By Arne Bjørge. Institute of Marine Research. c/o Dept of Biosciences, University of Oslo
This is the only Pinniped species named after a Norwegian. The species was first described by the Norwegian zoologist Erling Sivertsen in 1953.
Erling Sivertsen (1904-1989) was a Norwegian zoologist. Internationally he was most recognised as an expert on Pinnipeds and Crustaceans. He was director at the Royal Norwegian Society of Sciences and Letters (Det Kongelige Norske Videnskabers Selskab) in Trondheim, and he obtained his doctoral degree at the University of Oslo in 1942. The dissertation described the biology of the harp seal, Pagophilus groenlandicus, and was based on biological material collected by himself on five trips onboard Norwegian sealing vessels in the Russian White Sea from 1928 and onwards. He also published research on the family Otariidae (sea lions and fur seals) based on material collected in Antarctica during the four Norvegia-expeditions in 1927-1931. He became member of The Norwegian Academy of Science and Letters (Det Norske Videnskaps-Akademi) in 1954, and he was created Knight 1st Class of The Royal Norwegian Order of Saint Olav in 1972. But when Erling Sivertsen in 1953 described the Galápagos sea lion as a new species, he named this species after another Norwegian zoologist, Alf Wollebæk. Why did he do that?
Zoologist Alf Wollebæk
Alf Wollebæk (1879-1960) was director at the Zoological Museum in Oslo (currently part of the Natural History Museum at the University of Oslo). He started his career in marine zoology as an assistant for Johan Hjort at the Marine Biological Station in Drøbak, Norway. In the period 1900-1907 he was zoologist at the Society for Promotion of Norwegian Fisheries (Selskabet for de norske Fiskeriers Fremme) in Bergen. He was then affiliated to Bergen Museum for a brief period, until he in 1908 was employed by the Zoological Museum at Tøyen in Oslo. Here he wrote many articles and books about Norwegian and international fauna. In the period 1926-1958 was he an active member of the Norwegian-Russian Commission for Sealing. He was awarded the King’s Medal of Merits in gold for his scientific work in 1959.
The Norwegian Galápagos expedition in 1925-1926
In 1925 Wollebæk was the leader of a scientific expedition to Galápagos. The background for this expedition was that the very dynamic whaling shipowner August F. Christensen in 1914 got permission to conduct whaling off the coasts of Peru and Ecuador. Then he started to plan for a colony of Norwegian whalers in the area. Other sailors recommended to Christensen that the Galápagos Islands that belonged to Ecuador, will be the ideal location for such a colony. Ten years later Christensen had managed to obtain status as Norwegian consul to Ecuador, a position he used to negotiate a deal stating that Norwegian settlers on Galápagos had the right to 20 hectare land, ten years of tax exemption and exclusive rights to all fishing, hunting and harvesting on unpopulated islands. When the first expedition was realized in 1925, had Wollebæk made a deal with Christensen that he and the taxidermist Erling Hansen should join the expedition. This two-man strong scientific expedition lasted for five months before Wollebæk and Hansen returned to Norway.
Post Office Bay
The Norwegian colonists settled in Post Office Bay on the uninhabited island Floreana. Post Office Bay had its name from a barrel that for several centuries had served as post box. Sailors could leave letters there in hope that other seafarers will pick them up and forward them to land. Post Office Bay was most likely the base camp also for Wollebæk and Hansen, although they visited most of the other island in the archipelago during their five months stay. According to Grant and Estes (2016) was the first biological research station in the archipelago built in Post Office Bay by Wollebæk’s expedition in 1925. This house built from lava blocks is currently the oldest standing building on the island. In addition to build a biological research station, did Wollebæk’s expedition collect information on and biological samples from more than 500 species. The analyses of this material resulted in more than 20 articles and books. Unfortunately, these were published in Norwegian only, and did not receive the international attention they deserved. But the skull Sivertsen used for his description of the Galápagos sea lion as a new species was collected and brought home by Wollebæk’s expedition.
«They are tame as livestock”
Wollebæk (1934) wrote that the Galápagos sealion was Otaria jubata. He further wrote: «They are tame as livestock and for that reason easily harvested. But under the equator, they have little blubber and the fur is of poor quality. Still thousands have been slaughtered.» Wollebæk (1934) also noted that the same species was distributed southward along the west coast of South America, around Cape Horn and north to La Plata on South America’s Atlantic coast. Wollebæk obviously mistook the sea lions on Galápagos to be the same species as the South American sea lion currently named as Otaria flavescens. The species name jubata was possibly an old synonym for jubatus, the current species name for the Steller sea lion, but this species has now been classified in a separate genus Eumetobias. Steller sea lion, which is a very large Pinniped, males can weigh more than a metric ton, occurs in the northern Pacific Ocean, far from Galápagos.
