L
ClVI 1995/J: 14
Intemqtioß"ll Council for
the Exploration 01' the Sea
Baltic Fi'ih Committec
THE STRUCTURE OF BALTIC SPRAT POPULATION
AS A BASE FOR THE ASSESSlYmNT OF THE STOCK
by
•
F _Shvetsov, A. Kozlovsky. A. Rudneva
Latvian Fisheries Research Institute
6, Daugavgrivas st., Riga, l V-1007, Latvia
Abstract
•
lnvestigations on distribution of Baltic sprat during the spavming period and data
on genetio-biochemical studies allow to accept the hypothesis on populational
unit'! of Baltic sprat.
The genetic composition and density characteristics of the Baltic sprat population
is heterogeneous. The distribution of genotypes has selective character and the
,selectlvity ls accomplished in relation to thermlc factor. The consideration of
populational structure is proposed as a regular distribution of genotypes in
heterogeneous environment.
It is proposed to devide the population in several stock units which are considered
as temporary regional unlts of stock management. This division is proved on the
base of medium-term (2-5 years) data on abundance and distribution of
concentrations of Baltic sprat.
Introduction
The necessity to regulate the BalUc sprat fishery put forth the problem of studies in
sprat populational structure. For this purpose special methods of investigations
were applied, Le., morphometric approach (Biryukov N.P., 1980), studies of sprat
otolith structure (Aps R.A. et 0.1. 1986), genetle and blochemical analysis (Aps
R.A., Tanner R.H., 1979; Veldre L.A., Veldre I.R., 1979; Koval L.l., 1979;
Kozlovsky A.Y., 1988). In some cases authors revealed characteristics allov.. .ing to
make statistically reliable distinctions between separate snmples of sprat. Bnsing
on those distinctions some authors distinguished populations (Biryukov, 1980) or
subpopulations (Aps, Ustinova, 1986) of Baltie sprat. Division of 8altie sprat into
Rstock units" identified with popUlations or subpopulations was used for separate
stock assessment till1991.
However, studles of Ichthyoplankton (Gmuman, 1980, 1981, 1983) demonstrated
tf1e integrity of Baltic sprat spawning area, but investigations of sprat migrations
and distribution (Shvetsov F.G., Gradalev E.8., Kalejs M.V.,1988; Shvetsov F.G.,
Gradalev E.B., 1989) showed the absence of clear boundaries bet..veen spawning
concentrations, mlxing and splitting of sprat concentrations, changes of their
abundance in different years, high migrational ability of younger aga groups. All
these data along with the material on Baltic sprat growth (Aps R., Gentzens B.,
Shirokov S., Ustinova L., 1989) yield the basis to confirm the concept of Baltie
cprat populational unity. Thls hypothesis was suggested a!ready in 1978 (Aps
R.A., 1978), but up to now it existed together with the mentioned hypotl1eses of
Bnltie sprat division into loeal populations.
Statistie~d
differences bet\veen sampies that have been exposed by morphometric
and genetie-biochemieal methods may contradict the biological data on
populational unity only as long as the problem ranging these differences remains
unsolved, Le. , whether these differences are in or inter populations (Alekseyev.
1984).
The major argument as regards this direction is either presence or absence of
reproductive isolation.
Sprat distribution during spawning.
Sprat spawning period stretches from the end of Febn.mry-March till .August. The
earliest time of sprat spawning is recorded in the south-westem part of the 8altic
Sea (the Bomholrn region), but advancing
to the east ad to the north the
•
•
spawning period shifts to later times. May-June manifests the peak of sprat
spawning. During this period spawning is recorded in all areas of the seu.
Therefore the analysis of sprat distribution for thjs period can most vividly show If
there is or no reproduetive isolation between sprat from different parts of the Baltie
Sen.
