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Changes in the spawning ecology of the Lake Ohrid trout Salmo letnica (Karaman)
205Proceedings of the 2nd Congress of Ecologists of Macedonia
Introduction
The Lake Ohrid fish fauna is represented with 17
autochtonous species from four families: Salmonidae
(2), Cyprinidae (12), Cobitidae (2) and Anguillidae
(1). Among them the most important, as from scien-
tific point of view as well in whole, are the two, up to
know, distinguished endemic and relic trout: Salmo
letnica (Karaman) and Acantholingua ohridana
(Steind.) According some authors (Karaman 1924;
Stankovic 1960; Berg 1932) these species had inhab-
ited the lake soon after its formation.
The so-called Ohrid trout, Salmo letnica, from vari-
ous authors (Stefanovic 1948; Stankovic 1960; Di-
movski, Grupce and Spirkovski 1992; Spirkovski
CHANGES IN THE SPAWNING ECOLOGY OF THE LAKE OHRID
TROUT, Salmo letnica (Karaman)
Zoran SPIRKOVSKI
Hydrobiological Institute, 6000 Ohrid, Republic of Macedonia zoranspi@hio.edu.mk
Spirkovski Z. (2004). Changes in the spawning ecology of the Lake Ohrid trout, Salmo letnica (Karaman)Snow
boundary - theoretical aspects and reconstruction during the würm climate minimum in the southwest part of the
Republic of Macedonia. Proceedings of the 2nd Congress of Ecologists of the Republic of Macedonia with
International Participation, 25-29.10.2003, Ohrid. Special issues of Macedonian Ecological Society, Vol. 6, Skopje.
The investigations of the spawning of the Lake Ohrid trout, comprised from several subpopulations (forms) within
the same lake ecosystem, during the past already seven decades has been always one of the main subject in the
lymnological investigations of Lake Ohrid.
Unlike the usual population fluctuations within the dynamics of the ecosystem which were recorded during the first
5,5 decades (since 1934/35 year), in the last 1,5 decade and mainly in the last five years very significant and
unfamiliar changes were recorded for the process of the natural spawning of this trout.
Namely, changes were registered as in the composition of the spawning population as well in the abundance of
present spawning nests in all of the up to date natural spawning sites and grounds.
Due to this changes - which are mainly provoked by human activities like fishing, disruption of the spawning
grounds, over fishing, pollution etc. - the population recruitment was drastically affected by reducing the reproductive
capacity.
Key words:Lake Ohrid trout, spawning, recruitment, reproductive capacity
1991, 1992) has been considered like polymorph spe-
cies regarding the taxonomical and ecological fea-
tures. According the forth-mentioned authors four
forms of Ohrid trout can be distinguished with differ-
ent place, time and substrate for spawning (Tab. 1).
This species, in the conditions that are present in the
lake, reaches weight of 1 kg in the seventh year of its
life with an average total body length of 420-460 mm,
while the maturity among males occurs in the 4th year
and 5th for the females.
As it can be seen from the table this four forms (or
according different authors, subspecies or even spe-
cies Kottelat 1997) differ mostly in their spawning
ecology. But, as the Lake Ohrid trout is also the most
important fishing object, in order to maintain the nat-
Tab. 1. Spawning periods, substrate and regions of Lake Ohrid trout forms
Tab. 1. Periodi na mrestewe, substrati i regioni na formite od ohridskata pastrmka
Zoran SPIRKOVSKI
206 Zbornik na trudovi od 2-ot Kongres na ekolozite na Makedonija
ural population in the lake in optimal abundance,
and to allow fishing in the same time, in 1935 was
established the process of artificial spawning. Name-
ly, during the natural spawning period ripped par-
ents were fished and the striped eggs were fertilized
and further on incubated in the hatchery in the Hy-
drobiological Institute in Ohrid, from where after-
wards, depending on the region of collecting the eggs,
the offspring was released into the lake. This was
mainly done on the East coast of the lake and mainly
with the form S.l.typicus. Later on, this became prac-
tice also with the S.l.aestivalis form. In the early six-
ties of the last century, another hatchery was estab-
lished on the north part of the lake in order to per-
form the artificial spawning of another form
S.l.balcanicus. At the begining of this process pa-
rental individuals were mainly collected from the
River Crni Drim the outlet of Lake Ohrid. This proces
was never applied to S.l.lumi which was entering the
small tributaries for spawning, but usualy in the fish
catch it could be found in the lake.
