NOTES 
On the Herding of Prey and the Schooling of the 
Black Skipjack, Euthynnus yaito Kishinouye 
While participating in the Bikini Scientific 
Resurvey in the northern Marshall Islands in 
the summer of 1947, the authors observed three 
medium-sized black skipjack ( Euthynnus yaito 
Kishinouye) herding a closely packed school 
of several hundred scads ( Decapterus sanctae- 
helenae (Cuvier)) over a large coral head in 
Rongerik lagoon. For fully a 3-hour period the 
aquatic life on and about this coral head was 
studied by use of the skin-diving technique, and 
during this time this unusual group passed back 
and forth frequently, apparently unconcerned 
about our presence. Since Kishinouye’s reference 
to such herding activity by tuna (Tokyo Imp. 
Univ., Col. Agr. Jour. 8(3): 382, 459, 1923) 
is couched in generalities, and since our ob¬ 
servations on the black skipjack are contrary to 
statements made by this author, we place these 
underwater observations on record to clarify 
several moot points in the feeding and schooling 
habits of this species. 
The predilection of these pelagic fish for this 
coral head is understandable on the basis of the 
part such coral heads play in the general eco¬ 
logical features of a lagoon in the Marshalls. 
The coral head, typical of many, rose about 75 
feet from the lagoon floor to approximately 25 
feet below the surface of the water. It was 
roughly circular, about 75 yards across, with a 
rather steep talus slope forming its sides. The 
surface of the mound was covered with sand and 
larger coral fragments, interspersed with groups 
of living corals of numerous species and sparse 
patches of algae. Ecologically such coral heads 
seem to occupy a physical niche comparable to 
an oasis on land, as each supports a more 
luxuriant growth of organisms than does the 
surrounding terrain. Numerous species of com¬ 
mon coral fish, several medium-sized carnivorous 
fish, and many plankton-feeding fish habitually 
remain on and about these mounds. Thus the 
elements essential to food chains are more or 
less isolated in the vicinity of these coral heads, 
and there both scads and some species of tuna 
habitually forage. The fact that these condi¬ 
tions prevail afforded us an opportunity for re¬ 
peated observations upon these pelagic species 
from a unique vantage point. 
The three tuna usually followed the school of 
scads rather closely, with one tuna at each rear 
flank of the school and the third lagging behind 
them. Now and then the scads would turn off 
to one side, at which time the tuna on that side 
would move forward swiftly and herd them 
back into line. It became obvious that the school 
of scads was prevented from leaving the area 
over the top of the coral head, being herded back 
whenever it moved over deep water. On one 
occasion a laggard scad was swiftly picked off by 
the rearmost black skipjack; however, except for 
this incident the tuna made no attempt to prey 
upon the scads during our period of observa¬ 
tion. Scads are uncommon in the lagoons in the 
northern Marshalls and probably do not consti¬ 
tute a large proportion of the diet of this species 
of tuna. Studies made by Jack Marr and Os¬ 
good Smith of the U. S. Fish and Wildlife Serv¬ 
ice (unpublished data) on the food habits of 
33 black skipjack caught outside of the lagoons 
failed to show any scads in the diet of this 
species. Scads were most frequently encountered 
in the stomachs of the dog-tooth tuna ( Gymno- 
sarda nuda Kishinouye) which ranges in the 
same area. 
In his report on tuna herding prey, Kishi¬ 
nouye {op. cit.: 382) states: "Bonitos, except 
Euthynnus yaito, are said to be very clever in 
making a school of small fish very dense, by 
swimming around the school of the victims, and 
devouring stray or forlorn individuals gradually. 
On the contrary, tunnies and seerfishes swim 
into a school of victims, and disperse them. The 
feeding of fish seems not always the same 
throughout the year. The striped bonito is said- 
to decline to take bait in certain seasons, gen¬ 
erally in midsummer.” In his discussion of the 
food and feeding habits of the black skipjack, 
Kishinouye {op. cit.: 459) says that the species 
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