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Message Subject: Sag/Bay Walleye Jaw Tags & Transmitters update.

walleye express

Posted 3/11/2013 4:43 PM (#109203)
Subject: Sag/Bay Walleye Jaw Tags & Transmitters update.

Member

Posts: 2680

Location: Essexville, MI./Saginaw Bay.

I e-mailed my Fisheries DNR buddy a question yesterday about the walleye tagging program. This question has been on my mind for a while now and more recently with the surge of this years huge run of walleyes in the river. Below is my question and his very informative answer.

Question: I know that the walleye tagging program has been an ongoing project virtually for as long as the walleye replanting program started back in the late 70's/early 80's on Saginaw Bay. And I understand (for the most part) what information could initially be learned from the data that returned tags could give you. But is that datum (after this many years) still giving the Fisheries division any helpful information at all that they can use? You would think after so many years there would not be any more surprises and that money deligated for the tagging project could be better used someplace else in the Department.

Also, is there any new data that the transmitters have revealed about the walleyes migration habits?

Thank's bud, Dan.

P.S. And one more question about tags. What is the most unusual things you've ever learned from any walleye jaw tag return. Dan.

Answer: Dan:

All good questions and timely. I’m working right now on these very issues. The jaw tagging began in 1981 so it’s been going on for more than 30 years. From the tag returns, we calculate exploitation rate (the percentage of fish being harvested from the population). Also the mortality rates of the fish. Two essential statistics everyone needs to manage a fish population. Because the exploitation rate and mortality rate are actual ‘rates’ it’s a little like measuring the speed on your speedometer on your truck. It changes all the time so you don’t ever get the “final” answer. You have to keep monitoring it forever.

You are right, however, that after enough time, the effectiveness of the study changes (declines). This is because anglers become complacent with following through to return the tags. We’ve recently discovered that the “noncompliance” rate on tag returns is now over 4 times (meaning whatever tag numbers we get in, we have to multiply buy four to get the actual number). That’s pretty poor compliance. In the year 2000, it was 2.33X. So noncompliance is worsening as time goes on. All the tagging data goes into a computer model called the “Brownie model” (the inventor’s last name was ‘Brownie’).

More recently, I’ve developed a new computer model for Saginaw Bay walleyes. This kind of model is called a ‘statistical-catch-at-age’ model or just SCAA. It doesn’t need the tag returns at all but instead uses trends in each of the fisheries and our survey catches to estimate the same things (exploitation rate and mortality rates). SCAA models are regarded as ‘state-of-the-art’ stock assessment models and have several advantages over the Brownie model. The funding for the jaw tagging project is up for renewal so in light of its deficiencies and in light of the availability of the SCAA model, we are right now contemplating the future of the tagging project and possibly will suspend it.

This hasn’t been decided so far. As an alternative, we can restore the tagging project by beginning to (annually) include a subset of $100 reward jaw tags so we can update what the noncompliance rate is each year. If we have both the SCAA model and Brownie model, we are in our best position to manage the fishery. They use both on Lake Erie for example. I have a version of my SCAA that also incorporates the tag return analysis a sort of hybrid model that in theory should be optimal (the best).

I’m not eager to suspend the tagging study as it takes many years to rebuild the statistical power of the analysis if we suspend it even one year. We’re also beginning to question how representative the Tittabawassee River run of walleyes are for representing all the walleyes of Saginaw Bay. The estimates from the Brownie model and SCAA model don’t match up very well at all, suggesting that there may be some dynamics of the Tittabawassee River fish that make them unique (maybe behavior wise or growth rate wise). One improvement to the tagging study would be to diversify our tagging sources from just the Tittabawassee to several sources.

Not sure what was the most unusual thing we’ve learned from the jaw tagging. It was initially a surprise that so many tags came from outside the bay but that’s old news any more. The telemetry project is yielding some big surprises. It tells us that (at least in 2011) slight more than half the adult walleyes in the bay out migrated and as early as early June.

That’s way more and way sooner than I ever thought. Hard to know how typical 2011 was. We’re also discovering that if a fish went north to the straits in 2011, it did the same in 2012. If a fish out migrated and stuck around Oscoda in 2011, it did the same in 2012. If a fish liked to hang around the Charities in 2011, it did the same in 2012. If a fish went out around the thumb in 2011, it did the same in 2012. So these fish seem to be exhibiting habitual behavior. Why they do different things from each other, we still don’t know.

We also documented at least one walleye (telemetry tagged in the Tittabawassee River in 2011) that then spawned in the Thunder Bay River in 2012. Such ‘straying’ is generally regarded as rare even for walleye. From this it’s starting to look like the walleye population of Lake Huron is largely of Saginaw Bay origin and its management needs to consider all the surveys of harvest, not just the recreational catch in the bay and river system. Fascinating stuff. We plan to implant about 60 more this year and will this time use some sources outside the Tittabawassee (leaning toward the Shiawassee and the Au Gres River sources). This will likely be the last year of transmitter implanting but we’ll track with the receivers at least one more year beyond that.

We have our annual spring Fisheries workshops coming up in which we’ll be presenting all our survey findings at an evening meeting. See the attached flyer for time and place details. You should come to one of them.

Edited by walleye express 3/11/2013 4:44 PM

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