In Washington State, the approach to management of wild and hatchery steelhead trout Oncorhynchus mykiss has been to separate the timing of return and spawning by the two groups through selective breeding for early timing in hatchery fish. However, overlap in timing and spatial distribution could permit genetic and ecological interactions. To evaluate this management approach, we compared the timing, spatial distribution, and size of adult steelhead in the wild and newly established hatchery populations of Forks Creek, Washington. Hatchery fish tended to return and spawn about 3 months before wild fish but there was some temporal overlap. Radio‐tracking indicated that the spatial distributions of the populations overlapped considerably, permitting interbreeding and ecological interactions. However, the hatchery fish tended to stay closer to the hatchery, consistent with olfactory imprinting on the hatchery's water supply. Wild females were larger than hatchery females (median fork lengths were 670 and 644 mm, respectively), and wild males and females varied more in length than did hatchery fish of the same sex. In the first year in which naturally spawned offspring of hatchery fish might have returned, we observed a marked increase in early‐returning unmarked (i.e., naturally spawned) adults, suggesting that some hatchery fish spawned successfully in the creek.

We used multilocus microsatellite analysis to compare the reproductive success of naturally spawning wild steelhead trout (Oncorhynchus mykiss) with a newly established sympatric hatchery population in Forks Creek, Washington, U.S.A. Hatchery steelhead spawning in the wild had markedly lower reproductive success than native wild steelhead. Wild females that spawned in 1996 produced 9 times as many adult offspring per capita as did hatchery females that spawned in the wild. Wild females that spawned in 1997 produced 42 times as many adult offspring as hatchery females. The wild steelhead population more than met replacement requirements (approximately 3.7-6.7 adult offspring were produced per female), but the hatchery steelhead were far below replacement requirements (<0.5 adults per female). The survival differential was greatest in the freshwater environment (i.e., production of seaward-migrating juveniles), but survival at sea favored the hatchery population in 1 year and the wild population in the next. The poor performance of the hatchery population may be a consequence of spawning too early in the winter, generations of inadvertent domestication selection, or a combination of these two. Résumé :Une analyse des microsatellites à plusieurs locus nous a permis de comparer le succès de la reproduction chez des truites arc-en-ciel anadromes (Oncorhynchus mykiss) sauvages qui frayent naturellement à celui d'une population sympatrique nouvellement établie provenant d'une pisciculture à Forks Creek, Washington, É.-U. Les truites de pisciculture qui frayent en nature ont un succès reproducteur nettement inférieur à celui des truites sauvages indigènes. Les femelles sauvages qui ont frayé en 1996 ont produit 9 fois plus de descendants adultes par femelle que les femelles de pisciculture qui se sont reproduites en nature. En 1997, les femelles sauvages ont produit 42 fois plus de descendants adultes que les femelles de pisciculture. La population sauvage de truite dépasse les taux nécessaires pour le remplacement de la population (environ 3,7-6,7 descendants adultes produits par femelle), mais les truites de pisciculture sont bien en deçà de ces taux (<0,5 adulte par femelle). La différence dans la survie est maximale dans les environnements d'eau douce (i.e., la production des jeunes qui migrent vers la mer), mais la survie en mer a été plus grande une année chez les truites sauvages et l'autre année chez les truites de pisciculture. Il se peut que la piètre performance de la population de pisciculture soit due à une fraye trop hâtive en hiver, ou à des générations de sélec-tion involontaire de domestication, ou alors à une combinaison de ces deux facteurs.[Traduit par la Rédaction] McLean et al. 440

