1026 



Fishery Bulletin 97(4), 1999 



Number of specimens per tow 



100° 



Surface temperature 



Figure 1 



NOAA Ship D.S. Jordan cruise 8710. August-November 1987: (Ai sampling locations and iso- 

 lines of abundance for rhynchoteuthion squid paralarvae; (B) surface isotherms (°C). 



the band. A secondary patch of abundance (five sta- 

 tions with 20-90 rhynchoteuthions/tow) was sampled 

 by the MacArthur farther to the west (9-13°N, 121- 

 135°W) and appeared to be a westward extension of 

 the band of peak abundance. 



The primary band of maximum abundance was 

 approximately coincident with the 29 'C surface iso- 

 therm (Fig. IB). Peak abundance was found in the 

 vicinity of a very productive oceanographic upwelling 

 feature known as the Costa Rica Dome (Li et al., 

 1983). The secondary patch of abundance was in an 

 area with surface temperatures in the mid-28"C 

 range. It may be associated with a westward exten- 

 sion of the Costa Rica Dome, termed the counter- 

 current ridge (Fiedler et al., 1991). A plot of abun- 

 dance versus surface temperature shows a clear peak 

 between 27.5" and 31.0 C (Fig. 2). The three stations 

 with highest abundances were all in areas of 29.0- 



29.5°C surface temperatures (see vertical arrows in 

 Fig. 2). Abundance tapered off late in the survey al- 

 though surface temperatures remained above 27.5'C 

 (Fig. 3), within the optimum range indicated by peak 

 abundance. 



In addition to a biological-oceanographic pattern 

 of abundance, two other alternatives could explain 

 the pattern described here: 1 ) it could represent con- 

 centrated patches of recent hatchlings from isolated 

 egg masses; or 2) it could result from sampling error 

 associated with changes in towing characteristics of 

 the samplers (e.g. speed, duration). 



To address alternative 1, 1 examined size-frequency 

 distributions based on dorsal mantle lengths (DML), 

 both within individual samples and in the total 

 pooled population. For samples with > 100 specimens, 

 I measured a subsample of 100. 1 separated the sta- 

 tions into dusk tows (within one hour after local sun- 



