FISHERY BULLETIN: VOL. 72, NO. 2 



other is, say, a frequently met small, commer- 

 cially unimportant, Apogon. However, such dis- 

 crimination should be made: the first fish is a 

 wholesale consumer and also a supplier of impor- 

 tant food for other species; the other, although 

 frequently collected, occurs in small numbers, and 

 whatever its importance may be in its immediate 

 biotope, its effect on the whole ecosystem is of little 

 consequence. Therefore, in studying the impact of 

 one sea on the other, number of migrant species 

 should not be overemphasized and more attention 

 should be paid to species of ecological importance. 



Commercial Fish Populations as 

 Indicators of the Biological Effect 



The most important aspect of interrelations be- 

 tween two seas, especially where a new canal is 

 planned, are the ecological effects which influence 

 the human ecological conditions and economy. To 

 obtain a meaningful picture of the biological effect 

 of the Suez Canal on both seas, emphasis should be 

 put on changes which have considerably affected 

 the large or the commercial populations of either. 

 Obviously, almost any fish species which occurs in 

 great numbers and biomass becomes sooner or 

 later commercially important, either as a market- 

 able product or as a food to commercial piscivores. 



Changes in the quantity and composition of im- 

 portant commercial fishes are contained in most 

 fisheries statistics. Of course, this can only be 

 shown where fish landings are reasonably well 

 recorded and where the data obtained may be 

 evaluated to eliminate technological and 

 socioeconomical factors. 



Commercially Important Red Sea 

 Migrants 

 and Their Mediterranean Competitors 



A number of immigrant Red Sea species have 

 become commercially important in the Levant 

 Basin and/or provide food for both Red Sea immi- 

 grants and native fish populations. Sufficient data 

 are available to discuss the expansion of the Red 

 Sea lizardfish, Saurida undosquamls (Richard- 

 son), and the dynamics of its coexistence with its 

 main native competitor Merluccius merluccius 

 (Linnaeus), the hake. 



Unfortunately, other species which could serve 

 perhaps as better examples, the yellow-striped 

 goatfish, Upeneus moluccensis Bleeker, and its 

 Mediterranean counterpart the red mullet, Mul- 

 lus barbatus Linnaeus, or the barracudas, 



Sphyraena chrysotaenia Kiunzinger (a Red Sea 

 migrant), S. sphyraena (Linnaeus), and S. vir- 

 idensis Cuvier (both Atlantic species), cannot be 

 used for this purpose as the catch statistics do not 

 discriminate between the species of the same fam- 

 ily or genus. 



From the information available on the Mullidae 

 {Upeneus and Mullus), the following can be sum- 

 marized: Red mullets (Mullidae) represent one of 

 the most important components of the Israeli 

 trawl catches. Their share in the total trawl land- 

 ings varied between 1956 and 1970 from 29 to 

 46%, (Sarid, 1951-71). The bulk of the red mullets 

 consists of two species: the red mullet and the 

 yellow-striped goatfish. The latter species is a Red 

 Sea migrant. According to Wirszubski (1953) in 

 the late 40's the share of the yellow-striped goat- 

 fish in the Mullidae catch was 10 to 15%. Four 

 years later, Oren (1957) estimated on the basis of 

 Gilat's unpublished data that Upeneus formed 

 over 83% of the total number of red mullets caught 

 in trawls during the first half of 1956. 



These are two closely related fish species, very 

 similar in their appearance and behavior and ap- 

 parently competing for the same food (E. Gilat, 

 pers. comm.). Although the red mullet evidently 

 prefers cooler and, thus, in periods, deeper waters 

 than the yellow-striped goatfish (Ben-Yami, 1955; 

 Ben-Tuvia, in press), they mostly occupy overlap- 

 ping territories. One of them-the invader- 

 succeeded in becoming a majority during 1955 

 (Ben-Yami, 1955; Oren, 1957). Since 1956, fluc- 

 tuations continue to occur in the Mullus to 

 Upeneus ratio. Ben-Tuvia (in press) estimates the 

 average share of the latter fish in the catches of red 

 mullets to be approximately 30% . 



What are the reasons for such fluctuations? 

 What are the factors which determine whether a 

 fish which has crossed the canal will establish 

 itself as a sizeable population? 



Is it possible that after some years of blooming a 

 migrant population will recede into its previous 

 state, and why? Will an expanding migrant popu- 

 lation contribute to the total fish biomass in the 

 new area, or come at the expense of the other 

 fishes? 



SOURCES AND RELIABILITY 

 OF DATA 



Fishery Statistics 



All fisheries data presented in the graphs and 



360 



