fishes (Cooke et al. 2002; Wikelski & Cooke 2006; Arlinghaus et al. 2007a), it is important that the findings of physiological studies be interpreted correctly and used appropriately. It is difficult to translate the physiological results of C&R research into best practices given the limitations listed previously. Where investigators have identified physiological consequences of C&R, findings must therefore be interpreted cautiously with results not extrapolated beyond the boundaries of their study design. For instance, Wedemeyer and Wydoski (2008) examined the physiological response of some economically important salmonids to C&R fishing, and they interpreted many significant trends between angling duration and blood parameters as ‘transient’ effects, ‘generally mild’ and of ‘little physiological consequence’, without fully exploring a broader suite of metrics (e.g. cortisol) shown to be associated with angling stress in other recreational fishes. Moreover, their study was restricted to moderate water temperatures, like many C&R studies (reviewed in Gale et al. in press). The results of their study were then noticed by the angling community, which further extrapolated the findings on angling web sites, message boards and blogs, inferring that C&R in general has negligible consequences on trout and without considering how factors not explored in their study such as water temperature could alter the outcome for the fish. Consequently and likely quite unintentionally on the part of researchers, peer-to-peer communication pathways common within the recreational angling community could foster a shift of the social norm about the potential conservation value of C&R. When management implications arising from C&R physiological studies are presented in the peer reviewed literature, authors should thus provide appropriate caveats, context and draw conclusions carefully. Although the interpretation of physiological data can be subjective, it is suggested that such findings always be viewed in the context of the broader stress response and recovery probable for a given species/population (Fig. 1).”
Cooke et al. have summarized important steps to take for minimizing mortality in C&R fisheries in an effort to standardize these protocols according to scientific principles (see Arlinghaus et al. 2007, Pelletier et al. 2007):
"General guidelines for catch-and-release recreational angling to conserve fishery resources:
Minimize angling duration
The duration of the angling event increases the physiological disturbance from which the fish has to recover. Angling results in a combination of aerobic and anaerobic exercise that causes a number of physiological changes such as the depletion of energy reserves, accumulation of lactate, and alterations in acid/base status. Studies have shown that these physiological disturbances are generally more severe with increasing angling duration. In addition, the length of time required for physiological variables to return to resting levels tends to increase with angling duration.Therefore, anglers should try to land fish as quickly as possible to minimize the duration of the exercise and the related physiological disturbance.There are techniques for achieving shorter angling durations, such as choosing equipment that matches the size of fish that are expected to be encountered.
Minimize air exposure
Air exposure is harmful to fish. Air exposure occurs upon capture when a fish is removed from the hook, weighed, measured and/or held for photo opportunities. When a fish is exposed to air, the gill lamellae collapse causing the gill filaments to stick together. This has several negative physiological implications. It can cause severe anoxia. Fish that are exposed to air typically experience greater acid/base disturbance (fluctuation of pH in the blood) than those which are not. When fish are exposed to air for a significant length of time, they require a much longer time to return to their normal state. Furthermore, extended air exposure (beyond a species-specific timing threshold) can eventually result in permanent tissue damage or death. Although different fish species vary in their tolerance to air exposure, it is recommended to minimize the duration of the air exposure whenever possible.
Avoid angling in extreme water temperatures
Most fish are ectothermic (they cannot regulate their own body temperature) so the environment regulates their temperature. Any changes in the ambient water temperature can have a significant impact on their cellular function, protein structure, enzyme activity, diffusion rates and metabolism. In addition, the amount of dissolved oxygen in water is lower at higher water temperatures. Angling stressors tend to be magnified at higher water temperatures as reflected in strong relationships between water temperature and mortality for several species. On the other hand, extremely cold temperatures likely also have detrimental effects, although this has been poorly studied to date. Although individual species exhibit different thermal tolerances, catch-and-release angling has the potential to be harmful at extreme water temperatures. In some jurisdictions, there are restrictions on angling when water temperatures exceed some threshold. Since water temperature exerts control over almost all physiological processes in fish, extreme water temperatures are undoubtedly conditions in which fishes are most vulnerable and where angling should be avoided.
Use barbless hooks and artificial lures/flies
Hooks are used to capture fishes. Therefore, hook design is an important element to consider when attempting to reduce hooking related injuries and mortality. Hooks with barbs can lead to greater injury than barbless hooks and even contribute to mortality, although the literature accounts are disparate. However, barbless hooks can minimize the amount of harm caused by reducing tissue damage at the point of hook entry and by reducing the amount of time required to remove a hook. Since there is no barb, the hook can easily be removed. Some studies show that circle hook can be an effective tool in catch-and-release fisheries, when used properly under certain conditions [see section on circle hooks]. The type of bait used is another important factor in fish injuries. Live/organic baits (e.g., worms) used on hooks can be ingested and the hook becomes lodged into the viscera. This makes it hard to remove the hook and it will likely cause damage to the vital organs/tissue during the process. Artificial lures or flies do not get ingested as much so there is minimal damage to the vital organs/tissues from the hook(s). Barbless hooks and artificial lures/flies can greatly reduce handling time, hooking injuries and the likelihood of mortality.
Refrain from angling fish during reproductive period
The reproductive period is the time during which fish attept to produce off-spring and is thus critical for sustaining fish populations. Angling fish during their reproductive period canl reduce the number of off-spring that could contribute the population. Some species, like the largemouth bass, provide parental care and protection for their off-spring. If this dad is removed from the nest, even for a brief moment, its off-spring become extremely vulnerable to predators. Thus, angling immediately prior to or during the reproductive period could affect fitness and should be avoided."
