Perrin et al.: Geographic variation in cranial morphology of Stenella attenuata 



341 



4 Hedgepeth, J. B. 1985. Database for dolphin 

 tagging operations in the eastern tropical 

 Pacific, 1969-1978, with discussion of 1978 

 tagging results. Southwest Fisheries Center 

 Admin. Rep. No. LJ-85-03, 40 p. 



and west would show close morphologic affinities. 

 He analyzed large-scale dolphin distribution pat- 

 terns and environmental patterns based on re- 

 search-vessel surveys conducted in the eastern tropi- 

 cal Pacific from June through November, comparing 

 his results with those of Au and Perryman (1985). 

 Reply's ( 1990 ) distributional compari- 

 sons between seasons indicated that 

 along 10°N S. attenuata and S. 

 longirostris occur in relatively high 

 density west of 120°N during the 

 summer. Furthermore, they were not 

 in high densities along 4°N between 

 90 and 120°W, and along 6°N between 

 88 and 110°W — regions with rela- 

 tively high concentrations of these 

 two species in the winter (Au and 

 Perryman, 1985). Reilly. (1990) indi- 

 cated that "One hypothesis suggested 

 by these complementary changes is 

 an intraregional, seasonal move- 

 ment." Data from mark-recapture ef- 

 forts (Perrin et al., 1979b; 

 Hedgepeth 4 ) are consistent with re- 

 spect to the hypothesized direction of 

 such migrations, although the dis- 

 tances are greater than those sug- 

 gested by the very limited data from 

 these studies. Reilly ( 1990) also noted 

 that the suggested movement pat- 

 terns are at least partially explainable 

 based on seasonal atmospheric and 

 oceanographic changes in the region. 



Morphological-environmental 

 covariation 



In the earlier study of S. attenuata, 

 Schnell et al. (1986) assessed envi- 

 ronmental-morphological covariation 

 for a similar, although not identical, 

 set of environmental parameters. 

 Since their investigation was re- 

 stricted largely to eastern blocks, dif- 

 ferent findings with respect to 

 covariation are possible. Schnell et al. 

 (1986) noted that the strongest mor- 

 phological-environmental associa- 

 tions involved solar insolation (Jan.). 

 Sea surface temperatures also co- 



varied with a number of morphological characteris- 

 tics, as did oxygen minimum layer (depth). 



The environmental principal components indi- 

 cated that a number of environmental measures 

 have a north-south component (see Fig. 9A), while 

 others (particularly thermocline depth and water 



Skull W 

 (al Panetals) 



a 144 5 mm 

 140 J 

 1362 



J I I 



D 



D 











□ 



D 



05 07 



15 17 



05 07 



11 13 



17 19 



Figure 1 1 



Geographic variation in (A) skull width (at parietals) and (B) ther- 

 mocline depth (winter). Darkened part of bar indicates value for par- 

 ticular latitude-longitude block. 



