Love et al Potential use of offshore marine structures In rebuilding an overflsfied rockflsfi species 



385 



of eight platforms in the Santa Barbara 

 Channel (Fig. 2) using the Delta research 

 submersible, a 4.6-meter, 2-person vessel 

 operated by Delta Oceanographies of 



^ J Of 34 30'! 



Oxnard, California. In the platform mid- 

 water, we conducted surveys along each of 

 the platform's horizontal beams, located at ^-^^ 



20- to 30-m intervals between near-sur- 

 face waters and the bottom. The shallowest 

 beams were situated at depths of 15-34 m; 34 k 



thus the uppermost parts of the platform 

 were not surveyed. On the seafloor, fish 

 surveys were conducted next to the plat- 34 oc 



form bottom and over the shell mounds 

 that surround platforms. Because of poor 

 water visibility, we were unable to survey 

 either the platform bottoms or the shell 

 mounds of four platforms (i.e.. A, B, C, and 

 Hillhouse). We conducted belt transects on 

 the shell mound at an average distance of 

 approximately 7.75 m from the platform 

 and around the platform base and horizon- 

 tal beams at a distance of approximately 

 2 m from the platform, while the submers- 

 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 

 an aid to estimate their lengths. Submersible surveys 

 were conducted during daylight hours between one hour 

 after sunrise and two hours before sunset. During each 

 transect, the researcher made observations from a view- 

 ing port on the starboard side of the submersible. An 

 externally mounted hi-8-mm video camera with associ- 

 ated lights filmed the same viewing fields as seen by the 

 observer. Images recorded by the camera were laid down 

 on tape. The observer identified, counted, and estimated 

 the lengths of all fishes and verbally recorded those data 

 on the videotape. All fishes within two meters of the 

 submersible were counted. Fish lengths were estimated 

 by using a pair of parallel lasers mounted on either side 

 of the external video camera. The projected reference 

 points were 20 cm apart and were visible both to the 

 observer and in the video camera image. We assumed 

 that bocaccio 20 cm or less were YOY, in accordance with 

 growth studies of bocaccio. 



Many years of experience along the Pacific Coast 

 have shown that if the Delta is moving at a constant 

 and slow rate of speed, as in these surveys, there is 

 very little obvious effect on most fishes, particularly 

 rockfishes (M. Love-; O'Connell^ Yoklavich^). Certainly, 

 we noticed virtually no movement from most of the 



120'30' 120°20' 120°10' 120"00' 119"50' 119"40' 119"30' 119"20' 119'10'W 

 I \ \ \ I I , I I 



Sania 

 Barbara 



2 Love, M. 2002. Unpubl. data. Marine Science Institute, 

 University of California, Santa Barbara, CA, 93160. 



■* O'Connell, V. 2004. Persona! commun. Alaska Depart- 

 ment of Fish and Game, 304 Lake St. Room 103 Sitka, AK 

 99835. 



^ Yoklavich, M. 2004. Personal commun. NOAA/NMFS 

 Santa Cruz Laboratory, 110 Shaffer Road Santa Cruz, CA 

 95060. 



^3nta 



San Miguel 

 I 



Ventura 



sland^l Island _ S^— ^ x-s. 



Santa Cruz 

 Island 



Anacapa 

 Island 



Figure 2 



Location of all oil and gas plat- 

 forms in the Santa Barbara Chan- 

 nel region of California. Platforms 

 surveyed during October 2003 are 

 named. 



fishes in our study as the research submersible passed 

 by. Unless hidden in complex substrate, fishes as small 

 as about 5 cm in length are readily visible within two 

 meters of the submersible. 



Using the data from these surveys, we computed the 

 densities (number offish per m-) of YOY bocaccio at the 

 midwater horizontal beams, bottom (when surveyed), 

 and shell mounds (when surveyed) of each platform. 

 From these density estimates, we calculated the abun- 

 dance of YOY bocaccio at each platform (for protocols 

 see Love-^). 



These abundance estimates are conservative for four 

 reasons. First, we conducted the platform surveys about 

 two meters from the platform and our belt transects 

 count only those YOY bocaccio within two meters of 

 the submersible. Particularly in platform midwaters, 

 densities of YOY rockfishes tend to be lower outside the 

 platform framework (the zone traversed by the submers- 

 ible) than inside. Second, beginning a few months after 

 settling on platforms, the more open water species, such 

 as bocaccio, blue, widow, squarespot, and yellowtail 

 rockfishes, become less closely associated with structure. 

 There appears to be an ontogenetic shift away from a 

 close association with habitat to a wider association, 

 where these fish wander away from the immediate vicin- 

 ity of the platform. This shift is particularly true dur- 

 ing years with high densities (as in 2003), when large 

 schools wander freely within the relatively open waters 

 of the platform jacket. Third, as noted above, at each 



5 Love, M. 2005. Methods used to estimate abundance in 

 numbers of young-of-the-year (YOY) bocaccio. Website: 

 http://www.id.ucsb.edu/lovelab [accessed on 26 September 

 2005]. 



