Horie, Shoji

Mori, Syuiti

Negoro, Kenichiro

Suzuki, Norio

Yamamoto, Kokichi

English

Kyoto University Research Information Repository

RIGHT:URL:CITATION:AUTHOR(S):ISSUE DATE:TITLE:First Report of the RegularLimnological Survey of Lake Biwa(Oct.1965-Dec.1966) (I) : GeneralRemarkMori, Syuiti; Yamamoto, Kokichi; Negoro, Kenichiro;Horie, Shoji; Suzuki, NorioMori, Syuiti ...[et al]. First Report of the Regular Limnological Survey of Lake Biwa(Oct.1965-Dec.1966) (I) : General Remark. Memoirs of the Faculty of Science, KyotoUniversity. Series of biology. New series 1967, 1(1): 36-401967-10-14http://hdl.handle.net/2433/258767     IIVIEI•lolRs eF nE FAcuLTy oF SclENs cE, Kyo'Iro UNIvERITy, SERIEs oF BIoLoGy                      Vol. I, )<rio. 1, pp. 36-4e,Nov. 1967First Report of the Regular Limnological Survey           of Lake Biwa(Oct. 1965-Dec. 1966)                     I. General Remark*                                  By           Syuiti )VIoRi, Kokichi YAiMAMoTo, Ken-ichiro NEGoRo,           Shoji HoRiE, and Norio SuzuKI            Otsu Hydrobiologi'cal Station, Kyoto University, Otsu   Lake Biwa, the largest Iake in Japan situated in the iniddle of Shiga Pre-fecture, is practically a depression lake, and its history is believed to go back asfar as several million years. The general morphometric characters are asfollows :                                    Maximum Length of Shore Latitude Longitude Altitude Length Breadth Shoreline Area Development   (N) (E) (m) (km) (km) (km) (km2)  350 15' 1360 05t 85.6 68.0 22.6 188.0 679.5 2. 04Maximum MeanDepth Depeh Volume (m) (m) (km3) 104.0 4!.2 27.8   The general characteristics of the lake follows its long histor>r and its topo-graphical complexity, witla alluvial sanddunes and deltas, long sandy shores,rocky headlands, and towering islets, that have contributed to form the cradle ofthe particular biota. The northern part is about eleven times as large as thesouthern; its depth exceeds 30 meters for its greater part (more than 649of ofthe area of the northern part) and the water is general]y clear and oligotrophicwith some exceptions at several inlets. It has been 'found that distinct thermalstratification usually occurs from April to December and the water temperatureat the surface layer rises to about 28-300C in suiinmer, while the temperatureat the hypolimnion remains at about 70C. In winter, water comes into circu-lation so as to show a nearly uniform temperature of about 6-70C. Contrary•to the northern part, the southern part is evenly shallow, less than 6-7 metersin depth, with rather turbid and mesotrophic water, or even polluted to someextent near Otsu City. XVater temperature fluctuates between about 300C in * Conteributions from the 6tsu Hydfobiological Station, Kyoto University, }siiO. 188.First Report of the Regular Limnological Survey of Lake Biwa 37summer and 20C in extreme winter for the whole layer and sometimes the surfacefreezes in the sheltered places arottnd the shore.   Provided vLJith these geological, physical and climatic situations, Lake Biwaretains hues of both temperate and sub-tropical ]akes and secures richness andlaeterogeneity of habitat for lives, These dominant chracteristics of the lakeadinittedly have shared in establishing and differentiating organisms of inanykinds, and as a result, many endemic species here are found. For example,about 100 species of freshwater fish are found in Japan, of which about 60species, including 6 or 7 endemic species, are Iiving in Lake Biwa. Also, asregards the freshwater molluscs, abotit 40 species otit of 60 Japanese species canbe found in this lake, of which about 18 species are endemic.   