Environmental influence on the seasonal movements of satellite-tracked ocean sunfish Mola mola in the north-east Atlantic

Abstract

Background: Determining the habitat use of mobile marine species is important for understanding responses to climate change and aids the implementation of management and conservation measures. Inference of preferred habitat use has been greatly improved by combining satellite-based oceanographic data with animal tracking techniques. Although there have been several satellite-tracking studies on ocean sunfish Mola mola, limited information is available about either horizontal or vertical environmental preferences. In this study, both geographical movements and diving behaviour of ocean sunfish were explored together with the environmental factors influencing this species' space use in the north-east Atlantic. Results:Habitat selection of electronic-tagged sunfish (n = 22 individuals; 0.6-1.4 m total length, TL) was investigated using geolocations from Argos-linked and pop-up satellite archival transmitters. Satellite tracking (up to 171 days, mean 66 days) revealed seasonal movements: northward in spring-summer and southward in cooler months. Sunfish spent extended periods in three focal areas, the Gulf of Cadiz, north-east Iberia and the Alboran gyre, which are characterised by the presence of frontal features with elevated primary production. Habitat modelling revealed that sea surface temperature and thermal gradients significantly influenced sunfish distribution. Diving profiles, extending from the surface to a maximum depth of 704 m, revealed different depth-use patterns not linked to geographical region or water column stratification. Overall, a size-related movement pattern was detected with larger individuals (>0.92 m TL) travelling further, exploiting greater depth ranges and spending more time at depth than smaller fish. Conclusions:Ocean sunfish in the north-east Atlantic displayed seasonal movements, primarily driven by thermal preferences, extending into higher latitudes in summer. Moreover, fish also occupied productive frontal areas for long periods, presumably for improved foraging opportunities. Lastly, sunfish showed considerable variability in diving patterns which likely reflect the tracking of planktonic prey distributions.

New insights into ocean sunfish (Mola mola) abundance and seasonal distribution in the northeast Atlantic

“…25 suggest that sunfish spend time in surface waters in order to rewarm following deep dives. Their tagged sunfish experienced ambient temperatures of 16–22 °C at the surface, and <10 °C at depths over 100 m. In our study, sunfish were recorded in sea surface temperatures ranging from 12.3–15.8 °C in summer, consistent with other studies in the region 17 and 8.6–11.9 °C in winter, the minimum value of which is below the thermal preference reported in other studies 2, 25 . This represents an average difference of 6.1 °C between surface and bottom waters in summer and 2.5 °C in winter.…”

“…Seasonal inshore migrations around the English Channel have also been reported, which are thought to coincide with invasions of medusa, salps and ctenophores, key food sources for sunfish 2 . Results from our surveys show that some sunfish are present in the waters of the northeast Atlantic year-round, and the seasonal differences in abundance provide evidence for some seasonal movement in line with recent tagging studies 17 . Seasonal movement may be to more southerly waters or inshore waters which were not covered in the current study, or sunfish may spend more time at depth in the winter months.…”

Records of ocean sunfish Mola mola along the Norwegian coast spanning two centuries, 1801–2015

“…One purpose may be to avoid excessively warm waters (exceeding 25° C) in late spring and summer, or to access upwelling areas and areas of zooplankton blooms that develop as waters warm at higher latitudes, e.g . in the North Sea (Sousa et al, ). In the latter study, no M. mola occupied waters with SST below 9° C, which may explain their southward movement in the autumn.…”

“…Although basically a tropical and subtropical species, M. mola , being a deep diver, has a broad thermal tolerance. Its lower tolerance limit to sea surface temperature (SST) has been estimated as 8–11° C (Sims et al, ; Dewar et al, ; Sousa et al, ). Its preferred range of SST seems to be roughly 10–24° C and its optimum range around 15–20° C. It may dive to 800 m depth, but spends over 60% of its time in the upper 50 m of the sea (Potter & Howell, ).…”

Planning for dynamic process: An assemblage‐level surrogate strategy for species seasonal movement pathways

“…‘Along‐shelf’ movement pathways between northern and southern locations were most commonly captured by the surrogate (Figure a, Figure ) and are well documented in the literature (Callihan et al , ; Shepherd, Moser, Deuel, & Carlsen , ). This pathway is often associated with highly mobile species that are energetically capable of travelling long distances (Anderson, Gurarie, Bracis, Burke, & Laidre, ; Chapman, Feldheim, Papastamatiou, & Hueter , ; Sousa, Queiroz, Mucientes, Humphries, & Sims, ). Globally, this pathway is most often coupled with the timing and latitudinal progression of seasonal environmental processes (e.g.…”