Predicting the occurrence of Atlantic bluefin tuna (Thunnus thynnus) larvae in the northern Gulf of Mexico: building a classification model from archival data

Abstract

Although bluefin tuna are found throughout the Atlantic Ocean, spawning in the western Atlantic has been recorded predominantly in the Gulf of Mexico (GOM) in spring. Larval bluefin tuna abundances from the northern GOM are formulated into an index used to tune the adult stock assessment, and the variability of this index is currently high. This study investigated whether some of the variability in larval bluefin tuna abundances was related to environmental conditions, by defining associations between larval bluefin tuna catch locations, and a suite of environmental variables. We hypothesized that certain habitat types, as defined by environmental variables, would be more likely to contain bluefin tuna larvae. Favorable habitat for bluefin tuna larvae was defined using a classification tree approach. Habitat within the Loop Current was generally less favorable, as were warm‐core rings, and cooler waters on the continental shelf. The location and size of favorable habitat was highly variable among years, which was reflected in the locations of larval bluefin tuna catches. The model successfully placed bluefin tuna larvae in favorable habitat with nearly 90% accuracy, but many negative stations were also located within theoretically favorable habitat. The probability of collecting larval bluefin tuna in favorable habitat was nearly twice the probability of collecting bluefin tuna larvae across all habitats (35.5 versus 21.0%). This model is a useful addition to knowledge of larval bluefin tuna distributions; however, the incorporation of variables describing finer‐scale features, such as thermal fronts, may significantly improve the model’s predictive power.

Geographically and environmentally driven spawning distributions of tuna species in the western Mediterranean Sea

“…Standard length (SL, mm) of all tuna larvae captured was measured without correction for shrinkage, and those identified as yolk sac and pre-flexion developmental stages (< 4.5 mm) were merged into a class denominated 'stage-1.' Most studies using tuna larval data described spawning distribution for all developmental stages pooled together (Alemany et al 2010, Muhling et al 2010. The duration of the yolk-sac developmental stage in these larvae is very short (up to 1 d, Margulies et al 2007).…”

“…Thus it is difficult to infer the degree to which physi o logical limitations determine the timing of spawning during the early life stages of the 3 species. Nevertheless, data from other temperate spaw ning areas support a wider temperature range for bullet tuna larvae than the other tuna species (Boehlert & Mundy 1994, Muhling et al 2010. The tropical nature of bullet tuna and albacore is reflected in our analyses, since the effect of temperature residuals was only significant for bluefin tuna, with a preference to spawn in the colder than average water temperatures; this result fits well with bluefin tuna adults, which are less tolerant of warm waters (Blank et al 2004).…”

“…Descriptions of spawning habitats for tuna have focused on single species, mostly bluefin tuna, e.g. western Thunnus thynnus in the Gulf of Mexico (Teo et al 2007, Muhling et al 2010 and T. orientalis in Japan (Kimura et al 2010, Kitagawa et al 2010. Only 1 study compared habitat characteristics among tuna species using univariate models (Alemany et al 2010).…”

A comparison of sampling methods for larvae of medium and large epipelagic fish species during spring SEAMAP ichthyoplankton surveys in the Gulf of Mexico

“…Major circulation patterns in the deep Gulf, off continental shelves, are defined by dynamics of the Loop Current and anticyclonic and cyclonic eddies (Vukovich et al 1979;Vukovich and Crissman 1986;Biggs 1992;Castellanos and Gasca 1999), and by wind-driven and convective mixing (Muller-Karger et al 1991;Melo Gonzalez et al 2000). Previous studies have associated increased larval pelagic abundance with some of these specific mesoscale features (Richardson et al 2009;Muhling et al 2010;Rooker et al 2012;Lindo-Atichati et al 2012). The scombrid vertical distribution may be the result of diel vertical migrations, associated with predator avoidance, or the pursuit of prey (Hillgruber and Kloppmann 2001;Catalán et al 2011), passive dispersal caused by water density caused by relative density differences in the larvae, differences in larval development, or physical forcing due to oceanographic conditions, e.g., mixed layer depth, strong pycnocline, advection).…”

“…Many of these taxa have shown vertical and horizontal distributions (Davis et al 1990;Boehlert and Mundy 1994;Hare et al 2001;Prince et al 2005;Richardson et al 2009;Muhling et al 2010;Lindo-Atichati et al 2012;Rooker et al 2012) that would suggest direct or indirect competition with bluefin tuna larvae. Thus, it is necessary to obtain accurate data regarding their distributions, which will depend highly on the sampling effectiveness of the particular gear used in surveys.…”