383 Abstrac t —Although bocaccio (Se- Potential use of offshore marine structures bastes paucispinis) was an economi- cally important rockfish species along in rebuilding an overfished rockfish species, the west coast of North America, overfishing has reduced the stock bocaccio (Sebastes paucispinis) to about 7.4% of its former unfished population. In 2003, using a manned Milton S. Love1 research submersible, we conducted fish surveys around eight oil and gas Donna M. Schroeder1 platforms off southern California as William Lenarz2 part of an assessment of the potential 3 value of these structures as fish habi- Alec MacCall tat. From these surveys, we estimated Ann Scarborough Bull4 that there was a minimum of 430,000 Lyman Thorsteinson5 juvenile bocaccio at these eight struc- tures. We determined this number to 1 Marine Science Institute, University of California be about 20% of the average number Santa Barbara, California, 93160 of juvenile bocaccio that survive annu- E-mail address (for M. S. Love: [email protected] ally for the geographic range of the 2 P.O. 251 species. When these juveniles become Kentfield, California 94914 adults, they will contribute about one percent (0.8%) of the additional 3 NOAA/NMFS Santa Cruz Laboratory amount of fish needed to rebuild the Santa Cruz, California 95060 Pacific Coast population. By compari- 4 U.S. Minerals Management Service son, juvenile bocaccio recruitment to 770 Paseo Camarillo nearshore natural nursery grounds, Camarillo, California 93010 as determined through regional scuba surveys, was low in the same year. 5 Western Fisheries Research Center This research demonstrates that a U.S. Geological Survey relatively small amount of artificial 6505 NE 65th St. nursery habitat may be quite valuable Seattle, Washington 98115 in rebuilding an overfished species. Beginning in 1995, annual surveys of length). In the midwaters of most Cal- fish assemblages at oil and gas plat- ifornia platforms, there are only low forms and natural reefs throughout densities of predatory reef fish species, southern California were conducted such as kelp bass (Paralabax clath- with a research submersible (summa- ratus) and cabezon (Scorpaenichthys rized in Love et al., 1999, 2000, 2003). marmoratus), or semipelagic, large Many California oil and gas platforms predatory species, such as Pacific bar- harbor three fish assemblages: those racuda (Sphyraena argentea) and yel- that occupy the shell mound area sur- lowtail (Seriola lalandi). The proper rounding the base of the platform; disposition of the approximately 6000 those that occupy the waters adja- marine offshore oil and gas platforms cent to the platform bottom, and those and associated structures now in ser- that occupy the midwater. Rockfishes vice worldwide is in dispute. There (genus Sebastes), of about 35 spe- are 27 platforms off California and, cies, dominate these assemblages. as in other parts of the world, there is The shell mound assemblage is com- considerable debate over the ultimate posed primarily of juvenile rockfishes, fate of these structures once they are dwarf rockfishes, and other species; uneconomical to operate (Schroeder the platform bottom assemblage is and Love, 2004). In this article, we composed of adult and subadult fishes; focus on the role that some artificial and the midwater assemblage of most structures play as rockfish nursery platforms (and the bottoms of some habitat off California. Manuscript submitted 2 September 2005 mid-depth platforms) is dominated During some years, we have noted to the Scientific Editor’s Office. by young-of-the-year (YOY) and older particularly high densities of YOY bo- Manuscript approved for publication juvenile rockfishes that comprise at caccio (Sebastes paucispinis), widow 26 September 2005 by the Scientific Editor. least 28 species. These fishes are (S. entomelas), squarespot (S. hop- Fish. Bull. 104:383–390 (2006). rarely more than 20 cm long (total kinsi), and blue (S. mystinus) rock- 384 Fishery Bulletin 104(3) fishes around a number of these platforms. Similar high densities of young rockfishes were noted in the late 1950s at two nearshore platforms off Santa Barbara (Carlisle et al., 1964). The densities of YOY rockfishes are usually higher at platforms than at most natural outcrops (Schroeder et al., 2000; Love et al., 2003). As on natural outcrops, however, YOY rockfish recruitment to platforms is highly variable from year to year. In 2003, while conducting fish surveys around eight oil platforms in southern California, we ob- served high densities of YOY rockfishes (e.g., bocac- cio and widow rockfish), YOY lingcod (Ophiodon elongatus), and one-year-old vermilion rockfish (S. miniatus) (Fig. 1). Given the uncertainty regarding the role that platforms might play as fish habitat, A we were interested in understanding how important young bocaccio, and by extension the platforms, might be to the stock and populations of this spe- cies