Assemblage Structure of Fish at Offshore Petroleum Platforms on the San Pedro Shelf of Southern California

Abstract

Offshore petroleum platforms in California's Santa Barbara Channel have been shown to be of ecological importance for local fish populations; however, before our investigation, no data existed on the fish assemblages associated with the platforms on the San Pedro Shelf further south. Our surveys of these platforms in 2006 and 2007 indicate that there is a core group of warm—temperate nearshore reef species in the midwater depth (<30 m), including California sheephead Semicossyphus pulcher, blacksmith Chromis punctipinnis, garibaldi Hypsypops rubicundus, opaleye Girella nigricans, and kelp bass Paralabrax clathratus. Platforms located further from shore (i.e., offshore platforms [>14 km]) had a strong seasonal presence of pelagic fishes (primarily jack mackerel Trachurus symmetricus) and recruit blacksmiths. At platforms closer to shore (i.e., inshore platforms [<4.8 km]), sea basses (Serranidae) and surfperches (Embiotocidae) were predominant; only slight seasonal variations were observed, which were attributed to prespawning aggregations of barred sand bass Paralabrax nebulifer. At the offshore platforms total fish density had a negative relationship with depth but a positive relationship with water temperature; conversely, total fish biomass exhibited a positive relationship with depth but a negative relationship with temperature. In contrast, at the inshore platforms both total fish density and biomass increased with increasing water temperature. With the exception of blacksmiths, nearshore reef fishes showed significantly greater densities of adults than juveniles. Furthermore, some species were observed spawning at these structures. Therefore, the San Pedro Shelf platforms may provide suitable habitat for several species of nearshore reef fish. Removing the upper levels and superstructure of the offshore platforms to a depth of 25 m (the partial removal decommissioning option) would eliminate critical habitat for several fish species and result in a potential loss of 95% of the total fish density and 77% of the total fish biomass, thus reducing the productivity advantages of some of these structures.

Trophic relationships among scorpaeniform fishes associated with gas platforms

“…A pelagic component in a varying level of abundance has also been recorded near offshore oil and natural gas platforms (Franks 2000;Neira 2005). This pattern is confirmed for many platforms that were investigated in different areas of the world, such as southern California (Love et al 2000;Martin and Lowe 2010), Gulf of Mexico (Hastings et al 1976;Stanley and Wilson 1997), African western coast (Gerlotto et al 1989), North Sea (Jørgensen et al 2002), and the Mediterranean (Andaloro et al 2011;Consoli et al 2007;Fabi et al 2004), although species composition varies according to the specific area concerned.…”

Oil platforms off California are among the most productive marine fish habitats globally

“…However, some smaller-bodied species, such as halfbanded rockfish (S. semicinctus) and squarespot rockfish (S. hopkinsi), also contributed substantial amounts of secondary production because they were very abundant. We should also note that the contributions of species that tend to be more prevalent in shallow water (19,40) are likely underestimated in our platform estimates because these shallower depths were not well sampled on some platforms (Table S2). However, this effect will be minimized for deeper platforms because shallow depths make up a relatively small proportion of their submerged surface area.…”

“…Because rockfishes tend to have high site fidelity (44)(45)(46), the calculations of the Somatic Production component also assume immigration and emigration rates are equal. Furthermore, previously observed seasonal changes of the fish communities on platforms, at least for more shallow depths, consisted primarily of the presence or absence of pelagic species (40) and these types of transient, highly mobile species (e.g., jack mackerel, Trachurus symmetricus, Pacific sardine, Sardinops sagax) were excluded from the data used for our production estimates. Finally, our Recruitment Production component is also conservative in a similar manner as the mortality function, as it does not include the production of fishes that recruited to the habitat and grew for some period, but died before being observed during the annual survey (6).…”

Red Snapper Distribution on Natural Habitats and Artificial Structures in the Northern Gulf of Mexico

“…Platform structures in particular may harbor greater abundances per unit of sea floor because they provide more three-dimensional habitat space on a given footprint of the sea floor (Martin and Lowe 2010). However, unlike the apparent situation in the study by Claisse et al (2014), wherein platforms appeared to increase the actual level of fish production, the production versus attraction debate is still unresolved for GOM Red Snapper.…”