With a view to the objectives of the work to be carried out by the consultant and outlined in detail in his terms of reference he attempted to seek as much information as possible to provide the factual basis for a) an understanding of catch declines and b) for the formulation of a programme of fisheries management which would increase lake fish production especially carp and eel species. Due to the extremely limited information about Lake Ioannina the work had to be started with a brief survey within the time and means provided. It is therefore clear that a survey as such permits only a limited evaluation e.g. of the size and composition of fish stocks and their response to fishing, technical alterations of the lake and related hydrological and ecological matters. It is, however, anticipated that for the present time and until trained Greek personnel may become available for more detailed research, the results of investigations obtained by the consultant would help to stipulate the ad hoc programme requested by the Greek Government for the improvement of eel and carp stocks in Lake Ioannina.
The Lake Ioannina (Pamvotis, Janina, Ioannina, Laspista name for the former northern part, which was drained as from 1958) covers 22 km2 and is thus the largest lake in the Epirus area (Fig. 1). The lake's level is almost 470 m above NH (wintertime) and drops to 469 during months of August to October. Maximum and average depths vary accordingly: 8 m (7 m) and 3 m (2 m), respectively. Length of shoreline (perimeter) is 21 km at midwater level. The lake whose maximum length and width are 8.5 and 3.5 km respectively, may be divided, for descriptive purposes, into the larger southern part and the smaller northern one which are divided by a “bottleneck” between the eastern part of Ioannina town and the lake's island (Fishermen's Island). It is said that both basins have never been completely separated from each other.
Prior to 1958, i.e. before reclamation work was begun, the northern part of the lake extended for about 12 km to NNW forming an additional lake area (called “Laspista”) whose length and width varied in accordance with the lake's level which in turn is governed by the amount of water it receives from springs situated within the now marginal area and from rivers which are formed during the wet season, springing on the SW slope of Mitsikèli Mountain, as well as by the topographical height of numerous sinkholes (“catavothres”). Hence it follows that the former extension of the lake almost exclusively corresponds with both the amount of water received and that drained through the sinkholes, (whose exact position is not known exactly) finally leading the water to the Kalamàs River entering the sea north of Igoumenitsa.
In the course of the reclamation work, which aimed at increasing the agricultural area, especially north of the Lake Ioannina, the former Laspitsa part was drained completely by means of a main drain. It receives the excess water of Lake Ioannina, the amount of which is controlled by a sluice gate constructed near the village of Perama. Both drain and excess water finally disappear at the village of Podoromi through an artificial subterraneous tunnel, and reappear after 4.2 km as a waterfall, the height of which is between 30 and 35 m. This forms a nameless tributary of the River Kalamas whose natural flow is interrupted by a newly established river dam near by Igoumenitsa, which serves the purpose of irrigation.
As a follow up result of the reclamation work at Ioannina the former lake Laspista disappeared. Its area was about 10 km2 (minimum surface during summer and autumn time) which would almost equal a third of the former total lake area or which would make up about a half of the total lake area at the present time.
There is no doubt that the stock of eels exploited prior to the reclamation work was derived from elvers which must have passed the numerous subterraneous water passages in order to reach the lake. The Greek Government Organization of Land and Water Use built during autumn 1973 a connexion between the main drain, just before it leads to the opening of the subterraneous tunnel and a nearby dried up sinkhole in order to feed the latter with drain and excess water. It was felt that this device would serve as a passage for elvers which may enter from the tributary formed by the above-mentioned lake and drain water. Unfortunately, there are no indications as to where the water from the sinkhole would eventually reappear, i.e. above or below the waterfall, this permitting elvers to pass.
The amount of water leaving the exit at Perama varies in accerdance with rainfall and springwater discharge. Thus the sluice gate is accordingly operated in order to maintain a constant water level. This was determined by the reclamation authority to dry up about 10 percent of the former Lake Ioannina, in addition to the complete drainage of the Laspista area. As another follow up result, a considerable part of the former marginal areas became dry and would no longer serve as spawning and nursing grounds, as in the Laspista area.
Nothing is known about the age of the lake. The consultant is inclined to believe that the lake is to be considered as an extremely recent one since the rate of endemism is outstandingly low, if not non-existent. The lake's location suggests that the present lake came into existence because a number of the sinkholes, which previously drained and collected rain and spring water between the Mitsikéli and Kassidiáris western and eastern slopes respectively, had been destroyed by earthquakes, common in the region. It is quite likely that the lake's extension could have varied considerably since it came into existence. It would therefore seem likely that the swamps near Parasalomos, about 80 km north of Ioannina and drained nowadays by numerous riverlets forming the Kalamàs River, might have formed a larger lake whose southern extension is surrounded by limestone mountain chains prevailing all over the drainage basin.
Light penetration is extremely restricted by suspended matter. Close to the centre of the lake visibility was about 1.5 m near the littoral belt less than one metre. The colour of the water changed from brownish-greyish in the open water area to greyish within the marginal area. No algae blooming was observed, but is reported by fishermen for the month of August.
The following hydro-chemistry data were obtained:
|Depth (m)||O2 (mg/litre)|
|0||6.9||(measured at 15.00)|
Temperature at varying depths:
|0||19.0||(measured at 15.00)|
Alkalinity (“SBV” acid binding capacity = 1/10 pHCl/l)
3.6 . 3.9 (mEg) 1/10 HCl
ph = 7.5
No liberation of biogenetic CaCO3 could be observed. Hence it follows that measured SBV and pH are both in equilibrium (i.e. no excess of free CO2).
