Operational Plan for the Restoration of Diadromous Fishes to the ...

The process begins with defining the objectives of the sampling program, and then
defines the target population(s) and the attribute(s) that are of interest. Next, the
sampling frame requirements and materials are specified, as are the sampling
design requirements to meet the objectives. A sampling design and final sampling
frame are created, and the design is then used to select sampling sites from the
frame. The results are output as an ESRI shapefile with an attribute table. Overall,
this must be an iterative process, balancing various sampling objectives with
achievable sampling effort. There will be a tradeoff between sampling for status and
trends verses sampling to test specific hypotheses. The objectives must balance
these competing needs given a certain amount of effort. The sample design should
also address both short and long term needs. Sampling to assess particular
management actions may require a very different design than that needed to asses
naturally reproducing populations.
Sample Size for Electrofishing
Sample size and power present many challenges. We have chosen to sample at
least 5-10 sites per drainage statewide based on the analyses described below
(also, see Figure 2):
“We recommend a minimum of 5 – 10 sites be sampled annually within a HUC of
interest using either multiple pass removal estimates of mean density or mean
CPUE methodologies. This amount of sampling effort will provide 80% power in
detecting a trend in the index of abundance for annual rates of change between 0.1
and 0.2. Although the ability to detect smaller changes is desirable, the amount of
sampling required to detect such changes greatly increases at annual rates of
increase less than 0.1 and may not be feasible with limited sampling resources.
Annual rates of change of 0.1 to 0.2 correspond to approximately a doubling or
tripling of the index of abundance in a 10 year period. Because of the natural annual
variation in parr abundance, anything less than a true doubling of abundance may
be of little to no significance in overall population growth rates of Atlantic salmon.”
(from J. Sweka, J. Trial, and J. Kocik, draft White Paper on Atlantic Salmon Stock
Assessment Status and Needs, April 7, 2008.).
While trend detection is one goal of juvenile assessment, other goals such as
describing the status of juvenile abundance, or mechanistic relationships between
environmental variables and juvenile abundance, survival, or growth, are critically
important. Therefore, the sampling we describe here is a minimum to detect trends
and describe status, but more in depth sampling may be required for some
objectives.
The 5-10 sites will represent annually sampled sites where full population estimates
are performed. In addition, a rotation of sites that includes CPUE and population
estimates will be sampled. The design of this will be specific to the drainage, but will
be based on a three year rotation, where each site will be visited every third year,
PRFP Page 192