AN UPDATE OF THE AZORES BAITBOAT FISHERY CATCH PER UNIT EFFORT STANDARDIZATION FOR

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1 SCRS/2015/062 Collect. Vol. Sci. Pap. ICCAT, 72(1): (2016) AN UPDATE OF THE AZORES BAITBOAT FISHERY CATCH PER UNIT EFFORT STANDARDIZATION FOR M. Sculley 1, J.G. Pereira 2 and M. Schirripa 3 SUMMARY An updated index of abundance in biomass for bigeye tuna from the Azorean baitboat fishery in the Atlantic is presented for The standardization analysis procedure included the following variables; year, quarter of the year, and vessel category. A delta log-normal model was used to standardized the data using significant variables determined as those which explained >5% of the total deviance. The patterns observed in the standardized CPUEs are consistent with those observed previously: large variability until approximately 1995, a decline in CPUE after 1995, and an increase in CPUE after 2004 until the present. RÉSUMÉ Une mise à jour de l'indice d abondance en biomasse du thon obèse émanant de la pêcherie de canneurs des Açores opérant dans l Atlantique est présentée pour la période La procédure d analyse de la standardisation a inclus les variables suivantes : année, trimestre de l année et catégorie de navires. Un modèle delta log-normal a été utilisé pour standardiser les données au moyen de variables significatives déterminées comme celles expliquant >5% de l'écart total. Les tendances observées des CPUE standardisées sont cohérentes avec celles observées préalablement, à savoir une variabilité importante jusqu'en 1995, une baisse de la CPUE après 1995 et une augmentation de celle-ci après 2004 jusqu'à présent. RESUMEN Se presenta un índice actualizado de abundancia en biomasa de patudo de la pesquería de cebo vivo de las Azores en el Atlántico para El procedimiento de análisis de estandarización incluyó las siguientes variables; año, trimestre del año y la categoría de buque. Se utilizó un modelo delta lognormal para estandarizar los datos mediante variables significativas determinadas como aquellas que explican > 5% de la desviación total. Los patrones observados en las CPUE estandarizadas son coherentes con los observados previamente: gran variabilidad hasta aproximadamente 1995, un descenso de la CPUE después de 1995 y un aumento de la CPUE después de 2004 hasta la actualidad. KEYWORDS Bigeye, Abundance, Time series analysis, CPUE, Azores baitboat 1 Rosenstiel School, University of Miami, 4600 Rickenbacker C. Miami, FL, USA mjohnston@rsmas.miami.edu 2 Universidade dos Açores, Departamento de Oceanografia e Pescas, Rua Professor Dr. Frederico Machado, Horta Azores, Portugal 3 NOAA Fisheries, Southeast Fisheries Center, Sustainable Fisheries Division, 75 Virginia Beach Drive, Miami, FL, , USA. 190

2 Introduction The Azores baitboat fishery catches bigeye tuna seasonally in the spring and early summer. The data available includes daily information on the catch by species for every individual Azorean tuna baitboat vessel since 1963, including data from logbooks and a scientific observer program. These data do not include catches from Madeira, a Portuguese archipelago off the northwest coast of Africa where a portion of the fleet fish during part of the year. The Azores baitboat fishery has been described in detail previously by Pereira et al. (2011). The standardizations presented here are an update of this previous analysis and includes catches from 1963 through 2014, including earlier data than those standardized previously, which started in Methods: The Azores database is detailed by trip and contains catch data for bigeye tuna from Catch per unit effort for the Azores baitboat fishery is in kg of fish per trip. The fishery tends to be seasonal, with the largest catches occurring in quarters two and three (Figure 1). The fleet operates five different classes of vessel size. The smallest boats (V0010, V1012, and V1218) have relatively small catches, and the majority of the catch is from the two largest size classes of vessels (Figure 2). The database contains a large number of zeros due to the seasonal nature of the fishery; therefore they must be included in the standardization. Methods used to standardize data were nearly identical to those used previously for the Azores baitboat fishery, as described by Pereira et.al (2011). A delta-lognormal model was used to model the CPUE data. The proportion of positive catches were modeled using a binomial GLM model with a logit link function and the log-transformed positive catches were modeled using a Gaussian GLM with an identity link function. Three explanatory variables and their interactions were included in the full model. The final model included those variables which explained at least 5% of the total deviance, a method used previously for this fishery (Pereira, et. al 2011). All interaction terms were dropped from both models and Vessel class was dropped from the proportion positives binomial model (Table 1). Lognormal estimates also included a logarithmic bias back-transformation correction factor. Final standardized CPUE was obtained by multiplying the proportion positive and positive catches models. Results Annual standardized CPUE indices and the estimated CV are in Table 2. The annual indices varied without trend for the majority of the time series, until around 1995 (Figure 3). After this period there was a significant decline in CPUE followed by an increase again starting in 2003 until With further analysis, the variations in the CPUE index are correlated to the changes in the Atlantic Multidecadal Oscillation index (Figure 4), and the decrease in 1995 occurs when the AMO switches from positive to negative (Figure 5). As in the past, the diagnostic plots show a good model fit to the data (Figure 6), however in the future it may be worthwhile to explore including the summer AMO index as an explanatory variable which may reduce the variability observed in the standardized CPUE. Standardized CPUEs in the current analysis is in general agreement with previous standardizations (Figure 7). References Pereira, J.G.; Ortiz, M.; and Cass-Calay, S.L. (2011) Standardized catch rates for bigeye tuna (Thunnus obesus) from the Azores baitboat fleet Collect. Vol. Sci. Pap. ICCAT, 66(1):

3 Table 1. Deviance table for both the proportion positive and positive catches models. Significant variables are highlighted. Model Degrees of freedom Residual Deviance Change in Deviance % Total Deviance Binomial Year % year + quarter % year + quarter + Vesselclass % year + quarter + VesselClass+ year*season % Positive Catches Year % year + quarter % year + quarter + Vesselclass % year + quarter + Vesselclass + year*season % year + quarter + Vesselclass + year*vesselclass % year + quarter + Vesselclass + quarter*vesselclass % Table 2. Standardized CPUE values and their CVs. Year Standardized CPUE Standard Deviation Normalized CPUE CV

4 Figure 1. Annual average nominal CPUE by vessel class for the Azores baitboat fishery. 193

5 Figure 2. Average nominal CPUE by season for the Azores baitboat fishery. Figure 3. Annual standardized CPUE (line) and nominal CPUE (points) normalized to the mean. 194

6 Figure 4. Correlation of Atlantic Multidecadal Oscillation index with the standardized Azores baitboat CPUE indices. Figure 5. Azores baitboat standardized CPUE plotted against the Atlantic Multidecadal Oscillation index average for quarters 2 and

7 Figure 6. Diagnostic plots for the Azores baitboat fishery standardization. Figure 7. Standardized CPUE from previous analysis (Pereira, et. al 2010, blue line) and the current analysis (orange line). 196

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