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INFLUENCE OF TEMPERATURE AND DEPTH ON SPAWNING SITE SELECTION OF PIKEPERCH
(Sander lucioperca (L.)) IN THE HELSINKI SEA AREA
Erkki Fontell, Hannu Lehtonen and Jyrki Lappalainen, Department of Limnology
and Environmental Protection, PO
Box 65, FIN-00014 University of Helsinki, Finland, hagnu.lehtonien(&,dhelsinki.fi
Introduction. The spawning of pikeperch in the
Gulf of Finland generally takes place in late May-
June (Erm 1976, Lehtonen et al. 1996, Lappalainen et
al. 2003). Successful reproduction and development
of larvae and juveniles occur almost entirely in
sheltered archipelagoes and bays (Lehtonen et al.
1996). In these parts of the Baltic Sea suitable low
salinities and temperatures are found. To be able to
reproduce and form viable populations, pikeperch
depend on areas where water warms up early in the
spring/summer.
Before spawning the males build nests with a
diameter of about 0.5 m and at depth of 5-10 cm
situated on the sandy grounds. The highly sticky eggs
are laid in 34 layers on twigs, roots or aquatic plants
(Virbickas et al. 1974). However, females can lay
their eggs also on stones and other hard substrates,
for example, on artificial spawning substrates.
Typical to pikeperch both in the Baltic Sea and lakes
is that males guard the eggs until hatching. The
purpose here was to study the dependence of
pikeperch spawning on temperature, depth and
location in the western Helsinki sea area by using
artificial spawning nests.
Methods. The study area was situated in the western
Helsinki sea area. The bottom consists mainly of clay
and the water is very turbid.
Altogether 276 nests were set on potential spawning
areas. Nests were made of 80-100 cm long spruce
twigs which were tied with wire to a brick. Each nest
consisted of 3 twigs and the total coverage of a nest
was thus about 0.5 m'1. Nests were set in rows by
fastening them to a line at intervals of 10 m. The
study area was divided into squares (500 x 500 m)
and S
rnd nest.
Nests were examined weekly between 26 May
and 29 June 1999. The coverage of pikeperch eggs
was estimated as percentage and depth, temperature
and salinity were measured over each spawning nest.
Results. The first observations of pikeperch eggs
were made in late May at the depth of 4.9-5.5 m and
at a temperature of 6.20C (Table 1). However, the
bulk of eggs were laid on spruce twigs at the depths
of 2-3 m and at temperatures between 13-19'C.
Salinity varied in spawning sites between 4.0-5.9 ppt.
Altogether pikeperch eggs were found on 12 nests
and on 6 nest rows (Figures 1 and 2). Spawning sites
were located in compact areas in different parts of the
study area and when eggs were found usually also the
neighboring nests were used. Only in one case
solitary nest was spawned. The spawning continued
through late June (Table 1).
Table 1. Date, water temperature, depth zone and
salinity when pikeperch eggs were found.
Date
28 May
1 June
14 June
14 June
14 June
15 June
22 June
n
Co
(A
a1)
c
0
L)
.0
E
z
Bottom
oc
6.2
13.6
20.9
20.7
21.2
18.9
19.1
19.1
Surface
oc
12.6
14.2
22.0
21.8
21.5
21.3
20.5
w~ ~ ~~2.  2-  5.1
Depth
zone m
4-6
2-3
1-2
2-3
2-3
1-2
2-3
Salinity
ppt
5.9
5.6
4.0
4.1
4.2
4.6
5.1
e)
0)
CT)
4 a)
3 3
.0
C
2 -
0
1 E
z
<1  1-1.9 2-2.9 3-3.9 4-4.9  5-6
Depth zone (m)
all nests      nests with eggs
0
0 1 2 3 4 5km
Figure 1. Location of nest sets. Sets with eggs are
marked with circles.
Figure 2. Depth distribution of all spawning nests
and the numbers of nests with pikeperch eggs.
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