Northwest Fisheries Science Center

Biological Metadata and Data Library


Observer Coverage Rates

Observer coverage rates are defined as the percentage of landings that were observed out of the total landings for a target species. The coverage rates are calculated by taking the total weight of target species landings on observed vessels in a particular sector and dividing by the total weight of target species landings of that entire sector. Target species for observed sectors include Pacific Coast Groundfish Fishery Management (FMP) groundfish (excluding Pacific hake), sablefish, California halibut, pink shrimp, and state-managed or groundfish nearshore species.

Total Catch of Individual Species

Observed total catch is summarized in each sector for individual species or to the appropriate level of taxonomic identification within the WCGOP data. Total catch is calculated as the sum of observed discarded catch weight plus the observed retained catch weight. Because both the observed discarded and the observed retained weights are estimates, the observed total catch contains an element of uncertainty.

Spatial Data Products

Areas fished by each sector are mapped and summarized by scientists to review changes in fishing behavior and potential data bias. Detailed maps of tow/set-level fishing locations can not be released due to confidentiality mandates. However, aggregated (i.e., non-confidential) temporal and spatial data products can be presented.

Maps representing the annual spatial distribution of fishing operations recorded in fleet LE trawl logbooks and observed tows are one such product. Trawl tows were assigned to 10 × 10 km grid cells based on either the geographic coordinates of a tow start location or the intersection of a trawl towline model (a line drawn from the start to end location of a trawl tow) . Grid cell shading reflects the number of trawl logbook tows, with darker shading indicating more tows. The circles overlaid on each cell reflect the number of observed tows, with larger circles indicating more tows. Grid cells with the darkest shading and the smallest circles indicate fishing locations that received less observer coverage relative to fleet-wide fishing effort.

Maps representing the spatial distribution of only observed fishing operations can also be represented for other fleets which lack spatial information contained in mandatory logbook programs. However, maps do not necessarily reflect sector-wide effort. In one product, the fixed gear fleets were represented by assigning the set (start location of fishing) and haul (location of gear retrieval) to 20 × 20 km grid cells. The fishing effort associated with each fixed gear fishing event was divided equally between the set and retrieval locations. The data were combined across years to create non-confidential data products.

We urge caution when utilizing these data products due to the complexity of groundfish management and fleet harvest dynamics.


For observation and analyses purposes, the U.S. West Coast groundfish fishery and other state-permitted fisheries can be segregated by fishery sector specific criteria, which can vary by permit structure (federal and state), fishing target, gear type and harvest specifications.