Salmon

The general names salmon and trout represent a number of different fish species that are born in freshwater, migrate to the ocean to mature, and then migrate back to inland freshwaters to reproduce. This migration is called a salmon run. Reproduction consists of a female laying eggs in a streambed’s gravel, the male fertilizing the eggs, and then the development of young fish; the entire process is called spawning.

Salmon populations exist in the Atlantic Ocean, the Pacific Ocean, and some large lakes, but all salmon populations have undergone declines over the past century, possibly due to altered habitat and overfishing. (When fewer salmon migrate in freshwater rivers and streams, bears, river otters, mink, and eagles are threatened because salmon make up a large portion of their diet and protein needs.) Most salmon species are fall spawners, meaning they travel hundreds of miles upstream from the ocean in time to spawn in the fall. The young stay at the spawning site for up to two years before heading to the ocean in the spring. Because each generation of salmon depends on safe, clean, flowing rivers and streams, riparian destruction has been endangering salmon for several years. Salmon runs in the Pacific Northwest have declined to 1–3 percent of the levels they attained when Lewis and Clark visited in the early 1800s.

Ideal riparian habitat for salmon consists of the following factors: year-round flow of cool (below 68°F, 20°C), clear water; streams with pools and riffles; clean and exposed spawning gravel; stable stream banks; dense shade canopy from trees; a supply of small branches fallen from trees; adequate supply of insects to eat; and an abundance of hiding places. Hiding places include shade-covered pools, rocky nooks, overhanging vegetation, and stationary tree branches, leaves, or other plant debris. Riparian destruction affects many of these vital factors. Even riparian habitats that people think are well maintained may be the biggest threat to salmon. Cutting down trees and clearing out overhanging vegetation allows more sunlight to warm the waters where salmon migrate. These warmer waters interfere with the normal physiology of adults and the survival of the young.

Scientists have begun to track Pacific salmon populations to assess the threats to the fish’s survival. To do this they catch salmon with nets at the river’s mouth and gently push a transmitter that holds an antenna into the fish’s stomach. This method has been used in the Oregon Rogue River Spring Chinook Conservation Plan. Since the Rogue River was dammed in the 1970s, yearly runs of chinook salmon fell from 28,000 on average to 9,000 in 1990 and fewer than 3,000 today. The scientist Tom Satterthwaite explained in 2008, “Results from this year will tell us how best to capture and tag fish, and most importantly, the minimum number of fish that need to be tagged to get statistically reliable results. We need to know this number because successful upstream migration of tagged chinook in other rivers varies from 30 percent to 90 percent, and in the Rogue, these fish face added stress from high summer water temperatures.” These studies may help explain the reasons behind salmon losses in the past several decades.

Source of Information : Green Technology Conservation Protecting Our Plant Resources