Offshore distribution, population size estimates, and productivity data for marbled murrelets in California and Oregon, 1989-2009

We evaluated spatial distribution and estimated population size and productivity of Marbled Murrelets offshore of California and Oregon from Moss Landing, California north to Coos Bay, Oregon from 1989 to 2009 using transect surveys from boats. From 1989 to 2000, we used a methodology with set distances from shore outward to 5000 meters offshore from which we derived population estimates and described distribution from shore. We found that we observed the majority of murrelets at the distances of 800 and 1400 meters so we started coastal surveys at these distances along the entire coast from Point Lobos, California to Coos Bay, Oregon from 1991 to 2000. From 2001 to 2009, our selection of transect locations changed as we participated in population monitoring for Marbled Murrelet Effectiveness Monitoring for the Northwest Forest Plan, where locations were divided into Primary Survey Units of 20 kilometers each along the shoreline with nearshore and offshore sampling areas. This data publication also includes boat surveys conducted during two oil spills that occurred in and offshore of Humboldt Bay, California in 1997 and 1999. During surveys, all species of birds and marine mammals encountered along the transects are recorded. Data are provided as both Microsoft Access databases (combination of ACCDB and MDB files) and comma-separated values files. Associated geospatial data for surveys are also included.
These data, collected offshore of northern California and Oregon, were used for the monitoring of Marbled Murrelet (Brachyrhamphus marmorata) populations.