The salmon fishery on Sakhalin is of great importance to the local economy and for the livelihoods of many people, including indigenous people in the north of the island. The two most common species involved in the commercial fishery are:
• Chum salmon or dog salmon, (Oncorhynchus keta); and
• Pink or humpback salmon, (O. gorbusha).
Together these two species constitute approximately 95% of the total commercial catch on Sakhalin Island, with cherry salmon (Oncorhynchus masou) and silver (coho) salmon (Oncorhynchus kisutch) making up the rest.
Given the commercial importance of salmonids, significant research, surveying and monitoring has been undertaken over the last 50+ years by Soviet and Russian fisheries agencies and research institutions in order to assess the status of stocks, the distribution and quality of spawning areas and the general biology of these species. On Sakhalin, this effort has focused on pink and chum salmon because of their overwhelming importance as a natural resource to the economy.
As part of the development of baseline data for the Sakhalin II Project, much of the available literature from these studies was compiled (e.g. SakhNIRO 1998, 2000), along with river specific surveys undertaken by SEIC, to inform the river classification process and the development of the crossing strategy.
The following sections provide a brief synopsis of the life cycles of the main
salmon species, as derived from the available data, and information on variations in phases of the cycles where these occur on the island.
3.7.1 Pink Salmon
This is a typical anadromous fish (those that spend most of their lives in the ocean but migrate to fresh water to spawn) with a two-year life cycle, shorter than other salmon species. As a result pink salmon is the smallest of the Pacific salmon, averaging 1.3-1.4 kg at maturity and seldom growing larger than 3-4kg.
Adult pink salmon leave marine waters in the late summer and early autumn (see Figure 3-13), their migration normally coinciding with the summer mean water flow period and ending near the autumn flow increase (see Section 3.2 for details of river hydrology). The timing of the spawning migration varies slightly across the island, with the run starting earlier in the east and south and lasting longer in the south (see Table 3-12).
Table 3-12: Timing of spawning migration of pink salmon (from SakhNIRO 1998)
Once they begin to spawn, male pink salmon develop a prominent hump in front of the dorsal fin. For this reason, pink salmon are commonly called humpback salmon. Males also develop a characteristic elongated snout and large teeth. They usually spawn in-streams that are not fed by lakes and typically their spawning grounds are only a short distance from the ocean.
Spawning sites are characterised by clear water with gravel/pebble substrate and minimal sand content. Water depth at pink salmon spawning grounds varies from 0.2 to 1.6 m and current velocity 0.2-1.1 m/s (SakhNIRO 1999).
Pink salmon redds (depressions in the gravel where eggs are laid) require a continuous water flow (up-welling or hyporheic flow) through the gravels for successful hatching to occur. Approximately 45 to 90 days after spawning, the eggs hatch and the young fish (alevins) remain buried in the substrate,
surviving on their yolk sac. From early-mid April young fish (fry) start to leave the gravel bed and move into the water column and begin migration to the sea.
The migration of pink salmon fry varies across the island with migration occurring earlier in the south (late April to mid-June) than in the north (mid-May to the end of June). Seaward migrating pink salmon fry have an average weight of 230-250 mg and length of 30-35 mm and feed in the ocean for over a year before returning to their natal streams.
Figure 3-13 Salmonid fish spawning periods
The pink salmon stock in the Sakhalin-Kuril Islands region is relatively high in comparison with many other areas in the north Pacific. In the 1990s the average annual catch of pink salmon was 72,500 tonnes, up from 13,000 tonnes in the 1950’s when intensive drift fishing at sea led to large declines in Pacific salmon populations. The current high stock levels are largely due to the intensive cultivation of fish in hatcheries, which has occurred since the 1970s, the natural recovery of stocks and potentially the influence of climate change.
On Sakhalin, the 1980s saw considerable changes in the artificial cultivation of pink salmon with the optimisation of the growing and timing of release of fry.
The renovation of hatcheries has also helped to ensure that stocks and catches of pink salmon have been at very high levels during the 1990s (see Table 3-13).
Table 3-13: Catch of pink salmon in Sakhalin 1989-1999. From SakhNIRO (2000) Year
Embryo and larva in river gravels Fry and alevin freeswimming
Freeswimming juveniles in river (2-5 years) Adults wintering in estuaries and in coastal waters
Pink salmon Spawning
Embryo and larva in river gravels Fry emerge and migrate to sea
Chum salmon Summer spawning
Autumn spawning (larger numbers compared to summer) Embryo and larva in river gravels
Fry emergence Fry migrate to sea
Cherry salmon Spawning
Embryo and larva in river gravels Fry emergence
Free swimming juveniles in river (2-3 years)
Silver (coho) salmon Spawning
Embryo and larva in river gravels Fry emergence
Free swimming in river (2-3 years) Migration to sea (2-3 year old fish)
Sep Oct Nov Dec
May Jun Jul Aug
Jan Feb Mar Apr
1989 7.39 8.5 43.84 7.63 0.43 1990 2.12 0.64 7.62 0.25 0.25
1991 6.21 29.72 42.96 8.6 4.35
1992 3.32 4.8 13.72 1.21 0.04
1993 3.10 3.17 11.34 11.60 1.57
1994 1.63 10.46 28.80 0.67 0.12
1995 2.93 23.10 20.85 12.09 1.43 1996 1.61 3.85 6.22 4.14 0.12 1997 1.57 15.73 27.98 20.18 2.87
1998 2.00 4.76 16.19 5.64 0.06
1999 0.11 15.53 42.66 19.46 2.49
3.7.2 Chum Salmon
The chum salmon is the most widely distributed of the Pacific salmon species, breeding on both sides of the Pacific from San Francisco to Bering strait, and from Providenia Bay to Peter the Great Bay and Tumen-Ula River on the Asian coast. On Sakhalin Island the chum salmon ranks second, in terms of abundance and commercial importance, to the pink salmon.
Although it occurs throughout the rivers of Sakhalin, this species only attains relatively high abundance in the river systems of the northeast, particularly the Tym, and some rivers in the southwest of the island.
Chum salmon spawning runs occur twice a year, in the summer and autumn, with the number and location of migrating fish varying according to the season.
The summer chum salmon spawning run begins during the first half of July, simultaneously with the pink salmon spawning run. The main spawning grounds of summer chum are located in the Longari River, where it dominates above other salmon species, and also in the upper reaches of the Poronai River – from the mouth of the Valza River to its source. The run peaks at the end of July – to the beginning of August (see
Table 3-14). The average length of a spawning chum salmon is 62 cm, weight, 3.3 kg, and gravid females carry approximately 2400 eggs. Summer chum salmon spawn in similar in stream habitats to pink salmon; i.e. clean gravels with hyporheic flow. The downwelling of oxygenated stream water through redds, mixing with the colder temperatures of groundwater, creates an environment ideal for egg development. Leman (1993) reported that 30-40%
of Kamchatka River summer chum salmon spawned at sites influenced by hyporheic flow.
The autumn chum salmon spawning run is larger and more economically important than the summer run and takes place in river basins from the end of August till November (see Table 3-14).
Table 3-14: Timing of spawning migration for chum salmon
The largest autumn runs occur in the Tym River and in the rivers of southwest Sakhalin; however individuals can be found in almost all Sakhalin rivers (SakhNIRO 1999). In the Tym the average size of autumn chum salmon
ranges from 67 to 74 cm, weight ranges from 3.3kg to 4.6kg, and gravid females will carry from 2,900 to 3,100 eggs. In smaller rivers the length and weight of fish averages 52-66 cm and 2.2-4.2 kg respectively. Smaller females can carry 2,600-2,800 eggs.
