User:SpikeToronto/Steelhead

The steelhead trout(Oncorhynchus mykiss) is the sea-run form of the rainbow trout, Oncorhynchus mykiss. Among anglers, the steelhead is legendary: it is the most beautiful and most sought after trout in the coastal rivers of western North America. For a young angler fishing with a dew worm and float, that first steelhead is something that will never be forgotten, and even for the seasoned veteran the adrenaline rush that follows when a steelhead takes a riffle-hitched fly from the surface is indescribable. Once experienced, you are hooked for life, hopelessly addicted, and forever in the thrall of this the most magnificent of all trout.

Distinct From the Rainbow Trout
Steelhead, while of the same species as stream/lake resident rainbow trout (Oncorhynchus mykiss), are evolutionarily/behaviourally distinct by virtue of their anadromous (sea-going) life history. Moreover, even in watersheds where the two forms (resident and anadromous) co-exist, they have become reproductively isolated through differences in spawning time, biology and habitat selection. Finally, they are recognized as "distinct" by North American Fish and Wildlife agencies with the legal authority for their management and conservation. This includes recognition under major legislation like the US Endangered Species Act (http://ecos.fws.gov/speciesProfile/SpeciesReport.do?spcode=E08D), state and provincial legislation, and indeed there are even steelhead-specific angling regulations in the 5 MoE regions in which steelhead are naturally found.

Geographic Distribution
Originally, the geographic distribution of the rainbow trout was restricted to western North America and northeastern Russia (the western side of the Kamchatka Peninsula and some rivers tributary to the Sea of Okhotsk) [1]. During the late 19th and 20th centuries, however, humans expanded the geographic range of rainbow trout and this species now occurs in cool waters on every continent except Antarctica. In North America, the species’ native range extended from the Kuskokwim River, Alaska, to northwestern Mexico (the Rio del Presidio). Geographically, most of the native Mexican rainbow trout populations are isolated from the species’ continuous range, and from one another, and their taxonomic relationships to other rainbow trout populations are still uncertain [1]. For steelhead, the latitudinal range in North America is slightly narrower than the latitudinal range of freshwater-resident rainbow trout. Thus, originally, steelhead occurred in most rivers with direct access to the sea from southern California to the north side of the Alaska Peninsula (Port Moller).

Relationship to the Rainbow Trout
The major difference between steelhead and rainbow trout is that steelhead are anadromous, whereas rainbow trout are freshwater-residents. Anadromy is the technical term for fishes that spawn in fresh water but do most of their growing in the sea and return to fresh water to breed [2]. It is generally accepted that for salmonids (Family Salmonidae*) fresh water is the ancestral environment, and that anadromous forms have evolved from freshwater-residents [3, 4]. Gross (1987) used life-history theory to explain the evolution of anadromy. In an equation Gross summarized the conditions under which anadromy is expected to evolve. Basically, his model argues that if the benefits of migration to and from the sea (in terms of ultimate reproductive success) outweigh the costs of the migrations (energy costs and increased risk of predation), then anadromy will evolve. For most salmonids the key benefit of anadromy is a major increase in growth rate in the sea. Consequently, anadromous individuals grow larger than their freshwater-resident counterparts. Thus anadromous males, and especially females, are at a reproductive advantage relative to freshwater-residents: large males usually dominate small males on the spawning grounds, and large females produce disproportionately more eggs than small females.

Apparently, anadromy evolved independently in rainbow trout in different river systems and even on different continents (northeastern Eurasia and western North America). Thus, steelhead are not a distinct genetic race of rainbow trout; instead, they are a life history form that has evolved many times from genetically different forms of the rainbow trout. There are two distinct lineages of rainbow trout in western North America [1, 5, 6, 7], and Behnke (2002) treats the two lineages as subspecies — the coastal rainbow trout (O. m. irideus) and the interior, or Columbia, redband trout (O. m. gairdneri). Although molecular studies [7, 8] cast doubt on the subspecific status of these lineages, there is no doubt that steelhead have evolved in both lineages. The fact that steelhead have repeatedly evolved from resident rainbow trout does not mean that there are no genetic differences between steelhead and rainbow trout in the same river. Indeed, in many western North American rivers, there is evidence of genetic divergence between resident rainbow and anadromous steelhead [9, 10, 11,12]. This divergence is driven by a phenomenon known as size-assortative mating (i.e., large females tend to pair with large males) and slight differences in breeding seasons between resident rainbow and steelhead [12].

