FISHERY BULLETIN: VOL. 71, NO. 2 



I I I I I I I I I M I I M M I I I I I I I I \i I I I I I 



■oesTnucTion i. 



ALBACORE CATCHES 

 (No. Fish /Line Hour) 



TTT 



I I I I I I I I I I I I I I I I I I I I 



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Figure 19. — Catch rates of albacore (fish landed per 

 line hour) while the Cayuse steamed during daylight 

 hours. Numbers above histograms indicate catch per 

 line hour. Numbers encircled below a group of histo- 

 grams denote the calendar day during the cruise (27- 

 2 August). 



made on the first half of the cruise, which 

 corresponds to the trend of catches by com- 

 mercial boats in the area (Figure 1). Fish 

 ranged from 57 to 80 cm fork length. Catches 

 were made along much of the cruise track 

 and were not confined to one local area. Within 

 individual days, however, highest catches often 

 occurred along the offshore edge of the plume. 

 For example, on 28 July peak catches of 3.3 

 and 2.9-5.0 fish/line hr were made in the 

 vicinity of 82.0"/oo and 16°C surface water 

 (Figures 14 and 17). These were areas along 

 the edge of the plume where the horizontal 

 temperature and salinity gradients were more 

 intense than in other areas (Depoe Bay Stations 

 85-95 and 115-135 (Figure 15)). Lowest catches 

 on 28 July of 0.6 fish/line hr were made within 

 the core of the plume at Stations 105-115 

 where salinity was 31.5"/oo or lower and 

 temperatures were above 16°C. Catches also 

 declined along the northernmost cruise track 

 as the ship entered a finger of 16 °C and 32"/oo 

 water on 30 July. 



On 31 July, after the major drop in average 

 catches by the fleet, largest catches (2.7 fish/ 

 line hr) were not in the general area of previous 

 high catches on 28 July but farther offshore, 

 160 miles off Cape Lookout. In this area the 

 16°C isotherm sloped to the surface (Figure 



16), again indicating a horizontal thermal 

 gradient. 



A few fish were caught on 1 and 2 August, 

 in nearshore waters, 25-50 miles off Depoe 

 Bay. No fish were caught in the same area 

 6 days earlier. During the intervening time, 

 the mixed layer depth deepened and trans- 

 parency increased at the stations where fish 

 were caught. At the station 25 miles offshore, 

 for example, the extinction coefficient was 0.17 

 on 27 July compared with 0.11 on 2 August; 

 the depth of the 15 °C isotherm descended 

 from 5 to 30 m. Thus nearshore catches late 

 in the cruise may be correlated with increased 

 water clarity and increased depth of favorable 

 water temperatures. 



Albacore Food Habits 



The proportion of fishes, crustaceans, and 

 squids found in the stomachs of albacore caught 

 from the Cayuse is illustrated in Figure 20. 

 In general, albacore caught within 130 miles 

 of shore had been feeding largely on fishes, 

 whereas squids and sometimes euphausiids 

 were more important constituents of stomach 

 contents farther offshore. An "S" within the 

 pie diagrams denotes where saury, Cololabis 

 saira, was the predominant food (>50% of 

 the wet weight biomass). 



On 28 July when large catches were made 

 by the Cayuse and the commercial fleet, alba- 

 core were observed jumping at the surface 

 in pursuit of saury. On this day sauries con- 

 stituted nearly all the stomach contents of 

 albacore, many of which had full stomachs. 

 Saury predominated only twice in stomachs 

 of albacore examined from offshore (beyond 

 long 127°W), on 29 July and 1 August, but 

 composed most of the stomach contents of 

 albacore examined off the Columbia River on 

 30 July. Thus saury was the main forage of 

 albacore along the outside edge of the Columbia 

 River plume, but usually not beyond the plume 

 during 28-30 July. After 30 July, saury was 

 a less important food item, and ragfish, Icosteus 

 ae)iigmaticiiH, and rockfish, Sebastes, were 

 more common than they were earlier. In addi- 

 tion, sergestid shrimp constituted all the 

 stomach contents of two albacore caught near 



500 



