ignomonicM

ignomonicM estimates stage-specific natural mortality (M) using a gnomonic time-interval approach to quantify ontogenetic variation in marine species.

Key Features:

• Gnomonic Approach: Segments the life cycle into gnomonic intervals whose durations increase proportionally with elapsed time from birth to estimate mortality across developmental stages.
• Data Requirements: Requires number of gnomonic intervals, egg stage duration, longevity, and fecundity as explicit input variables.
• Deterministic and Stochastic Approaches: Provides deterministic calculations yielding fixed M_i per interval and stochastic assessments that propagate uncertainty by treating mean lifetime fecundity (MLF) as a primary source of variability.
• Auxiliary Information Integration: Incorporates additional temporal data linked to specific gnomonic intervals to refine mortality estimates.
• Reproducibility and Verification: Has been tested for reproducibility and verification across reports for estimating M across ontogenetic stages.

Scientific Applications:

• Ecological Modeling: Supplies stage-specific M estimates for incorporation into ecological models.
• Fisheries Management: Aids fisheries management by identifying life stages most affected by natural mortality and assessing impacts of fishing pressures.
• Model Input Data: Provides variable natural mortality across ages as input data for population and stock assessment models.
• Case Study: Demonstrated with Pacific chub mackerel (Scomber japonicus) to illustrate data collection and mortality estimation across life stages.

Methodology:

Divides the life cycle into gnomonic intervals and calculates interval durations and natural mortality (M_i) from provided biological data (number of intervals, egg stage duration, longevity, fecundity), supporting deterministic calculations and stochastic assessments that incorporate mean lifetime fecundity (MLF) as a source of uncertainty.