translation series no. 2356 - pêches et océans canada research board of canada translation series...
TRANSCRIPT
FISHERIES RESEARCH BOARD OF CANADA
Translation Series No. 2356
Causes of the mass mortality of the oyster (Ostrea edulis L.) in limski Canal, Istra, 1960
by Miroslav Nikolic
Original title: Uzroci Masovnog Ugibanja Kamenica
From: Acta Adriatica (Adriatic Journal), 11(31) : 227-238, 1964
Translated by the Translation Bureau(VR) Foreign Languages Division
• epartment of the Secretary of State of Canada
Department of the Environment Fisheries Research Board of Canada
Marine Ecology Laboratory Dartmouth, N. S.
1973
19 pages typescript
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1Q72
A.driatica (Adriatic Journa1) Vol.XI, Mo. 31, 1964, op 227-233 (Lusoslavia)
• CAUSES OF 7a7L i'iASS MORTALITY OF THE OYSTER (Ostrea edulis L.) ILÏ Ln.SKI CANAL, ISTRA, 1960.
Ey Miroslav NikoliC, Institute of • Marine Biology in Rovinj, Yugoslavia.
Introduction 227*
-Durin?.7: the period molluscs have been reared in Limski
Canal . (Lim Inlet), each year the average mortality rate in
oysters has fluctuated between 10 and 20% (A 1 1 6 d i 1905).
The causes for such mortality, which is considered to De
within a normal range, are the following:
a) careless handlinP; durin the required operations
In oyster production;.
• ID) buffeting of waves which causes damage to individual
sections of the equipment in a rearing station and
consequently, to the molluscs also;
Numbers in the right-hand margin indicate the corresponding pages in the original.
7530-21-02g-533Z
2
c) Continuous attacks of varying intensity by fish
Particularly by the gilt-head bream (Sparus auratus L.):
d)- occaSional attaCks. by the -Hspoiler" - the turbellarian
Stylochus pilidium Lang. A more widespread attack
by this organism was recorded in the literature in
19314 (j.ytinski-Sal z, 1935). The mortality
rate of 87, which was registered at that time applied •
only to the oysters 8 to 35 mm in length, while
" - other - sizes- did not smffsr.
Near the end of 1960, the sudden death of oYsters of
all sizes occurred in the Limski Canal. Because of controversial
opinions about the causes of that mass mortality research was
initiated. Scientistst investigations in the field, obemical
analyses by the InStitute of Chemical and Technological Research
in Ljubljana (Yuc7oslavia) and our own analyses provided the
basis for conclusions outlined at the end of this study.
Mortality rate fluctuation
In ord ,, r to r.hef%ir the mo ,-tality rate, ten sites were
chosen in the valleys where the rearing ponds are situated.
The number of animals involved in this investigation 228
totalled 16,452, the research extending over a period of
seven months.
The highest mortality was recorded in 1960, in the
months of October and Novemper while in December it went down
considerably. At the beginning of 1961 it continued to drop.
PEP.I.17011.0
NAVI
K- Art i.GADEP.A I
3
Table 1 - Mortality rate (percentage) shown for eaCh site, in each month and for different age grouc.
Site (Station) (Age 1960 1961 r,-rouc) Nov. Dec. Jan. Feb. Mar. Apr. Total
Dno Lima
1( 'I. --- r.nj eria i _ • _
1031. °it) t.-)Ë morlanly XII 1 i.t 111 IV I..14:upno
---
V ES KO•12•0*
•P
33,7 3,3 (33,4 C-.1059 30,2 1,0 1,0 2,4 1,1 2,2 33,3
•
B6,5 61 - -4,9 • 1,5 3,1- 2,0 05,5 C-19:39 16,1 11,9 ' 7,3 0,6 30,5
K-1 iM9 47,5 4,7 5,4 • 1,3 2,8 2,9 75,1
0-1053 02,4 14,7 7,8 5,6 13,8 4,3 77,0
ADEUA II 1.:-.1.550 1),8 3,7 3,5 -1,9 10,3 C-1939 46,7 8,1 5,3 4.8 3,0 . 3,4 67,3
• - C-1950 68,4 • 6,9 70,0
.L-1LISLA',•_4.1ZO3'A •
C-1950 (33,1 611 1
, . C ER1ZER A I 0-1959 6_1,4 12,11 7,0 8,0 3,4 1,7 74,9
60,0 13,a 1,3 1,3 0 . 1,3 02,5 ..
