Salmon Essay, Research Paper
A number of recent studies shown the fact that many stocks of Pacific salmon are threatened with extinction. For example, the Wilderness Society estimates that naturally reproducing Pacific salmon are mostly extinct or imperiled in 56% of their historic range in the pacific Northwest and California.(Francis, Mantua, Hare) because of this fact, many scientists are trying to determine the areas of risk for North Pacific salmon population and find the ways to reduce the risk in these areas.
May be the most important thing in such a research is to determine the factors we consider to be risky and what risk is.
The word risk can mean more than one thing. It can mean a specific undesirable outcome or some measure of the effect of that bad outcome, such as the loss of some amount of money in gamble. Risk can also mean the probability or chance that this outcome will occur. We use the word risk to mean an economical measure of the amount lost when an undesirable outcome occurs. Understanding the biology of salmon links us to the possible outcomes resulting from our actions. Understandings of the services humans expect to derive from salmon and other animals, links us to what we might lose under various unwanted outcomes.
A very important point is that it is not the risk to salmon stocks that will motivate expensive conservation actions; it is the risk to benefits these salmon populations afford humans. Obvious services are things like inputs to commercial, subsistence, or recreational fisheries. Less obvious services that many humans desire are ecological inputs like providing food for bears and other wildlife or just the esthetic value of their existence. Most people can see how salmon is important to people now and impor
Marine Factors
The complex events and processes that control growth and survival of salmon stocks during marine residence according to Shelton and Koenings include 2 important phases: (1) nearshore rearing in the initial year at sea, and (2) subsequent seasons in more offshore conditions.
The behavior of juvenile salmon upon entering salt water has evolved to optimized growth and survival. As soon as physiologically capable of withstanding full-strength seawater and having attained a needed size, young salmon generally migrate to the northern reaches of the Gulf of Alaska, a region entirely within US waters. There are several exceptions to this rule but the degree of their stability is not very clear. There are several factors that have their influence upon juvenile salmon during this stage:
1. Availability of suitable forage increases many fold as the juveniles proceed north. Forage density is 2 to 3 times greater on the continental shelf, and it increases to roughly 5-fold further north, especially in the highly productive nursery area west of Prince William Sound.
2. Ocean habitats north of the Queen Charlotte Islands exceed the range of certain known predators, such as Pacific hake Merluccuis productus and jack mackerel Trachurus symmetricus, which can prey heavily on juvenile salmon in the south. Predation is considered to be the most significant source of mortality for juvenile salmonids in the marine environment.
3. Water temperatures optimal for growth of juvenile salmon are often exceeded off British Colombia in June and off Southeast Alaska in July and August. Waters that are too warm decrease food-conversion efficiency in salmon. The observed active