Estimation of Pup Production of Hooded and Harp Seals in the Greenland Sea in 2007: Reducing Uncertainty Using Generalized Additive Models

The pup production of the Greenland Sea populations of hooded and harp seals were assessed in
aerial surveys using two aircrafts for reconnaissance flights and photographic surveys along transects
over the whelping areas from 14 March to 3 April 2007. One helicopter, operated from the applied
expedition vessel, flew reconnaissance flights, monitored the distribution of seal patches and
performed age-staging of the pups. The total estimate of hooded seal pup production was 16 140
(SE = 2 140, CV = 13.3%), which is similar to an estimate obtained for comparable surveys in 2005.
The total pup production estimate obtained for harp seals was 110 530 (SE = 27 680, CV = 25.0%),
which is slightly higher than an estimate obtained for a similar survey in 2002. The pup production
and the uncertainty of the pup production estimate were estimated using a standard method
for analyzing this type of survey data and a recently developed method that utilized Generalized
Additive Models (GAMs). Using the two estimation methods on data from all three surveys (2002,
2005, 2007), comparable estimates of pup production were obtained. In scenarios where pups were
clustered, the estimated uncertainty of the pup production estimate was much lower for the GAM
method than for the conventional method. This resulted in a considerable reduction of the estimated
coefficient of variation. In scenarios where pups were uniformly distributed, both methods performed
the same.