Since mid 1990s the Kinneret ecosystem has undergone limnological structure modifications [1] -[7] . The crucial change was the decline of Nitrogen accompanied by a slight increase of Phosphorus concentrations in the epilimnion. Ensuing lowering of the epilimnetic TN/TP mass ratio was resulted in. The newly developed nutrients ratio created a change of the trophic status from P to N limitation. Under N limitation the contribution of recycled P by zooplankton might enhance phytoplankton growth [4] [7] [8] . The practical implication of that is a threat on water quality, resulted by Cyanobacteria blooms increase. The decline of N was recorded in the epilimnion of Lake Kinneret as early as mid 1980s. Before mid 1980’s the availability of N was sufficient, and P was limited. A slight Increase of P together with N decline created N limitation for Peridinium growth but it is optimal for Cyanobacteria [1] [4] [8] and also for diatoms and chlorophytes. As a consequence Peridinium declined and other algae (Cyanophyta, Bacillariophyta, Chlorophyta) were enhanced. The decline of water level which caused a decrease of the thermocline depth, is attributed to the higher frequency of droughts, which reduced input of both water and nutrients (mainly Nitrogen). In addition, sewage effluents were treated and reused. The result was divertion of Nitrogen from the lake. Moreover, the frequency of dust storms in the Hula Valley was reduced and fishponds area was restricted from 1700 to 350 ha. All these anthropogenic activities caused a reduction of external N flux into Lake Kinneret. Due to the N limitation, and the Peridinium decline [1] [4] [8] , the nano-phytoplankton, dominated by Cyanobacteria, especially Microcystis spp. occupied the free (no Peridinium) niche. These changes initiated modifications of food resources and feeding habits of fish. Peridinium gatunenze was the major food component of the most valued native fish, Sarotherodon galilaeus, in the lake [1] [5] -[7] . It is likely that in the present conditions the impact of recycled P by zooplankton may not be negligible [8] . Zooplankton is the major food constituent of the food of the endemic Cyprinid, Bleaks [5] -[7] . For the improvement of water quality in Lake Kinneret the maintenance of high grazing pressure by zooplankton on nano-phytoplnkton is advisable. Therefore, partial removal of (unwanted) bleaks by fishery management and introduction of the exotic Silver Carp (Hyphophthalmichthis molitrix), an efficient consumer of Microcystis, will be beneficial. A cardinal question is therefore raised: If intensification of zooplankton predation is not advisable and Bleaks are not commercially deserved, and if the market demands of S. galilaeus, which is presently consume zooplankton, are the highest, who is more appropriate component as consumer of zooplankton? Bleaks or S. galilaeus.

If fishing would be ceased-proliferated bleaks would be resulted and suppression of S. galilaeus is therefore predicted.

When algal photosynthetic activity is carried out under N limitation their nutrition value is lower, and therefore limits zooplankton growth [9] . Zooplankton is also important in lakes because their excretions contributes inorganic N and P for phytoplankton and bacterial production. Urabe [10] demonstrated regeneration of N and P by zooplankton and their subsequent utilization by phytoplankton. Zooplankton biomass in Lake Kinneret declined from 1970 until early 1990s but increased afterwards. Both, biomass and size frequency of cladocerans were affected by fish predation [5] . It is likely that elevation of zooplankton biomass contributes to suppression of nano-phytoplankton biomass whilst P regenerated by zooplankton will improve their growth. There are two contradicted processes: fish (mostly Bleaks) zooplanktivory effect which reduce pressure from nano-phytop- lankton and P regeneration by zooplankton which enhance algal growth. The control of nano-phytoplankton is aimed at ensuring water quality and can be achieved by Bleaks removal. The recovery of S. galilaeus population together with renewal of Bleak fishing will probably release zooplankton sources to S. galilaeus and enhance reduction of zooplankton predation pressure. The combined manipulation of recovered S. galilaeus, and low Bleaks biomass (by fishing) is an advantage for zooplankton increase. High zooplankton is optimal for S. galilaeus recovery, fishermen income and ensure water quality. The implications for lake management are as follows.

The changes of the phytoplankton community structure affected both water quality and the pattern of energy flow through the food web channels. Presently, the major stock of carbon, that was stocked within the Peridinium bloom was replaced by nano-phytoplanktonic components, mainly Cyanobacteria. Because of these changes, zooplankton became major food resource for S. galilaeus which potentially competing with Bleaks. Cyanobacteria species included toxins (Microcystins) causing concern about safety of water supply. The achievement of fish population reclamation is therefore, primarily aimed at S. galilaeus enhancement and could be accomplished by, among others, reduction of Bleaks pressure from zooplankton.

