NOTE 
Daylight Surface Occurrence of Myctophid Fishes 
Off the Coast of Central America 
Franklin G. Alverson 1 
The CAPTURE off the coast of Central America 
of Benthosema pterota (Alcock, 1891), by Cali- 
fornia-based tuna clippers, on three known occa- 
sions, at the surface during daylight hours is 
worthy of note. Myctophids are ordinarily be- 
lieved to be bathypelagic in nature and asso- 
ciated with the twilight zone of the sea. The fact 
that myctophids make nocturnal migrations to 
the surface has long been known and many spec- 
imens have been taken at the surface during the 
hours of darkness. 
The first daylight capture of Benthosema pte- 
rota was recorded 13 mi. west of Cape Blanco, 
Costa Rica, on March 14, 1952, by the tuna clip- 
per "Anna M.” The fish were taken with a dip 
net at 1300 on a clear day from the fishing 
racks of the vessel. The water was clear and the 
surface temperature was 82.5 °F. The skipper, 
Ted Sorensen, reported three "balls” of reddish- 
brown bait at the surface with yellowfin tuna 
( Neothunnus macropterus ) feeding voraciously 
on them. The fish, as described by Sorensen, 
were in tight elliptical aggregations measuring 
about 10 ft. in length and 3 ft. in depth. The 
tuna feeding upon the myctophids refused the 
fish ( Cetengraulis mysticetus) used by this ves- 
sel for live bait when it was offered to them. 
A second capture of the species at the surface 
during daylight hours was reported by a crew 
member of the tuna clipper "Sun Traveler”; the 
capture was made on March 15-20, 1954, 65 
mi. southwest of Cano Island, Costa Rica. Mr. 
Joseph Silva observed the fish at 10:00. They 
also appeared as a reddish-brown "ball” being 
fed on by skipjack ( Katsuwonus pelamis ) , yel- 
1 Inter-American Tropical Tuna Commission, La 
Jolla, California. 
lowfin tuna, and sea birds. Four other small 
schools were seen in the same locality. The clip- 
per left the immediate area at this time and re- 
turned at 16:00 the same day. At this time, the 
schools of myctophids were still on the surface 
and when the vessel drew close they took shelter 
under the stern, evidently for protection from 
the yellowfin and skipjack. Specimens were 
easily captured with a dip net from the racks 
on the stern of the vessel. 
A third occurrence of this species on the sur- 
face during daylight hours was noted on April 7, 
1955, at 13° 19' N. and 91° 16' W. by the 
crew of the tuna clipper "Commadore.” The 
fish were again captured with a dip net from 
the stern of the vessel while it was fishing for 
yellowfin. The fish again appeared as reddish- 
brown "balls” on the surface. 
The table below gives the size range and 
mean standard length for the three samples of 
Benthosema. 
Although only three samples have been ob- 
tained by the author, apparently the sighting 
by fishermen of myctophid schools on the sur- 
face during daylight hours in the spring of the 
year is not uncommon. Mr. Edward Silva, man- 
aging owner of the "Santa Rosa,” says that fish 
fitting the description of myctophids have been 
taken by clippers and attempts made to use 
them as tuna bait. Flowever, the fish scaled 
easily, were weak, and were unsatisfactory for 
bait. Mr. Manuel Luz, former skipper of the 
"Saratoga’” said he has seen many small "balls” 
of bait in the waters off Costa Rica during the 
spring of the year that fitted the same descrip- 
tion. He also noted that the fish made poor bait 
because they scaled easily and were too weak 
for retention in the bait wells. 
NO. 
DATE OF 
CAPTURE 
NO. 
MEASURED 
MEAN STANDARD 
LENGTH (mm.) 
RANGE IN 
STANDARD LENGTH 
(mm.) 
1 
March 14, 1952 
49 
39.0 
35-47 
2 
March 15-20, 1954 
43 
46.3 
38-54 
3 
April 7, 1955 
50 
35.2 
32-40 
483 
