Stocking of exogenous, hatchery-reared white-spotted charr Salvelinus leucomaenis has been conducted throughout much of their range in Honshu Island, Japan, to increase angling opportunities. Although the native charr populations are thought to have declined because of hybridization with introduced fish, their distribution and genetic status have been uncertain. Fine population structures of charr in the upper Tone River drainage were examined using mitochondrial DNA and microsatellite analyses so as to clarify the presence of native populations. One common mtDNA haplotype was detected in all populations in the Ohashi River and Watarase River, and four and one tributary populations were monomorphic for such haplotypes, respectively. However, several haplotypes, considered to have originated from stocked hatchery fish, were observed in the stocked and the remaining populations. Judging from the genetic integrity over a fine geographic scale, the former were considered as indicative of native populations and the latter as admixtures with hatchery fish. Comparisons of genetic diversity, deviations from the Hardy-Weinberg equilibrium, principal component analysis, and relatedness estimations based on microsatellite DNA can also provide evidence for distinguishing native populations from those influenced by hatchery fish.
Rotationalˆshing in mountain streams is a potential inlandˆsheries management practice for the sustainable exploitation of natural stocks. To evaluate the eŠects of rotationalˆshing on enhancement of white-spotted charr and masu salmon stocks, we investigated changes in the abundances of theseˆshes in two streams where this management practice was applied. Generalized linear mixed models showed that the density of catchable-size (>150 mm) of both species increased during two closed years and three closed years in one stream. In another stream, the density of catchable-size charr did not increase during two closed years. The density of new recruits
Mortality and growth of Japanese charr Salvelinus leucomaenis and masu salmon Oncorhynchus masou masou after catch and release were examined in experimental ponds, using hatchery-rearedˆsh divided into smaller (< 15 cm in total length) and larger (>15 cm) size groups. When the hooks stuck in the mouth and were removed for both species, the mortality within 21 days after catch and release was low (0 15.0) for each size andˆshing gear (bait and ‰y-ˆshing, using barbed hooks). When hooks in baitˆshing were removed from the esophagus, mortalities were relatively high (66.7 in the smaller sized charr and 45.0 in the larger sized salmon). All thê sh of both species and both size groups were alive when the hooks in ‰y-ˆshing were removed from the mouth, however the mortality was relatively high (40.0) when the hooks were not removed from the mouth of the larger sized charr. Of all theˆsh that died, 63.0 and 98.1 died within 3 and 14 days after catch and release, respectively. There was no negative eŠect of the catch and release on the growth and condition factor of both species and both size groups. These results suggest that catch and release is eŠective for conserving Japanese charr and masu salmon populations in rivers and lakes when anglers pay attention to the removal of hooks.
The dominancy of semi-wild and hatchery-reared white-spotted charr Salvelinus leucomaenis juveniles was evaluated using pair-wise enclosure tests and field stocking tests. The semi-wild S. leucomaenis originated in a hatchery, being stocked into the test stream as eyed-eggs. In the pair-wise enclosure test, the semi-wild S. leucomaenis dominated the hatchery S. leucomaenis that were of a similar standard length (L(S) ). The semi-wild S. leucomaenis were subordinate to hatchery S. leucomaenis that were > 11% larger in LS . In the field stocking test, the abundance and growth of semi-wild S. leucomaenis was decreased in the presence of larger hatchery S. leucomaenis (14% larger LS ). Taken together, these results suggest that larger hatchery S. leucomaenis ecologically suppress the smaller semi-wild S. leucomaenis. Salvelinus leucomaenis juveniles that are stocked with the intention of supplementing natural populations should be < 10% larger than their wild counterparts at the time of stocking to minimize their competitive advantage. The semi-wild and hatchery S. leucomaenis used in both tests were genetically similar individuals, suggesting that the differences are due to the early rearing environment of either a natural stream or hatchery. The hatchery S. leucomaenis have lower levels of aggression as a result of selection in the hatchery rearing environment. Rearing in a natural stream from the eyed-egg stage is likely to increase their lowered aggression.
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