fit_agTrend_ssl: Site-level fitting function
In dsjohnson/agTrendTMB: Interpolate Survey Counts For Site-Level Aggregating

Fit separate discrete-normal distribution models to an Steller sea lion counts at a single site

fit_agTrend_ssl(
  .x,
  model,
  obl.corr = FALSE,
  map.override = NULL,
  silent = TRUE,
  debug = FALSE,
  force = FALSE
)

`.x`	Data frame for an individual site. Must have been passed through prep_for_fit first!
`model`	Model for interpolation: 'const', 'lin', or 'gp' (see Details)
`obl.corr`	Logical. Should correction be made for oblique photos.
`map.override`	List. method for overriding parameter parameters set to fixed values. This should rarely need to be used
`silent`	Logical. Run without messages
`debug`	Logical. Step into fitting function for interactive evaluation
`penalty`	Wiggliness penalty for 'gp' model

There are 3 models which can be used for within site interpolation:

const This interpolates using a simple mean and variance for the site
lin A linear fit with time is used for interpolation
gp i.e., Gaussian Process. This model used a time trend plus a random walk of order 2 (RW(2)) to interpolate counts. Further, the RW(2) process can be further restrained to minimize 'wiggliness' of the curve when necessary. This prevents overfitting of the curve.

A list with the following elements: