Life History and Habitat Requirements of Upper Skeena River Pacific Salmon

By Ryan McGraw

INTRODUCTION In August of 2004, a class from the University of California at Davis will be traveling to the headwaters of the Skeena River in British Columbia. From the headwaters, we will be rafting roughly 180 miles downstream, stopping at tributaries along the way to conduct various surveys. One of the surveys we are conducting is designed to find out which fish species are present in the upper reaches of the Skeena River watershed. The Skeena River, located in mid-British Columbia, Canada, enters the Pacific Ocean at Chatham Sound of Prince Rupert. It is the main river of the system, with important tributaries such as the Babine River, the Kispiox River, and the Bulkley River. The Skeena River has historically been inhabited by the First Nations, who have long sustained subsistence fisheries on the river and surrounding tributaries. Not until the mid-1800s were there any non-First Nation influences in the basin, when trading posts were established and a small gold rush occurred. As a result of little exploitation, a pristine setting, and readily available diverse habitats, this river system is known to be one of the most productive salmon streams in the world. Five species of Pacific salmon migrate up the Skeena River to find suitable spawning habitat for reproduction, and four species venture into the upper watershed and tributaries. The purpose of this paper is to summarize the life histories and spawning habitat requirements of the four species of Pacific salmon likely to be encountered in the upper reaches of the Skeena River, where we will be traveling. Although Pink salmon (Oncorhynchus gorbuscha) are known to migrate up the Skeena River, it is unlikely that we will encounter any in the area of interest because the migration is too far. Therefore, we will examine the life histories and spawning habitat requirements for chum salmon (Oncorhynchus keta), sockeye salmon (Oncorhynchus nerka), coho salmon (Oncorhynchus kisutch), and chinook salmon (Oncorhynchus tshawytscha).

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GENERAL PACIFIC SALMON LIFE HISTORY Although Pacific salmon life histories do vary according to species, they all follow a general trend. Pacific salmon are anadromous fishes, meaning that they are born in freshwater streams, migrate to the ocean, and then return to their natal freshwater grounds where they will spawn. When they spawn, the female will build a nest, or redd, by turning on her side and furiously tailing at gravel substrate until she digs a hole in the stream bottom. During this time, adult males are both courting the female and fighting amongst themselves for the rights to spawn with the female. Younger, precocious males, termed “Jacks,” do not participate in the courtship or fighting rituals, but rather wait until the mating pair is releasing sperm and eggs and then sneak up and quickly release their sperm into the redd. After the redd has been created, sperm and eggs are simultaneously released (figure 1) and the female covers the redd with gravel. A female will often make multiple redds, and she will actively defend them until she dies, typically within a couple weeks after spawning. Males will attempt to fertilize as many redds as possible until they die. This life strategy of dying after spawning once is called semelparity. After a certain amount of time (determined by species and environmental factors), the embryos hatch, and the juveniles live in the gravel as alevins, obtaining nourishment from a yolk sac. Once the yolk sac is consumed, the alevins emerge from the gravel as fry, and the cycle repeats. Each species of Pacific salmon has its own modification to this general life history.

Figure 1. Two adult chum salmon releasing sperm and eggs into a redd. (Groot and Margolis 1991)

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Chum salmon Chum salmon (figure 2), are the second largest Pacific salmon in size. They will grow up to 109 cm long and 20.8 kg in weight (Groot and Margolis 1991). Upon hatching, chum salmon alevins will live in the gravel bottom of the stream until conditions are suitable for them to begin their seaward journey. After 2-5 months in the gravel, they will work their way up through the gravel and leave the nest. Now called fry, these juvenile chum salmon will typically begin their migration to the sea at the first nightfall. If their nest is near the mouth of the river, they will often complete the journey in one night. If the nest is a considerable distance from the ocean, they will usually travel only by night until they reach the mouth of the river (Scott and Crossman 1973). These fry will then live in the Pacific Ocean for the next few years, feeding voraciously while growing to their maximum potential.

Figure 2. Chum salmon migrating upstream to spawn (NMFS 2004).

