Journal of Advanced Marine Science and Technology Society, Vol. 24, No. 2, pp. 19–30, 2018

Original Paper Multiyear use for spawning sites by crucian carp in , Japan

Yoshio Kunimune*1, Yasushi Mitsunaga*2

*1 Graduate School of Agriculture, Kindai University, 3327-204 Naka-machi, Nara, Nara, 631-8505, Japan *2 Faculty of Agriculture, Kindai University, 3327-204 Naka-machi, Nara, Nara, 631-8505, Japan, [email protected]

Received: July, 10. 2018, Accepted: October, 19. 2018

Abstract From April 2008 to July 2009, an acoustic telemetry study on crucian carp was conducted in Lake Biwa, Japan. Twenty Nigorobuna, ten gengoroubuna and one captured during spawning seasons were released with ultrasonic transmitters in the South Basin. Signals from the tagged fish were detected by 28 ultrasonic-receiver stations installed around Lake Biwa. Seasonal preference of habitats was examined by distance-based analysis. Seasonal distributions of nigorobuna and gengoroubuna in Lake Biwa were observed including consecutive two spawning seasons. It was revealed that seasonal migration patterns of nigorobuna and gengoroubuna were different. Nigorobuna appeared mainly around the release site all the year round, while gengoroubuna migrated to the North Basin after their spawning season, where they stayed during the non-spawning season, and moved to the South Basin in the next midwinter, where they stayed until the end of the next spawning season. It was also revealed that gengoroubuna preferred lower water temperature than nigorobuna. Gengoroubuna moved faster than nigorobuna and ginbuna. There were high-degree correlations in distance ratios of each station during spawning seasons in the release year and the next year in both nigorobuna and gengoroubuna, suggesting a multiyear use for the same spawning site. Through these results, deeper understanding of these endangered fish species in Lake Biwa and information to help the development of effective conservation programs would be provided.

Keywords: crucian carp, acoustic telemetry, seasonal migration, reproductive homing

1. Introduction or submerged-plant zone along the shoreline (Yamamoto et Lake Biwa is the largest natural lake in Japan and can be al., 2006; Suzuki et al., 2007). The spawning sites extend into divided into North Basin and South Basin by the narrowest influent streams, satellite lakes, irrigation channels or paddy region. Lake Biwa is one of a small number of ancient lakes waters connected to the lake and so on. There are many in the world and provides habitats to many endemic species spawning sites along the coast of the South Basin (Kohashi et (Rossiter, 2000). Of 71 fish species living in Lake Biwa, 13 al., 1994; Yamamoto et al., 2006). Larva and early juvenile of species are endemic including 7 cyprinid fish species (Yuma these crucian carp feed on zooplankton as its initial feed et al., 1998). Crucian carp living in Lake Biwa consist of two (Nakamura, 1969; Hirai, 1972; Nagoshi, 1977). Juveniles of endemic species, nigorobuna auratus grandoculis nigorobuna and gengoroubuna form schools when they reach (CAG) and gengoroubuna Carassius cuvieri (CCU), and one up to 1.6 cm and 1.8 cm of body length respectively, and epidemic species, ginbuna Carassius auratus langsdorfii move away from the shoreline (Hirai, 1972; Nagoshi, 1977; (CAL). Although the endemic species are endangered, they Usuki et al., 1994). Around this period, their feeding habits are also important fishery resources. These crucian carps are begin to diverge. Nigorobuna and ginbuna mainly feed on medium-sized cyprinoid fish (maximum body length: BL benthos and periphyton, while gengoroubuna mainly feed on > 40 cm) (Nakamura, 1969). Nigorobuna is a high-value fish- phytoplankton (Hirai, 1972; Nagoshi, 1977). These fish spe- ery resource as the main ingredient of Funa-, a traditional cies are familiar in Japan, but there is little knowledge about fermented food. Gengoroubuna have been cultured and intro- where and how they live after this period because Lake Biwa duced into lakes and ponds all over Japan. It is now one of the is too large to get the information about their locations. Basic most familiar targets of recreational fishing. However, the knowledge in their distribution by life cycle is critically population of these endemic fish species in Lake Biwa recently important for conservation of these resources. Recently it has has decreased drastically (Yuma et al., 1998; Yamamoto et al., been possible to acquire information about the locations of 2006) and they got registered in Threatened Category IB of fish living in vast and deep water areas by using acoustic the Red List of Ministry of the Environment, Japan in 2007. telemetry (Lucas and Baras, 2000). Kunimune et al. (2011) The spawning season of crucian carp in Lake Biwa is April reported that nigorobuna which spawned in the South Basin to June (Hirai, 1972; Nagoshi, 1977). They spawn in emergent stayed near their spawning sites all the year round and that