In accordance with the extension of the floral associations occurring in the marginal area of Lake Ioannina about one tenth of its surface is occupied by a weed belt with the exception of the area bordering Ioannina. Main floral components are Phragmites, which form a dense belt of varying depths covering the littoral stretches along the NNE, SE and part of the SW shoreline, as well as almost the total shoreline of the island. Iris, Scirpus, Sagittaria, Hydrocharis, Potamogeton, Ranunculus, Ceratophyllum associations are scattered mainly beyond the Phragmites belt (and in between) towards the Carex zone which forms the transitional area to terrestric plant associations.
The fish occurring in the lake are either known as members of the Epirus and northwestern Greek region fauna or have been introduced by man within the last 40 years, i.e. carp and tench. Others, endemic already to the area were added, such as the Aristotelis catfish and others. (See Table 1). From the survey it would appear that in accordance with the food and feeding habits, all members of the occurring fish fauna should be classified as transitional types between plankton and bottom feeders. The food content in the digestive tract of all species observed contained plankton (zoo-and phytoplankton), bottom dwelling organisms, such as snails (shells) as well as epiphythes and plant mains.
With the exception of droumitsa, which prefers the cold springs for spawning, all other species are to be classified as warm water fish preferring the marginal weed belt for spawning purposes. For all species spawning would occur within the months May to June although, as happened during the present survey, spawning was delayed due to unfavourable weather conditions. With the exception of droumitsa, all other species belong to the ecological group of plant spawners, preferring the Carex zone, inundated during spring time. It is to be noted that in accordance with the water level fluctuations, a considerable part of the spawning area becomes dry after the end of May which would account for a serious annual loss of recruits. The water level fluctuation would, however, not seem to have the same effect upon droumitsa, which, as mentioned, spawns in the immediate neighbourhood of cold water springs. The preference for cold water environment appears to be rather unusual for a member of the northern cyprinids. It is only natural that the disappearance of the shallow Laspista part has considerably reduced the area of favourable spawning places for almost all the fish species thriving in the lake.
As a result of brief growth studies it was revealed that carp, tench and Barbus are extremely slow growing in Lake Ioannina, as is shown by the following total length figures (in cm):
|Age classes (years)|
Remarks It was at first thought that the ageing of carp was subjected to a misreading of growth rings on scales since carp would grow under similar ecological conditions much faster. However, the extremely clearly developed growth marks on tench scales supported to a good degree the above statement drawn up for carp.
It is to be understood that the figures included in the above table derived only from a very limited number of samples and would thus require a further detailed study of the growth pattern of fish from Lake Ioannina which may be initiated when trained local personnel is available.
In contrast to carp and eel, droumitsa seems to exhibit a much faster growth, reaching after one year a length of 14 cm, and 19 cm after the second year, respectively. This growth, compared with Rutilus growth in northern and middle European waters, is remarkably good and would thus suggest that this lake species is in much better ecological relation to its habitat than both the afore-mentioned oyprinids, carp and tench.
From the food composition (see also 2.2.4) it appears that the entire fish fauna competes with each other as far as food and feeding places are concerned. This feeding behaviour would account for the rather slow individual growth, with the exception of droumitsa. This species is known to be preying vigorously upon carp eggs as soon as they are laid down. The most thoroughly surveyed carp spawning places beyond the Phragmites belt, along the northern lake shore, revealed that only an extremely small number of eggs could be detected although spawning had recently been completed. The same losses occured in the spawning areas of Lake Ozeron, where spawning was observed, and whenever the eggs were shed they were promptly taken by an uncountable number of Droumitsa.
Due to the absence of piscivorous fish species in Lake Ioannina there is no ichthic food chain to be expected. The number of members of the different populations are thus exclusively controlled by fishing activities, rate of reproduction and recruitment and natural mortalities. Losses caused by diseases and/or parasites have not been observed during the survey, nor were they reported by fishermen.
The number of commercial fishermen reported varied from 102 (1951) and 75 (period 1967–72). Each fisherman (altogether forming the Fishermen's Cooperative Ioannina) owns a small wooden boat, made locally, powered by an outboard motor with either 3 to 4 or 6 hp. The gear consists of gillnets (varying mesh sizes, from 20 to 60 mm bar-mesh sizes), trammelnets (inner yarn with 40 to 60 mm bar-mesh sizes) altogether totalling a length of 2 000 m/fisherman. The depths of the nets are either 1.5 or 3.0 m. Besides, fyke nets and fence traps are used near the exit of the lake, which, however, would not appear to be too common, nor effective as could be seen from the catches. All species of the lake are commercially exploited and sold for human consumption with the exception of droumitsa, a species sold to nearby trout farmers as trout feed. The demand for the latter is steadily growing and would thus explain the increase in the catch, which substitutes to a certain extent carp production, although droumitsa prices are far below those of carp (see Tables 2 and 5). The average production per fisherman lies around 3 t annually.
There are no figures available as to the number of non-commercial fishermen, nor their total oatch/year. On the other hand, there are many local people seen fishing whose daily catch may be 0.5 kg fish per person, mainly small tenches. A rough estimate would point to 100 sport fishermen fishing at least 100 days per year. Their capture may be in the neighbourhood of 5 mt annually.
As is shown in Table 2, the total commercial catch per year varies around 300 t to which 5 t obtained by sport fishermen may be added. Hence it follows that the annual production of the lake expressed in terms of fish removed annually from an area of 1 ha is around 305 000 - 2 200 ha - almost 139 kg/ha. This figure is to be considered high for lakes in non tropical regions.
The fishing rights rest within the Greek Government, which rents the lake to the Fishermen's Cooperative at a fixed price for a five years period. The price is usually based upon 0.5 Drachmai 1 per kg of fish caught per year.
1 1 US$ = 30 Drachmai
Sport fishing so far is free of charge and anyone is permitted to fish.
With the exception of May, fishing is permitted the whole year round. Minimum sizes were established for tench and carp but apparently these regulations are not strictly enforced.