Monitoring Pinniped Predation on Salmonids at Alsea River and Rogue River, Oregon: 1997-1999

Identification Information

Citation

Originator: Reimer, Susan D., Robin F. Brown, Bryan E. Wright, and Mark I. Dhruv

Publish Date: 2001

Online Link: None

BPA Project #:

Contact Information

Agency: Oregon Department of Fish and Wildlife

Name: Cedric Cooney

Job Position: Natural Resources Data and Systems Manager

Telephone: 503-947-6094

E-Mail Address: cedric.x.cooney@odfw.oregon.gov

Description

Abstract: The co-occurrence of abundant pinnipeds (seals and sea lions) and depressed salmonid stocks has been identified as a potentially significant problem in the recovery of some salmon populations. The Alsea River and Rogue River were chosen as study sites to test research methodologies and to estimate the consumption of salmonids by pinnipeds. These study areas were selected because pinnipeds were abundant and common year round; detailed information on salmonid stocks and pinnipeds at these sites were available; and the physical nature of the areas appeared to allow use of the available research methodologies. Predation observations and pinniped counts (from shore and boats), and collection of Pacific harbor seal (Phoca vitulina richardsi) fecal (scat) samples for food habits analysis were conducted at both sites from September through November in 1997, 1998, and 1999. In scat samples collected at the Alsea study area 28 species of fish and cephalopods were identified as harbor seal prey (an additional 19 prey items were identified to genus, family or order level). Pleuronectids (English sole, Parophrys vetula, rex sole, Glyptocephalus zachirus and butter sole, Isopsetta isolepis) were among the most frequently occurring prey items in the scat samples. Pacific herring (Clupea pallasii) and Pacific staghorn sculpin (Leptocottus armatus) were also among the most common prey species taken by seals. The frequency of occurrence of salmonids (Oncorhynchus spp.) found in the Alsea samples ranged from 4.3% in 1997 to 7.4% in 1999. In the Rogue study area 32 species of fish and cephalopods were identified as seal prey (22 additional prey items were identified to the genus, family, order level). Pleuronectids were also important prey species for seals in the Rogue River area, including rex sole, slender sole (Lyopsetta exilis), English sole and Dover sole (Microstomus pacificus). Rockfish species (Sebastes spp.), Pacific hagfish (Eptatretus stoutii), Pacific lamprey (Lampetra tridentata), and Pacific whiting (Merluccius productus) were also frequently occurring prey species. The occurrence of salmonids in the Rogue samples ranged from 10.3% in 1998 to 14.8% in 1997. Numbers of harbor seals counted in the study areas ranged from 200-700 in the Alsea River and from 100-200 in the Rogue River. California sea lions (Zalophus californianus) and Steller sea lions (Eumetopias jubatus) were common in the Rogue River, but rare in the Alsea system. The lower 8-12 miles of the rivers were surveyed weekly by boat to document the occurrence of pinnipeds. The abundance of pinnipeds observed in the rivers above the estuaries of both systems was difficult to estimate, but probably amounted to fewer than several dozen animals at any time. Observations of pinniped foraging activity were made from 9-31 observation sites in the Alsea River study area and from 11-14 sites in the Rogue River study area. Data on predation events, species of prey, numbers of pinnipeds, and observation conditions were recorded. Total hours of observation per year ranged from 552 to 1,119 in the Alsea River and from 814 to 961 in the Rogue River. Numbers of observed predation events on salmonids ranged from 1-24 in the Alsea study area and from 32-39 in the Rogue study area. Total estimated predations ranged from 4 salmonids (CV=80%) to 177 (CV=19%) at the Alsea River and from 218 (CV=16%) to 249 (CV=12%) at the Rogue River. These estimates apply only to daylight hours and only to the sites sampled within each estuary. They therefore provide a lower bound on total adult salmonid predation.

Purpose:

Time Period of Content: 1997-1999

Geographic Extent: Alsea River and Rogue River, Oregon

Status: Final

Use Constraints:

Format: PDF

Data Quality Information

Lineage-Source: In Partial Fulfillment of Requirements for: PSMFC/ODFW Subcontract Nos. 99-006 and 00-06 NOAA Grant No. NA87FX0464

Data Information

No data information was supplied.

Entity and Attribute Information

Attributes Description: Field attribute information is available in the attached file(s).

Is a physical copy maintained for reference at Headquarters? Unknown