The `menhaden`

data frame has 15 rows and 4 columns.
Age, fecundity-at-age, partial recruitment, fraction mature, and nautral mortality data for menhaden
to calculate eggs-per-recruit.

`menhaden`

This data frame contains the following columns:

- age
vector of ages

- fecundity
vector of weights at spawning for each age

- partial
partial recruitment vector

- pmat
vector of fraction of females mature at age

- M
vector of natural mortality value-at-age