Member
Posts: 2680
Location: Essexville, MI./Saginaw Bay. | I think you'll see what I was talking about in this relevent section of the ODNR report. Pay special attention to the catch to age population and recruitment in the second and third paragraphs down. These smaller walleyes in there much smaller numbers (as they grow) will be the dominent catchable fish in the years to come.
Taken from 2010 Review of Lake Erie Walleye Fisheries.
Review of Walleye Fisheries in 2010
Fishery effort and walleye harvest data were combined for all jurisdictions and
Management Units (Figure 1) to produce lake-wide estimates. The 2010 total estimated
lake-wide harvest of walleye was 2.116 million walleye (Tables 1 and 2), with a total of
1.997 million walleye harvested in the total allowable catch (TAC) area. This harvest
represents 91% of the 2010 TAC of 2.200 million walleye and includes walleye
harvested in commercial and sport fisheries in Management Units 1, 2, and 3. An
additional 115,057 walleye (5% of the lake-wide total) were harvested outside of the
TAC area in Management Units 4 and 5 (referred to as Unit 4 in the Tables). The sport
fish harvest of 1.153 million walleye in 2010 was nearly unchanged from the 2009
harvest of 1.166 million, but was 53% below the long-term (1975-2010) average of
2.458 million. The 2010 Ontario commercial harvest was approximately 0.962 million
walleye lake-wide, with 0.939 million caught in the TAC area (Table 2). Ontario does not
conduct angler creel surveys annually. The most recent Ontario creels were completed
in 2008, 2004, and 2003 in walleye MUs 1, 2 - 3, and 4 - 5, respectively. If the 2010
Ontario sport harvest was comparable to these earlier reference years, then Ontario
lake-wide sport harvest would be approximately 48 thousand walleye, with 46 thousand
harvested within the TAC area. Combined with reported commercial walleye harvest in
the TAC area, this total harvest would represent 104% of the Ontario TAC allocation of
0.947 million walleye. Ontario commercial harvest data in this report have not been
2
adjusted by the 3.3% deducted from individual transferable quotas for icing fish. Taking
into account Ontario’s commercial icing protocol and unknown sport harvest, it is
possible that Ontario exceeded the 2010 TAC, but if so, by an amount less than 1%.
The Ontario commercial harvest was 11% lower than the 2009 harvest and 46% of the
long-term average (1978-2010; Table 2, Figure 2).
Sport fishing effort increased 6% in 2010 from 2009, to a total of 2.8 million angler hours
(Table 3, Figure 3). Compared to 2009, sport effort increased in Management Units 1
and 4, but decreased in Management Units 2 and 3. Lake-wide commercial gill net effort
in 2010 (4,937 km) decreased 38% from 2009 to the lowest effort observed since 1975
(Table 3, Figure 4).
Sport harvest per unit of effort (HUE, walleye/angler hour) in Unit 1 (0.47 walleye/angler
hour) decreased (16%); however, in Management Unit 2 (0.39 walleye/angler hour),
Management Unit 3 (0.52 walleye/angler hour), and Management Unit 4 (0.30
walleye/angler hour), rates increased by 7%, 18%, and 18%, respectively, compared to
2009. In Management Unit 1, the sport harvest rate was 15% below the long-term
average (0.46 walleye per angler hour; Table 4, Figure 5). In contrast, the sport harvest
rates in Management Unit 2 (22%), Management Unit 3 (46%), and Management Unit 4
(41%) were all above the long term means in 2010. The 2010 lake-wide average sport
HUE of 0.39 walleye/angler hour was 9% lower than the long-term mean of 0.43
walleye/angler hour.
In 2010, total commercial gill net harvest per unit effort (HUE; 194.9 walleye/kilometer of
net) increased 43% relative to 2009, and was 62% above the long-term lake-wide
average (120 walleye/kilometer; Table 4, Figure 5). Commercial gill net harvest rates in
2010 increased for each Management Unit compared with 2009. Increases of 59%,
37%, 36%, and 65% were recorded for Management Units 1 through 4, respectively.
