One critical issue surrounding river biomonitoring is the minimum amount of sampling distance required to adequately represent the fish assemblage of a reach. Determining adequate sampling distance is important because it affects the estimates of fish assemblage integrity and diversity at the local and regional scales. We sought to answer the sampling distance question by sampling 45 raftable Oregon river reaches for an entire day and then assessing the minimum effort needed to collect 95% of the species obtained in 75% of the reaches sampled. We also resampled 10 reaches to estimate the measurement and sampling period errors. Fish were collected by means of an electrofishing raft, and physical and chemical habitats were sampled to aid in data interpretation. The collected numbers of species were typically only 0–3 species fewer than those predicted for true species richness by simulated species accumulation curves and nonparametric models. We concluded that a sampling distance equal to 85 times the mean wetted channel width produced repeatable results and 95% of the fish species that were usually collected in 100 channel widths or 8 h. Collection of all fish species in a reach was estimated to require an average of 300 channel widths.

The complementary use of otolith chemistry and radiotelemetry demonstrates that bull trout Salvelinus confluentus from the Hoh River, Washington, exhibit considerable life history variability. Adult bull trout lived exclusively in the river, inhabited freshwater for prolonged periods and later became anadromous, or were anadromous and made multiple migrations between freshwater and salt water. Twenty of 40 radio‐tagged juvenile bull trout emigrated to the ocean at lengths ranging from 243 to 360 mm (mean, 287 mm), which is the first published verification of anadromy at this life history stage. Otolith chemistry analyses of 105 bull trout that were incidentally killed in commercial gill‐net fisheries revealed that 85% had migrated from freshwater to the sea at least once and that 75% had migrated multiple times. Anadromous females produced 95% of all individuals examined, but both anadromous and nonanadromous females produced progeny that were anadromous. Age at first seaward migration ranged from 3 to 6 years, 88% first emigrating to sea in their third or fourth growth year. For ages 3 and 4, anadromous individuals were larger than those that remained in freshwater. A wide size range (287–760 mm, 0.2–4.9 kg) of bull trout were killed in commercial fisheries; ages 3–5 composed 88% of the total bycatch. Relocation data from radio‐tagged juvenile and adult bull trout provided important insights on anadromous movements that helped to validate inferences drawn from widely oscillating strontium levels in otolith chemistry. In view of the direct mortality in gill‐net fisheries, an understanding of the age‐specific movements and life history variability of anadromous bull trout will be crucial to future conservation efforts, which should focus on improved monitoring of recreational and commercial bycatch in Pacific salmon fisheries.

No abstract

We conducted an experiment to assess the effects of radio‐ tagging on adult spring Chinook salmon Oncorhynchus tshawytscha during the late stages of their spawning migration. Fish were captured at Roza Dam, Yakima River, Washington (river kilometer 208). Each fish had a radio tag inserted into the stomach via the esophagus and was then transported to a raceway and held for 50 d to assess survival. In the same raceway we also held a control group that was handled but not tagged and a group with externally attached transmitters. Survival of fish with gastrically implanted radio tags was low (10%), while 70% of controls and 90% of fish with externally mounted tags survived to the end of the experiment. Postmortem dissections revealed that after implantation, some radio tags had migrated from the stomach position to the posterior digestive tract and peritoneum. Fish from all treatments exhibited some level of tissue degeneration of the gastrointestinal tract. Gastric implantation should be used with caution, particularly for fish at vulnerable life stages. For spring Chinook salmon in the Columbia River basin, tagging with gastric implants should be conducted early in the freshwater migration to improve survival and reduce tag effects. Received September 30, 2011; accepted June 4, 2012

The use of radiotelemetry revealed that adult bull trout Salvelinus confluentus moved between freshwater and the Pacific Ocean and between watersheds along coastal Washington. Forty-seven of 82 radio-tagged bull trout implanted in the Hoh River and Kalaloch Creek basins were anadromous, and 23 fish were relocated in five different estuaries up to 47 km south of their tagging locations. Anadromous bull trout typically entered the Hoh River from May to July, ascended as far as 78 km upstream to spawning areas by September, and returned to the ocean to overwinter. This is the first study to verify that anadromy is a primary life history form in coastal bull trout. The presence of anadromy and the irregular periods of freshwater, estuarine, and marine residence observed in this study are consistent with observations reported for other Salvelinus species. These results also demonstrate that anadromous bull trout inhabit a diverse range of estuarine, freshwater, and marine habitats. Their affinity to estuaries and their observed temporal movements suggest that bull trout optimize winter refugia and forage opportunities and are susceptible to incidental mortality in gill-net and recreational fisheries directed at other Pacific salmonids. An understanding of the extent of anadromy, sources of mortality, and diversity of habitats occupied by bull trout is informative in the establishment of appropriate conservation and recovery strategies for this species.* Corresponding author: sambrenkman@nps.gov.