Graduate Thesis Or Dissertation
 

Effects of diet and crude oil ingestion on growth and biochemistry of captive-reared pigeon guillemots (Cepphus columba)

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  • The pigeon guillemot (Cepphus columba) population in Prince William Sound has failed to recover from declines that occurred both before and after the Exxon Valdez Oil Spill (EVOS). Post-spill studies of pigeon guillemot breeding biology have identified three potential factors limiting recovery: (1) predation on eggs and nestlings; (2) declines in the proportion of high-lipid, schooling forage fish (sand lance [Ammodytes hexapterus], herring [Clupea pallasi], and capelin [Mallotus villosus]) in the diet; and (3) continued exposure to residual oil from the spill. This laboratory study with captive-reared pigeon guillemots at the Alaska SeaLife Center investigated two aspects of the species' biology that are relevant to restoration in the aftermath of EVOS. First, we investigated the role of dietary factors (prey type, quantity of food consumed, dietary fat content, and energy intake rate) in limiting the growth, development, survival, and fledging condition of nestling pigeon guillemots. The objective was to understand how changes in prey availability and prey quality might affect pigeon guillemot productivity. Second, we fed nestlings sublethal doses of weathered Prudhoe Bay crude oil (PBCO) and then measured several potential biomarkers of effects from this pollutant. These dose-response experiments were designed to (1) better understand the impact on nestling guillemots of petroleum hydrocarbons in food, (2) calibrate existing and potential biomarkers of exposure to PBCO in pigeon guillemots in a controlled, laboratory setting, and (3) develop better nondestructive biomarkers of exposure to PBCO in pigeon guillemots in particular, and seabirds in general. Results of feeding experiments indicated that most variation in nestling growth rates could be explained by variation in daily energy intake. The type of forage fish consumed, the lipid or protein content of the forage fish, and even the quantity of food consumed daily did not have as strong an effect on nestling guillemot growth as did daily energy intake. The metabolic efficiency and growth performance of nestling guillemots was not enhanced on high-lipid diets, contrary to results with nestlings of some other seabird species. Instead, structural growth (wing length) in nestling guillemots was somewhat stunted on high-lipid diets. These attributes of guillemot nutritional requirements are associated with the guillemots' nearshore foraging niche and high food provisioning rates to nestlings. The average lipid content of sand lance, juvenile herring, and capelin may represent the optimal dietary lipid content for nestling pigeon guillemots. This study supports the hypothesis that guillemot productivity is limited by the availability of these forage fishes through effects on energy provisioning rates to nestling guillemots. Consequently, recovery of pigeon guillemot populations injured by EVOS is likely linked to recovery of these key forage fish stocks. Results of the oil-dosing experiments indicated that nestling guillemots are resistant to small doses of weathered PBCO in their food. No nestlings died or suffered noticeable health effects following dosing. The high dose in this study (0.5 ml kg⁻¹ day⁻¹) was sufficient to induce hepatic cytochrome P450A1 (a liver enzyme indicative of contaminant exposure), but growth rate, fledging mass, and blood chemistry were largely unaffected. None of the 12 plasma or hematological markers examined responded in a dose-dependent manner to ingestion of weathered PBCO, except lactate dehydrogenase (LDH). Although baseline stress hormone (corticosterone) levels were not different between oil-dosed and control nestlings, a standardized acute stress protocol revealed that corticosterone was more elevated during stress for oiled nestlings compared to controls. Although we were not successful in identifying a noninvasive biomarker (e.g., growth) or a blood biomarker (e.g., haptoglobin) of crude oil exposure in nestlings, we were able to confirm that levels of hepatic cytochrome P4SO1AI and corticosterone during stress were elevated by the sublethal doses administered during our experiments. Based on this and other studies, it is unlikely that the failure of pigeon guillemots to recover from EVOS is due to effects on nestling health of residual oil in food.
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