•
•
In May of 1977-1979 we earried out detailed trawl surveys eovering the sea area
from the 80rnholm island to the Gulf of Flnland. Surveys were performed on board
of fishery vesse/s using eommereial pe/agie trawls. In order to exelude the effeet of
sprat migrations on the pattern of its distribution the surveys were made in chort
time, no more than in 120 hours. About 12 sister-ships participated there at the
same time. Data given in Fig. 1 show that separated , isolated concentrations
were never deteeted in all yeurs of surveys. Sprat 'tiUS found ever/'I'....hero trom the
Bornholm island to the Gu/f ot Fin/and. However, sprat distribution je not
homogeneous in the considered area: several regions with higher density of
concentrations ean be dlstingulshed. As a rufe these regions are located above the
Bornholm deep - the Stolpen grove, the Gdansk hollow and the Gotland deep. It
ean be explained by the taet that in that period the bulk of sprat still remnins in
deep sen layers limited by isooxygen 1 mlll from below and by k~oterm 40C trom
above. Naturally these layers belng tavourable habitat tor cprat are located only in
deep sea layers. It should be noted that the loeations of regions with high sprat
density eoncentrations may differ sufficiently from year to year. For example, in
1978 three eentres of concentrations eould be clearly distinguished: 1st wns in
Subdivision 25, 2nd was In Subdivision 26 (in the Gdansk hollow), an 3rd wac in
Subdivision 28 (in the Gotland deep). In 1979 within the whole considered sea
area sprat was reprenented as a single concentration with one centre in the
southern part of the Gotland deep. This can be explained by the fact that deep
water layers ot the Baltie Sea were weil aerated eausing everywhere the formation
of a quite large water layer favourable for sprat habitat (the thickness of a layer
exceeded 30 m bet\veen isoterm 400 and Isooxygen 1 ml/02). But in 1979 signe of
stagnation already appeared. Though in the Gdansk hollow and in the southern
part of the Gotland deep the conditions tor sprat habitat were favourable (layer .
thickness of sprat habitat was 30 m and more), still in the central and northern part
of the Gotland deep (Subdivision 28) the thiekness of this Inyer lessened till 15 m
in May due to worsening of oxygen eonditions. This was probably the eauoc tor
migration ot a conslderable part of sprat trom Subdivision 28 to Subdivision 26
\vhere maximum densities of eoneentrations were observed.
Thus, tor Baltie sprat It is impossible to single out isolated eoncentrations of zprat
in reproduetive period.
Hence it can be assumed that there is a single sprat popUlation in the Baltie Sea.
.. i
...
Populational structure is a regular distribution of genotypes in
heterogeneous medium..
':0 • •
Genetic and biochemicat investigations carried out in 1986-1989 revealed .high
inter-populational heterogenelty of Saltle sprat. For the analynls of sampten we
used genotype frequeneies of HAO-dependent malat-dehydrogenase (MOh). We
eonsidered 233 samptes (21862 ind.) whleh eovered almost all Battle sprat habitat.
However, even regarding the mass character of material the comparison of mean
frequeneies of M Oh gave rellable results only in several eases (Kozlovsky, 1988).
Reliable differences are recorded only sometimes and only on the level of
genotype trequencies being of an irregular and unstable in time character.
Heterogeneity of Saltic sprat population that is unconvincing comparing genotype
frequeneles of different sprat eoneentratlons still becomes evident when
comparing sampies taken from the density centres and from the periphery of a
eoneentration (Tabte). In camptes the genotype frequencies hnving differencec
within one eoneentration quite analogounly vary in other eoncentrationn. Thus.
nlthough MOh MM and MOh MS genotypen gravitated to the centre3 of
concentrations, still the rest of genotypes (MOh FF, MOh FM, MOll FS, MOh 55)
belonged to a more or less extent to the periphery of those concentrations.
•
Therefore heterogeneity of separate concentmtions, and the whole Baltic $pmt
population is reallned in non-rundom and lnhomogeneoun distribution of
genotypes. The best illustration of non-random genotype distribution ie tl1e
distribution of the most widely spread genotype MDh MM (Fig. 2).
The preference of one genotype tor the centre but another tor the periphery of
concentrations points to the probable selectivity as regards environmental factors.
by the relationship of distribution ...':ith
This assumption is also allowed
temperature factor. It seems to be logic to use data on functional differencec of
isozymes MOh, their differences at thermal stability, facts about cline variabi!ity
(Kirpichnikov, 1987, Golubtsov, 1988).
