BEN-YAMI and GLASER: INVASION OF SAURIDA UNDOSQUAMIS 



tables are based on statistics collected by the De- 

 partment of Fisheries (Sarid, 1951-71). These are 

 in general reliable, and the proportion of the hake 

 and the lizardfish in the total trawl catch is well 

 represented. The figures, however, may be biased 

 in some aspects, and the following must be borne 

 in mind: 



1. The catch per unit effort for all fish and for 

 each of the two species separately is expressed in 

 kilograms per day at sea of a trawler. The Israeli 

 trawlers operating in the Mediterranean during 

 1950-70 were powered by 110-to 240-horsepower 

 engines. The average power per trawler varied 

 with time, due to transfer of some to the Red Sea, 

 loss of others, and acquisition of new vessels and 

 engines. It increased steadily in the 50's, de- 

 creased in the early 60's, and started increasing 

 again during the recent years (Table 1 ). Therefore, 

 when examining the data in Figure 5A and B, it 

 should be remembered that the unit of effort var- 

 ied from year to year. 



2. The total fishing effort and the total catches 

 fluctuated partly because of the changing 

 socioeconomical and geopolitical conditions, 

 which determined the extent of the fishing 

 grounds on which the Israeli trawlers could oper- 

 ate in the Mediterranean, and its effect on the size 

 of the active trawling fleet. 



3. The character and extent of the trawling 

 grounds available to and/or preferred by the 



fishermen partly affect the data: In deepwater op- 

 erations the hake is one of the main fish caught 

 (Ben-Yami, 1971; Zismann, 1971), while the 

 lizardfish is almost absent. In shallow water, 

 trawling depends on the accessibility of the 

 southern trawling grounds, which fluctuated with 

 the Egypto-Israeli relations. On these grounds 

 good summer catches could be obtained in shallow 

 waters, conditions preferred by some skippers to 

 deepwater trawling. 



From 1953 to 1960, some of the Israeli trawlers 

 operated during the summer months in the north- 

 eastern area of the Mediterranean, between Cy- 

 prus and Turkey, mostly in the Bay of Tarsus. 

 Their catches were included indiscriminately in 

 the general statistical data. In these catches, 

 the lizardfish greatly outweighed the hake. There- 

 fore, the catch composition data for these years 

 may be slightly biased in favor of the lizardfish 

 and to the disadvantage of the hake as compared 

 with the other years, but by no means to a degree 

 which might change the general picture. 



Sea Temperature 



In order to study effects of changes in the en- 

 vironmental factors on the catches of the hake and 

 the lizardfish, the temperatures recorded from the 

 sea between Ashdod and Tel Aviv, an area 



Table 1. — Changes in the fishing effort, catch and catch-per-effort, 1950-1970, in the Israel Mediter- 

 ranean trawling fishery.* 



'The data do not include research and training vessels, and vessels which fished less than 100 days per year (E. Grofit, 

 private communication). 



361 



