PRIMARY RESEARCH PAPER

Distribution of egg strands of perch (Perca fluviatilis L.)with respect to depth and spawning substrate

Martin Cech Æ Jirı Peterka Æ Milan Rıha ÆTomas Juza Æ Jan Kubecka

Received: 8 December 2008 / Revised: 5 April 2009 / Accepted: 6 April 2009 / Published online: 3 May 2009

� Springer Science+Business Media B.V. 2009

Abstract The distribution of egg strands of perch

Perca fluviatilis was studied in relation to water

depth and spawning substrate during late April and

early May 2007 in Chabarovice Lake, Czech Repub-

lic, using SCUBA divers and parallel transects. The

depth distribution of egg strands differed significantly

between the two sampling dates, being much deeper

in early May compared to late April. Perch used at

least seven different spawning substrates of which the

most important were curly pondweed Potamog-

eton crispus, worm weed Artemisia sp. and common

reed Phragmites communis. However, while living

submerged vegetation, although more abundant, was

generally avoided, dead submerged vegetation was

strongly preferred. It appears that dead vegetation is

an ideal spawning substrate for perch since placement

of the egg strands over those hard, complex three-

dimensional structures ensures that the eggs remain

well oxygenated 24 hours a day. Factors with

significant influence on the distribution of egg strands

were as follows (in order of decreasing influence):

depth of deposition, type of spawning substrate, date

of spawning and temperature at the depth of

deposition.

Keywords Chabarovice Lake � SCUBA diving �Aquatic vegetation � Curly pondweed

Potamogeton crispus � Common reed Phragmites

communis � Eurasian water milfoil Myriophyllum

spicatum

Introduction

European perch Perca fluviatilis L. is often assumed

to spawn in the shallow water of rivers, lakes and

reservoirs, where the majority of gelatinous egg

strands are deposited to a maximum depth of 2 m

(Holcık, 1965; Frank, 1967; Stehlık, 1969; Viljanen

& Holopainen, 1982; Treasurer, 1983; Urho, 1996;

Smith et al., 2001). Lang (1987), however, reported

perch spawning at 3–5 m and Craig (1987) from 0.5

up to a depth of 8 m. The results of Kubecka (1992)

have suggested that during the spawning period,

warming of surface water could shift the depth of

peak spawning activity from shallower towards the

deeper layers, so that at the end of a prolonged

spawning period, the peak activity could be found in

a depth of 6–9 m. Similar results were found by

Gillet & Dubois (1995, 2007).

Perch spawn over a wide range of substrates

including sand, boulders and gravels, submerged or

emergent aquatic vegetation, roots and stumps of

Handling editor: J. A. Cambray

M. Cech (&) � J. Peterka � M. Rıha � T. Juza �J. Kubecka

Biology Centre, Academy of Sciences of the Czech

Republic, Institute of Hydrobiology, Na Sadkach 7, 370

05 Ceske Budejovice, Czech Republic

e-mail: carcharhinusleucas@yahoo.com

123

Hydrobiologia (2009) 630:105–114

DOI 10.1007/s10750-009-9783-z

trees, dead branches dipping into the water, dislodged

trees lying on the bottom and other materials (e.g.

Zhakov, 1964; Frank, 1967; Pivnicka, 1979; Viljanen

& Holopainen, 1982; Treasurer, 1983; Craig, 1987;

Lang, 1987; Urho, 1996; Pedicillo et al., 2008).

Although the preference for submerged vegetation

sensus lato as a spawning substrate seems to be obvious

in perch, most studies do not provide any evaluation of

this preference (Frank, 1967; Holcık, 1969; Craig,

1987; Gillet & Dubois, 1995; Urho, 1996).

The present study focussed on the distribution of

egg strands of perch with respect to depth and

spawning substrate in a relatively deep lake, charac-

terized by large stands of submerged vegetation (both

dead and alive), i.e. the study area represents a water

body with no limitations to perch spawning activity

concerning depth and spawning substrate.

The main questions were (1) whether perch really

prefer spawning in very shallow areas up to a depth

of 2 m or whether the depth of spawning is more

likely controlled by the presence of appropriate

spawning substrate, or by the optimal temperature

for egg development and (2) whether perch use all

available spawning substrates (all types of submerged

vegetation in particular), in proportion to those

available in the lake, for deposition of their egg

strands. Thus, the main aim of this study was to find

and evaluate factors influencing the deposition of egg

strands in the system without any obvious limitation

to perch spawning and to provide recommendations

for management.