19 Yoshio Kunimune, Yasushi Mitsunaga gengoroubuna migrated seasonally between the North and rowest region. There are as many as 120 influent rivers, while South Basins based on their telemetry experiment in 2007. Seta River is the only effluent river located at the south end of They also discussed the relation between the difference in sea- Lake Biwa. The area and the water volume of the North Basin sonal distribution patterns and high water temperature in the are 11 times and 99 times greater respectively than that of the South Basin in summer. Nigorobuna stayed in the South South Basin. Most of the rainwater in the catchment area is Basin, while gengoroubuna migrated to the North Basin to collected in the North Basin, flows down into the South Basin, avoid the high water temperature. and then outflows into Seta River. The North Basin is deep Natal homing for spawning has great adaptive significance (average depth: 43 m, maximum depth: 104 m) and has a to reproductive strategy (Leggett, 1977; Dittman and Quinn, steeply angled topography and few observed littoral zones. In 1996; Odling-Smee and Braithwaite, 2003). It has been contrast, the South Basin has a mean water depth of only 4 m reported that many fish species including cyprinoid fish use the and the entire South Basin is classified as littoral (Tsujimura et same spawning site every year (L’Abee-Lund and Vbllestad, al., 2000). The North Basin is mesotrophic and the South 1985; Lucas and Batley, 1996). Many of such fish appear to Basin is eutrophic. Emerged and submerged plants grow along have a habit of natal homing to maintain its strains and genetic the shoreline and in the littoral zones. In spring and summer, diversity (Odling-Smee and Braithwaite, 2003). these plants grow in large areas of the South Basin and pro- The objects of this study were to confirm reproducibility of vide spawning grounds to many fish species. the telemetry experiment performed by Kunimune et al. (2011) 2.2. Experimental fish to review the seasonal distributions of crucian carps, including Nigorobuna and gengoroubuna captured using eight set nets migration patterns, habitat preferences and moving speeds, belonging to Otsu Fisheries Cooperative off the west coast of furthermore, to characterize the usage of spawning sites in the South Basin from 21 April to 26 May 2008 were used for consecutive two spawning seasons. Through this work, deeper the experiment (Fig. 1, Table 1). This series of capture had understanding about these endangered fish species in Lake been granted exceptional permission by the governor of Shiga Biwa and information to help development of effective con- prefecture. Body measurements and inspection of gonads of servation programs would be provided. the fish were performed during the surgeries for acoustic telemetry. All of the experimental fish were supposed to be not 2. Methods younger than 3 years old based on the previous study of these 2.1. Study area fish species (Tomoda, 1960; Nagoshi, 1977; Nishimori, 1994). Lake Biwa having an area of 670 km2 is the largest natural Fish species was identified by body shape and density of the lake in Japan (Fig. 1). It can be divided into the northern part first gill raker before surgery (Tomoda, 1960) and a small (North Basin) and the southern part (South Basin) by the nar- specimen was obtained from anal fin of each fish for subse- quent random amplified polymorphic DNA (RAPD) assay (Suzuki et al., 2007). If the results of fish species identifica- tion by external appearance and RAPD assay were inconsis- tent, RAPD assay was repeated once more. When the assay provided the same result as the previous assay, the result was adopted. In this way, one fish identified as nigorobuna by external appearance was considered to be ginbuna according to the result of RAPD. Thus twenty nigorobuna (CAG 24–43), ten gengoroubuna (CCU 12–21) and one ginbuna were pro- vided for the acoustic telemetry. 2.3. Acoustic telemetry According to the method described by Komeyama et al. (2007), an ultrasonic transmitter (V13-1L; Vemco Ltd., Canada) was surgically implanted into the abdominal cavity of each specimen. The fish were anesthetized by immersing them in lake water including 0.05% 2-phenoxyethanol for 3 to 5 min- utes. Each surgery took approximately the same time of 5 minutes. The ultrasonic transmitter with a weight in water of Fig. 1 Study area. Each solid circle indicates a station (St.) where 6 g sent out 69-kHz coded ultrasonic signals. These signals a receiver was installed. The numerals on each map are the had individual ID information and were transmitted randomly station numbers. The receivers at St. 13 and St. 14 were installed on the boundary between the North and South at intervals of 30 to 90 sec for about 450 days until the batter- Basins. ies ran down. The weight of the transmitter was not heavier

20 Multiyear use for spawning sites by crucian carp

Table 1 Summary of acoustically tagged fish. Tagged fish ID Release date Sex Body length (cm) Body weight (kg) Carassius auratus grandoculis CAG24 21-Apr F 34.5 1.35 CAG25 22-Apr F 29.5 0.80 CAG26 23-Apr F 37.0 1.95 CAG27 24-Apr F 35.0 1.30 CAG28 25-Apr F 33.5 1.20 CAG29 26-Apr F 34.0 0.95 CAG30 27-Apr F 32.0 1.05 CAG31 30-Apr F 35.7 1.15 CAG32 1-May F 39.0 1.55 CAG33 5-May F 40.0 1.65 CAG34 6-May F 30.5 0.80 CAG35 9-May F 32.0 0.90 CAG36 10-May F 33.0 0.80 CAG37 12-May F 39.5 1.30 CAG38 13-May F 35.5 0.95 CAG39 16-May F 29.5 0.70 CAG40 17-May F 29.0 0.60 CAG41 18-May F 30.0 0.85 CAG42 19-May F 31.5 0.90 CAG43 22-May F 34.0 1.05 Carassius cuvieri CCU12 21-Apr F 37.0 1.80 CCU13 2-May F 40.7 2.05 CCU14 5-May NC 33.2 1.50 CCU15 9-May F 33.0 0.95 CCU16 19-May M 28.5 0.60 CCU17 21-May M 36.3 1.25 CCU18 22-May M 32.5 1.15 CCU19 23-May F 34.8 1.30 CCU20 23-May F 36.0 1.55 CCU21 26-May F 36.0 1.65

