Research Document 1998/90

Decrease in percentage of wild chinook salmon entering the Strait of Georgia in 1996

By Z. Zhang, R.J. Beamish, and B.E. Riddell

Abstract

Otolith microstructure was used to identify hatchery-reared, wild ocean and wild stream-type chinook in their first and second ocean years in the Strait of Georgia. Samples used for the analysis were collected in the early summer, late summer and late fall in 1995, 1996 and 1997. The percentage of wild fish dropped from 71.5% in late summer to 36.8% in the late fall of 1995, and more dramatically from 61.4% in the late summer to 19.2% in the late fall of 1996. The low percentage of wild chinook in 1996/1997 may indicate that wild chinook may be in low abundance in the 1998 and 1999 fisheries. There also was a general decrease in lengths of each rearing type from the 1995/1996 samples to the 1996/1997 samples, suggesting that ocean conditions were possibly less favourable for growth in 1996/1997.

It is difficult to interpret all of the results, as migration behaviour, sample sizes and a general poor understanding of the marine phase of the life history of chinook complicates any interpretation. However, the change in 1996/1997 to a relatively high percentage of hatchery-reared fish is noteworthy. We also suggest that it is time to improve our understanding of the marine stage of the various rearing types that make up the Strait of Georgia chinook fishery.

Complete document (PDF, 828 KB)

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.