Pink salmon (Oncorhynchus gorbuscha)
It is not difficult to distinguish this salmon from other species. Their scales are small and numerous (more than 170 scales in the first horizontal row above the lateral line), it has a remarkably thin caudal peduncle, and big dark dots on the body and caudal fin. The average weight of pink salmon is about 1.5 kg. Most males are bigger than females and can reach over 5 kg. The smallest adult fish are males; they could be as small as 0.35 kg. In the years when pink salmon are very numerous, their average size becomes smaller — it depends on the abundance of food in the ocean.
Pinks are the smallest and the most numerous salmon of the Pacific Ocean. Pink salmon have mixed rations predominately of crustaceans but also some fish. In many river systems of the Russian Far East this salmon makes up over 80% of commercial catches. Only in a few rivers are chum or sockeye salmon more numerous.
The life cycle of this salmon is the simplest. The spawning run into the freshwater begins in June, most fish enter rivers in July, and some enter in August. Most fish spawn in August. A typical pink salmon spawning site is a shallow tailout of a pool or a riffle with a pebble bottom; the water in such areas normally goes down through the pebbles into the alluvial layers. They are quite the engineers. The fish dig pebbles with their tails and make redds — holes or cavities in the bottom. Mostly females do this work. The hole creates a small eddy or backcurrent, which prevents the eggs from being taken away by the current. Into this cavity the female lays eggs; at the same time the male, holding side-by-side with her, discharges his sperm onto the eggs. Then the fish continue digging the bottom a little upstream from the redd, so the current covers the eggs with pebbles.
As a rule, salmon fry hatch in November, but they stay in redds till the spring. During the winter, small fish feed from the yolk sac, which will disappear only in April or May. Simultaneously with the snowmelt, small pink salmon immediately move downstream into the salt water. Migrating little salmon are only about 2.5 cm long. Pink salmon fry have no parrmarks — they are a tiny bright silver fish. Pinks are the only salmonid with no parr stage in the life cycle.
The downstream run of pink salmon coincides with the period of spring flood in a given basin. In freshwater, salmon fry are common food for different birds (terns, gulls, etc.) and freshwater fishes such as char, rainbow trout, Arctic grayling, or coho salmon parr. In the brackish water of the estuaries, lots of salmon fry are eaten by rainbow smelt and lampreys. There is information that in many rivers of the region smelt and lamprey are the most important cause of the fry mortality during the first month of life.
Escaping all of that, the small pink salmon go far from their native shores into the North Pacific, for one whole year — until the following summer.
More than 99.9% of pink salmon entering freshwater are one plus year old; this means they have been in the ocean one full year plus part of the next summer. Less than one fish out of a thousand coming back home is over two years old. This causes total genetic isolation of generations, reproducing in odd and even years — in fact they are different stocks.
From this you can see that the life cycle of pink salmon (the time from spawning till spawning) is two years. This two-year cycle determines the two-year periodicity in the numbers of fish in generations. For example, a huge number of spawning fish in 1981 had formed a mighty generation, which has come back in 1983. A low density of pink salmon on spawning grounds in 1982 determined a very poor “return” in 1984. So, the even-year population at that time was much less numerous than the odd-year population.
After entering the river, pink salmon change their bright silver color to olive-white-green. Dark spawning males differ from silver ones by much longer jaws and especially by their big, flat hump. This hump is the most conspicuous sign of the species. For this reason the second name of this fish in America is “humpback” or “humpy.” The Russian name of the species (gorbusha) also means “something with a hump.” In fact, the scientific Latin name has come from this Russian word.
Pink salmon do not have good homing skills. The self-reproducing unit of this salmon (stock or population) is much bigger than other salmon species — both by the specimens’ number and by the surface of used spawning grounds. Pink salmon stocks normally contain tens of millions of adult specimens. This salmon uses spawning grounds in the main channel of the river, in pools and riffles with current and pebble bottoms. Most pink salmon spawn within 80–120 km from the sea. In years with a good run, the spawning grounds are often overcrowded. When later spawning fish are digging on the bottom, many redds of earlier spawning are destroyed.
The introduction of pink salmon in the Kola Peninsula rivers was justified in the nineteen. The eggs have been brought here from the Russian Far East since 1956. In the first years after the introduction the pink salmon has began to explore new territories. After feeding in the White and Barents Seas, the adult salmon were entering the rivers of the vast territory – from Norway to the Pechora River.
The average size of the pink salmon entering the Murmanskaya Oblast rivers is remaining about the same as in the donor population, but the weight of the fish has increased. The average body weight of fish in the Ola River (Sea of Okhotsk) is 1.1 kg, and on the Kola Peninsula it is about 1.5 kg. This indicates a rapid growth of pink salmon and its good food availability in the White and Barents Seas. The average fecundity of the females has also increased.
The lack of a homing has helped the pink salmon to quickly spread over the North Atlantic and the Arctic Ocean. In the summer, the species is feeding in the waters of the White, Barents, and in the western parts of the Karskoe Sea, and on the Russian territory it is entering the rivers from the Kola Peninsula to the Yamal and Pechora. Pink salmon is also distributing to the west – to Norway, Sweden, Iceland, Great Britain, Spitsbergen and the Faroe Islands. Self-reproducing populations of this salmon have already formed in the rivers of Norway.