Mattole Salmon Group

Mattole Salmon Group
April 24, 2007


The 11th Annual Summer Steelhead Dive in the Mattole River watershed was held on July 14-15, 2006. Forty-seven local fish enthusiasts donned their wetsuits and snorkeled throughout 24 reaches of the Mattole River to find the elusive summer steelhead. Thank you to divers from the MSG, MRC, Mattole community, USFWS, NMFS, Nick's Interns, and Americorps who contributed their time and expertise to make the 2006 dives a success.

Adult Summer Steelhead enter the river in spring, before the river mouth closes. They oversummer instream, then spawn during the ensuing rainy season. "Half-pounders" are immature steelhead that enter the river in the spring, then feed instream until the following winter. They migrate to the ocean again before returning to the river to spawn.

Steelhead per mile observed

Nineteen adult summer steelhead (>16 inches long) and thirty-eight "half-pounders" (12-to 16-inch steelhead) were observed in 64.85 miles surveyed in 2006. Most summer steelhead were observed in characteristic oversummering habitat: deep pools, under large wood or riparian cover, and in thermal refugia.

Direct dive observation of adult steelhead (>16"), "half-pounders" (12"-16"),and miles surveyed in the summer months, 1996-2006.

Eleven years of summer steelhead dives indicate that temperature and physical stream characteristics influence summer steelhead distribution in the Mattole. Upstream of McKee Creek (River Mile 42.8), few summer steelhead are observed, likely due to lack of deep pool habitat as well as low flow during recent summers. Most summer steelhead have been observed from McKee Creek (RM 52.8) to Dry Creek (RM 30.4). Cool summer water temperatures here and presence of deep pools represent the best oversummering habitat for adult steelhead in the Mattole.

Less frequently, summer steelhead are observed in cool, favorable microsites in the lower river. Summer steelhead also oversummer in Honeydew and Bear Creeks, the two largest tributaries to the Mattole.

Steelhead counts by MSG divers during the Summer Steelhead Dive have shown a noticeable decline in recent years. Over the past four years, MSG divers observed less steelhead per mile (both adults and "half-pounders") than in the seven years prior. From 1996-2002, the average numbers of adults observed per mile was 0.56; in comparison, an average of 0.29 adults per mile were seen during the 2003-2006 survey years. "Half-pounder" sightings per mile have shown an even more severe decline; an average of 1.57 "half-pounders" per mile were seen in 1996-2002, while an average of 0.63 "half-pounder" sightings per mile occurred in 2003-2006.

For more information:
707/629-3433 or
www.mattolesalmon.org


This article can be found online at www.treesfoundation.org/publications/article-275

Forest & River News is produced by Trees Foundation. For more information contact:
Mattole Salmon Group
PO Box 188
Petrolia, CA 95558
Email: evenson@igc.org
Phone: (707) 629-3670