Brassy minnow Hybognathus hankinsoni, a threatened species in Colorado, live in harsh, fluctuating stream environments subject to summer drying and winter freezing in the western Great Plains and yet may be capable of rapid dispersal and reproduction during the wet season. We studied brassy minnow populations at multiple spatial scales in the Arikaree River basin of eastern Colorado to determine the underlying mechanisms driving local extinction and colonization and regional persistence. Habitat units in three 6.4-km segments, arrayed across a gradient of stream intermittency from perennial to seasonally dry, were sampled five times in 2000 and 2001, the two driest summers on record. Logistic regression showed that brassy minnow were more likely to persist through summer drying in deeper pools connected to other habitat units and were more likely to persist in pools in the more perennial segments. The main cause of fish extirpation was pool drying, which logistic regression showed was more likely in shallower pools and in the drier segments. Despite poor adult survival in the drier segments, larval brassy minnow were widely distributed in all segments in early summer of both years, indicating substantial movement for recolonization. The dynamic nature of plains streams and the large spatial scales over which brassy minnow carry out their life history require research and management at the intermediate segment scale for effective conservation.
Estimates of the relative fitness of hatchery- and natural-origin salmon can help determine the value of hatchery stocks in contributing to recovery efforts. This study compared the adult to fry reproductive success of natural-origin summer chum salmon ( Oncorhynchus keta ) with that of first- to third-generation hatchery-origin salmon in an experiment that included four replicate breeding groups. Hatchery- and natural-origin chum salmon exhibited similar reproductive success. Hatchery- and natural-origin males obtained similar access to nesting females, and females of both types exhibited similar breeding behaviors and durations. Male body size was positively correlated with access to nesting females and reproductive success. The estimates of relative reproductive success (hatchery/natural = 0.83) in this study were similar to those in other studies of other anadromous salmonids in which the hatchery population was founded from the local natural population and much higher than those in studies that evaluated the lifetime relative reproductive success of nonlocal hatchery populations.
After hatchery‐reared salmonids are released into the wild, their survival and performance are frequently lower than those of wild conspecifics. Additionally, negative effects of hatchery fish on wild fish are cited as factors affecting the recovery of salmonid populations. Alternative hatchery rearing environments and release practices have been proposed to mitigate both problems. We investigated the postrelease growth, survival, habitat use, and spatial distribution of hatchery steelhead Oncorhynchus mykiss fry reared in conventional and enriched environments and compared their performance with that of naturally reared steelhead fry from the same parent population in two streams. Average instantaneous growth rates differed between streams but not among the three rearing groups. The survival of naturally reared fry was significantly greater than that of both types of hatchery fry (relative survival = 0.33) but did not differ between the conventional and enriched environments. Naturally reared fry grew and survived equally well regardless of the type of hatchery fry with which they were stocked. Supplementation increased fry population size in all stream sections but produced hatchery‐biased populations. Steelhead fry preferred pool habitat within stream sections, but pool use was affected by an interaction between rearing environment and stream. Hatchery fry had more clumped spatial distributions than naturally reared fry, which were affected by a significant interaction between rearing type and stream. Hatchery rearing type and stream had no effect on the spatial distribution of naturally reared fry. We conclude that (1) hatchery steelhead fry released in streams grow as well as naturally reared fry but do not survive as well, (2) enriched hatchery environments do not improve postrelease growth or survival, and (3) upon release, fry raised in enriched hatchery environments affect the growth and survival of naturally reared fry in much the same way as fry reared in conventional hatchery environments.
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