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

Abstract

The spawning habitats of many large marine pelagic predators are poorly known. This lack of knowledge hampers conservation efforts that are aimed at identifying critical habitats for the spawning of these species. We hypothesized that phylogenetically related species show different adaptations and respond differently to environmental and geographical cues for when and where to spawn. We tested this hypothesis on a 5 yr data set (2001 to 2005) from the Balearic Islands region (Mediterranean Sea), targeting the early larval stage of 3 abundant species of tuna: bluefin tuna Thunnus thynnus, a large migratory oceanic species; albacore T. alalunga, a smaller species; and bullet tuna Auxis rochei, often found closer to coastal areas. The spatial distribution of spawning locations at the regional scale differed for the 3 tuna species. Bluefin tuna relied heavily on environmental signals, and therefore their spawning habitats can vary depending on the environment. In contrast, the spawning habitat of albacore and bullet tuna was driven mostly by geography and was less variable over contrasting environmental conditions. These regional adaptations for spawning habitats among the 3 tuna species may play a critical role in offspring survival and species interactions, and should be taken into account when establishing conservation practices.KEY WORDS: Spawning strategy · Spawning habitat · Regional scale · Spatial distribution · Large predators · Migratory strategy · Mediterranean · Tuna Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 463: [273][274][275][276][277][278][279][280][281][282][283][284] 2012 ted dispersal abilities and complete their life cycle in relatively closed spatial areas. It is possible that within similar geographical ranges, species with different life history traits can reproduce and thrive, but also show adaptations to local spawning habitats at smaller spatial scales.The cues and clues that fish respond to in their decisions regarding when and where to spawn can be geographically and environmentally based (Bailey et al. 2004, Ciannelli et al. 2007). Some species may adapt to spawn in geographic areas where the environment tends to be more stable, and where habitat characteristics are optimal for the survival of later larval and juvenile stages. Other species may adapt toward a more opportunistic strategy and spawn within specific environmental ranges of a larger geographic area. Depending on the physical tolerances of the species, the 2 strategies can show any degree of mixing. At a regional spatial scale (e.g. around the Balearic Islands), the prevalence of one or the other spawning strategy can be correlated with specific life history traits. The important question then is how species' life history traits and spawning strategies are linked. Providing an answer to this question would allow us to generate hypotheses on how spawning strategies are regulated across a wide range of species, and thus to determine their importance in fisheries...

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

“…However, these hypotheses do not seem applicable to Mediterranean islands, since waters surrounding them are even more oligotrophic than those closer to the neighbouring mainland coasts and, at least in the case of Atlantic bluefin tuna, adult fishes migrate into the Mediterranean from much more productive Atlantic areas for spawning, not for feeding. Our present results should be in accordance with the hypotheses from Alemany et al (2010) and Reglero et al (2012), who suggested that precisely the oligotrophic character of waters surrounding some Mediterranean islands, such as those of the Balearic archipelago, should increase the tuna larvae survival rates due to the scarcity of predators and competitors, particularly in the upper mixed layer of the water column that tuna larvae inhabit. Moreover, these authors hypothesized that the complex hydrodynamic scenario resulting from the interaction of inflowing recent Atlantic surface waters and resident waters modulated by the islands' topography, characterized by the presence of mesoscale hydrographic features such as fronts and eddies, would constitute a strong retention zone and a favourable habitat for larval survival, enhancing encounter rates between tuna larvae and potential preys (Reglero et al 2012).…”

“…As a result, detailed knowledge about spawning locations and larval habitats for tuna species have been mainly restricted to the northern and central sectors of the Mediterranean Sea (Alemany et al 2010, Reglero et al 2012.…”

Misidentification of bluefin tuna larvae: a call for caution and taxonomic reform

“…Larval surveys can also help to determine community assemblage dynamics in order to develop additional data for the development of ecosystem-based management approaches Much of our understanding concerning favourable environmental conditions for spawning of BFT comes from research based in the western Mediterranean Sea. Larval surveys in this area have shown that changes in relative abundances of different species are directly influenced by hydrodynamics (Alemany et al 2010;Reglero et al 2012).…”

“…BFT larvae are most abundant in surface waters ranging between 23-28°C, where two water masses collide and create complex hydrodynamic conditions lacking strong, directional flows (García et al 2005a;Reglero et al 2012;Muhling et al 2013). As Mediterranean waters are generally oligotrophic and do not provide ample food for the high bioenergetic demands of quickly developing BFT larvae, spawning typically occurs at the formation of frontal structures, the boundaries of anti-cyclonic gyres, and upwelling zones typical of oceanic islands, wherein both food particles and larvae are entrained (García et al 2005a;Aguilar et al 2009;Mariani et al 2010;Lindo-Atichati et al 2012).…”

“…The Balearic Islands in the western Mediterranean are arguably the most productive of BFT spawning areas (Alemany 2008;García et al 2013b). Within these waters, BFT larvae tend to be more abundant in areas where incoming Atlantic water masses and resident surface Atlantic waters, already modified by a longer stay in the Mediterranean, converge (García et al 2005a;Alemany et al 2006Alemany et al , 2010Reglero et al 2012). The discovery of low nutrient concentrations and reduced primary production in some areas with high concentrations of larvae have led some researchers to suggest that predation on non-BFT fish larvae and cannibalism plays an important role in the survival and development of BFT recruits.…”