FRA

　In the Yukawa river, Nikko, Japan, catch-and-release （C&R） regulation has been adopted in all the fishing area since 2002. A questionnaire to the anglers was conducted throughout the fishing season （May 1 to September 30） in 2002 and 2003 to examine the effect of C&R regulation on sustaining brook trout （Salvelinus fontinalis） stocks. Compared to 2001, the numbers of angler were increased in 2002 and 2003, by 27.4% and 34.2%, respectively. Among the 3 angling methods （fly, lure, bait）, the percentage of fly-fisher, who had supposedly practiced C&R even before 2002, has increased in 2002 and 2003, by 20.5% to 83.8% and by 24.8% to 88.1%, respectively. Catch rate （number of fish caught/angler-hour） in 2002 and 2003 has also increased by 0.03 to 1.05 and by 0.19 to 1.21, respectively. Brook trout populations were found to remain abundant even after the fishing season by mark-recapture method （Petersen's method）. These results indicate that C&R regulation in the Yukawa river, which was accepted favorably by the anglers without serious troubles, was effective to sustain brook trout stocks.

We have developed a database system for the observation records of the small bathythermograph system SBT-500 and their related data during longline operations. The purpose of this database is to summarize and hold SBT-500 data and related data such as cruise, longline operation type, fishing gear type, biological data by species, calibration data for the sensors, and oceanographic data in order to assist analyses for studies in various fields. These data are stored in individual tables or directories in a personal computer and linked together. Using this database, analyses of 1） oceanographic conditions, 2） hooking depth, temperature and time of captured species and 3） underwater shape of longline gear can be conducted, not based on temporally and spatially limited small data sets but instead using a large amount of linked data. So far there are over 20,000 records stored, and once more data are gathered, even more reliable analyses will be possible.

　Sargassum horneri is one of the main components of Sargassum beds which play important roles in the coastal fisheries resource enhancement. Differentiation in seasonality, mainly in maturation season, has been known among local populations of this annual species, although ecological information about them has been rare. In the western Seto Inland Sea, spring-maturing populations, which is the common type in the western part of Japan, and autumn-maturing populations have been reported to coexist in the same sea area. The present study was conducted to investigate the ecological and physiological backgrounds of the phenological differentiation among S. horneri populations in and around Hiroshima Bay. The outline of the study is as follows;
1. Seasonal differences in growth and maturation were observed among S. horneri populations inhabiting along the transect from the innermost to the exterior area of the bay. Populations in the inner area started marked increase in plant length due to rapid stem elongation in summer, and mature in autumn to early winter. On the contrary, populations at the mouth or exterior area of the bay started to elongate in autumn, and although receptacle formation began during winter, the peak of gamete release was in spring. Transplant experiment indicated that the maturation season of the population was an inherent feature, which was not affected by ambient conditions at the transplant site.
2. The difference in seasonality between spring- and autumn-maturing populations was attributable to the different seasonal course of their developmental stages in their respective life cycles. Plant reaction to various daylength and temperature, which are important factors regulating algal seasonality, was examined on each developmental stage, i.e., the early developmental stage, the rapid elongation stage and the maturation stage. The two type populations reacted quite differently, especially to daylength conditions. For spring-maturing populations, stems elongated under 12h-day or shorter day conditions and receptacle formation was more promoted under longer day conditions within 8 h- to 14 h- day conditions. Growth and maturation of the autumn-maturing populations, on the contrary, were day-neutral.
　The inherent characteristics of their maturation seasonality were also observed in the outdoor culture experiments of refrigerated （stocked under low temperatures for certain durations） and forced （promoted growth in incubators） seedlings. The seedlings kept their original seasonality of maturation despite the control procedures described above.
3. The seasonal mortality and colonization ecology was investigated at each habitat of a spring- and autumn- maturing population.

　For both populations, the mortality rate was high just after the embryos attached to the substrata, and when plants began to elongate. The autumn- maturing population had to spend winter and early spring as germlings, which is generally regarded to be a stage of high mortality. However, germling mortality rate of the autumn-maturing population was low during winter and early spring, though their growth was very slow due to low temperature. Survival in this early developmental stage enables them to establish a stand in their habitat.

　Experimental blocks were set monthly or bimonthly to investigate seasonal algal colonization at habitats of the two S. horneri populations. At a habitat of the autumn-maturing population, colonization of S. horneri had been inhibited on the blocks placed in summer during 3 years because of the stable establishment of perennial red algae on summer blocks. Competition with these red algae was considered to affect seasonal chance of colonization and could be a selection pressure on the maturation seasonality of S. horneri. On the contrary, at a habitat of spring-maturing population, S. horneri succeeded to colonize and grow on all blocks despite of season the blocks were placed. Alternate change in physical conditions at the habitat, i.e., moderate turbulence by waves in winter and calmness in spring, was considered to be advantageous for colonization and survival of S. horneri embryos released in spring, through the reestablishment of algal succession on substrata.

　As a conclusion, seasonality differentiation among S. horneri populations in and around Hiroshima Bay is ecotypic, which is based on genetic difference rather than phenotypic plasticity. They have developed different physiological mechanisms related to their different seasonality. Seasonality ecotype of S. horneri in the study area could be an adaptive form to the ecological conditions at each habitat, to ensure sustainable establishment of the populations.