C-1833 07,7 . 0,5 • 4.5 . 1,3 73,0 CERIZERA. II 0-1953 63;5 0,3 9,1 4,3 4,3 7,2 77,3
1:.-1.3.30 ,. , 5,1 1,1. 1.3 17.7
C-. um 03,3 13.3 11,5 4.4 72,9 7;11‘.41J A • C-1950 ' 03,0 12,2 10,4 3,9 3,1 4,7 - 74,1
- K-1060 1,1 .,,- 3 1,7 5,9 .
C-19:1 0 00,,Ï3 '1,9 7:9 1 , 3 .t 3,8 3,3 70,7 . 3 5.9 0-1930 54,3 3» 8 , 0,3 i .8 61,8
- s ST .1; G A . K-1039 42,0 5 5 5,7 q9 -,-, 2,9 3,3 53,5 . • C-1050 •
K-1000 00,0 •13,0 5,6 3_2 1,1 3,0 p0,1
Note: C = cemented in fours; K = attached to sticks.
until April', when a normal mortalitY rate was reached again.
It can be seen from these data that the oldest'animals
suffered most (two and a half years old - 76.66%), one year
old somewhat less (5346 - 61.81%) and the six months old
the least (36.66). The variation in mortality rate for
' .rom lifferent control sitee (oyster beds) was minimal.
In order to find the cause of this high mortality, 229
the oysters themselves had to be examined first of all.
Their shells were not damaged and had no unusual deformities.
A thin layer of brown silt was easily visible on them. On the
external surfaces of the shells no living organisms were
observed. The "spoilers" - turbellarians of the species
.Stylochus °indium Lang - were not found. Likewise, eggs of
this orP;anism were not found, although it leaves them usually .
on the inside surface - of the shell. The animals were well
nourished it is therefore assumed that death occurred.
quite rapidly. The .edible portion usually decayed very-soon
(within a day or two), so that in most cases only the adductor,
muscles and the shell were found. Gills and other -parts of
the body were covereCL wibh a layer of silt and .mucus. No other
changes were noticed.
For chemical analyses, eleven samples were collected
representing both live oysters and dead ones with dried,edible
portions from the Limski Canal, and live specimens from the
natural oyster beds elsewhere. These samples were sent to the
Institute of Chemical and Technological Research in Ljubljana
for chemical analyses.
Table 2. r_Qhemical analysis of the edible portion of oysters • (Ostrea edulis L.)
•Sample No. Inorganic ash SiO
2 e •
Tabc7. ,i 2. - KcJi:s1.•.; fflzulizi.z. ,jc,‘th - ih tlij:?lovo. k' ;:;c (asu ed.7.ais L.)
. .
1r..t•1.z.,1( Peil,2.n S102 l'e203 C.....0 11.•pf) Na Cu. C1 P205 Sa -
1 )3,40 0,04 0,15 3,07 0,111 3,34 0,0027 5,40 1,53 1,04
2 • 1 2 ,75 (J,20 0,1 13 1. 2 0 Mg 3,16 el 1,01 1 , 2: 0 3 10,60 0,18 0,17 1,69 0,97 4,04 0,0141 (3,53 1,81 1,10
4 12,82 0,11 0,11 0,87 0,74 3,07 0,0138 5,06 1,66 0,95
12,17 0,10 0,12 1,77 0,65 2,70 0,0197 4,16 1,53 0,08
• • C 14 • 8.3 0,133 0,14 2,54 0,7'i 3,23 0,0146 5,28 1,53 0,91
7 16,40 0,32 0,25 0,83 0,85 4,78 0,01 88 0,09 1,70 0,08
8 17,7,3 0,73 0,25 1,14 1,00 • 4,21 0.0171 7,00 - 1,25 1,13
9 14,70 0,16 0,13 0 ,72 1,01 3,30 0,0037 6,12 1,79 0,96
10 10,88 0,41 0,89 • 0,46 0,90 5,50 0,0027 6,25 2,14 0,99
11 16,70 0,52 0,33 1,50 0,02 3, 89 0.0090 6,77 1,51 1,14
Svi rezultati su u izraèunati na sulm tvar Uzorci 1, 2, 3 i 4su 21e sheU;;.e iz nanaln. tizorel 5 1 6 su 'iive Skoljke a prirodnill stbsniSta lizorei 7, 8, 9, 10 ill su mrtve Prûljke iz
. . _
All the results are shown in % of dry matter. Samples 1, 2, 3 and. L. are live oysters from Limski Canal. samples 5 and 6 are live oysters from the natural beds. Samples 7, 8, 9, 10 and 11 are dead oysters from Limski Canal.
