North-South Differentiation of Blenniid Fishes in the Central Pacific 
Donald W. Strasburg 1 
Differences in the number of fin rays, scale 
rows, rings of bony armor (family Syngna- 
thidae), and other meristic characters have 
long been employed as criteria for separating 
species and subspecies of fishes. With the 
recent increased interest in Central Pacific 
ichthyology numerous forms have been 
shown to exhibit minor differences in meristic 
characters between various geographical areas, 
and relatively extreme populations have been 
described as specifically or subspecifically 
distinct, depending upon the magnitude of 
the differences. The term subspecies has been 
a particularly popular one to apply to slightly 
divergent populations as it connotes both 
similarity and dissimilarity. In the Pacific, 
however, its use has been confusing from the 
standpoint of zoogeography, for often little 
or nothing has been said about gene inter- 
change, effects of environmental factors, or 
method of distribution over vast expanses of 
ocean. For example, Herald (in Schultz et al ., 
1953: 267, 273-275) distinguishes two sub- 
species of the pipefish Corythoichthys flavofas- 
ciatus on the basis of minor differences in 
meristic characters, and then says that the two 
forms are separated by a distance of 6,000 
miles, with no other representatives of the 
species between them. A less extreme situa- 
tion is Schultz’s (in Schultz et al., 1953: 292- 
297) erection of several subspecies of Atherion 
elymus based on slight differences in other 
meristic characters. In this case the forms 
occur in the Philippine, Marshall, and Ma- 
riana Islands, which are relatively close to- 
1 Department of Zoology, Duke University. 
gether compared to previous example, but 
considerable "island-hopping” must occur if 
there is interbreeding. 
In the course of reviewing the blennioid 
fishes of the Hawaiian Islands the writer’s 
attention has been drawn to a similar situa- 
tion in that certain Hawaiian blennies bear a 
marked similarity to others from the Marshall 
Islands. The minimum distance between these 
two areas is about 1,400 miles, with practically 
no islands in between. Examination of spec- 
imens from Wake Island, one of the few 
intermediate geographical areas, indicated a 
rather surprising degree of intermediacy with 
respect to several morphological characters. 
Two hypotheses were formulated as a result 
of this discovery: 1) that there might be a 
traffic of fishes between the Marshalls and 
Hawaii by way of Wake, with a resultant 
possibility of gene interchange; and 2) that 
perhaps the intermediate nature of the Wake 
specimens was due to the intermediacy of 
some factor in the physical environment. 
In considering the first hypothesis it is 
noteworthy that the prevailing ocean currents 
affecting the Hawaiian-Marshallese area act 
so as to move water from the Hawaiian Islands 
toward the Marshalls (Sverdrup et al ., 1946: 
chart 7). Consideration of this fact makes it 
obvious that if there is a movement of shore 
fishes between the Hawaiian and Marshall 
Islands it must normally be one-way, its 
point of origin being in Hawaii. If this is so 
then the high degree of endemism present in 
the Hawaiian shore fishes (reckoned as great 
as 52.6 per cent by Jordan and Evermann, 
1905: 32) becomes a curious anomaly, as does 
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