7028
Vlaams Instituut voor de Zee
Flmdun;· Ma:i1.? Jnelituts
ICES
C.M.
1986/L: 15
Sess.R.
GROWTfl, PRODUCTION AND FOOD CONSUMPTION OF A FISH
COMMUNITY IN THE SHALLOW SUBTIDAL OF A SANDY BEACH
by
A.Cattrijsse, E.Van Landtschoote & O.Hamerlynck
Marine Biology Section, State University Gent
Ledeganckstraat 35, 9000 GENT
In 1985 monthly fishing was done in the undeep C4-5m
below Mean Sea Level) sublittoral of a sandy beach between
Knokke (Belgium) and Cadzand Cthe Netherlands) in the mouth
of the Western Scheldt estuary.
A 1.90 m beam trawl with a 5 mm mesh C10 mm
stretched), pulled by a small boat, was used to sample the
demersal ichtyofauna.
Hauls were done over a distance of
700 m, indicated by two series of posts on the beach.
One
haul took 10 to 15 minutes, depending on the trawling
direction and the current.
As a rule 7 trawls were done so
a surface of approximately 10000 m2 was investigated.
Fishing started 1 hour before low tide in the morning, the
last trawl ending two hours later.
In September 24-hour fishing was done at two-hour
intervals.
Fish smaller than 120 mm were immediately
anaesthesized in a solution of benzocain Cethyl-4-amino
benzoate) in seawater to prevent regurgitation of the
stomach content.
Less than 15 minutes after capture, both
fish and crustaceans were preserved in a 7% solution of
neutralized formaline in seawater.
Thirty species of fish were caught .
important species being :
The most
Clupea harengus (herring)
Sprattus sprattus (sprat)
Gasterosteus aculeatus C3-spined stickleback)
Pungitius pungitius C10-spined stickleback)
Syngnathus rostellatus CNilsson's pipefish)
ngonus cataphractus Chooknose)
Liparis liparis (see-snail)
nmmodytes tobianus (sandeel)
Pomatoschistus microps (common goby)
Pomatoschistus lozanoi CLozano's goby)
Pomatoschistus minutus (sand goby)
Pleuronectes platessa (plaice)
Limanda limanda Cdab)
Solea solea (sole)
1.
2.
Gasterosteus aculeatus, Pungitius pungitius and
Pomatoschistus microps were only present in the wintermonths.
These species are migrants from the nearby more
brackish inlet of the nature-reserve "Zwin" and the Western
Scheldt estuary.
For juveniles of the commercially important species
Pleuronectes platessa~ Solea solea, Limanda limanda~ Clupea
harengus and Sprattus sprattus, the area fulfils an
important role as a nursery.
DENSIT.Y_
Absolute densities were calculated for the most
abundant species, using netefficiencies from Kuipers
C1975), Doornbos & Twisk (1984) and Doornbos (unpublished
data) for this type of fishing gear.
Dab and sole did not reach high densities yearround.
Pomatoschistus minutus and P.Jozanoi together reach a
yearly average density of 1 individual per 2 m2.
Density
of P.Jozanoi is 4 times higher than P.minutus density.
average density.
Cnumbers/m2/year)
species
Pomatoschistus minutus
P.Jozanoi
Pleuronectes platessa
Clupea harengus
0. 1
0.4
0. 1
0.3
density
Limanda limanda (December)
Solea solea (September)
Cnumbers/m2~
0. 1
0. 1
Biomasses were calculated using standard length ashfree dryweight CAFDW) regression-equations.
Clupea
harengus was excluded from further calculations because
this pelagic species cannot be sampled quantitatively with
a beam trawl.
Moreover it was found that different cohorts
moved in and out of the area yearround.
P.platessa reaches the highest value : 0.8 g AFDW I
m2/year.
P.minutus and P.Jozanoi together reach a value
that is half that of plaice.
species
biomass
Cg AFDW/m2/year)
P.minutus
P.Jozanoi
Pleuronectes platessa
0. 19
0.20
0.77
3.
E_FODUCTION
The growth rate method (Crisp, 1984), proved to be
the only method applicable to the dataset.
The
instantaneous growth rate "G" was calculated by exponential
interpolation of the data of the growth curve (figure 1,
curve was fitted by eye), the latter being obtained by "de
visu" cohort separation.
The yearly production of 0+
juveniles of plaice "born" in the winter 1984-1985 is
estimated to be : 0.06 g AFDW/m2/year
CONSUMPTION
In September fishing was done during a 24-hour period.
At two-hour intervals 2 to 4 hauls were done.
