Early life ecology of Japanese smelt（Hypomesus nipponensis）in Lake Abashiri,a brackish water, eastern Hokkaido, Japan

Early life ecology of Japanese smelt, Hypomesus nippoensis MCALLISTER was examined in this study. In Lake Abashiri
connected with the Okhotsk Sea through the Abashiri River, the mean annual total catches of smelt is over 200 tons,
which is the highest in Hokkaido and also a superior rank among the areas of production of smelt in Japan. Smelt in
Lake Abashiri hatches out in inflow river of the lake in early spring. After hatching out, the larvae migrate to the lake
and pass the larval stage until late spring. When the larvae grow and shift to the juvenile stage in early summer, most
of juveniles migrate to the sea（sea migrating type），however, some of them remain in the lake（lake residence type）.
That has been kwown as the divergence of life history of smelt in Lake Abashiri. The sea migrating type returns to
the lake in late autumn and both types pass under the lake ice in winter. After ice melting, they migtare to the inflow
river for spawning and terminated their lives in one year almostly. It is known that the survival from egg to juvenile
stages fluctuates largely in each year from the past study in this lake. The cathches almost consist of 0＋ population.
Although the total catches fluctuate every year, that mechanisms related to the environmental factors are not well
understood. The aims of this study are to find the mechanisms of population dynamics and the life history divergence
of smelt, especially focusing on the relationships between early life ecology and biological, physical environments.
This study was conducted from1994 to 1998,and main items of the surveys were as follows（No.1-3 in 1995to 1997,
No.4-6 in 1994 to 1997, No.7 in 1998） : 1.Habitat environments during the larval stage. 2.Distributions of larvae in
the lake. 3.Growth and feeding ecology of larvae. 4.Habitat environments during the juvenile stage. 5.Growth and
feeding ecology of juvenile. 6.Relationships between the divergence of life history and enviromental factors. 7.
Comparisons of the habitat environments between the lake and coastal waters. The results obtained from this study
are as follows :
The physical environments in the lake during the larval stage were uniform horizontally. The abundances of
microzooplankton increased in this period rapidly, when the surface water temperature reached to 10-15℃ throughout 1995 to 1997. After declining the microzooplankton abundance, the copepod abundance increased clearly except for1996.The dominant species were brackish water species, Keratella cruciformis（rotifer） in microzooplankton community , and also brackish water species, Sinocalanus tenellus（copepod） in copepod community. After immediately hatching out, the larvae with yolk were abundant around the inflow river of the lake, however, no clear patterns could be found in the horizontal distributions of abundances and body length frequency of the yolk absorbed larvae in each sampling day. On the other hand, the clear characteristics were found in the vertical distributions , which the larvae distributed in the deep layer during the day and in surface at night. These vertical migrations thought to be related to the feeding, since the numbers of gut contents of larvae were more abundant than those collected in the day.
The incidence of the feeding larvae increased, as declining of the yolk larvae. The larvae fed on the rotifers at the
initial feeding period and the peak of rotifers abundance were coincident with the first feeding period of the larvae.
The larvae growing to 10mm in total length shifted their main prey organisms to copepods in 1995 and 1997 year class, while copepods were not observed in the gut contents of the 1996 year class. Further the survival index （the ratio of juvenile abundances to spawned egg） was the lowest in1996year class.
The averages of the water temperature, salinity, chlorophyll a concentration and abundances of crustacean plankton
during the juvenile stage throughout July to September in each year were not different significantly, except for salinity. Juve niles grew logarithmically from July to September in 1994,1995 and 1997 year class, from August to September in 1996 year class. The growth rates calculated by means of wet weights were 0.043-0.075/day in each year class. The significant positive correlation was found between the growth rate and salinity. Stomach fullness indices of juveniles became to be high in the early morning or late evening. The evacuation rates estimated from field observations was 0.1974/hour at 22℃. The food consumption rate was estimated 3.0-6．1％ of the wet weight of juvenile.
A large number of juvenile migrate to the sea from July to August in each year, after immediately the abundance of juveniles in the lake reached to maximum. The clear negative correlation （Y＝1572.6e－0.0408X, r＝0.996）was found between the available abundance of crustacean plankton per a juvenile（X：104 inds./m3/juvenile）and the number of sea migrating juveniles（Y : No. of juveniles /day）．Transfer efficiency from primary to juvenile production was estimated1.2% in the lake.
The coastal waters were occupied by high saline water originated from Soya Warm Current during the ocean life stages of juveniles in July to October. The sae water temperature was almost constant at 15℃, while the lake water temperature changed from 10 to 20℃ largely. The body sizes collected in August in the sea were larger than those collected at the same time in the lake. However, the abundance and biomass of copepods which are the main prey animals of the juveniles were higher in the lake than coastal waters from May to November. It was suggested that the salinity and lower constant water temperature in the sea were favorable for the growth of juveniles, if the available prey animals were enough.
It could be concluded that the copepod abundances when the larvae shift their preys from rotifers to copepods might play an important role in the survival and growth of the early life of smelt. Anavailable abundance of crustacean plankton per a juvenile in the lake was one of the important factors determining the life history divergence. Sea migrating type grows larger than lake residence type and returns to the lake, although sea migrating type probably encounter many risks（predations, competitions, transfer etc）．On the other hand, lake residence type can inhabit under the less predation than sea migrating type. The divergence of life history would play an important role in the maintenance of smelt population in Lake Abashiri.