Once the chum salmon mature into reproductively capable adults, typically at 3 to 5 years of age (Love 1996), they will prepare to make their spawning run into fresh water. There are usually two runs of chum, with the early run (summer run) spawning in the main stem of the river and the late run (fall run) spawning in the tributaries (Love 1996). Before migrating upriver, chum will aggregate at or near the mouth of their natal river and wait for river runoff to increase before they begin their migration upstream into freshwater. Chum will not typically make extremely long migrations, due in large part to

Page 3 of 13 R.D. McGraw June 14, 2004 the fact that they are poor jumpers and cannot negotiate the barriers that other salmon can. Therefore, they will typically spawn below the first significant barrier in the stream. However, some runs of chum are among the longest of any salmon, such as in the Yukon River, Alaska where chum are known to migrate over 2,000 Km (NWFSC web site). In rivers where extensive inland migration is observed, such as the Yukon River, the gradient is low and few waterfalls or other barriers are present. Once the chum enter the river, they begin to search for habitat suitable for spawning. A female will look for possible nesting sites by pointing her nose to the gravel bottom and slowly swimming upstream until she has found a suitable area. These areas are typically located just upstream of turbulent areas or areas where there is upwelling that increases oxygen flow through the redd. According to Groot and Margolis (1991), chum salmon prefer to spawn in gravel 3.1 cm to 15 cm in diameter. When a redd site has been selected by the female, she will move the gravel by tailing at the bottom until it is sufficiently deep. According to Bruya (1981, in Groot and Margolis 1991), the mean depth of a chum redd is 42.5 cm, with the highest offspring survival rate at depths of 20-50 cm. The female then places herself in a “crouching” position, and the male will move up along side her. The eggs and sperm are released simultaneously and deposited in the redd. The female immediately moves directly upstream of the redd and begins to tail at the gravel again. At first she tails lightly, helping the fertilized eggs to settle in the redd, and then she begins to tail more forcefully, pushing gravel on top of the redd to cover and protect the fertilized eggs. The female will then proceed to make another redd and repeat the same cycle multiple times, while the male either leaves in search of another female already in the process of building a redd or actively defends the spawning female. Juvenile emergence time and survival before hatching is dependent largely on three factors: temperature, dissolved oxygen levels, and percent of fine sediment (Groot and Margolis 1991). Higher temperatures typically allow the eggs to hatch sooner and the alevin to emerge as fry sooner than do cold temperatures. Furthermore, cold temperatures can be a cause of juvenile mortality. Schroeder (1973, as cited in Groot and Margolis 1991) found significantly higher mortality for eggs incubated below 1.5°C.

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Survival is also decreased by low dissolved oxygen levels. Koski (1975) determined that there are significant declines in survival below 2 mg/l of dissolved oxygen. Finally, fine sediments, defined as sediment that is less that 1 mm in diameter, can have a significant impact on survival. Fine sediments, such as sand or silt, can fall between rocks in the redd and suffocate the eggs. They can also slow the water flow through the redd (decreasing oxygen) and physically prevent alevin from hatching and/or moving through the gravel substrate to the surface. Once the embryos hatch, the alevins will emerge from the substrate in the following 2-5 months, and the entire life cycle will start anew. On the Skeena River, we expect to see chum salmon migrating long distances into the upper portions of the main stem. There are few large natural barriers that will impede the migration of spawning adults upriver, and the river is moderately low gradient throughout. Although spawning adults will likely be observed in the main stem of the river, we expect to see the majority of the fall-run chum spawning in tributaries during our study.

Sockeye salmon Sockeye salmon (figure 3), show the most variability of the Pacific salmon life histories. While most individuals are anadromous, sockeye salmon utilize lakes for spawning and rearing habitat, and will often remain in fresh water throughout their lives (then referred to as Kokanee salmon).

Figure 3. An adult male sockeye preparing to spawn. (The Salmon Site 2004)

