Studying small purse-seine vessel fishing behavior with tuna catch data: Implications for eastern Pacific Ocean dolphin conservation

Despite achievements in dolphin conservation for the tuna purse‐seine fishery of the eastern Pacific Ocean, debate continues about the magnitude and importance of dolphin mortality caused by small (unobserved) vessels. In‐port sampling of tuna catch size composition is a potentially cost‐effective m...

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Bibliographic Details
Published in:Marine mammal science 2013-10, Vol.29 (4), p.643-668
Main Authors: Lennert-Cody, Cleridy E., Rusin, Jeremy D., Maunder, Mark N., Everett, Edward H., Largacha Delgado, Erick D., Tomlinson, Patrick K.
Format: Article
Language:English
Subjects:
Animal and plant ecology
Animal, plant and microbial ecology
Animals
Applied ecology
Autoecology
Biological and medical sciences
Cetacea
Dolphins & porpoises
ETP
Exploitation and management of natural biological resources (hunting, fishing and exploited populations survey, etc.)
Forestry
Fundamental and applied biological sciences. Psychology
General forest ecology
Generalities. Production, biomass. Quality of wood and forest products. General forest ecology
International Dolphin Conservation Program
Mammalia
Marine
monitoring
Mortality
Ports
random forests
Sea water ecosystems
Studies
Synecology
Thunnus
Thunnus albacares
Tuna
tuna-dolphin
Vertebrata
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Summary:Despite achievements in dolphin conservation for the tuna purse‐seine fishery of the eastern Pacific Ocean, debate continues about the magnitude and importance of dolphin mortality caused by small (unobserved) vessels. In‐port sampling of tuna catch size composition is a potentially cost‐effective means of identifying unobserved vessels that may be catching tunas associated with dolphins because yellowfin tuna caught in association with dolphins are larger, on average, than those caught in other types of purse‐seine sets. A classification algorithm to predict purse‐seine set type (“dolphin” vs. “nondolphin”) was built from port‐sampling data on yellowfin tuna length‐frequencies and the date and location of fishing of large (observed) vessels. This classification algorithm was used to screen the port‐sampling data of small vessels collected during 2006‐2009, assuming the fishing practices of the two groups resulted in similar catch characteristics. From these results, hypothetical time series of dolphin mortality for small vessels were constructed and incorporated into a population dynamics model, along with mortalities of large vessels. Results suggest that any dolphin mortality of small vessels is unlikely to be substantially affecting trends in dolphin abundance. These results underscore the importance of in‐port sampling, in combination with at‐sea observation and fishery‐independent surveys, to effective management.
ISSN:0824-0469
1748-7692
DOI:10.1111/j.1748-7692.2012.00608.x