Historical 3-D map of Astoria Canyon. Click image for larger view.

Biology

In 1803, at the request of President Thomas Jefferson, the U.S. Congress authorized exploration of lands west of the Mississippi River in what would become one of the most storied chapters of American exploration. Led by Jefferson’s secretary Meriwether Lewis and Lewis’ friend, William Clark, the party of thirty-three individuals dubbed Corps of Discovery made its historic crossing of what is now the western United States between 1804 and 1806, ending its journey at the Pacific Ocean at the mouth of the Columbia River. This first organized exploration of the American west was marked not only for its bold thrust into the unknown but also for its scientific return. Descriptions of hundreds of plants and animals previously unknown to science were a lasting legacy of their expedition. However, one area of the North American continental platform inaccessible to the Corps of Discovery was the continental shelf and slope beneath the Pacific Ocean. Now, nearly two hundred years later, exploration in the spirit of Lewis and Clark will resume in a submarine canyon during the summer of 2001 during an expedition befittingly named Lewis and Clark Legacy. Beginning just ten miles west of the present mouth of the Columbia River, a corps of ocean explorers will map, probe, and document physical and biological systems in the depths of Astoria Canyon, the westernmost portion of the Columbia River drainage system, and Heceta Bank, a nearby underwater plateau. Today, due to its depth and inaccessibility to commercial and sport fishing, the canyon is a virtually unexplored biological haven and thought to be a refuge for fish and unusual invertebrate communities.

Modern Context and Need for the Expedition

Large decreases in both fish and invertebrate communities around the world have deepened anxiety about the long-term health of seafloor ecosystems. This concern is heightened by the likelihood that human activities may be responsible for a large portion of these decreases. The true human impact on the extent of these declines is unknown, however, because in many areas exploitation by commercial interests preceded exploration by the scientific community. A major difficulty in studying and monitoring many of the easily accessible seafloor habitats is their disturbed nature. A new thrust in ocean exploration can have a positive impact on this situation because there is a good chance that there are ecosystems off the west coast, such as Astoria Canyon, that have been left relatively undisturbed due to remoteness and/or rough bottom characteristics. It is ironic that even after more than 40 years of ocean research off the west coast of the U.S., there are many places virtually unexplored by modern technology. During the summer of 2001, marine habitats of Astoria Canyon, a relatively "neglected" major submarine province, will be a focus of ocean exploration in the Northeast Pacific Ocean.

Francis Shepherd, an early pioneer of marine geology, first described Astoria Canyon in the 1930s. Initially called the Columbia Canyon, its name was changed to Astoria Canyon on an early map, and this became its official name. Little research has been done on the canyon since the 1960s and early 1970s when scientists at Oregon State University and University of Washington initially described of its sediments, water movements, and biology.

Overview of the Expedition

There are three phases to the Lewis and Clark Legacy Expedition. First is detailed mapping of Astoria Canyon. Second is exploration of the Canyon’s geological and biological features using remotely operated vehicles (ROVs). And third is exploration of the habitats and fisheries of Heceta Bank, a heavily fished submarine plateau on Oregon’s outer continental shelf. The goals of the expedition are to:

Produce a detailed map of Astoria Canyon to 2,000 meters depth;
Identify the canyon’s major geologic provinces and unusual features such as seeps, recent landslides, and unusual ecological systems;
sample and preserve representative elements of the canyon’s biological and geological feature;
translate the excitement of exploration of a submarine canyon to the public and educational communities;
compare fish and invertebrate populations of similar habitat found in Astoria Canyon and Heceta Bank; and
report on the major results of the explorations.

Phase 1 – May 29 through June 16

The first phase of the expedition was a detailed sidescan sonar survey of the upper portion of Astoria Canyon from the continental shelf break down to about 2,000 meter depth. Previously available sonar data provided an excellent overview of the canyon’s geologic features and a baseline for more detailed studies. However, deep-towed sidescan sonar will provide higher resolution imagery necessary to identify in greater detail the rock outcrops, possible methane seeps, and unusual features such as submarine sediment slides that will be targets for ROV exploration of the canyon during Phase 2 of the expedition. The Phase 1 survey used a chartered deep-towed sidescan / bathymetric mapping system on the vessel Auriga, sailing from the port of Seattle, Washington.

Phase 2 – June 26 through July 3

Phase 2 of the expedition consists of a series of dives using the ROV named ROPOS, deployment of instruments to measure physical and chemical characteristics of the waters of the canyon, biological sampling through the use of sonar and trawls, and hydroacoustic monitoring of biological and geological sounds in the canyon. The ROV dives will cover approximately 40 kilometers along the upper part of the canyon over a range of depths from 200 to 2,000 meters (650 – 6,560 feet). Each dive will give scientists a chance to "visit" the canyon using a network of cameras, instruments and sensors that are mounted on the ROV. By looking into never before seen areas along the canyon walls, the scientists will see what fish and other marine life live there, how ecosystems are arranged at different depths, and information concerning the chemical and physical properties of the water and seafloor.