The study is part of a long-term project focussing

on succession processes in a restored opencast mine

lake where aquatic restoration has been applied.

Materials and methods

Study area

The study was carried out in the oligo- to mesotro-

phic Chabarovice Lake, Czech Republic (80 km

north-west of Prague), which has an area of ca.

200 ha, volume of 18 9 106 m3 and maximum depth

of 20 m (Fig. 1a). Secchi depth exceeded 7 m for

most of the year.

Chabarovice Lake is a newly restored, opencast

mine lake where aquatic restoration started in 2001.

The lake contains large stands of submerged

vegetation composed of curly pondweed Potamog-

eton crispus, Eurasian water milfoil Myriophyl-

lum spicatum, common stonewort Chara vulgaris

and Canadian waterweed Elodea canadensis. Due to

the seasonal succession of vegetation, the last two

species are much more abundant mainly later in the

year (July–October; J. Peterka, M. Rıha, M. Cech,

unpublished data).

During the filling of the lake, young trees and their

dislodged branches, bushes (especially black elder

Sambucus nigra), beds of common reed Phrag-

mites communis, worm weed Artemisia sp. and

common rush Juncus effusus became submerged in

large numbers (J. Peterka, M. Rıha, M. Cech, unpubl.

data). Today they have created a unique habitat of

dead vegetation with complex three-dimensional

structures (Fig. 1b).

The ichthyofauna of the lake consists of 12 fish

species, but only rudd Scardinius erythrophthalmus

(L.) (58% in abundance of fish [ 0?), perch

Perca fluviatilis L. (25%) and roach Rutilus rutilus

(L.) (14%) reach ecologically significant levels

(Kubecka et al., 2007). Despite the extensive stocking

programme focussing on larger individuals of pike

Esox lucius L., zander Sander lucioperca (L.) and

wels catfish Silurus glanis L. (since 2005; for

biomanipulation purposes), perch is still the most

abundant predatory fish in the lake, with a unimodal

cohort of older fish of standard lengths of 240–

340 mm (Kubecka et al., 2007; Fig. 2).

Sampling

Three SCUBA divers monitored the depth distribution

of egg strands and spawning substrates of perch in

depth layers of 2–4, 4–6 and 6–8 m during 24–26 April

and 2–3 May 2007. On the same dates, additional dives

were made to depths [8 m (Fig. 1c, d). The divers

swam parallel to each other at minimum horizontal

distances of 5 m apart, each sampling the space of 3 m

to each side of him. Simultaneously to this SCUBA

research, the whole littoral zone of the lake (depth layer

0–2 m) was sampled visually from the boat using

polarized glasses.

During the first sampling survey, the divers

recorded the type of substrate on which individual

egg strands were deposited, the depth of their

deposition, the sizes of the egg strands (length, width;

using ruler, for which the egg strands were unravelled

106 Hydrobiologia (2009) 630:105–114

123

Fig. 1 A map of Chabarovice Lake and its location in the Czech

Republic. a Contour map of the lake. Numbers indicate bottom

altitude in metres above sea level. Black dot indicates the place

where temperature and dissolved oxygen were measured in the

whole water column on 24 April and 3 May. Black triangles

indicate locations where surface water temperature was mea-

sured daily from 15 March. b Schematic distribution of potential/

main spawning substrates for perch in spring 2007. For a better

view, the proportion of individual types of submerged vegetation

is enhanced two times compared to the real situation (cf.

Table 1). c, d Schematic distributions of individual diving

localities where three divers simultaneously monitored egg

strands and spawning substrates of perch in parallel swimming

trajectories. c 23–26 April 2007 (starting with a night dive on 23

April). d 2–3 May 2007. Grey areas indicate daytime diving

localities for counting of perch egg strands; black areas indicate

night diving localities for monitoring of the proportion of still

unspawned perch females in the population. Numbers indicate

dive order

Hydrobiologia (2009) 630:105–114 107

123

carefully, measured and then fixed again on the

spawning substrate) and whether eyed eggs were

visible (developmental stage VI according to Guma’a,

1978). Above-mentioned information was noted

underwater on a plastic slate for each individual egg

strand. On each consecutive dive (mean duration ± SD

72 ± 11 min; mean length ± SD 850 ± 317 m),

individual divers regularly changed the depth layer

that they were monitoring in order to randomize

sampling error and to avoid decompression sickness.

