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Location: Essexville, MI./Saginaw Bay. | We've been having an ongoing discussion on my fishing board (at times heated) about why we're getting the overall huge size and condition this year of Salmon on Lake Michigan, along with the future prospects including all the forecasts and parameters of any future plants and return runs. Thought some of you Salmon Heads on this board might like to read a couple of recent E-mails I solicited and posted on my board from a couple of the biologists about what they have concluded.
Hi Dan,
If you or Dave don’t mind, I’d like to jump in to the discussion to say that your observations are spot on. Dave Warner and I published a paper relating alewife abundance to salmon survival rates. In addition, we’ve done many salmon diet studies over the years (see Jacobs et al) as well as conduct an overall comparison of predator-prey levels (e.g., Red Flags report). Those studies provide evidence for what many anglers already know: alewife and salmon are highly linked in a predator-prey dynamic.
To state where we are now, I would characterize the prey fish population on Lake Michigan as very stressed. We have a truncated age composition (2010 and 2012 are the dominate year classes in the population) and minimal levels of alternate prey (e.g., smelt or bloater) available to predators. The very large sizes of salmon on Lake Michigan this year were actually predicted by Warner and I because we documented a near alewife year-class failure in 2011 via the lakewide acoustic and midwater trawl survey. If salmon survival (abundance, not size) is regulated by the alewife born in the same year, then a 2011 alewife year class failure would result in a very poor year class of salmon. Case-in-point, every indicator suggests that 2-year old salmon are relatively absent from the fishery.
Without competition for the remaining 2010 and 2012 alewife year classes, the 2010 (age 3) Chinook salmon are reaching very large sizes…but here is the important part, not because alewife biomass has increased, but because Chinook competition for them has likely decreased.
Because of the above situation, our managers have agreed to a substantial cut in Chinook salmon starting in 2013. Because of that cut, I’d predict that salmon abundance increases temporarily next year (because of the age 2 chinook salmon linked with the last strong alewife year class in 2012), but with a drop in size. In 2015, however, we will likely see a drop in both abundance and size as the 2010 and 2012 alewife year classes become scarce.
Let me know if there is anything else I can do to help.
Randy
Randall M. Claramunt
Michigan Department of Natural Resources
Charlevoix Fisheries Research Station
96 Grant Street, Charlevoix, MI 49720
[email protected]
Office: 231-547-2914 xt. 224
Dan,
Randy just said what I spent an hour writing up! I'm going to provide you what I wrote up anyway. Randy and I are on the same page (as usual) but I have provided a few more details on the prey fish side of things.
For starters, folks need to realize that there are two primary prey fish (or baitfish, as some call them) surveys on Lake Michigan and two on Lake Huron. These surveys (bottom trawl and acoustic) are the only lakewide or nearly lakewide surveys that are done in these lakes and the data from these surveys are what is used as prey abundance data by fishery managers (primarily the states) when considering whether stocking levels are reasonable. The bottom trawl surveys in the main basin of these lakes are done by USGS Great Lakes Science Center, and the acoustic surveys (which are my primary responsibility as a USGS employee) are done by USGS, MDNR, and USFWS (in the last few years only) on Lake Michigan and by USGS or USGS and USFWS on Lake Huron.
Secondly, folks can and should take a look at the Michigan DNR web page http://www.michigan.gov/dnr/0,4570,7-153-10364_52259_63282-297817--... or the Wisconsin DNR page http://dnr.wi.gov/wnrmag/2012/12/salmon.htm. These pages talk about the current stocking levels and plans for the next few years. If you want more details on how the states decided to reduce stocking in 2006 (the last time cuts were implemented) and 2013, you should contact the fish chiefs or any state biologist you know for the respective states.
The stocking cuts of the last decade (2006 and 2013) have likely had different effects because of the timing. Fish hatched or stocked at the time of the 2006 stocking cut are no longer alive. However, the impact of this cut persisted in that it set the stocking levels that were in place through spring 2012, which determined the stocking level to cut from in 2013, but also influenced how many Chinook were out in the lake eating alewife, getting caught, or spawning and dying. Fish stocked/hatched in 2013 have likely not reached the point of having their largest impact on the alewife population yet because they are so small/young.
