PCWA-L 480.pdf - PCWA Middle Fork American River Project ...

Creating a Cohort
not grow to 2,155 grams, it grew to 90 grams, and so the software would try a P-value equal to 0.5
(or 50% of maximal consumption). The software iteratively recalculates the growth of your fish
based on different P-values until it finds a P-value (or proportion of maximal consumption) that
aliows your fish to grow from 60 to 90 grams. Once the software has determined the P-value, It, '
can use-that P-value in subsequent Run calculations.
Calculating a P-value based on a change In mass is the most common method; however, you
have the option of calculating your P-value based on total consumption during your simulation. For
example, your cohort might grow to some unknown mass based on a known yearly consumption
of 1,400 grams of food and a start mass of 200 grams, Based on your input data files and the
basic physiology of your fish, it might have a maximum consumption (which is equivalent to a Pvalue
of 1) of 6,800 grams of prey per year. Since your cohort didn't consume 6,800' grams of
prey, the software will use a lower P-value .and recalculate total consumption and repeat the
process until calculated consumption equals the consumption of 1,400 grams that you entered.
The resulting P-value might be around 0.48.
• Fit to end weight: Check this option if you would like the software to calculate your'
cohort's P-vaiue (proportion of maximal consumption) based on its change in mass
during the simulation.
• Fit to consumption: Check this option If you would like the software to calculate
your cohort's P-value (proportion of maximal consumption) based on its total
consumption of prey during the simulation.
Additional Analyses: With the possible exception of Input predator energy density, the
additional analyses are optional.
• Input predator energy density: Predator energy density is the joules per gram wet
body mass of your fish. in the real world your cohort's energy density wili fluctuate
over time. If you have prepared a predator energy density inpui file that represents
these changes, then select the Input predator energy density option and you'li be
prompted for that file in the User Input Data Files setup. otherwise, you can accept
the default value copied from the software's database for this species. If the
software's database contains no default energy density, then you will be required to
select this option.
• Spawning: Does your cohort spawn during your simulation? If so, select this option
, and you'll be prompted for the spawn day and percent body mass spawned in the
User Input Parameters setup.
'. Population mortality,: Your cohort can represent a population of fishes if you select
this option. This option assumes that you will provide mortality data (in the form of
percent of popUlation dying over time) during the User Input Data Files setup.
• Nitrogen and phosphorus analysis: Select this option if you would like to
determine the conversion of nitrogen and phosphorus from that which is contained in
the prey's flesh to that which is regenerated by the pred.ator. If you select this anaiysis
you will be prompted for prey concentration input data files and assimilation efficiency
input data files during the User Input Data Flies setup.
• Contaminant analysis: Select this option if you would like to model the changes in
contaminant concentration in the predator based on the contaminant concentrations
in its prey. If you select this anaiysis you wili be promptE1d for a prey concentration
input data file and an assimilation efficiency input data file during the User Input Data
Files setup. In addition, you must decide upon the mechanism by which the predator
will eiiminate some of the contaminants it has consumed.
• Net assimilation efficiency: Select this option if your predator will
assimilate contaminants based soleiy upon data provided in the contaminant
4-5