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Hatcheries have been built and operated to buffer salmon and trout populations from overfishing and to compensate for habitat lost or degraded by human activities. These facilities are now so prevalent that in some cases hatchery-produced salmon outnumber salmon produced in the wild. By default, this makes them an important component in the current ecology and evolution of salmonids. Hatcheries differ from natural environments in many ways, and among the most fundamental is the necessity that humans select fish for breeding instead of allowing natural processes of mate choice and competition. We examined the mating system for steelhead trout ( Oncorhynchus mykiss) at Forks Creek Hatchery in southwest Washington and investigated factors affecting selection of individual steelhead for spawning by the hatchery staff. Despite efforts by the staff to not spawn selectively, data on steelhead spawned over 7 years revealed selection for large adult body size and early reproductive timing and a tendency for size-assortative mating (i.e., large with large). Selection on size was related to selection on reproductive timing because early returning fish tended to be larger than those returning later. To improve the fitness of both hatchery fish destined to spawn in the wild and hatchery fish designated to be spawned in the hatchery, a better understanding of factors associated with the range of reproductive success and mate-choice mechanisms in the wild is vital. This knowledge may then be applied to artificial propagation programs designed for conservation or enhancement. Reproducción No Aleatoria, Sesgada por Tamaño y Tiempo en una Población de Cultivo de la Trucha ArcoirisResumen: Los criaderos de peces se han construido y operado para amortiguar el exceso de pesca en poblaciones de salmón y trucha y para mitigar la pérdida o degradación de hábitat por actividades humanas. Estas instalaciones son tan prevalecientes actualmente, que en algunos casos el salmón producido en criaderos sobrepasa al producido en el medio silvestre. Por defecto, esto las hace un importante componente en la ecología y evolución actual de salmónidos. Los criaderos difieren del medio natural en muchas formas, entre las más fundamentales está la necesidad de que humanos seleccionen a los peces reproductores, en lugar de permitir procesos naturales de selección de pareja y competencia. Examinamos el sistema de apareamiento de la trucha arco iris (Oncorhynchus mykiss) en el Criadero Forks Creek en el suroeste de Washington e investigamos los factores que afectan la selección de individuos para desove por parte de trabajadores del criadero. A pesar de los esfuerzos de los trabajadores por no desovar selectivamente, los datos de desove de truchas a lo largo de 7 años reveló la selección de talla corporal adulta grande y sincronización reproductiva temprana y una tendencia al apareamiento por clases de tamaño (i. e., grande con grande). La selección de la talla se relacionó con la selección de la sincronía reproductiva debido a que peces que retornaban te...

We describe the results of four picture-recognition memory experiments, over which we systematically manipulated four variables: stimulus duration, stimulus contrast, the duration of a blank gap between successive presentations of the same stimulus, and the presence or absence of a noise mask that immediately followed stimulus offset. The patterns of obtained data confirmed a simple extension of a theory previously used to account for digit-recall data. This theory consists of a low-pass linear-filter front end that generates a sensory response from the physical stimulus, followed by an information-sampling process whose instantaneous sampling rate is based in part on the sensory-response magnitude. The data confirm both qualitative and quantitative theoretical predictions, some of which were previously untestable in digit-recall tasks because of ceiling effects that were not present in our picture-recognition tasks. We describe the role of our theory within the broader family of picture-memory theories, and we briefly discuss our theory's unification of two salient facets of visual behavior: information acquisition on the one hand, and phenomenological appearance on the other hand.At its most basic level, the standard informationprocessing view of visual perception and memory is the following. A visual stimulus contains information. When a person views a visual stimulus, information contained in the stimulus is encoded via a set of sensory, perceptual, and cognitive processes, resulting in a memory representation of that stimulus that serves as the basis for a response in a later memory task.The kinds of mental processes that intervene between stimulus presentation and the memory test, along with the nature of the memory representation, are presumed to depend upon the type of stimulus and task. The possible stimulus-task combinations range in complexity from the relatively simple (for example, detection of a patch of light on a black background) to the relatively complex (for example, delayed recognition of a naturalistic picture). Each stimulus-task combination presumably requires its own set of specialized mental processes. Even the simplest stimulus-task combination-detection of a patch of light-involves processes that have been examined in great detail, and yet are still not completely understood. Picture recognition is much more complex because there are an unlimited number and variety of pictures in the visual world; thus highlevel mechanisms for pattern recognition and categorization that are not needed to detect a patch of light are almost certainly required.Despite these differences in the kinds and complexity of processing involved in different stimulus-task combinations, there are also important similarities. In particular, regardless of the stimulus or task, the early stages of the visual system are generally assumed to produce a sensory representation of the stimulus that is closely linked to the physical properties of the stimulus. Then the information from the stimulus contained in the sensory re...