Hatchery origin fish spawn earlier and their progeny emerge
earlier than their wild counterparts, but have no competitive advantage in a
western Washington stream, according to a recent study.
The study compared spawn timing of winter steelhead adults,
along with the length, condition and abundance of hatchery, hybrid and wild
steelhead fry in the Willapa River system, finding that the later spawn timing
and later emergence coincided with better stream conditions for survival.
Wild winter steelhead in Forks Creek, a tributary of the
Willapa River in southwest Washington, spawn later than the hatchery fish that
have been allowed to spawn in the creek, and the wild progeny emerge when water
temperatures are warmer and streamflow is lower, conditions more conducive to
Earlier emerging hatchery fish are caught in higher water
and occasional scours and, consequently, survival is lower.
The wild steelhead in Forks Creek have adapted to local
conditions, whereas the hatchery fish have yet to adapt, a not so surprising
conclusion of the study.
“It's becoming increasingly clear that you can't just look
at hatchery and wild fish in a vacuum,” said Marissa Jones, a graduate student
at the University of Washington School of Aquatic and Fishery Sciences at the
time of the study, and currently education specialist with NOAA Fisheries.
“Ecological and environmental factors interact throughout fishes' lives to
shape relative survival.”
Wild fish may have benefited because they were locally adapted
to conditions in Forks Creek, Washington, the authors speculated. The eggs and
fry of early spawning hatchery fish might have been destroyed or physically
displaced downstream by high river flows in the winter and early spring.
“However, it’s important to keep in mind that other traits –
other biological and behavioral differences between hatchery and wild fish –
could have also contributed to the underrepresentation of hatchery-lineage fry
in our sample,” Jones said.
“Consequences of Emergence Timing for the Growth and
Relative Survival of Steelhead Fry from Naturally Spawning Wild and Hatchery
Parents,” was published online August 12, 2015, in Transactions of the American
Fisheries Society (http://www.tandfonline.com/doi/abs/10.1080/00028487.2015.1057346?journalCode=utaf20)
In addition to Jones, authors are James E. Seeb, research
professor, U of W School of Aquatic and Fishery Sciences; Kenneth I. Warheit,
manager, Molecular Genetics and Fish Health Laboratories, Washington Department
of Fish and Wildlife, affiliate associate professor, U of W School of Aquatic
and Fishery Sciences; Todd R. Seamons, research scientist, WDFW; Thomas P.
Quinn, professor, U of W School of Aquatic and Fishery Sciences; Lisa W. Seeb,
research professor, U of W School of Aquatic and Fishery Sciences.
Hatchery steelhead were intentionally released in 1996 and
given the opportunity to spawn in the same areas used by the small, local, wild
steelhead population. The hatchery fish, not native to the system, were from
the Chambers Creek stock, a stock commonly used in hatcheries to supplement
recreational fishing opportunities that has been intentionally bred to spawn
several months before wild steelhead in the region.
The researchers sampled fry about 1 to 3 months after they
emerged from gravel nests and used a panel of genetic markers to identify
whether the young fish were from the wild population, the hatchery population,
or hybrids of the two populations.
“We found that the majority of the fry had at least one wild
parent (wild or hybrid lineage), despite the fact that earlier studies found
plenty of adult hatchery fish on the spawning grounds,” Jones said. “We then
compared the estimated emergence dates of wild, hatchery, or hybrid lineage fry
to environmental conditions in the river. Our simple model suggested that the
wild and hybrid fry emerged after the arrival of milder, spring conditions.”
Other studies have reached different conclusions. A study of
Atlantic salmon found that early emerging offspring had “the highest rates of
survival and largest final body size, despite experiencing the harshest environmental
conditions,” according to Jones’ study.
Another study of coho salmon found that the early emerging
fry – those first to seek food and space first – had an equal competitive
advantage with later emerging fry.
These studies suggest that there is an “advantage for
hatchery or hybrid fry in our system, as they were longer than wild fish and
were present in the river before the wild fish emerged.”
In the current study,
wild fish were smaller than hatchery (the largest) or hybrid fish, but all measurements
were taken at the same time, so the hatchery and hybrid fish had had more time
This study found that these advantages were “insufficient to
counterbalance any adverse effects of early development/emergence or the
effects of redd scour and superimposition.”
Although there were plenty of hatchery fish on the spawning
grounds, the authors speculate that some of the hatchery redds were scoured due
to the higher flows earlier in the year or that the wild fish that spawned
later simply superimposed their redds over the hatchery fish-produced redds.
“We hesitate to speculate about the specific consequences
for other salmonids or other rivers, but we think that the most salient point
is the importance of bringing ecological and environmental effects into our
understanding of hatchery-wild dynamics,” Jones said.
It is important to note that the study was based on a single
cohort and one season of environmental conditions. The outcome might have been different with
different environmental conditions, a different species with different life
history, or in a system that was dominated by snowmelt rather than rainfall,
“Indeed, in one of our earlier papers (Seamons et al. 2012)
we found anecdotal evidence that hatchery fish fared better in one year with a
mild winter,” Jones said.
Nevertheless, in all cases, factors like intraspecific
competition and environmental conditions are still important. This study is
part of a large and growing body of literature that attempts to bring what we
know about fish biology into the conversation about hatchery and wild
salmonids, according to Jones.
It is “important to keep the nuances and caveats in mind
when extrapolating to broad-reaching implications of this type of research,”