Cormorants in Israel
The Great Cormorant (Photo 1 and Photo 2) is included in the Avifauna of Israel. The old shallow lake Hula located north of Kinneret was densely populated by Cormorants (Photo 1). Fish aquaculture development in the Hula Valley (northern part of Israel) attracted Cormorants to the region and fish predation by them was intense. During 1950-1990 cormorants densely populated the Hula valley causing damage to aquaculture and to the T
Photo 1. Cormorants in the old Hula Lake. Photo Source: P. Merom.
Photo 2. Microscopical photo of Lake Kinneret Fish Otolithes. Source: Y. Artzi.
Lake Kinneret. However, a successful deportation of them in the north enhanced inland migration to other parts of the country. Active deportation of Cormorants by the farmers was carried out again and the birds found a refuge in Lake Kinneret. The Great Cormorant (Phalacrocorax carbo) is a worldwide well- known migratory fish predator bird. The migration of the Cormorant to Israel is part of a routine annual cyclic behavior. Cormorants stay in Israel during November-March. They migrate from Europe and leave Israel back to European countries where they breed during Spring-Summer. Prior to the drainage of the old Lake Hula and the wetlands in the vicinity, the Cormorant stayed in the Hula Valley (Photo 1), whilst during 1960-1990 a major part of the population maintained a daily migration to adjacent reservoirs and Lake Kinneret. A minor part of the Cormorants also populated the Mediterranean coastal zone. During the period of 1960-1990, the major fish predation pressure was achieved on fish ponds and reservoirs in the coastal plain, the Hula, Jordan and the Beith-Shean Valley and Lake Kinneret. National Fish Breeders Organization operated deportation of Cormorants from Fish-Pond regions to find a protected refuge in Lake Kinneret. The outcome of that policy created a situation of one food resource for them, Lake Kinneret, and several night-stay sites in the vicinity. That was a shift from aquaculture damage to disturbance to the Kinneret ecosystem management.
Fishermen and fishery managers consider Cormorants as a competitor. The conflict between Cormorants and fisheries, especially when integrated into lake management design, is a wide internationally known issue. Cormorant damages to fishery and lake management are drastic not only in Europe but in other parts of the world as well   . The Cormorant population in Europe has increased during the last 25 years due to the implementation of endangered birds’ protection policy adopted by the European Economic Community (EEC). An International workshop was organized by FAO-EIFAC in Brussels  . Representatives from 24 European countries attended (FAO/EIFAC 2008; Carss, 2002). The final report was completed in 2008 (FAO/EIFAC 2008). This workshop concept included the need for long-term sustainab
Awareness about the potential damage to the Kinneret ecosystem by Cormorants was recently initiated. The Nature Protection Authority (NPA) carried out a survey on the population density of Cormorants, their daily migration, feeding rate and food composition  . The objective of the present study is to summarize ava
The practical significance of the presented paper is the need to implement the concept of nature protection on one side and improvement of management operation of Lake Kinneret. Although the issue resembles a contradiction between those two objectives, a reasonable gap bridging contact is predicted.
A survey of feeding habits, population density of the Great Cormorant (Phalacrocorax carbo) in the Lake Kinneret region was carried out during 2010-2012. The documented results were published in 2011  and revised in 2012. A study of the feeding rate and composition was carried out by a collection of freshly egested pellets (regurgitated) of the Cormorant underneath Eucalyptus trees in the vicinity to the most northern end of Lake Kinneret at the Jordan inlet zone. The pellets were analysed microscopically by identify and count Otholites in each one of them. The number of preyed fishes was estimated by considering the number of Otolithes counted per pellet (each individual fish has 2 Otolithesd) (Photo 2). The number of ingested fishes per individual bird was averaged, with SD calculations of all sampled pellets per month (Table 1). These groups of trees are ut
Additional information about Cormorant densities was supplied by fishermen observing several flock flights arriving at the lake from several southern and eastern night stay sites.
In the early 1990’s a survey was carried out on the content of Cormorant gut by shooting 60 birds during daytime and doing a gut content analysis.
A literature survey was implemented from which critical information was taken: da
Fishery data in Lake Kinneret was provided by the Fishery Department, Lake Kinneret Branch, Agriculture Ministry
The Cormorant issue was initiated as a result of practical difficulties of the management design of water quality combined with fishery. The required outcome of the present lake situation was a compilation of the entire available information and data sources which directed the efforts towards the methods usage for the present study.