Reflecting these circumstances, a great deal of liinnological works have hi-therto been made in Lake Biwa, most parts of which are shown in the literatur-elist edited by Dr. M. U6no (l943), Drs. T. Taketani, Y. Shiraishi, M. Tanal<a(1958) and by the Research Group for Biotic Resources of Lake Biwa (1962).Except only two, however, they are all short term works, covering not morethan 3 or 4 years, and so they can not reveal long tefm variations or trends inlimnological conditions of Lake Biwa\' .   The exceptional worlcs mentioned above Iiave been performed by thpv FisheriesExperiment Station of Shiga Prefecture. This Station was founded in l900and since 1910 the fundamental data on water temperature were publislaed. In1931 the observation on water teinperature, transparency, p}i[, dissolvecl 02 con-tent and plankton content was performed once a month selecting 4 points acrossthe ]al<e froin Hikone (east coast) to the mouth of River Ado-gawa (west coast)in the northern part of the lalge, and in the next year (1932) the general surveywas executed at scores of points covering the whole lake at each season. From1933 to 1947 variotts rnodes of observations were tried year after year. Relatixfelyregular survey was commenced since 1948, once a month, selecting 5 pointstraversing from Hikone to the mouth of River Ado-gawa. The items for obser-vation were weather, water temperature, transparency, color of water, wave,p}{[, 02 content, NH3-N, N02-NT, Ni03-NT, POlj-P and planl<tons. During 1955to 1966 other 6 points were added to the above points, all in the northern partof the lake, of which 3 were situated on the line traversing from the mouth ofRiver Ane-gawa to the mouth of River Chinai-gawa and the other 3 were on theline traversing from the mouth of River Echi-gawa to Omatsu-zaki.   All w6rks mentioned above were scarecely done in the southern part of tlaelake, but in 1961 the points of observation, 6 in total, were so arranged as todistribute longltttdinally from northern end to soueher.n end of the lcake, of which2 were situated in the southern part of the lake. The items of observationwere principally the same as before. However, this method was tried only inthis year, and from the next year up to the present time the general method was*Long term variation of geological scale was recently studied by Dr. S. Horie (un- published), but this kind of work is not touched in the present paper. 38 Syuiti MoRi, Kokichi YA,x•Efx,x•lo'ro, Ken-ichiro NEGoRo, Shoji HoRiE, Norio SuzuKireturned to the former traditional one.    Besides this work, tlaey have been making regular observation on some sidesof life histoi-y, such as fecundity and body size of spawning adult at the spawningplaces near river mouth, and distribution of f'ry in the whole lake, and so on, ofthe fish, Ayu (Plecoglossus altivelis Tem. & Schl.), the most important cona-mercial fish in this lake. This work has been continued since 1946.    Needless to say of the superior value ot' a]1 these works mentioned above, notonly from the fundamental scientific point of view but also t'rom the commercialfislaing practices. HoNvever', there are some weaknesses in their works. First,they have no data on benthic animals, which is indispensable not only for knowi'nglake conditions but also food materials for fish. Secondly, they have scarecelyregular data about the southern part of !he lake, where the character of the lakeis remarkably different from the northern part, richer in nutritional conditionsor more advanced in eutrophication and more closely related to the lives of notonly citizens of Otsu City (the capital of Shiga Prefecture) but also the peopleinhabiting alongside of effluent River Yodo-gawa (the second densely populatedarea in Japan).    On the occassion of the Otsu Hydrobio]ogical Station moved to the new sitein autumn of 1964, where was much more suitable for performing this kind offield work than it had been at the old site, we planed to begin a new !'egularlimnologica] survey. XVe are thinking to perform this work permanently andto offer regular limnological data as long as it continues.    