The sizes of the egg strands were relatively

uniform (mean length ± SD 133.8 ± 44.5 cm; mean

width ± SD 7.7 ± 2.6 cm) and did not differ

between individual depth layers (F4, 261 = 1.35,

P = 0.25). The sizes of the spawning perch female

reconstructed from the width of individual egg

strands using the equation of Dubois et al. (1996)

revealed that a unimodal cohort of larger females was

significant participant in the spawning (Fig. 2). This

finding differed from the earlier study of Gillet &

Dubois (2007) from Lake Geneva in which larger

females spawned later in the season than their smaller

conspecifics. For that reason, the demanding moni-

toring of egg strand size was omitted during the

second sampling survey in order to save time while

extending the sampling area.

Substrate surveys using SCUBA divers were

carried out in Chabarovice Lake in September 2006

(J. Peterka & M. Rıha, unpubl. data) and in April and

May 2007 (this study). Former maps of the open cast

mine Chabarovice just before filling were used to

locate dead vegetation, especially in deeper parts of

the lake. For the purpose of the present study, the

categories of recorded perch spawning substrate were

chosen as follow: (i) curly pondweed, (ii) worm

weed, (iii) common reed, (iv) common rush and other

‘‘soft weeds’’, (v) Eurasian water milfoil, (vi) trees

and branches including black elder, (vii) common

stonewort, (viii) bare bottom especially mud and (ix)

others (Fig. 3).

In addition to the daytime dives, night dives on 23

and 25 April and 2 May were focussed on searching

for pregnant perch female (unspawned fish with

extreme bulging of the belly), to be sure whether the

main spawning period was still in progress or had

already ended (Fig. 1c, d).

Temperature and dissolved oxygen in the whole

water column were measured using a calibrated YSI

556 MPS probe on 24 April and 3 May (midday).

Surface water temperature was measured daily

(morning) from 15 March at three separate locations

around the lake shore (Fig. 1a) in order to catch the

beginning of the perch spawning period at 8–10�C

(Kubecka, 1992).

The data were tested using one-way ANOVA for

unequal n (size of egg strands in individual depth

0

10

20

30

40

50

60

180

195

210

225

240

255

270

285

300

315

330

345

360

375

390

405

Standard length (mm)

No

. of

ind

ivid

ual

s

egg strands (2007); n=266

gillnets (2006); n=325

0

100

200

300

5 50 95 140

185

230

275

320

365

0+

1+ 2+ ≥3+

n=1889

Fig. 2 Comparison of the length-frequency distribution of

perch older than 1? caught in the gillnets during the complex

fish stock assessment of Chabarovice Lake in early September

2006 (Kubecka et al., 2007) and the reconstructed size of

spawned perch females during the first sampling survey (late

April 2007) calculated from the width of egg strands using the

equation of Dubois et al. (1996). The small graph shows the

size and age structure of the whole 2006 population of perch in

the lake (Kubecka et al., 2007). Axes titles are the same as in

the main graph

108 Hydrobiologia (2009) 630:105–114

123

layers—see above; period-related depth distribution of

egg strands), v2-test (spawning substrate preferences)

and multi-factorial ANOVA (factors influencing the

distribution of egg strands). The depth of egg strand

deposition, temperature at the depth of deposition, type

of spawning substrate and date of sampling were

entered into the multi-factorial ANOVA as predicted

variables. Since not all types of spawning substrate

were present at all depths (Fig. 1), the basic categori-

zation was as follows: ‘‘bare’’—bare bottom especially

mud, ‘‘dead structures’’—all types of dead submerged

vegetations, ‘‘living structures’’—all types of live

submerged vegetations. Using this simple categoriza-

tion, those three basic spawning substrates were

present in all the depth layers sampled (0–2, 2–4,

4–6, 6–8, 8–10 and[10 m).