From the results obtained; it can be concluded that
there is no great variation in the chemical composition of the
edible portion.. Oysters from the natural beds have a slirehtly
higher content of CaO - 1.77 to 2.54%, as compared to 0.46 -
1.69 in the oysters from the artificial breeding grounds.
That.increase for oysters from natural beds may be attributed .
to a greater age and to life in the sea where there is a higher
content of calcium. The increased content of asli in the dead
oysters from Limski Canal - 14.70 to 17.23%, as against 12.17
eto_16..60A_in _live:oysters from both-natural-grounds-and Limski -
Canal - could be attributed indeed to the increased content • -
of silicon, iron and aluminum which were also found in the
'sediment layer.
Oceene-re -ehio -eeserch 230
he follewing measurements' were taken in thè Limski
Canal: temperature, degree of oxygen content of sea water,
salinity and turbidity (transparency).
The sea temperature and oxygen content fluctuated
within a range correspondim3 to the normal conditions prevailing
in Limski Canal. The recorded temperature in 1960 ranged from.
9.6°C (winter) to 25.3 00 (summer), while the oxygen content
was somewhat higher than it had been recorded in other years -
84.2 to 106.8 (1960). As will be seen in further presentations,
salinity is a very important factor in the - life of oysters.
In the outer hall of the inlet (from the mouth towards the
interior) the sea water reached a maximum salinity of 37.50 °/00
and 38.e °Apo(D ,, c.-Feb.), /ihile the minimum was rather
irregular - 35.61700 to 36.17 Q/oo (pril) and somewhat more
stable in August (34.16 °/oo - 34.18 °/oo). Since the breeding
area is located in the second (or inner) hall of the inlet, -
this latter section is of greater interest to us. The salinity
of sea water in that section varies; it is subject to -
substantial and sudden changes, particularly at the surface,
and deuends on the amount of precipitation and on the under-
water sources of fresh water. It happens sometimes that the
231
:0,1> ,
",IRSAR
,
5 4 3 -
ROVIN)
i>)
water On the surface is nearly fresh (Vatova1950,
Mar1nkov1c1959).
The Limski Canal has a great number of underwater
sources of fresh water."Vatova-(1950) registered 15'of
them. The more important ones are at Punta Simija and Pija
Fera. ;.ccor.ir to V a t o v a'(1950), At Punta Simija the
fresh water .es?ows in f rom an underwater cavern. In the
immediate vicinity of that source the salinity was 5.260/00
(Nov., Dec.) .and 4.24°/oo . (February)_, whilel.n March the water
was completely fresh. The salinity of the sea water at Pija
Fera ranged from 0 to
(July to'September) and 29..18°Jc° (November). The zreater the
amount of precipitation the greater the flow of the fresh
water sorings and the more the salinity is reduced in the
vicinity of these sources. - !
5.4e/oo (Feb. to April), 3.17 to 6.49 °/oo
hûrtiroldim iy. /. 1. ,)! Ut • . . _ . .
Pfmtaja br. 1 — I>no /Arno, Stailuel „ 2 -- Veq:r.ovo
„ „ 3 —
„ — r .
•.„ Year4p.icicre, „ 7 — •13ijcla „ — CL.ra 1. ,
8 „ D • - (....'erlzern u. „ „ 10 --
Sodium (Nem) - • •
.
" re•
grams • . 10:520 • . . 0.3915 • . . 0.9642
milliwavesl 457. 0 19..6 79.3
555.9
501.0 -- - 51,7--
•0.01 3.21
The Institute of Chemical_and Technological :Research_
performed the analysis of sea water. The sea water used for
analysis was clear and colourless. One litre of that water
contained the followin7:
Cations
motal
Chloride ( 0 1 - ) • • • "7'111 e ( SO/ = ) ilydrophosphue (rieG4 ) . Hydrocarbonate (HCO 3- ) .
Anions • • • •
11.8757
• 17.780
• 0.0o14 • 0.196
Tota l
• • • • • 0
• • Aluminum oxide CA2 ,70 1 ) • • Sum of all solid mâtler . . Density at 19°C • 0
PH . • • • • residue after evaporation •
. 20.4574
• 0.0084 • 0.0023 • 0.007 • 32.345 • 1.023 • 7.7 0 • 33.357
Ferric oxide (Fe9 0.1 )
1This may mean either millivolts or °/oo, or perhalbs mhos. The term has been translated exactly as it stands, since the method of determination is not given. Revisor.
Precipitation
In addition to temperature, oxygen content, salinity,
turbidity and Chemical analysis of the sea water, the total .
amount of precipitation in this region has also been measured..
