Keith R. Parker

Effects of the Exxon Valdez Oil Spill on Birds: Comparisons of Pre- and Post-Spill Surveys in Prince William Sound, Alaska

We used data from pre- and post-spill surveys to assess the effects of the Exxon Valdez oil spill on the abundance and distribution of birds in Prince William Sound, Alaska. We conducted post-spill surveys during mid-summer (1989-1991) in 10 bays that had been surveyed prior to the spill (1984-1985) and that had experienced different levels of initial oiling from the spill (unoiled to heavily oiled). We evaluated whether there were changes in overall abundance across all bays between the pre-spill and post-spill sampling periods, and changes in abundance in unoiled/lightly oiled bays versus moderately/heavily oiled bays that would suggest oiling impacts. Of 12 taxa examined for changes in overall abundance, 7 showed no significant change, 2 (Bald Eagle and Glaucous-winged Gull) increased in abundance, and 3 (Red-necked Grebe, Pelagic Cormorant, and Pigeon Guillemot) decreased in abundance during all three post-spill years. Of the 11 taxa examined for differences in use of oiled versus unoiled habitats, 7 showed no significant response, I (Black-legged Kittiwake) exhibited a positive response to oiling, and 3 (Pelagic Cormorant, Black Oystercatcher, and Pigeon Guillemot) exhibited negative responses to initial oiling. We conclude that the impacts of this oil spill on abundance and distribution of birds were most evident in 1989, the year of the spill, and were most pronounced for Pigeon Guillemots. By 1991, signs of recovery were evident for all taxa that showed initial oiling impacts.

Bioavailability of polycyclic aromatic hydrocarbons from buried shoreline oil residues thirteen years after the Exxon Valdez oil spill: A multispecies assessment

Seven taxa of intertidal plants and animals were sampled at 17 shoreline sites in Prince William Sound ([PWS]; AK, USA), that were heavily oiled in 1989 by the Exxon Valdez oil spill (EVOS) to determine if polycyclic aromatic hydrocarbons (PAH) from buried oil in intertidal sediments are sufficiently bioavailable to intertidal prey organisms that they might pose a health risk to populations of birds and wildlife that forage on the shore. Buried residues of EVOS oil are present in upper and middle intertidal sediments at 16 sites. Lower intertidal (0 m) sediments contain little oil. Much of the PAH in lower intertidal sediments are from combustion sources. Mean tissue total PAH (TPAH) concentrations in intertidal clams, mussels, and worms from oiled sites range from 24 to 36 ng/g (parts per billion) dry weight; sea lettuce, whelks, hermit crabs, and intertidal fish contain lower concentrations. Concentrations of TPAH are similar or slightly lower in biota from unoiled reference sites. The low EVOS PAH concentrations detected in intertidal biota at oiled shoreline sites indicate that the PAH from EVOS oil buried in intertidal sediments at these sites have a low bioavailability to intertidal plants and animals. Individual sea otters or shorebirds that consumed a diet of intertidal clams and mussels exclusively from the 17 oiled shores in 2002 were at low risk of significant health problems. The low concentrations of EVOS PAH found in some intertidal organisms at some oiled shoreline sites in PWS do not represent a health risk to populations of marine birds and mammals that forage in the intertidal zone.

Toxicity of weathered Exxon Valdez crude oil to pink salmon embryos

Research was conducted at the University of Idaho (Moscow, ID, USA) on the toxicity of weathered Exxon Valdez crude oil to embryos of pink salmon from 2001 to 2003 for the purpose of comparing these data with those from the National Oceanic and Atmospheric Administration Fisheries Laboratory at Auke Bay (AK, USA). Mortality reported at Auke Bay for embryos chronically exposed to very low concentrations of aqueous solutions of weathered oil, measured as dissolved polycyclic aromatic hydrocarbons (PAHs), was inconsistent with that in other published research. Using the Auke Bay experimental design, we found that toxicity is not evident in pink salmon embryos until chronic exposure to laboratory weathered and naturally weathered oil concentrations exceeding 1,500 and 2,250 ppm, respectively, representing a total PAH tissue burden in excess of 7,100 ppb. Effluent hydrocarbons also drop well below concentrations sufficient to cause harm over the time frame of a few weeks, regardless of oiling level. Resolution of differences with Auke Bay involved the source of contributing hydrocarbons. The experimental design did not exclude dispersed oil droplets from the aqueous solution; thus, toxicity was not limited to the dissolved hydrocarbon fraction. The implications of the present results are discussed regarding the toxic risk of weathered oil to pink salmon embryos in streams of Prince William Sound (AK, USA).