Autumn spawning chum salmon prefer to spawn in sheltered places in small rivers where the bottom is covered with fine pebbles and gravel. Current velocity at these spawning grounds varies from 0.1 to 0.9 m/s, with fish laying fewer eggs at sites where flow rates are higher (Rukhlov 1982). Water
temperature is also an important factor in spawning site suitability and, while river water temperature during the spawning period usually falls from 8 to 1°C, spawning sites are selected where upwelling waters wash the redds with water at a constant temperature of 3-4°C for the entire winter period (SakhNIRO 2000). In situations where small rivers completely freeze to their base mass mortality of eggs and alevins may occur.
Chum Salmon incubation lasts 120-150 days. Alevins lie motionless in river gravels and absorb their egg yolk. Juveniles (fry) come out of the gravel substrate at the beginning of April and then feed in the area of their spawning grounds for one to two months eating microscopic or near microscopic
plankton, as they grow they start to eat small insects and insect larvae that fall into the water. In May, when they reach 38-40 mm in length they begin
migrating to the sea, where they typically spend a couple of months in
estuarine, tidal and nearshore waters prior to moving out into the open ocean.
Fish will spend 3-4 years feeding in oceanic waters before migrating back to their natal rivers.
As noted above, the commercial importance of this species centres on the autumn migration, when the bulk of fish are caught in coastal waters. The chum salmon stock in the Sakhalin-Kurils region has been low in recent years (1989-2000, see Table 3-15) and the catch of this species over the period has been in the range of 2.2 – 5.8 thousand tonnes. Traps and coastal fishing gear are normally used but at sites where artificial cultivation (hatcheries) takes place, they are caught next to fish screens.
Table 3-15: Catch (tonnes) of chum salmon in Sakhalin 1989-2000 (SakhNIRO, 2000)
This species has a distribution throughout the North Pacific Ocean from central California, Alaska, through the Aleutian Islands, Kamchatka, to Hokkaido, Japan. In Sakhalin, the silver salmon is not numerous and mainly
occurs in the rivers of the northeast of the island and those flowing into Terpeniya Bay. The ecology of the coho salmon and cherry salmon is similar and it is thought that the latter species replaces the coho in the warmer, southern regions.
The silver salmon undertakes it spawning migration later than all of the other Pacific salmon species. The spawning migration can be highly protracted and continue from early September through to mid-December in some seasons. In the in Tym river, the dates of coho spawning migration vary from year to year, but migration typically occurs during the first half of September through to December (Gritsenko 1973).
Spawning sites comprises sections of main river channel and tributaries with upwelling groundwater and with current velocities ranging from 0.08 to 0.7 m/s (SakhNIRO 2000). Females dig out redds up to 70 cm deep with a mean size of 1.8 m x 1.2 m and typically lay about 800-1,100 eggs. After 50-150 days, depending on the water temperature, the alevins hatch from the eggs and remain largely motionless within the gravel bed. The alevins start leaving river gravels and enter the water column at night in late May-mid-June.
During their first year, silver salmon fingerlings normally inhabit cut-off channels and tributaries of the main channel of the spawning river where deeper pools, log jams and banks with overhanging tree roots and debris occur (Tschaplinski and Hartman 1983). These sites are often characterised by low current velocities and fine sediment deposition and in the
spring/summer support the larvae of chironomid midges, which form the main prey items for the young fish. These channels and ponds can often harbour large numbers of fish and are thought to provide refuge during the winter months, as total freezing of the river is less likely and therefore mortality rates may be much lower than in mainstream channels. Over time the fingerlings establish small home ranges, which they aggressively maintain, and also move to deeper waters. The fish actively hunt mayflies, flies, and mosquitoes and during the spawning season of pink and chum salmon they also feed on the eggs released from spawning sites.
The typical silver colouration of the migratory phase of this species develops in fish aged 2-3 years old. In the Tym River, this silver form normally appears in the upper reaches of the river in late May and in the middle reaches by early/mid-July with the majority migrating to the open sea by August.
SakhNIRO (2000) report, using collated survey data, that the bulk (90%) of initial migrants from the river systems of northeast Sakhalin are three-year-old fish. Once at sea, sliver salmon spend a year feeding prior to returning to their natal rivers for spawning.
