Geology topics

D.D. Roby

Publications and source records attributed to D.D. Roby.

21 records · Page 2Linked to original sources

USGS2002

Response of pigeon guillemots to variable abundance of high-lipid and low-lipid prey

Populations of the pigeon guillemot (Cepphus columba) and other piscivores have been in decline for several decades in the Gulf of Alaska and Bering Sea, and a decline in abundance of lipid-rich schooling fishes is hypothesized as the major cause. We tested this hypothesis by studying the breeding biology of pigeon guillemots during 1995-1999 while simultaneously measuring prey abundance with beach seines and bottom trawls. Our study area (Kachemak Bay, Alaska) comprises two oceanographically distinct areas. Populations of a lipid-rich schooling fish, Pacific sand lance (Ammodytes hexapterus), were higher in the warmer Inner Bay than in the colder Outer Bay, and sand lance abundance was higher during warm years. Populations of low-lipid content demersal fishes were similar between areas. Chick survival to age 15 days was 47% higher in the Inner Bay (high-lipid diet) than in the Outer Bay (low-lipid diet), and estimated reproductive success (chicks fledged nest-1) was 62% higher in the Inner Bay than in the Outer Bay. Chick provisioning rate (kJ chick-1 h-1) increased with the proportion of sand lance in the diet (r2=0.21), as did growth rate (g day-1) of younger (beta) chicks in two-chick broods (r2=0.14). Pigeon guillemots in the Inner Bay switched to demersal prey during years of below-average sand lance abundance, and these birds reacted to 38-fold interannual changes in sand lance abundance with reductions in beta chick growth rates, with no decline in beta chick survival. In contrast, the proportion of nests experiencing brood reduction in the Outer Bay (demersal diet) increased >300% during years of below-average demersal abundance, although demersal fish abundance varied only 4-fold among years. Our results support the hypothesis that recovery of pigeon guillemot populations from the effects of the Exxon Valdez oil spill is limited by availability of lipid-rich prey.

Oecologia↗

USGS2000

Comparison of pigeon guillemot, Cepphus columba, blood parameters from oiled and unoiled areas of Alaska eight years after the Exxon Valdez oil spill

In 1997, we compared the haematological and plasma biochemical profiles among populations of pigeon guillemots, Cepphus columba, in areas oiled and not oiled by the 1989 Exxon Valdez oil spill (EVOS) that occurred in Prince William Sound (PWS), Alaska. Pigeon guillemot populations in PWS were injured by EVOS and have not returned to pre-spill levels. If oil contamination is limiting recovery of pigeon guillemots in PWS, then we expected that blood parameters of pigeon guillemots would differ between oiled and unoiled areas and that these differences would be consistent with either toxic responses or lower fitness. We collected blood samples from chicks at approximately 20 and 30 days after hatching. Physiological changes associated with chick growth were noted in several blood parameters. We found that only calcium and mean cell volume were significantly different between the chicks in oiled and unoiled areas. Despite these differences, blood biomarkers provided little evidence of continuing oil injury to pigeon guillemot chicks, eight years after the EVOS. Preliminary data from adults indicated elevated aspartate aminotransferase activity in the adults from the oiled area, which is consistent with hepatocellular injury. Because adults have greater opportunities for exposure to residual oil than nestlings, we recommend studies that fully evaluate the health of adults residing in oiled areas. (C) 2000 Elsevier Science Ltd.

Marine Pollution Bulletin↗

USGS2000

Sexing adult black-legged kittiwakes by DNA, behavior, and morphology

We sexed adult Black-legged Kittiwakes ( Rissa tridactyla ) using DNA-based genetic techniques, behavior and morphology and compared results from these techniques. Genetic and morphology data were collected on 605 breeding kittiwakes and sex-specific behaviors were recorded for a sub-sample of 285 of these individuals. We compared sex classification based on both genetic and behavioral techniques for this sub-sample to assess the accuracy of the genetic technique. DNA-based techniques correctly sexed 97.2% and sex-specific behaviors, 96.5% of this sub-sample. We used the corrected genetic classifications from this sub-sample and the genetic classifications for the remaining birds, under the assumption they were correct, to develop predictive morphometric discriminant function models for all 605 birds. These models accurately predicted the sex of 73-96% of individuals examined, depending on the sample of birds used and the characters included. The most accurate single measurement for determining sex was length of head plus bill, which correctly classified 88% of individuals tested. When both members of a pair were measured, classification levels improved and approached the accuracy of both behavioral observations and genetic analyses. Morphometric techniques were only slightly less accurate than genetic techniques but were easier to implement in the field and less costly. Behavioral observations, while highly accurate, required that birds be easily observable during the breeding season and that birds be identifiable. As such, sex-specific behaviors may best be applied as a confirmation of sex for previously marked birds. All three techniques thus have the potential to be highly accurate, and the selection of one or more will depend on the circumstances of any particular field study.

Alaska↗