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All offshore oil and gas platforms have finite economic life spans. One of the decommissioning options for these platforms is complete removal, requiring the use of explosives to dislodge the support structure from below the seafloor. Off California, this decommissioning option would kill large numbers of platform-associated and commercially important groundfishes that inhabit the bases of the platforms, and may potentially affect regional fish populations. Capturing and translocating fishes before removing a platform might mitigate the effects of platform removal. In this study, we acoustically tagged 79 rockfishes and lingcod from three oil platforms in the east Santa Barbara Channel and translocated them to a natural reef inside a state marine reserve at Anacapa Island to determine whether individuals would home back to their platforms of capture, or take up residency at their new location. Movements between natural and platform habitats were monitored over a two-year period. Twenty-five percent of all tagged fishes translocated to a natural reef returned to their home platforms relatively quickly, traveling distances from 11 km to ≥18 km, in 10.5 h to 17 d. Those that did not home took up residency at Anacapa Island, moved to Santa Cruz Island or out of the range of detection. Although a small proportion of fish (25%) homed back to the platforms, a higher proportion (75%) remained at their platforms of release. Those that homed back to their platform of capture did so relatively quickly (avg 15 ± 31 d). Lingcod had the highest probability of homing back to their platform of capture, typically doing so in < 1 day. These results suggest that fish translocation may be a successful, but costly mitigation strategy for platforms that require full decommissioning and that some species may be more successfully translocated than others.
One of the primary challenges to detecting anthropogenic environmental impacts is the high degree of spatial and temporal variability inherent in natural systems. Planned or routine events that result in disturbance to populations and communities provide an opportunity for scientists to apply well-replicated and statistically powerful sampling designs to assess subsequent biological effects. For example, a thick layer of sessile invertebrates is the prominent biotic feature of intertidal and shallow subtidal portions of offshore petroleum platforms in southern California. Given the central role of such invertebrates in providing food and shelter, their presence can reasonably be expected to influence associated fish community structure. At one platform on the San Pedro Shelf, invertebrate biomass was completely removed from support pilings and horizontal crossmembers to a depth of 20 m with high-pressure water during a standard “hydrocleaning” event in November 2007. Three nearby platforms remained undisturbed, providing a unique opportunity to test for disturbance-related changes in the local fish assemblage and the overall time course of community recovery. The potential impact of the abrupt and intense removal of the invertebrate layer was assessed with survey data collected periodically for one year prior- and one year post-hydrocleaning in a modified Before-After-Control-Impact (BACI) design. Asymmetrical multivariate analyses of variance revealed a significant effect of disturbance to fish, driven largely by reductions in the abundance of numerically dominant blacksmith (Chromis punctipinnis). Nevertheless, the system was surprisingly resilient, recovering to pre-disturbance conditions within ten months. Our results demonstrate that a well-replicated BACI sampling design can detect even subtle biological changes in response to disturbance, a key step towards developing a mechanistic understanding of community disassembly in the face of increasingly frequent and intense perturbations.
Size can play an important role in determining reproductive success through the establishment of dominance hierarchies and mate selection. We explored the relationship between size of individuals and courtship success in the kelp perch, Brachyistius frenatus, off the coast of southern California at Santa Catalina Island. Courtship displays were timed and the length of the interaction was used as a proxy for courtship success. In addition, we observed how much of their time individuals spent performing different activities throughout the day in two adjacent habitats dominated by different macroalgae. We found that body size played a significant role in determining the success of courtship. Large males were slightly more successful than small males, but the male: female size ratio was the best predictor of mating success of male B. frenatus, with males that were large relative to the female they were courting being most successful. Time allocated to different activities varied significantly with time of day and habitat. A greater proportion of time was spent on foraging in the morning than in the afternoon, and females spent more of their time foraging than did males. Behaviors other than foraging were only observed in one habitat type (understory algae) and courtship behavior was only observed during the afternoon. Smaller males tended to spend more time searching for receptive females than did larger males.
The research presented here represents an analysis of pier-based subsistence fishing in Los Angeles County. The researchers conducted surveys and participant observation at 4 field sites on Los Angeles piers. Subsistence fishing among populations in the mainland United States has been neglected as a significant activity of research interest. This may be in part because individuals engaged in subsistence fishing are often members of long established poor, indigenous or diasporic communities. With this project, we analyzed particular marine cultural phenomena, otherwise invisible in a highly bureaucratized system of fisheries management and risk analysis, by researching and describing some of the fishing practices and fishers of Los Angeles County's piers. Ethnographic survey research reports on the unique demographics, risk perceptions, and sociocultural aspects of distinct pier-based fishing communities in Southern California.
There is a growing interest in managing wetland restoration and conservation projects to maximize carbon sequestration. We measured soil organic carbon storage and methane flux from two southern California salt marshes which had been restored for 2 and 22 years. We hypothesized that organic carbon would accumulate following restoration and that methane flux would be negligible in both sites. While methane flux was minimal, soil organic carbon content was generally higher in the more recently restored site. Although there is a potential for carbon sequestration in salt marshes, tracking this process through time may be complicated by initial site conditions.