Regulators in many countries have adopted quotas as a means of dealing with the open access problem inherent in fisheries. Unit quotas for the Norwegian purse seine fleet were introduced in 1996 but consolidation of licenses has been in place since 1978. The current Norwegian regulatory system does allow for some transferability of quota. The purpose of this paper is to employ an index approach to investigate the result of changes in regulatory quota policy by decomposing vessel profitability by prices, productivity, vessel size and stock levels. The index decomposition approach was introduced by Fox et al. (2003) based on the Törnqvist (1936) index. The index can be defined over different structures of the fleet and different time periods to measure the impact of regulatory changes on the individual factors generating profit. The study uses a large individual vessel data set for the period 1994-2013. The data set provides detailed descriptions of revenues, harvests, costs, inputs and vessel characteristics. In addition, the sale of vessels and quota can be tracked over the period allowing a measure of the impact of regulatory change on consolidation of vessels and changes in capital structure overtime. This index approach, although not causal in the sense of Dickert and Schweder (2015), can measure the importance of individual output prices, factor prices, vessel structure, ownership, and stocks changes impacting profitably. Results suggest that changes in regulatory quota policy impacting the purse seine fleet has increased profitability, reduced the number of vessels and greatly increased vessel size.