Life Cycle
Oncorhynchus mykiss usually spawns in the spring at water temperature ranging from about 4-10º C; water velocities of 0.30–0.90 m/s, and depths of 0.15–2.5 m [13]. These numbers, however, are dependent on fish size. Thus, large-bodied populations (e.g., steelhead and the Gerrard rainbows of Kootenay Lake) spawn in faster (0.50–0.90 m/s) and deeper (1.75–2.00 m) water over larger substrates than small-bodied populations. Like other salmonines*, female rainbow trout choose the spawning sites and, apparently, prefer sites with subgravel water flow. Females excavate a nest by turning on one side and strongly beating their caudal fin [14]. This digging motion creates a vortex that loosens and lifts gravel that is then moved downstream by the current. The size of gravel moved is variable and depends on female size and water velocity. In the later stages of nest excavation, the female begins to “probe” the nest by erecting the anal fin and sinking down into the deepest part of the nest. This behaviour may be used to test the depth of the nest. Typically, female steelhead pair with a dominant steelhead male but usually the pair is also accompanied by an entourage of smaller satellite and “sneaker” males. Some of these satellite males may be resident rainbows but like many anadromous salmonines, some young steelhead males do not migrate to sea. Instead, they remain in fresh water and reach sexual maturity without migrating. These factors often result in a predominance of males on spawning sites. The dominant male is aggressive and attempts to drive-off other large males, satellites, and sneakers. The dominant male courts the female by “quivering” (a series of high-frequency but low-amplitude body flexures) and “crossing-over” (a side to side movement of the male over the caudal peduncle of the female). As actual spawning approaches, the male positions himself alongside the female and quivers when she is probing the nest. At first, the female continues to lift herself out of the nest. Eventually, however, she “crouches” (stays down) in the nest and the dominant male positions himself alongside the female and quivers. Both sexes arch their backs slightly, gape, tilt their bodies to the outside, and vibrate their tails rapidly. At this point, satellite males and sneakers crowd into the nest, and as the pair release eggs and sperm, these accessory males ejaculate. Since the dominant male is closest to the female, he usually fertilizes most of the eggs; however, there is genetic evidence that, in some years, small males collectively may be more successful reproductively than anadromous steelhead males [15]. After spawning, the female moves slightly upstream and begins gentle digging movements that force the fertilized eggs into interstices at the bottom of the nest. These digging movements gradually become more vigorous and gravel is displaced downstream over the nest, thereby covering the embryos. After a short rest, she moves to the upstream edge of the nest, digs another nest, and deposits more eggs. Each new nest is immediately upstream of the last nest. This sequence is repeated a number of times and, eventually, results in a large redd (a sequential string of nests excavated by a single female).

Steelhead produce about 3,000–14,000 eggs and although the size of fertilized eggs varies among populations, it is usually averages about 5.0 to 7.0 mm. Development rate of the embryos varies with temperature and hatching occurs after about 60 days at 5 degrees (C) and 18 or 19 days at 14 degrees (C) The optimum incubation temperature is around 8–12 degrees (C) and temperatures below 5 degrees (C) and above 13 or 14 degrees (C) produce increased egg mortality and sub-vital fry [16, 17]. Newly hatched embryos (called alevins) have a large yolk sac and are negatively phototactic. They remain in the gravel until most of the yolk sac is absorbed. Depending on temperature, the alevins emerge from the redd about 32 to 42 days after hatching. The newly emerged, free-swimming young are termed fry, and they are about 21-25 mm when they first emerge from the gravel.

Typically, steelhead reach a length of about 100 mm in their first summer of growth. Water temperature, food availability, habitat conditions, population, and interactions with other species all influence the growth rates of fry; however, water temperature appears to be the most pervasive factor influencing growth. Thus, in northern rivers and cold headwater streams fry average about 35–50 mm FL (fork length) by the end of their first growing season, whereas fry in southern rivers often exceed 120 mm FL by late fall. During the stream phase of their life history steelhead fry and juveniles (parr**) defend feeding territories and forage primarily on drifting invertebrates [18]. They normally rear in streams for 1-3 years before undergoing a series of physiological and morphological changes (smolting) that prepare them for life in the sea. Apparently, body size rather than age governs whether or not they will smolt. Thus, smolting usually occurs at, or above, about 160 mm in length [19, 20]. This threshold size is rarely reached until the end of the second (in southern populations) or third (in northern populations) summer of stream life. The seaward migration of smolts occurs in the spring.

Most southern steelhead populations spend 1 or 2 years at sea before maturing and returning to fresh water to spawn, whereas most northern populations mature after 2 or 3 years at sea [21]. Consequently, southern populations spawn for the first time at age 3 or 4, and most northern populations at ages 4 to 6. Unlike Pacific salmon, steelhead are iteroparous (i.e., they can spawn more than once in their lifetime); however, repeat spawning is relatively rare, usually less than 10% (mostly females) live to spawn a second time, and very few spawn more than twice. Thus, the maximum age achieved by steelhead is usually around 8 or 9 years.

