Effects of Temporal Aggregation in Fishery Supply Models
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. For more information or to comment on this project,
contact ron.felthoven@noaa.gov.
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