Kazuyoshi Nakata

COMPETITION FOR SHELTER OF PREFERRED SIZES BETWEEN THE NATIVE CRAYFISH SPECIES CAMBAROIDES JAPONICUS AND THE ALIEN CRAYFISH SPECIES PACIFASTACUS LENIUSCULUS IN JAPAN IN RELATION TO PRIOR RESIDENCE, SEX DIFFERENCE, AND BODY SIZE

Abstract Intra- and inter-specific competition for shelter, in relation to prior residence, sex differences, and body-size effects, was studied in the laboratory to assess the potential impact of the alien crayfish species Pacifastacus leniusculus on the endangered Japanese endemic crayfish species Cambaroides japonicus. The resident was placed in an aquarium, which contained a single shelter of preferred size for both C. japonicus and P. leniusculus. After 24 h, the intruder was introduced into the aquarium. In the experiments using different sex pairs of crayfish of approximately equal size, male residents had a significant prior residence effect against female intruders in both crayfish species in the intraspecific contests. However, residents of P. leniusculus dominated C. japonicus regardless of the sex in interspecific contests. In experiments using male crayfish pairs of different sizes, larger individuals had more successful possessions of the shelter against smaller individuals regardless of crayfish species. The body-size advantage strongly influenced the outcome of the both intra- and inter-specific contests regardless of residents or intruders and overcame the prior residence effect in both species. These results suggest that P. leniusculus is superior to C. japonicus in shelter competition if P. leniusculus invades the habitat of C. japonicus.

New records and distributions of two North American branchiobdellidan species (Annelida: Clitellata) from introduced signal crayfish, Pacifastacus leniusculus, in Japan

This is the first report of two North American branchiobdellidans, Sathodrilus attenuatus Holt, 1981, and Xironogiton victoriensis Gelder and Hall, 1990, on the signal crayfish, Pacifastacus leniusculus (Dana, 1852) introduced into Japan from the Columbia River system, northwestern North America. Signal crayfish from 12 localities in eastern and northern Hokkaido, Japan, were examined and each supported S. attenuatus. In addition, an individual of this species was found on preserved material from Ishikawa Prefecture, central Honshu. All of these branchiobdellidans reported in Hokkaido most probably came from the original population of signal crayfish introduced into Lake Mashu, Hokkaido, Japan, in 1930. It is suggested that the use of non-pathogenic branchiobdellidans, when present, provides an easy method for tracing the spread of crayfishes around Japan and could also be applied in other countries and continents. Specimens of X. victoriensis were only found on crayfish in a stream at Akashina in Nagano Prefecture, central Honshu, Japan. Although the signal crayfish appears to be displacing the endemic Japanese crayfish, C. japonicus, no native branchiobdellidans were found on any of the introduced signal crayfish examined.

Asymmetry in Mutual Predation between the Endangered Japanese Native Crayfish Cambaroides Japonicus and the North American Invasive Crayfish Pacifastacus Leniusculus: A Possible Reason for Species Replacement

Abstract Asymmetry in mutual predation can be important in species replacement between native and invasive species. Mutual predation between the endangered Japanese native crayfish species Cambaroides japonicus and the North American invasive crayfish Pacifastacus leniusculus was studied to assess the potential impact of P. leniusculus on C. japonicus. We made laboratory experiments to examine mutual predation (i) between individuals in pairs of the same and different species and (ii) among a group comprising single and mixed species. We also made field surveys to clarify the frequency of cannibalism of the two species. In laboratory experiments, the frequency of cannibalism was low by both two species, but predation by P. leniusculus on C. japonicus was severe and most P. leniusculus survived both in different species pairs and in mixed species groups. In field surveys, remains of the two crayfish species, which may have been caused by predation by the same species, i.e., cannibalism, were scanty. The results suggest that asymmetry in mutual predation can be an important cause of species replacement of the native C. japonicus by the invasive P. leniusculus in the field.

