Precision of Data from Alternative Fisheries Monitoring Sources: Comparison of Fisheries-dependent Data Derived from Electronic Monitoring, Logbook and Port Sampling Programs from Pelagic Longline Vessels Fishing in the Palau EEZM_effects_2018R1.pdf

KEY FINDINGS
• Catch rates from electronic monitoring (EM) data were about an order of magnitude higher than from logbook data. The species richness from logbook data was about half of that from EM data. Logbook data are very likely inaccurate due to substantial underreporting.
• There were no significant differences in catch composition, nominal mean catch rates, and mean discard rates from logbook data with versus without EM systems. The presence of EM appears to not change logbook data recording.
• Port sampling data from trips with EM coverage lacked information on the total retained catch of non-tuna and non-billfish species, while the EM data recorded 22 species other than tunas and billfishes were retained in the three trips. Port sampling data from trips with EM coverage provided information on retained catch rates for only bigeye and yellowfin tunas and billfishes, representing a very small proportion of the number of retained species.
• The mean retained tuna catch rate from EM data was 41% higher than that from port sampling data. Port sampling data indicated that 46 bigeye and 144 yellowfin tunas were retained, while EM data indicated that 45 bigeye, 172 yellowfin and 11 other tuna species were retained. Based on limited available data, port sampling produces imprecise estimates of retained species catch rates relative to estimates from EM coverage.