Biological and physical processes in and around Astoria submarine Canyon, Oregon, USA

Abstract

Astoria Canyon represents the westernmost portion of the Columbia River drainage system, with the head of the canyon beginning just 16 km west of the mouth of the Columbia River along the northern Oregon and southern Washington coasts. During the summer of 2001, physical, chemical, and biological measurements in the canyon were taken to better understand the hydrodynamic setting of, and the feeding relationships among, the pelagic and benthic communities. Results show that currents were strongly tidal, and transport, where measured, was primarily up and into the canyon below shelf depth as previous studies in the canyon have shown. Temperature time series suggests that the largest diurnal oscillations occurred at, or were trapped near, the bottom of the canyon. Within the upper canyon, subtidal temperature was correlated with upper-level shelf-edge currents, linking subtidal upwelling events in the canyon with near-surface subtidal along-shore flow. Invertebrates, such as shrimp, euphausiids, and squid, as well as mesopelagic fishes, dominated the Isaacs–Kidd midwater trawl catches along the canyon walls. Large trawl catches were comprised mainly of hake and rockfishes (shallow trawls) and macrourids, scorpaenids, stomiids, and zoarcids (bottom trawls). Gut-content analysis of rockfishes and lanternfishes revealed substantial use of midwater prey such as euphausiids and mesopelagic fishes. The δ 13C values of fishes and invertebrates reflected local primary production, as indicated by particulate organic matter (POM) δ 13C values from samples collected at various depths along the axis of the canyon, as well as across the canyon at several sites. The δ 15N values of fishes and invertebrates indicated lanternfishes, along with euphausiids, amphipods, shrimp and squid, may be important dietary components of higher-trophic-level fishes in both the benthic and benthopelagic food webs. The δ 13C and δ 15N values of Sebastes species showed significant enrichment in the adults of species that are largely piscivorous relative to the values of adults of more omnivorous species.