Fig. 3 Examples of typical

spawning substrates of

perch in Chabarovice Lake

in spring 2007. a Common

reed at a depth of 1–2 m

(live plants, not shown) and

at a depth of 2–5 m and 7–

10 m (dead plants). b Black

elder mostly at a depth of 7–

8 m and [15 m. c Worm

weed at a depth of 2–5, 6–9

and [12 m. d Curly

pondweed at a depth of 2–

8 m. e Eurasian water

milfoil at a depth of 3–7 m.

f Common rush at a depth

of 1–5 m and 7–10 m. gDead trees and branches

mostly at a depth of 7–9 m

and [15 m. a, b, c, f and gare dead plants, bushes and

trees drowned during the

filling of the lake. Actual

depth of each finding is

stated in the photograph

Hydrobiologia (2009) 630:105–114 109

123

Results

During two sampling surveys of the lake, 14 dives

were carried out (3 night dives, 11 day dives,

comprising 50 h underwater) during which 896 indi-

vidual egg strands of perch were found (n24–26 April =

266; n2–3 May = 630). Night dives revealed that

during the first survey a significant proportion of the

females had not spawned (nobserved adult perch = 153;

nobserved pregnant female = 27). No egg strands were

found to be close to hatching, i.e. in an eyed eggs

stage. Throughout the daylight hours, males were

frequently ‘guarding’ the spawning substrate. They

were waiting for females in between stalks and

branches or they were slowly cruising in close

proximity to those structures. In contrast to females

occurring in shoals in deeper open water, males

showed very poor avoidance reaction and occasion-

ally attempted to approach the SCUBA diver.

During the second survey, night observations of resting

fish revealed that all females had spawned their eggs

(nobserved adult perch = 88; nobserved pregnant female = 0).

No males were observed ‘guarding’ the spawning

substrate at any depth. At that time, many egg strands

were close to hatching or in the process of hatching

(embryos leaving the egg envelope). In the depth

layers of 2–4 and 4–6 m, egg strands of 76.5% and

82.3%, respectively, were in the eyed eggs stage (at

least); however, in the 6–8 m depth layer it was only

3.9%, whereas in the depth [8 m, it was 0%.

The depth distributions of egg strands differed

significantly between the two sampling dates (F1,

894 = 31.09, P \ 0.001; Fig. 4), being much deeper

in early May compared to late April. On the same

dates, continuous warming of the upper layers of the

water column was recorded (temperature increase of

[1.5�C in the 2–4 m depth layer and [1.9�C in the

4–6 m layer from late April to early May sampling;

Fig. 5). However, on both dates egg strands were

found at up to 16.6 m deep (2 records in late April

and 20 records in early May below 15 m). In late

April, the peak of perch spawning activity was in the

2–4 m depth layer, however, less than 2 weeks later

the peak was at 6–8 m. Only during the first sampling

survey, four egg strands were found in the 0–2 m

layer (Fig. 4), but even at this time no egg strands

were found in water shallower than 1 m.

Perch used at least seven different spawning

substrates in the lake, mostly dead or live plants,

branches and dead trees. The most frequently used

were curly pondweed, worm weed and common reed

(85.7% of egg strands during the first survey and

71.0% of egg strands during the second survey were

deposited on those substrates; Fig. 6). Clearly, perch

did not use all the available spawning substrates

(basic tested category: bare bottom vs. submerged

vegetation) in proportion to their presence in the lake

(v224�26April

¼ 1341:60; d.f. = 1, P \ 0.001 and

v22�3May

¼ 3460:20; d.f. = 1, P \ 0.001). According

to the value of the Ivlev index, perch strongly opted

for submerged vegetation (Table 1). Moreover, in

both sampling surveys, a significant difference was

also found in their preference for different types of

submerged vegetation (v224�26April

¼ 595:60; d.f. = 6,

0 50 100 150 200 250 300 350

0-2

2-4

4-6

6-8

8-10

>10

Dep

th (

m)

No. of egg strands

24 – 26 April (n=266)

2 – 3 May (n=630)

Fig. 4 Depth distributions of egg strands of perch in

Chabarovice Lake in spring 2007 during 24–26 April (mean

depth 5.3 m) and 2–3 May (mean depth 6.3 m)

5 10 15 20

T (°C) O2 (mg l-1)

0

2.5

5

7.5

10

12.5

15

5 10 15 20

T (°C) O2 (mg l-1)

Dep

th (

m)

T (°C)O2 (mg l-1)

(a) (b)

