Two studies have serendipitously captured brief observations of feeding in elephant seals. The first was via a video camera anchored to the seafloor at a depth of 894 m in the Barkley Canyon, west of Vancouver Island, Canada. Footage was captured of a free-ranging northern elephant seal (M. angustirostris), of unknown sex, predating a soft-bodied hag-fish (Eptetratus sp., 25/June/2012, https://bmscblog. wordpress.com/2013/04/03/citizen-scientist-spots-a-hungry-elephant-seal-in-barkley-canyon/ (accessed 14/05/2020). No pre/post-ingestion behaviour was witnessed but the seal captured Eptetratus sp. by suction feeding and swallowed it immediately at depth.

The second study captured video footage of M. leonina attacking Patagonian toothfish (Dissostichus eleginoides) hooked on commercial longlines near Heard Island [9] (https://doi.org/10.1371/journal.pone.0172396.s004,and.s005). Although the behaviours recorded were in a somewhat artificial setting (i.e. a lit environment with tethered prey), the footage provides insights into the behaviour of the seals as they encountered benthic prey at depths in excess of 1000 m. Seals swam close to the sea-floor and undertook brief (meters) excursions from the seafloor as they circled hook-caught fish of ~ 1 m in length. Prey capture behaviour included a “head-down” orientation and a turn toward the surface following seizure of the prey item.

Three adult male M. angustirostris have been observed consuming large-bodied elasmobranchs such as stingrays (Urolophus halleri), blue sharks (Prionace glauca) and spiny dogfish (Squalus acanthis) head-first at the seas-surface [10]. There was one report of a male M. leonina feeding at the sea-surface on what was believed to be a large fish, perhaps a D. eleginoides, that was presumed captured in about 1000 m of water to the northwest of South Georgia (53º39' S, 38º24' W) [11].

Here, we supplement the record for M. leonina with a further sighting of a sub-adult male (aged 6 - 8 y) swallowing head-first a draughtboard shark (Cephaloscyllium laticeps) in the near-shore surface waters (≤ 70 m) of south-east Tasmania (43º11' S, 147º58' E; Fig. 2). Combined, those five surface observations suggest large hard-bodied prey items captured at depth are bought to the sea-surface for manipulation prior to ingestion.

What is currently (2020) known of adult male Mirounga foraging behaviours is outweighed by what is known for adult females and juveniles, and for that reason, some male behaviours have been assumed from other age/sex classes. But, behaviours inferred from single-sensor TDR deployments do not always equate with those derived from complementary multi-sensor studies, nor might they be applied across species or even between age classes within species [12-15]. This makes the observations described here valuable for understanding specific foraging behaviours of adult male Mirounga spp.

The behaviours of male M. leonina captured directly by video camera [9] conformed well to behaviours inferred from TDR records. For example, there were small excursions from the seafloor that are characteristic of “wiggle” type anomalies commonly seen in elephant seal feeding dive profiles (Fig. 1A). The head-down orientation observed by video just prior to prey capture has also been digitally recorded and termed “up-ending” in the benthos (Fig. 1B), [16]. It was also clear from the video that not all wiggles and head-down orientations were prey capture attempts, some were searching activities. More- over, up-ending events seem to equate more closely to prey capture attempts than wiggles in feeding dives, confirming the usefulness of complementary sensor deployments.

Observations of Mirounga spp. feeding on large prey items at the sea-surface offer an alternative explanation for the precipitous drops in stomach temperature that have been termed “drinking events” (Fig. 1C), [17]. Practically speaking, stomach temperature telemetry uses measured changes in a predators’ core body temperature to imply consumption of ectothermic prey and/or the ingestion of water [18]. Changes in stomach temperature for one free-ranging female M. angustirostris, whose dive behaviour appeared to be unconstrained by bathymetry, occurred during the bottom phases of putative type D pelagic foraging dives (Fig. 1C) [19]. Feeding was inferred from anomalies in stomach temperature that were associated with increased swim velocity and wiggles (Fig. 1C), and importantly an upward movement through the water column to shallower depths [17]. Unlike other studies [18, 19], Horsburgh and others [17] recorded decreases in stomach temperature at the sea-surface which they assigned to drinking events (Fig. 1C). However, deliberate drinking of seawater in pinnipeds seems equivocal. Harbor seals (Phoca vitulina), for example, did not drink seawater voluntarily [20] but a captive leopard seal (Hydrurga leptonyx) drank large quantities of seawater when placed in the ocean [21].

All Mirounga spp. observed feeding at the surface were manipulating large, hard-bodied, deep-dwelling benthic prey species ([10, 11,] this study) which can reach at least 1.5 m in length [22]. Since the ingestion of large prey causes a rapid decrease in stomach temperature [18], we consider the stomach temperature changes that recorded at the sea-surface by Horsburgh et al. [17] as evidence for the ingestion of large prey. If it is a requirement for Mirounga ssp. to surface to manipulate large prey items prior to ingestion, it follows that anomalously long intervals between dives in the TDR records (known as extended surface intervals [8]) could indicate successful capture of large prey items.