Chaetognaths off Peru — Bieri 
263 
Fig. 14. The relationship of the 1941 and 1952 plankton samples to the physical environment off Peru. The 
extent in time of El Nino, El Aguaje, and upwelling are taken from Sverdup, Johnson, and Fleming, 1942. The 
average surface temperature in degrees centigrade and surface salinity in 0/00 are based on Coast and Geodetic 
Survey publications 280 and 281. The increase in temperature and concurrent decrease in salinity during the 
months of January through April are conspicuous. 
The August 1952 samples, indicating cool 
water conditions, are probably more repre- 
sentative of the usual conditions off Peru than 
are the May 1941 samples because the Peru 
coast is characterized by relatively cool water 
(Fig. 14). El Nino was apparently above aver- 
age strength in 1941 as indicated by the heavy 
rainfall that year (Sverdrup et al ., 1946; Sears, 
1953). The chaetognath population in the 
surface water off Peru in May 1941 is thought 
to have been formed from individuals brought 
in from the west by El Aguaje and mixed 
with the remnants of a population brought 
down from the north by El Nino earlier in 
the year. 
Sagitta pulchra , a common species in the 
Gulf of Panama, was not found in the 1941 
samples. This species might occur off Peru at 
the height of unusually strong penetration of 
water from the north. 
REFERENCES 
Baldasseroni, V. 1915. Chetognati dalle 
publicazioni R. Istituto di studi superior 
di Firenze. IN Raccolte planctoniche fatte dalla 
R. Nave " Liguria ’ nel viaggio di circonnavi- 
gazione del 1903-05, 2(5): 85-118. 
Bowman, T. E. 1955. A new copepod of the 
genus Calanus from the northeastern Pacific 
with notes on Calanus tenuicornis Dana. 
Pacific Sci. 9(4): 413-422. 
Daken, W. J., and A. N. Colefax. 1940. 
The plankton of the Australian coastal 
waters off New South Wales. Sydney Univ., 
Dept. ZooL, Monog. 1(1): 63-70. 
Faure, M. L. 1952. Contribution a E etude 
morphologique et biologique de deux chae- 
