IMMIGRATION OF FISHES THROUGH THE SUEZ CANAL^ 



Adam Ben-Tuvia^ 



ABSTRACT 



The number of Red Sea fishes found in the eastern Mediterranean amounts to 36 species. Twelve 

 immigrants, namely: Spratelloides delicatulus , Herklotsichthys punctatus, Tylosurus choram, Sebas- 

 tapistes nuchalis, Epinephelus tauvina, Autisthes puta, Pelates quadrilineatus, Silago sihama, Rhon- 

 sicus stridens, Crenidens crenidens, Rastrelligerkanagurta.Scomberonwrus commerson, were found in 

 the last 12 yr. The southward migration, from the Mediterranean to the Red Sea is almost negligible. 

 Only Liza aurata, Dicentrarchus punctatus . and perhaps Carcharhinus plumbeus can be regarded as 

 Mediterranean immigrants. 



In studying the immigration of fishes through the 

 Suez Canal, three zooecological areas must be 

 taken into consideration: 1) the northern Red Sea; 

 2) the eastern Mediterranean; and 3) the Suez 

 Canal itself in which many marine animals from 

 the two neighboring areas have found a perma- 

 nent habitat (Steinitz 1968). 



The prevailing hydrographic conditions differ in 

 these three areas, although the salinities and 

 summer temperatures are to some extent similar 

 (Morcos 1967, 1970; El-Saby 1968; Oren 1970; 

 Oren and Hornung 1972). Temperature and salin- 

 ity are the main abiotic factors influencing the 

 distribution of organisms over large zoogeo- 

 graphical areas. Often they also have a decisive 

 influence on the ecological distribution of species 

 in various biotopes of an area. 



The process of immigration is highly selective. 

 Common species of the home seas are not necessar- 

 ily successful immigrants in a new region. Similar 

 effects have been shown to occur in many forms of 

 colonization (MacArthur and Wilson 1967). The 

 adaptation of a species to a new area requires 

 adjustment of its reproductive processes, espe- 

 cially with regard to the correct timing of spawn- 

 ing in order to ensure suitable physical and ecolog- 

 ical conditions for the development and survival of 

 the young stages. 



It is evident that the direction of immigration is 

 mainly from the Red Sea into the Mediterranean 

 (Figure 1). The possible causes of such one way 

 immigration have been discussed elsewhere ( Aron 



'This paper was read at the 17th International Zoological 

 Congress in Monte Carlo, 25-30 September 1972; some changes 

 were introduced to include more recent information on immi- 

 grants. 



^Department of Zoology, Hebrew University of Jerusalem, 

 Jerusalem, Israel. 



Manuscript accepted June 1977 



FISHERY BULLETIN: VOL. 76, NO. 1, 1978. 



and Smith 1971; Ben-Tuvia 1971a, 1973; Por 

 1971a, b). 



Thirty-six Red Sea or cosmopolitan species can 

 be regarded as Suez Canal immigrants. Twelve of 

 them were found within the last 12 yr. Evidently, 

 immigration is a continuous process, and over 

 time the probability of suitable species of fishes 

 entering the Suez Canal and colonizing the new 

 region increases. Time also plays an essential role 

 in the biological processes of adaptation of the 

 species to the modified conditions of life. More 

 resistant species, endowed with greater plasticity 

 of genetic characters, can form local "races" within 

 a few generations by natural selection in the new 

 environment (Kosswig 1974). But first they need a 

 firm foothold on the other side of the Canal, geo- 

 graphically close to the parental stock and in 

 places where conditions are not drastically dif- 

 ferent from their normal habitat. 



Recently I had an opportunity to collect samples 

 from the Gulf of Suez (Ben-Tuvia and Grofit 1973), 

 Suez Canal (Steinitz and Ben-Tuvia 1972), and 

 Bardawil Lagoon (Ben-Tuvia 1975a) which re- 

 vealed interesting data on the distribution of im- 

 migrants. Many of the species which have success- 

 fully colonized the eastern Mediterranean, such as 

 Saurida undosquamis , Leiognathus klunzingeri, 

 Upeneus moluccensis, and U. asymmetricus, and 

 which are abundant there, are also dominant 

 species on the trawling grounds of the Gulf of Suez. 



High percentage of Red Sea fishes found in the 

 hypersaline Bardawil Lagoon on the northern 

 coast of Sinai indicates that it may serve as a 

 stepping stone in the immigration of Red Sea 

 fishes into the Mediterranean, especially if we re- 

 gard it as a part of the system of lakes and lagoons 

 of the Isthmus of Suez (Por 1971a). Among 55 



249 



