Pelagic habitat and offspring survival in the eastern stock of Atlantic bluefin tuna

Abstract

In this manuscript, we test how an understanding of geographical variation in larval fitness in relation to temperature and habitat use could be a useful method to improve our understanding of recruitment and develop better indices of annual recruitment. On the basis of the assumption that growth and survival of tuna larvae are influenced by temperature, we have developed a potential larval survival index for Atlantic bluefin tuna (Thunnus thynnus) by combining empirical data from egg and larval rearing experiments with temperature data from hydrodynamic models. The experiments were designed to test the full range of temperature variability that bluefin larvae would experience in the field and provide a mechanistic understanding of the processes driving egg and larval survival. We then developed a biological model using the temperature-related growth expressions and a size-dependent survival function for the larvae. The biological model was applied to a time-series of spatially explicit temperature data for the western Mediterranean from the Strait of Gibraltar to 6°E, which includes the major recognized bluefin tuna eastern stock spawning area, the Balearic Sea. Our results show that areas with high probabilities of larval survival coincide with those that would be considered as optimal based on other data sources (ichthyoplankton surveys, spawning female locations from commercial fisheries data, and adult tracking data). However, evidence of spawning has been found in areas with suboptimal thermal habitats, as predicted by the model, which we discuss regarding sampling effort and salinity fronts. There was a good match between the survival index and recruitment indices from standardized CPUE fisheries data. These results have implications for our understanding of the recruitment process of the eastern stock of Atlantic bluefin tuna, since they suggest that the combined effects of temporal and spatial variability of the environment drive recruitment success, which has important implications for the management of the species.

Modeling environmental influence on Atlantic bluefin tuna bycatch by Mexican longliners in the Gulf of Mexico

“…Arrizabalaga et al () also found these environmental preferences for BFT species in a broad study covering the Atlantic, Pacific, and Indian oceans. Even though the preferential thermal range derived from the model was much lower than the recognized spawning temperature threshold of 24°C (Schaefer, ), recent estimations set the thermal conditions of the spawning season onset closer to our results (Alemany et al, ; Gordoa & Carreras, ; Reglero, Balbín, et al, ; Reglero, Ortega, et al, ). In addition, greater BCPUEs were found related to negative SLA, an indicator of mesoscale cyclonic eddies, which associated with increased productivity (Biggs & Muller‐Karger, ; Gasca, ) have been recognized as key areas for reproduction and recruitment of many fish species (Bakun, ; Condie & Condie, ; Condie, Mansbridge, & Cahill, ).…”

“…An appropriate spatiotemporal management strategy involves understanding the spatial distribution of both target and bycatch species and the environmental factors forcing those distributions (Cruz, Machete, Menezes, Rogan, & Silva, ; Druon, Fromentin, Aulanier, & Heikkonen, ; Fromentin & Powers, ; Roe et al, ; Williams, Kirby, & Beverly, ). Previous studies have linked ABFT distribution with environmental features within feeding (Druon et al, ; Royer, Fromentin, & Gaspar, ) and spawning grounds in both the Mediterranean Sea (Alemany et al, ; Druon et al, ; Muhling et al, ; Reglero, Balbín, et al, ) and the GoM (Muhling, Lamkin, & Roffer, ; Muhling et al, ; Teo & Block, ; Teo, Boustany, Block, & a., ). Research in the GoM has focused mainly on US waters, leaving a significant information gap concerning the Mexican part of the Gulf.…”

Common dolphinfish, Coryphaena hippurus, spawn at their easternmost Atlantic range adjacent to the Mediterranean Sea

“…Massutí and Morales‐Nin (1995) suggested a spawning migration of adult dolphinfish from Atlantic waters to Mediterranean spawning grounds similar to the well‐documented migration of bluefin tuna spawners. Nonetheless, the two cases differ in that the spawning of Atlantic bluefin tuna does not take place until the migrants are well into the Mediterranean, beyond the Alboran Sea (Medina et al ., 2002; Reglero et al ., 2019). In contrast, as shown here, the dolphinfish does spawn in the GoC during summer months (July through September).…”

Challenges for Sustained Observing and Forecasting Systems in the Mediterranean Sea

“…The recovery of the Eastern Atlantic bluefin tuna population during the last decade, after a long period of continuous and alarming decrease, is a successful example of how science and operational oceanography can trigger advances in the sustainability of fisheries and species conservation. At SOCIB, the combination of hydrodynamic models, remote sensing and in situ data has enabled the development of techniques for predicting both the spawning and larval habitat distribution, and the survival rate of the egg and larvae in the Balearic Sea (Álvarez-Berastegui et al, 2016;Reglero et al, 2018). These novel predictive capabilities have been applied to the standardization of larval abundance indices used to evaluate the trends of adult tuna populations during the last two decades (Ingram et al, 2017;Álvarez-Berastegui et al, 2018a), and to integrate environmental variability into the short-term forecasting of the survival of larvae and the derived immature individuals.…”