F: female, M: male, NC: not confirmed

than 2% of the weight of the fish. After surgery, the fish were 27 were added one after another during the study (Table 2). rested for at least 3 hours in the recovery tank into which fresh Each receiver was fixed about 0.5 m from the bottom of the lake water was pumped up. After ensuring emission of signals lake with a hydrophone directed to the water surface. Because from the transmitter the fish were released at Wakamiya fish- the receivers of St. 22, 25 and 27 were installed on the moni- ing port near the set nets (Fig. 1). One of the nigorobuna indi- toring towers which located at a point of 60, 75 and 90 m deep viduals, CAG25 was recaptured 7 days after release by a set of the North Basin, they were fixed respectively on the side- net located about 7.1 km north of the release site. Because of board of each tower at about 1 m below water surface with a the recapture, the fish was dead, and the transmitter was hydrophone directed to the bottom. The receiver of St. 20 got reused to another fish, CAG43 (Table 1). out of order from 29 October 2008 to 18 March 2009 and Signals from acoustically-tagged fish were automatically could not acquire any data during this period. According to received by 28 ultrasonic receivers (VR2 series; Vemco Ltd.) the preliminary study conducted to measure the potential dis- around Lake Biwa (Fig. 1, Table 2). Each station (St.) was tance of signal receiving at the center of the South Basin in numbered 1 to 28 from south to north. Sts. 17, 19, 22, 23, 25, April 2007, the receiver could receive signals from the trans-

21 Yoshio Kunimune, Yasushi Mitsunaga

Table 2 Summary of stations. Station No. Water depth (m) Structural object Additional instal 1* 1 Pier 2* 2 Artificial spawning bed 3* 4 Monitoring tower 4 2 Water intake tower 5 2.5 Artificial spawning bed 6* 3.5 Pile of set net 7 3.5 Pile of set net 8 3.5 Pile of set net 9* 4.5 Pile of set net 10* 3.5 Pile of set net 11 3.5 Pile of set net 12* 2 Artificial spawning bed 13 1.5 Bridge column 14* 6.5 Bridge column 15* 10.5 Pile of set net 16 2.5 Artificial spawning bed 17 2 Pier 16-Mar-09 18 12 Pile of set net 19 11 Pile of set net 18-Mar-09 20 2 Artificial spawning bed 21* 2 Artificial spawning bed 22 60 Monitoring tower 30-Jul-08 23 10 Water intake tower 19-Mar-09 24* 13 Pile of set net 25 75 Monitoring tower 19-Mar-09 26* 1.5 Artificial spawning bed 27 90 Monitoring tower 30-Oct-08 28* 3 Artificial spawning bed

* A temperature data logger was installed.

mitter up to 200 m apart. Received data were stored in the expressed as a percentage as per equation below, memory of each receiver and manually downloaded into a PC every 4 months. Appearance ratio (%) = 2.4. Water temperature (Number of recorded fish/Number of released fish) × 100 At 13 Sts. (1–3, 6, 9, 10, 12, 14, 15, 21, 24, 26 and 28) of (1) the total 28 Sts. (Table 2), water temperature was monitored at intervals of 30 minutes by temperature data loggers (DST- To examine the seasonal selection and preference of the Milli; Star-Oddi, Iceland) placed just above the receiver habitats of the fish, distance ratio for each St. was calculated by hydrophone from 4 April to 27 July 2008. distance-based analysis (Conner and Plowman, 2001; Conner

2.5. Data analysis et al., 2003). Distance ratio (Di) was the ratio of actual dis-

Assuming that the spawning period of nigorobuna and gen- tances between fish and each station (Ui) to theoretical aver- goroubuna was April to June in Lake Biwa (Tomoda, 1960; age distance (Ri) as follows (Kunimune et al., 2011): Nakamura, 1969; Hirai, 1972; Nagoshi, 1977), the study D = U / R (2) period was divided into five experimental period three months i i i N each; April to June, July to September, October to December R = rij / N (3), i ij of 2008, January to March, and April to June of 2009. Appearance ratio of crucian carp at each station was where N is the total number of stations (St.) and rij is the dis-

