Herring WG stomach based index

[sgaichas]

Initial index worked using forage index predators and spatial footprint in Spring and for an Annual model. Work identified by Herring WG in March 2024:

• Get a working Fall model by changing spatial footprint to include only strata where herring are observed in stomachs
• Curate the predator list: instead of the full bluefish piscivore list, apply criteria that include predators with herring in stomachs at 5 or more stations

[sgaichas]

Work in progress at https://noaa-edab.github.io/forageindex/HerringWGindex_footprint.html