Declining Marbled Murrelet density, but not productivity, in the San Juan Islands, Washington, USA

Abstract

ABSTRACT The Marbled Murrelet (Brachyramphus marmoratus) is federally threatened in part of its range in western North America. Information on density and productivity is important for managing populations. Over an 18-yr period, we monitored murrelet density and productivity ratios during the breeding season along 170 km of shoreline of the San Juan Islands, Washington, USA. While murrelets occur throughout the coastal marine waters of Washington, the San Juan Islands support higher densities of murrelets during the breeding season than most other areas. From 1995 to 2012, the average density of adult murrelets declined significantly from 11.16 to 5.76 murrelets km−2, a decline that mirrored large-scale at-sea surveys in Washington. Despite this consistent and ominous decline in overall murrelet density, the density of juvenile murrelets and murrelet productivity ratio (juveniles:adults) did not decline over this time period. Thus, the declining density of murrelets in the San Juan Islands was due to decl...