BULLETIN OF MARINE SCIENCE, 61(1): 147–157, 1997

SURVIVAL AND GROWTH OF THE JAPANESE CAMBAROIDES JAPONICUS IN A SMALL STREAM IN HOKKAIDO

Tadashi Kawai, Tatsuo Hamano, and Shuhei Matsuura

ABSTRACT Growth over the life cycle, including seasonal variation, of the Japanese crayfish, Cambaroides japonicus (de Haan, 1841), was examined for a population found in a stream in Hokkaido, northern Japan. The growth equation estimated for males was Lt = 106.6 (1- exp (-0.02987 (0.08333t + 0.9444 + 0.3279 sin (0.5236t - 0.6947)))) and for females, Lt = 126.2 (1-exp (-0.02413 (0.08333t + 1.213 + 0.2768 sin (0.5236t - 1.548)))), where Lt is the carapace length (mm) measured from the posterior of the eye socket to the posterior margin of the carapace at age t (months after settlement in July). The longevity of males is esti- mated to be 11 yr, and females 10 yr. Both sexes become sexually mature 5 or 6 yrs after hatching.

The Japanese crayfish, Cambaroides japonicus, is a species indigenous to northern Ja- pan, found only in Hokkaido, Aomori, Akita, and Iwate Prefectures (Okada, 1933). It reaches approximately 5 - 6 cm in total length, and has been utilized as a food in Tokachi, Hokkaido. However, as many of the natural habitats of C. japonicus have been destroyed by human activities, aquaculture of this crayfish has been proposed for the future. It is therefore important to know the ecology of this species to assess its suitability in an aquaculture program. Previous studies have been limited to the reproductive cycle and molting season, etc. (Kurata, 1962; Kawai et al., 1994b; Kawai et al., 1995a), and information on the ecol- ogy of C. japonicus is scarce. Thus, we have studied the growth characteristics using growth equations and a life table of C. japonicus in its natural habitat, and the data are compared with other Astacoidea. We briefly discuss the possibility of aquaculture for this species in Hokkaido.

MATERIAL AND METHODS

Specimens of Cambaroides japonicus were collected from June 1990 through to June 1992, from a stream, near Atsuta, Hokkaido (Fig. 1). The stream flows into Ishikari Bay and is fed by many springs which maintain the water level. The stream is approximately 1 km in length, with a maximum depth of 5 cm and maximum width of 1 m. Collections of crayfish were carried out at 3 - 4 wk intervals throughout the period of the investigation. The total number of samples was 36. Twenty five sampling stations were established in the stream, and sampled with a 1-m2 quadrat. Crayfish were collected by hand from underneath boulders or fallen leaves. We measured carapace length, CL, from the posterior portion of the eye socket to the posterior margin of the carapace, to the nearest 0.1 mm, using hand-held calipers. Sex of the crayfish was determined by the presence or absence of the gonopore at the base of the 3rd pereopods and from the morphology of the 1st and 2nd pleopods following Holdich and Reeve (1988). Gonopore and pleo- pods of “juveniles” less than 10 mm in CL were extremely small and could not be used to determine the sex of these specimens. All of the specimens were released after measurment. Yearly fluctuations in the breeding season and individual densities in the study stream are small (Kawai et al., 1994b) and the authors expected little variation in the yearly growth pattern of C. japonicus. Thus, all the sampling data were summarized by calender month. Since no molting occurred during winter, from November to May, and growth resumed from June in the natural habitat (Kawai et al.,

147 148 BULLETIN OF MARINE SCIENCE, 61(1): 147–157, 1997

Figure 1. Map showing the study site in Hokkaido, northern Japan.

1994b), data for the period from November through to May were collected. Since C. japonicus live in a small stream, it was difficult to collect large sample numbers and to make a polymodal histogram from a single year’s sampling. Therefore, we treated each year separately. First, we estimated the growth in the field based on growth information derived in a laboratory which had conditions similar to study habitat (Kawai et al., 1995b). Next, we separated modes by two methods: moving averages and by using no average. Both procedures were compared to estimate growth and the moving-average method provided the better fit. Frequency data were classified by size classes as moving means over three CL-class intervals. The most reasonable width of the class interval, 0.4 mm, was adopted after applying several different widths to the data set. Separation of overlapping age groups was accom- plished using a computer analysis based on the maximum likelihood method (Akamine, 1985; Fournier et al., 1990). Juveniles were also analysed by the method described above. Since the sex ratio of this species is 1:1, irrespective of season and body size (Kawai et al., 1995a), each size class of juveniles was divided equally into males and females. The ordinary von Bertalanffy equation and the sine-wave von Berterlanffy equation (Pauly and Gashutz, 1979) were applied to all data. A computer was used to fit the data by the Marquardt method with Akaike’s Information Criterion (AIC), employed as a measure of goodness of fit (Akaike, 1973). During the regular sampling it was difficult to sample smaller crayfish which hide among small stones and gravel. To calculate the actual density of each year class and to construct a life table, additional sampling was conducted on 14 September 1994. Approximately 50 m2 were sampled with a 1-m2 quadrat placed at 20-m intervals along the stream. The top 5-cm layer of the sediment was collected by a shovel and the samples were transported to the laboratory after being fixed in 10% formalin, where the specimens were sorted from the gravel. Sizes and sexes of the crayfish were determined as described above.