During 2006-2012, there was one alewife year class in 2010 that was almost 3 times the average density (age-0 fish per hectare, with the average being 1,280) observed in 17 years of acoustic surveys (our best measure of alewife abundance in the year they are born), three alewife year classes that were well below the average, and three alewife year classes that were about average. This variation in alewife year class sizes is important because we believe, based on work I did with Randy Claramunt and Dave Clapp from Michigan DNR Charlevoix, that a strong alewife year class leads to higher survival for the Chinook salmon that are stocked/hatched in the same year as the strong alewife year class. If you'd like a copy of this paper, let me know. Recent evidence for this includes a) high numbers of age-2 Chinook in 2012, which were most of the 12-15 pounders that so many people were catching, and b) somewhat elevated numbers of wild age-2 salmon in 2012 (hatched in 2010) compared to other years when there was not a strong alewife year class. Additionally, our data indicate that a small or weak alewife year class leads to lower abundance of Chinook hatched/stocked the same year and an average alewife year class leads to average abundance of Chinook.
So, during the period 2006-2012, there were at best three average or near average Chinook year classes (2007, 2008, 2012), three that were below average (2006, 2009, 2011), and one large or strong year class (2010). I believe that the patterns in Chinook abundance (in part the result of stocking cuts made in 2006) and alewife abundance (above average in 2010, well below average in 2011-2012) led to a situation in which the Chinook salmon hatched in 2010 had less competition for food than some other recent year classes, which resulted in better survival and growth. As a result we had fairly abundant 2 year old Chinook in 2012 and fairly large three year old Chinook in 2013.
The facts that I can provide you from the acoustic survey are that in 2012, alewife biomass was the fourth lowest of 17 years. Furthermore, data from this survey indicated that 93% of the alewife biomass was in just two year classes/ages (the 2010 and 2012 year classes), and only one of those was old enough to reproduce (the one hatched in 2010). It just so happens that Chinook really target the bigger alewife. The 2012 alewife age composition was quite different from the past when there were older, larger alewife present. Larger, older female alewife produce more eggs than smaller, younger alewife.
The facts I can provide you from the bottom trawl survey are that in 2012, the biomass of alewife was 20% higher than in 2011. While some think that this is clear evidence of an increase, in reality, because of the uncertainty in the estimates, the 2012 value was not significantly different from the 2011 value. Furthermore, the values in 2004-2012 are perhaps 20-30 % of the long term average, indicating that there are fewer alewife now than in the late 1980s and 1990s. Much like the acoustic survey results, the bottom trawl data indicate that the 2010 alewife year class was a strong one and the population is dominated by this year class, with no fish older than age-4.
Both of these surveys in 2012 indicated that even with the 2006 stocking cuts, the Chinook abundance was still large enough to have immense effect on alewife abundance. Both of the surveys indicated that much of the alewife biomass was in the form of fish that are too young to spawn, which is not good. That is likely why the state resource managers are intent on cutting stocking. So the forum contributor who suggested that DNR does not care about the baitfish is pretty far off base.
Finally, I will try to provide some facts about the Red Flags system that was mentioned. This system is intended to help managers (the states) determine if Chinook stocking levels are fine, too low, or too high to provide decent catch rates and salmon size. The process is still in development, but it will likely include three indicators that will be used to evaluate the system. One is the Chinook biomass in the lake divided by the alewife biomass in the lake (called the predator-prey ratio). The second will be the weight of an age-3 Chinook, which is a measure of how well the salmon are growing. The third is the condition of an age-3 Chinook, which is a measure of how fat the fish is for a given length. The most recent values of these measures will be compared to some range that we think is biologically meaningful. This process is still being developed, but within the next year or less it will be finalized. In the interim, as it says on the MDNR web site above, Chinook salmon weight at age-3 will be used to gauge stocking rates in the 2013-2015 period.
I hope that has helped some without being too boring. Thanks a lot for your interest!
Dave Warner
Research Fishery Biologist
USGS Great Lakes Science Center
1451 Green Road, Ann Arbor, MI 48105
734-214-9392 |
Lake Michigan Salmon.