The mentioned assumption is testified by revealed reliable dependence of M Oh
. MM genotype frequency on the average tempemture of spmt shoaJs distribution
(Fig. 3). But this dependence is a linear dependence only within Ule boundaries of
aseparate sprat concentratlon being especially pronouneed during spnvming
period.
As a whole the populational dependence is described by a CUNe remotely
resembling a sinusoid (Fig. 4,5).
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L
Even if the mechanism of this dependence is not quite clear, its stability, relative
permanence of the optima testify to the exlstence of real temperature effect on
distribution of Saltie sprat MDH-genotypes. Investigations of sprat migrations und
distribution anyhow point to the decisive significance of temperature factar on
formation of wintering and spawning concentrations (Rechlin, 1967 I Shvetsov,
Gradalev, Kalejs. 1988; Shvetsov, Gradalev, 1989)
•
•
Inter-populational spatial heterogeneity promoted by genotypes selective
distribution at the same temperature faetor seem3 to be the neees:~mry property of
$prat population living in heterogeneous medium. Hence it 3eems quite logic to
postulate the Interrelation between the environment
and the genotypic
composition of population during formation of eoncentrations, and in the end,
spatial structure of Baltie sprat population.
Populational strueture of Baltie sprat eannot be considered as a system of local
populations due to isolation between spawnlng eoncentrations or groupe of
coneentrations. However, the existence of clearly pronounced, especiaHy in
wintering period, centres of sprat coneentrations, a!lows to assume interpopulational division of Saltic sprat. However, populational structure of 8altic nprat
cannot be eonsidered as a system of sUbpopulations as weil, because thls
treatment contradicts with the problem of criterion.
What faetors are sufficient to distinguish subpopulations for Saltie sprat? Whether
the lack of considerable sprat migrations (Apo, Ustinova. 1986; Shvetoov.
Gradalev, Kaieis, 1989), the differenees in age composltlon (Apo, Shlrokov,
Ustinova, 1990), indicate the existence of subpopulations or they only describe the
peculiarities of stretched Baltie sprat popUlation? To our opinion the reproductive
criterion cannot be practically applied for detection and description of Baltic sprat
sUbpopulations .
Basing on the existing material on population studies we may suggest another
approach to sprat popUlation ·structure. We claim that unified but genetieally
heterogeneous population spread and is to be spread inhomogeneously in
heterogeneous medium. Due to temperature conditlons thls inhomogeneity has a
regular character revealing itself both in formation of high density zones, Le.
eoneentrations, and in genetie heterogeneity of the eoneentrations.
Thus populational structure of Baltie sprat can be considered as a regular
distribution of genotypes forming the popUlation in heterogeneous medium.
•Stock unit- is a temporal regional unit of fishery management.
..
Ttle necessity to structurize Baltic sprat stretctled population may somellOW arise
when there ls a need to avert or weaken the sequences of local overcatchee.
Stock units may be represented both by the whole population, and by stable (at a
certaln period of time) concentrations differing trom each other by euch
characteristics of abundance dynamics as age composition~ growth, ete. Tlle
choice of stock units number is to be taken basing on middle-annual data (2-5
years) on abundance and distribution of Saltic sprat population. Therefore, "stock
unit" Is 0. sprat group that ie discrimlnated tor practical purposes, or a
concentration with abundance dynamics differing from other concentrations: with
temporal, though incomplete division; and considered as a regional unit for Baltlc
sprat stock management.
•
REFERENCE
1. Aleksejev F.E. 0 teoreticheskih predposylkah i metodikah rybohozjaistvennyh
populacionnyh iss!jedovanij 11 Vnutrividovaja differenciacija morskih promyslovyh
ryb i bespozvonochnyh. Trudy AtlantNIRO. - Kaliningrad, 1984. - S. 5-19.
2. Aps R. A. K voprosu 0 strukture populjacil baltijskogo shprota 11 Problemy
sovrjemjennoi ekologii ( Issljedovanija prirodnyh ekosistem Estonii). Mater. resp.
konf. - Tartu, 1978. - S. 105 - 106.
3. Apo R. A., Tanner R.H. 0 polimorfizmje myshechnyh esteraz baltij;;kogo
shprota (Sprattus sprattus) 1/ Biohimicheskaja i populacionnaja genetika ryb. -L.,
1979. - S. 91 - 93.
