Analysis of the daily catch and effort data of the bluefin Algarve trap fishery during the years 1898-1900

Summary This paper is based on the recently recovered daily catch and effort data of the Algarve traps during the 1898-1900 period. The 18 traps that were then active in the Algarve South of Portugal were targeting the 2 migrations of BFT, toward and from the Mediterranean Sea. Their bluefin catches was significant, corresponding to average yearly catches of 61.000 bluefin, i.e. approximately 7900 t. Migration dates and durations in and out the Med are estimated based on the daily CPUEs of the traps. Migration patterns have been very stable during the 3 years. The entry migration took place during 42 days, and during 53 days for their return. Daily catches are showing large waves of tunas during the 2 migratory phases. It can be hypothesised that each of these tuna waves are spending about 52 days in the Med, and that each of these tuna groups are stable groups of schools that are consistent between their arriving and returning migrations. Migration trajectories along the Algarve coasts can be estimated from the daily CPUEs of the various traps and they appear to be variable between the various phases of the entry and returning migrations. The daily data by trap show that most traps catch entering BFT, but at quite low CPUE, when only few traps are efficient to catch the returning bluefin, but with much larger CP UEs. The analysis of catch and CPUEs during the entry and returning phase allows to conclude that the catchability and fishing mortality of the bluefin stock in the Algarve trap fishery was much larger during the return phase. Additional daily data from other traps, historical and contemporary, should be collected and analyzed in order to provide more comprehensive results on migration, stock structure and exploitation rate of the stock.