Taiga Yodo

Predicting invasions of North American basses in Japan using native range data and a genetic algorithm

Abstract Largemouth bass Micropterus salmoides and smallmouth bass M. dolomieu have been introduced into freshwater habitats in Japan, with potentially serious consequences for native fish populations. In this paper we apply the technique of ecological niche modeling using the genetic algorithm for rule-set prediction (GARP) to predict the potential distributions of these two species in Japan. This algorithm constructs a niche model based on point occurrence records and ecological coverages. The model can be visualized in geographic space, yielding a prediction of potential geographic range. The model can then be tested by determining how well independent point occurrence data are predicted according to the criteria of sensitivity and specificity provided by receiver–operator curve analysis. We ground-truthed GARPs ability to forecast the geographic occurrence of each species in its native range. The predictions were statistically significant for both species (P < 0.001). We projected the niche models on...

Righty fish are hooked on the right side of their mouths :observations from an angling experiment with largemouth bass, Micropterus salmoides

Abstract The development of muscles and bones in fish is laterally asymmetric (laterality). A “lefty” individual has a “C”-shaped body, with its left-side muscles more developed and the left side of its head facing forward. The body of a “righty” is the mirror-image. This laterality causes asymmetric interactions between individuals of different fish species, in that a righty or lefty fish consumes more lefty or righty fish, respectively. To investigate the coupling mechanisms between body asymmetry and predatory behavior, we conducted angling experiments with largemouth bass (Micropterus salmoides). We used the position of the fishhook set in the mouth to indicate the movement direction of the fish when it took the bait. Righty fish had more hooks set on the right side, whereas lefty fish had more on the left side, indicating that righty fish moved more to the left, and lefty fish moved more to the right, in successful catches. The relationship between the hooked position and movement direction was confirmed by video-image analysis of the angling.

Impact of indigenous egg eaters on the early survival of exotic smallmouth bass

Exotic species become invasive aliens when they have an adverse effect on the community of the recipient ecosystem, and their spread among closed water systems is of recent concern for the conservation of native biodiversity in Japan. Smallmouth bass (Micropterus dolomieu Lacepède) is recognized as one of the worst 100 alien species, being undesirable because of its trophic level as a top predator. Smallmouth bass that have been illegally introduced into Lake Aoki, central Japan, in the 1990s for the purpose of sports fishing have seriously affected the lower trophic levels in the lake including fisheries resources, while a strong effort to remove them has proved to be limited in usefulness. We intended to identify indigenous agents that have a potential to control smallmouth bass in the lake. Snorkeling observations in the daytime revealed that Japanese dace (Tribolodon hakonensis Günther) intruded into smallmouth bass’ spawning nest as a school and were able to consume the eggs while the male bass was guarding the nest. Consequently, the proportion of lost eggs owing to the predation reached 92.4% per clutch on average, proving that native cyprinids are able to function as an efficient egg predator that reduces the survival of smallmouth bass. We consider that employing the indigenous egg predator can be a practical means to eradicate exotic smallmouth bass, combined with the removal of stones on the nest as a subsidiary step to expose smallmouth bass eggs to predation by Japanese dace.

Difference in response by two cyprinid species to predatory threat from the nocturnal catfish Silurus asotus

Response to predators may not be identical between different prey species with different life histories and body sizes, particularly when the threat of predation is not great. To clarify this hypothesis, we introduced two prey species (10 Japanese dace, Tribolodon hakonensis, and 10 pale chub, Zacco platypus) into each experimental pond (in total, 8 ponds × 4 trials) in which benthic algae had been allowed to grow. The presence or absence of Far Eastern catfish, Silurus asotus, and a refuge for prey fish was used to produce four treatments. The presence of catfish and/or a refuge did not affect either the feeding behavior or growth rate of Japanese dace. In contrast, when catfish were present and no refuge was available, the incidence of bottom feeding for pale chub greatly decreased. Pale chub growth rate was low when catfish were present and a refuge was available, indicating that pale chub spent more of their time in the refuge and lost opportunities of acquiring food. Japanese dace can reach a threshold size at which the prey are safe from predation, but pale chub cannot, and this may explain the differences in response to predators of the two species.

Contrasting life history patterns of the goby Rhinogobius similis in central Japan indicated by otolith Sr:Ca ratios

Rhinogobius similis a common goby, widely distributed in Far East Asia, is characterized by an amphidromous life history, adult fish inhabiting the lower reaches of rivers, and larvae in the freshwater area being swept downstream to the sea and returning to the river following a period of pelagic marine existence. Individuals were collected from 6 stations in the Ibi, Nagara and Kamo Rivers, central Japan, and their otolith strontium and calcium environmental signatures examined using electron probe microanalyses. The otolith Sr:Ca ratios of R. similis from the Kamo River suggested a typical amphidromous life history, whereas those of fish collected from the Ibi River suggested two types of migratory life history pattern: amphidromous and river resident. In contrast, the otolith Sr:Ca ratios of fish collected at two stations upriver of a dam in the Nagara River estuary suggested an artificially landlocked life history. Emergent plant vegetation in the lower reaches of the Ibi River created slow currents and pools in the river, thereby possibly enhancing the likelihood of a river resident life history. In the Nagara River, however, landlocked specimens had been obstructed in their downstream migration by the dam. It is suggested that R. similis in central Japan has a variable migratory life history pattern, allowing the species to persist in upstream habitats in large rivers.