ADF&G study begins to answer whether hatchery salmon produce fewer offspring

Feb 21, 2019

A researcher pulls ear bones from a pink salmon on the banks of Hartney Creek near Cordova. The ear bones, or otoliths, help researchers identify hatchery salmon.
Credit Aaron Bolton, KBBI News

After about five years of work, the Alaska Department of Fish and Game’s hatchery-wild study is beginning to answer crucial questions: do hatchery pink salmon produce fewer offspring compared to their wild counterparts and do they affect the productivity of the wild stocks they spawn with?

After Prince William Sound hatchery pink salmon were found straying into wild streams far from home, various stakeholders began debating whether hatchery salmon are harming wild stocks.

Fish and Game set up a study to answer some questions within that debate: whether pink salmon stocks across Prince William Sound are genetically similar and to calculate how many hatchery fish stray into wild streams. Fish and Game is also conducting a similar study on chum salmon in Southeast Alaska.

The study found that pink salmon stocks in Prince William Sound are genetically similar and that stray rates can vary from stream to stream depending on proximity to hatcheries, migration patterns and other factors.

Now, Fish and Game scientists are beginning to answer another question. 

“The third was to quantify the impact of straying – hatchery pink salmon in Prince William Sound and chum salmon in Southeast Alaska – on fitness of natural stocks,” Fish and Game’s Christ Habicht said “That’s the part that now has the very first set of results.”

Habicht is leading the study, and what he’s saying here is that Fish and Game is just beginning to see whether there are genetic differences when it comes to how many offspring hatchery and wild pink salmon produce in natural streams. Results for the chum salmon portion of the project haven’t been released.

The study examined five wild pink salmon streams in western Prince William Sound. Fish and Game genetically matched hatchery and wild parents with their offspring in order to calculate reproductive success.

The first results detail both even and odd-year runs from 2013 to 2016 in Hogan Bay.

“In the even year, we found that hatchery origin females produced about half as many progeny as the natural origin females,” Habicht explained.

He notes that the study didn’t collect enough fish during the first year of fieldwork in 2013 to make the same determination for the odd-year runs. Habicht adds that the even-year results also show that all spawning combinations were present in Hogan Bay.

“Some progeny came from natural-natural fish. Some came from hatchery-hatchery crosses, and some progeny came from a hatchery female mated with a natural male or a natural female mated with a hatchery male,” Habicht said.

That’s also note worthy because Fish and Game has known for some time that hatchery and wild pinks stray from their natal streams, but it didn’t know whether hatchery and wild fish would have success spawning together.

While all of this is big news, Habicht said the first set of results may not tell the whole story.  

“So, we’re being a little bit cautious about how to interpret one set,” he added. “I think that the next step of course is to get replication across streams, to get replication across years and to see if the patterns we’re observing in this first set and this first stream are similar to the patterns we see in other streams.”

Even if results are replicated in various streams over time, Habicht notes that this study is not designed to answer why there may be reproductive differences between wild and hatchery pinks.

Another batch of results could be released in the next month or so, but it’s unclear when Habicht and his team will finish analyzing thousands of samples collected from all five streams through the end of this upcoming summer.

Still, the results from Hogan Bay are likely to make a splash when they are presented to the Alaska Board of Fisheries’ Hatchery Committee on March 8 in Anchorage. The committee is revisiting the state’s hatchery policies and it will evaluate hatchery programs around the state.