Verification and identification of clonal lines induced by chromosome manipulation in Japanese flounder（Paralichthys olivaceus）
I. Verification and identification by DNA fingerprintings

DNA fingerprints were applied for confirmation and identification of clones induced by the suppression of the first
cleavage in Japanese flounder, Paralichthys olivaceus. The samples used were 9 homozygous and 3 heterozygous
clonal lines. Verification and detection of clonal lines were done by the multilocus DNA fingerprinting and the PCR
（polymerase chain reaction）-based DNA fingerprintings, RAPD（random amplified polymorphic DNA）and TREP
（tandem repeat primed）．All the fragaments of multilocus fingerprinting were shared among individuals within the
same clonal lines. However, in normal diploids, the pattern of the bands detected were different among individuals.
PCR-based fingerprintings were distinguishable between 9 different clonal lines by DNA banding pattern. DNA
fingerprinting analyses would be suitable for the application in studies on inbreeding and for the identification of
individuals and families.

Field experimental transplantation to restore depleted stock of the surf clam Mactra chinensis

Field experimental transplantation was conducted to examine the efficient method for restoring depleted stock of
the surf clam Mactra chinensis off the coast of Shimamaki west Hokkaido, Japan. In August 2000 and October 2001,
the clam （total weight＝460 and 323kg, mean shell length＝75.6 and 75.4mm）,which were collected from neighboring coast（Yoichi west Hokkaido）,were transplanted to two experimental sites with each area of 100m2 （depth＝10m）,respectively. Survival of the clam after transplanting was examined by counting the remained clam at each site by SCUBA diving, and annual recruitment was estimated by counting newly settled juveniles collected using a Smith-McIntyre grab sampler in the clam bed including both experimental sites. The clam density in both sites
decreased markedly for 17 or 18 months after transplanting by bottom disturbance due to wave action, but then remained approximately steady（mean density＝27-29 ind./m2）to the end of the experiment（the29th or 39th month after transplanting）.
It was suggested that a maximum density of the clam should be adjusted to be 27-29 ind./m2 to practice the clam transplantation efficiently when the clam about 75mm in shell length would be used. The newly settled juveniles were absent in the clam bed in 2000,in which spawning of the transplanted clam was not expected,although they occurred in the clam bed entirely with density of 2.2-2.9 ind. /0.1m2 in 2001-2003, in which the transplanted clam could spawned. However, an evidence to show that such juvenile recruitment would be due to the clam transplantation was not obtained.

Study on the size of sea cucumber, Apostichopus japonicus,Juveniles Released in the Soya Sea Area

Artificial seeds（21,000）of sea cucumber were divided into two groups by their size : large（average length 29.4mm）and small（average length 15.6mm）.They were released in the Soya port on 8August,2000. Follow-up checks were carried out at 2months, 3.5months,1year, and 2years after release. Released sea cucumbers of the large and small groups grew to be approximately 1.7 and 3.2 times in length, respectively, at 2months after release. Significant reduction in number was observed right after release ; that decrease was more pronounced in the small group. Subsequently, no reduction was observed for both groups. These reductions were inferred to result from death or disappearance out of that location ; the major reason seemed to be that the seedlings were washed out by the tide. Two-year remaininng rates were 47.0％ and 7.4％ for the large and small group, respectively. The large group demonstrated a high remaining rate, indicating the effectiveness of 30mm seedlings.

The number of eggs discharged by female plants of Sargassum confusum（Fucales ; Phaeophyta）

The number of eggs discharged by female plants of Sargassum confusum was investigated for plants sampled at Shiribeshi off southwestern Hokkaido. The number of eggs discharged by a female plant was estimated to vary from 106 to 107. The number of reproductive cells of Fucales algae were few in comparison with that of Laminariales algae.
It was suggested that Fucales algae such as Sargassum confusum were taxonomic group which has an ecological character of increasing the survival rate by producing few but large reproductive cell.

Separation usingotolith for two species of genus Ammodytes（sand lances）.（Short Paper）