An assessment of Kitsumkalum River summer chinook, a north coast indicator stock

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Abstract

In 1984, the Kitsumkalum River summer chinook stock was chosen for monitoring under the chinook ‘key-stream’ program, which was initiated in response to objectives set out in the Canada-U.S. Pacific Salmon Treaty. The goal was to use escapement and exploitation information from this stock as an indicator of harvest and exploitation rates on B. C. north coast chinook. To that end, Peterson escapement estimates have been generated annually along with associated biological information. In addition, between 30 and 250 thousand coded-wire-tagged (CWTd) fed-fry have been released annually since 1979 (except 1982) to provide estimates of harvest and exploitation rates.

This paper represents the first comprehensive compilation and examination of the data collected to date. Most information from 1984-1996 has been obtained or derived from data contained in a series of published manuscript reports (see Data Sources). Data for 1997 and 1998 are unpublished. Two weaknesses in the data are apparent. The few CWT recoveries some years, particularly in the escapement, have probably led to exploitation rate estimates of low precision. In addition, low numbers of aging samples some years likely led to under-sampling of some age classes in the escapement. Changes to program operations have recently been made to address these two problems.

Since 1984, escapement of this stock has varied between 5 and 24 thousand fish, with peak abundance occurring from 1987-1990. With the exception of 1987, adult production for this stock has been declining since the early 1980’s which has led to several years of low escapement. Poor fry-to-age-two (FAT) survival of the 1986, and the 1988-1990 broods, contributed to lower escapement in 1991 and 1995, respectively. However, because the CWT fry releases used to estimate FAT survival spend a year in freshwater before entering the ocean (stream-type stock), it is not known whether this high mortality was due to poor freshwater or marine conditions, or a combination of the two. The cause of the poor 1997 escapement, the lowest recorded since the start of this program, is uncertain. FAT survival was only slightly below average for the major contributing broods to that run (brood years 1991 and 1992). However, circumstantial evidence suggests that wild fry may have suffered higher than normal mortality during the egg-to-fry stage, which would not be reflected in FAT survival estimates. While egg-to-fry survival is not currently monitored, high water events during and just after spawning in 1991 and 1992 may have adversely affected egg survival those years. Low flow conditions may have also adversely affected early survival of the 1985 brood.

Stock-recruit analyses indicate that this stock has been exploited at an unsustainable level most years since the start of the monitoring program. While fishing-related mortality has occasionally reached above 60%, mean mortality has been about 45% (excluding natural mortality). However, as a result of recent harvest restrictions on Canadian fisheries, exploitation rates for the most recent completed brood (1992) declined to 39%, and was only 20% for the 1998 calendar year (1992-1995 broods). That year, Canadian fisheries accounted for only 21% of Kitsumkalum chinook harvested. Nevertheless, it is recommended that exploitation of this stock not be increased, at least until brood survival improves.

Assuming exploitation rates remain low in 1999, then based on estimated FAT survival rates for the incomplete 1993 and 1994 broods, and the relatively strong return of five year olds in the 1998 escapement, total 1999 escapement of Kitsumkalum chinook should exceed the 1998 level of 11,065 fish.