RELATIVE ABUNDANCE OF LARGE WHALES AROUND SOUTH GEORGIA (1979–1998)¹

Abstract

To assess large‐whale stocks following the cessation of land‐based South Georgia whaling in 1965, we report three independent sighting databases: a cruise in 1997, observations from Bird Island (NW of South Georgia) between 1979 and 1998, and mariner sightings between 1992 and 1997. All species were rare, with sightings of southern right whales being the most common event. Two right whales photographed off South Georgia matched animals known from Peninsula Valdés, Argentina, a population known to be growing at 7%per annum. In contrast, blue and fin whales appeared to be less abundant. A single blue whale mother‐calf pair was observed off the Shag Rocks in February 1997. Extirpation of animals from this particular feeding ground is the most likely reason for ongoing low numbers of all species. Other factors may include competition for krill by traditional predators such as penguins and seals and more recently by humans, an unusually high rate of natural mortality, habitat change such as alteration in sea ice coverage, and/or the impact of ongoing whaling. The history of this critical area of large‐whale habitat and this report demonstrate the need for improved, consistent longterm monitoring of population trends for these depleted stocks.

Oceanic circumpolar habitats of Antarctic krill

“…The period for which krill data is available, from 1926 to 2004, follows a major perturbation of their predators, with a large proportion of fur seals, southern right, humpback and blue whales removed before 1926 (Laws 1985, Moore et al 1999b). These comprise both shelf-based and pelagic foragers, so it is hard to predict how their removal might affect krill distribution.…”

Changes in distribution, relative abundance, and species composition of large whales around South Georgia from opportunistic sightings: 1992 to 2011

“…Decades later, sightings are still relatively rare, and little is known about the populations that utilize South Georgia waters as feeding grounds (Moore et al 1999, Reid et al 2000, Hedley et al 2001, RossiSantos et al 2007). Southern right whales and humpback whales that breed off the coast of South America (Peninsula Valdés, Argentina, and Abrolhos Bank, Brazil, respectively) have been traced to South Georgia feeding grounds; however, these are limited cases representing only a handful of individual whales (Best et al 1993, Moore et al 1999, Rowntree et al 2001, Stevick et al 2006, Zerbini et al 2006, Engel & Martin 2009, Valenzuela et al 2009).…”

“…Southern right whales and humpback whales that breed off the coast of South America (Peninsula Valdés, Argentina, and Abrolhos Bank, Brazil, respectively) have been traced to South Georgia feeding grounds; however, these are limited cases representing only a handful of individual whales (Best et al 1993, Moore et al 1999, Rowntree et al 2001, Stevick et al 2006, Zerbini et al 2006, Engel & Martin 2009, Valenzuela et al 2009). This Minke whales recorded may also be of the species B. acutorostrata Kemp & Bennett (1932) general lack of knowledge stems from the inherent difficulty associated with studying cetaceans in the Antarctic; research in the area is quite costly, and sighting conditions are often unfavorable.…”

“…Catches at South Georgia included: blue, fin, sei, humpback, minke, southern right, and sperm Physeter macrocephalus whales, most of which were depleted to <10% of their original stock size (Tønnessen & Johnsen 1982, Best 1993, Clapham & Baker 2009). When whaling ceased in South Georgia in 1965, a reported 175 250 whales had been processed at the land-based whaling stations alone since 1904 (Committee for Whaling Statistics 1942, 1951, 1953, 1954, 1955, 1956, 1957, 1958, 1959, 1960, 1961, 1962, 1963, 1964a,b, 1965, 1966, Tønnessen & Johnsen 1982, Moore et al 1999); in all, over 2 million whales were taken in the Antarctic between 1900and 2005(Clapham & Baker 2009.…”

Satellite-monitored movements of humpback whales Megaptera novaeangliae in the Southwest Atlantic Ocean

“…However, no direct evidence was provided to substantiate these proposed migratory connections. In recent years, studies involving sighting surveys, photo-identification, and molecular genetics have been conducted on the humpback whale wintering ground off Brazil and the presumed high-latitude feeding grounds near SG and the AP (Moore et al 1999, Rosenbaum et al 2000, Stevick et al 2004). These studies were also unable to determine migratory connections of whales wintering off Brazil.…”