Habitat use, vertical and horizontal behaviour of Atlantic bluefin tuna (Thunnus thynnus) in the Northwestern Mediterranean Sea in relation to oceanographic conditions

Abstract

We investigated the habitat utilization, vertical and horizontal behaviour of Atlantic bluefin tuna Thunnus thynnus (ABFT) in relation to oceanographic conditions in the northwestern Mediterranean Sea, based on 36 pop-up archival tags and different environmental data sets. Tags were deployed on early mature ABFT (127-255 cm) between July and November in 2007-2014, on the shelf area off Marseille, France. The data obtained from these tags provided 1643 daily summaries of ABFT vertical behaviour over 8 years of tag deployment. Based on a hierarchical clustering of this data, we could identify four principle daily vertical behaviour types, representing surface (≦10m) and subsurface (10-100 m) orientation, moderate (50-200 m) and deep (≧200m) diving behaviour. These vertical behaviour types showed seasonal variations with partly opposing trends in their frequencies. Accordingly, ABFT were more surface orientated during summer, while moderate diving behaviour was more common during winter. Depth time series data further revealed inverted day-night patterns for both of these periods. Tagged ABFT frequented the surface waters more regularly during daytime and deeper waters during the night in summer, while the opposite pattern was found in winter. Seasonal changes in the vertical behaviour of ABFT were accompanied by simultaneous changes in environmental conditions (SST, chla, thermal stratification). Accordingly, surface orientation and moderate diving behaviour appeared to be triggered by the thermal stratification of the water column, though less pronounced than previously reported for ABFT in the North Atlantic, probably indicating adaptive vertical behaviour related to the availability of epipelagic food resources (anchovies and sardines). Deep diving behaviour was particularly frequent during months of high biological productivity (February-May), although one recovered tag showed periodic and unusual long spike dives during summer-autumn, in relation to thermal fronts. Regional effects on the vertical behaviour of ABFT were identified through GAMs, with surface orientation being particularly pronounced in the Gulf of Lions, highlighting its suitability for an ongoing annual aerial survey program to estimate ABFT abundance in this region. In addition, increased levels of mesoscale activity/productivity (e.g. related to oceanic fronts) were detected in an area regularly utilized by ABFT, south of the Gulf of Lions, underlining its attractiveness as foraging ground. Kernel densities of geolocation estimates showed a seasonal shift in the horizontal distribution of ABFT from this "high-use" area towards the Gulf of Lions during summer, probably linked to the enhanced Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site.

Residential movements of top predators in Chile’s most isolated marine protected area: Implications for the conservation of the Galapagos shark, Carcharhinus galapagensis, and the yellowtail amberjack, Seriola lalandi

“…Transmitted data from all MiniPAT tags were de-coded with the manufacturer's cloud-based portal software and analysed using the RCHIVAL package (Bauer, 2020a) in R 3.5 (R Core Team, 2018). Likelihood areas were generated from the 'netcdf' files in the GPE 3 model runs using the get_geopos function in the R package RCHIVALTAG (Bauer, 2020a).…”

“…and 'classify_DayTime' functions in the R package RCHIVALTAG (Bauer, 2020a), which uses daily geolocation estimates from the tags as input data. To determine the general patterns of diel vertical behaviour per fish, their hourly changes in depth via box plots were analysed.…”

Surfacing and vertical behaviour of Atlantic bluefin tuna (Thunnus thynnus) in the Mediterranean Sea: implications for aerial surveys

“…Atlantic bluefin tuna Thunnus thynnus (ABFT) are a highly migratory, opportunistic predators that can forage throughout the water column to depths greater than 1000 m. Despite their physiological capabilities, ABFT prefer the epipelagic zone, where they frequently feed on schools of small epipelagic fish such as sardines and anchovies (Lutcavage and Kraus, 1997;Fromentin and Powers, 2005;Bauer et al, 2017). This behavior facilitates the detection of tuna schools from afar and led to the use of spotter planes in tuna purse-seine fisheries (Farrugio, 1977;Basson and Farley, 2014).…”

“…changes in the "surface availability") of tunas can significantly affect the number of schools observed at the sea surface (Bauer et al, 2015b), accounting for this variability is a key step to provide a robust abundance index. Several studies have sought to determine the factors driving the vertical behaviour of bluefin tuna (Walli et al, 2009;Galuardi and Lutcavage, 2012;Marcek et al, 2016;Bauer et al, 2017, Eveson et al, 2018. Archival tagging data from the Atlantic Ocean have demonstrated that the vertical behaviour of ABFT is influenced by the thermal stratification of the water column (Brill et al, 2002;Walli et al, 2009;Galuardi and Lutcavage, 2012).…”

Loggerhead sea turtle (Caretta caretta) diving changes with productivity, behavioral mode, and sea surface temperature

“…However, some studies demonstrate that ocean temperature and foraging resources can interact and are important determinants for diving behavior. For example, elephant seals ( Mirounga leonina ) in the Southern Ocean dived deeper to forage and spent less time at those depths with increased water temperature [7], whereas Atlantic bluefin tuna ( Thunnus thynnus ) in the Mediterranean Sea dived deeper when biological productivity was high [8], and the depths reached in the North Atlantic for tuna were correlated with thermocline depth [9]. For sea turtles specifically, relationships between diving and interacting oceanographic conditions such as sea surface temperature (SST) and foraging resources have rarely been tested, although a few studies point to the potential importance of these factors.…”