22 Multiyear use for spawning sites by crucian carp

tance from St.i to St.j. The distance ratio (Di) shows the degree ≦ 24 hours. of preference of fish to the station (St.i). The smaller the dis- 3. The signal should not be received at multiple Sts. simul- tance ratio is relative to 1.0, the more the fish prefer the St. taneously. Conversely the larger the distance ratio is relative to 1.0, the 4. Calculation should be done only for adjacent Sts. on time more the fish avoid the St. Using the water temperature data series data. collected by the temperature loggers, daily average water tem- perature maps were created by Geographic Information Sys- In this way moving speed data for each fish were obtained. tem (GIS) software (ArcGIS9.3, ESRI, USA). The water Outliers were excluded from these data using Smirnov-­ temperature at Sts. with no logger was interpolated from the Grubbs’ test with a 5% level of significance. Then values of temperature map. In order to assure the accuracy of this moving speed were compared between fish species using method, a preliminary experiment was conducted. The water Mann-Whitney’s U test. Two ginbuna were misclassified as temperature was measured at 18 sites in the South Basin for nigorobuna during identification by external appearance and 17 days in May to June 2008 and compared with the value implanted transmitters in (CAL1, BL 33.0 cm; CAL2, BL interpolated from the temperature map. There was no signifi- 31.5 cm). CAL1 and CAL2 were released in 2007 and 2008 cant difference between the measured temperature and inter- respectively, and the data of these fish were included for anal- polated temperature (n = 18, P > 0.1, t-test). ysis of moving speeds. In April to July 2008, there were two groups of experimen- tal fish. The first group was consisted of the fish which were 3. Results released in 2007 by Kunimune et al. (2011) and from which 3.1. Seasonal distribution signals were still received (CAG2, 3, 5, 7, 9 and 16; CCU4, 5, During April to June of 2008, the first spawning season 6, 7 and 10) and another one consisted of new acoustically-­ after release, signals from the experimental fish except for one tagged fish which were released in 2008. For all of these fish, nigorobuna (CAG39) and one gengoroubuna (CCU18) were the daily average water temperature at the St. which received detected. Afterward number of fish which signals could be signals from an individual fish was defined to be ambient detected began to decrease. Nevertheless four nigorobuna water temperature (AWT) of that fish on that day. Monthly (CAG32, 33, 37 and 41) and five gengoroubuna (CCU13, 16, AWTs of nigorobuna and gengoroubuna were compared using 17, 20 and 21) were detected until the second spawning sea- Mann-Whitney’s U test. son in 2009. For each of the fish released in 2007 or 2008 whose signals Seasonal distributions of nigorobuna and gengoroubuna were detected again during the next spawning season (April to were depicted on a map as appearance ratios (Fig. 2a–e). No

June) in the South Basin, the distance ratios among Sts. during signal was received by St. 23–28. Distance ratios, Di’s of each each of those two spawning seasons were compared using St. were given in Fig. 3a–e for each experimental period. Spearman’s rank correlation test. CCU7 which had been Nigorobuna appeared mainly around the release site during released in 2007 stayed at St. 26 and 28, the northern most the first spawning season, Sts. 8, 9, 7, 6, 10 and 3 in ascending detection sites and did not migrate back to the South Basin in order of distance ratio (the same rule applies to the following) the spawning season of 2008 (Kunimune et al., 2011). This and any migration to the North Basin was not observed except fish was excluded from the comparison. that one fish appeared around St. 15 on 25 April. During the Using the data collected from the fish released in 2007 same period gengoroubuna preferred Sts. 2, 3, 1, 6, 7 and 9 (Kunimune et al., 2011) and 2008, horizontal moving speed (Fig. 2a, 3a) while they were detected in a wider area than (BL/s) was estimated. It was impossible to trace swimming nigorobuna by St. 1 through St. 17. courses of fish in exact detail in telemetry study, so it was During July to September of 2008, six nigorobuna (CAG26, assumed that fish moved in a straight line from one St. to 33, 37, 38, 40 and 41) and two gengoroubuna (CCU13 and another. Therefore moving speed might be underestimated 17) were detected. Nigorobuna preferred Sts. 2, 5, 4, 3, 9 and when the interval between receptions or the distance between 7. Preference of gengoroubuna shifted to the North Basin, and Sts. for two consecutive signals from one fish was long. In it preferred Sts. 18, 20, 21, 15, 22 and 14 (Fig. 2b, 3b). addition, as errors in moving distance depended on the diame- The difference of appearance of nigorobuna and gengorou­ ter of the reception area, relative errors might be significant buna was the most evident during October to December of when the distance between Sts. was too short. Thus criteria 2008 (Fig. 2c, 3c). Four nigorobuna (CAG33, 37, 38 and 41) were set arbitrarily as follows in attempting to calculate mov- were detected, mainly around the release site and preferred ing speed of crucian carp swimming freely in Lake Biwa. Sts. 9, 8, 7, 10, 6 and 3. Three gengoroubuna (CCU13, 16 and 21) were detected and preferred at Sts. 18, 20, 15, 14, 16 and 13. 1. The distance between Sts. should be ≧ 1 km and ≦ 5 km. During January to March of 2009, four nigorobuna (CAG32, 2. The interval between receptions should be ≧ 1 hour and 33, 37 and 41) appeared all over the South Basin and preferred

