Kruuk et al. (1989) used a stratified sample to estimate the number of otter (Lutra lutra) dens along the 1400-km coastline of Shetland, UK. The coastline was divided into 242 (237 that were not predominantly buildings) 5-km sections, and each section was assigned to the stratum whose terrain type predominated. Then sections were chosen randomly from the sections in each stratum. In each section chosen, the investigators counted the total number of dens in a 110-m-wide strip along the coast. The data are in file otters.dat. The population sizes for the strata are as follows:

Estimate the total number of otter dens in Shetland, along with a standard error for your estimate.