Tl~is
paper not to be cited without prior reference to the authors
TCES Stn.tuary meeting 1993
C.M. 1993/L.:23, Ref:J
IN SITU FOOD CONSUMPTION BY YOUNG BALTIC SEA HERRIN!"! (CLUPE;-'
llARENGUS) - A TEST OF A BIOENERGETICS l\10DEL
by
Fredrik Arrhenius & Sture Hansson
•
Department of Systems Ecology, S-l 06 91 Stocl<JlOlm, SWEDEN
ABSTRACT
The food of juvenile herring was daminated by zooplankton, mainly copepods (Acartia spp. a.nd
Eurytemora affinis) and cladoeerans (Bosmina longispina maritima and ?leopsis polyphemoides) in
the summer. The food consumption decreased with body sizes and temperature from 20 % of body
w ight d- I in the summer to 4 % d- I by the end of Oetober far young-of-the-yc;ar. There was a
diurnal variation in stomach ful1ness, wirh one maxima in the morning and ane in [he evening.
Model simulation of the food eansumption demon trate that a bioe!1ergeties model based on c:at:J
_
mainly from adult fish, was valid also for young-of-the-year herring.
1
__
_------l
1. Introduction
(
lil tish biology, bioenergetics models' have been devel-
oped. with which food consumption is estimated from
. growth data (Hewett & Johnson, 1992). Generally these
, iJ.."
"
'
, .:.'models are based on a more or kss general bioenergetics
:'~'::'~ssumptions'and
for each sp~cics specific para~eters.
.....
,
~.·Most bioenergetics model are based on parameters de-
'~'.
: '>;';'rived frcfil'~~udies of adult fish, while few models are
::, built fromd'r;ta for juvenile fish. We don't know the error
.• ~.' behind these figures, but for yellow perch (Perea
-; ;'flaveseens) parameters of respiration and consumption
:~ tür adult fish have been shown to be in appropriate for
~;;.!..-
young-of-the-year (YOY) fish (post, 1990).
•
For. bioenergetics model. a common short-
~ •. comming
is that they never have been tested against
. ;-: realistic consumption data. Hansen et al. (1993) pointed
• out, that for more campIete studies
Oll
bioenergetics of
fish, information for larval and juvenile under field
-
.' condition are badly needed. It has been suggested that of
'-
,-~
larvae and juvenile fish can have a major impact on
zooplankton production and community structure
(Hansson, et al. 1990, Rudstam, et al. 1992, Arrhenius &
Figure 1. The sludy area with the sampling stations for collec
Hansson, 1993) and therefore it is important to investi-
tions of YOY herring and zooplankton.
gate the validation on field estimates vs. model predicexperiment. A minimum sampIe of 10 fish per'length
tions.
The objectives of this study were to measure the
class was taken within 10 minutes every 2h. On the first
food consumption and diel patterns of feeding activity of
sampling two stations with different depth, were used in
juvenile herring (elupea harenglls L.) and compare that
the same area, as small larvae were in shallower water
with estimates given by the bioeriergetics inodel for
than large larvae
herring (Rudstam, 1988).
fish were immediately preserved in 70 % ethanol.
(c.f.
Ur ho &' Hild~n, 1990): Cap'lure
...~.
2. i\lethods und material
.2.2 Diel feeding patterns and daily rations
In the laboratory, the totallength of each fish. i. e. kngth
2.1 Fish samp!ing'
from the tip of the snout to the end of the tail fin. was
Using small charges of explosives (15-120 g of Primex
measured to the nearest 1 mm and the wet weight was
17 mm, Nitro Nobel AB). helTing were sampled in the
measured to the nearest 1 mg. The dry weight of the
northern Baltic proper (Figure 1) during five 24-h
stomach contents were determined drying oven at 60°C
periods between July - Oclober 1992. Collections were
for 3 days. Water temperature was measured at each 24-h
made at approximately 2 hintervals during euch 2-l-h
sampling.
l-,
2
•
• ~ "\'
t
",,,<:1,,
Dicl feeding patterns were evaluated by determining at 2-h intervals. to the
n~arest 0.001
f'
preserved in 4 % form<:lin. ßefore counting under an
mg the mean
inv.::rted microseope, the zooplankton samplcs were s:!b-
stomach wntent in dry wcight. From these data. daily
sa~pJed
rations were estimated by the method by E1liott &
eaeh sampIe were detcrn1ined to lowest taxonomie level.
