Impacts from Partial Removal of Decommissioned Oil and Gas Platforms on Fish Biomass and Production on the Remaining Platform Structure and Surrounding Shell Mounds

Abstract

When oil and gas platforms become obsolete they go through a decommissioning process. This may include partial removal (from the surface to 26 m depth) or complete removal of the platform structure. While complete removal would likely eliminate most of the existing fish biomass and associated secondary production, we find that the potential impacts of partial removal would likely be limited on all but one platform off the coast of California. On average 80% of fish biomass and 86% of secondary fish production would be retained after partial removal, with above 90% retention expected for both metrics on many platforms. Partial removal would likely result in the loss of fish biomass and production for species typically found residing in the shallow portions of the platform structure. However, these fishes generally represent a small proportion of the fishes associated with these platforms. More characteristic of platform fauna are the primarily deeper-dwelling rockfishes (genus Sebastes). “Shell mounds” are biogenic reefs that surround some of these platforms resulting from an accumulation of mollusk shells that have fallen from the shallow areas of the platforms mostly above the depth of partial removal. We found that shell mounds are moderately productive fish habitats, similar to or greater than natural rocky reefs in the region at comparable depths. The complexity and areal extent of these biogenic habitats, and the associated fish biomass and production, will likely be reduced after either partial or complete platform removal. Habitat augmentation by placing the partially removed platform superstructure or some other additional habitat enrichment material (e.g., rock boulders) on the seafloor adjacent to the base of partially removed platforms provides additional options to enhance fish production, potentially mitigating reductions in shell mound habitat.

A Comparison of Fish Community Structure at Mesophotic Artificial Reefs and Natural Banks in the Western Gulf of Mexico

“…Although a proportion of these platforms will be accepted into RTR programs, much of this habitat will be permanently removed from the northern GOM ecosystem. As such, it is critical to determine the effects these changes in habitat may have on marine fish populations (e.g., Claisse et al 2015).…”

“…Whether these observed increases in fish densities represent increased production (i.e., stock enhancement) or simply the redistribution (i.e., aggregation) of existing biomass has been and is currently vigorously debated (Bohnsack 1989;Carr and Hixon 1997;Grossman et al 1997;Lindberg 1997;Shipp and Bortone 2009;Cowan et al 2011;Claisse et al 2014Claisse et al , 2015. Generally, this uncertainty is driven by a lack of fishery-independent studies comparing artificial reefs with their natural counterparts, leaving significant knowledge gaps regarding the relative value and function of artificial reefs in supporting fisheries productivity.…”

Assessing drivers of rocky reef fish biomass density from the Southern California Bight

“…This large and complex region, including 8 Channel Islands, has as much coastline (~1200 km) as the rest of California, and its dynamic oceanography and high production make it an optimal natural experiment to explore the relationship among physical and biological processes (Emery 1960, Hickey 1993, Atwater 1998, Pondella et al 2015a. Recent studies of secondary production in the SCB have elevated the region's importance, as the most productive studied marine habitats have been found here, yet secondary production rates and standing stocks exhibit significant spatial variation (Claisse et al 2015, Pondella et al 2015b. For nearshore rocky reefs, indicative of these cool nutrientrich currents is the hallmark giant kelp Macrocystis pyrifera, a well-documented habitat-forming species that is highly productive (Bell et al 2015) and supports a diverse assemblage of fishes (Stephens et al 2006).…”

Environmental Impacts of the Deep-Water Oil and Gas Industry: A Review to Guide Management Strategies

“…Some authors note that the physical presence of oil and gas infrastructure may protect fished species or habitats by de facto creating fisheries exclusion zones (Hall, 2001;Love et al, 2006), by establishing new reef habitat (sensu Montagna et al, 2002), and by functioning as fish aggregating devices (Hinck et al, 2004). Although the value of oil and gas infrastructure in secondary production and fisheries, particularly in deep waters, is controversial (Bohnsack, 1989;Baine, 2002;Ponti, 2002;Powers et al, 2003;Fabi et al, 2004;Kaiser and Pulsipher, 2006), there is some evidence to suggest that this can occur (Claisse et al, 2015). Oil industry infrastructure may therefore have some positive effects, even in deep water (Macreadie et al, 2011), principally in terms of creating refugia from fishing impacts (e.g., Wilson et al, 2002).…”