RESULTS

Mean water temperatures of the stream during the recruitment season, May to June, were uniform: 1990, 15.9° C; 1991; 15.5° C; and 1992, 15.4° C. Therefore, recruitment seems to be constant every year, and females carrying eggs were caught during May and June in both 1991 and 1992 (Kawai et al., 1994b). Carnivorous fish and other large were not KAWAI ET AL.: SURVIVAL AND GROWTH OF THE JAPANESE CRAYFISH 149

Figure 2. Size distribution of Cambaroides japonicus in a small stream in Hokkaido. Solid triangles are the mean of the Gaussian distributions described by the dotted curves. The numerals above the triangles indicate the number of months after hatching.

observed in the stream. The total numbers of C. japonicus sampled during the regular collections were 1454 males, 1453 females and 318 juveniles. Mean individual density was 3.6 inds. m-2 calculated as (1454 males + 1453 females + 318 juveniles)/(1 m2 x 25 stations x 36). The CL of the largest individual was 34.2 mm for males and 31.6 mm for females. The number of normal distributions of overlapping age cohorts was 9 - 11 for males and 9 - 10 for females in each month. A newly settled cohort appeared in July (Fig. 2). The reproductive season of C. japonicus occurs over the summer (Kawai et al., 1994b) and we believe hatching and settlement occur in July. Modes in the monthly samples were determined from growth information derived from laboratory studies. We estimated the growth in the field based on laboratory observa- tions since the laboratory conditions were similar to stream habitat (Kawai et al., 1995b). Molting frequency per year in the laboratory of C. japonicus of each sex is two or three molts per individual for the < 10 mm CL size class, one or two molts for individuals ≥ 10 and ≤ 18 mm, and only one molt for individuals > 18 mm (Kawai et al., 1995b). Their growth factor, calculated as (100 x post-molting CL)/(pre-molting CL) following Mauchline (1977), was approximately 110, irrespective of sex and body size. Based on this growth 150 BULLETIN OF MARINE SCIENCE, 61(1): 147–157, 1997

Figure 3. The fit of the ordinary Bertalanffy growth equation and the Pauly and Gashutz equation to the mean carapace length data of Cambaroides japonicus collected from in a small stream in Hokkaido. factor, the annual CL growth in the natural habitat was estimated as approximately 1.1 for large individuals and 1.3 for small individuals. In any one month, the mean of each cohort in Figure 2 is equivalent to the CL multiplied by the year-younger cohort by 1.1 - 1.3. Therefore, we suggest that the normal distribution (Fig. 2) is representative of single year- class cohorts. Male: Lt = 106.6 (1-exp (-0.02987 (0.08333t + 0.9444 + 0.3279sin (0.5236t - 0.6947)))) (1) KAWAI ET AL.: SURVIVAL AND GROWTH OF THE JAPANESE CRAYFISH 151

Figure 4. Size distribution of Cambaroides japonicus in substrate samples from 50 m2 in a small stream in Hokkaido on 14 September 1994. Solid triangles are the mean of Gaussian distributions described by the dotted curves. The numeral above triangles denote the predicted year of hatching.

n = 69, AIC = -62.45 Lt = 55.47 (1-exp (-0.005782 (t + 7.594))) (2) n = 69, AIC = 9.626 Female: Lt = 126.2 (1-exp (-0.02413 (0.08333t + 1.213 + 0.2768sin (0.5236t-1.548)))) (3) n = 69, AIC = -17.16 Lt = 54.46 (1-exp (-0.005844 (t + 8.059))) (4) n = 69, AIC = 35.64 where Lt is CL at age t (months) after settlement (Fig. 3). 152 BULLETIN OF MARINE SCIENCE, 61(1): 147–157, 1997

Figure 5. Age-and size-specific survivorships (lx) and mortality rates (qx) for Cambaroides japonicus. Values are from Table 1. Dotted curves indicate the 95% confidence limits of expectations.