4. Aps R. A., Ustinova L. A. Ob izmjenchivosti zon roste otolitov baltijskogo
shprota 11 Fischerei - Forschung. - Rostock. 1986. - Jg. 24, H. 2. - S 47 - 49.
5. Aps R. A., Shlrokovs S. V., Ustlnova L. A. Struktura populacii baltijskogo
shprota 1/ Sovrjemjennyje problemy promyslovoi okjeanologii: Tez. dokl. Ylll
Vsjesojuznol konferencii. - L., 1990. - S. 34 - 35.
6. Birjukov N. N. Baltijskij shprot biologocheskoje sostojanije i tlozjaistvjennoje
ispolzovanije. - L.: Izd - vo LGU, 1980. -141 s.
7. Veldre L. A. Veldre I. R. 0
baltijskoi kilki (Sprattus sprattus)
• L.. 1979. - S. 83 - 89.
njekotoryh biohimicheskih pokazatjeljah krovi
1I 8iohimichjeskaja i populacionnaja genetika ryb .
•
,
!
-
8. Golubcov A S. Vnutripopulacionnaja izmjenchivoGt zhyivotnyh i bjelkovyj
polimorfizm. - M.: Nauka, 1988: - S. 131 -133.
9. Gmdaljev J.B., Kozlovskij A J., Shvjecov F. G. Vlijanlje gldrologichjeckih
faktorov na rasprjedjeljenije, plotnost I geneticheskij sostav skopljenij baltijskogo
chprota 11 Povjedjenije ryb: Tez, dokt. Vsjesojuznogo r:ovjer:hchanija. - M., 1989. 8.16-17.
.'
10.Gmuman G. B. Ekologlchjeskije osobjennosti vosproizvodstva osnovnyh
pelagofilnyh ryb v Baltijskom morje /1 Fischerei - Forschung. - Rostock, 1980. -
Jg.i8,H.2. -So 77-81.
.
'
11.Grauman G. 8. Passivnyje migracii baltijskogo shprota na rannih stndijah
ontogeneza // Fischerei - Forschung. - Rostock, 1981. - Jg. 19, H. 2. - S. 75 - 78 .
12.Grauman G. B. Sezonnyje koljebanlja chisljennosti ikry i Iichinok baltijskogo
shprota 11 Ficcherel- Forschung. - Rostock, 1983. Jg. 21, H. 2. - S. 50 - 53.
13.Kirpichnikov B. S. Genetika i selekcija ryb. - M.; Nauka, 1987. - S. 250 - 262.
14.Koval L. 1. Vnutrivldovaja Izmjenchivost nespeclfichJeckih ectera! i
malatdegidrogenazy u shprota Sjevjernogo I Baltijskogo Morje! 11 Ekologichjesknjn
fiziologija i biohimija ryb: Tez. dokl. IY Vsjesojuznoi konferjencii. - Astrahan, 1979.
- T. 2. - S. 215.
15.Kozlovskij AJ. Prjedvaritjelnye rezultaty izuchjenija struktury baltijskogo
shprota genetiko - biohimichjeskimi metodami /I Fischerei - Forschung. - Rostock,
1988. - Jg. 26, H. 2. - S. 74 -76.
.
"
16.Shvecov F. G.•Gradaljev J. B.. Kalejs M. V. Dinamika sjezonnogo i
mjezhgodovogo rasprjedjeljenija shprota v vostochnol chastl BaltlJskogo morja v
zavisimocti ot okeanologichjeskih faktorov 11 Fischerei - Forschung. - Rontock,
1988. - Jg. 26, H.2. - S. 70 - 74.
17..Shvecov F. G. ,Gradaljev J. B. 0 nagulnyh migracijah shprota v podraijonah
IKES 26 i 28 Baltijskogo morja // Fischerel- Forschung. - Rostock, 1989. - Jg. 2;',
H.2. - S. 54 -58.
.
.'
18.Aps R.,Gentzen B..Shirokov S.,Ustinova L. Allometric Growth of the Bnltic
Sprat. -ICES, C.M. 1989/J:6. -16p.
