Eyes in the sky: linking satellite oceanography and biotelemetry to explore habitat selection by basking sharks

Abstract

Background: Satellite-based oceanographic data products are a valuable source of information on potential resource availability for marine species. Satellite oceanography data may be particularly useful in biotelemetry studies on marine species that feed at low trophic levels, such as zooplanktivorous whales, sharks, and rays. The basking shark, Cetorhinus maximus, is a well-documented zooplanktivore in the western North Atlantic, yet little is known of its movements and spatial ecology in this region. A combination of satellite tag technologies were used to describe basking shark movements with respect to concurrent satellite-observed oceanographic conditions in order to test for selection of these environmental variables. Results: Satellite-linked 'smart' position only transmitting tags (SPOTs, N = 10) were used to assess horizontal movements, activity space, and habitat selection, while pop-up satellite archival tags (PSATs, N = 7) were used to describe depth preferences of basking sharks during summer and fall. The duration of SPOT tracks ranged from 5 to 45 days. Basking sharks used relatively small activity spaces in three focal areas off Massachusetts: Vineyard Sound, the Great South Channel, and Cape Cod Bay. These sharks appeared to select areas with shallow bottom depths, high primary production and chlorophyll concentrations, and steep surface gradients, but significant selection for these variables was only detected between mid-August and mid-October when the sharks were primarily located in Cape Cod Bay. Conclusions: Basking sharks in the southern Gulf of Maine during summer and fall focus their activities in discrete areas likely to support high primary and secondary productivity. Habitat selection may also be influenced by mating and social activity at times, but further research is needed to differentiate these behaviors from foraging activity. Satellite-based biotelemetry and oceanography are powerful tools that together can provide valuable new insights into habitat selection patterns of highly mobile marine species.

Basking Shark (Cetorhinus maximus) Movements in the Eastern North Pacific Determined Using Satellite Telemetry

“…Baduini (1995) and Darling and Keogh (1994) reported that individual basking sharks spent up to 30 or 42 days in Monterey Bay, CA, or Clayoquot Sound, Vancouver Island, Canada, respectively. Similar short-term residence times have been reported for basking sharks in coastal regions in the Atlantic Ocean (Sims et al, 2003;Gore et al, 2008;Sims, 2008;Skomal et al, 2009;Curtis et al, 2014;Doherty et al, 2017;Braun et al, 2018).…”

“…C. pacificus developmental stages (C) IV and V contain a large lipid droplet and are energetically dense. The CIV and CV stage of C. finmarchicus are targeted by basking sharks in the western North Atlantic (Baduini, 1995;Siders et al, 2013;Curtis et al, 2014). Off CA the CIV and CV stages occur year around but are most abundant in surface waters from April through October (Johnson and Checkley, 2004), although high concentrations of CV can also be found at depth during periods of diapause (see below).…”

“…Unfortunately, which taxa they were targeting is not known. While copepods are thought to be the preferred prey (Baduini, 1995;Sims and Reid, 2002;Siders et al, 2013;Curtis et al, 2014), stomach contents from basking sharks foraging in deep waters in the Northwest Pacific Oceans included small crustaceans of up to 5.4 cm (Mutoh and Omori, 1978). One factor that suggests the basking shark was targeting copepods is the early ascent prior to dusk, which is unusual for pelagic fish that target the sound-scattering layer (Carey and Robison, 1981;Carey and Scharold, 1990;Musyl et al, 2004;Dewar et al, 2011).…”

“…While basking sharks are circum-global in distribution, they are most commonly reported in the temperate, coastal waters of the northern hemisphere in the Atlantic and Pacific Oceans (Compagno, 1984;Ebert, 2003;Sims, 2008;McFarlane et al, 2009;Curtis et al, 2014). In the eastern North Pacific (ENP), aerial surveys, sightings and catch data indicate their range is from Southeast Alaska to Baja California, Mexico.…”

Convergent Foraging Tactics of Marine Predators with Different Feeding Strategies across Heterogeneous Ocean Environments

“…This is not generally possible for pelagic macropredatory sharks because environmental fields of their schooling fish prey for example are very difficult to obtain over sufficiently large scales to support analysis in relation to pelagic shark movements and behavior (for exceptions see Makris et al, 2006Makris et al, , 2009. Previous biotelemetry studies in the North Atlantic have revealed that basking sharks undertake extensive horizontal and vertical movements associated with oceanic and inner-shelf frontal zones, areas typically characterized by high primary production and zooplankton densities (Sims et al, 2003;Skomal et al, 2009;Curtis et al, 2014;Doherty et al, 2017), and also highlighted behavioral shifts in vertical movements linked to changes in the behavior of zooplankton (Sims et al, 2005). In contrast to filter feeding, the blue shark (Prionace glauca) is an oceanic, ram-feeding macropredator occurring in all tropical and temperate seas; in the Atlantic Ocean, blue sharks range from Newfoundland to Argentina in the west, over the entire mid-Atlantic, and from Norway to South Africa in the east (Compagno, 1984;Motta and Huber, 2012).…”