Simulated likelihood methods for complex double-platform line transect surveys

The conventional line transect approach of estimating effective search widt h from the perpendicular distance distribution is inappropriate in certain types of surveys e.g., when an unknown fraction of the animals on the track line is detected, the animals can be observed only at discrete points in t ime, there are errors in positional measurements, and covariate heterogenei ty exists in detectability. For such situations a hazard probability framew ork for independent observer surveys is developed. The likelihood of the da ta, including observed positions of both initial and subsequent observation s of animals, is established under the assumption of no measurement errors. To account for measurement errors and possibly of her complexities, this l ikelihood is modified by a function Estimated from extensive simulations. T his general method of simulated likelihood is explained and the methodology applied to data from a double-platform survey of minke whales in the north eastern Atlantic in 1995.