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Fishery Bulletin 89(1). 1991 



gear (e.g., trawls, gillnets) is difficult at best; there- 

 fore, the number of fish caught per angler/hour (CPUE) 

 was used to estimate the relative abundance of fish 

 near oil and gas platforms. 



Artificial reefs have been reported to concentrate 

 scattered fishes and/or elevate secondary production 

 by increasing the growth and survival of new individ- 

 uals. However, few studies have examined the tropho- 

 dynamics of these systems (Bohnsack and Sutherland 

 1985). The attraction/production paradigm should not 

 be viewed as a black and white issue, but as a gradient 

 depending upon species, life-history stage, type of ar- 

 tificial reef, etc. (Bohnsack 1989). Many species offish 

 around oil and gas platforms are trophically indepen- 

 dent of the structure (e.g., pelagic fishes), but may use 

 the platform for other purposes (e.g., optical stimulus, 

 shelter, protection from predation, seasonal move- 

 ments, spawning and orientation) (Gooding and Mag- 

 nuson 1967, Hunter and Mitchell 1967, Klima and 

 Wickham 1971, Wickham et al. 1973, Gallaway et al. 

 1981a, Continental Shelf Associates 1982). 



Factors that may explain the congregation of fish 

 around artificial reefs are poorly known (Grove and 

 Sonu 1983). Some theories on factors influencing the 

 abundance and attraction of fish to artificial reefs in- 

 clude shape and complexity (Hunter and Mitchell 1968, 

 Luckhurst and Luckhurst 1978, Grove and Sonu 1983, 

 Chandler et al. 1985), size of the artificial reef (Hunter 

 and Mitchell 1968, Huntsman 1981, Grove and Sonu 

 1983, Turner et al. 1969, Rousenfell 1972, Ogawa 1982, 

 Vik 1982), age of the artificial reef and seasonality 

 (Turner et al. 1969, Molles 1978, Stone et al. 1979, 

 Smith 1979, Lukens 1981, Stephens and Zerba 1981). 

 Colonization of natural and artificial reefs did not follow 

 the MacArthur and Wilson (1967) model of species 

 equilibrium for insular biotas according to Smith (1979) 

 and Lukens (1981). They found the strong seasonal ef- 

 fects in the northern Gulf of Mexico produced seasonal- 

 ly stable communities with regular fluctuations in 

 diversity and abundance. 



The objective of this study was to determine if a rela- 

 tionship exists between the relative abundance of 

 selected fish species near oil and gas platforms off the 

 Louisiana coast and (1) physical platform variables 

 (e.g., water depth, submerged surface area, volume of 

 water enclosed by the platform, mode of platform 

 operation, platform age), (2) temporal variables (e.g., 

 linear, quadratic, and cubic functions of date), (3) 

 meteorological and geological variables (e.g., air tem- 

 perature, wind speed and direction, mean sediment 

 size), and (4) angler characteristic variables (e.g., fish- 

 ing method, boat length, total engine horsepower, 

 presence of electronic fishing aids). 



Materials and methods 



Between September 1986 and March 1987 we solicited 

 120 recreational anglers from fishing clubs across Loui- 

 siana to maintain logbooks. In addition, 23 of the 

 charterboat operators listed in National Marine Fish- 

 eries Service records and Coleman (1984) volunteered 

 to maintain logbooks. Logbook data were collected 

 from March 1987 to March 1988. The design of the 

 logbook and data collected were based on the Lake Erie 

 Angler Diary Program (Sztramko 1986) and logbook 

 criteria outlined by Demory and Golden (1983). Infor- 

 mation obtained from the logbooks included: date of 

 trip, number of anglers, oil and gas platform fished, 

 fishing time (not including travel time), fishing method, 

 bait used, and the species and number of fish caught. 

 Due to the difficulty in identification of some fish 

 species, snapper other than red snapper, groupers, 

 sharks, and silver and sand seatrout were classified as 

 other snapper, groupers, sharks, and silver/sand sea- 

 trout respectively. Other data acquired from logbook 

 participants included boat length (m), total engine 

 horsepower, and the presence of electronic fishing aids 

 (e.g., LORAN, graph recorders, and echosounders) 

 which assisted in the capture of fish. 



We also measured characteristics of the platform, 

 surrounding sediments, and weather which we con- 

 sidered important. Submerged surface area (m 2 ), vol- 

 ume of water enclosed by the structure (m 3 ), and the 

 number of legs, wells, and structural crossmembers for 

 each platform utilized by the logbook participants were 

 calculated from drawings and information provided by 

 offshore oil operators. Water depth (m) and age of the 

 structures were supplied by the Minerals Management 

 Service. Surface sediment sizes (^m) adjacent to oil and 

 gas structures were taken from Coleman et al. (1986). 

 Meteorological data, including average daily wind 

 speed (km/hour), direction, and temperature (°C), for 

 the New Orleans International Airport were obtained 

 from the Louisiana State Climatology Office. 



To account for seasonal differences in abundance, 

 linear, quadratic, and cubic orthogonal polynomials of 

 the 12 months of the study were used. Orthogonal 

 polynomial contrasts are by definition uncorrelated, 

 thus enabling the unique contribution of the linear, 

 quadratic, or cubic effects of time to be identified. 



CPUE was calculated as the number of fish caught 

 per angler per hour of fishing. Prior to any analysis 

 that assumes data normality, the distribution of CPUE 

 data was tested and found not to be normal. Therefore, 

 in order to approximate the normal distribution, the 

 CPUE data were transformed by ln(CPUE + 1) due to 

 the large number of zero values in the original data 

 (Pennington 1983, 1985). 



