Nonrandom, Size‐ and Timing‐Biased Breeding in a Hatchery Population of Steelhead Trout

Abstract

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...

Colour-assortative mating among populations ofTropheus moorii, a cichlid fish from Lake Tanganyika, East Africa

“…Hendry et al 2004;Østbye et al 2004;Fraser & Bernatchez 2005;Hendry & Day 2005;McLean et al 2005), or size (e.g. McLean et al 2005). Given that there are no detectable differences in overall morphology, ecology, spawning behaviour and timing in T. moorii, and since local differences in natural selection are improbable, we consider colour-assortative mating based on female preferences as the most likely explanation for our finding of a marked degree of colour-assortative mating in T. moorii.…”

“…McLennan & Ryan 1999), differences in spawning time and/or locality (e.g. Hendry et al 2004;Østbye et al 2004;Fraser & Bernatchez 2005;Hendry & Day 2005;McLean et al 2005), or size (e.g. McLean et al 2005).…”

Variation in reproductive success and effective number of breeders in a hatchery population of steelhead trout (Oncorhynchus mykiss): examination by microsatellite-based parentage analysis

“…Further, males chosen by hatchery staff for spawning may be unsuitable in a manner discernable only by conspecific females (e.g., in poor condition; without 'good genes'), and individuals that would achieve few or no matings in the wild may be spawned preferentially in the hatchery (e.g., if few males were present on the spawning day, they were all spawned). When many males were present, smaller males tended to be excluded from spawning though the process was not systematic (McLean et al 2005); in BY 1996 81% of males were not spawned, in BY 1997 63% of males were not spawned and in BY 1998 21% of males were not spawned.…”

“…Different factors should shape reproductive success in a salmonid hatchery, as selection is no longer imposed by competition, mate choice, and predation but human-related processes play a larger role (McLean et al 2005). Indeed, body size was statistically unrelated to reproductive success of male and female steelhead at Forks Creek Hatchery; however, both fecundity and reproductive timing affected the reproductive success of females.…”

“…Arrival date, which is correlated with maturation date, strongly affects reproductive success in hatcheries because fish that return at the beginning of the run are often more likely to be spawned (McLean et al 2005); (but see Tipping and Busack 2004), but once the hatchery's capacity has been met, additional fish may be killed but not spawned, or released to spawn in the river. This practice commonly results in a shift to earlier arrival (and spawning) dates in subsequent generations in the hatchery (Flagg et al 1995;Quinn et al 2002).…”