and out of specified currents, 3) relating the time scales of 

 current variability to the duration of pelagic lifespans of lar- 

 vae by aging techniques (especially otolith ring counts) , 4) mon- 

 itoring spawning and recruitment of shore fishes in relation to 

 the dynamics of the offshore current field. Some other aspects 

 for such an interdisciplinary study also have been discussed by 

 Richards (1982) . 



OCEAN EDDIES AND PLANKTON 



Mesoscale eddies, in general, are the features of ocean cir- 

 culation which most likely entrain planktonic organisms, thereby 

 affecting their transport (Wiebe et aj,. 1976, Cox and Wiebe 1979, 

 Angel and Fasham, 1983). In particular, recent findings on the 

 variable nature of ocean circulation around islands and along 

 coasts (for review see Chopra 1973, Hogg e_t a_l. 1978) and the 

 increasing understanding of eddy entrainment and advective 

 processes provide a potential solution to the anomolous spawning 

 seasons of tropical marine fishes at some locations. The vari- 

 able occurrence of mesoscale ocean eddies (on the order of 

 monthly and perhaps seasonal periods) and the peak reproductive 

 season of coastal marine animals (with planktonic larvae) may be 

 synoptic. We are studying such a case in the Hawaiian Islands. 



We will discuss the potential role of eddies in marine biol- 

 ogy as a general phenomenon. Among the specific details yet to 

 be carefully considered are any potential differences that may 

 exist according to the type of eddy involved (Angel and Fashman 

 1983) . Two types of eddies are known: warm-core or anticyclonic 

 eddies and cold-core or cyclonic eddies. In the northern hemi- 

 sphere anticyclonic eddies rotate clockwise and cyclonic eddies 

 rotate counterclockwise. Eddies develop by a variety of physical 

 mechanisms including wake phenomena in the lee of islands and by 

 extreme meanders of a strong stream current. Whether or not the 

 way in which an eddy is generated has a subsequent impact on its 

 biological function is unknown. Robinson (1983) recently has 

 compiled a comprehensive review of the role of eddies in marine 

 science. 



A more general physical feature relating to the distribution 

 of pelagic fishes and ichthyoplankton are thermal fronts. Ther- 

 mal fronts are sharp gradients of temperature with distance. The 

 expression of fronts can result from several sources, including 

 the edges of eddies, upwellings, current shears, convergence and 

 divergence zones, jet streams and, vertically, at the thermo- 

 cline. To what degree pelagic larvae of shore fishes are able to 

 select locations within currents by temperature or other cues is 

 unknown. The overall correlation of fish distributions across 

 fronts in general has yet to be determined. The possibility also 

 exists that various fronts may differ in some physical way that 

 is detectable by fishes but which we have not yet recognized. 

 There are, however, good examples of the distribution of mycto- 

 phid fishes consistent with thermal patterns across fronts and 

 eddies (Brandt 1981, 1983; Brandt and Wadley 1981). Myctophids 

 are mesopelagic fishes whose entire lifespans are spent in the 

 open sea. 



30 