By studying the monthly precipitation values for the
year 1960 it became evident that the greatest amount of
precipitation oCcurred in the months of March, July, September,
October, November and December, and in April 1961. For
comparison, precipitation in other years is also given•
9
(1927-1928 and 1953 to 1961). It is evident from these data
that the total annual precipitation was within the range of
622.2 to 907.0 mm. 1n1960, however, it increased to 1207.4 mm,
that is, it was approximately one third more than in the
rainiest year previously recorded. Naturally, because of the
increased amount of precipitation in 1060, te underwater
springs of fresh water described earlier, had increased also
and, in addition, much of fresh water had poured down the steep
banks as run -off during the rainy days. As a consequence,
there was a significant freshening of the sea' water at different
levels below the surface and, particularly, at the surface.
Accordinn: - to V
on the decrease
for a period of
occurred.
a t o'v a (1950), the,rain had a great effect
of salinity of sea water in the Limski Canal
more than a month after the precipitation
Table 3. - Monthly fluctuation in salinity of the sea water in years 1927-1928 and 1957-1961.
;7 1.a .r./.1rt .i rr) gcc7i. -n.c.':1:.u. 1927-1928. :1951- 1 961.
232
3. —
19131. 1,110 inc,
)
- . .
JAN 1:1UAR
A1:11111, 3.42-36,8k
JU • 36.5.;5-37.1.5
AJrI UST 3-1,“3—:!6,39 SEP . FEMBAR 34,25-36 0::TO.F; 33.06-3 NOV:;',M1,3A .R. 29,34 --nr.c o
\23.
M,12-31,89 25,97-37,P0 3 0,32-3(,:.;5
32,21-37,43
33.33-37,01 32.25—:37.34 2:S.44-37,57 37,05
2
34.43-37,63 36.'3P-37,975 36,92-57.90 32,07— • ,56
,64—?7,0(5
21,6-37.55
I
20,E6-34.93
:r • 35-35.17
35,70-36,0a
31,17-35,05
31,20-372,23 i3-37‘,P1 35.58‘-35 1;7
33.7,5-37,21 3.C,29-36..58
35,99-37,r*
2.7
ej
,1A
2/1.5
92,0 043,5 1
11
1
U ;WA GODIN.,1 1H
0 8,■ Cfel 1.1.1 fi 0 Vil,
Table 4. - Precipitation in the region of Rovinj in the Period 1927-1928 and 1953 to 1961. -(for each month and yearly)
1 0
tube/a 4. — Prcr,-17.d obrp-ina. n vocirus.ju za 1 927—.1.92;;1'. 1953-1961. g.
Preep.il..icm.: 1927. 111 25 . 1253. 1053. 1055. 1953. 1957.
JA.1:,"AR
1953. 1 950; 1095 . 1931.
23„9 25.3 , 59,n 23.0 39,0 40.9 30.0 52,3 65,3 60.5
...- 20.3 57 .8 1:.., - - - 2(ki - - - 9.54 • 45,3 - - 10,0_ PT 1 ' 9 3 110.3 3•A2 64..3 85.9 17.3 55.7 5 -,1 11`.'.7
API'..1. 7_, ::. 3.1 17.0 ....,.• .,.„,, 7:),P r 1.9 T i;1.; () 5.) 114,0 7 0 3:-)„-3 1)..5 5.1.0 1:3,1
2 7,4 5".7 15,9 42.7 1 25,:1 . 22,0 67 ..3 62.1
JUI,I 1,7 14.0 92,0 68.5 14'.«:.7 31.3 4 7. ; 57,8 25. 3 122 . 4 A f_1(.7,UST 15.8 -1!4.:1 4:1.9 /1,3 1.32.0 23.2 :,',5,1 1 -.,.1 1,3'.,3 /:.."1:,PVT.- ',1. ".P.R., 74,7 1 65.7 50.0 31,1 67,7 19,1 34,4 32,7 9.1 , 129.4
oKToBAr. 6J
33,5 t; 112,1 132.1 .:i 1 .1 60, ; ,i _
80,8 111,1 54,2 20:),2
N 0 V E 'T.1-; A R 51 2 105.5
, P2.‘; 55.5 - 114.1 — 110.3- - 62.3 - - 126.2 —98,1- - 154.2 DEC1 7:7■113 AR :39,2 42,9 ■■ 3,13 9,5,1s 22.9 i 6,6 36.3 113;2 2.02.9 - 1'27,0
U I:: 15 2 N 0 5/1,1: 0 91.1.- 6 2 1,6 6.,'.2.1 920 2 510,2 622,2 793,0 957.0 1 207,4 T-otal
500 rrm, - 1000
1227
,COrnin - 70 100
1953 -; c;11
(.0
19•55 ...• 6:90
1956 .2! r)
• 1.957 • 72 ?
