Spatially explicit estimates of stock size, structure and biomass of North Atlantic albacore tuna (Thunnus alalunga)

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Abstract

The development of the ecosystem approach and models for the management of ocean marine resources requires easy access to standard validated data sets of historical catch data for the main exploited species. They are used to measure the impact of biomass removal by fisheries and to evaluate the models outputs, while the use of a standard data set facilitates models inter-comparison. Unlike standard stock assessment models, new state-of-the-art ecosystem models require geo-referenced fishing data with the highest possible spatial resolution. This study presents an application to the North Atlantic albacore tuna stock with a careful definition and validation of a spatially explicit fishing data set prepared from publicly available sources (ICCAT) for its use in a spatial ecosystem and population dynamics model (SEAPODYM) to provide the first spatially explicit estimate of albacore density in the North Atlantic by life stage. Density distributions together with the fishing data used for the estimates are provided at

Figures

  • Table 1. Total annual catch 1960–2008 (tonnes) used in SEAPODYM North Atlantic albacore simulation compared with total annual catch by all fisheries declared in the ICCAT database. Difference in tonnes and corresponding percentage of coverage.
  • Table 2. Revised definition of fisheries for the North Atlantic albacore (E: effort; C: catch) to be used for SEAPODYM application. LL: longline; TROL: trolling; MWTD: mid-water trawling; BB: baitboat pole and line; Tro: tropical; subTro: subtropical; t: metric tonnes.
  • Figure 1. Annual catch of North Atlantic albacore tuna by flag. (a) All aggregated catch declared to ICCAT, and (b) available georeferenced catch data used with SEAPODYM.
  • Figure 2. Spatial distribution of mean annual catch of North Atlantic albacore by longline (green) and surface (blue) fishing gears during the periods 1960–1986 and 1987–2008. The circles are proportional to the catch, with the same scale for both panels.
  • Figure 3. Time series of annual catch data with geographical coordinates used in the simulation with SEAPODYM and total annual catch declared to ICCAT for the main North Atlantic albacore tuna fisheries over the historical fishing period. When data were declared in number of fish, a conversion factor has been used, i.e., 16 kg fish−1 for Japanese, Chinese Taipei and US longline, and 8 kg fish−1 for French and Spanish surface fisheries.
  • Figure 4. Length frequency data before (a) and after (b) January 1987. The data samples are aggregated at different spatial resolutions illustrated by rectangles with grey shading proportional to the number of samples (black and white color bar from 0 to 200 samples). In the center of each region, a circle gives the predicted mean size of fish (the larger the circle, the larger the mean size of fish in the catches) and the variance associated with this mean (color bar). Data are presented for high (top) and medium (bottom) resolution. The low-resolution data (three geographical boxes: 90◦ W–10◦ E; 30–6◦ N, 80◦ W–0◦; 60–30◦ N, 60◦ W–20◦ E; 6◦ N–30◦ S) are not shown.
  • Figure 5. Left: South Pacific size-at-age (top) and weight-at-length (bottom) relationships used in SEAPODYM simulation (black curve) compared to other functions proposed in the literature. Right: population structure (average 1971–2000) in % tonnes resulting from the optimization with SEAPODYM and the NCEP-ORCA2-PISCES environmental forcing. References for weight at size: (0) this study (Hoyle and Davies (2009) for South Pacific albacore), (1) Santiago (1993) for North Atlantic albacore, (2) Penney (1994) for South Atlantic albacore, (3) Chen et al. (2010) for North Pacific albacore, and (4) Megalofonou (1990) for Mediterranean albacore. References for size at age: (0) this study (adapted from MULTIFAN estimate in Santiago and Arrizabalaga (2005), (1) Bard (1981), (2) ICCAT (1996), (3) Santiago and Arrizabalaga (2005), (4) Bard (1973), (5) Gonzales-Garces (1983), (6) Fernandez (1992), and (7) Yang (1970).
  • Figure 6. Seasonal average (1991–2000) distributions of North Atlantic albacore in the second (left) and fourth (right) quarter for larvae (no. km−2), young immature fish (g m−2) and adult mature fish (g m−2). Circles are proportional to observed catch. Fisheries selecting small size fish (< 85 cm, T10 to B13) are superimposed on young fish distributions, and those selecting large size fish (> 85 cm, L1 to L9) on adult fish distributions.

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Lehodey, P., Senina, I., Dragon, A. C., & Arrizabalaga, H. (2014). Spatially explicit estimates of stock size, structure and biomass of North Atlantic albacore tuna (Thunnus alalunga). Earth System Science Data, 6(2), 317–329. https://doi.org/10.5194/essd-6-317-2014

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