Variation in use of the Klamath River estuary by juvenile chinook salmon

Use of the Klamath River estuary by young-of-the-year (YOY) chinook salmon, Oncorhynchus tshawytscha, varied between high (1993) and low (1994) river flow years. From May to September, mean flows in the Klamath River were 400 m(3)/s in 1993 and 109 m(3)/s in 1994. In the lower Klamath River estuary, YOY chinook salmon catch-per-unit-effort was higher during 1994 than during 1993. Also, weekly mean fork lengths of YOY chinook salmon in the Klamath River estuary after mid-duly were significantly smaller in 1994 than 1993. These observations suggest that more estuarine rearing by YOY chinook salmon took place in the low flow year of 1994 than the high flow year of 1993, potentially because of better up-river rearing conditions in 1993. in 1993, most YOY chinook salmon reached the estuary at a size large enough to immediately enter the ocean. In 1994, many juvenile chinook salmon may have been forced downstream by increasing water temperatures before they reached optimal size for ocean entry. Thus, they were more likely to rear in the estuary.