MMS ENVIRONMENTAL STUDIES PROGRAM: ONGOING STUDIES
MMS OCS Region: Pacific
Title: Assessing the Fate of Juvenile Rockfishes at an Offshore Platform and Natural Reef in the Santa Barbara Channel, California
Actual Costs: $250,000.00 Period of Performance: FY2004-2006
Conducting Organization: University of California-Santa Barbara, CA (Contact: Milton Love)
MMS Contact: Dr. Ann.S.Bull
Description:
Background
A major question in the platform reefing debate deals with the issue of whether platforms are important to rebuilding local fish stocks whose populations have been seriously depleted. Because fish populations are usually limited by available energy, recruitment, or habitat, it is important to determine if platforms serve as new or additional spawning habitat and/or provide critical habitat for early life history stages. Results from MMS funded research during the mid-1990’s show that platforms uniquely serve as shallow, offshore habitat that is suitable for recruitment of a number of fish species that also recruit to nearshore natural reefs. Several species, such as bocaccio, widow and blue rockfishes have recruited in far greater numbers to platforms than to most of the natural reefs that have been surveyed. The length of time that many rockfish larvae and juveniles can stay in the plankton and their mortality rate during their planktonic dispersal stage is well known. The variation in recruitment of many rockfish species is linked to surface currents because many of these species remain near the surface and drift with currents for weeks to months, then at a competent stage; individuals recruit to habitat that is suitable for settlement. Funded in part by MMS, Dr. Libe Washburn and his laboratory at the Institute for Computational Earth System Science (ICESS), at the University of California at Santa Barbara have been monitoring the surface circulation patterns around platforms using high frequency Coastal Ocean Dynamics Applications Radar (CODAR) systems. The radars provide near-continuous surface current observations every hour over an area extending from about 3 km to about 50 km from the coast. The CODAR installation for the entire Santa Barbara Channel will be completed in FY 2003. Although CODAR was originally developed to predict the movement of spilled oil, an equally important use is related to the study of the recruitment of marine larvae to coastal populations. Data from CODAR is provided to the public and easily obtainable over the Internet.
Objectives
This study has several objectives designed to determine the importance of a platform as a nursery ground by estimating the proportion of young rockfishes that, if a platform did not exist, would survive to settle out at a natural reef. (1) Characterize the larval and early juvenile fish assemblages during rockfish recruitment at a platform and at a natural reef site(s) in the Santa Barbara Channel. (2) Evaluate the degree to which the pattern of surface circulation identified by CODAR can account for temporal and spatial variation in recruitment to both sites. (3) Using CODAR surface circulation data identify the direction and distance of pathways from the platform to natural reefs during rockfish recruitment. (4) Determine what percent of rockfish larvae would likely die before reaching the natural reefs, if the rockfish did not encounter and settle at the platform. 
Methods
This study will trap larvae and early juvenile stages of rockfish on a regular basis during a lengthy recruitment period at a platform and at the nearest natural reefs site. Both active and passive collections using light traps and various plankton nets are proven tools for sampling early life history stages at both locations. Samples of larval and juvenile fishes would be preserved, enumerated, and identified to the lowest possible taxonomic level. The youngest, preflexion larvae, would be measured to the end of the notochord (notochord length: NL) and postflexion larvae and juveniles would be measured to the end of the vertebral column (standard length: SL). In the event that the number of fish in a sample was greater than 50 for any single species, the largest, smallest and a random subsample of 50 individuals would be measured. Light trap samples would be standardized to a catch-per-unit-effort (CPUE) of fish per 10 min. Plankton net samples would be standardized to the number of fish per 100 m3 (density). Density and abundance estimates will be made using the standardized data. Examination of surface circulation patterns in the vicinity of a platform and at natural reefs, when pulses of rockfish recruitment are known to occur, will be used to determine the degree to which the pattern of surface circulation identified by CODAR can account, in part, for temporal and spatial variation in recruitment to both sites. Rigorous statistical analyses will be used to correlate surface patterns with presence of rockfish recruits at both sites. Using CODAR data, the direction and distance of pathways from the platform to natural reefs will be determined. A directional histogram of radar-derived trajectories will show the degree to which surface currents potentially carry larvae in any given direction from the platform site. The histogram will be used to predict where the young rockfishes that settled at a platform would have gone, if the platform had not existed. Knowing how long it would take rockfish larvae to reach suitable natural reefs, and what percent of these larvae would likely die before reaching these reefs, will then provide a sense the importance of a platform as a nursery ground.
Importance to MMS
The fate of spent offshore oil platforms in California recently has been a subject of considerable debate, much of which is focused on the potential importance of the platforms as artificial reef systems. Knowledge of the potential importance of platforms to the recruitment and survival of depleted rockfish stocks is essential for fully evaluating the various options proposed for decommissioning California’s offshore oil platforms. 
Current Status:
This study is in its final phase. Statistical analyses are complete and the draft Technical Summary and Final Reports will be received by MMS for review in December 2006.
Final Report Due: 12/2/2006
Publications: Nishimoto, M.M. and L. Washburn. 2002. Patterns of coastal eddy circulation and abundance of pelagic juvenile fish in the Santa Barbara Channel, California, USA. Mar Ecol Prog. Ser. 241: 183–199, 2002.

Emery, B.M., Washburn, L., Love, M.S., Nishimoto, M.M., and J.C. Ohlmann. 2006. Do platforms off California reduce recruitment of bocaccio (Sebastes paucispinis) to natural habitat? an analysis based on traje4ctories derived from high-frequency radar. MMS 2006-052.
Affiliated WWW Sites: http://www.lovelab.id.ucsb.edu/index.html
Revised date: November 30, 2006
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