Fig. 5 Comparison of the vertical profiles of temperature and

dissolved oxygen measured at noon on a 24 April and b 3 May

2007 in Chabarovice Lake. Grey bars indicate the depth layer

where most egg strands occurred during the first (24–26 April)

and the second (2–3 May) sampling surveys

110 Hydrobiologia (2009) 630:105–114

123

P \ 0.001 and v22�3 May

¼ 1141:50; d.f. = 6, P \0.001). While live submerged vegetation (curly

pondweed, Eurasian water milfoil and common

stonewort) was generally avoided, despite comprising

74.3% of all the submerged vegetation, dead

submerged vegetation was highly preferred (except

of common rush and other ‘‘soft weeds’’ which were

used in accordance with their occurrence and except

for trees and branches, including black elder, which

were mostly too deep to be chosen as a spawning

substrate during the first sampling survey). In late

April, the most preferred substrate for egg strand

deposition was worm weed followed by common

reed, while in early May the most preferred was

common reed, followed by trees and branches,

including black elder and worm weed (Table 1).

A multi-factorial ANOVA revealed that the dis-

tribution of egg strands of perch was highly influ-

enced by all the factors—the depth of deposition,

temperature at the depth of deposition, type of

spawning substrate and date of sampling—used as

predicted variables. The most important factor was

the depth of deposition (F5, 504 = 8.08, P \ 0.001),

followed by the type of spawning substrate (F2,

504 = 13.60, P \ 0.001), date of spawning (F1,

504 = 22.95, P \ 0.001) and temperature at the depth

of deposition (F6, 504 = 3.63, P \ 0.01).

Fig. 6 The composition of spawning substrate for perch in

Chabarovice Lake in spring 2007 during the first days of

spawning and at the end of spawning when most of the

spawning events occurred in deeper parts of the lake (cf.

Fig. 4). � Indicates dead plants, bushes or trees (cf. Fig. 3).

‘‘Others’’ category includes: emergent vegetation, technical

carpet and fence wire-cloth

Table 1 Ground coverage of potential/main perch spawning substrates in Chabarovice Lake in spring 2007 and the Ivlev electivity

index for those substrates during the first days of perch spawning (24–26 April) and at the end of spawning (2–3 May)

Spawning substrate Ground

coverage (%)

Share in submerged

vegetation (%)

Ivlev electivity indexa

April May

Bare bottom, especially mud 85 -0.91 -0.97

Submerged vegetation (dead or alive) 15 0.73 0.74

Curly pondweed 65.3 -0.28 -0.47

Worm weedb 5.1 0.75 0.54

Common reedb 5.7 0.42 0.69

Common rush and other ‘‘soft weeds’’b 6.7 -0.06 0.22

Eurasian water milfoil 5.5 -0.57 -0.59

Trees and branches including black elderb 8.2 -0.67 0.58

Common stonewort 3.5 -0.79 -1.00

Note that at the beginning of perch spawning period (late April) ‘trees and branches including black elder’ were mostly too deep

(C7 m) to be chosen as a spawning substrate, since the majority of perch spawning activity took place in the 2–4 m and 4–6 m depth

layers (cf. Figs. 3 and 4)

Bold numbers indicate significant positive or negative electivity for individual spawning substratesa According to Ivlev (1961)Ei defined as: Ei = (ri - ni)/(ri ? ni), where i is a type of spawning substrate, r is share (%) of substrate

in the total amount of used spawning substrates and n is share (%) of substrate in the lake (for individual types of submerged

vegetation it is share of substrate in the total amount of submerged vegetation). Values close to -1 indicate strong avoidance of

spawning substrate and values close to ?1 indicate strong preference of spawning substrate. Values higher than -0.3 and lower than

0.3 are regarded not to be significantly different from 0b Dead plants, bushes or trees (cf. Fig. 3)

Hydrobiologia (2009) 630:105–114 111

123

Discussion

According to the Czech Hydrometeorological Insti-

tute (unpubl. data), winter 2006/2007 was the warm-

est winter since 1922. For that reason, routine

SCUBA diving for monitoring of perch spawning

activity started in Chabarovice Lake very early, on 19

March with further attempts on 15 and 22 April. Up

to the latest of these dates, no egg strands were

observed.

The first bright white egg strands were recorded

during the night dive on 23rd April. The same night

diving, as well as night diving on 25th April, revealed

that a significant proportion of the perch females

remained unspawned. Hence, the first sampling

survey (24–26 April) could be considered as the

beginning of the perch spawning period (Craig,

1987).

