JOHNSON: DISPERSAL OF LOBSTER LARVAE 



useful to examine the results of certain neuston 

 and 1-m net tows, especially those taken during 

 David Starr Jordan cruise 65 where 28.5% of 35 

 neuston tows yielded one or more larvae, and two 

 tows contained eight and nine larvae respectively. 

 All but two of the neuston tows that were positive 

 for larvae were taken during dusk or darkness. 

 The 1-m net tows taken simultaneously from 200 

 to m yielded no larvae in either the nighttime or 

 daytime tows. This discrepancy is rather surpris- 

 ing and the cause is not clear. But it may indicate 

 that larvae are so scarce and widely dispersed 

 vertically at depth that the 1-m net does not filter 

 enough water to be effective at depth and its pas- 

 sage through the immediate surface layer is very 

 brief, whereas the neuston net, although filtering 

 less water, caught larvae because of their active 

 concentration in a very narrow horizon at the very 

 surface during conditions of reduced light. Other 

 observations in the field (Chittleborough and 

 Thomas, 1969) and in laboratory experiments 

 (Ritz, 1972) demonstrate this behavioral response 

 of phyllosoma leading to a migration into surface 

 layers at night. 



In David Starr Jordan cruises 57 and 60 the 

 trawl and neuston tows show that larvae do get 

 into the North Equatorial Countercurrent (Fig- 

 ures 1 and 2). This is an expected correlation 

 with the physical studies of the countercurrent 

 which indicate that some variable transverse 

 circulation does occur across the current such 

 that water is drawn in at the surface along the 

 southern boundary and a loss occurs across the 

 northern boundary (Wyrtki, 1967). The 

 Equatorial Undercurrent at the Equator, is 

 another possible route for return to the 

 Galapagos and surrounding area. 



Williams (1972), in presenting a hypothetical 

 model of an eastward passive migration of skip- 

 jack tuna from the central Pacific spawning 

 area in recruitment of the fisheries in the east- 

 ern Pacific, has reviewed hydrographic details 

 relative especially to the position, speed, and 

 seasonal interruptions of the North Equatorial 

 Countercurrent. The seasonal fluctuations of 

 this current could aid or retard the passive 

 migration of tuna larvae and juveniles from the 

 spawning grounds depending upon the degree of 

 coordination with the season of spawning. Much 

 of this transport mechanism might apply also to 

 the return of the long-lived lobster larvae. But 

 it is not known if there is a significant season- 

 ahty in the release of the larvae in the adult 



habitat that might fortuitously correlate with 

 the North Equatorial Countercurrent and thus 

 enhance the likelihood of return of larvae that 

 have drifted to the west. Data from EAS- 

 TROPAC suggest a very long breeding season 

 for the tropical species as judged by the persis- 

 tent occurrence of early larval stages (III-IV) in 



I5°N 



10° A- - 



s-s 



125° 



IIS^W 



120° 



JORDAN 77 



Stations with available 

 plankton sannples: 



• 5'x5' net 



A midwater trawl 



D neuston net 



Rp. Panu/irus penicillatus 



Pg. " gracilis 



So. Scyllorides astori 

 number of ptiyllosomo 

 larvae taken (Arabic No.) 

 stage of phyllosoma 

 larvae taken (Romon No.) 



Figure 4.— RV David Starr Jordan cruise 77 station pattern with 

 number and stage (Roman numeral) of piiyllosoma larvae taken at 

 station indicated. Neuston net tow is shown where larva was taken. 



645 