Persson (1978). Encuat;on rates were calculated from
Biomass were estimated from va!ues on individual wet
the dec1ine in intestinal traet content in dry weight as
weights (Henroth, 1985), of which 5 % was assum,-,d to
proportion of body mass during nonfeeding periods
be carbon (Mullin. 1969). Thc sampies were e0ur;td,
,,,.~ assuming an exponential evacuatioll rate (Persson, 1986).
plankton was identifiedaceording to dcvdopmenl stage
'" ',c'
.
"
~::., The assumption was that the herring don't feed during
. '"' ..... darkness butonly evacuate the gut content. We ealculate
(Kolt. 1953) and :lt kost 500 specimen froln
(adult, copepodite and nauplii) :lnd sex.
;:,:-;~
'
J'
the evacuation rate between approxirnately one hour after
.~~:
sunset and one hour before sunrise. For two of the
sampling dates (August 5-6, September 16-17). sampling
•
-
intervals were shorter than 24-h, duc to hard weather
-''"'
'0 04
.
condition, therefore the data have been extrap01ated
*'01)
(figure 3 c & e).
;,
- Specific growth rate
'\ '- '- fl""growm,~/
.c
~
o
So 0.2
8
6 §
.c
~ 0.3
2.3 Feeding
":-
10
0.5
':oE)
"'"
'<3
4 .~
2
0.1 +,=-.--......---.--.,...-_.__-.----+ 0
240
280
320
200
Date
When possible, 10 fish were laken at random from each
sampIe and length interval. Individual stomach were
analysed using a stereo mieroscope and an inverted
Figure 2. Fitted growth curve. und calculated specific growth
microscope. Eaeh prey was determined to the lowest
rate for young-of -the-year herring in the northem Balti.: Sen,
possible taxonomie level. If a stomach eontained a large
from Arrhenius & Hansson (1993).
number of prey, a subs<:mple of 200 items was analysed.
The contents of a slomach was expressed as the percent•
ages of different taxa, calculated from the number of
2.5 Bioenergctics model
identified items. From these percentages, means were
calcul:lted 10 represent diet of fish ut difft>rent stati0ns
A bioenergetics moder of iildiviuual Baltic herri,ng hus
and dates. In order to eharacterise the feeding of herring.
been developed by Rudstam (1988), using software de-
the eleetivity wcre ealculated (Chesson, 1933).
veloped by Hewett & Johnson (1992). Thc parameters
. used in the model were derived from a variety ofsoul'ces
2.4 Zooplankton
but in all cases were from adult fish.
We compared thc model predictions of daily
From each sampling oceasion, a zooplankton sampIe
consumption with the field estimates from gut evacuation
taken with a WP-2 have been analysed. We assumed that
rated and fullness. The input parameters for juvenile
the rnesozooplankton used by the fish was found in the
herring used in the bioenergctics model, were taken from
uppern10st 10 (Station 1-3 in Figure 1) and 30 m (Station
leES-area 28-29 in Arrhcnius & Hansson (1993). The
4 & 5 in Figure 1), respectively. The plankton net were
growth rate were derived [rom growth in length and
towed vertically from the depth tu the surface at a speed
length-wcight relationship in the model (Figure 2).
of 0.5 rn/s. SampIes was filtered through 90 ~m nets and
Temperature regime ,vere taken from this study.