During the N limited period, since mid 1990’s, considerable changes in the fishery were recorded in Lake Kinneret (Figures 1-7). Landings of Bleaks, Tilapias (O. aureus, S. galilaeus) and Tristramella sp., significantly declined during the 2000’s but were affected by different factors: Tilapias by several factors as described previously and Bleaks by fishing stop (Figure 1, Figure 4). Figure 2 and Figure 5 confirm the linear relation between

landings of S. galilaeus and other Tilapias. Therefore, the percentage of S. galilaeus landing from the total Tilapias catch is increasing when total Tilapias decline. Polynomial regressions (Figure 6, Figure 7) confirm the timing relation between landings of Tilapias and Bleaks but insignificant for Barbels. That is probably because the affected factors to those discussed in this paper are not relevant to Barbels. The population of S. galilaeus sharply declined, resulting in reductions in fish annual yields from 350 tons during the 1990’s to 8 tons in 2008 (Figure 4). Δ ¹³C analyses of S. galilaeus indicated a slight change of the trophic status of this fish during 2008- 2009: from −21.7‰ to −24.1‰ [2] probably due to the partial shift of the feeding habit of S. galilaeus from Peridinium to zooplankton.

S. galilaeus fishery is not limited by market demands but only by its catchability. S. galilaeus is routinely stocked since 1958 but its introduction was reduced from late 1990’s (Figure 10). Fingerlings of S. galilaeus, are successfully raised in artificial ponds located in the Ginosar, Aquaculture Research Station, in the vicinity of the lake by experts of the Fishery Department. About 1000 - 1200 adult couples, males and females, of S. galilaeus are collected in the lake and placed in each 1 ha of two pond. The bottom of these ponds is covered by Plastic sheet with concrete bricks scattered on it. These bricks successfully create simulation of spawning ground. The full process of courtship, egg laying, fertilization, mouth breeding and the larval-fingerling growth maintenance is done in the ponds. The fingerlings are raised by feeding with artificial food (pellets). The fishes in the ponds are supplied by optimal maintenance conditions of feeding, aeration and water exchange which continue until fingerlings weight is raised to 5 - 10 g/ind. Fingerlings are gradually collected and transferred immediately into the lake. Stocking season is from August to October and number of introduced fingerlings is financially limited by nurseries maintenance expenses.

Bleak fishery was totally ceased after 2000 because of market limitations (low commercial value), leading to a dramatic increase of their population in the lake [11] . A prominent increase of fish densities was indicated probably due mostly to bleak shoals (Figure 6). Because Bleaks are not fished as before the 2000’s because of the market demands dependence their catch is not representing their population in the lake.

Nevertheless, the S. galilaeus landings sharply declined (Figure 8, Figure 9). Illegal small mesh size of the gill net fishery was unfortunately also recorded.

At present there seems to be competition for zooplankton food source between Bleaks and S. galilaeus. If hydrological conditions will be improved and additional supply of external Nitrogen will be enhanced, and the epilimnetic stock of N will be restored, the Peridinium blooms re-appearance is predicted. Such cases were already sporadically documented during the winter floods in 1992 and 2003. If nutrient availabilities return to the previous conditions, and planktonic food resources as well, the present status of S. galilaeus could probably reversed to previous situation. If Peridinium blooms returns, the presence of S. galilaeus is desireale for suppressing the Peridinium biomass because this fish consume this algae more efficiently than any other fish in the lake [5] -[8] . The ecological contribution of S. galilaeus to the ecosystem flow through the consumption of Peridinium biomass that was common in the past and could easily reappeared. Consequently, the actual advisable management is proposed at optimal fishery with benefits of both water quality protection and fisher (presently approved title for fishermen) income.

The answer given in this paper is an objection to the proposition submitted to the Ministry of Agriculture and water Authority of three years total ceased-fishing (CeFi) in Lake Kinneret. The Israeli government approved the CeFi proposal but a group of scientists and Fisher opposed it and after intensive professional discussions the government withdrew and canceled the fishing stop resolution. The justification of it was evidently approved by the recovery of Tilapias landings later. Essentially, it was predicted that total elimination of fishery, will give an open niche for proliferation of the Bleak population (Figure 6) leading to reduction in zooplankton biomass, and increase in nano-phytoplankton. Therefore, S. galilaeus population would not recover because bleak is a more efficient predator of zooplankton [5] [6] .

Conclusively, the CeFi proposal would culminate deterioration of water quality without advantage to Fisher crops. Objections to CeFi proposal were accompanied by constructive proposals like radical removal of Cormorants, enforcement of the use of larger (legal) mesh size for gill nets and others. A new program which replaced the governmental CeFi resolution was accepted including, among others, Cormorant deportation, stocking enhancement of large size (5 - 10 g/ind) fingerlings, renewal of Bleak fishing and usage of larger fishing mesh size.

