Sea Lion Islands Group IMMA

Criterion C: Key Life Cycle Activities

Sub-criterion C1: Reproductive Areas

SLI is the main current breeding colony of southern elephant seals in the Islands, with 730 breeding females in 2022 (the only other notable colony is Carcass island with 173 breeding females in 2016, Galimberti & Boitani 1999). The whole Sea Lion Island population (i.e., all individuals aged 1 year or older) is estimated at 2542 individuals. The number of breeding females has been almost steady from the late 1980s to 2003, and then started increasing at a mean annual rate of 2.1%. Even if it represents only a small proportion of the regional breeding stock (South Georgia, ~113,000 breeding females: Boyd et al., 1996; Valdés Peninsula, Argentina, ~14,000 breeding females: Lewis et al., 2004) it is the biggest share of southern elephant seals breeding in theIslands. It is the remnant of a previously-large breeding population that was decimated by intensive and indiscriminate sealing in the 1800s (Strange, 1972), and its slow recovery is therefore considered an important contribution to local biodiversity and to gene flow between the South Georgia and Valdés Peninsula breeding areas (Fabiani et al., 2003).

Sub-criterion C2: Feeding Areas

The Sea Lion Island Group is the only documented area of the Islands that is regularly visited by killer whales and in which killer whales of different family units and groups aggregate, mainly for the purpose of hunting pinnipeds. Anecdotal evidence, including stranding of individuals, indicate that killer whales have been visiting Sea Lion Island for a long time. A brief study was carried out in November 2004 and November 2005, documenting 82 sightings (Yates et al., 2007). Since 2013 Sea Lion Island killer whales have been regularly monitored by the Elephant Seal Research Group (www.eleseal.org) both from land and using unmanned aerial vehicles (UAVs). Killer whales visiting SLI can be classified as resident and transient. Resident individuals are killer whales observed for long periods of time during the year and during consecutive seasons, while transient individuals are killer whales that appeared multiple times but irregularly during the years and for short periods. Altogether, the Sea Lion Island photo- identification catalogue (available online from the ESRG website) includes 45 live individuals (2 individuals died during the study), 15 of which are currently resident.

In the Sea Lion Island Group, killer whales hunt mainly southern elephant seals, although they often try to hunt southern sea lions, in most cases unsuccessfully. They hunt adult elephant seals (mainly females, but occasionally also males) during the breeding season (Sept-Nov), weanlings during the post-weaning fast (Nov-Dec) and different classes of seals during the moulting season (Dec- Apr). Although southern elephant seals are probably not the main food source of Sea Lion Island killer whales (ESRG, unpublished observations and simulation of energy budget), their regular and extended presence during the seal breeding and molting season suggests that seal predation is an important seasonal component of the diet (for the resident individuals), and is definitely a very important part of the social behavior, and the learning of hunting and prey handling skills. While most direct observations of killer whales hunting are at Sea Lion Island and Rum Island, all the islands in the group are included in the IMMA because: 1) there are time gaps in the killer whale daily presence at Sea Lion Island, and direct and UAV observations show that when they leave they frequently move towards the outer islands; 2) anecdotal observations reported by overflying airplanes and vessels indicate that killer whales visit the outer islands, and Sea Lion Easterly in particular, which is an important elephant seal molting site; and 3) all the five islands of Sea Lion Island Group show favorable conditions for the hunting of southern elephant seals, in particular during the molting season. It is therefore reasonable to conclude that the entire island group provides habitat suitable for killer whale foraging.

Criterion D: Special Attributes

Sub-criterion D1: Distinctiveness

At Sea Lion Island killer whales show peculiar social behaviours, including socio-sexual behaviour, play behaviour among calves and adults, and socialization among different groups. Moreover, they exhibit a range of specialised southern elephant seal hunting tactics, including patrolling in front of harems waiting for breeding females to return to sea and hunting of weanlings in and around tidal pools and inlets.

Although foraging at elephant seal haul out sites is common among killer whales, a specific family unit uses a unique hunting technique for southern elephant seal weanlings that consists of entering a very small tidal pool, called the “weanling pool”, connected to the open sea by a narrow channel (about 2-3 m large and deep) and only accessible during medium/high tide and when swell is not too strong. The “weanling pool” is an aggregation point for southern elephant seal weanlings that use it as a place to socialize and train for swimming and diving. Killer whales capture weanlings inside the pool or around the nearby flat rocks, and carry the live prey into open water where it is often played with for a long period and then shared amongst the family unit and with other groups that might be present (including the two resident males). This behaviour is potentially risky for the killer whales that could get trapped into the pool if the sea conditions are not evaluated carefully, and there is some evidence that it is transmitted across generations within the family group, although only a very limited numbers of individuals use this technique regularly.

An additional interesting feature of the site is that killer whales sometimes strand alive on the Sea Lion Island sand beaches (total of 7 recorded stranding since 1986, including an adult male that subsequently died; Otley 2012 and ESRG unpublished data, but likely more since most of the Islands coasts are remote and uninhabited). These are non-intentional stranding and seem to be related to the southern elephant seal hunting techniques, which involve patrolling very close to the beaches, often in very shallow waters, and to the calves play behaviour, that often happens just a few meters away from the shoreline.