Acoustic tag study compares wild/hatchery migration habits

April 13, 2007 Columbia Basin Fish and Wildlife Bulletin

What are the differences between survival and migration traits of wild and hatchery steelhead smolts?

An Oregon Department of Fish and Wildlife research project will attempt to answer that question and others over the next few months.

The Alsea steelhead acoustic project will determine the migration habits and survival traits of two groups of hatchery smolts and one group of naturally-reared steelhead smolts.

Each of the three groups had 75 smolts implanted with acoustic transmitters. Each transmitter has a unique code that can be picked up by acoustic receivers placed throughout the Alsea River and estuary.

The receivers will determine when the tagged fish move through an area in the river or estuary-- ODFW staff placed 15 acoustic receivers in the Alsea River, 14 receivers in the Alsea estuary, and 5 receivers in the ocean near the mouth of the estuary.

"We are looking at these groups of smolts to see if they are moving down the river at the same time, whether they are using the estuary for the same duration, and whether they are using the same areas of the estuary for rearing," said Steve Johnson, ODFW assistant project leader. "Ultimately, we hope to understand what percentage of each group survives their journey through the river and estuary and successfully enter the ocean."

According to Johnson, the two groups of hatchery smolts have been reared under similar conditions, but differ in their degree of domestication.

One group represents the "traditional" broodstock line that has been used at the North Fork Alsea Hatchery for many years.

The second hatchery group represents a new broodstock line that was developed recently by bringing naturally reared adults into the hatchery for spawning.

The migration patterns and survival rates of these two groups are being compared to smolts that have reared naturally in a tributary of the North Fork Alsea near the hatchery.

The acoustic tags have a battery that lasts approximately 70 days. The ODFW research and monitoring group that is performing the study will collect data from the receivers on a weekly basis. The acoustic tags are used because they can be detected in both salt water and fresh water and trace fish that are several hundred yards away.

The $70,000 research project is a collaborative effort among ODFW and researchers with the Environmental Protection Agency at the Hatfield Marine Science Center at Newport, Oregon. Funding for the research comes through a grant from the ODFW Fish Restoration and Enhancement Program and additional funds from the Oregon Hatchery Research Center.