CORRECTING AERIAL SURVEY COUNTS OF HARBOR SEALS (PHOCA VITULINA RICHARDSI) IN WASHINGTON AND OREGON

Aerial surveys of harbor seals on land produce only a minimum assessment of the population; a correction factor to account for the missing animals is necessary to estimate total abundance. In 1991 and 1992, VHF radio tags were deployed on harbor seals ( n = 124) at six sites in Washington and Oregon. During aerial surveys a correction factor to account for seals in the water was determined from the proportion of radio-tagged seals on shore during the pupping season. This proportion ranged from 0.54 to 0.74. Among the six sites there was no significant difference in the proportion of animals on shore nor was there a difference in age/sex categories of seals on shore between sites. The pooled correction factor for determining total population abundance was 1.53. An additional 32 seals were radio tagged in 1993 at one of the sites used in 1991. Comparing data from the two years, we found no interannual variation. Aerial surveys of all known harbor seal haul-out sites in Washington ( n = 319) and Oregon ( n = 68) were flown during the peak of the pupping season, 1991–1993. The Washington and Oregon harbor seal population was divided into two stocks based on pupping phenology, morphometics, and genetics. Mean counts for the Washington inland stock were 8,710 in 1991, 9,018 in 1992, and 10,092 in 1993. Oregon and Washington coastal stock mean counts were 18,363 in 1991, 18,556 in 1992, and 17,762 in 1993. Multiplying the annual count by the correction factor yielded estimates of harbor seal abundance in the Washington inland stock of 13,326 (95% CI = 11,637–15,259) for 1991, 13,798 (95% CI = 11,980–15,890) for 1992, and 15,440 (95% CI = 13,382–17,814) for 1993. In the Oregon and Washington coastal stock the corrected estimate of harbor seal abundance was 28,094 (95% CI = 24,697–31,960) in 1991, 28,391 (95% CI = 24,847–32,440) for 1992, and 27,175 (95% CI = 23,879–30,926) for 1993.     

A.T----C.G transversions and their prevention by the Escherichia coli mutT and mutHLS pathways

Summary Escherichia coli mutT strains are strong mutators yielding only A · T C · G transversion mutations. These are thought to result from uncorrected (or unprevented) A · G mispairings during DNA replication. We have investigated the interaction of mutT-induced replication errors with the mutHLS-encoded postreplicative mismatch repair system. By measuring mutation frequencies in both forward and reversion systems, we have demonstrated that mutTmutL and mutTmutS double mutators produce no more mutants than expected from simple additivity of the frequencies in the single mutators. We conclude that mutT-induced A · G replication errors are not recognized by the MutHLS system. On the other hand, direct measurements of mismatch repair by transfection of bacteriophage M13mp2 heteroduplex DNA as well as mutational data from strains other than mutT indicate that the MutHLS system can repair at least certain A · G mispairs. We suggest that A · G mispairs may exist in several different conformations, some of which are recognized by the MutHLS system. However, the A · G mispairs normally prevented by the mutT function are refractory to mismatch repair, indicating that they may represent a structurally distinct class.     

Polarized dosimetry method for Gafchromic EBT3

PurposeTo analyze the changes in the polarization state of the flatbed scanner light caused by the EBT3 films and to propose a new method for correcting the lateral effects.Methods and materialsThe polarization changes induced by radiochromic films are analyzed using linear polarizing film. Based on the results, the linear polarizing films are used in the scanning process of the EBT3 films. This method is tested against the conventional EBT3 dosimetry using a series of simple regular beams and 21 cases of IMRT.ResultsThe mean results are statically different from the conventional dosimetry with EBT3. Depending on the transmission axis of the polarizing sheet, the results are better or worse compared to conventional dosimetry EBT3 film. When the transmission axis of the polarizing sheet is parallel to the coating direction, the dosimetry results are better and its variability is smaller. However, when the polarizer transmission axis is perpendicular to the coating direction, results are worse as well as its variability.ConclusionUsing a polarized film with the polarization axis parallel to the coating direction of the radiochromic film, and preferably above it, significantly improves the dosimetry results and is an easy and inexpensive way to correct the lateral artifacts of the conventional EBT3 dosimetry.     

Intensity-based energy transfer measurements in digital imaging microscopy

Investigation of protein-protein associations is important in understanding structure and function relationships in living cells. Using Förster-type resonance energy transfer between donor and acceptor labeled monoclonal antibodies we can assess the cell surface topology of membrane proteins against which the antibodies were raised. In our current work we elaborated a quantitative image microscopic technique based on the measurement of fluorescence intensities to calculate the energy transfer efficiency on a pixel-by-pixel basis. We made use of the broad excitation and emission spectrum of cellular autofluorescence for background correction of images. In addition to the reference autofluorescence images (UV background) we recorded three fluorescent images (donor, acceptor and energy transfer signal) of donor-acceptor double labeled samples, and corrected for spectral spillage of the directly excited donor and acceptor fluorescence into the energy transfer image. After careful image registration we were able to calculate the energy transfer efficiency on a pixel-by-pixel basis. In this paper, we also present a critical comparison between results obtained with this method and other approaches (photobleaching and flow cytometric energy transfer measurements).     

Estimation of the Transition/Transversion Ratio

A simple method for estimating the transition/transversion ratio was developed. This method can be applied to not only two sequences but also more than two sequences. The statistical properties of the method and some other methods were examined by numerical computation and computer simulation. The results obtained showed that, in terms of bias and variance, the new method gives a better estimate of the transition/transversion ratio than do the other examined methods. The new method was applied to human and chimpanzee mitochondrial control region sequences. Received: 22 September 1997 / Accepted: 1 November 1997     

Maximum likelihood population size estimation of harbour seals in the Dutch Wadden Sea based on a mark–recapture experiment

1. The harbour seal population Phoca vitulina in the entire Wadden Sea was severely depleted due to a virus-epizootic during 1988. A comprehensive study on the population biology and activity patterns was subsequently initiated to design a management and conservation plan. The main objective of this study was to estimate harbour seal abundance in the different regions of the Wadden Sea.
2. We investigated the potential of a mark–recapture experiment using VHF radio-tags in combination with repeated aerial surveys to estimate the number of harbour seals in the Dutch part of the Wadden Sea. The number of harbour seals hauled-out and the presence of any radio-tagged seals was monitored during seven aerial surveys of all known haul-out sites in the Dutch Wadden Sea over the 1994 breeding season.
3. A maximum likelihood (ML) estimator was developed to infer the rate of tag-loss and the size of the local prepupping population.
4. The ML estimate of the number of harbour seals in the Dutch Wadden Sea was 1536 (95% confidence limits were 1225 and 2200). The corresponding maximum proportion of seals hauled-out was 68%.
5. The use of VHF radio-tags which can be monitored from the air provides a way of correcting aerial survey counts for the proportion of harbour seals hauled-out during the surveys. Since haul-out behaviour may be influenced by local conditions, such as exposure time of sand banks, we recommend this technique be repeated in other areas of the Wadden Sea rather than using the estimates from the current study in other areas.