391 



Abstract — To investigate the pos- 

 sibility that oil and gas platforms 

 may reduce recruitment of rockfishes 

 iSebastes spp.) to natural habitat, we 

 simulated drift pathways (termed 

 "trajectories" in our model) from an 

 existing oil platform to nearshore 

 habitat using current measurements 

 from high-frequency (HF) radars. The 

 trajectories originated at Platform 

 Irene, located west of Point Concep- 

 tion, California, during two recruiting 

 seasons for bocaccio iSebastes paii- 

 cispinis): May through August, 1999 

 and 2002. Given that pelagic juvenile 

 bocaccio dwell near the surface, the 

 trajectories estimate transport to 

 habitat. We assumed that appropriate 

 shallow water juvenile habitat exists 

 inshore of the 50-m isobath. Results 

 from 1999 indicated that 10% of the 

 trajectories represent transport to 

 habitat, whereas 76% represent trans- 

 port across the offshore boundary. 

 For 2002, 24% represent transport 

 to habitat, and 69% represent trans- 

 port across the offshore boundary. 

 Remaining trajectories (14% and 7% 

 for 1999 and 2002, respectively! exited 

 the coverage area either northward 

 or southward along isobaths. Deploy- 

 ments of actual drifters (with 1-m 

 drogues) from a previous multiyear 

 study provided measurements origi- 

 nating near Platform Irene from May 

 through August. All but a few of the 

 drifters moved offshore, as was also 

 shown with the HF radar-derived tra- 

 jectories. These results indicate that 

 most juvenile bocaccio settling on the 

 platform would otherwise have been 

 transported offshore and perished in 

 the absence of a platform. However, 

 these results do not account for the 

 swimming behavior of juvenile bocac- 

 cio, about which little is known. 



Do oil and gas platforms off California reduce 

 recruitment of bocaccio (Sebastes paucispinis) 

 to natural habitat? An analysis based on 

 trajectories derived from high-frequency radar 



Brian M. Emery' 



Libe Washburn'^ 



Milton S. Love (contact author)^ 



Mary M. NIshimoto' 



J. Carter Ohlmann" 



' Institute for Computational Earth System Science 

 University of California 

 Santa Barbara, California 93106-3060 



2 Department of Geography 

 University of California 

 Santa Barbara, California 93106-4060 



^ Marine Science Institute 

 University of California 

 Santa Barbara, California 93106-4060 

 E-mail address (for M S Love, contact author) lovecailifesci ucsbedu 



" Institute for Computational Earth System Science 

 University of California 

 Santa Barbara, California 93106-3060 

 and 



Scripps Institution of Oceanography 

 La Jolla, California 92093-0213 



Manuscript submitted 20 July 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 6 October 200,5 by the Scientific Editor. 



Fi.sh. Bull. 104:391-400 (2006). 



The 27 oil and gas platforms off south- 

 ern and central California have limited 

 life spans. Many of these structures 

 have been in place for over 20 years 

 (Love et al., 20031, and it is expected 

 that some of these platforms will be 

 decommissioned in the near future. 

 Because decommissioning may entail 

 full removal of the platform, agency 

 personnel tasked with determining 

 the best course of action in regard 

 to the platforms would likely benefit 

 from an understanding of the role that 

 platforms play as fish habitat (Schro- 

 eder and Love, 2004). 



The platforms harbor high densities 

 of many species of fishes, although 

 species compositions vary with plat- 

 form bottom depth (Love et al., 1999a; 

 1999b; Love et al., 2003). About 35 

 species of rockfishes (genus Sebastes) 

 dominate the three distinct assem- 

 blages found around many platforms 

 in the Santa Barbara Channel and off 

 central California: the bottom, shell 

 mound, and midwater assemblages. 

 Fishes around platform bottoms tend 



to be adult and subadult individuals. 

 Those on the shell mounds are usual- 

 ly adults of dwarf species or juveniles 

 of larger taxa. The midwater assem- 

 blages are composed almost entirely 

 of juvenile fishes. Some of these juve- 

 nile fishes are one and two-year old 

 individuals, but most are young-of- 

 the-year (YOY) rockfishes. Densities 

 of YOY rockfishes around platforms 

 are usually far higher than those 

 at nearby natural reefs (Love et al., 

 2003). These observations have raised 

 a concern (e.g., Krop').) that platforms 



' Krop, L. 1997. Environmental user 

 group representative, disposition 

 panel. In Proceedings: Public work- 

 shop, decommissioning and removal 

 of oil and gas facilities offshore Cali- 

 fornia: recent experiences and future 

 deepwater challenges, September 1997 

 (F. Manago, and B. Williamson, eds.), 

 p 172. Mineral Management Service 

 OCS Study 98-0023. Coastal Research 

 Center, Marine Science Institute, Univ. 

 California, Santa Barbara, California, 

 93106. MMS Cooperative Agreement 

 Number 14-35-0001-30761. 



