walleye express
02-28-2005, 05:32 PM
A recent E-mail letter from my DNR bud on their recent 2004 Saginaw Bay fisheries assessment meeting.
Hi Dan:
Sorry I haven't gotten back to you sooner. Things are crazy-busy around here. Here's the 2004 findings in a nut shell:
The Good News: 2004 walleye and perch year classes were again very large (compared to past years). Neither was as large as the enormous 2003 year class but still very large. The 2004 walleye year class (as measured as Young-of-the-year or age-0 in September) was 2.7x as much as the old 1998 record (the 2003 year class was 4.8x as much). So the 2004 year class was about 55% as much as the 2003 year class (measured by YOY catch rate in our trawl samples) and is the second strongest ever measured (since monitoring began in 1971).
For yellow perch, the trawl catch rate in 2004 (of YOY) was 66% as much as the old 1982 record, making it the third strongest we have ever measured. The 2004 perch year class was much less than in 2003 (2003 was 3.3x as much as the 1982 year class). When graphed out, the 2004 year class doesn't look like much next to the giant bar for 2003, but it is still very large.
So the good news is the very strong percid (walleye & perch) production has continued for a second year in a row. Only 19% of the walleye YOY had OTC marks meaning that like 2003, it was largely a result of natural reproduction.
The bad news is that catch rate of yearling walleye and perch in 2004 (stemming from the huge year classes in 2003) was not nearly as much as we had hoped. The worst of it is for perch where upwards of 97% of the huge 2003 year class didn't survive to the fall yearling size in 2004. The news is a little better for walleye, where the 2003 year class did produce a very large yearling catch rate but it didn't' amount to any more than the 1998 year class did when they reached the yearling size. So the 2003 year class is still strong, and will definitely be noticed in the fishery, but it lost a lot of the magnitude that it was initially showing.
Why the reduction in perch and walleye year class strength? There are two reasons I think. First alewives and gizzard shad were largely gone from the bay in 2004 and everything seemed to be feeding on young perch and even young walleyes. This is as you would expect under the circumstances so some of the loss was to predation. There was even some cannibalism going on with walleye which is not unheard of but unusual for Saginaw Bay. The other reason is that the average size of the young walleye and perch in 2003 was much smaller than in past years. This is to be expected in a high density situation. We know that the smaller a fish is going into winter, the harder a time it will have surviving. So we likely lost a lot of our 2003 young percids during the overwinter period to thermal stress, especially given that the 03/04 winter was another relatively harsh one. One last possible explanation is that we are missing them in our assessment gear. Possibly because of their smaller size or high abundance, they have moved to parts of the bay where we can't reach with our gear or even left the bay. I kind of hope this is the case but I really doubt it.
Also, the average size of YOY walleye and perch in 2004 was again very small compared to past years, even smaller than in 2003. Consequently, we are unsure what to expect in terms of their survival. Fortunately this winter is shaping up to be a little more mild so maybe they will do better than the 03 year class did.
So why are we getting these big year classes? Its not exactly known for certain but the two main reasons are suspected to be ideal climate and the absence of alewives. Big walleye and perch year classes were also produced in other parts of the Great Lakes in 2003 so apparently there was something of a geographic or regional effect. That suggests a climatological effect. We've seen that before. We've also known for a long time that alewives are a formidable predator and competitor with newly hatchery walleye and perch fry. We've theorized for a long time that if we could get lower alewife numbers, we'd enjoy better walleye and perch production. That seems to be exactly what's going on. Incidently, we are also seeing greatly improved lake trout recruitment in the main basin and some evidence of lake herring expansion. We think this likely traces back to the decline in alewives too.
So where does this leave us? Like I said last year, it raises a lot of questions. On the whole, I think this is a very positive turn of events for Saginaw Bay, to see that it is still capable of producing large walleye and perch year classes. The relatively poor survival of this new production is frustrating, however. It may have been that the magnitude of the 2003 year class was simply too much to sustain. Maybe more intermediate (but still strong) year classes like that of 2004 will do better. We'll see in time. The 2003 walleyes will likely start recruiting to the fishery sometime this summer (reach 15" in length) so we'll begin to see some benefit of all this to the fishery. The size may not be impressive for a while , but the catch rates should be very good. The large size will come in time as these fish grow older and in the mean time, there are some older walleyes still out there too.
