Browsing by Author "Schirripa, Michael"
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- Spatial and temporal size distribution of swordfish in the Atlantic Ocean: implications for conservation and managementPublication . Rosa, Daniela; Schirripa, Michael; Gillespie, Kyle; Macías, David; Forselledo, Rodrigo; Mourato, Bruno; Kai, Mikihiko; Arocha, Freddy; Su, Nan-Jay; Kerwath, Sven; Bahou, Laurent; Pappalardo, Luigi; Diaz, Guillermo A.; Lino, Pedro G.; Salmeron, Francisca; Urbina, Josetxu Ortiz de; Cardoso, Luis Gustavo; Sant’Ana, Rodrigo; Travassos, Paulo; Santos, Miguel N.; Erzini, Karim; Domingo, Andrés; Báez, Jose Carlos; Hanke, Alex; Brown, Craig; Coelho, RuiSwordfish (Xiphias gladius) is a common target species of surface pelagic longline fisheries. In the Atlantic Ocean and Mediterranean Sea, swordfish is managed as three separate stocks, all having management measures in place to rebuild or conserve the stocks, including minimum landing sizes. The objective of this study was to review size data for swordfish in the Atlantic Ocean, model the sex-specific size distribution and determine areas where there is higher likelihood of capturing undersized fish. The size distribution differed between males and females and varied by quarter, indicating movements of large fish between temperate and tropical waters. Undersized fish seems to occur in association with coastal waters, with higher proportions in the Northwest Atlantic and tropical areas. This study provides a better understanding of the temporal and spatial size and sex distribution of swordfish and presents insights into the distribution of undersized swordfish that is subject to management measures.
- Testing robustness of CPUE standardization and inclusion of environmental variables with simulated longline catch datasetsPublication . Forrestal, Francesca C.; Schirripa, Michael; Goodyear, C. Phillip; Arrizabalaga, Haritz; Babcock, Elizabeth A.; Coelho, Rui; Ingram, Walter; Lauretta, Matthew; Ortiz, Mauricio; Sharma, Rishi; Walter, JohnEnvironmental variability changes the distribution, migratory patterns, and susceptibility to various fishing gears for highly migratory marine fish. These changes become especially problematic when they affect the indices of abundance (such as those based on catch-per-unit-effort: CPUE) used to assess the status of fish stocks. The use of simulated CPUE data sets with known values of underlying population trends has been recommended by ICCAT (International Commission for the Conservation of Atlantic Tunas) to test the robustness of CPUE standardization methods. A longline CPUE data simulator was developed to meet this objective and simulate fisheries data from a population with distinct habitat preferences. The simulation was used to test several statistical hypotheses regarding best practices for index standardization aimed at accurate estimation of population trends. Effort data from the US pelagic longline fleet was paired with a volume-weighted habitat suitability model for blue marlin (Makaira nigricans) to derive a simulated time series of blue marlin catch and effort from 1986 to 2015 with four different underlying population trends. The simulated CPUE data were provided to stock assessment scientists to determine if the underlying population abundance trend could accurately be detected with different methods of CPUE standardization that did or did not incorporate environmental data. While the analysts’ approach to the data and the modeling structure differed, the underlying population trends were captured, some more successfully than others. In general, the inclusion of environmental and habitat variables aided the standardization process. However, differences in approaches highlight the importance of how explanatory variables are categorized and the criteria for including those variables. A set of lessons learned from this study was developed as recommendations for best practices for CPUE standardization.