23 Yoshio Kunimune, Yasushi Mitsunaga

Fig. 2 Seasonal distribution patterns for both nigorobuna (open bar) and gengoroubuna (solid bar) during the five experimental periods. Each bar indicates percentage of appearance ratio (% = [number of recorded fish]/[number of released fish] × 100). The numerals on each map are the station numbers. a: Apr.–June 2008, b: July–Sept. 2008, c: Oct.–Dec. 2008, d: Jan.–Mar. 2009, e: Apr.–June 2009. around the release site (Sts. 7, 9, 8, 6, 3 and 1; Fig. 2d and 3.2. Water temperature and appearance ratio Fig. 3d). The appearance area of four gengoroubuna (CCU13, during the spawning period 17, 18 and 21) extended south compared to the previous Monthly average water temperature of the south end of the period, and they appeared extensively from St. 1 through St. North Basin and the South Basin from April to July in 2008, 22. They were frequently detected at Sts. 2, 3, 1, 6, 7 and 9. as well as total appearance ratios of the fish released in 2007 During April to June of 2009, the second spawning season and 2008, are shown in Fig. 4a–d. During this period, there after release, four nigorobuna (CAG32, 33, 37 and 41) and was a mild water temperature gradient so that it increased five gengoroubuna (CCU13, 16, 17, 20 and 21) were detected, from the south end of the North Basin to the south end of the and all of them stayed in the South Basin. Nigorobuna appeared South Basin. Average water temperature remarkably got mainly around the release site as before at Sts. 9, 8, 10, 4, 7 higher and higher by the month. In April and May, both nigo- and 11 (Fig. 2e, 3e). Gengoroubuna preferred mainly Sts. 2, 3, robuna and gengoroubuna were detected all over the South 1, 6, 7 and 9 similarly to the previous spawning season. Basin with a central focus on the release site. In June and July, there was a clear tendency that the main appearance sites of

24 Multiyear use for spawning sites by crucian carp

Fig. 3 Habitat preferences of nigorobuna (open bar) and gengoroubuna (solid bar) in each season from distance-based analyses (Mean dis- tance ratio + SD). Dashed line indicates the prediction from the null hypothesis. If the distance ratio is <1, then the station was pre- ferred. Alternatively, if the distance ratio is >1, then the station was avoided. a: Apr.–June 2008, b: July–Sept. 2008, c: Oct.–Dec. 2008, d: Jan.–Mar. 2009, e: Apr.–June 2009. gengoroubuna shifted to the south end of the North Basin. (P > 0.1). Monthly average AWTs of nigorobuna and gengoroubuna for this period of four months are given in Fig. 5. AWT of both 4. Discussion nigorobuna and gengoroubuna elevated with a rise of lake Seasonal distributions of nigorobuna and gengoroubuna in water temperature. However, AWT of gengoroubuna was con- Lake Biwa were observed including consecutive two spawning stantly lower than that of nigorobuna. Particularly AWTs of seasons. It was revealed that seasonal migration patterns of gengoroubuna in June and July were significantly lower than nigorobuna and gengoroubuna were different (Fig. 2, 3). those of nigorobuna (n = 93, 104 in June; n = 38, 20 in July: Acoustically-tagged nigorobuna released in the South Basin P < 0.01). appeared mainly around the release site all the year round. In 3.3. Distance ratios in consecutive two spawning contrast, an obvious seasonal migration pattern was observed in seasons gengoroubuna. Acoustically-tagged gengoroubuna released in Distance ratios during spawning seasons in the year of the South Basin migrated to the North Basin after their spawn- release and the next year are shown in Fig. 6a–d for the fish ing season, where they stayed during the non-spawning season, released in 2007 and 2008. There were highly significant cor- and moved to the South Basin in the next midwinter, where relations in both of the years in nigorobuna (n = 102, r = 0.76 they stayed until the end of the next spawning season. These in 2007; n = 68, r = 0.92 in 2008: P < 0.001) and less signifi- findings indicate that nigorobuna stayed around spawning sites cant correlations in gengoroubuna (n = 88, r = 0.50 in 2007; all the year round, while that main habitat of gengoroubuna n = 110, r = 0.63 in 2008: P < 0.001). was the North Basin and used the South Basin for spawning 3.4. Moving speed because the tagged fish were captured and released during their Moving speed records were obtained from time series data spawning season and confirmed their gonadal maturation. of nigorobuna (n = 442), gengoroubuna (n = 215) and ginbuna During the procedures of tagging, many fish excreted eggs or (n = 8) respectively (Fig. 7). The average moving speed of milt from their cloacas. All fish except one gengoroubuna had gengoroubuna was significantly higher than those of nigoro- matured gonads and were considered to have spawned just buna and ginbuna (P < 0.01) and there was no significant dif- before capture or to be ready to spawn. Komeyama et al. (2008) ference between the moving speed of nigorobuna and ginbuna reported that nigorobuna released in the South Basin stayed

25 Yoshio Kunimune, Yasushi Mitsunaga

Fig. 4 Monthly appearance ratios of nigorobuna (open bar) and gengoroubuna (solid bar), and water temperature gradient with contours on the map from April to July in 2008. The numerals on each contour line are the average water temperature. There was a mild water temperature gradient so that it increased from the south end of the North Basin to the south end of the South Basin. Average water temperature remarkably got higher and higher by the month. a: April, b: May, c: June, d: July.