3
J
Table I. Estimated fish length (in 5. mm intervD.1s), wet weight, daily food ration and evacuation rate cf juvenile herring in 1992.
Tempcrature was taken cvery date bClwecn 0-10 m in July-August and 0-30 m in September-Oetober. Th·~ number of fish analysed
(181'.5) is not eglial to the number of fish killed at different sampling dates and depths.
3 Results
little or not at all during darkness. There was a tendency
towards two maxima each day, one in the morning und
3.1 Fish sampling
one in the evening, and the times for these maxima
varied depending on the time for sunset and sunrise.
Herring (Clupea harengus) were caught at aIJ depths in
Estimates of gastric evacuation rate (Table I)
each station, but showing a diel cycle with generally
and daily rations were highest during July-August,
Th~
c;dropping in t!1e autumn. For small juveniles. in the
depth of catches varied between 0-35 m, depending on
summer daily food consumption was about 20 % of the
the season and water temperature (Table 1).
body weight whiJe for larger juveniles in late fall daily
closer to the surface during night than during day.
consumption was about -+ %.
3.2 Diel feeding patterns and daily ratians
3.3 Feeding
Thc stomach content varied with time of da)' for each
diel series (Figure 3 a-t). The content of the stomachs
Crustacean zooplankton dominated the stomach content
v. as lowcst during nighttime. j ndicating that herring fed
ofjuvenile herring, and the copepods were elearly domi4
. ,"
~ ,.,,"" .~
,~
4..,-____________
..
_
~I
3
nating (Table 2). Among eapepods. Acartia spp. (Acartia
bifilosa, Giesbreeht, and/ar A. longiremis (Liljeborg»
I
and Eurytemnra affinis hirundoides (Nordquist) wcre
I
dominated. Copepod nauplii were relativeiy eommon in
the stomuch~. Copepods were also the dominant prey
July 15-16
.
.....
3,
2). Olher copepods \vere only in small numbers in the
~
JI'
I
..,
..... - - ~
items in thc herring stomaehs in August-Getober (Table
3m
... ."
.'
stomaehs. In July und early August respectively, the
c1adocerans Bosmina IOllgispilla maritima, P.E. Müller,
and Pleopsis pol)pFzenzoides, Leuekart, was eonsumed.
Rotifers were rare and tintinnids were absent.
o-I---------.l....;..J...-,""--'-------I
August 5-6
3
•
....
~.
..,
DClad0EIT
2
O-l---,---------'--'------i
August 26-27
'<)
3
;s:
o
Oth
a
-,
:cOll
6A
2
Date
O+--------.--;.....:::l:=-------i
September 17-18
Figure 4. Electivity indices (Chesson, 1983) for juvenile
3
hening between July and the end of Getober far 4 prey groups:
2
Cladocerans (Clad), copcpoditcs and adults of Ew}'telllora /
•
-----~
Telllora (E), Acartia (A) and other corepods (Oth. primarily
Pseudocalanus).
0-1----------'---'------1
Gelaber 27-23
3
Juvenile hcrring, selccted c1adoeerans over
2
eopepods and Acartia over other eopepod species (Figure
4). Cladoeerans were not selected exeept at the shallow
.l-~-'-I
-'--,--!
:;:"""'I-~:::;:I
o
IOlO
1400
,_1_'+;-1!>......
'
18'~J
22'1() 02'l'1
station in July sampIe. These pattern was not as clear and
':::.-•..,--'----i
06'10
I (Jl<l
differ during sampling dates.
3.4 Zooplankton
Figure 3 a-f. The diel cycle of food content in herring stomach
far each sampling antI sites. Each point represent the averJge
In terms
stomach content at each sampEng time. The period between
copepods in July and in autumn and rotifers in August
sunset arid sunrise is also marked (-). DJtes with shOiter
sampling intcrvals. the dala have bcen extrapolated (- -
of abundance, zooplankton was dominated by
(Figure
-).
