Vitality, survival, and death

Factors that influence discard mortality and survival, Davis 2002

Correlation and association of stressor factors (operational, biological, and environmental) with death are often mistaken for causes of death.

On the subject of causes for death; physiologists, medical researchers, doctors, and veterinarians do not have knowledge about the actual causes for death. We talk about causes for death, but these are circumstantial descriptions and risk factors that may lead to internal animal states that result in death. Important to distinguish between cause and effect and associations or correlations supporting causes for death. For discard mortality we have a series of associations and correlations among fishing factors and mortality. If we understood causes for death then we could directly predict death by measuring those internal causal states and rates. Instead we are left with using indirect measures for circumstances that may lead to and support death. Whole animal state is most directly linked with potential death and survival. Therefore measurement of animal state, independent of context, is essential to identify causes for death. Recent studies of anticipatory physiological regulation may be important clues to the causes for death, given the central role of regulation in maintaining body integrity and survival (Ellis and Del Giudice 2014).

Vitality is an integrated measure of animal state, without confounding influences of other factors; motivation, size, sex, and context. Vitality can then be linked as a master variable with stressor factors (operational, biological, environmental) to predict death and survival.  Of course the occurrence of accidents (predation, crushing and wounding by fishing gears, pollution) limits our ability to predict mortality. But the internal causes for death are still the same in accidental death. 

The reverse side of the coin, what is life and survival? Clearly there are degrees or levels of life, referred to as quality of life. Death appears when these qualities are extinguished. Very hard to define life qualities unless you see vitality. The "welfare" debate is a sidetrack because it fails to address the differences between stress (adaptive and maladaptive) and loss of vitality. Stress is a useful adaptive mechanism for animals until it becomes maladaptive, leading to allostasis.Then loss of vitality becomes more important until vitality is fully impaired and death occurs.