But due to different factors affecting the trout popu-
lation as a whole in the lake, during the last two or
three decades, during the spawning season in the lake
could be distinguished for sure just two forms -
S.l.typicus and S.l.aestivalis due to their totally dif-
ferent time of spawning; in winter and in summer re-
spectively. S.l.lumi hasn't been reported in the catch
for years ago and for S.l.balcanicus evidences are
showing that this form has been absent also. It is worth
to mention here that, again, due to different factors,
the population of the so called “summer form”
S.l.aestivalis is diminishing. Having noticed these
changes in 1997 special notice was paid to this prob-
lem, which this paper more or less is dealing with.
Materials and methods
For the purpose of this survey, the spawning grounds
in the East region of Lake Ohrid (Fig. 1) during the
fishing period of the natural spawning of S.l.typicus,
which takes part from 21st January till 20th March
each year, were monitored. During this period the
whole fish caught from the commercial fishery were
counted with respect to their sex. The collected data
were grouped per existing landing sites: Ohrid, Pestani
and Trpejca in the direction North-South respective-
ly. For calculating the fishing effort data it was al-
ways taken into account the same number of fisher-
man and same number of equal fishing gear - gillnets
with mesh size 45 and 50 mm from knot to knot for
the period 1997, 2001-2003 year.
From other hand during the period 1997-2003, bio-
metric measurements (length, weight, sex and fish
scales for determining age) were performed on repre-
sentative and statistically significant fish samples. For
the purpose of this paper weight and age were not
considered.
Also, the collected eggs during the spawning period
per year were counted by volumetric method and in
Fig. 1: Part of the East coast of Lake Ohrid (Photo:
P.Boev)
Sl. 1: Del od isto~noto krajbre`ie na
Ohridskoto Ezero (Foto: P.Boev)
Tab. 2. Fishing effort during the spawning period of Lake Ohrid trout per landing site and total
Tab. 2. Ribolovni napregawa vo tekot na mrestitelniot period na ohridskata pastrmka
Changes in the spawning ecology of the Lake Ohrid trout Salmo letnica (Karaman)
207Proceedings of the 2nd Congress of Ecologists of Macedonia
this paper are presented only per year using longer
time scale period (1984/2003).
Results and discussion
When referring the data in Tab. 1, quite evident is
the decrease of number of the matured fish, present
on the spawning grounds as well the huge decre-
ment of the fish caught per day at the same sites
with the same gears and their same number. The most
significant is the comparison between the data from
1997 and 2003, where for the same total number of
fishing days for all landing sites is 48 days but with
drastic difference in the number of fish caught - 12686
in 1997 versus 2998 in 2003 when it represents only
1/4 of the one in 1997. This is strong argument for
the severe reduction of the trout population in the
lake itself, within just several years.
From other hand the data shown in Fig. 2 are ex-
Fig. 2: Changes of the relative length and sex composition of the spawning population of Lake Ohrid trout in
the professional catches for the period 1997 - 2003. In 1998 fishing during spawning period was banned.
Sl. 2: Promeni vo reltivniot dol`inski i polov sostav na mrestitelnata populacija na
ohridskata pastrmka vo profesionalnite lovini za periodot 1997-2003. Vo 1998 godina
ribolovot za vreme na mrestot ne be{e dozvolen.
Zoran SPIRKOVSKI
208 Zbornik na trudovi od 2-ot Kongres na ekolozite na Makedonija
pressing the population condition of the spawners.
Several moments can be considered from them. If
we consider the length and sex composition of the
spawning population in 1997 like the one that is the
closest to normal population distribution of the trout
in terms of catch able range (according the used fish-
ing gears - gill nets with mesh size 45 and 50 mm)
than in different years we have different situations
like: smaller number of length (age) classes, domi-
nancy of young (non matured) fish, dominancy of
males versus females, discontinuity in the presence
of subsequent length (age) classes. These moments
are clearly expressing another negative situation -
the disruption of condition of the Lake Ohrid trout
population as well.
Hence, we can withdraw two main conclusions that
the Lake Ohrid trout population is affected not only
by abundance reduction but also with disruption in
the population conditions in terms of self-recruitment.
This can be supported also by the data in Fig. 3, about
the number of collected eggs during the spawning
period. For better comparison for this purpose a larg-
er time scale period is given (1984-2003). The high-
est value of 20.5 millions eggs was obtained in 1991
when more than 37 tones of trout were caught during
the spawning period and the lowest 2.65 millions eggs
in 2003 when 3,3 tones of trout were caught. Both
values of the eggs and trout caught in the forth-men-
tioned years differ with ten times. These data once
again are expressing the worsened condition of Lake
Ohrid trout.