5 & 6). Among copepods, Eur)'temora and
Acartia dominated. Together they constitute at least half
5
..---------------------
---
Tabie 2. E~timated proportions 01' zooplankton in hcrring stomaehs (% by volumc) and proportions oi iJentified zooplankton taxa (%
·
by numbcrs). Proportion wcre calculated as the average of proportions in individual fish. Lcngth of fish. number of stomJl:hs
analyzed (N). number 01' cmpty stomaehs (E) ami the total number cf idcmilied prey itcms are also given. Prop.: proportion; zoopI.:
zooplankton; id.: identified; ad&cop.: adult nnd copepodites: BaI.: Bai.mus; E/T: cI/Y)'iemora/Tcmora:
A: Acartia;
Unid.:
unidentitied; Dos.: Bosmina; PIe.: Pleopsis; Ker.: Kcratella
. ...:...~
,;.
.,
Date Stn Time
..... ,..,.
..
~';'~!
:;;~
'~~~~
':":,.;
:.!~..
--
._'
Fish
N
lengl!'.
interval
(mm)
E
Prop.
Zoop!.
(%)
No.of
NilUpl.
identified
Cop. BaI.
prei'
Cop~poda
C1adocera
(3d & cop. )
EiT
A
Other Unid.
Dos.
Other
wopl
PIe.
E~
Ker.
"
July 16-17
3m 18.00
-18.00
18.00
10 m 19.00
19.00
19.00
August 5-6
10m 20.30
20.30
20.30
·"20.30
20.30
August 26:27
15 m 19.15
19.15
19.15
19.15
September 17-18
20 m 20.15
20.15
-:::0.15
Oelober 27-28
35 m18.15
18.15
18.15
25-29
30-34
35-39
30-34
35-39
40-14
10
10
10
6
10
10
100
0
0
0
0
0
100
100
100
100
100
978
989
999
421
955
957
1.8
1.2
42
11.4
10.7
5.7
0
0.4
0.0
0.7
0.1
0.3
100
100
100
100
100
356
280
941
957
963
14.8
10.7
11.3
4.7
1.8
3.8
3.0
1.6
3.1
2.7
30-34
35-39
40-14
45-19
50-55
10
10
0
0
0
0
0
45-49
50-54
55-59
60-64
4
10
10
10
0
0
0
0
100
100
100
100
393
998
963
898
20.6
14.6
13.1
4.6
2.0
3.1
1.5
60-64
65-69
70-74
9
10
10
0
0
0
100
IDO
100
8')0
927
998
6.2
11.3
10.1
0
0
0
70-74
75-79
80-84
2
4
5
0
0
0
100
100
'. 100
200
400
500
12.5
6.5
8.6
0
r
4
3
0
10
0.1
0
0
95.5
0.4
95.2
0.2
(J.1
51.7
55.9
0
0
0.2
0.7
0.7
u.7
1.7
2.4
92.2
26.6
23.5
20.3
0.5
0.3
0.1
0.8
0
1.2
1.2
0.6
2.5
2.3
1.0
2.8
0
59.:
1.8
60.6
64.9
66.9
65.8
1.3
3.1
1.9
5.0
13.0
17.3
11.7
16.2
19.2
19.6
13.4
32.6
35.5
48.3
53.3
396
52.7
1.3
1.8
0.6
0.2
0
0
8.4
U
0
0
0
0
0
0
3.8
84.1
83.3
81.6
0
0
0
7.0
10.2
11.6
gO.5
820
79.4
0
1.0
0.4
0
0.3
0
0
0
0
0
0
0.1
0.1
2.1
1.8
3.4
0.5
1.3
1.1
3.2
0
0
1.1
1.4
0.9
4S.0
1.1
1.1
0.9
1.2
0
0
0
0
0.7
0.7
0.4
0.3
8.6
7.7
11.7
0
0
0.4
0.2
0.3
0.6
0.5
0.8
0.5
0
0.8
0.2
0.8
1.1
0
0.4
0.4
0.5
0.2
2.0
0.8
0.7
'J.5
0.3
1.0
0.8
0.3
0.5
1.0
46
2.2
0
1.9
0.9
3.6
2.1
5.1
10.5
-l.8
1.0
0.5
1.1
0.6
0
0
1.4
1.9
1.4
2.8
1.3
0.3
2.7
0
0
1.9
1.8
0
0
0
0
0
0
0
0
0
0
•
167
of the biomass. Other common copepods were Temora
longicomis (P. !\'lüller) and Pseudocalanus millutes
5000.----:==-------::::::-
m
IOllgatus. Among cladocerans, Bosmina and Pleopsis
~onstitutes
4000
95-100 % of the numbers and Keratella spp.