Fishing success was largely based on two age groups, ages 7-and-older fish (largely
composed of the 2003 year class) and age 3 fish (the 2007 year class) evident from the
age composition in the harvest. Ages 7-and-older walleye comprised 63% of the lakewide
sport fishery harvest and 36% of the total commercial fishery harvest (Tables 5
and 6). The 2007 year class (age 2 walleye) represented 21% of the total sport harvest
and 42% of the total commercial harvest (Table 6). Lake-wide, ages 7-and-older fish
accounted for 51% of the harvest, while the 2007 year class contributed 31%. The low
contributions from the age 4, 5, and 6 cohorts (2006, 2005, and 2004 year classes,
respectively) is an indication of their relatively low abundance.
Across all jurisdictions, the mean age of walleye in the harvest ranged from 5.4 to 7.3
years old in the sport fishery, and from 4.1 to 7.8 years old in Ontario’s commercial
fishery (Table 7, Figure 6). The mean age of walleye increased in the sport fishery for
the 4th consecutive year, but decreased for a second consecutive year in the
commercial fishery. The mean age in the sport fishery was 6.1 years, above the longterm
(1975-2009) mean of 4.2 years, and the highest recorded since at least 1975. In
the commercial fishery, the mean age was 4.6 years, higher than the long-term (1975-
3
2009) mean of 3.6 years, and the 3rd highest in the time series (1975-2010). The mean
age of the total harvest in 2010 (5.4 years) was the highest in the time series (1975-
2010). This reflects the continued dependence of the fisheries on the 2003 (age-7) and
2007 (age-4) year classes, with little contribution to the fisheries from any other cohort
in 2010.
Catch-at-Age Population Analysis and Abundance as fallows.
The WTG continued to use the Automatic Differentiation Model Builder (ADMB) catchat-
age analysis to estimate walleye population abundance from 1978 to 2010 (Walleye
Task Group 2001). The model continues to include fishery data from the Ontario
commercial fishery (west and central basins) and sport fisheries in Ohio (west and
central basins) and Michigan (west basin). Since 2002, the standard WTG model has
included 3 index gill net surveys. Over the years, evidence mounted that pooling the
Michigan and Ohio gill net surveys had both a logical and statistical basis. In fall 2010,
after conferring with Michigan State University’s Quantitative Fisheries Center, the WTG
elected to combine the MI and OH index gill net survey data sets for the WTG 2011
model. This two-survey configuration will now be considered the standard model
configuration.
The model assumes log-normal distributions for catch-at-age (ages 2 through 7+, i.e.,
seven and older) and fishing effort. Natural mortality (M) is fixed in the model for all
ages and years at 0.32. The key parameters, including age-2 recruitment and
population size in the first year of the model, fisheries catchability, and selectivity, are
estimated using a maximum likelihood approach with a concentrated likelihood
configuration. The abundances-at-age were derived from the estimated parameters
using an exponential survival equation. Since 2010, lambdas have been derived based
on an expert opinion approach described in the Review of Lambda Weightings
section of the 2010 Walleye Task Group Report (WTG 2010).
The ADMB estimate of age-2 abundance in the last year of the model is known to have
the highest error bounds, since the model contains little data about this year class. In
2010, the age-2 estimate for 2009 (i.e., the 2007 year class) was assessed to be an
outlier by the WTG, and the WTG substituted an alternate age 2 estimate for the 2007
year class in 2009 (WTG 2010). In late summer 2010, the WTG requested guidance
and recommendations from the Quantitative Fisheries Center (QFC) at Michigan State
University on how best to assess status of the age-2 abundance estimated by the
ADMB model for the most recent year of the fishery. The QFC recommended that the
WTG utilize the regression estimate of abundance derived from the age-0 interagency
trawl catch rate for that cohort as the age-2 estimate. By consensus the WTG adopted
that recommendation and will continue to use the regression estimate for the age-2
estimated abundance in the latest year of the fishery. See Recruitment Estimator for
Incoming Age 2 Walleye and 2011 Population Size Projection section below for
details on methodology. The 2010 west-central population estimate from the 2011 WTG model was 22.966
million age 3 and older walleye (Table 8, Figure 7). The 2011 model estimate of age 2
fish in 2010 (2008 year class) was 11.201 million fish. The regression estimate of age 2
fish in 2010 was 3.731 million fish (Table 9). The total 2010 west-central population
estimate (age 2 regression estimate for the 2008 cohort plus age 3 and older walleye
estimate from 2011 WTG model) was 26.697 million walleye (Table 8). Two age groups
accounted for 79% of the 2010 stock size. Abundance of age-3 fish (2007 year class)
was estimated at 13.322 million fish, while age 7 and older fish (mainly 2003 year class)
abundance was estimated at 7.834 million. There were an estimated 9.642 million age 4
and older walleye in 2010. The abundance of the 2003 year class at age-2 in 2005
(68.824 million) is now estimated to be 26% higher than the strong 1982 (54.051 million)
yearclass and 49% higher than the 1986 (45.164 million) year class at age-2 (Table 8).