REPRODUCTION OF THE ALIEN CRAYFISH SPECIES PACIFASTACUS LENIUSCULUS IN LAKE SHIKARIBETSU, HOKKAIDO, JAPAN

Abstract The reproduction of the alien crayfish species Pacifastacus leniusculus inhabiting Lake Shikaribetsu, Hokkaido, Japan, was studied from August 2002 to August 2003. Spawning was for a short period after mating in mid October. The eggs developed to eyed stage in June the following year and hatched in mid July. After remaining with their mother for several weeks, the juveniles became independent between late July and August. The egg numbers attached to pleopods of this crayfish significantly increased with the female body size. The time of spawning in Lake Shikaribetsu was similar to that of this crayfish living in North America and Europe reported by previous studies, but the time of egg hatching was later in Lake Shikaribetsu compared with some populations in North America and Europe. A comparison of our results of the reproduction of P. leniusculus with that of the endangered Japanese endemic crayfish species Cambaroides japonicus reported by previous studies showed that P. leniusculus has a markedly higher reproductive ability than C. japonicus in terms of egg numbers.

Coexistence of two North American invasive crayfish species, Pacifastacus leniusculus (Dana, 1852) and Procambarus clarkii (Girard, 1852) in Japan

KAZUYOSHI NAKATA14), KIMIHIRO TSUTSUMI2), TADASHI KAWAI3) andSEIJIGOSHIMA1) *) Laboratory of Marine Biology and Biodiversity, Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611, Japan 2) Zukosha Co., Ltd., 1-17 Kita, 18 Nishi, Obihiro, Hokkaido 080-0048, Japan 3) Hokkaido Nuclear Energy Environmental Research Center, 261-1 Miyaoka, Kyowa, Hokkaido 045-0123, Japan

Timing of egg hatch of amphidromous freshwater shrimps in a small river (the Nishida River), western Japan

Larvae of amphidromous freshwater shrimps, which include species of fisheries importance, are released by adult females in freshwater areas of rivers and they drift downstream to the sea. Information on the timing of egg hatch is important to understand the ecology of the amphidromous freshwater shrimps. March et al. clarified that in amphidromous shrimps living in tropical streams, larval drift occurred at night and was slight during the day at low and mid-altitude sites, and no diel pattern was discernible at a high-altitude site. However, the shrimp species was not identified in their study. The methods of larval species identification of Japanese freshwater shrimps were previously developed based on the chromatophore distribution patterns of larvae, enabling us to study reproductive biology of these shrimp species. The purpose of the present study was to clarify the timing of egg hatch of shrimps, with the identification of shrimp species, in a small temperate river in western Japan. Drifting zoeae were hourly sampled during a 72-h period between 2 and 5 July 1998 at two study stations (St. A and St. B) of the Nishida River, Shimonoseki City, Japan (Fig. 1). St. B was located at the lower limit of the freshwater area of the river and St. A was in the middle area, and 1070 m upstream from St. B. Adults of amphidromous freshwater shrimps were observed at high density near the two study stations in preliminary investigations before the present study (Fig. 1). A plankton net with a square mouth (opening, 30 cm ¥ 30 cm; length, 90 cm; mesh size, 212 mm) was used for the sampling. The net was fixed in the study stations for 5 min every hour. Water velocities of the four corners and the center of the net opening were measured using a current meter (Pocket Tachometer Model 3631; Yokogawa, Tokyo, Japan; accuracy, 0.02 cm/s). Filtrated water volume was calculated as follows: filtrated water volume (m) = area of net opening (0.09 m) ¥ average of the five current velocities (m/s) measured ¥ sampling time (300 s). The cross-section of the river at St. B was rectangular in shape because of the head construction (a concrete structure as a river bed retaining work). Therefore, the amount of flow was calculated as follows: the amount of flow (m/s) = river width (7 m) ¥ water depth (m) ¥ the speed of flowing water (m/s). Samples collected were fixed in the 5% formaline and were immediately observed, based on the method by Kikkawa et al. Shrimp species and zoeal stages were identified, based on the methods by Kikkawa et al. and Wada et al. Zoeae (408) were collected at St. B, but no zoea was captured at St. A. Shrimp species and their numbers of zoeae collected at St. B were: Caridina leucosticta (167), Macrobrachium japonicum (10) *Corresponding author: Tel: 81-29-879-6775. Fax: 81-29-879-6748. Email: nakata55@pwri.go.jp Present address: River Restoration Research Team, Water Environment Research Group, Public Works Research Institute, 1-6 Minami-Hara, Tsukuba, Ibaraki 305-8516, Japan. Received 3 October 2005. Accepted 20 February 2006. FISHERIES SCIENCE 2007; 73: 961–963