Robert L. Emmett

Nocturnal Feeding of Pacific Hake and Jack Mackerel off the Mouth of the Columbia River, 1998-2004: Implications for Juvenile Salmon Predation

Abstract Predation by piscivorous marine fishes has been hypothesized to be a primary source of marine mortality for Pacific Northwest juvenile salmon. During the springs and summers of 1998-2004, we collected predator and prey fishes (forage and juvenile salmonids) at the surface at night off the mouth of the Columbia River. Pacific hake Merluccius productus had relatively low percentages of empty stomachs during cool-ocean years (2000 through 2002) and high percentages during 1998, a warm-ocean year. Euphausiids and fishes were the most commonly eaten prey for both species. Pacific hake and jack mackerel Trachurus symmetricus appeared to show some diet selectivity, eating some fish, including salmonids, in a higher proportion than found in the environment. Both Pacific hake and jack mackerel ate juvenile salmonids, but at very low amounts. After considering population sizes in the study area, these two predators do not appear to be responsible for the death of large numbers of Columbia River juvenile sa...

Introduction of a Siberian Freshwater Shrimp to Western North America

Robert L. Emmett1,∗, Susan A. Hinton1, Daniel J. Logan2 & George T. McCabe, Jr.1 1Northwest Fisheries Science Center, National Marine Fisheries Service, 2725 Montlake Blvd, East Seattle, WA 98112-2097, USA; 2National Marine Fisheries Service, Protected Resources Division, 777 Sonoma Street, Room 325 Santa Rosa, CA 95404, USA; *Author for correspondence (e-mail: robert.emmett@noaa.gov; fax: +1-541-867-0389)