466 
PACIFIC SCIENCE, VoL IX, October, 1955 
sumably in the Palmyra inshore fish fauna 
as a whole) that does not get north is cal- 
culated as 29/33 of the number that does. 
Consequently column A is assigned a width 
slightly less than the combined widths of B 
and C, which had been calculated previously. 
Similarly, the width of F is based on an in- 
shore Oahu rotenone station from which 69 
species in the same groups were collected. Of 
these, 17'do not get as far south as Johnston. 
Hence F is assigned a width about one third 
(actually 17/52) of the combined widths of 
C and E. 
The fact that there are 16 Hawaiian species 
found at Johnston but not, apparently, farther 
south and 14 Central Pacific species that get 
to Johnston but not farther north indicates 
that at the present time Johnston is acting as 
a filter bridge for fishes passing in both direc- 
tions. The nature of the filtering effect on 
northbound and on southbound species must 
now be considered. 
Starting at the south, a very large compo- 
nent of the two poison stations run at Palmyra 
(29 of 52 species) is not known in Johnston 
or Hawaii. Two very striking members of this 
component are the genera Lutjanus and (ex- 
cept for a single species) Epinephelus. One 
immediately wonders if these fishes never got 
to the northern islands or whether they got 
there but have been unable to survive there 
because of unsuitable ecological conditions. 
If the latter were correct, one would suspect 
the colder water temperatures in the north to 
be either the direct or indirect cause of the 
unsuitability. There are certain indications 
that distance rather than water temperature 
has been the primary cause in preventing 
Central Pacific species from reaching Johnston 
and Hawaii. One of these is provided by the 
fishes of Japan. The southern Japanese Islands 
are separated by no such deep-water distances 
from tropical Pacific islands as Johnston is 
from Palmyra, but surface water temperatures 
in southern Japan are at least as cold as those 
of the Hawaiian Islands (Sverdrup, Johnson, 
and Fleming, 1946: charts II and III, and fig. 
32B). Nevertheless, 15 species of Epinephelus 
(Tanaka, 1931: 26) and 14 species of Lutjanus 
(Kamohara, 1954: 114) are recorded from 
Japan. This suggests that the Hawaiian water 
temperatures would not be unsuitable for at 
least some species of Lutjanus and Epinephelus. 
An attempt to find an area separated from the 
tropical Pacific by a deep-water barrier as 
great as that isolating the Hawaiian Islands 
and Johnston leads to an examination of the 
tropical American data. Snodgrass and Heller 
(1905: 338) list some 13 species of inshore 
tropical Pacific species as occurring in the 
islands of the west coast of the Americas. 
Of these, none belong to the genera Lutjanus 
or Epinephelus or to any of the other species 
that are not represented at Johnston and 
Hawaii. To state this last matter positively, all 
13 have representatives in the Hawaiian Is- 
lands today. These two straws in the wind 
indicate that the great diminution in species 
between Palmyra and Johnston is caused pri- 
marily by (deep-water) distance rather than by 
temperature. Such a distance effect could, of 
course, be either primary or secondary. If 
primary, the fishes themselves have been un- 
able to get to Johnston; if secondary, the 
fishes may have been able to get there but 
the organisms they depend upon for a liveli- 
hood have not. Though there is no way of 
determining which of these two possibilities 
has been realized, it seems improbable that 
such unspecialized carnivorous genera as Lut- 
janus and Epinephelus would have found the 
food supply inadequate, had they arrived 
there. 
Of those tropical fishes that have reached 
Johnston, the great majority seem to have 
passed on through to Hawaii. There are, how- 
ever, 14 species that are not known north of 
Johnston. Some of these, e.g., Epihulus insi- 
diator , are quite striking members of the 
tropical Pacific fauna, and it seems improb- 
able that they should go unrecorded in the 
Hawaiian fauna if they exist there. One sus- 
pects that the reason they have not crossed 
the minor water gap between Johnston and 