Unusually, warm weather for the next 2 weeks

caused shortening of the spawning period (Gillet &

Dubois, 1995), since all the perch females recorded

during the night dive on 2nd May had already

released their eggs. Many egg strands, especially in

shallower depth layers (depth 2–6 m), were close to

hatching or in the middle of hatching. The difference

of 10–11 days corresponds well to the period of time

required for perch embryo development at tempera-

tures between 13 and 15�C (Guma’a, 1978). That was

why the second sampling survey (2–3 May) could be

referred to as the end of the main perch spawning

period.

During both sampling surveys, all but four egg

strands were found deeper than 2 m, which is in sharp

contrast to previous studies from various lakes and

reservoirs (Holcık, 1965; Frank, 1967; Stehlık, 1969;

Viljanen & Holopainen, 1982; Treasurer, 1983; Urho,

1996; Smith et al., 2001) but corresponds with the

findings of Lang (1987) and Gillet & Dubois (1995,

2007) from Lake Geneva, on the Swiss–French

border and with the findings of Probst et al. (2009)

from Lake Constance, on the Swiss–Austrian–Ger-

man border. The avoidance of the 0–2 m depth layer

as a spawning habitat is surprising since boulders,

beds of live common reed, bundles of common rush

and other ‘‘soft weeds,’’ while not as abundant as in

deeper layers (except of boulders), are generally

considered to be a suitable spawning substrate for

perch (Treasurer, 1983; Lang, 1987; Urho, 1996;

Smith et al., 2001).

It is most likely that, in Chabarovice Lake, the perch

avoided the shallowest littoral habitats due to relatively

high temperatures ([14�C), which may cause a

significant increase in egg mortality (Guma’a, 1978;

Sandstrom et al., 1997) and/or due to the supposed

damaging effect of waves (Probst et al., 2009).

Chabarovice is an opencast mine lake and the whole

surrounding landscape is deforested which makes the

lake vulnerable to winds from all directions. It has

already been described that strong winds provide a

potential mechanism for blowing perch egg strands

ashore (Clady & Hutchinson, 1975; Jones, 1982).

Similarly, there is evidence that ultraviolet radia-

tion can lead to a high mortality rate of perch eggs

incubated in the surface waters of lakes with low-

dissolved organic carbon (DOC) levels (Williamson

et al., 1997). Huff et al. (2004) have shown that 92%

of the eggs spawned in a low-DOC lake were located

at depths greater than 3 m, while 76% of eggs in the

higher-DOC lake were spawned in water less than

1 m deep. Unfortunately, the values of DOC were not

measured during the current study but during the first

sampling survey 87.2% of egg strands were deposited

at depths greater than 3 m and during the second

sampling survey this portion increased to 96.7%.

In Lake Geneva, perch have been reported to spawn

on both natural and artificial spawning substrate to a

maximum depth of 12–15 m (Gillet & Dubois, 1995;

Dubois et al., 1996; Gillet & Dubois, 2007). In

Lochaber Lake, Nova Scotia, females of the closely

related yellow perch Perca flavescens (Mitchill)

deposited their egg strands to a maximum depth of

12 m (Alto & Newsome, 1989). Similarly in Lake

Giles, Pennsylvania, spawned egg strands of yellow

perch were sporadically observed up to a depth of 15 m

(Huff et al., 2004). In the case of Chabarovice Lake,

however, egg strands were found up to a depth of

16.6 m during both sampling surveys. It seems that, at

least to this depth, their deposition and further devel-

opment was not limited by temperature (ca. 8.5�C),

dissolved oxygen (ca. 8.5 mg l-1) or suitable spawn-

ing substrate (worm weed, trees and branches includ-

ing black elder).

Previous studies from Rımov Reservoir and Lake

Geneva have shown that during the spawning period

warming of surface water could shift the depth of

perch spawning activity from shallower (depth 0–

4 m) towards deeper (depth 6–12 m) layers

(Kubecka, 1992; Gillet & Dubois, 1995, 2007), and

112 Hydrobiologia (2009) 630:105–114

123

these results are well supported by the data from

Chabarovice Lake. At the beginning of the spawning

period, the peak of perch spawning activity was

observed in the depth layer 2–4 m, however, less than

2 weeks later the peak of spawning activity was

observed in the deeper layer at 6–8 m.

