BEN-YAMI and GLASER: INVASION OF SAURIDA UNDOSQUAMIS 



gales of anticyclonic depression origin, during the 

 same winter (Ben- Yami, 1955); 3) the hake made a 

 very poor appearance in the 1955/56 Israel trawl 

 catches (Figures 5, 8), decreasing to approxi- 

 mately 40^c of its 20 yr average (Figures 5, 8) in 

 the catch and to approximately 42% of its 20 yr 

 average (Figure 5) in its catch per fishing day. 

 Since then, such low catches of the hake only oc- 

 curred in 1960/61 and in 1966/67. In all three 

 cases, the drop in the hake catches seems to be 

 associated with drought: it followed the 

 January-April drought in 1955, in 1959/60 and 

 1966/67 it followed a drought in the preceding 

 winter (Figure 8). 



Trawl Fishery's Rapid Development 



The rapid intensification of the Israel trawl 

 fishery 1949-54 (Table 2) was probably another 

 important factor contributing to the expansion of 

 the Red Sea lizardfish. The landings, which before 

 1940 were 100 to 500 tons, rose to approximately 

 1,000 tons/year during 1950-52 and to almost 

 1,500 tons in 1954, when the first commercial 

 catches of the lizardfish were taken. 



Before 1950, the Israeli trawlers did not fish in 

 waters deeper than 50 to 60 fm. Since 1950, 

 deepwater trawling operations have been carried 

 out, and hence there has been considerable exploi- 

 tation of the hake resources (Ben- Yami, 1971). 



DISCUSSION AND CONCLUSIONS 



The set of conditions which prevailed just before 

 and during the explosion of the Red Sea lizardfish 

 population and which, apparently, facilitated this 

 explosion included: 



1. "Preparation" of the area due to the 

 intensification of the trawling fishery by the factor 

 of 3-4 (Table 2); 



2. Water temperature conditions which contrib- 

 uted to good survival of several strong year 

 classes of lizardfish; 



3. A combination of climatic (drought) and 

 water temperature conditions which caused the 

 withdrawal of the hake from most of the trawling 

 grounds, leaving ample space for the spread of the 

 lizardfish. 



It is possible that the population of the Red Sea 

 lizardfish in the Levant Basin has been and, with- 

 out these conditions, might have remained "dor- 

 mant" and suppressed by its competitors and by 

 unfavorable environmental conditions. It may 



have been still waiting for its opportunity to ex- 

 pand. 



The fluctuation in the abiotic conditions, subse- 

 quent to the lizardfish explosion years, seems to be 

 correlated with the fluctuations in the catches of 

 both the lizardfish and the hake, though with an 

 "anomaly" in 1961-63 when, in spite of two con- 

 secutive warm winters, the proportion of hake in- 

 creased in comparison to the lizardfish. Here, e.g., 

 the abundant rains of 1961-62, or other factors 

 might have intervened (Figure 8). 



The hake is much more sensitive to the fluctua- 

 tions of physical conditions than the lizardfish, as 

 may be seen from the shape of the respective col- 

 umns in Figure 8. The declines in the hake catches 

 indicate either recessions in the population or a 

 geographical retreat from the usual fishing 

 grounds, probably into deeper and cooler waters, 

 or a combination of both. 



An interesting feature of the fluctuation of the 

 hake proportion in catches is that so far they are in 

 phase with those of the solar activity index (Fig- 

 ure 8), though this correlation may be purely inci- 

 dental. 



The interrelations discussed in this paper are 

 very complex. Different and, perhaps, even vari- 

 able time lags have to be employed to correlate 

 abiotic, biotic-natural, and man-activated 

 (fisheries) factors. A study for further pursuit 

 along this line will require the application of com- 

 puter technique. Unquestionably, a good oppor- 

 tunity for studying the influence of environmental 

 conditions on the relationship of competing mi- 

 grant and native species was lost when data on 

 the Mullus-Upeneus and Red Sea Barracuda- 

 Atlantic Barracuda proportion in catches were 

 not collected during the past years. Such 

 studies should be undertaken in the future. 



An examination of the available statistical data 

 (Sarid, 1951-71) could not establish any sig- 

 nificant influence of the appearance of the Red 

 Sea lizardfish in the total trawl catches on the 

 landings, catch per unit effort, or returns of the 

 trawl fishery. Undoubtedly, the lizardfish is not 

 just an additional inhabitant, and its invasion did 

 not enrich the existing ecosystem in terms of 

 biomass. It occurs in the catches at the expense of 

 other fish, partly its competitors, such as the hake, 

 and partly its prey, such as the yellow-striped 

 goatfish, red mullet, etc. 



The proportion of the lizardfish in the trawl 

 catches has never, after its 1954-56 invasion, been 

 less than 13%, although there have been several 



371 