in the region. Because of the severely overfished status of bocaccio and because a stock assessment model had been developed by NOAA Fisheries, we focused our attention on this species. Along the Pacific Coast of North America, bocaccio have been reduced to about 7.4% of their unfished population (MacCall1). Bocaccio are relatively long- lived (to over 50 years) and have extremely variable annual juvenile recruitment success; over natural outcrops, large year classes are found about once a decade (Tolimieri and Levin, 2005). YOY bocaccio settle from a juvenile micronektonic stage to shallow high-relief habitats (such as kelp beds) and usually migrate into deeper waters within one year. Histori- B cally, the species was abundant from Oregon to at least northern Baja California (Love et al., 2002). In this article we focus on the large recruitment of YOY bocaccio observed at platforms in the Santa Barbara Channel in 2003. We estimate the mini- mum number of YOY bocaccio at eight platforms in the Santa Barbara Channel, southern California, and estimate the contribution these juveniles may make (as surviving adults) to the rebuilding of the overfished stock. We also compare the densities of YOY bocaccio around the platforms with those determined during the same year in studies on natural reefs throughout southern, and parts of central, California. Material and methods C Between 10 and 15 October 2003, we surveyed the jacket (horizontal beams and vertical supports) Figure 1 Examples of young-of-the-year (YOY) and other juvenile fishes found in high densities at platform Gilda, October 1 MacCall, A. D. 2003. Status of bocaccio off California 2003. (A) YOY bocaccio (Sebastes paucispinis); (B) a YOY in 2003. In Status of the Pacific coast groundfish fish- lingcod (Ophiodon elongatus); (C) one-year-old vermilion ery through 2003 stock assessment and fishery evalu- ation (vol. 1), v + 56 p. Pacific Fishery Management rockfish (Sebastes miniatus). Council, 7700 NE Ambassador Place, Suite 200, Portland, OR 97220. Love et al.: Potential use of offshore marine structures in rebuilding an overfished rockfish species 385 of eight platforms in the Santa Barbara 120°30′ 120°20′ 120°10 120°00′′ 119°50′ 119°40′ 119°30′ 119°20′ 119°10′W Channel (Fig. 2) using the Delta research submersible, a 4.6-meter, 2-person vessel Pt. Arguello operated by Delta Oceanographics of 34°30′N Santa Oxnard, California. In the platform mid- Pt. Conception Barbara water, we conducted surveys along each of the platform’s horizontal beams, located at Hillhouse 34°20′ Holly 20- to 30-m intervals between near-sur- Santa Barbara Ch C Ventura face waters and the bottom. The shallowest a B nnel Gilda beams were situated at depths of 15−34 m; 34°10 ′ A thus the uppermost parts of the platform Grace San Miguel Santa Rosa Island were not surveyed. On the seaf loor, fish Island Gail surveys were conducted next to the plat- 34°00′ Anacapa form bottom and over the shell mounds Island Santa Cruz that surround platforms. Because of poor Island water visibility, we were unable to survey either the platform bottoms or the shell C mounds of four platforms (i.e., A, B, C, and AL Hillhouse). We conducted belt transects on IF Figure 2 ORNIA the shell mound at an average distance of Location of all oil and gas plat- approximately 7.75 m from the platform forms in the Santa Barbara Chan- Area and around the platform base and horizon- Detailed nel region of California. Platforms tal beams at a distance of approximately surveyed during October 2003 are 2 m from the platform, while the submers- named. ible maintained a speed of about 0.5 knots. Divers estimated transect lengths by first estimating velocity over a short course, using twin laser beams as fishes in our study as the research submersible passed an aid to estimate their lengths. Submersible surveys by. Unless hidden in complex substrate, fishes as small were conducted during daylight hours between one hour as about 5 cm in length are readily visible within two after sunrise and two hours before sunset. During each meters of the submersible. transect, the researcher made observations from a view- Using the data from these surveys, we computed the ing port on the starboard side of the submersible. An densities (number of fish per m2) of YOY bocaccio at the externally mounted hi-8-mm video camera with associ- midwater horizontal beams, bottom (when surveyed), ated lights filmed the same viewing fields as seen by the and shell mounds (when surveyed) of each platform. observer. Images recorded by the camera were laid down From these density estimates, we calculated the abun- on tape. The observer identified, counted, and estimated dance of YOY bocaccio at each platform (for protocols the lengths of all fishes and verbally recorded those data see Love5). on the videotape. All fishes within two meters of the These abundance estimates are conservative for four submersible were counted.