1 950 7.9.9
1.061 ..
1
' 1 17.4
X i ••
. 13 91
X1 1 _
-SR E Diy ..1/1.1 ( MJES EN L--:. M [
CSOHINA 1-: 5h )2 3.) 60/..).,.V.1;
1:11 1. Ulzupga 1;s ■ IfOina go ii!:11i , l ■ c,rnin n flosiniu uw. 1. 'h (lrP.):" 1 11 jo«t•cq pu c: t ions IU F:ocinj (rdnu total)
M 2. SrecInjnlz. ni.ic.1::C.21:t 1 - Fo. 2 . Thc ,n,:ounr Of pri . eipilaf/o; s at govinj (a niqc - poqr averag (')
Fig.l - The total annual precipitation in Rovinj. Fig.2 - The average monthly precipitation in Rovinj
(for a 9-year period).
-èteml
11 ■.■
Turbidity. of the sea.
The Limski Canal is a sea inlet approximately 11 kilo-
metres long, penetrating the land in a west-east direction.
With the influx of fresh water (surface run-off and underwater
springs), large amounts of red soil and clay enter this inlet.
mbe ..eicler.2 of soiD in the fres'nened sea ater create
of "emulsion" and settle to the sea bottom only when the
salinity of the water is restored. For that reason we find
a layer of grayish mud at the bottom of the first third of the
inlet, (i.e. the innermost section), and grayish mud with a
surface layer of brown-coloured mud in the second third of . the -
inlet. The bottom of the last third e the inlet is'grayish
mud with a reddish surface layer. Very soon after.e•tering
into the sea water,_ the suspended particles of red soil and
clay.also settle on the shells of various organisms and
Penetrate into them, particularly when the . animal is filtering
the -surrounding water in its feeding and breathinçe operations.
A large amount of sediment was found on the shell surfaces
facing the surface of the sea above. The wet sediment had a
dark brown and occasionally, a grayish-red colour. According
to the analysis by the Institute of Chemical and Technological
Research, this sediment, when dried at 105 °C, had the following
composition:
Silicon dioxide (Si02 ) • . 29.4% Ferric oxide (Fe203) . . . 9.0 Aluminum oxide (Al2 0 3 ) . . 7.8 Lime (CaO) 16 L.
Iviagnesium (Mg0) . . . 9.8% Phosphoric pentoxide
(P205). . 0.2 Lost dVirlg drying
(112 0- 4- CO, 4- .organic mÉitter). • .27.4
12
234 . A Sample of turbid sea water taken October_18th,_1960, -
--at the innermost end of the Limski - Canal -(the -Inn° Lima'
station) showed that, on that day, there was about 0.68 grams
of Silt in one litre of sea water.
of the s ,,e in the Lirrslei Canal
-.:.ecause an artificial enrichment of the sea with
nutrient salts was performed in the Limski Canal in the period
1959-1960i -it was- necebbary - tO study'some details of that -
operation.
The artificial fertilization was carried out by a
previously proven method (B u 1 j a n 19.57), in several
applications in approximately 2,600,000 cubic metres of water.
According to our calculations, the quantity of Phosphate in
each lot thrown into the water in 1959 amounted to 28 -101 mg
per cubic metre, and in 1960 - from 14 to 33 mg per cubic metre
of sea water. The fertilizers that were used, mainly . super-
phosphates, were diluted in the sea water, according to the
scientist who carried out this fertilization program, in the
ratio of 1:1,000,000. From the results of chemical analysis
by the Institute of Chemical and Technological Research we can
see that the superphosphate which was used can be dissolved
at the rate of 2.56 grams of P20 5 per litre of distilled water
(pH = 4.0), and at the rate of only 1.74 grams of P20 5 2- 5 per
litre of the sea water (pH = 5.0). The density of sulphuric
acid used was 1.835, which corresponds to a 94% sulphuric
acid solution. The_mixture of 100 grams_of _superphosphate and
3.-5 millilitre of sulphuric acid in 100 millilitres of sea
water resulted, after mixing, in a very thick paste.
ce ,zallnity of the sea on the
vitality of oysters
The outimal salinity of the sea for the s -oecies Ostrea
edulis L., according to Ra n s o n (1951), ranges from 31 to
3 5 KD. The reduction of salinity affects the life and health
of molluscs. As we have seen in the enclosed tables, the
salinity in the Limski Canal fluctuated between 4.72 °/oo and
38.06°/oo (1960).