the presence of predators and physical environment. It was also revealed that gengoroubuna preferred lower water temperature than nigorobuna (Fig. 5) suggesting that water temperature might play a role in causing differences between seasonal migration patterns of these fish species. In addition, AWTs and habitats of the fish by month (Fig. 4, 5) suggested that gengoroubuna might move to the North Basin when water temperature of their habitat in the South Basin elevated to a specific temperature during the spawning season. Also in their Fig. 5 Monthly average ambient water temperature (AWT) of nigorobuna (open bar) and gengoroubuna (solid bar) from previous telemetry experiment in 2007, Kunimune et al. (2011) April to July in 2008. (Mean AWT + SD). * significantly had observed that one gengoroubuna (CCU5) moved from the different by Mann-Whitney’s U test at P < 0.01. South Basin to the North Basin in a short time. These findings suggest that seasonal migration of gengoroubuna between the there almost all the year round. Kunimune et al. (2011) conducted South and North Basins does not occur gradually for optimal a telemetry experiment on nigorobuna and gengoroubuna environment condition but that it occurs and completes and first demonstrated that these fish species had different quickly in a short time triggered by a threshold for AWT. The seasonal migration patterns. Reproducibility of their results fact that nigorobuna preferred the South Basin all the year was confirmed in this study. The fact that these closely related round unlike gengoroubuna may indicate that the former can fish species living in the same water area have distinctly tolerate large seasonal fluctuation in water temperature in the different seasonal migration patterns is interesting with respect South Basin better than the latter. Fujioka (2002) reported that to survival strategies. This should be further discussed in terms nigorobuna juveniles could grow at high water temperature of adaptabilities to various factors such as food availability, (30°C) as well as at 24°C. Fukusyo (1968) compared cruising

26 Multiyear use for spawning sites by crucian carp

Fig. 6 Comparison of distance ratios in consecutive two spawning seasons by Speaman’s rank correlation test. a: nigorobuna released in 2007, b: gengoroubuna released in 2007, c: nigorobuna released in 2008, d: gengoroubuna released in 2008.

depends on a trade-off between the hatching rate of eggs deposited at low water temperature and the survival rate of yearling fish in winter. There have been no reports about the relationship between water temperature and cues to start spawning, hatching rates of eggs or survival rates of young fish for nigorobuna and gengoroubuna. The timing of spawn- ing may have critical effects on the hatching rate and the sur- vival rate of larval and juvenile fish. A detailed comparative Fig. 7 Average moving speed of nigorobuna (CAG), ginbuna study on the relationship between environmental factors and (CAL) and gengoroubuna (CCU) (Mean speed + SD, BL/s). spawning of nigorobuna and gengoroubuna should reveal the * significantly different by Mann-Whitney’s U test at P < 0.01. adaptation to environment and the reproductive strategy in these fish species. There were high-degree correlations in distance ratios of performance of gengoroubuna, Carassius auratus each St. during spawning seasons in the release year and the auratus and hybrid F1 between female ginbuna and male next year both on nigorobuna and gengoroubuna (Fig. 6) sug- kinbuna Carassius auratus sp at various temperatures. The author gesting that these iteroparous fish might use the same spawn- found that all crucian carp gave the best cruising performance ing sites every year. Generally, migration back to its birthplace at 28°C in the flow rate of 45 cm/s and that gengoroubuna for spawning has been considered to have great adaptive sig- could swim longer than goldfish and hybrid F1. At 31°C; nificance to reproductive strategy in that mature fish migrate however, cruising time of gengoroubuna drastically decreased simultaneously to the most optimal site for the development to the level lower than goldfish and hybrid F1. This report of eggs and fries to maximize breeding success (L’Abee-Lund might indicate that gengoroubuna could not tolerate high and Vbllestad, 1985). Strict natal homing has been recognized water temperature than Carassius auratus sp. in salmonid fish (Dittman and Quinn, 1996; Odling-Smee and There are many observations that water temperature serves as Braithwaite, 2003). With advances in telemetry technologies, a cue to start spawning (Franklin and Smith, 1963; Malmqvist, natal-homing cases in fish have been recognized (Lucas and 1980; Lucas and Batley, 1996) especially in Barbus barbus Batley, 1996; Malmqvist, 1980; Baras and Philippart, 1999; (Baras and Philippart, 1999). In this rheophilous cyprinoid Robichaud and Rose, 2001), although no natal-homing cases fish, the threshold water temperature to start spawning in Carassius sp. have been reported. Correlations of distance