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Upon emerging as fry, sockeye will either run downstream or upstream into a nursery lake, depending on where they were spawned. Once in the lake, the juveniles will rear for 1-3 years, although some migrate directly to the ocean (Love 1996). After smoltification, or undergoing the physiological processes necessary to inhabit saltwater, the sockeye will migrate out to sea in large schools (Groot and Margolis 1991). According to Foerster in 1968 (as cited by Groot and Margolis 1991) smolt do not start migrating toward the ocean en mass until lake water temperatures rise above 4.4°C. Sockeye will typically spend the next 1-4 years at sea and often make extensive migrations throughout this time (Love 1996; Groot and Margolis 1991). Mature sockeye at sea migrate to their natal river for spawning via a highly tuned orientation system. They first migrate to a convergent point where they meet other sockeye preparing to migrate up the same natal stream. According to Groot and Margolis (1991), these preparatory migrations can be as long as 2,200 km in the ocean. As sockeye begin their upstream migration toward natal spawning grounds, they travel in large schools in the slower water parts of the river, such as eddies and slack-water. Although some sockeye spawn near the mouth of the river, it is not uncommon for sockeye to migrate upstream in excess of 965 Km (Love 1996). Sockeye usually spawn in mainstem streams just below rearing lakes, or in tributary streams just above rearing lakes. However, sockeye will also spawn in lakes, the main stems of river, and tributaries in areas where there is significant upwelling of groundwater. Selection sites of redds tend to be influenced by the type of substrate, usually a course gravel, and water flow through the redd. Depth does not appear to be a crucial factor in redd selection, as sockeye have been observed building nests in extremely shallow water and at depths of 30 meters. According to Groot and Margolis (1991), depths of 3-4 m are a commonly reported average for sockeye redds. Once a redd site has been selected, a female will dig a depression in the substrate, and orient herself in a position to maximize egg deposition in the depression. The male will then move close to the female, and orient his vent near the females. Eggs and sperm are then deposited simultaneously, and the female will cover the redd with gravel within 10-15 seconds of mating. The female will often have multiple redds, which she will actively defend until death, and the male will attempt to mate multiple times with multiple females until death.

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According to Foerster (1968, as cited in Groot and Margolis 1991), alevin will typically hatch 74 to 171 days after fertilization. Bannon (1987, as cited in Groot and Margolis 1991), suggests that yolk absorption occurs between 88 and 444 days after fertilization, at which time the juveniles are considered fry. Upon emergence from the gravel substrate, fry migrate to nursery lakes for 1-3 years before returning to the ocean. Given that sockeye are strong swimmers and are known to make long migrations, it is highly likely that we will observe them in the upper reaches of the Skeena River. Furthermore, there are many tributaries entering the Skeena River that flow out of lakes that could provide excellent nursing habitat for sockeye. We expect to see sockeye spawning at the heads of riffles and at the tails of pools in tributaries as well as in the main stem of the Skeena River.

Coho Salmon Coho salmon (figure 4), are widely distributed and have been documented with lengths from 52.7 cm to 88 cm, and weights ranging from 1.2 kg to 6.8 kg. Size distributions are influenced by such factors as age, sex, and migration timing, and are variable from one population to the next.

Figure 4. Migrating coho salmon (OPR 2004).

Coho exhibit a typical Pacific salmon life history, of anadromy and semelparity. Fry will rear in freshwater streams for just over one year, sometimes up to 3 years depending on stream conditions. Once they have grown to 100-130 mm in length, they

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undergo smoltification and begin their seaward migration (SCFB 2004). This out migration usually coincides with increasing stream discharge in late spring through summer, and occurs most often in a temperature range of 5.0°C to 13.3°C (Groot and Margolis 1991). Many studies have found that, upon entering the ocean, Coho will stay near their natal stream for the first few months (Shapolov and Taft 1954, Milne 1964, Chamberlain 1907, and Godfrey 1965). After a few months, Coho tend to disperse, often staying within the continental shelf. However, Godfrey (1965, as cited in Groot and Margolis 1991) recovered one tagged Coho 2,200 km south of the initial tagging site. Most coho mature after one winter at sea and prepare to make their freshwater migration to spawn. Coho prefer to spawn in coastal streams or tributaries of larger rivers rather than the main stem of the rivers (Scarnecchia and Roper 2000). They form groups, which can be small or large depending on run timing, and move upstream during the day. Coho are strong swimmers and have been observed leaping barriers up to 2 m in height (Love 1996). They make the third longest upstream migration, up to about 240 km, of the Pacific salmon behind sockeye and chinook salmon (Groot and Margolis 1991). Redds are generally located at areas where highly oxygenated water flows through the gravel, such as at the heads of riffles. Females select redd sites based on several factors, including gravel size, water velocity, and water temperature. Some 85% of redds are dug in gravel sizes equal to or smaller than 15 cm in diameter, and typically have a low percent of fine sediment (Groot and Margolis 1991). According to Gribonov (1948), preferred water velocity is usually between 0.30 m/s to 0.55 m/s. The optimum temperature range for incubation, as defined by Davidson and Hutchinson (1938), is 4°C to 11°C. Once a nesting site is selected, the female digs a redd in the same fashion as all Pacific salmon. The male positions himself in such a way that his vent is very near to the females, and eggs and sperm are released simultaneously. The female will immediately cover that nest with gravel, and move on to create additional redds, which she will protect until death. The male, as in other species, will fertilize as many redds as possible from multiple females until death.

