Anadromous salmonid diversity and abundance worldwide have been adversely impacted by anthropogenic forces, and millions of dollars are spent each year on stream habitat restoration and enhancement. However, there is a paucity of data comparing site use by salmonids before and after enhancement implementation, and few studies examine the specific environmental conditions that determine whether salmonids utilize an enhanced site. This study examines the use of gravel augmentation to improve spawning site utilization by Chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (Oncorhynchus mykiss) on the Lower American River, California, USA. Spawning increased across all augmentation sites for both species, although there were species‐specific and year‐specific differences in the degree to which a site was utilized and in the spatial distribution of redds in relation to substrate size, habitat features and other redds. There were also differences in redd architecture across sites that were related to differences in gravel size. This study illustrates that gravel augmentation projects can enhance spawning habitat for salmonids where spawning beds have degraded but that species‐specific and site‐specific attributes and gravel size can influence the relative effectiveness of a project. Copyright © 2013 John Wiley & Sons, Ltd.

Fourteen years (1996–2009) of juvenile Chinook salmon, Oncorhynchus tschawytscha (Walbaum), migration data on the regulated Stanislaus River, California, USA were used to evaluate how survival, migration strategy and fish size respond to flow regime, temperature and spawner density. An information theoretic approach was used to select the best approximating models for each of four demographic metrics. Greater cumulative discharge and variance in discharge during the migration period resulted in higher survival indices and a larger proportion of juveniles migrating as pre‐smolts. The size of pre‐smolt migrants was positively associated with spawner density, whereas smolt migrant size was negatively associated with temperature and positively associated with discharge. Monte Carlo techniques indicated high certainty in relationships between flow and survival, but relationships with juvenile size were less certain and additional research is needed to elucidate causal relationships. Flow is an integral part of the habitat template many aquatic species are adapted to, and mismatches between flow and life history traits can reduce the success of migration and the diversity of migratory life history strategies. The analyses presented here can be used to assist in the development of flow schedules to support the persistence of salmon in the Stanislaus River and provide implications for populations in other regulated rivers with limited and variable water supply.

–  Life history strategies and migratory patterns of 71 adult radio‐tagged bull trout, Salvelinus confluentus, were studied in the Secesh River watershed within the South Fork Salmon River (SFSR) sub‐basin in west‐central Idaho, USA during 2003 and 2004. In both years, upstream migrations occurred during late June and early July, migrations into two spawning tributaries during late July and early August, spawning from mid‐August through mid‐September, and rapid downstream (postspawning) migrations from late August to mid‐September. Primary over‐wintering areas were Loon Lake, the lower Secesh River (downstream of Loon Creek), and the lower SFSR (downstream of the confluence with the Secesh River). Loon Lake evidently provides sufficient production to allow the adfluvial life history strategy to persist and predominate in the Secesh River, while the fluvial life history strategy was previously found to predominate in the nearby East Fork SFSR. Adfluvial, nonconsecutive‐year migrations were the predominant life history strategy. Only seven fish made consecutive‐year migrations to Lake Creek; however, only one of these fish, a female, utilised a spawning tributary in both years and showed spawning tributary fidelity. Three consecutive‐year migrants and three in‐season migrants showed over‐wintering site fidelity by returning to Loon Lake in September, 2004. The life history variations observed for bull trout in the Secesh River watershed are similar to those observed for bull trout throughout their range and to those of other charr species worldwide, yet the development of distinct migration patterns demonstrate the adaptability of the species to a range of available habitats.

We used pattern recognition algorithms and image processing to identify individual Chinook salmon Oncorhynchus tshawytscha. Using melanophore spot patterns located on the dorsal head region, algorithms ranked all database images against each other. We coupled this technology with a graphical user interface to visually confirm or reject top-ranked algorithm results and tested this process on 295 juvenile Chinook salmon in seven photo sessions over a 251-d period. Juveniles began developing spots, identifiable in photo images, between 167 and 197 d after conception (52.7-mm fork length [FL]). Unique spot patterns appeared 197-232 d from conception, beginning at approximately 104-mm FL. Of 254 fish surviving the experimental period, 106 (42%) demonstrated identifiable patterns, 102 (40%) developed spots but patterns were insufficient for identification, and 46 (18%) exhibited a complete lack of spots. Spot patterns continued developing on individual fish by study end. On average, fish that developed recognizable spot patterns did so at approximately 140-mm FL. Once they did, reidentification was 100% correct in up to four subsequent trials. Patterns remained identifiable even after a 25-32% size increase over a 55-d period and as juveniles went through smoltification. Although patterns occurred at sizes typically larger than salmon observed at some California Central Valley monitoring locations, this technique provides a potentially valuable, noninvasive method of identifying individual salmon during emigration. Improved image collection techniques and use of body areas exhibiting identifiable patterns at earlier developmental stages may increase fish available for pattern identification. These results demonstrate the indexing of a large database using pattern recognition algorithms for Chinook salmon. The utility of such an approach may be valuable for addressing specific biological questions associated with massproduced (wild and hatchery), migratory salmonids, especially as individuals develop, grow, and move through the various habitats available to them.

Gravel augmentation is used in sediment‐starved streams to improve salmonid spawning habitat. As gravel is added to river channels, water surface elevations may rise in adjacent areas, activating floodplain habitat at lower flows, and floodplains inundate more frequently, potentially affecting the quantity and quality of juvenile salmonid rearing habitat. We analysed 5 years of juvenile Chinook salmon Oncorhynchus tschawytscha and steelhead Oncorhynchus mykiss data from snorkel surveys before and after gravel augmentation in the Lower American River, a low‐gradient, highly regulated alluvial river in California's Central Valley. We measured the quality and quantity of rearing habitat (current velocity and areal extent of inundated riparian vegetation) following gravel placement and tested whether these factors affected juvenile abundance. Gravel augmentation increased floodplain extent by 3.7–19.8%, decreased average flow velocity from 1.6 to 0.3 m s−1 and increased the amount of vegetative cover from 0.3% to 22.6%. Juvenile abundances increased significantly for both species following augmentation. However, the strength of the relationship between abundance and habitat variables was greater for smaller salmonids. These results suggest that, in addition to enhancing salmonid spawning habitat, gravel augmentation can improve rearing habitat where channel incision and/or regulated hydrographs disconnect floodplains from main river channels. Copyright © 2015 John Wiley & Sons, Ltd.