Juvenile wild steelhead are smaller than hatchery fish when they reach the ocean, but have a higher feeding success, are in better condition and grow faster than hatchery fish once they arrive in the marine environment, according to a recent study.
“Juvenile steelhead enter the marine environment each year at a similar size and condition, yet after a short period in the marine environment, they are feeding and growing at a much higher rate than in the estuary as they quickly move offshore and this growth depends on ocean conditions,” said Elizabeth A. Daly, senior faculty research assistant for the Cooperative Institute for Marine Resource Studies (Oregon State University and NOAA Fisheries), which is located at the Hatfield Marine Science Center in Newport, Ore.
The Bonneville Power Administration since 1998 has funded NOAA and CIMRS/OSU on an ongoing ocean research project on juvenile salmon marine survival.
The study measured and weighed both wild (unmarked fish) and hatchery juvenile steelhead in the Columbia River estuary and in the ocean. According to the report, wild steelhead were slightly shorter than hatchery fish as they entered the ocean, but were overall healthier, fed with greater success and grew faster than the hatchery juveniles.
“Juvenile Steelhead Distribution, Migration, Feeding, and Growth in the Columbia River Estuary, Plume, and Coastal Waters” will soon appear in the online journal Marine and Coastal Fisheries: Dynamics, Management, and Ecosystem Science, an open-access journal available to the public at http://www.bioone.org/loi/fidm.
The authors are Daly; NOAA Fisheries research fisheries biologists Richard D. Brodeur, Julie A. Scheurer, Laurie A. Weitkamp and Brian R. Beckam and Jessica A. Miller, associate professor of marine fisheries ecology at OSU.
“Very few studies have reported on the marine ecology of juvenile steelhead, certainly none with the wide array of data that we published,” Daly said.
Steelhead populations are in decline, with 11 out of 15 populations in the Columbia River basin currently listed as threatened or endangered under the U.S. Endangered Species Act.
Most salmon and steelhead restoration work and funding in the Columbia River basin is focused on the freshwater and estuarine aspect of their life history, which is the shortest and most stable part of their life.
“All the money in the world could be spent restoring their freshwater phase of their life, but if the fish leave there and go into poor ocean conditions, they will not make it back as adults, nor will endangered populations be restored, nor will we have learned anything about whether or not the fresh water restoration efforts have helped the salmon,” Daly said.
Biologists sampled juveniles in both the estuary and in the ocean. Estuary data were from a study of the spring out-migration period as they moved through the estuary. The marine data were from NOAA Fisheries’ pelagic trawl surveys that target the early marine phase of juveniles off the coasts of Oregon and Washington.
After leaving the Columbia River estuary, juvenile steelhead migrate directly westward into shelf waters where food is more plentiful during their first summer in the ocean, whereas other salmonids tend to migrate northward up the coast of Washington.
The study found that while in the estuary close to half the fish had empty stomachs. Only 40 percent of the hatchery steelhead and 53.3 percent of the unmarked steelhead had any food in their stomachs.
“Thus, the ability to move quickly through the estuary and into ocean habitats may confer survival benefits upon these juveniles,” the report says.
In contrast, in the ocean 87.9 percent of hatchery and 92.3 percent of unmarked fish had food in their stomachs. “Additionally, in all years, steelhead that were caught in the ocean had eaten significantly more food than steelhead that were caught in the estuary,” the report says.
On the other hand, there was little change in length of the fish. Estuary fish averaged 212.9 millimeters and ocean fish captured soon after entering the ocean were 217.5 mm. Ocean caught hatchery fish on the average were 22.3 mm longer than the unmarked fish. Estuary caught hatchery fish were 23.4 mm longer than unmarked fish.
Even with small differences in length between estuary and ocean fish, the condition of all the juveniles was much better, with both hatchery and unmarked fish in the ocean weighing more for a given body length than when they were in the estuary.
In the estuary, there was little difference in condition of the fish between hatchery and unmarked fish, but that changed after the fish arrived in the ocean and began to feed.
Unmarked fish had a “higher average body condition than hatchery fish across all years,” according to the study.
When gathering the juveniles, the biologists noticed that the ratio of hatchery to unmarked fish had changed. There were more unmarked steelhead in the catch than hatchery steelhead.
This “suggests that naturally produced steelhead are potentially surviving at a higher rate than hatchery fish,” according to the report.
“If unmarked fish are eating more and growing at a higher rate than hatchery fish in the marine environment, this could provide a survival advantage to the naturally produced fish,” the report concludes.
Daly noted some limitations in the study that she believes needs to be addressed in further research. Not all hatchery fish are marked (clipped adipose fin) and so the unmarked category as a defacto wild fish category in this study likely included some hatchery fish.
“If hatcheries would fully mark all their fish, we would know which are the naturally produced fish and this will assist us in determining how best to help native populations and what impact hatchery fish may be having on them,” she said.
In addition, the seining of salmonids in the ocean often occurs deeper in the water column than where many of the surface-oriented steelhead feed. Daly suggests raising the net in the water column and moving further offshore to sample in late April and all of May to capture the tail end of the steelhead population out of the Columbia River.
“During the recovery planning for steelhead populations, a better understanding of marine conditions that are important for optimal growth and survival will assist us in separating effective management practices for the improvement of steelhead populations while the salmon encounter variable ocean conditions,” Daly said.