Recruitment Estimator for Incoming Age-2 Walleye and 2011
Population Size Projection
A linear regression model was used to estimate age-2 walleye recruitment for 2010 and
2011. This regression utilizes estimates of age-2 walleye abundance from the catch-atage
analysis of the WTG model and walleye catches from pooled Ontario and Ohio
bottom trawling reported as number of young-of-the-year walleye per hectare (Table 9,
Figure 8). Linear regression used by the WTG to predict the abundance of these
cohorts excludes the most recent ADMB age-2 estimate (the 2008 year class), as it has
the widest estimation error due to the presence of only a single estimate of age in the
model time series. The 2010 age-2 population estimate (2008 year class) from linear
regression was 3.731 million walleye (Table 9). This cohort and the 2009 year class
(3.550 million walleye) appear comparable in strength.
The standard process for projecting age-3 and older abundance for the year in which
RAH is reported (i.e., 2011 in this case) involves applying statistical catch-age analyses
(SCAA) survival estimates from the last year in the ADMB model to the abundance
estimate of age-2 and older walleye in the last year (2010). Estimated age-specific
survival is a function of estimated instantaneous fishing mortality (F), selectivity, and
assumed natural mortality (M, 0.32) during 2010.
The 2011 estimated abundance of age-2 and older walleye is approximately 21.243
million (Table 10, Figure 10). It is projected that the 2003 year class (age-7) and older
cohorts will represent 25% (5.384 million), whereas the 2007 year class will comprise
41% (8.701 million) of the population in 2011. Walleye spawner abundance in 2011
(ages-4 and older) exceeds the estimated values for 24 of the 34 previous years
modeled (1978-2010). However, the spawner-recruit relationship for Lake Erie walleye
is poorly understood, with recruitment influenced by a combination of abiotic and biotic
factors.
Edited by walleye express 6/9/2011 3:57 PM
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Member
Posts: 2680
Location: Essexville, MI./Saginaw Bay. | Fishing success was largely based on two age groups, ages 7-and-older fish (largely
composed of the 2003 year class) and age 3 fish (the 2007 year class) evident from the
age composition in the harvest. Ages 7-and-older walleye comprised 63% of the lakewide
sport fishery harvest and 36% of the total commercial fishery harvest (Tables 5
and 6). The 2007 year class (age 2 walleye) represented 21% of the total sport harvest
and 42% of the total commercial harvest (Table 6). Lake-wide, ages 7-and-older fish
accounted for 51% of the harvest, while the 2007 year class contributed 31%. The low
contributions from the age 4, 5, and 6 cohorts (2006, 2005, and 2004 year classes,
respectively) is an indication of their relatively low abundance.
Across all jurisdictions, the mean age of walleye in the harvest ranged from 5.4 to 7.3
years old in the sport fishery, and from 4.1 to 7.8 years old in Ontario’s commercial
fishery (Table 7, Figure 6). The mean age of walleye increased in the sport fishery for
the 4th consecutive year, but decreased for a second consecutive year in the
commercial fishery. The mean age in the sport fishery was 6.1 years, above the longterm
(1975-2009) mean of 4.2 years, and the highest recorded since at least 1975. In
the commercial fishery, the mean age was 4.6 years, higher than the long-term (1975-
3
2009) mean of 3.6 years, and the 3rd highest in the time series (1975-2010). The mean
age of the total harvest in 2010 (5.4 years) was the highest in the time series (1975-
2010). This reflects the continued dependence of the fisheries on the 2003 (age-7) and
2007 (age-4) year classes, with little contribution to the fisheries from any other cohort
in 2010.
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