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Average incubation time for coho eggs, as defined by Pravdin in 1940 and Berg in 1948 (as cited in Groot and Margolis 1991), is 100-115 days. This time can increase or decrease significantly depending on factors such as temperature and dissolved oxygen. Once hatched, the alevin will stay in the gravel (figure 5) another 14 to 70 days depending on environmental conditions (Love 1996). Once the alevin deplete their yolk sac and transition to fry, the life cycle between generations repeats.

Figure 5. Coho in gravel before emerging as fry (Groot and Margolis 1991).

As Coho are known to be very strong swimmers and historically make long migrations, it is highly likely that they will be present in the upper Skeena River. We expect to observe migrating coho in the main stem of the Skeena, but not spawning here. Spawning coho are most likely to be seen in the tributaries feeding the upper reaches of the Skeena.

Oncorhynchus tshawytscha Chinook salmon (figure 6) are the largest of the pacific salmon, commonly reaching sizes of 45 kg (Groot and Margolis, 1991). They are anadromous and semelparous like all Pacific salmon, but show variation within this life-cycle that other salmon do not. The main difference is a division into two “types,” a “stream-type” and an “ocean-type,” as defined by Groot and Margolis (1991).

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Figure 6. A weary Chinook ready to spawn (PNNL 2004).

Stream-type chinook have long residence times in fresh water, often a year or more, and some precocious males do not run to the sea before spawning (Groot and Margolis 1991). The majority do migrate to the ocean however, and will spend 1-3 years there. Stream-type chinook utilize estuaries, though only for a short period of time, and will disperse along the coast and into open ocean within a couple weeks of migrating downstream (Groot and Margolis 1991). These stream-type chinook typically return to natal streams to spawn between the months of February and July, at an age of 4 to 8 years old. Ocean-type chinook, on the other hand, have very short residence times in fresh water. They usually begin their journey shortly after emerging from the gravel as fry and rear in the estuaries for no more than 60 days (Groot and Margolis 1991). After leaving the estuary for the ocean, they typically spend 2-4 years at sea before returning to natal streams to spawn (Scott and Crossman 1973). Spawning migrations occur in the months of July through September, and spawning chinook range in age from 3 to 4.5 years old. As we will be on the Skeena during the month of August, we will observe ocean-type chinook salmon. According to Scarnecchia and Roper (2000) and Love (1996), chinook spawn in the larger main stems of rivers and large tributaries and do not utilize smaller tributaries and coastal steams like coho salmon. Chinook are very strong swimmers and leapers,

Page 10 of 13 R.D. McGraw June 14, 2004 and are able to make the longest fresh water migrations of any pacific salmon (over 2,700 Km, on the Yukon River) (Scott and Crossman 1973). Nesting sites are selected by the female, depending on factors such as gravel diameter, subgravel flow, and temperature. Redds are typically located at the heads of riffles, where dissolved oxygen is high and subgravel flow is at a maximum (Groot and Margolis 1991). According to Scott and Crossman (1973), optimal temperature range is between 12°C and 14°C. They tend to spawn in deeper gravel than other Pacific salmon, because of their large body size and the large diameter of their eggs (Scott and Crossman 1973). Depth does not appear to be an important factor in nesting site selection, as Chinook have been observed spawning in water as shallow as 5 cm and as deep as 700 cm (Groot and Margolis 1991). Once a nesting site has been selected, the female will dig a redd that averages 3.66 m long and 0.305 m deep in size (Scott and Crossman 1973). Like all Pacific salmon, the male and female will release the sperm and eggs simultaneously into the redd, which the female immediately covers with gravel. The female will make multiple redds, and the male will spawn with multiple females. Both the male and female will die after spawning. Once fertilized, the eggs typically hatch between 32 days and 159 days, depending on temperature and dissolved oxygen (Love 1996). The alevin usually stay in the gravel for another 2-3 weeks based on environmental factors. Upon emerging from the gravel, stream-type and ocean-type Chinook return to the ocean to complete their life cycle. Chinook salmon, the strongest swimmers of the Pacific salmon, will be observed on the upper Skeena River. In particular, we will likely see them spawning in the main stem of the river at the heads of riffles and the tails of pools. We are not likely to observe them in the smaller tributaries as we will the other species of Pacific salmon.

