To process West Coast Groundfish Observer Program data for further analysis, we:
- Expand the subsample of species composition to the tow/set-level.
- Translate observer species codes to the corresponding fish ticket data codes used in the Pacific Fisheries Information Network (PacFIN) database.
- Match observed trips to fish tickets.
- Merge retained observer data and fish ticket data.
- Remove incompletely sampled and failed observer data.
The West Coast Groundfish Observer Program species composition sampling procedure allows for subsampling, so tow/set-level expansions are needed to estimate the total retained and discarded weight for each species. We calculate the subsample's weight by summing across the observed weights of the individual species using the equation:
![w subscript k equals Summation sign with s below it, X subscript ks]()
where:
Xks = observed weight of the species s in group k in the subsample
Wk = weight of the subsample from group k
The sampling ratio (Rk) used to scale the subsample weights to the total weight of the group is calculated by dividing the weight of the subsample by the total weight of the group:
![Capital R subscript k equals w subscript k divided by y subscript k]()
where:
yk = the total weight of group k
The tow/set-level expanded weight of species s in group k is calculated by dividing the species weight in the subsample by the sampling ratio:
![Capital X subscript ks equals x subscript ks divided by Capital R subscript k]()
where:
Xks = the weight of species s in group k
Tallying the weight (Xks) of the species (s) across all groups (k) within a tow/set estimates the total weight of the species retained or discarded.
Merging the retained catch records from the observer data with fish ticket data provides more accurate retained estimates at the haul-level. Observers record fish ticket number(s) for each trip, which are confirmed using vessel, port, and return date. The fish ticket weights are often more accurate as well as legally binding, so we adjust total observer-recorded retained weights to match total fish ticket landings on all trips that have reliable observer-recorded catch data or usable proxies for all hauls on the trip and fish ticket data present in PacFIN. This matching process requires the translation of WCGOP to PacFIN species codes, which ensures consistency across the two datasets and increases the accuracy of fleetwide estimations.
We scale the total fish ticket recorded weight within each group based on the adjustment factor, which is calculated as:
![capital A subscript mtk equals x subscript mtk divided by Summation with k below of x subscript mtk]()
where:
Amtk = adjustment factor used for group k in tow/set t in trip m
Xmtk = lbs in group k in tow/set t in trip m
We then calculate the haul-level retained weights as:
![equation5.png]()
where:
Cmk = lbs in group k for trip m recorded on the fish ticket
When we cannot match a group in our observer data to a fish ticket group, we do not adjust the observer data. We distribute groups found only on the fish tickets across the observed tows/sets based on the proportion within each tow/set, calculated as:
![equation6.png]()
where:
Bmt = the proportion of observed catch in tow/set t in trip m
We apply this proportion using the equation:
![equation7.png]()
where:
Cmtk = lbs in group k for tow/set t in trip m recorded on the fish ticket
