Sea Bird Food and Ocean Surface Fauna — Ashmole and Ashmole 
9 
fisheries, and consequent special interest in the 
biology of tunas, the effectiveness of tropical 
sea birds in catching juvenile tunas is worth 
emphasizing. King and Iversen (1962:301) 
said, "It was our hope that by means of mid- 
water trawls we would capture juvenile tunas 
of lengths above 12 mm. which were able to 
elude the plankton nets. In 274 hauls made with 
the four midwater trawls described in this re- 
port we captured only six juvenile tunas, which 
ranged from 18 to 60 mm. in length." In con- 
trast, in the 800 food samples which we ob- 
tained from birds on Christmas Island we found 
247 young scombrids of which 166 were in 
243 samples from Sterna fuscata. Of the latter 
group, 77 were examined in detail, and 69 
proved to be Yellowfin Tuna. The scombrids 
from S. fuscata ranged from about 2 cm to 1 1 cm 
in length (measured to the base of the tail), 
but over 70% were between 4 and 8 cm. Those 
obtained in samples from A. tenuirostris in- 
cluded about a third which were less than 2 cm 
in length. 
Since the birds eat mainly animals more than 
0.5 cm in length, a program using birds to detect 
seasonal or longer-term changes in the environ- 
ment could profitably be combined with other 
methods (such as use of the neuston net) of 
sampling the smaller organisms inhabiting the 
sea surface. If a version of this net could be 
arranged to fish clear of the bow wave of a 
small boat, it would permit quantitative sam- 
pling of the waters immediately around an 
oceanic island, to complement the sampling of 
larger animals, and a larger area, by the birds. 
The use of a small boat would of course also 
make it possible to obtain basic physical and 
chemical data requisite to an understanding of 
changes detected in the biota. 
ACKNOWLEDGMENTS 
The work on Christmas Island and in Hawaii 
was supported by a Yale University — Bishop 
Museum fellowship awarded to the second 
author. Grateful acknowledgment is made to 
H. Laurence Achilles, S. Dillon Ripley and 
Roland W. Force, and the others who helped to 
make this arrangement possible. For assistance 
in identifications of fish we are especially in- 
debted to Gareth J. Nelson and James W. Atz; 
Malcolm R. Clarke kindly undertook the identi- 
fication of the cephalopods. Garth I. Murphy 
and Richard S. Shomura generously allowed us 
to make use of their unpublished paper on "The 
abundance of tunas in the Central Equatorial 
Pacific in relation to the environment.” We 
thank Donald W. Strasburg and Philip Helfrich 
for their helpful comments on the manuscript. 
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