User:Gunnar Stark/Coho salmon

Description

Coho salmon from Oregon

During their ocean phase, coho salmon have silver sides and dark-blue backs. During their spawning phase, their jaws and teeth become hooked. After entering fresh water, they develop bright-red sides, bluish-green heads and backs, dark bellies and dark spots on their backs. Sexually maturing fish develop a light-pink or rose shading along the belly, and the males may show a slight arching of the back. Mature adults have a pronounced red skin color with darker backs and spots, with females having darker shades than males. Coho Salmon average 20 to 28 inches (50.8 to 71 cm) and 7 to 11 pounds (3.2 to 5.0 kg), occasionally reaching up to 36 pounds (16 kg). Size can vary depending on age and geographic location. Males tend to be slightly larger than females. Mature Adults also develop a large kype (hooked beak) which is used to attract a mate during spawning, with males having a more pronounced kype than females. Coho salmon kypes are lighter shades than other pacific salmon

Reproduction

Dead salmon, shortly after spawning. Live fish right after spawning will show the same white, rotting flesh shortly before death

Once the mature coho has reached 3-4 years old, it swim up freshwater rivers and streams to spawn (reproduce). Once reaching a suitable location, females "dig" a divot in the riverbed by flexing her tail and loosing rocks from the riverbed. This will be one of many of her nesting sites (sometimes she will create 6-7), called a redd. Females are extremely aggressive during this time towards other females over nesting sites, and towards males until she finishes digging. Males will then fight over females for who gets to mate with the female. Once the female has chosen a mate, usually the largest male, she will lay her eggs onto the redd, while the male simultaneously releases milt (sperm) onto the eggs. Other males will also sneak in to release their milt during this time. Once the female has laid all her eggs, she will cover the eggs with rocks and pebbles using her tail. Salmon have a trait called semelparity, where the adults will then stop eating as their body slowly deteriorates until they die.

Life Cycle

See also: Salmon run

The eggs hatch in the late winter or early spring after six to seven weeks in the redd Once hatched, they remain mostly immobile in the redd during the alevin life stage, which lasts for 6–7 weeks. Alevin no longer have the protective egg shell, or chorion, and rely on their yolk sacs for nourishment during growth. The alevin life stage is very sensitive to aquatic and sedimental contaminants. When the yolk sac is completely resorbed, the alevin leaves the redd. Young coho spend one to two years in their freshwater natal streams, often spending the first winter in off-channel sloughs, before transforming to the smolt stage. Smolts are generally 100–150 mm (3.9–5.9 in) and as their parr marks fade and the adult's characteristic silver scales start to dominate. Smolts migrate to the ocean from late March through July. Some fish leave fresh water in the spring, spend summer in brackish estuarine ponds, and then return to fresh water in the fall. Coho salmon live in salt water for one to three years before returning to spawn. Some precocious males, known as "jacks", return as two-year-old spawners. Spawning males develop kypes, which are strongly hooked snouts and large teeth.