15 research outputs found
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Marine bird aggregations associated with the tidally-driven plume and plume fronts of the Columbia River
Freshwater discharge from large rivers into the coastal ocean creates tidally-driven frontal systems
known to enhance mixing, primary production, and secondary production. Many authors suggest that
tidal plume fronts increase energy flow to fish-eating predators by attracting planktivorous fishes to feed
on plankton aggregated by the fronts. However, few studies of plume fronts directly examine piscivorous
predator response to plume fronts. Our work examined densities of piscivorous seabirds relative to the
plume region and plume fronts of the Columbia River, USA. Common murres (Uria aalge) and sooty
shearwaters (Puffinus griseus) composed 83% of all birds detected on mesoscale surveys of the
Washington and Oregon coasts (June 2003-2006), and 91.3% of all birds detected on fine scale surveys
of the plume region less than 40 km from the river mouth (May 2003 and 2006). Mesoscale comparisons
showed consistently more predators in the central plume area compared to the surrounding marine area
(murres: 10.1-21.5 vs. 3.4-8.2 birds km⁻²; shearwaters: 24.2-75.1 vs. 11.8-25.9 birds km⁻²). Fine scale
comparisons showed that murre density in 2003 and shearwater density in both 2003 and 2006 were
significantly elevated in the tidal plume region composed of the most recently discharged river water.
Murres tended to be more abundant on the north face of the plume. In May 2003, more murres and
shearwaters were found within 3 km of the front on any given transect, although maximum bird density
was not necessarily found in the same location as the front itself. Predator density on a given transect
was not correlated with frontal strength in either year. The high bird densities we observed associated
with the tidal plume demonstrate that the turbid Columbia River plume does not necessarily provide fish
with refuge from visual predators. Bird predation in the plume region may therefore impact early marine
survival of Pacific salmon (Oncorhynchus spp.), which must migrate through the tidal plume and plume
front to enter the ocean. Because murres and shearwaters eat primarily planktivorous fish such as the
northern anchovy (Engraulis mordax), aggregation of these birds in the plume supports the hypothesis
that it is the plume region as a whole, and not just the plume fronts, which enhances trophic transfer to
piscivorous predators via planktivorous fishes.Keywords: Marine birds, River plumes, USA, Tidal fronts, Columbia River, Predator prey interactions, Forage fish, Salmon, Washington, Orego
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Interannual variability in the Northern California Current food web structure: Changes in energy flow pathways and the role of forage fish, euphausiids, and jellyfish
The Northern California Current (NCC) is a seasonally productive and open ecosystem. It is home to both a diverse endemic community and to seasonally transient species. Productivity and food web structure vary seasonally, interannually, and decadally due to variability in coastal upwelling, climate-scale physical processes, and the migratory species entering the system. The composition of the pelagic community varies between years, including changes to mid-trophic level groups that represent alternate energy-transfer pathways between lower and upper trophic levels (forage fishes, euphausiids, jellyfish). Multiple data sets, including annual spring and summer mesoscale surveys of the zooplankton, pelagic fish, and seabird communities, were used to infer NCC trophic network arrangements and develop end-to-end models for each of the 2003–2007 upwelling seasons. Each model was used to quantify the interannual variability in energy-transfer efficiency from bottom to top trophic levels. When each model was driven under an identical nutrient input rate, substantial differences in the energy available to each functional group were evident. Scenario analyses were used to examine the roles of forage fishes, euphausiids, and jellyfish (small gelatinous zooplankton and large carnivorous jellyfish) as alternate energy transfer pathways. Euphausiids were the more important energy transfer pathway; a large proportion of the lower trophic production consumed was transferred to higher trophic levels. In contrast, jellyfish acted as a production loss pathway; little of the production consumed was passed upwards. Analysis of the range of ecosystem states observed interannually and understanding system sensitivity to variability among key trophic groups improves our ability to predict NCC ecosystem response to short- and long-term environmental change.This is the author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Elsevier and can be found at: http://www.sciencedirect.com/science/journal/00796611
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Baseline-Seabird-Assessment-Version 2.pdf
As part of the California Current Ecosystem Survey, NOAA Fisheries sponsored pairs of
seabird observers who collected quantitative information on marine bird species,
abundance, and behavior during all daylight hours when the ship was under way.
Observers participated on Leg 1 and Leg 2 of the April 2008 Miller Freeman survey, and
Legs 1, 2, and 3 of the July-August David Starr Jordan survey. OWET provided funding
for observers on Leg 2 of the April cruise and Legs 1 and 2 of the July cruise; data from
non-OWET funded legs are included for completeness.
This report is meant to provide a concise data summary of methods, survey dates and
locations, and relative abundance of bird species seen during the surveys. It is not a
final analysis, nor have data been fully processed to provide absolute abundances
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Baeline-Seabird-Assessment-Version 1.pdf
As part of the California Current Ecosystem Survey, NOAA Fisheries sponsored pairs of
seabird observers who collected quantitative information on marine bird species,
abundance, and behavior during all daylight hours when the ship was under way.
Observers participated on Leg 1 and Leg 2 of the April 2008 Miller Freeman survey, and
Legs 1, 2, and 3 of the July-August David Starr Jordan survey. OWET provided funding
for observers on Leg 2 of the April cruise and Legs 1 and 2 of the July cruise; data from
non-OWET funded legs are included for completeness.