and SYllchaeta spp. were dominated among rotifers.
....
o
In
, spite of high numbers, tintinnids generally represented
others
~
cladocerans []
o
--.,
rotifers
copepoJs
3000
2000
<1 % of the biomass.
'a--.
-~
loo01~
30/(
'T7-7'-":l
PI
o+"-"-""-'1.w:.....~""T'--=-"-"-T-"'-'-......,..........--..;..4
3.5 Bioenergetics model
920715 920805 920326 920917 921027
.
The results were analysed with linear regression analysis
Sampling day
(SYSTAT, 1992), using data from fjeld estimates as the
independent variable and data from model predictions as
Figure 5. Thc total abundance of zooplankton on the different
lhe dependent variable. There \vere no significantly differ
sampling stations. Thc three lirst was sampled bctwecn 0-10 m
between the model and fjeld estimates ef feod
(station 1-3 in Figurc I) and the last two was sampled 0-30 m
~,
consumption (Figure 7).
,.'"
(station 4-5 in Figure I).
6
•
rotir<.'r~
a)
~
=::J
Kcratel!a
0.3
S.,·nchae;a
1
1°
",c::
1
.2
O.~
.~
~
a.
ö:i
-0
0
o•
~
I
.c::JL
,
6
x
//
J
/0
I~~
I
0
k"0[!B)
0
x
/
J
0.1
I~!~ I
11
J:
1
'D
1000
July 15-16 3m
Juiy 15-16 !Om
ugust 5-6
x
August 26-_7
Septembe !7-18
Oetober 27-28
/. 6
0
J0
0
+6
+
0
0
0.2
O.l
0.3
Field estimates
Figure 7. The food consllmption prcdicted by the model against
b) c1adocerans
e
400
•
350
300
,.,
0
~,
c
-::l
:::
0
the field data. The black line is Ihe 1: I relation. Thc slope and
Podon
~
Pleopsis
the intercept do not differ signifieantly from 1 (n=21. 1'2=0.61.
Evadne
0
Bosmina
slopc=0.74, SE=O.14, p=O.07).
250]
200-
,
~,
4. Discussion
..::"
///~
r.~//),
~
/'1
100 f/:,( I >~
50
0
I
150
,,\'"
~~_r
I
Juvenile herring (Clllpea harenglls) foraged predominately on zooplankron. There were a shifr from clado./
ceran in early I ife stage to copepods in older stages on
juvenile. Herring prefened cladoceran over copepods in
hallower waters in the summer. There have been shown
in this area that cladocerans are selected over copepods
c
copepods
2000
e
1-00
,.,
o
Terno ra
8;]
PseudocolallLls
and the seasonal changes in proportions of copepods and
Il;i EllrytenlOra
c1adocerans consumed retlect he seasonai changes in
Acartia
zooplankton composition (Johansson. 1992, Rudstam et
al., 1992). The preferred species of cladocerans and
C
~
E
copepods were according to other studies on juvenile
1000
herring in the nonhern Baltic Sea (Hudd, 1982.
c:
Parrnanne & SjöblolTl, 19 4, Raid. 1985, Rudstalll et al..
