Estimation of total retained catch based on frequency of fishing trips, inspections at sea, transhipment, and VMS data

The satellite-based vessel monitoring system in the Norwegian Economic Zone provides detailed information about individual trips by vessels. Vessel sizes are available through official registries, and the storage capacity for fish is estimated using the established conversion factors as a function of the vessel's gross registered tonnage. Scientists have had access to the database of both transport and fishing vessels, with records for individual trips, in addition to information about the total round weight (whole fish) of cod and haddock for trips inspected by the coastguard. The analysis assumes that trips with complete documentation of the fish on board are a random sample, so allowing estimation of the mean amount of both cod and haddock per trip, and annual totals give the number of trips per vessel annually. ICES has accepted this methodology for estimating illegal, unregulated, and unreported (IUU) catches, which has resulted in 15 000-166 000 t (3-35%) being added to the officially reported landings of Northeast Arctic cod during the years 2002-2008. IUU landings have decreased in recent years, but are so important for assessment and management that estimates continue to be made annually.