FISHERY Bl'LLETIN: VOL. 83, NO. 3 



RAPIDLY MOVING RING 

 (C • 7 cm/s) 



SLOWLY MOVING RING 

 (C • 3 cm/s) 



b 



X (KM) 



500 



X (KM) 



500 



P'igure 9. -a) Same as Figure 8d except a moving ring is present at the shelf edge, with parameters A = 20 cm/s, L = 20 km, and c = 7 



cm/s. b) Same as (a) except c = 3 cm/s. 



dous. When the population catches up to the back 

 side of the eddy, the relative speed is so slight that all 

 of the organisms are diverted off the shelf and lost 

 from the system. 



In addition to the plots of density versus time and 

 along-shelf distance, it is extremely useful to con- 

 sider the net balances for larvae within the domain. 

 By integrating Equation (8) over x and t, using Equa- 

 tion (9) to evaluate the starting point contribution at 

 X = 0. we can calculate the percentages of the total 

 incoming population which are removed from the do- 

 main by three processes. First, there are biological 

 decreases of the net population (due to the integra- 

 ted \jiN term). It is important at this point to recall 

 that we consider this as representing both larval 

 death and metamorphosis. Therefore the recruit- 

 ment should be roughly proportional to this term. 

 (We do not consider the development time history of 

 the larvae here; clearly this model could be combined 

 with more detailed and complex larval development 

 models to attempt more sophisticated recruitment 

 predictions.) Secondly, there are losses due to advec- 

 tion off the shelf by the ring currents, and thirdly, 

 larvae can be lost out the downstream end of the do- 

 main. The 500 km length of the domain puts the end 

 of the model region near Cape May; exiting larvae 

 may be swept offshore into the Gulf Stream and, like 

 those drawn off by ring currents, presumably be lost. 



The magnitude of each of these terms is sum- 

 marized in Table 1 for the cases plotted in Figures 

 8b, d and 9a, b. Table 1 shows that the ring-induced 



advective losses from the population can be as large 

 as or larger than the biological (mortality and meta- 

 morphosis) losses. This is most dramatic when the 

 ring is moving slightly slower than the shelf water 

 currents. The recruitment should vary in a fashion 

 similar to the integrated biological causes term in 

 Table 1; thus we expect a strong year class when 

 rings are not interacting with the shelf waters, a 

 reduction when stationary or rapidly moving rings 

 are present, and a very sharp decrease in recruit- 

 ment if a slowly moving ring is near the edge of the 

 shelf at the time of spawning and larval develop- 

 ment. 



DISCUSSION 



Theoretically, the passage of warm core rings close 



Table 1.— Percent of total larval fish population entering the 

 domain. WCR = warnn core ring. 



324 