27 Yoshio Kunimune, Yasushi Mitsunaga ratios in the release year and the next year were higher in select different site or environments for spawning. Spawning nigorobuna which stayed in the South Basin all the year round sites have been characterized partially, and there have been a than in gengoroubuna which migrated seasonally between the few studies reporting differences between nigorobuna and South and North Basins, suggesting that the degree of fidel- gengoroubuna (Kohashi et al., 1994; Suzuki et al., 2007). It is ity to spawning sites might be different between these fish known that nigorobuna spawn at deeper areas than that of species. Lower fidelity may explain the fact that one individual gengoroubuna in emerged vegetation zones (Kohashi et al., of acoustically tagged gengoroubuna released in 2007 did not 1994; Suzuki et al., 2007). In addition, nigorobuna have been return to the South Basin and changed its spawning site to the recognized to run into rice paddies and spawn there (Kohashi north end of the North Basin during next spawning season et al., 1994; Ueno et al., 2002), unlike gengoroubuna. The (Kunimune et al., 2011). Though it was not clear whether the possibility of reproductive homing to the different site in cru- experimental fish in this study migrated to their birthplaces cian carp points out the importance of conserving spawning during spawning periods or not, natal homing might have sites for each species. The optimal site or environment for adaptive significance also for Carassius sp. which spawn in spawning might be naturally specified for each species. schools. Gengoroubuna swam faster than nigorobuna and ginbuna. 5. Conclusion Fujiwara et al. (1995) measured cruising speed of juvenile Conservation of endangered species involves complex prob- nigorobuna using a swimming tunnel. According to their lems especially when the species is industrially valuable. In study, the juvenile whose BL ≧ 16 mm swam at a rate of 0.4– this context, to set protected areas and limit harvest season 0.9 BL/s. Moving speed derived from a telemetry study often tightly, it is indispensable to be supported by convincing sci- be underestimated. Still, the moving speeds calculated for entific evidence. In the present study, apparent differences in the three crucian carp species in this study were consistent well ecology of nigorobuna and gengoroubuna, seasonal migration with their values derived from four assumptions and large patterns, preference of water temperature and moving speed sample number. It is necessary to continue to estimate the were suggested. Taking these characteristics into account and moving speed in the natural environment of each fish species locating their spawning site as accurately as possible in not in terms of energy consumption and growth strategy. Nigoro- only Lake Biwa but also surrounding waters could hopefully buna and ginbuna feed mainly on benthos and periphyton, restore the population of nigorobuna and gengoroubuna in the while gengoroubuna swims in intermediary water and feeds future. on phytoplankton (Nakamura, 1969; Hirai, 1972; Nagoshi, 1977). Kunimune et al. (2011) reported that gengoroubuna Acknowledgements migrated over a large region in the North Basin during the We express our sincere gratitude to Mr. Hiroyuki Ukai, an non-spawning season, which was thought to be feeding migra- administrative officer of the Fisheries Cooperative Association tion. Such a difference in feeding habit might have affected of and the set-net owner, for his kind assis- the moving speed. The high moving speed of gengoroubuna tance and advice. We also thank Prof. Toru Kobayashi, Kinki could increase the opportunity to filter phytoplankton, while University for his support in the RAPD assay. We also thank the low moving speed of nigorobuna might reflect foraging Prof. Takeshi Yamane and Prof. Tsutomu Takagi, Kinki Uni- for benthos. versity, Dr. Masanari Matsuda, Lake Biwa Museum for their In 2008, 88.1% stock of nigorobuna in Lake Biwa was esti- advice in this experiment. This research was partially sup- mated to be artificial seed as a result of extended seed release ported by the 21st Century Centre of Excellence program, (Shiga Prefectural Fisheries Promotion Foundation, Data Global Centre of Excellence program and the PRO NATURA for 2010 Resource Recovery Plan Promotion Project Review FUND. Meeting of Fishery Operators). Efforts such as exploring release sites to maximize survival rate have been exercised to References promote effective stock enhancement (Ueno et al., 2002; Baras, E. and J. C. Philippart, 1999. Adaptive and evolutionary Fujiwara et al., 2011). The results of this study suggest that significance of a reproductive thermal threshold in Barbus nigorobuna and gengoroubuna did multiyear use for spawning barbus. J. Fish Biol., 55, 354-375. sites and led to the idea that these crucian carp select spawn- Conner, L. M. and B. W. Plowman, 2001. Using Euclidean distances to assess nonrandom habitat use. In: Millspaugh J., Marzluff ing sites very strictly in alongshore emerged-plant zones. To J. (Eds.) Radio Telemetry and Animal Populations. Califor- maximize the survival rate, appropriate release sites should be nia, Academic Press, pp. 275-290. selected in the light of reproductive homing of wild fish. Conner, L., Smith, M. D. and L. W. Burger, 2003. A comparison of Although nigorobuna and gengoroubuna intercrossed easily in distance-based and classification-based analysis of habitat captivity (Kobayashi, personal communication), reproductive use. Ecology, 4, 526-531. isolation was secured in Lake Biwa. These crucian carp might Dittman, A. H. and T. Quinn, 1996. Homing in pacific salmon:

