Geology topics

Elizabeth M. Phillips

Publications and source records attributed to Elizabeth M. Phillips.

3 recordsLinked to original sources

USGS2019

Does perspective matter? A case study comparing Eulerian and Lagrangian estimates of common murre (Uria aalge) distributions

Studies estimating species' distributions require information about animal locations in space and time. Location data can be collected using surveys within a predetermined frame of reference (i.e., Eulerian sampling) or from animal‐borne tracking devices (i.e., Lagrangian sampling). Integration of observations obtained from Eulerian and Lagrangian perspectives can provide insights into animal movement and habitat use. However, contemporaneous data from both perspectives are rarely available, making examination of biases associated with each sampling approach difficult. We compared distributions of a mobile seabird observed concurrently from ship, aerial, and satellite tag surveys during May, June, and July 2012 in the northern California Current. We calculated utilization distributions to quantify and compare variability in common murre (Uria aalge) space use and examine how sampling perspective and platform influence observed patterns. Spatial distributions of murres were similar in May, regardless of sampling perspective. Greatest densities occurred in coastal waters off southern Washington and northern Oregon, near large murre colonies and the mouth of the Columbia River. Density distributions of murres estimated from ship and aerial surveys in June and July were similar to those observed in May, whereas distributions of satellite‐tagged murres in June and July indicated northward movement into British Columbia, Canada, resulting in different patterns observed from Eulerian and Lagrangian perspectives. These results suggest that the population of murres observed in the northern California Current during spring and summer includes relatively stationary individuals attending breeding colonies and nonstationary, vagile adults and subadults. Given the expected growth of telemetry studies and advances in survey technology (e.g., unmanned aerial systems), these results highlight the importance of considering methodological approaches, spatial extent, and synopticity of distribution data sets prior to integrating data from different sampling perspectives.

Washington↗

USGS2018

Selective occupancy of a persistent yet variable coastal river plume by two seabird species

Advances in telemetry and modeling of physical processes expand opportunities to assess relationships between marine predators and their dynamic habitat. The Columbia River plume (CRP) attracts sooty shearwaters Ardenna grisea and common murres Uria aalge , but how seabirds respond to variability in plume waters is unknown. We characterized seabird distributions in relation to hourly, daily, monthly, and seasonal variation in CRP location and surface area by attaching satellite telemetry tags to shearwaters in 2008 and 2009, and to murres in 2012 and 2013. We matched seabird locations to surface salinity from a high-resolution hydrodynamic model of the CRP and adjacent waters. Utilization distributions indicated high-use areas north of the Columbia River mouth and in continental shelf waters. Shearwater and murre occupancy of tidal (<21 psu), recirculating (21-26 psu), and boundary (26-31 psu) plume waters was on average 31% greater than expected and positively correlated with CRP surface area. Seabird latitude was positively correlated with latitude of the geographic center of the CRP, indicating that birds move in phase with the plume. We detected a threshold response of seabirds to plume size, and birds were closer to the convergent CRP boundary (28 psu isohaline) after a surface area threshold between 1500 and 4000 km 2 was exceeded. We conclude that shearwaters and murres selectively occupy and track plume waters, particularly dynamic boundary waters where foraging opportunities may be enhanced by increases in surface area and associated biophysical coupling that aggregates zooplankton and attracts prey fishes.

Marine Ecology Progress Series↗

USGS2017

Best practices for assessing forage fish fisheries-seabird resource competition

Worldwide, in recent years capture fisheries targeting lower-trophic level forage fish and euphausiid crustaceans have been substantial (∼20 million metric tons [MT] annually). Landings of forage species are projected to increase in the future, and this harvest may affect marine ecosystems and predator-prey interactions by removal or redistribution of biomass central to pelagic food webs. In particular, fisheries targeting forage fish and euphausiids may be in competition with seabirds, likely the most sensitive of marine vertebrates given limitations in their foraging abilities (ambit and gape size) and high metabolic rate, for food resources. Lately, apparent competition between fisheries and seabirds has led to numerous high-profile conflicts over interpretations, as well as the approaches that could and should be used to assess the magnitude and consequences of fisheries-seabird resource competition. In this paper, we review the methods used to date to study fisheries competition with seabirds, and present “best practices” for future resource competition assessments. Documenting current fisheries competition with seabirds generally involves addressing two major issues: 1) are fisheries causing localized prey depletion that is sufficient to affect the birds? (i.e., are fisheries limiting food resources?), and 2) how are fisheries-induced changes to forage stocks affecting seabird populations given the associated functional or numerical response relationships? Previous studies have been hampered by mismatches in the scale of fisheries, fish, and seabird data, and a lack of causal understanding due to confounding by climatic and other ecosystem factors (e.g., removal of predatory fish). Best practices for fisheries-seabird competition research should include i) clear articulation of hypotheses, ii) data collection (or summation) of fisheries, fish, and seabirds on matched spatio-temporal scales, and iii) integration of observational and experimental (including numerical simulation) approaches to establish connections and causality between fisheries and seabirds. As no single technique can provide all the answers to this vexing issue, an integrated approach is most promising to obtain robust scientific results and in turn the sustainability of forage fish fisheries from an ecosystem perspective.

Fisheries Research↗