Monitoring Kittlitz's and marbled murrelets in Glacier Bay National Park and Preserve: 2009 annual report

Hoekman, Steven; Moynahan, Brendan; Lindberg, Mark

SEAN has embarked on a two-year effort of evaluating alternative sampling and analytic strategies for monitoring. In 2009, we focused on testing current survey methods and better tailoring field and analytic methods to suit our study system. Specifically, our objectives were to 1) implement boat-based line transect surveys to estimate abundance and distribution of Kittlitz's murrelets, and secondarily of marbled murrelets, in Glacier Bay, 2) test the critical assumption of complete detection near the transect center line ("center line"), 3) compare line versus strip transect methods, 4) assess performance of 1 versus 2 observers, and 5) extend analytic methods to account for incomplete detection and species identification. During July 2009, we implemented a stratified, random, spatially-balanced sampling design with reasonable coverage of Glacier Bay and sampled 219 km on 53 transects. We estimated detection probability near the center line as 0.94 (SE = 0.03). Relative to 1 observer, 2 observers had 56% higher encounter rates, had >20% higher probability of species identification, and better met assumptions of line transect sampling. We identified 47% of observed murrelets to species and estimated detection of murrelet groups at 150 m from the center line was <50%. Using line transect methods in concert with novel analytic methods accounting for incomplete detection and identification, we estimated an abundance of 13,124 ± 4,602 (ݔ ±̅SE) Kittlitz's and 28,978 ±4,077 marbled murrelets on the water in our 1,092 km2 study area in July 2009. Please refer to the synthesis and program review report for monitoring of Kittlitz's murrelets in Glacier Bay National Park and Preserve which contains important findings that may affect the interpretation of abundance estimates (Hoekman, S. T. 2019. Kittlitz’s murrelet monitoring in Glacier Bay National Park and Preserve 2010–2018: Synthesis and program review. Natural Resource Report NPS/SEAN/NRR—2019/1957. National Park Service, Fort Collins, Colorado, https://irma.nps.gov/DataStore/Reference/Profile/2265288). The report summarizes the results of murrelet monitoring from 2010-2018, assesses monitoring performance and capacity to meet protocol objectives, and provides recommendations for potential enhancements to the monitoring protocol. Hoekman (2019) identifies misidentification and partial identification of murrelets which can bias abundance estimation and spatially-explicit density estimates, particularly for rare species, such as Kittlitz’s murrelets.

Monitoring Kittlitz's and marbled murrelets in Glacier Bay National Park and Preserve: 2009 annual report

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