Philosophy of using RAMP to measure vitality, survival, and mortality of animals

Blue sharks and food, WASC

Mortality can occur over varying time frames after an animal is exposed to potentially lethal stressors. The problem of mortality prediction is made more difficult by animal mobility, as animals can become hidden from observation, especially over longer time frames. Then indicator measures must be used to predict cryptic delayed mortality. What is an effective indicator for predicting mortality? Do we observe the animal immediately after stress induction and before leaving our presence, or do we observe the conditions in which the animal was stressed? 

A common approach to predicting delayed animal mortality is to observe the conditions in which stress is induced and use this information as an indicator for mortality.  Animals are experimentally exposed to important stressors and their combinations in a matrix of interactions. Then animals are sampled for mortality after holding them captive for short periods or tagging, releasing, and recapturing or using biotelemetry over longer time frames. Mortality, and its inverse, survival are then modeled from sampled combinations of risk factors. Since there are relatively unlimited sets of risk factors and their interactions, indicator models for mortality based on stressors often will not give realistic estimates or not include important conditions for stress induction.

Alternatively, animal impairment can be observed as an indicator for delayed mortality after exposure to risk factors. Reflex impairment occurs immediately in an animal when it’s neural, muscular, or organ systems are stressed. Summing presence or absence of several reflex actions calculates an index called RAMP (reflex action mortality predictor) which is a direct measure of reflex impairment and vitality. Correlation of RAMP with immediate and delayed mortality make it an indicator for mortality and survival. With RAMP, the approach of predicting mortality is based on direct observations of animal vitality. The animal continually integrates all the effects of experienced risk factors as reflex impairment and communicates it’s health state, vitality, and fitness through the language of RAMP. Other types of animal impairment that have been tested as potential indicators for mortality include physiological variables (cortisol, glucose, lactate, and electrolytes) and injury.  However these measures are not consistently correlated with delayed mortality.

In an effort to ameliorate mortality risk factors, a hybrid approach can be used for predicting cryptic delayed mortality that conserves and integrates information. Instead of asking the question “Does the animal die?” we can ask “When, where, and under what conditions does the animal die?” Animals are observed in experimentally controlled conditions of mortality risk (Davis 2002, Suuronen 2005). Then initial stressor conditions are sampled, as well as time courses for animal impairment and delayed mortality. Relationships between stressor factors, animal impairment, and delayed mortality can be identified and modeled. The resulting knowledge base can be used to test hypotheses about importance of mortality risk factors and efficacy of predicting cryptic delayed mortality using animal impairment as an indicator. Previous research has shown that reflex impairment measured as RAMP is a powerful predictor for cryptic delayed mortality (Davis 2010). After validation, RAMP can be used to test the effects of experimental or natural changes in mortality risk factors such as design of fishing gears, aquaculture rearing conditions, aquarium trade, pollution exposure, climate change, and other potentially risky situations.

Trawl bycatch reduction device, FRDC

The problem of using indicators to predict cryptic delayed mortality is simplified by shifting from modeling mortality in potentially unlimited sets of risk factors to direct, real time measurement of animal impairment and prediction of delayed mortality. This shift in focus to reflex impairment allows for real time testing of animal fitness in systems of interest and is a cheaper, more efficient use of limited research resources than using risk factor indicators for mortality prediction.

High discard survival merits exemptions to European Union ban on fishery discards

Atlantic cod, NOAA

The introduction of the obligation to land all catches (eliminate discards) in the recent reform of the Common Fisheries Policy (CFP) represents a fundamental shift in the management approach to European Union fisheries from regulation of landings to regulation of catch. Research has shown that not all discards die. In some cases, the proportion of discarded fish that survive can be substantial, depending on the species, fishery and other technical, biological and environmental factors. If these surviving animals are discarded instead of landed, they can contribute to future stock recruitment.

Article 15 paragraph 4(b) of the CFP regulation allows for the possibility of exemptions from the landing obligation for species for which "scientific evidence demonstrates high survival rates". Taking the first element of this "scientific evidence"- it is important that managers have guidance on protocols and methodologies that should be followed in order to ensure the results of such experiments are scientifically robust. Presently there are no such internationally agreed guidelines. EWG 13-16 has provided guidance on best practice to undertake survival studies. In this regard EWG 13-16 has identified three methodologies for conducting survival experiments i.e. captive observation experiments, vitality/reflex assessments, and tagging/biotelemetry experiments.

Captive observation experiments involve holding animals that have been captured after exposure to fishery stressors. Holding can be in tanks or net pens while short-term survival is observed.  Holding periods typically range from 3-21 days until mortality associated with experimental fishery stressors has abated. Discard survival rates in specific fisheries conditions are then modeled using data from holding experiments. Davis (2002) reviewed an array of potential explanatory variables for discard survival, which can be classified into three broad categories: biological (e.g. species, size, age, physical condition, occurrence of injuries), environmental (e.g. changes in: temperature, depth, light conditions) and operational (e.g. fishing method, catch size & composition, handling practices on deck, time exposed to air). The complexity and interactions of explanatory variables for discard survival could present a problem to fisheries managers because instead of simply asking “Can we discard this species?” it may be necessary to ask “when, where, and under what conditions can we discard this species?” A potentially unlimited variety of fishery condition combinations would need to be modeled for determining discard survival.

Effects of fish size, fishing gear type, and temperature on sablefish mortality, NOAA

Tagging/biotelemetry experiments are similar to captive observation experiments in that animals are captured after exposure to fishery stressors. Then animals are tagged, released, and monitored for survival either by recapture or by biotelemetry.  Survival observations can be made over periods of weeks, months, and years. In addition to the complications of fishery stressor variable interactions, these experiments have the additional complications of including sources of mortality associated with predation and food and habitat availability that are independent of the effects of the initial capture stressors.    

Vitality/reflex assessments are real time in situ determinations of animal vitality and health.  The animal integrates the effects of fishery stressors and lives or dies according to it’s level of vitality impairment. Davis (2010) has shown that calculation of an index for reflex impairment (RAMP, reflex action mortality predictor) based on summing observations of several reflex actions is a robust, quantitative measure of animal vitality that can include the effects of fishery stressors on animal survival. When animals are exposed to fishery stressors and captured, as described above for captive observation experiments and tagging/biotelemetry experiments, they exhibit various degrees of stress and impairment of vitality which can be associated with mortality and survival.  Correlation of RAMP scores with mortality or survival levels observed in captive observation experiments or tagging/biotelemetry experiments makes RAMP a proxy for mortality or survival (Raby et al. 2012). Further RAMP validation can be made by testing with additional holding or tagging experiments in fisheries of interest.

RAMP curves for Atlantic cod, Humborstad et al. 2009

Once validated, RAMP assessments could be used to identify species in a fishery that may have the potential to survive discarding, and that merit an exemption to the Landings Obligation. Where a large majority of individuals of a particular species demonstrated consistently high RAMP scores, and there were very few examples of immediate mortality, this would indicate that species may warrant further investigation to demonstrate its potential for short & long term survival, post-discarding. Using this approach, a large number of species could be assessed (quickly & inexpensively), over a wide range of conditions and for a variety of boats (& discarding practices) throughout the fishery. 

At the same time, continued development of innovative fishing gears and fisher avoidance of high bycatch areas and times can help reduce capture of unwanted species. RAMP can be used to evaluate the survival of animals that are impacted by fishing gears and escape before landing on fishing vessels. The banning of discarding will make the evaluation of mortality rates for animals escaping from fishing gears especially important. "Out of sight and out of mind" will not be a viable strategy with regards to evaluating fishing mortality for gears engineered to enhance escape of bycatch species.