From: The Status of Walleye in Nipigon Bay Area of
Concern: 2012
Prepared for Environment Canada
By: Terry Marshall,
Marshall Consulting
March 31, 2013
I am skipping over the
next 14 pages of the Report which covers the following topics:
Recent Research, assessment
and monitoring studies:
Genetics of stocks
Telemetry studies: seasonal movements and habitat use ( they
want to continue this study to see if there really are two distinct spawning
populations)
Walleye spawning observations and drift netting Nipigon
River
Walleye and Northern Pike abundance: Lake Helen
Fish Community assessment Lake Helen
Electrofishing surveys: Nipigon Bay and River
Fish Community Index Netting: Nipigon Bay
Walleye Population assessment: Nipigon Bay
STATUS OF WALLEYE STOCKS AND THEIR HABITAT IN THE NIPIGON
SYSTEM
Reference sites
Recovery of collapsed populations
In all cases, rainbow
smelt were also present in these water bodies which is an important
consideration if making
comparisons. The Nipigon Bay East area
has the greatest biomass of rainbow smelt documented in Canadian Waters of Lake
Superior (Yule et al 2008). The species
was also found to be generally of larger body size in this part of the lake. The presence of a large and abundant prey
such as rainbow smelt has a positive influence on walleye growth
energetics. In Western U.S. reservoirs,
growth rate increases once rainbow smelt became a large part of walleye diet
[Johnson and Goetti 1999; Groeb et all 2008]. On the other hand, rainbow smelt
may also compete with and prey on age-0 walleye which in some instances can
significantly reduce their density [Mercedes-Silva et al 2007].
STATUS INDICATORS
Walleye Population status
1.
Abundance remains low – approx. 5000 Lake Helen
2.
Density is increasing
3.
Growth rates are very high
4.
Mortality is very low
Walleye
Habitat status
Information
needs ;
Genetic
analysis of stocks
Population
monitoring and assessment
If
genetic analysis determines that two discrete populations exist, the size of
each must be determined independently.
CONCLUSIONS
There
have been many changes in the 50+ years since Ryder’s [1956] early studies and
the collapse of the walleye fishery in Nipigon Bay. There have been drastic shifts in the
composition of the aquatic community, along with significant improvements to
nearshore habitat within the Bay, and recent changes to the thermal properties
of the area brought about by climate warming.
Together , these present a new environment for walleye to which they
continue to adapt. This process appears to have promoted the development of two
separate stocks of walleye in the Nipigon system.
We
have a new population [or two] of
walleye here today, different from the historic population in terms of its
genetics, its spawning behaviour, and its annual movement patterns and use of
habitat. This population is thought to
be at a relatively low level of abundance compared with historic estimates, but
quite healthy in all other respects.
Growth rates are rapid and mortality is low. Together these traits suggest that large,
rapidly maturing fish are present and have the potential to produce quantities
of offspring in the future. Clean, high
quality substrate is available in unobstructed spawning areas in both Nipigon
and Jackfish rivers and it not constraining recovery.
On the basis
of this evidence, it is recommended that the BUI status of the walleye
population and their habitat in the Nipigon Bay AOC be updated to “ Not
impaired”.
The
40,000 fish target for Walleye recovery may never be achieved in light of all
the changes observed in this ecosystem [Colby 2007]. All that can be done to accomplish this has
been done. Maintaining fishing mortality
at a low level will help the walleye population expand to achieve its new
equilibrium.