3.1. Field Observations
The efficiency of fish predation capab
3.2. Otolithes Survey 
The statistical relation between the length of Otolithes (X) (Photo 2) and the length of preyed fish (Y) was calculated as follows  .
2) Bleaks: n = 30; r2 = 0.8492; Y = (1.857X)3.084
Percentage of prey partition by weight between Bleaks and Tilapias, average number of fish counted per pellet (±SD), number of analyzed regurgitated particles and fish weight (g) per bird per day are given in Table 1  .
Photo 3. Cormorant Flock on Lake Kinneret During day-feeding time. (Photo Source: J. Shapiro).
Table 1. Percentage of prey partition by weight of Bleaks and Tilapias, average number of fish counted per pellet (±SD), number of analyzed regurgitated particles and fish weight (g) per bird per day freshly collected in the night stay site of the Cormorant in the Lake Kinneret region  .
Results in Table 1 indicate that majority of preyed fish is due to Tilapias and a decline of the Bleaks part from January. The data is respective to mean weight of ingested fishes per individual Cormorant per day after value correction caused by intestinal degradation of the Otolithes. The mean TL of preyed fishes as indicated by Otolithe measurements was 138 mm and weight was 54 g, and the mean weight consumption per bird per day was 342 g, with a maximum of 1110 g. If consumption rates were calculated without correction of degradation coefficient the seasonal da
Results of earlier (1996) gut content survey carried out by shooting indicated lower levels of ingested fish weights: 105g and 545g for average and maximum, respectively.
Lake Kinneret is the only one natural freshwater lake in Israel. Prior to the “desalinization era” (started early 2000’s) this lake was the major source of domestic water supply. Presently, domestic supply of lake water was replaced by desalinized Mediterranean waters. Nevertheless, lake services aimed at fishery, tourism, aquatic recreation and nature conservation remained crucial. Therefore, lake management is aimed at optimization of objectives through equ
The history of inland migration of the Cormorant in Israel confirms the adaptation capab
4.1. Fish Consumption by the Cormorant
Several methods for the study of feeding rates of Cormorants were discussed. 1) Energetic balances based on physiological measures of birds in captivity. 2) Gut content analysis of birds k
Photo 4. Cormorant drying wings during day time. (Photo Source: Anonymous, Internet).
Photo 5. Cormorant colony at night stay site (Wings are not open). Source: Jan Sevcik www.naturfoto.CZ.
Zijlstra and Van-Eerden  observed only one regurgitation of particles a day containing only fishes preyed on during the previous 24 hours. They also confirm that the conservation Otolithes of large fishes are very well preserved in the pellets. Nevertheless, they  claimed that Cormorants in captivity behave significantly differently from those in natural conditions. A similar conclusion was also presented in  .
The existence of several night stay sites in the vicinity of Lake Kinneret was documented. Several flights and landings a day of Shags, coming from different directions to Kinneret were confirmed (person commun.). Consequently, the population size was corrected from 2500  to approximately 7000 with recalculating pellets counting from one per day per bird to a slightly higher value. Johnson and McCullough  carried out 8 years of research of quantitative assessment of the feeding habits of Shags (Double Crested Cormorant) in Lake Ontario. They  documented Shags’ colonies annual consumptions on 3 Islands of 34.4 × 106 preyed fish weighted 5300 tons.
4.2. The Role of Cormorants as a Top Predator
Since the mid-1990s, the Kinneret ecosystem has undergone changes in limnology     . The practical implication of Cyanobacteria blooms increase is a threat to water quality. Condition of N limitation and sufficient P is optimal for the growth of Cyanbacteria and also for Diatoms and Chlorophytes. This explains the decline in Peridinium and increase of the other phytoplankton. The decreased ep
Under the modified food web structure, T
4.3. The Crisis of T
During 2007-2008, Tilapia fishery in Lake Kinneret collapsed and landings declined from 200 - 400 tons annually to less than 10 tons in 2008   . We identified several causations for this decline: 1: Reduction of T
5. Summary and Conclusions
The information presented in a research about the potential impact of Cormorant on the Kinneret ecosystem that was carried out by NPA  was partly criticized and was completed from international resources. The number of Great Cormorant (Phalacrocorax carbo) wintering (from the end of October through March) in the Lake Kinneret Region is approximated as 6000 (5000 - 7000). The birds ut
Six thousand Great Cormorants preying daily 500 g fish per bird during 100 days removed 300 tons of sub-commercial-sized Tilapia (Mostly S. galilaeus) from the lake. However, we have to take into account that the fishes preyed on are below the commercial size of 100 g per fish, that is to say that the potential damage is bigger (legal size > 200 g/fish). Individual T
The field application of the present study is a practical design which is presently under consideration aim at achieving reduction of fish predation by cormorant without violating accepted legislations. In other words, to protect nature items together with improvement of fishery and water quality in Lake Kinneret.
