In the waters off Baja California the thermocline 

 is generally shallow and there is a correspondingly 

 high standing crop of zooplankton (Brandhorst, 

 1958). It is likely, therefore, that the seasonal shifts 

 in areas of good fishing for striped marlin would 

 coincide with the expansion and contraction of the 

 shallow thermocline areas. In other words, it seems 

 that the formation of good fishing grounds off Baja 

 California is related to shallow thermocline areas 

 where there is a more abundant food supply. 



Furthermore, the depth of the thermocline in 

 lower latitudes generally coincides with the depth of 

 the oxycline. Dissolved oxygen decreases rapidly 

 within the thermocline and becomes virtually 

 nonexistent below the bottom of the thermocline. 

 Concerning the relation between fish and dissolved 

 oxygen it was reported, for instance, that the 

 minimum volume-required by salmon is about 3 ml 

 per liter (Tamura, 1949). Banse (1968) indicated that 

 though the relation between fish catches and water 

 temperatures in Arabian Sea trawling grounds is not 

 too clear, the catches tend to fluctuate according to 

 levels of dissolved oxygen in the bottom water 

 layer. It is clear that the relationship between the 

 amount of dissolved oxygen and the distribution of 

 striped marlin should be studied as an important 

 aspect of fishery oceanography. 



ACKNOWLEDGMENT 



The author is most grateful to Shoji Ueyanagi, 

 Keiji Nasu, and Susumu Kume of the Far Seas 

 Fisheries Research Laboratory, and Masaki 

 Ebizuka of the Kanagawa Prefectural Fisheries 

 Experimental Station for their helpful criticism and 

 advice on this study. He also wishes to thank other 

 staff members of that Laboratory for supplying the 

 background data and for providing valuable sugges- 

 tions. Grateful thanks are also extended to Tamio 

 Otsu, National Marine Fisheries Service, Honolulu 

 Laboratory, who kindly helped in reviewing and 

 editing this report. 



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