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Chapter 5 -- Anadromous Salmonids and Their Habitats (continued)

Life History Patterns of Anadromous Salmonids (continued)

Chinook

Chinook (Oncorhynchus tshawytscha) are the largest of the Pacific salmon. Unlike steelhead, adult chinook die after making a single spawning migration. After emerging from the redd, chinook fry immediately begin moving downstream. In the Smith River, the downstream migration of chinook fry occurs mostly in spring but also during summer, and occurs even when habitat is not full. Rates of migration vary from zero to twelve kilometers per day. This migration occurs as a wave with the number of migrants increasing in March and April, and peaking in May or June (Reedy 1995). In 1994 in upper Mill Creek, peak outmigration of chinook occurred in early May (Rellim Redwood Company 1994, Table 29). By early summer, juvenile chinook are dispersed downstream into the mainstems and many have arrived at the estuary. In the Smith River system, fry take two weeks to four months to migrate to the estuary. They increase in size to fingerlings during their gradual downstream migration, "growing their way to the ocean." The wave of downstream migration decreases through July and August (Reedy 1995). Chinook fry rely heavily on estuary habitat for rearing. Most young fall chinook remain in the river for three to six months. In the Smith River estuary, the chinook may remain for one week to five months (Reedy 1995) typically remaining for 3 or 4 months (Waldvogel 1985, 1988). Juvenile chinook remain in tributaries and subbasin mainstems into September. Juvenile chinook are present in the estuary from June until the fall rains, and enter the ocean in late summer and fall. A percentage of chinook males return as "jacks" after only one year in the ocean. During fish surveys In Mill Creek from 1980-1987, between 12 and 34% of the observed chinook adults were jacks (Waldvogel 1985, 1988).

The Smith River supports four "races" of chinook spawning: three pulses of fall- and winter-run chinook and one pulse of spring-run chinook. These are probably the same four runs of chinook described in the oral history of the native Tolowa (McCain et al. 1995). Fall and spring runs of chinook differ not only in timing of adult upstream migration but also possibly in juvenile freshwater residence time. In other rivers, it is known that juvenile fall chinook generally spend a shorter time in freshwater than spring chinook juveniles (Meehan and Bjornn 1991). Although fall run chinook are the second most abundant anadromous fishery stock in the Smith River, they are considered a species of special concern (Nehlsen et al. 1991). The pre-spawners of this stock enter the river from September to January, and spawning occurs in three distinct pulses (Waldvogel 1988):

  • Mid-November to mid-December
  • Late December to mid-January
  • Late January to mid-February

Waldvogel (1988) observed that the timing of these pulses did not vary by more than one week when sufficient flows were present. He also estimates estuarine residence for juvenile chinook to be three to four months. Juvenile chinook first appear in the estuary in mid-May and appear to reside there through the summer. Chinook typically reach the sea as subyearling smolts and enter the ocean with the onset of the fall rainy season, normally three to six months after emergence. They typically reside in the ocean for two to five years (Waldvogel 1988). Among fall run chinook, most females return from the ocean at age 4 and males at age 3, 4, and 5.

The spring chinook life history pattern in the Smith River is not well known. It probably involves spending three months to one year rearing in freshwater, migrating to the ocean as subyearling or yearling smolts, returning to freshwater as adults in spring, and spawning in early fall. Spring chinook spawners are generally age 4, 5, or 6. This stock typically returns to the Smith River in mid-April and spawns in October. In contrast to fall chinook, when spring chinook enter the river they are not physiologically ready to spawn. Returning spring run adults reside in the river for the entire summer which makes them vulnerable to predators, illegal harvest, and other disturbances. If they survive through the summer, "springers" are able to spawn somewhat earlier than fall chinook. Spawning periods of fall and spring chinook typically overlap by several weeks. There has not been a large run of spring chinook in the last 50 years (Waldvogel personal communication 1996) and this stock has a "moderate" risk of extinction (Nehlsenet al. 1991). Vulnerable life stages appear to be juvenile over-wintering and adult summer residence.

Spring run chinook are also categorized as "stream-type" while fall chinook are considered "ocean-type". The stream-type designation refers to the longer freshwater residency of spring chinook as juveniles and adults. On the other hand, fall chinook are considered ocean-type because they spend more of their life in the ocean. Spring run, stream-type chinook are more common in northern regions and inland rivers in southern regions. Fall run, ocean-type chinook are more common in southern areas of the Pacific Northwest (Healey 1991). Spring run chinook tend to be abundant in longer river systems with significant snow melt runoff such as the Columbia, Klamath, and Rogue Rivers. In the longer river systems, the spring run life history pattern has a significant advantage over the fall run pattern. When precipitation and stream flow increase in the fall, the spring chinook are already a hundred or more miles upstream. Meanwhile, until stream flow increases, the fall run fish are waiting in or near the ocean. Therefore, the spring run fish can reach spawning areas in the headwaters weeks before the fall run fish. However, in short river systems such as the Smith, spring run fish probably reach spawning areas only a few days earlier than fall run fish. Thus, in short river systems, spring migration typically provides only a marginal advantage and presumably has the disadvantage of higher risk of predation all summer long. By this logic, the Smith River is not expected to support a large population of spring chinook (Waldvogel personal communication 1996).

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