During the winter spawning period of trout 5-6 years
ago, there were clearly designated zones in the upper
littoral, at water depths from 0.5 – 3 m, where the
trout mated and spawned. In these areas, the trout nest
density was 5-8 per 10m2. Today, it is almost impos-
sible to find nests in the whole upper littoral; the trout
spawning that is occurring is happening at greater
depths.
Overfishing seems to be the major cause of the de-
cline of the trout population. Controls on the num-
ber and size of fish must be implement and coordi-
nated on both sides of the lake. Because the fish in
the lake are one single, linked population, they must
be managed collectively, with similar requirements
in both Macedonia and Albania. The socio-econom-
ic pressures that have led to overfishing have im-
pacted the trout more than other fish stocks because
of greater demand and higher economic value of this
fish. To manage this fishery appropriately in the fu-
ture, stock estimates based on independent sampling
should be performed. With this information a sus-
tainable level of harvest might be estimated.
Reference
Berg,L.S.1932: Ébersicht der Verbreitung der Süss-
wasserfishe Europas. Zoogeografica, 1: 107-208
Dimovski,A., Grupce,R. & Spirkovski,Z. 1992: Tax-
onomical investigations of Lake Ohrid trout. The
compilation of scientific works from the sympo-
sium in Ohrid “The conditions and the perspec-
tives for protection of the Lake Ohrid and its sur-
roundings” (In Macedonian with English abstract).
Karaman,S. 1924: Pisces Macedoniae. Split: 1-90
Kottelat, M. 1997: European freshwater fishes. Bio-
logia, Bratislava, 52/ Supplement 5: 1-271
Spirkovski,Z. 1991: The autochtonous salmonid fish
of Lake Ohrid. Macedonian Veterinary Revue,
Skopje, I/II: 61-66.
Spirkovski,Z. 1992: The condition of the population
Fig. 3. Number of collected and incubated eggs of Lake Ohrid trout in the hatchery of the Hydrobiological
Institute - Ohrid
Sl. 3. Broj na sobrana i inkubirana ikra od ohridskata pastrmka vo mrestili{nite instalacii
na Hidrobiolo{ki zavod - Ohrid
Changes in the spawning ecology of the Lake Ohrid trout Salmo letnica (Karaman)
209Proceedings of the 2nd Congress of Ecologists of Macedonia
of ohrid trout Salmo letnica (Karaman) in the
Lake Ohrid and its artificial stocking. The com-
pilation of scientific works from the symposium
in Ohrid “The conditions and the perspectives
for protection of the Lake Ohrid and its surround-
ings”: 94-100 (In Macedonian with English Ab-
stract)
CHANGES IN THE SPAWNING ECOLOGY OF THE LAKE OHRID TROUT, Salmo
letnica (Karaman)
Zoran SPIRKOVSKI
Hydrobiological Institute, 6000 Ohrid, Republic of Macedonia zoranspi@hio.edu.mk
Summary
The spawning population of Lake Ohrid trout, Salmo letnica (Karaman) in the last three years has tremendous
decrement (Tab. 1). Also the population structure has significantly been worsened - smaller number of length
(age) classes, dominancy of young (non matured) fish, dominancy of males versus females, discontinuity in the
presence of subsequent length (age) classes (Fig.2). All these conditions are also negatively expressed in the
amount of collected trout eggs for stocking the lake (Fig. 3).
Considerable changes have been evidenced in the spawning grounds. During the winter spawning period of trout
5-6 years ago, there were clearly designated zones in the upper littoral, at water depths from 0.5 – 3 m, where the
trout mated and spawned. In these areas, the trout nest density was 5-8 per 10m2. Today, it is almost impossible
to find nests in the whole upper littoral; the trout spawning that is occurring is happening at greater depths.
Overfishing seems to be the major cause of the decline of the trout population. Controls on the number and size
of fish must be implement and coordinated on both sides of the lake. Because the fish in the lake are one single,
linked population, they must be managed collectively, with similar requirements in both Macedonia and Alba-
nia.
Stankovic,S. 1960: The Balkan Lake Ohrid and its
living world. W.Junk, Den Haag, Monogr.biol.9,
pp 357
Stefanovic,D. 1948: Race and ecological investiga-
tions on Ohrid salmonids. SAN, Beograd, Poseb-
na izdanja 139/38: 1-207 (In Serbian)
