Reproductive ecology and body burden of resident fish prior to decommissioning.

Abstract

From Significant Results: Task 1: In this study we collected 18 kelp bass (Paralabrax clathratus), 80 kelp rockfish (Sebastes atro­virens), and 98 Pacific sanddab (Citharichthys sordidus) from five offshore oil platforms and 10 natural areas during 2005-2006 for whole-body analysis of 63 elements. Forty-two elements were excluded from statistical comparisons for one of three reasons: they consisted of major cations that were unlikely to ac­cumulate to potentially toxic concentrations under ambient exposure conditions; they were not detected by the analytical procedures; or they were detected at concentrations too low to yield reliable quantitative measurements. The remaining 21 elements consisted of aluminum, arsenic, barium, cadmium, chromium, cobalt, copper, gallium, iron, lead, lithium, manganese, mercury, nickel, rubidium, selenium, strontium, tin, titanium, vanadium, and zinc. Statistical comparisons of these 21 elements indicated that none consistently exhibited higher concentrations at oil platforms than at natural areas. Eight comparisons yielded significant interactions between total length (TL) of fishes and the two habitat types (oil platforms and natural areas). This implied that relative differences in concentrations of several elements (e.g., titanium, vanadium, cop­per, rubidium, tin, and selenium) between each habitat type varied with TL of the fish species. To better un­derstand these interactions, we examined elemental concentrations in very small and very large individuals of affected species. Although significant interactions were detected for rubidium, tin, and selenium in kelp rockfish, the concentrations of these elements did not differ significantly between oil platforms and natural areas over the TL range of sampled fish.

Task 2: The otolith composition of kelp rockfish and Pacific sanddab differed between the two habitat types—the sampled platforms and natural sites—and among geographic areas although there were signifi­cant interaction (habitat x area) effects. Kelp rockfish collected from platforms tended to incorporate higher concentrations of Mg and Ba and lower concentration of Sr in otoliths compared to fish from natural habi­tat. In comparison, Pacific sanddab collected from platforms tended to have lower concentrations of Ba and Fe in otoliths compared to fish from natural habitats. Sr/Ca in otoliths of kelp rockfish tended to decrease eastward along the coastal shelf from Point Conception through the east Channel. Mn/Ca in otoliths of sanddabs from both habitat types was lower in the three westernmost geographic areas (Point Conception, west Santa Barbara, and east Santa Barbara) than in the eastern and southern areas (east entrance of the channel, offshore east channel, and Southern California Bight). Mn/Ca was not detectable in kelp rockfish otoliths. The success rate of correctly assigning fish to habitat type (platform or natural habitat) using a canonical discriminant function based on otolith element signatures differed between species. Ninety-four percent of kelp rockfish individuals were correctly assigned to habitat type based on the otolith signature of Mg/Ca, Ba/Ca, and Sr/Ca. A lower proportion, 64%, of Pacific sanddab correctly grouped into habitat type based on the otolith signature of Mg/Ca, Sr/Ca, Mn/Ca, Cu/Ca, and Ba/Ca—otolith element concentrations that individually varied between sanddab habitat types and/or areas. Success in discriminating otoliths of either species from the two different habitat types was not associated with seawater element concentrations. Results from this study imply that platform habitat “fingerprints,” unique microchemical markers, may be identifiable along the time-keeping, growth trajectory of the otolith to reconstruct the history of platform habitat use during lifetime of fish. Such reconstructions will require more study on the spatial variability of platform elemental signatures from all existing platforms and the temporal stability of platform markers.

Task 3: If fishes living around oil and gas platforms are being significantly impacted by pollution, it would be expected to impair their reproductive abilities. Atresia, the abnormal reabsorption of oocytes that are destined to be spawned, is one form of reproductive impairment. Atresia has been widely used as an indicator of pollutant-related reproductive impairment in fishes. We examined the occurrence of atretic oocytes in Pacific sanddab, Citharichthys sordidus, collected from two offshore platforms in the Santa Bar­bara Channel (B and Gilda) and from two natural reference sites (off the east end of Santa Cruz Island and in mid-channel off Rincon). While pronounced atresia was observed in a few fish at one natural site and one platform, there was no evidence of widespread pronounced atresia at any of the four sites. This study implies that fishes that lie on the bottom around platforms and consume prey that lives in that sea floor are not reproductively impaired.