Hypotheses concerning the decline and poor recovery of Pacific herring in Prince William Sound, Alaska

This paper updates previous reviews of the 1993 stock decline of Pacific herring (Clupea pallasi) in Prince William Sound, Alaska, and focuses on hypotheses about subsequent poor recovery. Recent age structured assessment modeling with covariate analysis indicates that the population dynamics of the sound’s herring are influenced by oceanic factors, nutrition, and, most substantially, hatchery releases of juvenile pink salmon. For the 1993 decline, poor nutrition remains the most probable cause with disease a secondary response. Concerning poor recovery, we examined 16 potential factors and found three to be causal: oceanic factors, poor nutrition, and hatchery releases of juvenile pink salmon. Absences of strong year classes at both Sitka and Prince William Sound after 1993 indicate the action of large-scale ocean processes. Beyond regional-scale environmental factors, two factors specific to the sound influence the population dynamics of herring and are likely impeding recovery. First, pink salmon fry releases have increased to about 600 million annually and may disrupt feeding in young herring, which require adequate nutrition for growth and overwintering survival. Juvenile pink salmon and age-1 herring co-occur in nearshore areas of bays in late spring and summer, and available data on dietary overlap indicates potential competition between the age-1 juvenile herring and juvenile pink salmon. Field studies demonstrate that juvenile herring reduce food intake substantially in the presence of juvenile pink salmon. Second, overwintering humpback whales may consume potentially large amounts of adult herring, but further studies must confirm to what extent whale predation reduces herring biomass.

CHANGING HABITAT AND HABITAT USE BY BIRDS AFTER THE EXXON VALDEZ OIL SPILL, 1989–2001

Evaluations of the ecological consequences of environmental accidents can benefit from a long-term perspective. To assess the effects of the Exxon Valdez oil spill on habitat use and occupancy during midsummer by marine-oriented birds over a 12-yr period following the spill in 1989, we conducted surveys in 10 study bays in Prince William Sound, Alaska, USA. These bays varied from completely unoiled to some of the most heavily oiled locations in the spill zone. We used oiling as a quantitative variable with and without habitat measures as covariates to assess spill effects and their changes over time. We also used oiling as a categorical variable (“oiled” vs. “unoiled” bays) to conduct between-year, repeated-measures analyses that used 1984 data as a baseline and to plot abundance trends by oiling category. We combined the results of these analyses in a “weight-of-evidence” approach to determine overall impacts and recovery for each species. To assess changes in habitat condition following the oil spill, w...

Caribou distribution near an oilfield road on Alaska's North Slope, 1978-2001

Abstract Previous research in the Milne Point oilfield in northern Alaska showed that the density of caribou (Rangifer tarandus) in the calving period within 1 km of a road was significantly lower after construction than before construction of the road. This was interpreted as displacement from the road and a functional loss of habitat and has been extensively cited as a documented effect of oilfield development on caribou. We continued this study with additional aerial surveys flown during 1991–2001 and compared caribou numbers and density in 6 1-km intervals from the road over 3 time periods: pre-road construction (1978–1981), early post-road construction (1982–1987), and recent post-road construction (1991–2001). During the recent post-road period, the densities of calves and of all caribou were not significantly lower within 1 km of the road than the densities in the pre-road period. In addition, calf density was higher in the interval within 1 km of the road than in the intervals 1–6 km from the road during the recent post-road construction period. The total number of calving caribou observed in the study area has declined since pre-road construction and early post-road periods, but we found no evidence that caribou using the area during calving avoided areas near the road during the recent post-road period. Numbers of caribou in the study area during the post-calving period (after 20 June) during 1991–2001 were highly variable, but generally were higher than during calving. Analyses of relationships between calving and post-calving caribou densities and distance intervals from Milne Point Road suggested that distributions of calves and adult caribou were not strongly influenced by presence of the road.