The Pauly and Gaschutz (1979) equation provided a better model for describing the data on the basis of the AIC (Akaike, 1973) which is used for a measure of the goodness of fit of the model. Therefore, we adopted equations (1) and (3) as the best growth equations for C. japonicus in the studied stream where the growth rate obviously oscillates seasonally. Growth equations were similar for each sex. The longevity of males is 11 yr and females 10 yr. The calculated Lmax is 106.6 mm and 126.2 mm for males and females, respectively (Fig. 3). Individuals (n = 405) of both sexes were obtained by the substrate sampling and the mean density for all samples was 16.2 inds. m-2. Ten numerical peaks were observed in both sexes in the CL frequency distribution (Fig. 4). We applied the ten peaks in CL for the age class cohorts from the information generated by growth curves (2) and (3) (Fig. 4). Ovigerous females of C. japonicus carry eggs (Kawai et al., 1994b), and juveniles hatch directly from the eggs without a planktonic stage (Kurata, 1962). The environment of the studied stream, particularly the water temperature, is apparently stabilized by the influx of spring water; KAWAI ET AL.: SURVIVAL AND GROWTH OF THE JAPANESE CRAYFISH 153

rofelbat-efilcitatsA.1elbaT sucinopajsediorabmaC ehtmorfnekaterashtgnelecaparacnaeM(. .)4erugiFnisnoitubirtsidnaissuaG

Srezi NgumbePgroportionsurvivinPyroportiondyinMortalit (dmeancarapacecfaptureaetthestartobetweenagxrate 2 A)gelmength,mmper50ageintervalXandx+1(dx/lx) x bx ax lx dx qx mealefeemalmealfeemalmealfeemalmealfeemalmealfemal 00.48.3011810010.0015.0008.1405.1408.140.14 12.67.549295028.500.8501.3001.2301.350.27 23.97.916765005.503.6203.1702.2104.310.34 31.310.3124442073.801.4003.0908.0909.230.22 43.514.5123431052.904.3102.0600.1004.220.32 59.711.8152327032.207.2108.0209.0201.110.13 62.023.0222020052.001.1802.0905.1001.450.55 72.323.32219901.0305.0808.0505.0207.500.33 87.426.5266506.0505.0507.0408.0301.810.66 94.829.7212909.0009.0109.0000.0110.001.00 therefore, recruitment seems to be constant every year. Using calculations from Hamano and Morrissy (1992), the proportion surviving (lx), proportion dying (dx) and the mortality rate (qx) were obtained. From these, we constructed a life table for C. japonicus using the data from the substrate samplings (Table 1). Regression equations calculated for lx and bx, lx and x, qx and x, and qx and bx, showed no difference between males and females (ANCOVA, P > 0.05). Thus, both sexes were combined to calculate the survivorship and mortality rate equations (Fig. 5). The lx declined gradually with increasing age or length, and qx in- creased in proportion to growth.

DISCUSSION

Growth of crayfish is related to the temperature and the number molts which occur during the warm season, June to October (Kawai et al., 1994b). As a result, the increase of CL is stepwise (Fig. 3). Other species common in temperate and/or subfrigid zones also show similar growth patterns (Corey, 1988; Momot, 1984; Tach, 1941). The CL at first maturity was 18 mm for females and 19 mm for males (Kawai et al., 1994b; Kurata, 1962). There- fore, individuals take 5 or 6 yr to mature (Fig. 2). The largest size is 34.2 mm for males and 31.6 mm for females, and these sizes differ from the Lmax calculated from growth equa- tions (1) and (3): males 106.6 mm and females 126.2 mm. The growth factor of both larger and smaller specimens of C. japonicus is equal (Kawai et al., 1995b). Hence we think the size of the largest crayfish in the field will increase under protected conditions resulting in low mortality pressure. The largest size of the signal crayfish, Pacifastacus leniusculus, collected in nature was also smaller than the calculated Lmax (Hamano et al., 1992). In the specimens collected from the substrate-quadrat samples, the density of each cohort decreased with increasing age and length, and variation in size increased with growth (Fig. 4). However, specimen characteristics from the periodic sampling were irregular and it was even more remarkable in the months when a few individuals were collected (Fig. 2). Indi- 154 BULLETIN OF MARINE SCIENCE, 61(1): 147–157, 1997