After trying sexreral preliminary surveys, the fi'rst regular survey was pe}ny-formed on the lst of October, 1965. As the survey points, we selected onepoint, Iel, in the northern part of the lake and three points, Iib2, Nb5 and Na2,in the southern part (Fig. I). Up to June of 1966 the survey was perforniedonce a month at Iel, and twice a month at three points in the southern part, butafter that time the 3atter was changed to perform once a month. Among thesepoints, Nia2 was shifted to Na3, about O.8 }<m south of the forrner, after iMarchof 1966, because the area around Na3 was designated to be a sPecially conservedarea in 1966 by the Prefectural Governinent. Similar environmental and bioticconditions were observed at both NEa2 and ls4ia3.    Most of the observations and collections were done in the beforenoon. Atthe point Ie 1 our boat was always naoored to the station-btioy which was fastenedby long chains to the lake bottom, ancl at other three points it was usuallyanchored directly.FirsL Report of the Regulair Limnological Survey of Lake Bi vva 39N4t')'(,rxxN"s.''-i gi.-' lr!o;S'rttt'rt/ff'fx.if1''  1   :i';'t•'  !f   t.tos''/t-" .-' av•  "  xt.' x'!s.rp  't.'''t.t.'''"  x.xi'jiiii,l,lliiiill,,,{.'k';lii.lil,.•.,,Sakaniolo -      Na3tt)t.su   opuk/1`e IsL/m      t'x /t•'    .. k," /t.,111,1,,'.••••""X''l).L/li}'iiM>i,illi,,,,.."itl',,lx Å~Å~ "'Y x,,X x .Sito4rn pt Å~VS//,"S..iW."Lt   /  Oki         Rii'ar            (}71.'    u,•,tt-1xk'N'l"""'x.    -"•'A tt e. tt ""   ,:OHikotiehlc 5 10 15KmFig. 1. }ivlap of Lake Biw-a with survey pointsFor further explanations see text.4,O Syuiti lNtioRI,  Situations and Kokichi YArtApt•ioTo, Ken-ichiro NEGoRo, Shoji }{[oRiE, NTorio conditions ot' the survey points are listed in Table 1.Table 1. Conditions of survey points and itemsSUZUI<ISurvey point PositionDepth I Bottom       iSurvey items    gi"Iel i•    i    i :;3.5 km off the coastof Omatsu. Typicalcondition of the nor-thern part of the lakels seen.lLi Aboutl 74 mls'INb2Nb5O. 1astrt km off the east co- of the southern pa-of the lake.Middle part ofsouthern partlake. theof theAbout2mAbout4.5 rni liVluddy li clay i          I gana '6r' 'I          i Sandy ' mudMud      kNa,:•,1'r 3o2a',ltg?Mf,gh[g,k•RuZ.tgi8,SX 'sb%ati,,,.,]                                                       '    Other methods are particularly exp]ained in detail in the following articles.    As this is the first report, it is inevitably confined only to present the actualclata ; after accumulating 2 or 3 year's data we should Iike to make general dis-CUSSIOIIS.    The perforiinance of tlitis work was only possible by kind cooperation of thestaff of the Station, XMr. Y. Nakajima, Mr. T. Ueda, Miss K. Nishitani andMiss Y. Adachi, We express here our sincere gratitude to them,                                 Mterature Fisheries Experiment Station of Shiga Prefecture, Business Report, 192!-1949. Fisheries Experiment Station of Shiga Prefecture, Research Report, 1950-1966,    No. 1 - 19. Research Group for Biotic Resources of Lake Biwa, 1962 : Literature list on the    study of Lake Biwa and abstract of important articles. Taketani, T., Shiraishi, Y-, Tanaka, M•, 1958 : Bibliography of Lake Biwa and the    surrounding district during 1943-1957. Pub. of the FreshvLrater Fisheries    Research Station of the Fisheries Agency, Materials for Research, ISTo. 21.  U6no, M., 1943 : Bibliography of Biwa-ko (Lake Biwa) and the surrounding district    Jap. J Limnol. 13, 113-141.Weather  Air temperature  Wind  CloudTransparencyWave conditionMud temperatureWater temperaturepHDissolved 02 contentPlanktonBenthos

First Report of the Regular Limnological Survey of Lake Biwa (Oct.1965-Dec.1966) (I) : General Remark

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First Report of the Regular Limnological Survey of Lake Biwa (Oct.1965-Dec.1966) (I) : General Remark

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