Theme E: Interactions between wild and released animals and their ecological and genetic implications
KEYNOTE: Species interactions
30 & 31. REARING AND GENETIC EFFECTS ON FITNESS OF ARTIFICIALLY-PRODUCED ANIMALS IN THE WILD: EMPIRICAL EVALUATION OF LARGE-SCALE FISHERY STOCK ENHANCEMENT PROGRAMS
Shuichi Kitada*, Katsuyuki Hamasaki, Kaori Nakajima, Yasuyuki Miyakoshi and Hirohisa Kishino
Tokyo University of Marine Science and Technology
4-5-7 Konan
Minato
108-8477 Tokyo Japan Shuichi Kitada
Downloadable Abstract
In conservation and population management programs, a release of artificially-produced animals is one of the most popular tools. Produced animals released into the natural environment (hereafter “in the wild”) interact with wild ones depending on the carrying capacity, and therefore should be compatible with wild ones in successful release programs. Since the late 1980s, there has been growing concern about the ecological and genetic effects of hatchery-reared fish on wild populations. One major source of concern is the replacement of wild fish by hatchery fish. Another concern is the deleterious genetic effects of hatchery fish on wild populations. Anomalous genotypic and phenotypic traits have been observed in hatchery populations since the early 1980s. Significant losses of genetic variation or changes in genotypic frequencies in hatchery populations have been reported for several species. There has been a general increase in awareness of the loss of genetic variation in hatchery populations.
The essential concern is whether the loss of genetic variation causes loss of fitness of hatchery and wild populations. Reisenbichler and McIntyre (1977) first found that the survival of hatchery-produced steelhead Oncorhynchus mykiss was lower than that of wild fish in natural streams. Recently, Araki et al. (2007a, 2007b), using microsatellite parentage assignments, discovered a considerable reduction in the reproductive success (RS) of hatchery-reared steelhead (F1 fish) when they bred in the wild. Araki et al. (2009) also found a carryover effect with an even lower RS in hatchery descendants (F2 fish born in the wild). The lower RS of hatchery fish could result in a reduction in reproductive potential of stocked populations when released fish significantly contribute to the population. However, the mechanisms causing the reduction in RS of steelhead are unknown, and it is not clear to what extent these results extrapolate to other species (Araki et al. 2009).
To address this issue, we investigated the causes of the lower RS of hatchery-reared steelhead, and whether the reduction in RS could be generalized to other species. We first tried to extend our understanding of the results of Araki et al. (2007a, 2007b, 2009). We then explored the statistical properties of the relative reproductive success (RRS) estimator on the basis of empirical RRS estimates of the steelhead. From this analysis, we hypothesize that rearing in a hatchery over one year affected the reproductive behavior of hatchery-reared steelhead, which resulted in the low RRS. We then examined whether the fitness reduction of hatchery-reared animals occurred in other species using three different types of large-scale release programs from Japan; the chum salmon Oncorhynchus keta (conducted over 100 years) and Japanese scallop Mizuhopecten yessoensis (~40 years) in Hokkaido, and red sea bream Pagrus major in Kagoshima Bay (KB) (~35 years), in which the impact of released fish to the commercial landings was significant and genetic monitoring was conducted.
The number of chum salmon returning and the catch of scallop have increased above historical levels with the increased number of individuals released (Fig. 1A, B). The commercial catch of released red sea bream in KB also increased after the start of the program, but has continued to decrease since early 1990, along with the decreased number of released fish. On the other hand, the wild catch has generally remained above the catch level at the commencement of release (Fig. 1C).
Most of the annual catch of chum salmon has been created from hatchery fish. Chum salmon returning to spawn are used for artificial propagation every year. Therefore, the case of chum salmon examines the effect of 3–4 months rearing on smolt-to-adult survival of hatchery fish (C[C×C], see Araki et al. 2007a). Catches of Japanese scallop consist of released individuals and wild descendants reproduced from released spat. Naturally-born scallop larvae are collected and bred in net cages for one year in the wild before release. The case of scallop examines the rearing effect on survival and the RS of released spat (W[W×W]) in the wild. The red sea bream program in KB has used nonlocal parents and their progeny for multiple generations kept in concrete tanks. The contribution of hatchery fish to commercial landings in inner KB (IKB) was high at 41.2 ± 26.8% during 1989 and 2004. The time for rearing before release is about 100 days, 50 days in concrete tanks and 50 days in net cages. The case of red sea bream examines the effects of both juvenile rearing and domestication selection of breeders during several generations on survival and RS of hatchery fish (C[C×C]) in the wild.
The increased return rate and the fishery production of chum salmon demonstrated no decline in smolt-to-adult survival in hatchery-reared fish. High survival rates and increased fisheries production of scallop also showed no reduction in survival and RS of released spat. In contrast, the recapture rate for one-year-old red sea bream decreased consistently, suggesting a decline in the survival rate of hatchery fish born from broodstock used to rear multiple generations. The result suggests that hatchery-reared red sea bream were affected by domestication selection of breeders and weaker fish were removed by natural selection in the wild. Nevertheless, the wild catch of red sea bream has generally remained above the catch level at the commencement of release, with a high genetic mixing proportion of hatchery fish in IKB (39.0% ± 73.8%). These results suggest that the juvenile rearing effect and domestication selection of breeders on survival and RS were cancelled by natural selection. A longer rearing duration in a hatchery decreases the effect of natural selection in early life stages, in which natural mortality is very high in aquatic animals. Empirical data teaches us that hatchery-reared animals with relaxed natural selection in captivity are again exposed to natural selection in species-specific survival and reproductive processes with wild animals.
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