Potential Utility of Using Fixed-wing Aircraft Either Alone or Jointly with Boats to Survey for Marbled Murrelets at Sea Draft report to the U.S. Fish and Wildlife Service

There is broad agreement both scientifically and politically that Marbled Murrelet populations, and their annual reproductive success, can not be monitored on their nesting grounds in old growth forest; instead, adult murrelets and their offspring must be monitored while they are on the ocean. Despite advances in our knowledge of the biology of murrelets at sea, a number of unresolved issues have prevented the development of an accepted standardized protocol for surveying for murrelets at sea. One such issue is whether murrelet survey data collected from fixed-wing aircraft can be useful by itself or in combination with data collected from boats by applying a visibility correction factor (VCF) to data collected from aircraft to correct for the reduced visibility of murrelets from aircraft relative to boats. This study addressed this issue. Using different methods, we calculated air:boat VCFs varying from 0.396 to 0.473 with coefficients of variation ranging from 6.0% to 95.9%. We conclude that aircraft may be useful for surveying for murrelets to address some questions, but probably are not accurate enough to provide sufficient statistical power for long-term monitoring programs. However, additional evaluation by biostatisticians and marine seabird researchers of various ratio estimators as appropriate VCF estimators is necessary before any firm conclusions can be reached.