So I am optimistic for the bay, but lots of unknowns still. These are some very interesting times to say the least.
-Dave
Hi Dan:
Sorry I haven't gotten back to you sooner. Things are crazy-busy around here. Here's the 2004 findings in a nut shell:
The Good News: 2004 walleye and perch year classes were again very large (compared to past years). Neither was as large as the enormous 2003 year class but still very large. The 2004 walleye year class (as measured as Young-of-the-year or age-0 in September) was 2.7x as much as the old 1998 record (the 2003 year class was 4.8x as much). So the 2004 year class was about 55% as much as the 2003 year class (measured by YOY catch rate in our trawl samples) and is the second strongest ever measured (since monitoring began in 1971).
For yellow perch, the trawl catch rate in 2004 (of YOY) was 66% as much as the old 1982 record, making it the third strongest we have ever measured. The 2004 perch year class was much less than in 2003 (2003 was 3.3x as much as the 1982 year class). When graphed out, the 2004 year class doesn't look like much next to the giant bar for 2003, but it is still very large.
So the good news is the very strong percid (walleye & perch) production has continued for a second year in a row. Only 19% of the walleye YOY had OTC marks meaning that like 2003, it was largely a result of natural reproduction.
The bad news is that catch rate of yearling walleye and perch in 2004 (stemming from the huge year classes in 2003) was not nearly as much as we had hoped. The worst of it is for perch where upwards of 97% of the huge 2003 year class didn't survive to the fall yearling size in 2004. The news is a little better for walleye, where the 2003 year class did produce a very large yearling catch rate but it didn't' amount to any more than the 1998 year class did when they reached the yearling size. So the 2003 year class is still strong, and will definitely be noticed in the fishery, but it lost a lot of the magnitude that it was initially showing.
Why the reduction in perch and walleye year class strength? There are two reasons I think. First alewives and gizzard shad were largely gone from the bay in 2004 and everything seemed to be feeding on young perch and even young walleyes. This is as you would expect under the circumstances so some of the loss was to predation. There was even some cannibalism going on with walleye which is not unheard of but unusual for Saginaw Bay. The other reason is that the average size of the young walleye and perch in 2003 was much smaller than in past years. This is to be expected in a high density situation. We know that the smaller a fish is going into winter, the harder a time it will have surviving. So we likely lost a lot of our 2003 young percids during the overwinter period to thermal stress, especially given that the 03/04 winter was another relatively harsh one. One last possible explanation is that we are missing them in our assessment gear. Possibly because of their smaller size or high abundance, they have moved to parts of the bay where we can't reach with our gear or even left the bay. I kind of hope this is the case but I really doubt it.
Also, the average size of YOY walleye and perch in 2004 was again very small compared to past years, even smaller than in 2003. Consequently, we are unsure what to expect in terms of their survival. Fortunately this winter is shaping up to be a little more mild so maybe they will do better than the 03 year class did.
So why are we getting these big year classes? Its not exactly known for certain but the two main reasons are suspected to be ideal climate and the absence of alewives. Big walleye and perch year classes were also produced in other parts of the Great Lakes in 2003 so apparently there was something of a geographic or regional effect. That suggests a climatological effect. We've seen that before. We've also known for a long time that alewives are a formidable predator and competitor with newly hatchery walleye and perch fry. We've theorized for a long time that if we could get lower alewife numbers, we'd enjoy better walleye and perch production. That seems to be exactly what's going on. Incidently, we are also seeing greatly improved lake trout recruitment in the main basin and some evidence of lake herring expansion. We think this likely traces back to the decline in alewives too.
So where does this leave us? Like I said last year, it raises a lot of questions. On the whole, I think this is a very positive turn of events for Saginaw Bay, to see that it is still capable of producing large walleye and perch year classes. The relatively poor survival of this new production is frustrating, however. It may have been that the magnitude of the 2003 year class was simply too much to sustain. Maybe more intermediate (but still strong) year classes like that of 2004 will do better. We'll see in time. The 2003 walleyes will likely start recruiting to the fishery sometime this summer (reach 15" in length) so we'll begin to see some benefit of all this to the fishery. The size may not be impressive for a while , but the catch rates should be very good. The large size will come in time as these fish grow older and in the mean time, there are some older walleyes still out there too.
So I am optimistic for the bay, but lots of unknowns still. These are some very interesting times to say the least.
-Dave