The results
are grouped in 12 trawls CTR 1-12).
P.Iozanoi was the most abundant species.
From every
trawl 12 to 15 P.Iozanoi of the 25-29 mm lenghtclass were
randomly chosen for stomach analysis.
All prey-items were
identified if possible up to species-level and dry weigth
CDW) of the entire stomach content was determined.
The daily food consumption was calculated using two
different methods :
method of Eggers (1977)
2.61 %of body weight CAFDW)
method of Elliot & Persson C1978)
3.06% of id.
Ann u a 1 food
cg_fl.§.~!I!.E..t
i o .!2.
The annual food consumption in g AFDW/m2 was calculated for
different daily consumption rates, estimating the duration
of the feeding season to be 300 days.
The total annual consumption for the two gobies and plaice
together is estimated to be 10 g AFDW/m2.
The latter being
responsible for 65 % of this value.
Expressed in units of
energy, both goby-species yearly consume 84000 kJ/m2.
species
P.minutus
P.Iozanoi
Pleuronectes platessa
2%
1 . 11
1. 22
4.62
3%
1. 67
1. 84
6.93
4%
2.22
2.45
9.24
4.
t;::J. .R. t:::. 0.. P....I....0.t.I. ... .R. J:.l..Y. T..I..IJ.'1. ?. .:. .
f.g..r.. ?..9•.!. .!2.9..
For P.!ozanoi of 25-29 mm
was calculated.
F . I.
=
~he
fullness
100 x OlJ stomach content /
index CF.I.)
A FOLJ fish
Using an arcsin-transformation, the mean F . I. (with
standard errors) for the 12 trawls are plotted together
with the tidal curve for Cadzand for 25-26 september 1985
(figure 2).
P.!ozanoi feeds mainly at night around high tide, a
second smaller peak was found also around l1igh tide during
the day.
P.~. D..?..Lt:.Y..
Supposing an increase in density is correlated with an
increase in (foraging-) activity , we conclude that gobies,
sole and plaice are night-active animals (figures 3,4,5).
f._?...?.. si. ._. P.X~. f.. . ~. r.. ~..!J..S. ~. § ..
Renkonen cluster-analysis on the data of the stomach
content of P.!ozanoi from the twelve trawls also shows a
qualitative change in the feeding preferences of this
species (figure 6).
At night most fish prey upon copepod
nauplii and adult Calanoidea.
Predation on Har~~cticoidea
is important only at low tide.
Most Amphipods were found
in the stomachs of fishes caugh~ during the d ay.
Fo1·
larger prey - items such as shrimps and mysids , and for
Cumacea and cypris-larvae of barnacles, no significant.
change in mean numbers per stomach was observed during the
24-hour period .
B.s;. Js.rr.?..~. .L~. 9.9. ~.~.§.n. t..
lJe acknowledge the logistic support of RiJkswaterstaat
Vlissingen Cthe Netherlands).
s. R. A.I. Y.. R..s. . . . r:. .LI..S. P.. :
~. J.I..
CRISP, D.J.
(1984), Energy flow measurements.
in IBP
handbook nr.16 : Methods for the study of marine benthos .
Blackwell Scientific Publications.
Oxford .
pp . 2B4-372
C1984), Density, growth and annual
DOORNBOS, G. & F . TlJISK
food consumption of plaice (Pleuronectes p!atessa).
Neth.J.Sea Res.
9(1)
69-85
Eggers,
M. D.
C1977) ,
Factors in interpreting data obtained
by diel s a mplin g of fi s h s tom ac hs .
34 : 290-294
J.Fi s h . Res. Board Ca n .
5.
Elliot, J.M. &L. Persson
(1977), The estimation of daily
rates of food consumption for fish.
J.Anim.Ecol.
47 : 977-991
KUIPERS, B.R.
(1975), On the efficiency of a two-metre
beam trawl for juvenile plaice CPLeuronectes pLatessa).
Neth.J.Sea Res.
9(1)
69-85
This poster is extracted from
CATTRIJSSE, A.
C1986), Experimenteel en veldonderzoek naar
de 24-uurskonsumptie en het voegingsritme bij Pomatoschistus spec. CPisces-Gobiidae).
unpublished M.Sc. thesis
State University of Gent, Marine Biological Section - 80 pp.
VAN LANDTSCHOOTE, E.
C1986), Ecologisch onderzoek van de
visfauna in de kustwateren ter hoogte van de Zwinmonding.
unpublished M.Sc. thesis- State University of Gent, Marine
Biological Section - 120 pp.
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