Mortality Flashcards
Key concepts associated with Mortality
There are various factors that may lead to mortality, both directly and indirectly. It is essential to comprehend these mechanisms and their cumulative impact. One of the significant drivers of population dynamics is mortality, whether it be natural or due to fishing. These parameters are crucial in age-structured population models.
How is mortality expressed?
as an instantaneous loss rate → rate of change in stock size at a particular moment (not over one year, one day, etc.)
How would you describe this equation?
What is Z represent?
typically used to denote the total instantaneous loss rate
What is important to note about absolute loss?
will depend on population size (decrease by larger amount when population large)
Instantaneous loss rate →
current population numbers can be described as the exponential decay of previous population numbers
N1/N0 is an expression of what?
Survival (S)
Survival
annual proportion of population that survives
What does this expression interpret?
Relationship between instantaneous mortality and annual survival rates
What does this expression interpret?
Total annual mortality rate
Additive rates
Instantaneous rates are additive
How would you go about solving this equation?
What is the total annual mortality rate for a fish stock that experiences 80% mortality during winter & spring and 40% mortality during summer & fall? (Hint: it’s not 120%)
Using the equation that looks at the relationship between instantaneous mortality and annual survival rates for both seasons. Then add those together to get the total annual mortality.
Why would you not just add the two percentages together?
: Z has no limit but A cannot exceed 1
What are the two components of mortality?
F & M
F
instantaneous fishing mortality rate
M
instantaneous natural mortality rate
Z =
F+M
F Includes
all deaths from fishing activities
Direct removals: fish caught & kept
Indirect removals: fish that are not kept but are still killed from fishing activities (discards, cryptic mortality)
M includes
mortality from many sources (starvation, disease, senescence, spawning stress, predation, abiotic factors, etc.)
Often assumed constant over life of fish
Explain Baranov’s catch equation:
WHy is Baranov’s catch equation so useful?
Links things that we observe (catch) with things we want to know about but don’t have numbers. Does this base on the exponential decay model.
M is a critical parameter in fisheries stock assessments. Why?
M relates directly to productivity of stock → higher M, higher optimal fishing mortality (generally)
WHy is M difficult to measure?
do not observe directly); easier for unfished populations (age/size composition of catch and exponential decay)
What are the different methods used to estimate M?
Information-intensive methods
Information-limited methods