The present study has shown that for egg strand

deposition perch do not use all the available spawn-

ing substrates in proportion to which they are present

in the lake. This is in agreement with previous studies

where perch generally preferred submerged vegeta-

tion and avoided bare bottom (e.g. Frank, 1967;

Holcık, 1969; Treasurer, 1983; Craig, 1987; Gillet &

Dubois, 1995; Urho, 1996; Nash et al., 1999; Smith

et al., 2001). Egg strands deposited directly on the

lake bottom may risk being smothered by silt or have

increased exposure to microorganisms (Smith et al.,

2001). They may also suffer from low levels of

dissolved oxygen, which is an important hazard for

developing embryos (Wootton, 1998).

The study of Chabarovice Lake, however, also

shows a significant difference in preference for

different types of submerged vegetation. While live

submerged vegetation (usually quite dense), although

more abundant, is generally avoided, dead submerged

vegetation (usually sparse) is highly preferred.

Perch egg strands deter predators (Newsome &

Tompkins, 1985); hence there is no apparent need to

hide them in dense vegetation. Moreover, dense, live

vegetation could deplete a reasonable amount of

oxygen from the surrounding water due to intensive

night respiration (Taiz & Zeiger, 2006). Since night

oxygen depletion, in the case of sparse dead

submerged vegetation (including periphyton), is of

much lower extent it seems reasonable that this type

of spawning substrate is highly preferred by perch.

The only exception is bundles of common rush and

other ‘‘soft weeds.’’ Due to its limited growth above

the bottom contour, this spawning substrate is

qualitatively somewhere between large, dead sub-

merged vegetation (common reed, worm weed, trees

and branches including black elder) and bare bottom.

Common reed, worm weed, trees and branches,

including black elder, are undoubtedly an ideal

spawning substrate for perch since placement of the

egg strands over those large dead structures, extend-

ing into the open water column, ensures that eggs

remain well oxygenated 24 hours a day (Reyes et al.,

1992). This finding is consistent with the results of

Nash et al. (1999) who used artificial spawning

substrates in Manchester Docks, UK, where perch

preferred branches of spruce Pilea abies, sycamore

Acer pseudoplatanus and willow Salix alba. It also

appears that hard, three-dimensional structures like

branches of spruce, sycamore and willow (Nash et al.,

1999) or stems of dead common reed, worm weed,

dislodged trees, bushes and their branches in general

(this study) are more appropriate substrates for egg

strand deposition by perch than the soft stems of any

live submerged vegetation.

Conclusion

The present study has shown that even in the system

without any ‘obvious limitation to perch spawning’

there are always some limitations. Perch did not use

for egg strands deposition shallowest littoral habitat

(high temperature causing increase of egg mortality,

damaging effect of waves) and when possible avoided

live submerged vegetation. Factors with significant

influence on the distribution of egg strands were as

follows (in order of decreasing influence): depth of

deposition, type of spawning substrate, date of

spawning and temperature at the depth of deposition.

In Chabarovice Lake, the most important substrates

for perch spawning—beds of dead common reed and

worm weed—reveal signs of progressive degradation

and this substrate will disappear from the lake within

several years. The spawning activity of perch in

shallower water (up to a depth of 7 m) will then have

to be concentrated almost exclusively on stands of live

vegetation whose presence in the lake is, however, less

predictable in time and depends on the weather

conditions during the year and the system of lake

filling. Moreover, the results have shown that live

vegetation is not much suitable spawning substrate for

perch. For that reason, installation of an artificial

spawning substrate (Gillet & Dubois, 1995; Dubois

et al., 1996; Nash et al., 1999; Pedicillo et al., 2008;

Probst et al., 2009) would, in the near future, be an

important means of both sustaining the stock of perch,

the main predatory fish in the lake, and for overall

management of the lake’s ichthyofauna.

Acknowledgements The authors thank B. Tlougan and M.

Burgis for careful reading and correcting the English and W.N.

Probst and one anonymous referee for valuable comments on

an earlier version of this manuscript. The study was supported

Hydrobiologia (2009) 630:105–114 113

123

by the Grant Agency of the Czech Republic (projects No. 206/

06/1371 and 206/09/P266), the Grant Agency of the Czech

Academy of Sciences (project No. 1QS600170504) and the

Palivovy kombinat Ustı nad Labem s.p.

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