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CONCLUSION Although Pacific salmon lead a general life history of anadromy and semelparity, there is a wide degree of variation in life history for each species. As a result, these fish do not always inhabit the same waters or utilize the same habitat, which is a key consideration for introductions and conservation (figure 7). Future conservation efforts need to examine the specific habitat requirements of the species they are hoping to conserve in order to effectively manage, maintain, or introduce populations of Pacific salmon.

Redd Time in Fresh Time in Gravel Depth Incubation Species water Ocean Size (cm) (cm) Temperature °C Chum 1+ Days 3-5 Years 3.1 - 15 42.5 6 - 8 Sockeye 1-2 Years 1-4 Years < 20 300 - 400 4.4 - 13.3 Coho 1-3 Years 1 Year < 15 10 - 54 4 - 11 Chinook (Stream type) 1 Year 1-3 Years 1 - 6 60 - 700 12 - 14 Chinook (Ocean type) 2-6 Months 2-4 Years 1 - 6 60 - 700 12 - 14

Figure 7. A summary of life history timing and habitat requirements.

The Skeena River basin is unique in that it offers such a wide array of habitat for these species of pacific salmon. As a result, large migrations of all species discussed in this paper are likely to be present as far as the upper reaches of this river. Further studies and surveys on this region will likely be useful in determining additional differences in habitat use among these species of pacific salmon.

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REFERENCES

Bruya, K.J. 1981. The use of different gravel depths to enhance the spawning of chum salmon, Oncorhynchus keta. M.Sc. thesis. University of Washington, Seattle, WA. 86 p.

Foerster, R.E. 1968. The sockeye salmon, Oncorhynchus nerka. Bull. Fish Res. Board Can. 11: 339-350.

Groot, C. and Margolis, L. (1991). Pacific Salmon Life Histories. Vancouver: UBC Press.

Koski, K.V. 1975. The survival and fitness of two stocks of chum salmon (Oncorhynchus keta) from egg deposition to emergence in a controlled-stream environment at Big Beef Creek. Ph.D. thesis. University of Washington, Seattle, WA. 212 p.

Love, M. (1996). Probably More Than You Want To Know About The Fishes Of The Pacific Coast. Santa Barbara: Really Big Press.

National Marine Fisheries Service. 2004. ‘Chum.jpg.’. http://www.nmfs.noaa.gov/prot_res/images/fish/chum.jpg. Date accessed: 5/26/2004.

Office of Protected Resources. 2004. ‘Coho Salmon’. http://www.nmfs.noaa.gov/prot_res/species/fish/coho_salmon.html. Date accessed: 5/26/2004.

Pacific Northwest National Laboratory. 2004. ‘Chinook Salmon’. http://www.pnl.gov/ecology/gallery/Animal/Chin.htm. Date accessed: 5/26/2004.

Scarnecchia, D.L. and Roper, B.B. 2000. Large-scale, differential summer habitat use of three anadromous salmonids in a large river basin in Oregon, USA. Fisheries and Management Ecology, 7 (3): 197.

Schroder, S.L. 1973. Effects of density on the spawning success of chum salmon (Oncorhynchus keta) in an artificial spawning channel. M.Sc. thesis University of Washington, Seattle, WA, 78 p.

Scott, W.B., and Crossman, E.J. 1973. Freshwater Fishes of Canada. Ottawa: Bulletins of the Fisheries Research Board of Canada.

Siskiyou County Farm Bureau Main Page. 2004. ‘Coho Habitat Requirements’. http://www.snowcrest.net/siskfarm/coholife.html. Date accessed: 5/26/2004.

The Salmon Site. 2004. ‘Salmon Pictures’. http://pictures.thesalmon.com.ar/. Date accessed: 5/26/2004.

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