ROPOS will make approximately 15-20 dives, each taking from 12 to 18 hours. Allowing for the rough terrain and the time needed for sample collecting, about 15 straight-line routes (transects) will be probed over the canyon walls and floor. Acoustic data collected by hydrophones in the area prior to and during the summer of 2001 will be analyzed, and all detected biological and geological sounds within the area such as fault movement, mass wasting, and whale and fish vocalizations will be located and identified as possible exploration sites for ROPOS. Portions of ROV transects will follow the guidelines that were developed for habitat-based studies of fishes and invertebrates with ROPOS on Heceta Bank. This will permit a direct comparison between the Astoria Canyon and Heceta Bank areas, and also contribute to the development of a growing database of habitat-specific abundance measurements for fishes and invertebrates along the Pacific Northwest coast.

To monitor oceanographic conditions during ROV dives, measurements of ocean conductivity, temperature, and depth will be taken, and optical and chemical sensors will be deployed to measure chemical constituents in the water. The information generated will help to determine distribution of dissolved and particulate materials (nutrients, organic matter) that can affect the health of organisms living on the canyon floor. To understand how these materials are transported through the canyon, two moorings with sensors to monitor current flow, particulate matter concentrations, and nutrient concentrations will be deployed. These measurements will be used to quantify the oceanographic conditions under which biologically important material is transported and concentrated within the canyon.

Exploring for large groups of fish and zooplankton will be conducted through straight-line acoustic sampling across the canyon using a towed echosounder or multibeam sonar. The accuracy of these acoustic transects will be established using two types of trawls. Small, non-swimming organisms that move primarily by ocean currents will be sampled with a towed midwater depth trawl. Free swimming organisms will be sampled through the use of rope trawl towed by a commercial fishing vessel, the F/V Sea Eagle.

All expedition activities during Phase 2, with one exception, will be staged from the National Oceanic and Atmospheric Administration research ship, Ronald H. Brown, sailing from the port of Vancouver, British Columbia.

Phase 3 – July 4 through July 13

The final phase of the Lewis and Clark Legacy Expedition will be to gather data on Heceta Bank from transects with ROPOS. Specifically, ROPOS will repeat historical transects of Heceta Bank from the 1980s, repeat Summer 2000 transects, conduct new transects to cover the entire geographical range of the Bank, and collect biological and geological samples. Phase three is being conducted in cooperation with another on-going interdisciplinary and comprehensive study of the habitats of the bank using state-of-the-art survey strategies, instrumentation, and data analysis. Phase 3 activities will be staged off the NOAA research vessel, Ronald H. Brown.

In 1998 an interdisciplinary group of scientists from federal, state, and academic institutions initiated a study of the habitat of groundfish populations on and near Heceta Bank, the largest and most important of the heavily fished rocky banks on the outer continental shelf off Oregon. Heceta Bank was the site of 58 submersible dives in the late 1980s that characterized the species composition of the Bank and provided important data on relationships between fish species and bottom type. The acquisition of a state-of-the-art, high-resolution sonar survey at this site in May 1998 provided a highly detailed, precisely navigated seafloor map of bathymetry (depth) and seafloor texture that serves both as a context for the 1980s data, and as a basis for a more comprehensive study of groundfish/habitat relationships over a larger area. This study was a combined approach using the new survey data, the historical data, and additional seafloor surveys in 2000 and 2001 to address the following questions: 1) At what scales are there quantifiable relationships between groundfish population and seafloor morphology/texture? 2) What are the factors that control these relationships? 3) What changes may have occurred in the fish populations after a decade? and 4) What are the characteristics and extent of natural refugia?

By re-examining the habitats of Heceta Bank and sampling its fish populations, the Lewis and Clark Legacy Expedition will be able to compare habitats and fish and invertebrate populations of Heceta Bank with those found on Astoria Canyon.

Fishery biologists anticipate that this information will lead to: 1) a more quantitative approach to mapping essential fish habitat for the U.S. Exclusive Economic Zone; 2) a model approach for characterizing and quantifying habitat associations of bottom-dwelling animals on a scale meaningful to the stock assessment of commercial species and conservation of benthic communities; and (3) opportunity to examine the possible impact of a decade of intense bottom fishing at a critical place on the outer continental shelf of the Northwest United States.

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