Jennifer E. McLean

Comparisons of Run Timing, Spatial Distribution, and Length of Wild and Newly Established Hatchery Populations of Steelhead in Forks Creek, Washington

Abstract 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 hatcherys water supply. Wild females were larger than hatchery females (median fork lengths were 67...

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

Conservation programs that release captive-bred individuals into the wild to mix with naturally produced individuals are an increasingly common method of supporting or enhancing weak or reduced populations that otherwise may not be self-sustaining. Captive and supportive breeding can be important conservation tools for species with small or declining populations; however, in the case of hatcheries producing salmonid fishes, detailed evaluation of spawning programs is rare. We examined variation in reproductive success, measured by adult offspring production, from three parental generations of hatchery-bred steelhead trout (Oncorhynchus mykiss) using an exclusion-based method of genetic parentage assignment. Reproductive success varied greatly among individuals (especially males) and was correlated with fecundity and maternal spawning date. Estimates of egg to smolt survival for the population as a whole among years ranged from 64% to 95%, marine survival ranged from 0.32% to 2.30%, and the number of adults produced per female ranged from 0 to 18 and the number of adults produced per male ranged from 0 to 32. The effective number of breeders ranged from 11% to 31% of the census population size for that brood year. These ratios fell within estimates from estimates of Ne/N in chinook (O. tshawytscha) and rainbow trout (O. mykiss) hatchery populations.

Marine population structure in an anadromous fish: life‐history influences patterns of mitochondrial DNA variation in the eulachon, Thaleichthys pacificus

Due to the apparent decline in size of a number of populations, eulachon, Thaleichthys pacificus, have recently become the focus of a conservation movement in the northeast Pacific. Little is known of the marine life‐history phase of this anadromous fish, and although it has been suggested that eulachon spawning in different rivers may form distinct populations, nothing is known of their population structure. Molecular genetic data were used to investigate population structure and possible management schemes. Mitochondrial DNA genotypes, determined through restriction fragment length polymorphisms (RFLP) analysis, were resolved in fish from several rivers throughout the geographical range of eulachon. Our data support the idea that extant eulachon populations result from postglacial dispersal from a single Wisconsinan glacial refuge. Further, while three of the 37 haplotypes recovered account for approximately 79% of the samples, many private haplotypes were observed, suggesting possible regional population structure. While a great deal of genetic variation was observed (37 haplotypes in 315 samples), an amova showed that > 97% of the total variation was detected within populations. As yet, it is unclear whether genetically distinct populations of eulachon exist, or if these fish may be treated as one or a few large populations. Results were tested against predictions made from hypotheses concerning the origin and persistence of subdivided populations in marine species, and seem to be more consistent with the Member–Vagrant hypothesis than isolation by distance. Eulachon present an interesting situation that illustrates the difficulties involved in defining management units in organisms with high levels of gene flow.

A front end to a theory of picture recognition

We describe the results of four picture-recognition memory experiments in 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 linearfilter front end that generates a sensory response from the physical stimulus, followed by an informationsampling 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 picturerecognition 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.

DOES SIZE MATTER? FITNESS‐RELATED FACTORS IN STEELHEAD TROUT DETERMINED BY GENETIC PARENTAGE ASSIGNMENT

Estimates of reproductive success and the factors that affect it can be inferred from observations of behavior or data on life history traits (e.g., dominance hierarchies, clutch size). Genetic parentage analysis, however, can precisely determine the number of offspring attributable to individual parents. We coupled multilocus microsatellite genotype-based parentage assignment exclusion testing with morphological and behavioral data to test hypotheses concerning the effects of specific traits on fitness of naturally spawning steelhead trout (Oncorhynchus mykiss). With eight microsatellite loci (mean heterozygosity = 89%), we examined two parental generations (n1 = 198, n2 = 226) and their offspring as smolts (age 2: n1 = 365, n2 = 285) and as adults (n1 = 81, n2 = 77) to determine the effects of size, reproductive timing, and origin (hatchery or wild) on reproductive success. The mating system was complex; monogamy, polygamy, polyandry, polygyny, and polygynandry were all observed. Males had a greater var...