Characterization of the spawning area of tuna species on the northern Tunisian coasts

Abstract

Summary:Early life stages of tuna species were investigated along the northern coasts of Tunisia in the summer of 2010, from 7 to 14 July. A total of 74 stations, distributed on a regular grid, were sampled. Larvae of five tuna species were identified: the Atlantic bluefin tuna, the bullet tuna, the Atlantic black skipjack, the Atlantic bonito and the albacore tuna. Larval distribution patterns show that Atlantic bluefin tuna and albacore tuna usually spawn in offshore oligotrophic waters and Atlantic black skipjack larvae on the continental shelf. The widespread distribution of bullet tuna larvae, suggests that it spawns on the entire continental shelf and over the shelf break. The results from the quotient analysis carried out to characterize the spawning habitat of each species, show that the input of recent surface Atlantic water (AW) masses play a key role in the spawning strategy of tuna species, particularly in the case of the Atlantic bluefin tuna, whose larvae were mainly caught in the mixed waters resulting from the interaction between recent AW and resident AW, as demonstrated by their preference for salinity values between 36.9 and 37.4.Keywords: tuna larvae; environmental variables; spatial distribution; spawning area; water masses; Mediterranean. Caracterización del área de puesta de especies de túnidos en las costas del norte de TúnezResumen: Se investigaron las fases larvarias tempranas de especies de túnidos a lo largo de las costas del norte de Túnez, durante el verano de 2010, del 7 al 14 de julio. Se muestrearon un total de 74 estaciones, distribuidas en una malla regular. Se identificaron larvas de cinco especies: el atún rojo, la melva, la bacoreta, el bonito y el atún blanco. Los patrones de distribución de larvas muestran que el atún rojo y el atún blanco desovan generalmente en aguas oligotróficas alejadas de la costa. Por contra, la localización relativamente más costera de las larvas de bacoreta indica que esta especie se reproduce sobre la plataforma continental, mientras que la amplia distribución de las larvas de melva sugiere que esta especie desova a lo largo de toda la plataforma y el margen continental. Los resultados del análisis de proporcionalidad, llevado a cabo para caracterizar el hábitat de puesta de cada especie, muestran que la entrada de masas de agua superficial atlántica (AW) reciente juegan un papel clave en la estrategia de desove de las especies de túnidos, sobre todo en el caso del atún rojo, cuyas larvas fueron capturadas principalmente en las aguas de mezcla, resultantes de la interacción entre el AW reciente y la residente, como lo demuestra su preferencia por los valores de salinidad entre 36.9 y 37.4.Palabras clave: larvas de túnidos; variables ambientales; distribución espacial; área de puesta; masas de agua; Mediterráneo.

Unveiling the Relationship Between Sea Surface Hydrographic Patterns and Tuna Larval Distribution in the Central Mediterranean Sea

“…The Atlantic waters then enter the Strait of Sicily, flowing toward Tunisia and the South of Sicily, from west to east (García Lafuente et al, 2002;Cuttitta et al, 2004;Bonanno et al, 2014). A consecutive sampling of tuna larvae over a 3-year period has shown that the presence of tuna larvae in Tunisia is also related to this water mass (Koched et al, 2012(Koched et al, , 2013(Koched et al, , 2016Zarrad et al, 2013). In contrast, little is known about the south of Sicily, an area characterized by high mesoscale variability, vortices, and meanders (García Lafuente et al, 2002) because of incoming Atlantic freshwater and warmer resident water (Robinson et al, 2001).…”

Reproduction of Atlantic bluefin tuna

“…In each of the two primary reproduction areas of the ABFT, specific spawning habitats have been identified (Figure 1), and their environmental features characterized (Alemany et al., 2010; Koched, Alemany, Rimel, & Hattour, 2016; Muhling, Lamkin, & Roffer, 2010; Reglero, Tittensor, Álvarez‐Berastegui, Aparicio‐González, & Worm, 2014; Teo & Boustany, 2016; Teo, Boustany, & Block, 2007; Teo, Boustany, Dewar, et al, 2007). Using oceanographic data, predictive models have been designed that provide spatial and temporal mapping of potential spawning habitats taking into account the changing environmental drivers (Álvarez‐Berastegui et al., 2014, 2016; Druon, 2010; Druon, Fromentin, Aulanier, & Heikkonen, 2011; Hobday et al., 2019; Reglero et al., 2012, 2014, 2019).…”