00
1992).
There was a difference between hallow water
and deep stations in the food content and in fish lenght.
Fish closer to the share had Illore cladoceran than copepods in their stomach and
we~e
also shorter in average
Figure 6. The abundanec of total rotifers (a), eladocerans (b)
lenght. Herring larvae seem to retained in the nearshore
and copepods (e). The dominating species within c;lch group
zone during the larval period to experience a temper:J.ture
regime similar to optimum for growth and to avoid
ur shown <;cparately.
predation (Urhü & Hilden. i 990).
7
."
tcmperature. It also indicate th:::t the available bio-
There were a diurnal dynamies of stornach fullncss with a tendeney that herring consume more in the
energetics model tor adult herring, can be used to
evening than in the morning, which has also been shown
mate the food consumption for juvenile hen:ing.
e~ti­
by Raid (1985). The gasll'ic evacuation rate were high in
~the
Acknowlcdgements: Sture Nellbring, Markus Nikula
summerand lower in the autumn except the Oetober
:-;:'v;; serie.
The evacuation rate are mainly govcrned by the
. and Joakim Westberg heJpe.d in thc field. Financiai
,;~; water temperature (Elliott & Persson, 1978) and more or
support was provided by thc Swedish Environmcntal
~' .. Iess
unaffected of fish size, food size and the frequency
Protection Agency, Swedish Natural Science Research
of feeding (EIliott, 1972, De Silva & Balbontin, 1974).
Council, Hierta-Retzius foundatio'l, Alice &. Lars Silens
:Thc high values in October maybe due to difficulty to
fund, Stockholm Centre for Marine Research and Nitro
'.
:~
.~':- . calculate the evacuation rate, because of low temperature
~ f·
. c..
.~,
-:~
"
Nobel AB .
and growth rate of herring.
S. Literature citcd
The food consumption decreases from 20 % of
body weight
d- I
in the summer to 4 %
d· 1 by
the end of
Abrams, P. (1937). The functional response of adaptivc
consumers of two resources. Theor. Popu!. Bio!.
32: 262-288.
Arrhenius, F., Hansson. S. (1993). [-oad consumption of
larval, young and adult herring and sprat in the
Baltic Sea. 1\lar. Ecol. Prog. SeI'. 96: 125-137.
Chesson, J. (1983). Thc estimation ami analysis of
preference and its relationship to foraging
models. Ecology 6..1-; 1297-130+.
De Silva, S. S., Balbontin, F. (1974). Laboratory studies
on food intake, growth und food convcrsion of
young herring, Ciupea hcrengus (L.).'J. Fish
Bio!. 56: 645-658.
Elliott, J. M. (1972). Rates of gastric evacuation in
brown trout, Salmo trutta L.. Freshw. Biol. 5:
287-303.
Elliott, J. M., Persson, L. (1978). The estimation of daily
rates of food consumption for fish. J. Anim.
Ecol. 47: 977-991.
Franek, D. (1.988). 0+ smelt (OsJlierus eperlmws L.) and
herring (Clupea harengus L.) in the food chain .
of the Barter Bodden. leES 1988 BALINo. 13.
Hansen, M. J., Boisclair, n., Branet, S. B., Hewatt, S.
W., KitcheIl, J. F., Lucas, M. c.,' Ney, J. J.
(1993) Applications of bioenergetics models 10
fish ecology and management: Where do we go
from here? Trans. Am. Fish. Soc. In press.
Hansson, S., Larsson, U., Johansson, S. (1990).
Selective predation by herring and mysids, and
zooplankton community strueture in a Bahic
Sea coastal area. J. Plankton Res. 12(5): 10991116.
Hay, D. E. (1981). Effects ofcapturc and fixation on gut
contents and body size of Pacifie herring. Rapp.
Cons. Int. Explor. Mer. 178: 395-400.
Hernroth, L. (1985). Recommendations on mcthods for
marine biological studies in the Baltic Sea.
