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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Watanabe (1958) states that both bigeye and 

 yellow-fin feed at night, with the bigeye the more 

 active feeder. He did not rejiort on albacore. 

 Matthews ^ conducted a histological examination 

 of the retinas of yellowfin, bigeye, skipjack, and 

 albacore. Among yellowfin, bigeye, and skipjack 

 he found little evidence of differences in visual 

 potentialities. According to Matthews: "The al- 

 bacore are quite another problem. Here are retinas 

 with cone potentials probably equal to those of 

 skipjack, yellowfin, and bigeye tuna, but in addi- 

 tion, from the evidence I have observed, possess 

 a greater development of their rods. This may 

 account for the fact that they are frequently taken 

 in turbid waters. . . ." He also stated that "One 

 can say that in the albacore there are at least twice 

 as many if not more rods than twin cones." 



Since the rods are used for night vision, it ap- 

 pears that albacore have retinas with a capability 

 for a comparatively keener vision at night or un- 

 der conditions of low illumination. Ikeda's 

 (1958) report of a luminous lure used at night by 

 Japanese longline fishermen that "is especially 

 good for albacore fishing" would tend to bear 

 this out. The descents of Beebe (1934) and others 

 attest to the amount of bioluminescence in the 

 oceans. Myctophids, euphausiids and other kinds 

 of crustaceans, and many cephalopods are noted 

 for luminosity (Marshall, 1954). Even fishes or 

 crustaceans which are not luminous may leave a 

 luminous trail as they swim through waters in- 

 habited by peridinians and other kinds of dino- 

 flagellates (Harvey, 1952). An albacore with a 

 theoretical capability of nighttime vision might 

 be able to spot these luminous trails and track 

 down its prey. 



VARIATION IN FOOD WITH WATER CLARITY 



In his paper on the effect of water clarity on 

 albacore catches, Murphy (1959) considered the 

 abundance of albacore as it is related to turbidity, 

 a function of the amount of particulate matter in 

 the ocean. He theorized that dense concentrations 

 of phytoplankton might obscure available tuna 

 forage from sight feeders, such as the albacore, 

 which then might temporarily leave an area that 

 had prior to the phytoplankton increase a forage 

 concentration sufficient to sustain them. 



In order to investigate the effect of water clarity 

 on the amount of forage present in the stomachs 

 of troll-caught albacore, stomach volumes were 

 plotted against the depth of Secchi disc observa- 

 tions made during eight cruises to the temperate 

 North Pacific. The results are shown in figure 16. 

 Secchi disc observations were used rather than 

 light penetration measurements made by a pho- 

 tometer because for some cruises only Secchi disc 

 readings were available. Also, Clarke (1941) and 

 Graham and Gooding,^ have shown there is good 

 agreement between observations made simulta- 

 neously with both the Secchi disc and the photom- 

 eter. Secchi disc observations were made either 

 once or twice a day while the vessels were running 

 between stations. When more than two observa- 

 tions were made on the same day the observation 

 made closest to the place of capture of the alba- 

 core was used. 



O "i — 



' M.itthews, D. C, A comparative histological stufly of thf 

 retinae of skipjack {Katsuwonus pelamis), yellowfin (Neothun- 

 nus macropterua) , bigeye (Parathunnus sibi), and albacore 

 (Oermo alalunga) tuna. Manuscript, Bureau of Commercial 

 Fisheries Biological Laboratory, Honolulu. 



10 15 20 ' 25 30 35 «J 



SECCHI DISC READINGS (METERS) 



Figure 16. — Variatiim in the volume of stonuuh contents 

 per pound body weight of 111 albacore caught by troll 

 in the temperate North racific, according to Secchi disc 

 readings. 



The points shown in figure 16 for stomach 

 volumes up to 3 cc./lb. body weight are fairly 



'Graham, J. J. and R. M. Gooding, Northeastern Pacific 

 Aihacore Survey. Manuscript, Bureau of Commercial Fisheries 

 Biological Laboratory, Honolulu. 