From the experiments carried oit in separate ponds the
following could be learned: oysters cannot tolerate -
a substantial reduction in salinity without harmful effects
upon their health or 111 e. The critical point at which their
life becomes threatened occurs when the salinity of sea water
reduced to 20 0/00 . At 38°/oo the oysters survived as long
as two months, deDending on the degree of their fitness and.
the temperature of the sea water in the ponds in which they
had a sufficient amount of oxygen but no food. In the 22 °/oo to
20°/oo salinity range that period was much shorter and varied
depending upon the temperature of the water. At higher
temperatures (20-25°C) oysters survived a shorter time, while
at lower temperatures (10-15°C) they were able to survive
longer. At 19°/oo salinity and less, the time was noticeably
14
shortened. At higher temperatures oysters could survive onlY
3 to 7 days, while at lower temperatures that period extended
to 14 days.
Mussels as members of the animal community in
the Li ki Canal
Mussels (Mytilus galloprovincialis Lmk) were also in
the same breedinr area, in the'region which was most exposed
to Changes in salinity. Although one could expect that in
such an environnent the mussels would suffer in the saMe way,
this however was not the case.
On the basis of - the examinationef the inussel populations
and their habitat, the following can be concluded:
1) during the mass mortality of oysters, only a small 236
number of mussels over one year old lived in the Limski Canal
and a great number of young ones, less than a y.ear old,
• 2) the mussels are much more resistant to changes in
salinity and can live in sea water with much lower salinity,
up,to 4°/00 (according to Lambert1950 and Ranso , n
1 951 ),
3) the mussels can filter the sea water more effectively.
In comparison with oysters this ratio is 9•:1 (L a m b e - r t 1950),
4) the mussels from Limski Canal have, on their Shells, •
fewer commensal organisms than have the 'oysters Or, scimetimes,..
do not have any at all, particularly the young ones. "
X Secchi
15
235 Table 5. — Sea transparency in the Limski Canal (Secchi 0.5 m)
Tcbcia. 5. -- .R-nzirrost mom, If, ka.nolu (Secci 0,5 In)
128. 1057. 1855. 1959. 1930. 1951.
January__ _ .
' .....A U NAR — ------ - q-,o------- 3.-r,5 - -- - - 0.L,5 -7,5 8 — 9 - February .F12.auli.A.ra 10 — 1'7 . .,.,:,
' - 9 5 11 —12 4.5— 7,:; March Mi • ., 11T 0,4-2 10 —11 12 —14' 5,5— 7,5 April : ,..1=1-7W-.. 5.5-10 15.3 0 —15 May- — . ' • 2 — 7- :. 5 9 --11 3 --1:'. June . _ ....,. , , . \ _ 1') 7• —13 3.5--•,:', july .T -7_;Li :2,5-17 11 —12 8,5-11 :3,5— 7,5 7
August - - ; AT-7--;I:r2T- — -- - 1 4 —19 - 8 —4 9 7 — 7.5 --7 —13.5 • 4.5— 9 4„5 — 8.5
5eptember SE 7-7-ri'..%1BArt 10 — 1 7 10,5-12,5 5 — 7,5 8,3— 9 5 —10.5 Uct ouer OKTOBAR 15,3-24 10,5-11,5 9 8 — 6.5 0,5— 3 4 -- 7
' November NOVirsIBAR 6,3-10,5 3 — 4,5 4 ...._... 5
Deceniber DEC2M- B..•=1.:R 5,5— 9,5 7,5— 8 11 7 — 7,5 1,2— 5,5 5 — 7
Table 6. — Salinity and transDarency of the sea at the'control stations in October, November and December 1960.