The catfish, Clarias gariepinus (syn. C. lazera) is a native tropical component of the Kinneret Ichthyofauna. This fish has a very low market demands and therefore its contribution to the total annual landings is negligible. The fish comprise < 5% of total landings. Very high density of catfishes are usually observed during summer-

fall season close to the introduction site of S. galilaeus fingerlings, probably for chasing vulnerable fingerlings prey. The food composition of Catfish was studied [12] during two seasons: 1973-1975 and 1981-1982. The composition of 264 alimentary canal of adult specimen (TL 23.8 - 83.0 cm; W= 0.15 - 5.7 Kg) was analyzed. More than 50 species of phytoplankton and zooplankton were recorded in the intestines of the Catfishes, beside other benthic and pelagic organisms and high plant debris. Nevertheless the major food component (recorded in >80% of analyzed fishes) was preyed Kinneret fishes of which Bleaks and Tilapias were the most common. Consequently, improvement of stocked fingerlings survival is recommended by removal or elimination of Catfishes from the vicinity of the stocking site. There is no evidence for enhancement of Catfish predation during the crisis period. The predatory impact of Catfish on other fish species in Lake Kinneret did not change but should be considered as one of the parameters for fishery improvement design.

The Great Cormorant (Phalacrocorax carbo) is a worldwide well-known migratory bird. The migratory Cormorants stay annually in Israel from November to March coming from Europe where they breed during Spring-Summer. Cormorant feed on fish throughout the year. Cormorant catch their fish prey by diving, commonly to depths between 5 and 15 m in Lake Kinneret (personal observation, unpublished data). Their diving lasts normally 20 - 30 seconds and they bring the prey to surface. Fisher and fishery managers consider cormorants as their competitor. The conflict between cormorants on one hand and fisheries and lake management on the other is focused at reasonable landings and ecological protection. The Cormorant damage to fishery and lake management are drastic not only in Europe but in other parts of the world as well (Takahashi, et al. 2006; Natsumeda et al. 2010). The cormorant population in Europe and consequently migration to Israel, has significantly increased during the last 25 years, mostly due to the implementation of endangered birds protection policy adapted by the EEC [21] .

Conclusions presented in a report of a European workshop that was organized by FAO-EIFAC in Brussel [21] emphasized the need for long-term sustainability proposal of aquatic ecosystems and aquaculture under the threat of predation damage caused to fish by cormorants. The conference background was the increase of cormorant population up to 1.8 million birds accompanied by severe damages to aquaculture, fish population in lakes and irreversible negative changes of vegetation. One of the recommendations documented in the final report is shooting about 43,000 birds annually.

The Great Cormorant (Phalacrocorax carbo) is a component of the native Avifauna of Israel. The old shallow

lake Hula located northern to Kinneret was densely populated by Cormorants. Fish aquaculture development in the Hula Valley attracted Cormorants to the region and fish predation was enhanced thoroughly. During 1950- 1990 the Cormorants caused severe damage to aquaculture and to the fish populations in Lake Kinneret. However, a successful deportation of them in northern Israel enhanced inland migration to other parts of the country. Active deportation of Cormorants by the farmers was carried out again, than the birds found a refuge in Lake Kinneret. Presently, about 7500 Cormorants stay in the lake Kinneret and in the vicinity during late September-Early March (170 days).

The feeding habits of cormorants indicate a daily ration varying between 300 and 1000 g/bird/day and the most common values are 500 and 700 g/bird/day [22] [23] . Analysis of the birds diet [24] revealed that during late September-November the prey is mostly comprised of Bleaks and other small Tilapias, and later, young sub- commercial sized S. galilaeus (35 - 50 g/ind) become the dominant component. We consider the Cormorant daily ration as 500 grams and number of birds-7000. Therefore the entire preyed fish biomass is the following: 7000 birds × 0.5 kg × 170 days = app. 400 tons of which 235 tons are probably S. galilaeus. The birds occupy during nights several sites covered by tall trees and bushes as resting stations and they are assembled in big flocks throughout early morning and noon time daily from all sites to prey fish in the lake. It has to be considered that the preyed S. galilaeus size (<100 g per fish) are below commercially permitted size that is to say that the potential damage is at least twice as high (legal fishing size > 200 g/fish). Fish specimen weighted 100 g, if not preyed might grow up to 200 g which can be legally marketed. Consequently, the commercial value of such losses is between 1.5 and 3.0 million US$. Such a damage to Fisher’s [25] income and ecologically to the system can be reduced by deportation of the cormorants. As the fishing pressure of Cormorant community is ecologically located on top of the tropho-pyramid, and high fishing pressure already exist by the commercial fisheries, S. galilaeus is fleeing to deeper depths as a refuge from Cormorant and fisher cannot find them. As the deeper feeding depths of S. galilaeus in the lake is inhabited by S. galilaeus fishing operation become more complicated and some of the fishing gear become irrelevant. The decline of the fishing yield in this case, is Inevitable. In this case, the decline of the catch does not necessarily the result of population decline in the lake but the opposite, and not fished. The recognition of continual changed dynamics of the target fish behavior as crucial for effective fishing and sustainable management of the ecosystem is ultimately required.