Effects of Temporal Aggregation in Fishery Supply Models

Summary

This research focuses on an assumption that is commonly made upon the production technologies that may give rise to biased estimates: the ability to aggregate a vessel’s daily fishing production cycle over individual fishing days to the trip level. To conform with temporal aggregation requires that, at given output prices, production over the course of a trip is characterized by no search or learning effects, no stock effects (fish are distributed uniformly over time). Furthermore, if vessels fish more than one site, temporal aggregation requires that fish be uniformly distributed across fishing sites. Temporal aggregation would then fail, for example, if fishers employ multiple fishing strategies during a trip such as fishing offshore for one species and then move inshore to a different ecological niche to harvest another (because stock distributions are not uniform across sites). In an application to the Hawaii longline fishery, aggregation consistency was rejected for all models and further tests on the technology using aggregated data were also biased. In particular, results obtained using aggregated data suggest that production is joint and that fishermen are either not able to target specific species or have implausible targeting strategies. In contrast, daily results identify plausible targeting strategies and suggest that several species, including swordfish, have separate production functions. Importantly, this implies that swordfish, which comprises a high percentage of fishery catch and revenue, can be managed independently. The work is being conducted along with the first author, Rita Curtis, at NOAA headquarters in Silver Spring, Maryland.

Source: Unpublished

For more information, please contact: Ron.Felthoven@noaa.gov