28 Multiyear use for spawning sites by crucian carp

Mechanisms and ecological basis. J. Exp. Biol., 199, 83-91. implications for river management. J. Appl. Ecol., 33, 1345- Franklin, D. R. and L. L. Jr. Smith, 1963. Early life history of the 1358. northern pike, Esox Lucius L., with special reference to the Lucas, M. C. and E. Baras, 2000. Methods for studying spatial factors influencing the numerical strength of year classes. behaviour of freshwater fishes in the natural environment. Trans. Am. Fish. Soc., 92, 91-110. Fish Fish., 1, 283-316. Fujioka, Y., 2002. Effects of hormone treatments and temperature on Malmqvist, B., 1980. The spawning migration of the brook lamprey, sex-reversal of Nigorobuna Carassius carassius grandoculis. Lampetra planeri Bloch, in a South Swedish stream. J. Fish Fish. Sci., 68, 889-893. Biol., 16, 105-114. Fujiwara, K., Usuki, T., Kobayashi, T. and E. Mizutani, 1995. Nagoshi, M., 1977. Ecological studies on the population of Gengoro- Importance of a Reed Community as a nursery for Nigoro- buna, Carassius cuvieri, in Lake Biwa-III, Yearly fluctua- buna, Carassius auratus grandoculis. Rep. Environ. Sys. tion of age composition and growth. Bull. Fac. Mie. Univ., 4, Res., 23, 414-419. (in Japanese with English abstract) 31-44. (in Japanese with English abstract) Fujiwara, K., Usuki, T., Nemoto, M. and S. Kitada, 2011. Early life Nakamura, M., 1969. Cyprinid fishes of Japan. Tokyo, Midori-­ ecology of nigorobuna Carassius auratus grandoculis in syobou. (in Japanese) reed zone of Lake Biwa and physiological adaptation to the Nishimori, K., 1994. The growth curve and the composition of body environment. Nippon Suisan Gakkaishi, 77, 387-401. (in length of nigorobuna which appeared in Yamanoshita-bay of Japanese with English abstract) Lake Biwa. Rep. Shiga Prefecture Fish. Exp. Station, 49-50. Fukusyo, K., 1968. The racial difference of temperature responses (in Japanese) among cyprinid fishes genus Carassius. Bull. Jap. Soc. Sci. Odling-Smee, L. and V. A. Braithwaite, 2003. The role of learning in Fish., 34, 876-881. fish orientation. Fish Fish., 4, 235-246. Hirai, K., 1972. Ecological Studies of fry and juvenile of fishes at Robichaud, D. and G. A. Rose, 2001. Multiyear homing of Atlantic aquatic plant areas in a bay of Lake Biwa-III: Relationship cod to a spawning ground. Can. J. Fish. Aquat. Sci., 58, of the food habits to the habitat of Nigorobuna (Carassius 2325-2329. auratus grandoculis) larvae. Jap. J. Ecol., 22, 69-93. (in Japa- Rossiter, A., 2000. Lake Biwa as a topical ancient lake. Adv. Eco. nese with English abstract) Res., 31, 571-598. Kohashi, K., Ijima, S., Sakai, A. and M. Ide, 1994. Spawning of cru- Suzuki, T., Kobayashi, T. and K. Ueno, 2007. Genetic identification cian carps in the major spawning site of Lake Biwa. Rep. of larvae and juveniles reveals the difference in the spawn- Shiga Prefecture Fish. Exp. Station, 52-53. (in Japanese) ing site among Cyprininae fish species/subspecies in Lake Komeyama, K., Mitsunaga, Y., Yamane, T. and M. Matsuda, 2007. Biwa. Environ. Biol. Fish., 82, 353-364. The influence of water temperature on the appearance of Tomoda, Y., 1960. Morphological studies on the crucian carp in common carp Cyprinus carpio around a set-net in the south Lake-Biwa-I. Nippon Suisan Gakkaishi, 26, 259-263. (in basinof Lake Biwa. J. Fish. Engineer., 44, 113-118. Japanese with English abstract) Komeyama, K., Mitsunaga, Y., Matsuda, M., Hiraishi, T., Kunimune, Tsujimura, S., Tsukada, H., Nakahara, H., Nakajima, T. and M. Y. and T. Yamane, 2008. Behavior of round crucian carp Nishino, 2000. Seasonal variations of Microcystis popula- monitored using acoustic telemetry in the south basin of tions in sediments of Lake Biwa, Japan. Hydrobiologia, 434, Lake Biwa. Nippon Suisan Gakkaishi, 74, 864-866. (in Japa­ 183-192. nese with English abstract) Ueno, S., Endo, M., Ohtani, H., Nakagawa, J., Kurohashi, N., Kunimune, Y., Mitsunaga, Y., Komeyama, K., Matsuda, M., Tazuke, M. and K. Hata, 2002. The role of paddy fields as Kobayashi, T., Takagi, T. and T. Yamane, 2011. Seasonal the spawning ground of fishes. Rep. Shiga Prefecture Fish. distribution of adult crucian carp nigorobuna Carassius Exp. Station, 92-93. (in Japanese) auratus grandoculis and gengoroubuna Carassius cuvieri in Usuki, T., Fujiwara, K., Mizutani, E. and S. Ujiie, 1994. The life his- Lake Biwa, Japan. Fish. Sci., 77, 521-532. tory of nigorobuna larvae and juvenile. Rep. Shiga Prefec- L’Abee-Lund, J. H. and L. A. Vbllestad, 1985. Homing precision of ture Fish. Exp. Station, 22-23. (in Japanese) roach Rutilus rutilus in Lake Årungen, Norway. Environ. Yamamoto, T., Kohmatsu, Y. and M. Yuma, 2006. Effects of sum- Biol. Fish., 13, 235-239. mer drawdown on cyprinid fish larvae in Lake Biwa. Lim- Leggett, W. C., 1977. The ecology of fish migrations. Annu. Rev. nology, 7, 75-82. Ecol. Syst., 8, 285-308. Yuma, M., Hosoya, K. and Y. Nagata, 1998. Distribution of the Lucas, M. and E. Batley, 1996. Seasonal movements and behaviour freshwater fishes of Japan: an historical overview. Environ. of adult barbel Barbus barbus, a riverine cyprinid fish: Biol. Fish., 52, 97-124.

29 Yoshio Kunimune, Yasushi Mitsunaga

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複数年にわたる琵琶湖産フナ類の産卵地利用 ―バイオテレメトリーを活用した行動追跡から―

國宗 義雄 *1 光永 靖 *2 *1 近畿大学大学院農学研究科，〒 631-8505 奈良市中町 3327-204 *2 近畿大学農学部，〒 631-8505 奈良市中町 3327-204

2018 年 7 月 10 日受付，2018 年 10 月 19 日採録

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