Species that have shown strong responses to protection are those that have moderate vagility in relation

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...

Life-history traits such as spawning migrations and timing of reproduction are adaptations to specific environmental constraints and seasonal cycles in many organisms' annual routines. In this study we analyse how offspring fitness constrains spawning phenology in a large migratory apex predator, the Atlantic bluefin tuna. The reproductive schedule of Atlantic bluefin tuna varies between spawning sites, suggesting plasticity to local environmental conditions. Generally, temperature is considered to be the main constraint on tuna spawning phenology. We combine evidence from long-term field data, temperature-controlled rearing experiments on eggs and larvae, and a model of egg fitness, and show that Atlantic bluefin tuna do not spawn to optimize egg and larval temperature exposure. The timing of spawning leads to temperature exposure considerably lower than optimal at all spawning grounds across the Atlantic Ocean. The early spawning is constrained by thermal inhibition of egg hatching and larval growth rates, but some other factors must prevent later spawning. Matching offspring with ocean productivity and the prey peak might be an important driver for bluefin tuna spawning phenology. This finding is important for predictions of reproductive timing in future climate warming scenarios for bluefin tuna.

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Despite being well adapted for feeding in cold water on their North Atlantic feeding grounds, Atlantic bluefin tuna undertake long migrations to reach warm, low productivity spawning grounds in the Gulf of Mexico and Mediterranean Sea. Environmental conditions within spawning areas have been presumed to benefit larval survival, through appropriate feeding conditions, and enhanced larval retention and growth rates. However, field collections and studies to explore the potential mechanisms are rare. In this study, a comparison of the environmental characteristics of both spawning sites was completed using standardized environmental data and modeling methods. Predictive models of larval occurrence were constructed using historical larval collections, and environmental variables from both in situ and remotely sensed sources. Results showed that larvae on both spawning grounds were most likely to be found in warm (23 to 28°C), low chlorophyll areas with moderate current velocities and favorable regional retention conditions. In the Gulf of Mexico, larvae were located in offshore waters outside of the Loop Current and warm eddies, while in the western Mediterranean, larval occurrences were associated with the confluence of inflowing Atlantic waters and saltier resident surface waters. Although our results suggested common themes within preferred spawning grounds on both sides of the Atlantic Ocean, the ecological processes governing larval survival and eventual recruitment are yet to be fully understood. KEY WORDS: Bluefin tuna · Spawning · Mediterranean Sea · Gulf of MexicoResale or republication not permitted without written consent of the publisher Editorial responsibility: Nicholas Tolimieri,