Station: Octob'er November, December S °/oo Secchi S°/oo Secchi S'Yoo Secchi
_ • •
Tabela 6. — Sanos j prczirr.ost rnora r.a izontroinint postajconct
za X. i i X7I !;CO. g0clinc
XI Xii Seccht S 0 : 00 Secchi
• DNO LIMA 23.0 1 33:10 3 4,72-21,47 1,2 \---ES.-7;•;:OVO 13,0 0.5 34.33 3 19,87-36.37 2.5
• PERUZOLO 18,0-19,0 3 • 34.29-34,45 4 — — '2■ AVI 22.5• — 3->.,45 — 34,23-38,92 3,5 . K..\...PjGA.1-DERA 1 • 9`).0 — 21
_ .34 — •—
. IAI1GADIM A II .19,7. ...... 3 — —
; B -1,TEL.A. GUOTA 19,0 2-3 34.38 - 3 • __, _. _ . _
! CERIZERA I' 22,5 ' 3 32,93 4 — -- 4. CERIZERA II 9 2 .73 — 34.11 — —
! ,5> I5IIJA ' 23,0 — ,
-- — —
Conclusions
1) A mass mortality of oysters in the Limski Canal
suddenly occurred in 1960, in the following manner:
oysters cemented in fours,' year of birth: 1958, 76.66% died,
oysters cemented in fours, " 1959, 61.81,
oysters attached to sticks, " 1959, 53.46%,
ovstrs ,r.,,ttecrl to stick, " 1960, 36.66%,
16
2) From the - inspection of dead oysters it was established
that they were not damaged and that they did not bear any signs
indicating the presence of "spoilers" or other parasites.
A lengthy illness can also be excluded as the cause of death,
because the dyin2: animals were sufficièntly fat.
5) :1'esuis of c'nstcal analyses of tIls sea water s
of the edible portion of oysters and of the sediment on their
shells prove that it was not the poisoning by the chemicals
used as fertilizers nor by the substances which were brought
into the sea by the influx of fresh water and Mud.
4) The whole year 1960 was rainy (1207.4 mm),:and the
hiP:hent precipitation was in the months . bf Februarv, March,
July, September, October, ',November and December. Althôugh the
remaining months had less rainfall; we can conclude, according
to Vatova(1950), who claimed that heavy rainfalls
continue to have an effect on salinity for oVer a month after
the precipitation occurred, that during the year 1960 there
was a -cOntinuous reduction - in the salinity'of the sa water
in Limski Canal. •
5) Large amounts of silt enter the water of Limski
Canal with precipitation, which then settle on the sea bottom
and on the shells and other parts of oyster bodies. The mucus
found on the bodies of molluscs is orobably a protective
material produced by the gills, according to Loosanof f.
(1961).
On the basis of what has been said above we can recon-
struct the orccess of destruction:
The reduction of salinity caused, first of all, the . _
_ destruction of the.commensal.organisms. This adversely affected
the micro-climate which, in turn, produced a negative effect
on the oysters' life. At the.same time, the reduction of
salinity had a direct effect on the oyster's body. Experiments
• iladf nrov -ed t-hst - a salinity of less than 20 °/oo is detrimental
--to their life. This, and lower salinity concentrations were
registered in 1960. The presence of silt in the water with •
reduced salinity made the already disturbed living conditions
even worse.
These. great disturbances occurred at a time when the
older animals, weakened after spawning, had not yet had time
to recover. For that reason they had a higher mortality rate.
.The young ones, which had not spawned yet, having grater
vitality and thus greater adaptive powers, had suffered a
lower percentage of casualties.
The mussels did not suffer due to their ability to live
• - in water of low,salinity, and to the fact that they filter the
sea water more effectively. Also, they have fewer commensal
organisms on them.
SuPporting the above statements are the studies of the
following researchers: Loosanoff 1952 and 1961,
Lambert 1950, Ranson 1951, Vatova 1950,
Bytinski-Salz 1935, and Korringa 1956.
18
18
Bibliogr.aphy
B 1 .1:.1 1,10 C1 R. A. IT IJ it. •
Aliod 1, I. 1.tl(J5: 1)1e AtisternzAtelit an e'er Nerci-Osilichm Ktlsie des Adriatisclien
Int.. 1• ISCLL \Viet). 1; ; ,1, 19;,7: • e,taj 0 rt.:,:ullattina eksp ....rimenata gnosiettia Mljetsllog iezera•
itt,% tt , t "VY, G,
13 •,‘. linski-Sal II. 1935: Ui 1.iicliIo (Stylocint.,.; pilidium Itanc,) dannoso ai
);_ r 1 • ; . :• al .Pr,-;31:eilvity. llapp. et Pi . oc:. •Ve.• ■ •:).
I 1.10 !L. Uxpl. JI.
, IliA' o :; h it 1' 1. 1_. V. iur 0l.trs it Vater of LOW Salinities,
Coro.. t,1 n I.,. "V. 11,1)1: 1 .11"ic..u13 rro,:tbidity en SO17■1C I.:arval and Adult Bivalves,
(:at 1 • 1h, 10 15n. •tturlh. ADP.
