Since the Ontario Ministry of Natural Resources has been making such good progress in the management of lakes in this province, you can expect to see some of this kind of influence on Mille Lacs. From the study,
Strategies for Managing Walleye in Ontario
Diagnostics and Sampling Standards
Biological Reference Points
Productivity of walleye lakes depends on the availability of suitable habitat, nutrient
levels, and climate. Maximum sustainable yield (MSY, kg.ha-1.year-1) can be estimated
by a formula provided by Lester et al. (2002):
MSY = 0.97 PTOHA TDS0.52 G1.30
where PTOHA is an index of habitat suitability, TDS (Total Dissolved Solids in mg L-1) is an
index of nutrients, and G (Growing Degree Days x 103
) is a climatic index. This index of
habitat suitability is a complex function of water clarity, lake bathymetry, and thermocline
depth (see Lester et al. 2002 for details). This formula implies that relatively large,
shallow lakes in Ontario with intermediate Secchi depth (e.g., 1-3 m), high TDS, and
high GDD tend to offer the highest walleye yields. It predicts the highest walleye yields
in Ontario inland lakes are approximately 3 kg.ha-1. These high yields are found in only
a few southern lakes.
Indications of Population Health
When MSY is viewed as a threshold, a desired state of the population can be defined by
critical levels of stock biomass and fishing mortality. These criteria depend on the
equilibrium (i.e., long term sustainable) relationship between biomass (B) and fishing
mortality (F) in which the equilibrium biomass of a stock decreases as fishing mortality
increases. Yield (= FB) therefore has a dome shaped relationship with fishing rate. The
peak of the yield curve (MSY) supplies a reference that identifies critical values of
biomass (BMSY) and fishing mortality (MMSY). These biological reference points can be
used to classify a fishery into one of four stages of development.
MSY-based definition of a desired state of a walleye population. In (a) the equilibrium
relationship between exploitable fish biomass (В) and fishing mortality (F) is portrayed. In (b) the
resulting equilibrium relationship between fish yield and fishing mortality is shown. The peak yield
(MSY) in (b) occurs when F = Fmsy and В = Вmsy. These criteria (dotted lines in (a)) identify four
stages of development (i.e., 4 quadrants).
Stage 1 (healthy) : low fishing mortality and high biomass. This state is
expected during the early stages of fishery development.
Stage 2 (overexploited - early) : high fishing mortality and high biomass. This
state is expected only during the early stages of overexploitation because stable
combinations of fishing mortality rate and biomass do not exist in this quadrant.
Stage 3 (overexploited - late) : high fishing mortality and low biomass. This
state indicates that the waterbody is being overexploited and that the expected
decline in fish biomass has occurred.
Stage 4 (degraded, recovering) : low fishing mortality and low biomass. This
state indicates that the stock was probably overexploited in the past and is
expected in the natural course of fishery development because anglers are likely
to shift their effort to other lakes once catch rates on one lake decline due to the
reduction in biomass. Stable (i.e., equilibrium) combinations of abundance and
mortality are not expected in this quadrant. If fishing mortality rate remains low, a
gradual transition to stage 1 should occur. This recovery process may be
inhibited by changes in the fish community resulting from heavy exploitation of
one species (Walters and Kitchell 2001).
Stage 1 is the desired state because it implies a fishery has not been exploited beyond
MSY and is thus consistent with the principle of sustainability. Maintenance of fisheries
in this state should represent a goal for management. More stringent criteria (i.e.,
harvest controls), aimed at sustaining higher fish abundance, may be preferred for social
or economic reasons. For example, the management objective might be to provide high
fishing quality. In this case, MSY criteria would not be appropriate. To offer higher
fishing quality, fish abundance must be sustained closer to the unexploited level. Thus,
Stage 1 would be defined by a higher fish abundance criterion and lower fishing mortality
criterion. This direction of change is acceptable; indeed, evaluation of its potential
benefits is encouraged. On the other hand, less stringent criteria allowing fisheries to
operate beyond MSY are not acceptable because they may compromise the
sustainability objective.
Sampling Standards and Protocols
Index netting surveys are intended to provide a relatively quick and inexpensive means
of assessing the health and relative abundance of the walleye population in a waterbody.
Standardized techniques are required to ensure that information can be compared with
similar data for other lakes and geographic regions. If the catchability and size
selectivity of the index fishing method is known, the absolute abundance of a stock and
its mortality rate can be estimated from catch data. These estimates can then be
compared to reference values determined for a particular stock. Standard netting
techniques described below are being calibrated through a variety of methods so that
diagnostic methods described above can be applied.
Two netting techniques: fall walleye index netting (FWIN) (Morgan 2000) and end of
spring trap netting (ESTN) (Skinner and Ball 2004), have been developed and field
tested as new provincial sampling protocols for walleye. Both techniques involve a
stratified sampling design, standardized gear specifications, depth criteria, and timing
I'm definitely not jumping on the bandwagon of 'faith' that this blue ribbon calvary is here to do anything other than find more ways to continue the current policy, & that policy is to manage for the use of gill nets....