No abstract

This study evaluated estuarine habitat use, life-history composition, growth and survival of four successive broods of coho salmon Oncoryhnchus kisutch in Salmon River, Oregon, U.S.A. Subyearling and yearling O. kisutch used restored and natural estuarine wetlands, particularly in the spring and winter. Stream-reared yearling smolts spent an average of 2 weeks in the estuary growing rapidly before entering the ocean. Emergent fry also entered the estuary in the spring, and some resided in a tidal marsh throughout the summer, even as salinities increased to >20. A significant portion of the summer stream-resident population of juvenile O. kisutch migrated out of the catchment in the autumn and winter and used estuary wetlands and adjacent streams as alternative winter-rearing habitats until the spring when they entered the ocean as yearling smolts. Passive integrated transponder (PIT) tag returns and juvenile life-history reconstructions from otoliths of returning adults revealed that four juvenile life-history types contributed to the adult population. Estuarine-associated life-history strategies accounted for 20-35% of the adults returning to spawn in the four brood years, indicating that a sizable proportion of the total O. kisutch production is ignored by conventional estimates based on stream habitat capacity. Juvenile O. kisutch responses to the reconnection of previously unavailable estuarine habitats have led to greater life-history diversity in the population and reflect greater phenotypic plasticity of the species in the U.S. Pacific Northwest than previously recognized.

We quantified the juvenile rearing and migratory patterns of individuals from a population of fall-spawning Chinook salmon Oncorhynchus tshawytscha in Oregon's Salmon River estuary using otolith microchemistry and microstructure. The study confirmed the daily periodicity of otolith growth increments in a natural fish population under field conditions and validated fundamental assumptions about increased otolith strontium : calcium values during entry into saline waters. The otolith results indicated that more than 75% of the subyearling Chinook salmon captured near the mouth of the Salmon River had entered the estuary during the summer and that two-thirds of these fish had spent more than a month in the estuary before capture. Unlike in other Oregon coastal estuaries, in which the fingerling-migrant portion of their life histories is dominant, approximately two-thirds of Salmon River Chinook salmon in upper-estuary marshes were early fry (,50mm) migrants. A much smaller proportion at the river mouth suggests that many fry migrants did not survive to the lower estuary or passed undetected during ocean emigration. Nonetheless, the otolith results reveal a substantially greater contribution of estuarine-rearing fry to the out-migrant population at the Salmon River than has been reported in other Oregon coastal basins. A small component of fall-migrating fish with long freshwater residence times also occurred at the river mouth. Most of these individuals had migrated quickly through the estuary. Rather than revealing a series of discrete ''types'' defined by the predominant rearing patterns in the population, the individual otolith results depict a continuum of freshwater and estuarine life histories that is consistent with reports of considerable phenotypic plasticity in Chinook salmon. Otolith analysis offers the potential to quantify the relative contributions of different juvenile rearing patterns to adult returns.

To comply with legal mandates, meet local management objectives, or both, many federal, state, and tribal organizations have monitoring groups that assess stream habitat at different scales. This myriad of groups has difficulty sharing data and scaling up stream habitat assessments to regional or national levels because of differences in their goals and data collection methods. To assess the performance of and potential for data sharing among monitoring groups, we compared measurements made by seven monitoring groups in 12 stream reaches in northeastern Oregon. We evaluated (1) the consistency (repeatability) of the measurements within each group, (2) the ability of the measurements to reveal environmental heterogeneity, (3) the compatibility of the measurements among monitoring groups, and (4) the relationships of the measurements to values determined from more intensive sampling (detailed measurements used as a standard for accuracy and precision in this study). Overall, we found that some stream attributes were consistently measured both within and among groups. Furthermore, for all but one group there was a moderate correlation (0.50) between the group measurements and the intensive values for at least 50% of the channel attributes. However, none of the monitoring groups were able to achieve high consistency for all measured stream attributes, and few of the measured attributes had the potential for being shared among all groups. Given the high cost of stream habitat monitoring, we suggest directing more effort to developing approaches that will increase the consistency and compatibility of measured stream attributes so that they will have broader utility. Ultimately, local monitoring programs should consider incorporating regional and national objectives so that data can be scaled up and the returns to limited monitoring dollars can be maximized across spatial scales.