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Fishery Bulletin 104(3) 



for at least 40 days, the nominal time the drifters were 

 tracked. Survival after 40 days along these trajectories 

 ranged from 9 to 45%. 



It is possible that juvenile bocaccio spend time away 

 from near surface waters during their planktonic larval 

 phase and therefore their trajectories may depend on 

 deeper currents. Previous observations in the study re- 

 gion show strong correlation between near surface and 

 deeper flows, indicating that inferences from surface 

 trajectories apply to deeper trajectories. Comparing 

 moored current meters at 5 and 45 m depth, Dever 

 (2004), Harms and Winant (1998), and Winant et al. 

 (2003) generally found a high correlation between cur- 

 rent directions, and a decreased flow speed at depth. 

 They also found that poleward flow at 45 m occurs 

 during the convergent and relaxation states, and equa- 

 torward flow occurs during the upwelling state. There- 

 fore, during relaxation and upwelling states, currents 

 at 45 m likely have similar directions, but lower speeds 

 compared with surface currents. During the convergent 

 state, currents at 45 m are opposite surface currents, 

 indicating that surface currents represent deeper cur- 

 rents only to some shallower depth. 



We assumed in this trajectory analysis that juve- 

 nile bocaccio effectively behave like passive particles. 

 We made this assumption for two reasons: 1) this as- 

 sumption allowed us to focus on the lower bound of 

 their range of possible swimming behaviors; and 2) 

 such an assumption also eliminated the need to ac- 

 count for their actual swimming behavior in the open 

 ocean, about which little is known. We do not assume 

 that juvenile bocaccio do not swim; rather, we assume 

 that they swim randomly such that their effective 

 transport is similar to that of passive particles. The 

 other behavioral limit of rapid, consistently directional 

 swimming behavior would likely alter the fraction of 

 bocaccio encountering shallow habitats versus the frac- 

 tion being advected offshore. Flume experiments with 

 visual cues for directional orientation demonstrate 

 that coral reef fish in the late pelagic stage can swim 

 up to -100 km in 8 days (Stobutzki and Bellwood, 

 1997); therefore behavioral modification of trajectories 

 could be very important. Larval and pelagic juvenile 

 fish may possess swimming and sensory abilities to 

 overcome passive drift in currents; however, some kind 

 of external reference is necessary for fish to detect and 

 respond to the direction of a current. In a review of 

 the behavior of larval and juvenile fish in the pelagic 

 environment, Leis and McCormick (2002) pointed out 

 that it is yet to be demonstrated that these early-stage 

 fish in offshore "blue water" can effectively modify 

 current-driven trajectories by orienting to cues from 

 settlement habitat located at a scale greater than sev- 

 eral kilometers away. A variety of near-field stimuli, 

 such as light and temperature gradients, sound, and 

 visible prey affect swimming behavior. Clearly more 

 research is needed to evaluate the effects of swimming 

 behavior of temperate reef fishes, such as bocaccio, in 

 order to model their dispersal. We speculate, however, 

 that the assumption of passive dispersal will remain 



an important lower bound on constraining effects of 

 swimming behavior. 



Smoothing and interpolation in the processing of the 

 HF radar velocity data limit the spatial resolution of 

 current fluctuations to scales of ~6 km, the diameter of 

 circles used to compute velocity vectors. Velocity struc- 

 tures smaller than this scale are not resolved but may 

 be important in determining trajectories. For example, 

 Helbig and Pepin (2002) found that errors in modeling 

 the spatial distributions of fish eggs in an embayment 

 increased as spatial resolution of a circulation mod- 

 el decreased. Assuming effects of unresolved velocity 

 structures on smaller scales act as a diffusive process, 

 we speculate that incorporating diffusion would cause 

 the locations of the boundary intersections to spread 

 to adjacent bins. In this case, peaks in the histograms 

 (such as in Figs. 2B, 3B, and 4) would decrease as 

 diffusion spreads boundary intersections to adjacent 

 bins. Velocity statistics at scales of the order of a few 

 km and smaller in our study area, however, are not 

 available for incorporating the effects of diffusion into 

 the trajectories. Results from actual drifters, which 

 do contain velocity structure unresolved by the HF 

 radars, are not very different from HF-radar-derived 

 trajectory results (Table 1), indicating that the effects 

 of unresolved variance are not large. For predicting 

 settlement to habitat, trajectory improvements gained 

 through the incorporation of smaller scale flow features 

 may be offset by assumptions of swimming behavior and 

 habitat location. 



Questions and issues have arisen in the decommis- 

 sioning process about the regional importance of plat- 

 form fish assemblages (Schroeder and Love, 2004). For 

 example, does removal of a platform impact the bocaccio 

 population? Based on our annual research submersible 

 surveys (detailed in Love et al., 2003) conducted in 

 1997, 1998, 1999, and 2001, estimates of YOY bocac- 

 cio at Platform Irene ranged from 61 (2001) to 41,000 

 (1999) (Lenarz-^). YOY bocaccio abundances can be 

 even higher than those observed at Platform Irene. We 

 have recently estimated that, during 2003, Platform 

 Grace, located in the Santa Barbara Channel, harbored 

 over 300,000 YOY bocaccio (Lenarz'M. Under even the 

 most conservative parameters, this would translate 

 into many thousands of adults (MacCalH). In addi- 

 tion, there is evidence that some of the bocaccio that 

 recruit to platforms as YOYs migrate, and thus seed, 

 natural reefs. Fish tagged at Platform A, located off 

 Summerland, CA, in the Santa Barbara Channel, were 

 later recovered over natural reefs over 100 km to the 

 north and south of that platform (Hartmann, 1987). In 

 another study, recruiting bocaccio became resident on 

 a deep-water platform and formed the highest density 

 of adult fish observed in the Southern California Bight 



■^ Lenarz, W. 2004. Personal commun. P.O. Box 251, Kent- 

 field, CA 94914-0251. 



-■ MacCall, A. 2004. Personal commun. NOAA National 

 Marine Fisheries Service, 110 Shaffer Road, Santa Cruz, 

 CA 95060. 