1 n k 0 1 é, 1\1 . Oet--atur...;ratiçït podruêju Rovinja i u Lims1,.:orn kr,flpi ta, Split.
1‘1 ;•. 1 . 1 ;; u i c. i 111f11: Ouc;:v.,,:fityrt 1:::1;a pocIruillt •
1 u 1., kuttlu 1./59-1081 godine, 11 drogriiski Godinjak 19 130.,
rt. n ri, C. 1951: Cul:ure. Pdris.
i ■ - a, A. i959: ul1 uutiCtiziont it -Intgraticile del Canal di Lenie in Istria, Nova Thalassia, Vol. 1 Ne. 8, Vene:da.
(Croatian entries - e, 3 and 9):
#2. Buljan, M. 1957: Report on the results of fertilizing the Venetian Lake by the new method. Acta Adriatica (Adriatic Journal) Vol. VI, No.' 6, Split (YugoslaVia.)..
#8. Marinkovi(), M. 1959: Oceanographic research in the Rovinj reRion and in the rirski Canal, "The Hydrogra'ohic Car Look 1953, Split (Hidroezrafski Godi"ânjak).
Marinkovi6, M. and Nikol Oceanographic research in the Rovinj region and in the Limski Canal in the period 1959-1961. "The Hydrographic Year Look 1960", Split (lugoslavia), (Hidrografski Godinjak 1960).
• .4, • .19
ee -
- s umm a r - y :
_. During the....decadei, .th•.t_ have _e_ipp ,:•:.d since the rearing of shellfish has begun in Liniski Kauai, the annual mortality percentage observed in. oystcr
•eached frmu 10 to 20')/ü. This mortality perccntage can be considered normal u-ider (ircumstanccs:
-a) ci;reit--. lit;ndling by forcible trï2.atment el plants (especially by. - ---- • --- - b) -■vavcs i:utf.:ting some pfirts of the :;nstallations, c) Ilqic.ss•of S'i;CrUS enratzie L.,
-ci) periodical aît.avizs by the harnif ,..!1 i libertarian Si7, iÙchlts piliditon Lang._
atl.ac.: r;:.4i.,t.c.rc•J in mortality at that Lime vas al.-..out. 87/0 in oysters from 3 to 35 nun in tength.
In October 1960 a iruss mortalit;\,7 (.>cetirrocl unexpectedly in oysters of all sizes.
Different opinions as to the causes were given. For this reason a number of investigations were carried out:
1. First of all, 10 positions were chesen at which data ‘vere taken on oyster mortality during a r...:1- iod of several months.
2. On thesc., posilions hydrographical data were m.easured. 3. Meteordgical information fol.' the saine area were registered.
.4. The oysters (shells F.ncl edible portions) were Lxarained. 5. The sett water, muddy sediments, employed fertiti,zers (superphosphate
and sulfuric acid), live oysters from the rearing.places and natural banks, and deaci oysters fi con the ut.:.;_tri tg piaces wet e analysed.
G. Different laboratory investigations of the influence exerted by low water salinity on oysters wet e-carrie.d out.
7. The mortality of mussels was e:c.ri-ipr.rcil with that of oysters. Hi re are the conclusions drawin en the basis of the above results:
1. The following irortality percent Mes were reSi...tcred .in 1960: inertality
oysters • year • 'percentage
cemented in fours 1953 76,66 cementcd in fours 1959 111,81 attached to sticks 1959 • 53,46 attached to sticks 19 5 0 30,66
2. Deacl oysters were not damaged. Parasites wt.‘re not found. Dying fat. ,
3. All chcmicat analyses (water, oystrs, fertiliser, etc.) excluded poisoning • by chemical subf"tances.
4. 1060 was very rainy,. pat ticulariy through most of February, Ma t ch, July, September, Octcher, November, and December. According to •Vntova (1950). the influence of salinity changes is r.otieod a mon th or more art.;m.. the .?nct of the main rainfalls. Therefore .we consider the whole of 1960 as a very rainy year.
5. The. surface ‘,va ter s.alinity in 1960 ‘..vas therefore orten between 4 11 '0 and .•
6. The. laboratory investigations have shown that salinity values under 20'u'd are harrnful to oysters. ' 7. Together with freshwater, lare_;e harmful quantities Of mud enter Lituski Kanal settling on shells and edible pertizuis of the animals.
!--3imilar results covcri ug other arpas other :peeic«,, were obiairml by Loosanoff 1952, 1961;.Lanthert 1950; «Ranson 1951; Vatova 1950; Bytinski-Sala 1935 ..indl(orringa1950. - . .