Effect of hypoxia, injury, and facilitated recovery on reflex impairment (RAMP) in migrating sockeye salmon

Sockeye salmon and Dolly Varden, J Armstrong/UW

A study on the effects of hypoxia and injury associated with gill net fisheries and facilitated recovery in sockeye salmon migrating in the Fraser River showed important results for the use of RAMP to measure sublethal effects of stressors (Nguyen et al. 2014).

The authors state:

“Here, we examined sources of delayed fisheries-related mortality in relation to three known factors influencing postrelease behavior and mortality in fish: physiological exhaustion (stress through air exposure), physical damage (via gill net entanglement), and facilitated recovery (using Fraser boxes). We used sockeye salmon (Oncorhynchus nerka) in the lower Fraser River as a model for this research, given conservation concerns regarding a number of sockeye populations (see Cooke et al. 2012). The study was designed to simulate gill net fisheries because high levels of delayed mortality may have important implications for harvest management in exploited and non-target salmon populations. Our primary objective was to distinguish the relative consequences of physical injury and air exposure stress using an experimental approach coupled with reflex assessments (Davis 2010), physiological sampling (non-lethal blood samples; see Cooke et al. 2005), and telemetry tracking of postrelease migration success (Donaldson et al. 2008). Specifically, we used assessments of reflex impairment and blood physiology to characterize the relative impacts of our experimental treatments. Our secondary objective was to test whether Fraser recovery boxes could reduce delayed mortality and improve migration speed for captured fish exposed to varying degrees of stress and injury.”

The study used experimental stressor treatments: C - Captured-only; A - captured and Air exposed; I - captured and Injured; IA - captured and Injured + Air exposed.

The authors found:

“RAMP is intended to be a rapid, simple, and inexpensive means of assessing fish vitality (Davis 2010). It has also been validated as a predictive measure for delayed mortality in coho salmon caught in beach seine fisheries (Raby et al. 2012). RAMP scores indicated sublethal effects resulting from the A treatment but not from the I treatment. Thus, either RAMP may not capture sublethal effects from injuries, even though fish were clearly stressed (elevated plasma lactate and cortisol), or the I treatment used here was not severe enough to impair reflexes. Further research investigating a large range of physical injury might be useful in resolving this issue. Until this is done, we believe it is unwise to rely solely on a RAMP score for predicting delayed mortality of injured migrating adult sockeye salmon. Previous studies show that RAMP scores are positively correlated with intensity of capture stressors (e.g., Davis 2005, 2007; Davis and Ottmar 2006; Humborstad et al. 2009; Raby et al. 2012), but none considered the potential linkage between RAMP and physical injury. Nonetheless, wounds inflicted in fish during capture, which can be highly variable, are a major source of mortality for discards and escapees (Trumble et al. 2000; Suuronen et al. 2005). In the interim, quantitative indexes for physical injuries in fishes have been developed and used in field settings such as visual assessments (e.g., Trumble et al. 2000; Davis 2005; Baker and Schindler 2009) or use of forensic techniques (e.g., fluorescein) to detect nonmacroscopic injuries (Noga and Udomkusonsri 2002; Davis and Ottmar 2006; Colotelo et al. 2009) and might be useful to include when predicting mortality.”

Clearly, further research and validation is needed to establish relationships between RAMP, injury, vitality, and mortality.  As suggested for fish that show barotrauma symptoms, it may be appropriate to consider the inclusion of scoring for presence or absence of injury types in combination with reflex impairment. The effects of injury on reflex impairment differ among species, as shown for fish (Davis and Ottmar, 2006) and crabs (Stoner et al. 2008). Also, at lower levels of stress in some species, reflex impairment may not occur, indicating that the animals are responding to stress in an adaptive manner. Consideration and inclusion of injury in RAMP is important because of it's potential relationship with delayed onset of disease associated with tissue exposure to pathogens.