Hydraulic Sampling Protocol to Estimate Natural Embryo Mortality of Pink Salmon

Abstract Productivity of naturally spawning salmon populations is sometimes estimated by sampling incubating eggs from the spawning grounds to assess survival by pumping water or an air–water mixture into the stream gravel and collecting eggs displaced by the resulting agitation. General knowledge regarding embryo sensitivity to physical shock indicates that this procedure may kill eggs if conducted before embryo development has advanced beyond blastopore closure, which is up to day 12 postfertilization. In 1998, we assessed the impact of sample timing on egg mortality estimates of pink salmon Oncorhynchus gorbuscha in 10 spawning streams in Prince William Sound, Alaska, by hydraulically sampling the same streams in September and again in October. The mean egg mortality was significantly higher in the early sampling period (63.6%) than in the later sampling period (22.8%). Results from examining stage of advancement at the time of embryo death indicate that sampling with hydraulic techniques will elevate ...

A Quantitative Ecological Risk Assessment of the Toxicological Risks from Exxon Valdez Subsurface Oil Residues to Sea Otters at Northern Knight Island, Prince William Sound, Alaska

ABSTRACT A comprehensive, quantitative risk assessment is presented of the toxicological risks from buried Exxon Valdez subsurface oil residues (SSOR) to a subpopulation of sea otters (Enhydra lutris) at Northern Knight Island (NKI) in Prince William Sound, Alaska, as it has been asserted that this subpopulation of sea otters may be experiencing adverse effects from the SSOR. The central questions in this study are: could the risk to NKI sea otters from exposure to polycyclic aromatic hydrocarbons (PAHs) in SSOR, as characterized in 2001–2003, result in individual health effects, and, if so, could that exposure cause subpopulation-level effects? We follow the U.S. Environmental Protection Agency (USEPA) risk paradigm by: (a) identifying potential routes of exposure to PAHs from SSOR; (b) developing a quantitative simulation model of exposures using the best available scientific information; (c) developing scenarios based on calculated probabilities of sea otter exposures to SSOR; (d) simulating exposures for 500,000 modeled sea otters and extracting the 99.9% quantile most highly exposed individuals; and (e) comparing projected exposures to chronic toxicity reference values. Results indicate that, even under conservative assumptions in the model, maximum-exposed sea otters would not receive a dose of PAHs sufficient to cause any health effects; consequently, no plausible toxicological risk exists from SSOR to the sea otter subpopulation at NKI.

There Is No Need To Be Normal: Generalized Linear Models of Natural Variation

Both ecological field studies and attempts to extrapolate from laboratory experiments to natural populations generally encounter the high degree of natural variability and chaotic behavior that typify natural ecosystems. Regardless of this variability and non-normal distribution, most statistical models of natural systems use normal error which assumes independence between the variance and mean. However, environmental data are often random or clustered and are better described by probability distributions which have more realistic variance to mean relationships. Until recently statistical software packages modeled only with normal error and researchers had to assume approximate normality on the original or transformed scale of measurement and had to live with the consequences of often incorrectly assuming independence between the variance and mean. Recent developments in statistical software allow researchers to use generalized linear models (GLMs) and analysis can now proceed with probability distributio...

On Drawing Conclusions Nine Years After the Exxon Valdez Oil Spill

Abstract We comment on the paper of Irons et al. (2000), which evaluated the status of several marine bird taxa in Prince William Sound, Alaska, nine years after the Exxon Valdez oil spill. We discuss concerns about the effects on the study design of inherent differences between the oiled and unoiled areas; about interpretations of results that use inconsistent criteria to define the spatial scales of analysis; and about explanations of underlying causes that are not empirically founded. These comments highlight general difficulties in assessing the effects of large-scale environmental perturbations. It is important to draw conclusions about the effects of such events, but the conclusions must be founded on accuracy in reporting study results, caution in interpreting the results, and adequate consideration of alternative causal explanations for the observed results. Acerca de Inferir Conclusiones Nueve Años después del Derrame de Petróleo del Exxon Valdez Resumen. Comentamos el artículo de Irons et al. (2000), que evaluó el estado de varios taxa de aves marinas en Prince William Sound, Alaska, nueve años después del derrame de petróleo del Exxon Valdez. Discutimos inquietudes acerca de los efectos del diseño del estudio en relación a diferencias inherentes entre las áreas afectadas y no afectadas por el petróleo; sobre las interpretaciones de los resultados que usan criterios incosistentes para definir las escalas espaciales del análisis; y sobre explicaciones de causas subyacentes que no están empíricamente fundamentadas. Estos comentarios resaltan las dificultades generales en establecer los efectos de grandes perturbaciones ambientales. Es importante inferir conclusiones sobre los efectos de dichos eventos, pero estas conclusiones deben considerar la presición de los resultados presentados, ser precavidas al interpretar los resultados, y considerar adecuadamente explicaciones causales alternativas para los resultados observados.