Stocks
Like Pacific salmon, steelhead return to their natal or home stream to spawn. This means that individuals are more likely to breed with others from the same river, or the same tributary, in which they were born. One advantage of homing is that it brings the fish back to a proven spawning site — the place where they were hatched! Over generations this fidelity to a natal stream allows natural selection to genetically fine-tune the population to local conditions — not only to the spawning site but also to the entire freshwater phase of their life cycle. Since no two streams are identical, this local fine-tuning leads to measurable genetic differences among populations from different rivers. These genetically fine-tuned populations are called stocks. Typically, the genetic differences among stocks are not absolute but rather relative differences in the frequencies of variant forms (alleles) of the same genes. These allele frequency differences among stocks are reflected in differences in run timing, body size, body shape, and state of maturity upon entry into fresh water. Nonetheless, there is usually some straying among stocks and this results in gene flow (the movement of alleles between populations). Thus, stocks in adjacent rivers often can be grouped together on the basis of shared genetic characteristics. Such groupings of genetically similar populations allow fisheries biologists to distinguish major geographic groups of populations. Thus, in North America, there are at least 18 distinguishable major groups of steelhead [21, 22]. Interestingly, the Kamchatka populations appear to be closest to the steelhead of Alaska and the north coast of British Columbia [7]. Finally, although these major geographic groups share certain characteristics, each of the major groups contains many different stocks with statistically different allele frequencies.

Run Timing
For anglers, one obvious difference among stocks, even within watersheds, is run timing. For example, along the west coast of North America there are steelhead entering one or more rivers in almost every month of the year. In spite of this variation in time of river entry, however, all North American steelhead stocks spawn in the late winter or spring. Traditionally, anglers and fisheries managers refer to steelhead runs that enter fresh water between May and September as summer-runs, while fish that enter fresh water from November to April are called winter-runs. Although summer- and winter-runs occur in both the inland and coastal steelhead lineages [7], most coastal populations are winter-runs and most inland populations are summer-runs. This generalization, however, is not absolute, and there are summer-runs in some coastal rivers. Typically, coastal summer-runs are associated with increasing water temperatures and partial migration barriers that are passable only during high water. Some coastal rivers contain both summer- and winter- runs. In such cases, winter-run fish usually occur in the lower parts of the watershed, whereas summer-run fish surmount partial barriers during spring freshet and move into the upper parts of the watershed. Often, where both summer- and winter-runs occur in the same river, they are similar genetically; however, occasionally there are significant genetic differences between different seasonal runs in the same river [22]. Another difference between summer- and winter-run steelhead is their state of maturation when they enter fresh water. Winter-run steelhead are almost fully mature when they enter a river. Thus, they ascend to their natal stream, and then usually hold in pools downstream of their spawning sites for a short time before they spawn. In contrast, summer-run steelhead return to fresh water with immature gonads, ascend their natal streams, and then hold for seven to ten months before they mature and spawn [23]. In some streams the holding areas are a considerable distance from the actual spawning sites. Consequently, deep pools with cover are an important habitat component for summer-run fish.

Conservation
In North America, wild steelhead are gradually fading from much of their southern range, and from southern California to southern British Columbia most wild populations are in steep decline. There are a multitude of reasons for the declines but directly, or indirectly, all are associated with human activities. Historically, the loss or degradation of freshwater habitats through forest harvesting, land clearing, dams, stream channeling, and water extraction were major factors in the declines. More recently, changes in ocean survival and unnatural concentrations of sea lice in areas with extensive fish farming operations probably have exacerbated these old problems [24]. Thus, although ocean survival seems to be a special problem for southern stocks, interception by commercial fisheries, and the loss and degradation of freshwater rearing habitats are still serious concerns.

One well intentioned, but contentious, human activity is supplementing declining wild stocks with semi-domesticated hatchery fish. Remember, that wild stocks are genetically fine-tuned to conditions in their home stream. In contrast, many hatchery operations use brood stock from some other river; however, even if the local wild population is used to produce hatchery brood stock, some degree of genetic change in hatcheries is inevitable [25]. If these hatchery fish then interbreed with the wild stock, the fitness — fitness is usually defined as the genetic contribution of an individual to succeeding generations relative to the contributions of other individuals — of the local wild stock will decline and eventually the wild stock will be lost. Although hatchery operations in themselves may not cause the extirpation of local stocks, they usually are unlikely to help in their conservation [25]. Still, in some situations (e.g., near large urban centres) where local habitats are so degraded that they will no longer sustain wild stocks, hatcheries may be the only alternative to extirpation.


 * The Family Salmonidae contains three subfamilies: the Salmoninae (trout, salmon, and their kin), the Coregoninae (whitefishes), and the Thymallinae (graylings). The term salmonid refers to any member of the family, whereas the term salmonine refers strictly to members of the subfamily Salmoninae (i.e., trout, salmon and closely related fishes).
 * The juvenile stage of most salmonines is commonly referred to as parr. The Oxford English Dictionary indicates the word first appears in print in the 17th century and was spelled as par, parr, or pare. The derivation of the word is unknown but it is thought to be of Scots origin and probably was first applied to the dark bands (parr marks) on the flanks of juvenile Atlantic salmon and brown trout.