Captive-breeding and catch-and-release’s effects on the reproductive success of Atlantic salmon (Salmo salar L.)

Captive-breeding programs as well as and catch-and-release are among the most commonly adopted conservation practices in recreational fisheries. However, risks and benefits associated with their implementation are rarely evaluated. In the case of Atlantic Salmon, while previous studies revealed that captive-bred fish show reduced fitness compared to their wild counterparts in nature. Yet, few examined the extent and causes of their reduced reproductive success or directly compared their contribution to enhance genetic diversity to that of wild fish, including mature male parr. Furthermore, only one study specifically measured the reproductive success of caught and released Atlantic salmon in natural settings, and no study to date evaluated if released salmon are able to reproduce when released at temperature above 20°C which is known to increase post-release mortality. Here, we use high-throughput microsatellite sequencing of 38 loci to accurately assign 2500 offspring to a comprehensive set of possible parents from a supplemented Atlantic salmon population in Québec, Canada. The resolved molecular pedigree provided informative insight on the reproductive pattern of both captive-bred salmon and caught-and-released salmon. Captive-bred salmon had fewer partners than their wild conspecifics which lead to a significant reduction of reproductive success relative to that of their wild counterparts. Supplementation of captive-bred salmon significantly contributed to increase genetic diversity but mature male parr did so to an even greater extent and significantly inflated the number of alleles found among offspring. Moreover, our results showed that that at least 83% of caught-and-released salmon did successfully reproduced although caught-and-released female salmon have a significantly reduced reproductive success, averaging 73% of the reproductive output of non-caught salmon. Reproductive success of released salmon was not influenced by water temperature over 20°C which suggests either that the studied population is locally adapted to warm waters or that they behaviorally regulated body temperature by accessing nearby thermal refugia. Our results should help refining managers’ ability to analyze the risks and benefits associated with captive-breeding and catch-and-release, and thus, optimize conservation practices used for the preservation of Atlantic salmon populations.

Mating structure of an endangered population of wild Atlantic salmon (Salmo salar) as determined using sibship reconstruction and a novel method of sex inference

The recent development of molecular genetic markers and methods of inferring relatedness among individuals using multilocus genotype information has allowed new insight into mating systems in the wild. Capitalising on the recently discovered linkage between the microsatellite locus Ssa202 and the sex-determining region of the Atlantic salmon Y chromosome, we developed a novel method to infer the sex of unsampled, wild-spawning parents of some of the few remaining wild, inner Bay of Fundy Atlantic salmon ( Salmo salar ). We inferred that most of the unsampled, reconstructed parents at the half-sib group level were likely polygamous females, while the parents at the full-sib group level (nested within half-sib groups) were likely monogamous males. Given the very low numbers of anadromous salmon returning to inner Bay of Fundy rivers to spawn, the putative male parents were likely mature male parr rather than anadromous males. This suggests that salmonid populations experiencing extreme declines may be composed of a high proportion of related individuals from relatively few sib groups and that mature male parr may provide an important genetic and demographic buffer to population decline.

Hybridization of the Atlantic salmon (Salmo salar L.) and brown trout (S. trutta L.)

Hybrids between the Atlantic salmon and brown trout can be identifi ed on the basis of genes coding for several protein and DNA markers. Hybrids are found in all regions where the Atlantic salmon and brown trout are sympatric. The main causes of the hybridization are the sneaking of mature male parr, escape and release of cultivated fi shes, unstable river discharges, and overfi shing. In numerous experimental crosses, the survival of F1 hybrids varies from zero (a complete loss) to normal. Post-F1 hybridization sometimes results in gynogenesis, hybridogenesis and introgression. The role of hybridization in the evolution of Salmo is discussed.

Effects of timing of nest entry and body size on the fertilization success of alternative male reproductive phenotypes of masu salmon (Oncorhynchus masou)

Using a natural population of masu salmon ( Oncorhynchus masou (Brevoort, 1856)) in a stream of Shikaribetsu Lake, Hokkaido, Japan, we combined behavioural observations with genetic parentage analysis to explore the factors affecting fertilization success achieved by alternative mating tactics (fighting by large migratory males and sneaking by small mature male parr). Larger males gained priority access to females; migrant males do this by holding a guarding position near the nesting female and mature male parr do this by adopting sneaker behaviour and attending spawning groups. Status of mature male parr was related to success of nest entry but not to timing of nest entry, although the timing of nest entry influenced fertilization success of sneakers and ejaculation simultaneous with pair spawning was needed for fertilization by sneakers. The relative body size of each male who successfully spawned with a female is also likely to determine the proportion of eggs he fertilized because larger males have larger ejaculate. These results provide insight into factors relating to variation in fertilization success, how body size dimorphisms may be related to fitness, and evolution of alternative mating tactics.

Spawning behaviour and success of mature male Atlantic salmon (Salmo salar) parr of farmed and wild origin

We examined genetic differences in the reproduction of an alternative maturation phenotype in Atlantic salmon (Salmo salar) by comparing the spawning behaviour and success among farmed, first-generation hybrid, and wild mature male parr raised in similar environments. Parr competed for spawning opportunities in the presence of either wild or farmed large males. There were no consistent differences among groups in aggression; however, there were differences in spawning participation with respect to large male origin and among parr types. There was a strong negative temporal effect on mature male parr spawning participation that differed by parr type; wild and farmed parr were most likely to participate in early spawnings, with hybrids being the most likely to participate in late spawnings. Overall, parr were also less likely to participate in spawnings involving large farmed males. Variance in reproductive success was higher among parr than among large males. Our results are consistent with the hypothesis that there are genetically based behavioural differences among mature male parr of farmed and wild origin that may potentially lead to differences in reproductive success.