Silver salmon is not considered to be a main commercial species and is normally taken during fishing for the autumn chum salmon run. However, SakhNIRO (2000) report that in some years significant migrations of this species (e.g. up to 40,000 fish in 1961) on the Tym River, make it of occasional commercial value. Subsequent to 1961, silver salmon numbers fluctuated in the range of 6,000 – 15,000 individuals. No sample taking or monitoring of the migration of this species up the main rivers is currently conducted (SakhNIRO 2000).
3.7.4 Cherry or masou salmon
The cherry salmon occurs in small numbers in Sakhalin rivers and is the first migratory Pacific salmon to appear in coastal waters, normally in mid- to late May in southern Sakhalin. Mass migration upstream occurs during the second half of June – mid-July with spawning occurring in late July – early August,
although this timing varies across the island (SakhNIRO 2000). Before spawning, the cherry salmon spends about two-eight weeks in the river, lingering in holes in the main channel and enters tributaries directly before spawning. An important factor in stimulating the spawning migration is a rise in water level and increase in river current velocity (e.g. as associated with spring-early summer floods), which permits fish to reach their spawning grounds, which are situated largely in the upper reaches of rivers. On the southwestern coast and in Aniva Bay, migration generally occurs mid-May to mid-June, while in northern Sakhalin (middle reaches of Tym river) mass migration occurs from the second half of July into the first half of August and spawning from late July to early September. In the rivers feeding into
Terpeniya Bay (e.g. Poronai River), the migration starts approximately a month earlier than in the Tym and spawning occurs early July to mid-August (Gritsenko 1973).
Normally, cherry salmon spawning areas are isolated from the spawning grounds of other salmon species. In southeastern Sakhalin (in the tributaries of Belaya river - the Naiba river basin) it spawns in areas of pebbles, with rocks and some sand and relatively high current velocities. In northern Sakhalin, spawning grounds are situated in the upper reaches of the main rivers and its tributaries. These sites tend to be small watercourses with an alternation of pools and riffles. Spawning redds are situated in areas where water depth is 10-25 cm, current velocity 0.2 to 0.8 m/s.
Alevin hatching occurs after 35–50 days and by about day 80-85, juveniles start moving into the water column where they begin actively feeding. They leave the redds by the second half of April (later in northern Sakhalin). Shoals of juveniles then disperse into the upper and middle reaches of the rivers where prefer sections of watercourses with a rapid, turbulent current and cover provided by bushes and log jams (SakhGu 2000). During the summer, young fish feed on a varied diet of airborne and aquatic insects as well as the eggs of pink and chum salmon. The duration of the river-dwelling stage of this species appears to be dependent on diet and generally during the second year in freshwater the juvenile population divides into smolts, which undertake migration to the open sea, and parrs that remain in the river for another year.
Some individuals achieve sexual maturity without leaving the rivers. These are dwarf males, which sometimes occur in large numbers in the upper tributaries and which actively take taking part in reproduction. The cherry salmon
migration in northern Sakhalin occurs at an older age (three years) compared with that in many other regions of the range, where the bulk of juveniles leave the rivers during the second year of life (SakhNIRO 2002). Cherry salmon smolts, among which females prevail, spend a large amount of time in the near shore zone where they feed on crustaceans and small fish, before moving offshore into open waters.
From a commercial perspective cherry salmon is of minor importance and is only caught in relatively large amounts in south-western Sakhalin during May-June, in the course of the pink salmon migration. Between the late 1950s and the late 1980, its catch normally did not exceed 5-10 % of the totals caught during the pink salmon migration, although in some years, it constituted up to 40 % in an area from Slepkovsky Cape to the Lopatin Cape (SakhNIRO 2000).
In the course of the pink salmon fishery in other parts of the Island, cherry salmon may be present as a bonus catch in small amounts, which is explained by its lower numbers and the fact that the bulk of fish have already entered the rivers for spawning.