FISHERY BULLETIN: VOL. 72. NO. ? 



Table 2. — David Starr Jordan cruise 65. Types of gear, total number of tows taken (the 

 successful number of which is shown in parenthesis) and the number of larval species 

 caught with different gear in unit areas 1-6. 



10 



19 



34 



02°57'S. During the EASTROPAC survey only 

 P. penicillatus was found at the western-most 

 stations at about long. 126°W near the equator, 

 a distance of about 2,000 nautical miles. These 

 P. penicillatus larvae might conceivably have 

 drifted eastward from the oceanic islands of the 

 south Pacific where the adult is known to occur. 

 But no other species common to the mid-Pacific 

 islands has ever been found in any part of the 

 eastern tropical Pacific survey areas except for 

 the two specimens of Parribacus sp. mentioned 

 previously. Obviously one sees here the working 

 of the East Pacific Barrier towards maintaining 

 a specific separation of west American and 

 Indo-Pacific lobster faunas. Panulirus 

 penicillatus, which occurs all the way through 

 the Pacific and Indian Oceans to the Red Sea, is 

 unique among lobsters in having successfully 

 overcome this barrier to become established on 

 offshore islands, but appears to have found ad- 

 ditional barriers that prevent establishment on 

 the coast of the mainland. George (1969) inter- 

 prets this as a failure to compete successfully 

 with the east Pacific mainland species that 

 have evolved there by natural selection. The 

 absence of P. penicillatus in the coastal envi- 



ronment may result largely fiom elimination of 

 the larvae by an admixture of inimical coastal 

 water as they approach the coast. This supposi- 

 tion is suggested by the fact that no larvae of 

 this species have thus far been found at stations 

 near the coast despite their capability of wide 

 dispersal offshore. 



Other Crustacea with relatively shorter 

 planktonic lives appear also to have migrated 

 eastward across the East Pacific Barrier (Chace, 

 1962; Garth, 1966). 



The countercurrents within the Equatorial 

 Current System provide possible routes for re- 

 turn of east Pacific species that have either for- 

 tuitously or through instinctive behavior shifted 

 into countercurrents, possibly through habits of 

 diurnal migrations, and that have not drifted 

 westward to a point of no return determined by 

 requirements inherent in their life cycle. 



To evaluate how effective these return routes 

 may be needs further study based on plankton 

 collections designed to elucidate the vertical dis- 

 tribution of the larvae and the diurnal migrations 

 that they undergo in relation to light, etc., and to 

 the depths of prevailing countercurrents in rela- 

 tion to adjacent currents. In this connection it is 



644 



