An alternative index of abundance for Atlantic skipjack (Katsuwonus pelamis) based on catch ratio and abundance of a reference species.

Indices of abundance, frequently based on catch rates per unit effort (CPUE), are one of the main inputs to tropical tuna stock assessments. While standardized longline CPUE series are routinely obtained and used in the stock assessments of yellowfin and bigeye tunas, the standardization of the effort in fisheries targeting skipjack tuna is more problematic, due to several factors that are known to affect the efficiency of the fleets but are difficult to quantify. In this scenario, alternative approaches need to be tested. In this document, we propose an alternative approach based on the ratio in the catch of skipjack vs yellowfin tuna, using the abundance of the reference species as an offset in the standardization