Long‐term translocation explains population genetic structure of a recreationally fished iconic species in Japan: Combining current knowledge with reanalysis

Abstract

Ayu (Plecoglossus altivelis altivelis) is an important freshwater fisheries resource and popular recreational fishing species in Japan that lives for only 1 year, with a single breeding season. To supplement increased recreational fishing demand for this species, more than 13 million wild-born landlocked juveniles are translocated every year from Lake Biwa into Japanese rivers, and more than 52 million hatchery-reared juveniles born from captive-reared parents have been extensively released. The translocation of landlocked juveniles and hatchery release has continued for more than 100 and 30 generations, respectively. Previous studies have reported that landlocked and amphidromous forms of Ayu easily hybridise, leading to concerns that the fitness of hybrid progeny would be reduced in the wild. However, limited information exists regarding the reproductive success of landlocked Ayu in translocated rivers, and to date no studies have evaluated the effects of translocation on population structure. Demonstrating that hybridisation occurs between the two forms is central to future management and conservation of this species. To address this, a literature search to summarise biological knowledge of Ayu and population genetic data screening was undertaken, and published genetic data sets covering a distribution range in Japan were reanalysed. Analyses provide strong evidence for very high gene flow between sampling locations. Genetic diversity is homogeneous in amphidromous samples. Bayesian admixture analysis infers widespread hybridisation in Japanese rivers (24 ± 8%). Maximum likelihood admixture graphs detect two migration events from Lake Biwa to rivers in the northern Sea of Japan and Hokkaido. Analyses consistently indicate that hybridisation between translocated landlocked juveniles and native amphidromous Ayu occurs throughout Japanese rivers. These results are discussed in relation to the management of this species.

Bacterial cold-water disease in ayu (Plecoglossus altivelis altivelis) inhabiting rivers in Japan

“…Most wild-born stocks comprise landlocked ayu caught in Lake Biwa; indeed, landlocked stock has been translocated into amphidromous populations in rivers throughout Japan for many years. Three concerns have been raised around the use of landlocked stock in relation to the conservation of natural amphidromous populations ( Takamura, 2009 ; Kitada, 2022 ). First, the translocated landlocked stock poses a risk of interbreeding with wild amphidromous populations.…”

“…Amphidromous stock is genetically more resistant to BCWD than landlocked and domestic stocks ( Nagai et al., 2004 ; Nagai and Sakamoto, 2006 ). For this reason, hatchery-born amphidromous stock is now produced and released into rivers in large quantities that surpass those of landlocked stock ( Kitada, 2022 ).…”

National scale genetic and oceanographic population connectivity in New Zealand kaimoana invertebrates

“…Population genetic studies may include the application of any number of these tools, but as new tools are constantly being developed, some data sets may warrant re-evaluation with new statistical analyses (e.g., Danielsdottir et al 2006, Safner et al 2011, Kitada 2022). Because of their economic and cultural significance in New Zealand three species stand out as obvious candidates for reanalysis: blackfoot paua (Haliotis iris), green-lipped mussels, (Perna canaliculus), and red rock lobster (Jasus edwardsii).…”