19.Rechlin O. Beobachtungen zum Vorkommen, zur Verbreitung und zum
Verhalten von Überwinterungsschwärmen des Sprotts (Sprattus sprattus L.) in der
nordöstlichen Ostsee 1/ Fischerei - Forschung. - Rostock, 1967. - Jg. 5, H. 2. - S.
33 - 38.
Distribution of genotyps in concentrations of Baltic sprat
-
-.-------Year,
season
sites
FF
FM
MM
Centre of
0.061
0.371
0.509
schoaling
Outskirts of
0.128
0.394
0.439
May-June
schoaling
_.
Centre of
0.079
0.384
0.489
1988
schoaling
f--.
1-.
Outskirts of
0.134
0.435
February
0.384
schoaling
-- -'
Centre of
0.044
0.396
0.516
1988
schoaling
-'
Outskirts of
0.081
0.374
March
0.455
schoaling
f--.
Centre of
0.092
0.380
1989
0.477
schoaling
Outskirts of
0.103
0.433
0.425
March
schoaling
-Centre of
0.072
0.386
0.513
1989
schoaling
Outskirts of
0.110
0.398
October
0.447
schoaling
..._-....._---_.- ----------..--_.._-------------_.
_
.
"
..'
>,' ,
Significance
Mean genotype frequencies
f--
1987
----r----------
-
r---
Sampling
MS
FS
S8
0.052
0.007
~
of difference
-0.032
0.007
0.003
0.034
0.013
~
0.032
0.015
~
0.1
0.02
---0.033
0.011
~
-0.030
0.050
0.010
0.041
0.010
-
0.025
0.012
Non-significant
Non-significant
~
--
- 1--'
0.018
0.011
~
-0.034
0.010
0.1
-
--------------'------
. '.'
..
'.'
. ...,
.,
Latitude
60 .,...-----~-~----........\IiI
59
58
57
56 _ . . . - -..
55
May,1979
May,1977
54 q - - - - t - - - - f - - - f - - - - I
15
17
19
21
23
15
17
19
21
23
15
17
19
21
23
Longitude
Rgure 1. Distribution of spawning sprat in thc Sattie sca (-5Q().. isolines of catch
offort, kg/hcur cf trawling)
r
• i
Latitude
59 -r--x-6;:f-....,..------~~~
56
57
56
55
May,1987
54
February,1 989
+-----+----r-----I
17
19
21
23
17
19
21
23
17
19
21
Longitude
Figure 2. Distribution of Mdh MM genotypes (..Q.500- isolines of genotypie
frequencies).
23
q
0.65 T
0551
0.50
045 j
0.40
.
•
•
1"=0.88
0.35 II •
1.5
•
A
t
0.60
2
2.5
3
3.5
0.65
0.60
•
0.55
•
• •
•
0.50
0.45
0.40
1
I
8
•
•
r=0.87
0.35
1.5
•
65
0.
0.80
2
2.5
3
3.5
1
C
0.55
•
•I
0.50
• ••
0.45
0.40
r=O.70
2
•
•
0.35
1.5
0
2.5
3
3.5
tC
Figure 3. Dependence of MdhMM frequencles In the sampies of Baltlc sprat from
mean water temperature (T0) in the layer of concentration of shoals
(May, June of 1988): A - SO 32, B -S028, C - SO 26.
q
0.55
.
'
1I
0.50.j.
0.45
J
••J • •
1)"
0.40
/1
2
0.35
•
•
....... .:
0.30
3
3.8
3.6
3.4
3.2
4
4.2
4.4
tC
Flgure 4. Dependence of MdhMM frequencies in the sampies of Baltic sprat trom
mean water temperature (T0) In the layer of concentratlon of shoals (SO
28 and 29); 1 - February. March of 1988. 2 - February of 1989.
q
0',551
0.50
•
J/I·
··· ,
. . 'r' "
0.45
. -~..'
--
\
\
0.40
0.35
2
j
-.\,
I
..
.
*":."....
. ~ ...
,,
"
':
3
0.30
6
4
8
10
12
14
16
tC
Figura 5. Dependance of Mdh MM frequencies in the sampies of Baltic sprat from
mean water temperature (T0) In the layer of concentratlon of shoals (SO
26 and 28); 1 - september of 1986, 2 - September of 1987, 3 - October of
1988.