!'.Iesozooplankton biomass assessment. Baltic
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model 2. An upgrade of a generalized
bioenergetics model of fish growth for
microcomputers. Uni\'ersity of Wisconsin St:a
October for juveniles. Similar speeific consumption rates
have been reported elsewhere by field estimates of daily
~:
',"
Rudst::<m et al., 1992).
'",
"7
rations (De Silva & Balbontin, 1974. Franek, 1988,
Despite that the bioenergetics model for herring
.. is based on data from adult fish, it does not predict consumption rates that differ significantly from those we
estimated for YOY fish. This is contrary to studies on
yellow perch (Perca flavescens) that measure invalid
parameters for larvae and juvenile with modeling with
adult parameters (Post, 1990). Still, the in situ estimates
are based on the variation in stornach content between
few individuals whereas variation in the model predictions are based on the variability in body size of larger
numbers of individuals. Since growth is cumulative and
the daily growth data used in the model is integrated over
time, but the model can't predict day to day variability in
consumption, but it can accurately predict cumulative
consumption. Therefore we need further investigation to
get more information on larval and juvenile on field
measurement of key parameters for the bioenergetics
model. \VC also need to investigate the maximum consumption (functional responses, e. g. Murdoch, 1973;
Abrams, 1987) in the field to redefine the maximum consumption function in the model.
This study show that the main diet for juvenile
herring is zooplankton and consumption decrease with
8
"
•
•
•
..
,-.
,
Grant Technical Report No. \\1S-SG-92-250.
2nd edition. p. 1-79.
Huud, R. (1982). Feeding of Baltic herring larvae
(Clupea harenglls L.) in the Gulf of Finland.
Finnish Fish. Res. 4: 27-34
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zooplankton eommunity strueture in the
northern Baltie proper. PhD thesis. tnst. Zoo!.,
Stockholm univ.
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subsampling of plankton. Aust. J. MGr.
Freshwater Res., 4: 387-393.
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ocean: the present status and problems.
Occanogr. Mur. Bio!. Rev., 7: 293-310.
Murdoch, ,)V. W. (1973). The functional response of
predators. J. App!. Eeo!. 10: 335-342.
Parmanne, R.• Sjöblom. V. (1984). The abundanee of
spring spawning Baltie herring 1arvae in the
Seas around Fin1and in 1982 and 1983 und the
eorrelation between the zooplankton abundanee
and the herring year dass strenght. ICES C.M.
1984/J:18
Persson, L. (1986). Patterns offood evaeuution in fishes:
a critieal review. Env. Bio!. Fish. 16(1-3): 5158.
Post, J. R: '(1990). Metabolie al!ometry of larval and
juvenile yellow pereh (Percafiavescens): In situ
estimates and bioenergeties models. Can. J.
Fish. Aquat. Sei. 47: 554-560.
Raid, T. (1985). The reproduction areas and eeology of
Baltic herring in the early stages of devlopment
found in the Soviet zone of the Gulf of Finland.
Finnish Fish. Res. 6: 20-34.
Rudstam, L. G. (1988). Exploring the dynamies of
herring eonsumption in the Baltic: Applieations
of an energetic model of fish growth. Kieler
Meeresforsch., Sonderh. 6: 312-322.
Rudstam, L. G., Hansson, S., Johansson, S., Larsson, U.
(1992). Dynamics of planktivory in u coastal
area of the northern Baltie Sea. Mar. Ecol.
Progr. Sero 80(2-3): 159-173.
SYSTAT. (1992). SYSTAT: Statistics, Version 5.2 Ed.
Evanston. 1. L.: SYSTAT Ine: 724 pp.
Urho, L., Hilden, M. (1990). Distribution patterns of
Baltic herring larvue, Clupea harenglls, L., in
the coastal waters off Helsinki, Finland. J.
Plankton Res. 12(1): 41-54.
9