Global monthly catch of tuna, tuna-like and shark species (1950-2021) by 1° or 5° squares (IRD level 2)

Major differences from previous work:

For level 2: 

• Catches in tons, raised to match nominal values, now consider the geographic area of the nominal data for improved accuracy.
• Captures in "Number of fish" are converted to weight based on nominal data. The conversion factors used in the previous version are no longer used, as they did not adequately represent the diversity of captures.
• Number of fish without corresponding data in nominal are not removed as they were before, creating a huge difference for this measurement_unit between the two datasets.
• Nominal data from WCPFC includes fishing fleet information, and georeferenced data has been raised based on this instead of solely on the triplet year/gear/species, to avoid random reallocations.
• Strata for which catches in tons are raised to match nominal data have had their numbers removed.
• Raising only applies to complete years to avoid overrepresenting specific months, particularly in the early years of georeferenced reporting.
• Strata where georeferenced data exceed nominal data have not been adjusted downward, as it is unclear if these discrepancies arise from missing nominal data or different aggregation methods in both datasets.
• The data is not aggregated to 5-degree squares and thus remains unharmonized spatially. Aggregation can be performed using CWP codes for geographic identifiers. For example, an R function is available: source("https://raw.githubusercontent.com/firms-gta/geoflow-tunaatlas/master/sardara_functions/transform_cwp_code_from_1deg_to_5deg.R")

Level 0 dataset has been modified creating differences in this new version notably : 

• The species retained are different; only 32 major species are kept.
• Mappings have been somewhat modified based on new standards implemented by FIRMS.
• New rules have been applied for overlapping areas.
• Data is only displayed in 1 degrees square area and 5 degrees square areas.

The data is enriched with "Species group", "Gear labels" using the fdiwg standards.

These main differences are recapped in the Differences_v2018_v2024.zip

Recommendations:

To avoid converting data from number using nominal stratas, we recommend the use of conversion factors which could be provided by tRFMOs.

In some strata, nominal data appears higher than georeferenced data, as observed during level 2 processing. These discrepancies may result from errors or differences in aggregation methods. Further analysis will examine these differences in detail to refine treatments accordingly. A summary of differences by tRFMOs, based on the number of strata, is included in the appendix.

Some nominal data have no equivalent in georeferenced data and therefore cannot be disaggregated. What could be done is to check for each nominal data without equivalence if a georeferenced data exists in different buffers, and to average the distribution of this footprint. Then, disaggregate the nominal data based on the georeferenced data. This would lead to the creation of data (approximately 3%), and would necessitate reducing/removing all georeferenced data without a nominal equivalent or with a lesser equivalent. Tests are currently being conducted with and without this. It would help improve the biomass captured footprint but could lead to unexpected discrepancies with current datasets.