At least one cow and calf were observed and 

 possibly a second pair (Table 1). This is the first 

 actual record of a blue whale calf in the tropics, 

 although historically it has been believed that 

 blue whales have their calves in the warm tropical 

 waters (Mackintosh 1966:126).3 



Steve Leatherwood, W. A. Walker, and D. W. Rice, 

 who contributed blue whale sighting data and 

 Karen J. Rice for technical assistance. Last, we 

 thank Robert Schoning of the National Marine 

 Fisheries Service for releasing this data for publi- 

 cation. 



Oceanoyraphic Features 



Literature Cited 



There are several unique oceanographic fea- 

 tures which relate to the sighting location of the 

 blue whales. Cromwell (1958) and Wyrtki (1964) 

 discussed the Costa Rican Dome which is located 

 at approximately lat. 9°N, long. 89°W. The dome is 

 apparently a permanent topographic feature (150 

 km X 300 km) and is formed by the convergence of 

 several major current systems. These currents 

 typically create an area of nutrient transport or 

 upwelling. High standing stocks of zooplankton in 

 the area near the Costa Rican Dome (lat. 7°25'N- 

 10°N) has been reported by several authors (Reid 

 1962; Blackburn et al. 1970; Holmes"*). Volkov and 

 Moroz (1977) suggested that the high stable food 

 base of the area creates a habitat suitable for 

 nonmigratory populations of baleen whales. 

 North Pacific blue whales may also use this area 

 for their winter feeding grounds. 



In conclusion, the recent sightings of blue 

 whales in the tropics indicates that North Pacific 

 blue whales have a wintering area to which they 

 return each year. Since most of the cruises have 

 occurred largely during the winter months, more 

 information must be collected to determine if 

 whales are found in this area the year round. The 

 high standing stock of zooplankton in this area 

 may indicate that this is a winter feeding area, as 

 well as a calving ground. 



AckiiDw ledgments 



We are particularly indebted to E. D. Mitchell, 

 Fisheries Research Board of Canada, for his criti- 

 cal evaluation of the manuscript. D. W. Rice, Na- 

 tional Marine Fisheries Service; K. S. Norris, 

 University of California at Santa Cruz, and Ron 

 Garrett, Wilderness Research Institute, also made 

 helpful suggestions on the draft. We also thank 



^The average water temperature for 1 1 sightings was 26.5°C. 



■'Holmes, R. W. 1970. A contribution to the physical, chem- 

 ical, and biological oceanography of the northeastern tropical 

 Pacific. (Unpubl. manuscr.) Institute of Marine Resources. 

 Scripps Institute of Oceanography, Univ. Calif La Jolla, Calif 

 AEC-UCSD-.34P99-4. 



BLACKBURN, M., R. M. LAURS, R. W. OWEN, AND B. 

 ZEITZSCHEL 



1970. Seasonal and areal changes in standing stocks of 

 phytoplankton, zooplankton, and micronecton in the east- 

 ern Tropical Pacific. Mar. Biol. (Berl.) 7:14-31. 

 Cro.mwell. T. 



1958. Thermocline topography, horizontal currents and 

 "ridging" in the Eastern Tropical Pacific. [In Engl, and 

 Span.] Inter-Am. Trop. Tuna Comm. Bull. 3:133-164. 

 HAR.MER. S. F. 



1931. Southern whaling. Proc. Linn. Soc. Lond. 142:85- 

 163. 

 INGEBRIGTSEN, A. 



1929. Whales caught in the North Atlantic and other 

 seas. Rapp. P.-V. Reun. Cons. Perm. Int. Explor. Mer 

 56:1-26. 



Kellogg, R. 



1929. What is known of the migrations of some of the 

 whalebone whales. Smithson. Inst., Annu. Rep. 1928, p. 

 467-494. 

 LEATHERWOOD, S., D. K. CALDWELL, AND H. E. WiNN 



1976. Whales, dolphins, and porpoises of the western 

 North Atlantic. A guide to their identification. U.S. Dep. 

 Commer., NOAA Tech. Rep. NMFS CIRC-396, 176 p. 



Mackintosh, N. A. 



1942. The southern stocks of whalebone whales. Discov- 

 ery Rep. 22:197-300. 



1966. Distributionof southern blue and fin whales. InK. 

 S. Norris (editor), Whales, dolphins, and porpoises, p. 

 125-144. Univ. Calif Press, Berkeley. 

 Nemoto, T. 



1964. School of baleen whales in the feeding areas. Sci. 

 Rep. Whales Res. Inst. Tokyo 18:89-110. 

 NlSHlWAKL M. 



1966. Distribution and migration of the larger cetaceans 

 in the North Pacific as shown by Japanese whaling re- 

 sults. In K. S. Norris (editor). Whales, dolphins, and por- 

 poises, p. 170-191. Univ. Calif. Press, Berkeley. 



Reid, J. L. 



1962. On circulation, phosphate-phosphorus content, and 

 zooplankton volumes in the upper part of the Pacific 

 Ocean. Limnol. Oceanogr. 7:287-306. 

 RICE, D. W. 



1974. Whales and whale research in the eastern North 

 Pacific. In W. E. Schevill (editor). The whale problem: a 

 status report, p. 170-195. Harvard Univ. Press, Cambr., 

 Mass. 

 TOMILIN, A. G. 



1957, Zveri SSSR i prilezhashchikh stran Vol. IX Kitoob- 

 raznye (Mammals of the U.S,S,R, and adjacent countries 

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 lated by Isr. Program Sci. Transl., Jerusalem, 1967, 717 

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