Occurrence of basking shark Cetorhinus maximus in southern Portuguese waters: a two-decade survey

Seasonal variations in the abundance and body size distribution of the ocean sunfish Mola mola in coastal waters off southern Portugal

“…Accordingly, the present investigation found SST and chl a (a widely recognized indicator of productivity; e.g. Breen et al ., 2017; Couto et al ., 2017) as determinants of M. mola abundance in southern waters of Portugal (Table 1). Mola mola abundance was positively correlated with both environmental variables.…”

“…Finally, an upwelling index (i.e. difference between coastal and offshore SST) was calculated using remotely sensed nocturnal SST (Aqua-MODIS, ; Krug et al ., 2012; Couto et al ., 2017).…”

“…Journal of the Marine Biological Association of the United Kingdom 1199 since SST in this area generally varies between 13 and 23°C yearround (Tunipex, 2017), a range of temperatures in which ocean sunfish are found worldwide (Sims et al, 2009a;Dewar et al, 2010;Potter et al, 2011;Thys et al, 2015;Sousa et al, 2016b). Interestingly and contrarily to other large migratory fish such as bluefin tuna (Thunnus thynnus), meagre (Argyrosomus regius) and basking shark (Cetorhinus maximus) that show only one peak of abundance in this area (mid-summer for tuna, late-summer for meagre and mid-spring for basking shark; Prista, 2013;Santos et al, 2016;Couto et al, 2017), M. mola revealed two peaksspring and autumn (greater values being registered in early May and both early September and early October). More so, the existence of spring and autumn abundance peaks is recurrent in this area (Poço, personal communication, 24 August 2017), and agrees with the seasonal latitudinal movements reported for ocean sunfish in the region (Sims et al, 2009a;Sousa et al, 2016b).…”

“…Conversely, chl a was also found as a determinant of M. mola abundance in the southern waters of Portugal (Table 1). Chlorophyll a is widely recognized as an indicator of productivity (Sims et al, 2003;Breen et al, 2017;Couto et al, 2017) and an association between predators and productive areas is frequently observed (Polovina et al, 2001;Kumari & Raman, 2010) as these areas should provide enhanced foraging opportunities. Concomitantly, M. mola abundance peaks coincided with the seasons exhibiting regular occurrence of phytoplankton blooms in the North Atlanticspring and autumn (Lalli & Parsons, 2006;Longhurst, 2007).…”