This report is meant to provide a concise data summary of methods, survey dates and
locations, and relative abundance of bird species seen during the surveys. It is not a
final analysis, nor have data been fully processed to provide absolute abundances
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Marine Bird Surveys: California Current Ecosystem Survey - Marine Bird Surveys April 2008 and July-August 2008
As part of the California Current Ecosystem Survey, NOAA Fisheries sponsored pairs of seabird observers who collected quantitative information on marine bird species, abundance, and behavior during all daylight hours when the ship was under way. Observers participated on Leg 1 and Leg 2 of the April 2008 Miller Freeman survey, and Legs 1, 2, and 3 of the July-August David Starr Jordan survey. OWET provided funding for observers on Leg 2 of the April cruise and Legs 1 and 2 of the July cruise; data from non-OWET funded legs are included for completeness. This report is meant to provide a concise data summary of methods, survey dates and locations, and relative abundance of bird species seen during the surveys. It is not a final analysis, nor have data been fully processed to provide absolute abundances
Characterizing juvenile salmon predation risk during early marine residence.
Predation mortality can influence the distribution and abundance of fish populations. While predation is often assessed using direct observations of prey consumption, potential predation can be predicted from co-occurring predator and prey densities under varying environmental conditions. Juvenile Pacific salmon Oncorhynchus spp. (i.e., smolts) from the Columbia River Basin experience elevated mortality during the transition from estuarine to ocean habitat, but a thorough understanding of the role of predation remains incomplete. We used a Holling type II functional response to estimate smolt predation risk based on observations of piscivorous seabirds (sooty shearwater [Ardenna griseus] and common murre [Uria aalge]) and local densities of alternative prey fish including northern anchovy (Engraulis mordax) in Oregon and Washington coastal waters during May and June 2010-2012. We evaluated predation risk relative to the availability of alternative prey and physical factors including turbidity and Columbia River plume area, and compared risk to returns of adult salmon. Seabirds and smolts consistently co-occurred at sampling stations throughout most of the study area (mean = 0.79 ± 0.41, SD), indicating that juvenile salmon are regularly exposed to avian predators during early marine residence. Predation risk for juvenile coho (Oncorhynchus kisutch), yearling Chinook salmon (O. tshawytscha), and subyearling Chinook salmon was on average 70% lower when alternative prey were present. Predation risk was greater in turbid waters, and decreased as water clarity increased. Juvenile coho and yearling Chinook salmon predation risk was lower when river plume surface areas were greater than 15,000 km2, while the opposite was estimated for subyearling Chinook salmon. These results suggest that plume area, turbidity, and forage fish abundance near the mouth of the Columbia River, all of which are influenced by river discharge, are useful indicators of potential juvenile salmon mortality that could inform salmonid management
Predator-prey interactions influenced by a dynamic river plume
Marine predator-prey interactions are often influenced by oceanographic processes that aggregate prey. We examined density distributions of seabirds and prey fish associated with the Columbia River plume to determine if variation in plume size (i.e., volume or surface area) or location influences predator-prey interactions. Common murre (Uria aalge), sooty shearwater (Ardenna grisea), and forage fish including northern anchovy (Engraulis mordax) and juvenile salmon (Oncorhynchus spp.) occurred disproportionately in plume waters relative to adjacent marine waters. Water clarity, an indicator of plume-influenced waters, was a significant predictor of seabird and prey densities throughout the survey area. Murres occurred within 20 km of the plume center of gravity (CG) whereas shearwaters occurred ~100 km north of the plume CG, concurrent with highest densities of prey fish. Global indices of collocation were relatively low between murres and prey, compared to high values between shearwaters and prey. Seabird densities were negatively correlated with plume size, suggesting that seabirds concentrate in the plume to maximize foraging effort. We conclude that variation in Columbia River plume size and location influences predator distributions, which increases predation pressure on prey, including threatened salmonid species.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
Data from: 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 of each sampling approach difficult to quantify. 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 density distributions 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 non-stationary, 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
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Marine bird colony and at-sea distributions along the Oregon coast: Implications for marine spatial planning and information gap analysis
Increasingly diverse interests in commercial and recreational use of marine resources are creating new challenges for coastal ocean management. One concern of increased offshore use and development off the Oregon coast is the potential impact on marine bird populations. We summarized the primary surveys of seabird breeding colonies and at-sea distribution along the Oregon coast to describe spatial patterns in species distribution and identify gaps where additional data are needed. The abundance of breeding birds during the summer (over 1 million in total, primarily Common Murre Uria aalge and Leach’s Storm-Petrel Oceanodroma leucorhoa) is greatest in northern and southern Oregon due to the availability of breeding habitat on large offshore rocks and islands. While there are fewer breeding colonies along sandy shorelines, the adjacent coastal waters are still frequented by breeding birds and nonbreeding migrants, but generally in lower densities during summer. Seabird density, and likely potential interaction with offshore structures, is greatest nearshore and steadily declines to lowest levels beyond the outer continental shelf. Dynamic soaring species, however, which have a greater potential to interact with taller structures such as wind turbines, tend to be more common on the middle to outer shelf. Species composition also changes dramatically among seasons. Low flying (< 30 m above sea level) diving species dominate in most seasons, however, which has potential conservation implications for interactions with structures above and below the water’s surface. Given the abundance of storm-petrels, increased light pollution is also a concern for these and other nocturnal, phototactic species. Dramatic declines or redistributions have occurred at some breeding colonies, indicating long-term planning should consider changing habitat requirements. The greatest data needs currently include fall/winter/spring at-sea distribution, summer distribution off southern Oregon, and more accurate estimates and monitoring of burrow-nesting seabirds. Oregon’s coastal waters provide habitat for a large portion of breeding and nonbreeding marine birds along the U.S. west coast and a thorough knowledge of their spatial distribution, seasonal abundance, and migration corridors is critical for well-informed marine spatial planning