.dleifehtniselamefaediocatsAfoytirutamtaegadnahtworG.2elbaT

Sy*stludafoezi Timetomaturit S*pecieslgength(mm)*aefterhatchinSourc (year) AstacusastacusT5L804)–Cukerzis(1988 AustropotamobiuspallipesC3L25 Lowery(1988 ) PacifastacusleniusculusC2L25 ShimizuandGoldman(1981 ) CambaroidesjaponicusC6L185y–Presentstud *Theaverageofadultfemales. **CL,carapacelength;TL,totallength. vidual densities calculated from the substrate quadrat samples, 16.2 inds. m-2 were approxi- mately five times of that of the regular collection, 3.6 inds. m-2, and the variation and den- sity of cohorts were probably due to sampling error during the regular collection. The sine wave model (Fig. 3) revealed negative growth during cold months. Hamano (1990) also adopted a sine wave growth equation for the stomatopod , Oratosquilla oratoria, and it also exhibited negative growth in the winter season. He thought that this phenom- enon was caused by a size-dependent mortality influencing the mean size of the cohort. The same reasoning may be applied to the present results. Furthermore, a sampling bias (due to the difficulty of collecting large individuals which hide under large boulders in winter) suggests negative growth during winter. The relationships between survival and age, and between survival and CL, are described by regression equations. New cohorts appear in July (Fig. 2) and 0-yr age juveniles become independent of parental care in September. Survivorship, however, is not assured as a result of parental care and the absence of a larval period. Therefore, each year class less than 10 mm in CL, showed similar mortality patterns (Table 1). Survival decreased with an increase in age and CL (Fig. 5). In comparison, survival of the North American crayfish, Orconectes neglectus chaenodactylus, gradually decreases after an initial high mortality of the 0-yr age group by predators, for example, the small mouth bass Micropterus dolomieui (Stein and Magnuson, 1976; Price and Payne, 1984). High survival of small individuals of C. japonicus here is probably due to the absence of predators in their natural habitat in Japan. Limiting predation on the Japanese crayfish in the natural habitat may be useful for the protection and enhancement of the stocks. The population of C. japonicus decreases with increasing age and body size (Fig. 5, Table 1), and older individuals of C. japonicus could not be collected in some months (Fig. 2). It is estimated that the largest mode number may denote the length of life of C. japonicus in the studied habitat. Longevity of C. japonicus in this natural habitat is similar for both sexes (Table 1, Fig. 3). Two phenomena in Astacoidea might cause longevity to be the same for both sexes (Price and Payne, 1984). One of them is that the frequency of ecdysis is the same for both sexes because the physiological and mechanical stresses caused by molting contribute to death in , and the preferential survival of females has usually been attributed to the fewer molts (Price and Payne, 1984). Another is that there is no sexual selection in the natural habitat (Andersson, 1982). In selective mating, genes from larger males, which live longer and can mate more frequently, may dominate in the population gene pool, perhaps directing selection toward greater male longevity (Price and Payne, 1984). Additionally, when males intraspecifically fight using its chelae, larger males with larger KAWAI ET AL.: SURVIVAL AND GROWTH OF THE JAPANESE CRAYFISH 155

chelae dominate smaller ones (Bovbjerg, 1956). Also, males of many Astacoidea usually fight intraspecific males using their chelae to gain the chance of mating with females dur- ing the copulation season (Ameyaw-Akumfi, 1979; Ingle and Thomas, 1974). Thus, che- liped loss in males in the natural habitat may indicate the presence of sexual selection in male crayfish. C. japonicus molt an equal number of times per year in each sex (Kawai et al., 1995b). Furthermore, the frequency of cheliped loss in male C. japonicus does not increase in the copulatary season (Kawai et al., 1994a). Thus, male and female C. japonicus have similar longevities in the natural habitat. Astacoidea are cultured worldwide, for example astacus, Austropotamobius pallipes, Cherax destructor, C. tenuimanus, P. leniusculus, and Procambarus clarkii, (Morrissy, 1979; Laurent, 1980; Shimizu and Goldman, 1981; Brewis and Bowler, 1982; Huner, 1985; Cukerzis, 1988; Sokol, 1988). P. clarkii, C. destructor, and C. tenuimanus are common in lower latitudes. In general, crayfish that are raised intensively in pond culture mature within 1 or 2 yr, and have high growth rates (Morrissy, 1979; Huner, 1985; Sokol, 1988). However, crayfishes that live at higher latitudes mature after more than 2 yr and do not have high growth rates (Table 2). Also the reproductive ability of C. japonicus is lower than that of P. clarkii and P. leniusculus, since adult female C. japonicus spawn only one time in a year and lay a smaller number eggs (Kawai et al., 1990). Furthermore, loss of chelae by C. japonicus occurred frequently in small habitats (Kawai et al., 1994a). We do not belive there is a good potential for intensive aquaculture based on ecology of C. japonicus. Thus, they should be propagated by management of the habitats where they naturally occur. To establish Japanese crayfish aquaculture, the natural habitat must be managed and pro- tected, and facilities constructed for extensive culture and sustained production.

ACKNOWLEDGMENTS

We thank C. P. Norman of the Seikai National Fisheries Research Inst. and P. J. Laurent of the Institute National de la Recherche Agronomique for their valuable advice on our manuscript.

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DATE ACCEPTED: October 18, 1996.

ADDRESSES: (TK) Hokkaido Central Fisheries Experimental Station, 238 Hamanaka, Yoichi, Hokkaido 046, Japan; (TH) National Fisheries University, Yoshimi, Shimonoseki 759-65, Japan; (SM) Department of Fisheries, Faculty of Agriculture, Kyushu University 46-04, Hakozaki, Higashi, Fukuoka 812, Japan.