Warm thanks and appreciation for assistance, data support and valuable information from field observations, and Fishery statistics are given to M. Lev-Kib- butz Ein-Gev Fishery Branch; Y. Fdida-Tiberian Fishery Organization; O. Sonin, J. Shapiro, and Z. Snovsky-Lake Kinneret Fishery Department, Agriculture Ministry.
 Takahashi, T., Kameda, K., Kawamura, M. and Nakajima, T. (2006) Food Habits of Great Cormorant Phalacrocorax carbo hanedae at Lake Biwa, Japan, with Special Reference to Ayu Plecoglossus altivelis altivelis. Fisheries Science, 72, 477-484.
 Natsumeda, T., Tsuruta, T., Kameda, K. and Iguchi, K. (2010) Winter Feeding of the Common Cormorant (Phalacrocorax carbo hanedae) in Temperate River in Japan. Journal of Freshwater Ecology, 25, 41-48.
 Artzi, Y. (2011/2012) The Great Cormorant Feeding Habits in the Lake Kinneret Region: 2010-2011. Annual Report, Nature Protection Agency (NPA) Part A (2011) and Revised Version (2012), 17 p. (In Hebrew).
 Shkedy, Y., Artzi, Y., Lider, N. and Hatzofe, O. (2013) Landing Decline in Lake Kinneret Resulted by System Instability but Not by Cormorant Activity. Ecology & Environment, 4, 32-37. (In Hebrew).
 Johnston, I.J., Harris, M.P., Wanless, S. and Graves, J.A. (1990) The Usefulness of Pellets for Assessing the Diet of Adult Shags Phalacrocorax aristotelis. Bird Study, 37, 5-11.
 Emmrich, M. and Duttmann, H. (2011) Seasonal Shifts in Diet Composition of Great Cormorant Phalacrocorax carbo sinensis, Foraging at a Shallow Eutrophic Inland Lake. Ardea, 99, 207-216.
 Zijlstra, M. and Van-Eerden, M.R. (1995) Pellets Production and the Use of Otolithes in Determining the Diet of Cormorant Phalacrocorax carbo sinensis: Trial with Captive Birds. Ardea, 83, 123-131.
 Johnson, J.H. and McCullough, R.D. (2007) Diet Composition and Fish Consumption of Double Crested Cormorant from the Pigeon Island Colonies of Eastern Lake Ontario in 2007. NYSDE Lake Ontario Annual Report 2007, 9 p.
 Gophen, M., Smith, V.H., Nishri, A. and Threlkeld, S.T. (1999) Nitrogen Deficiency, Phosphorus Sufficiency, and the Invasion of Lake Kinneret, Israel, by the N2-Fixing Cyanobacterium Aphanizomenon ovalisporum. Aquatic Sciences, 61, 293-306.
 Gophen, M. (2015) Experimental Study of the Aphanizomenon ovalisporum Response to Nitrogen Fertilization in the Sub-Tropical Eu-Meso-trophic Lake Kinneret (Israel). Open Journal of Ecology, 5, 259-265.
 Gophen, M., Sonin, O., Lev, M. and Snovsky, G. (2015) Regulated Fishery Is Beneficial for The Sustainability of Fish Population in Lake Kinneret (Israel). Open Journal of Ecology, 5, 513-527.
 Gremillet, D., Schmid, D. and Culik, B. (1995) Energy Requirement of Breeding Great Cormorant Phalacrocorax carbo sinensis. Marine Ecology Progress Series, 121, 1-9.
 Hatch, J., Brown, K., Hogan, G. and Morris, R. (2000) Great Cormorant (Phalacrocorax carbo). The Birds of North America Online. 553, 1-20.