Benthic and Pelagic Habitats of Red Crab — Boyd 
399 
Fig. 4. Chart of outlying occurrences of Pleuroncodes planipes and the limits of distribution of the 
species. The shaded area indicates the region of greatest abundance. 
be seen by examining Figure 4, which indicates 
the known range of the species. The western- 
most record is from the original species de- 
scription by Stimpson (I860), at 24°N, 
130°W, and is well within the North Pacific 
Equatorial Current. The few specimens that 
have been found in the western part of the 
range probably were swept away from coastal 
waters. These animals, caught in the Equatorial 
Current, may be assumed to be expatriates 
which do not contribute further to the main- 
tenance of the species. 
The occurrence of P. planipes north of its 
center of distribution depends upon a system 
of northerly-moving countercurrents. This sys- 
tem is composed of three parts which may 
have a common origin (Reid, I960): (1) the 
Davidson Countercurrent, which flows north- 
ward very close to shore between Point Con- 
ception and the Oregon- Washington area; (2) 
the Southern California Countercurrent, which 
moves nearshore water northward from south- 
ern Baja California and expands into a gyre 
inside the islands off southern California 
(Johnson, 1939), and then moves northward 
very close inshore around Point Conception; 
and (3) an undercurrent which transports 
deeper waters (at about 200 m depth) north- 
ward from Baja California. The undercurrent 
is the least understood of the three. The sur- 
face countercurrents are known to be seasonal, 
and have their strongest northward flow in 
January and February. These countercurrents 
account for the strandings of P. planipes at 
Monterey, California in March 1959 and again 
in January I960. 
The distribution of P. planipes in February 
I960 (Fig. 5) is drawn from analysis of plank- 
ton samples taken by the California Coopera- 
tive Oceanic Fisheries Investigation’s cruise 