Actually, the Galápagos sea lion is more closely related to the Californian sea lion. Several scientists have described the Galápagos sea lion as Zalophus californianus wollebaeki. That is as a subspecies of the Californian sea lion. In recent times, Dale W. Rice in 1998 was the first to argue that Sivertsen’s description of the Galápagos sea lion as a distinct species was correct (Rice 1998). This has more recently been confirmed by genetic studies (Trillmich 2015).
True fur seal
Wollebæk also wrote that there is also a true fur seal that is endemic to Galápagos, and he correctly referred to this species as Arctocephalus galapagoensis, although with a minor misspelling (Wollebæk 1934). Wollebæk wrote that the fur seal was very common in ‘the old days’ and congregated in large numbers at the rookeries in the breeding season. Wollebæk received anecdotes about annual harvests of 6-8,000 seals. Large catches had continued until the 1880-ies. The number of seals had declined rapidly, and fur seals were timorous and hardly seen when Wollebæk visited the Galápagos.
Sivertsen’s description of Zalophus wollebaeki
During his work on the taxonomy of the family Otariidae (based on material from the Norvegia expeditions and museum samples from Stockholm, New York and Washington), Sivertsen realised that skulls collected at Galápagos most likely were from sea lions and not fur seals as previously anticipated. However, the skulls were not accompanied with skin samples that could have clearly discriminated between fur seals and sea lions.
Sculls and conserved skin at the Zoological Museum
Then Sivertsen found two skulls from Galápagos archived at the Zoological Museum in Oslo. The skin associated with one of these skulls was also conserved. This clearly showed that the skulls were from sea lions. Sivertsen (1953) wrote that only the South American sea lion was previously reported from Galápagos. However, Sivertsen realized that these skulls were more related to the Californian sea lion than to the South American sea lion. He still meant that these skulls were sufficiently different from the Californian sea lion to qualify to be described as a separate species. Sivertsen chose the skull from an old male as holotype and the skull from a young female with associated stuffed skin as paratype his description of the new species from Galápagos (Wiig and Bachmann 2013). Sivertsen named the new species Zalophus wollebaeki after Alf Wollebæk, “in honour of the only collector who brought home both skull and skin of the new species” (Sivertsen 1953). As mentioned previously, several scientists argued that this was actually a subspecies of the Californian sea lion, until Rice (1998) and more recent genetic studies confirmed that Sivertsen was right.
About the Galápagos sea lion and its habitat
The Galápagos sea lion is described as endemic for the Galápagos Archipelago (the species only occurs at these islands), but from 1986 has a small group of this species periodically been observed at the island Isla de la Plata, closer to the mainland of Ecuador. The Galápagos sea lion is smaller than its more well-known relative, the Californian sea lion, Zalophus californianus. The two sexes of Galápagos sea lion are very different in size. This difference starts already at birth: females are born only six kg while males are eight kg at birth. Adult females range between 70 and 80 kg. Adult males weigh 140-180 kg (Melin & al. 2017). Females give birth to their first pup at an age of six years and the duration of the lactation period is almost two years. Sardines are the main food items for the Galápagos sea lion (Melin & al. 2017).
The marine environment of the archipelago
However, to understand the ecology of the Galápagos sea lion, it is essential to look at the marine environment of the archipelago. The unique marine ecosystem in the Galápagos Islands is to a large degree the result of the meeting of three main ocean currents. Perhaps the most important is the Humboldt Current named after the German explorer and writer Alexander von Humboldt that in 1846 described this current in his book ‘Kosmos – Entwurf einer physischen Weltbeschreibung’. The Humboldt Current is a cold current that runs up the whole west coast of South America and flows into the Galápagos waters from the southeast. It brings nutrients to the islands and is also one of the main drivers of the weather. The second current with an influence is the Panama Current that brings warmer waters to the Galápagos Islands from the northeast. Finally, the Cromwell Current (named after Townsend Cromwell; Cromwell & al. 1954) is a cold deep-sea and nutrient-rich current flowing from west to east along the equator. The current pattern, trade winds and the bathymetry (underwater landscape) at Galápagos force the cold and nutrient-rich water from the lower levels to the surface (upwelling) and provides good conditions for the sardines that are so important as food for the Galápagos sea lion. This cold water is also the habitat for the endemic Galápagos penguin, Spheniscus mendiculus, the only penguin species in equatorial waters.
El Niño a threat to the sea lions
The weather phenomenon El Niño (Bjerknes 1969; Trillmich and Limberger 1985) interrupts the upwelling at Galápagos in some years. This happens typically every five to seven years. Warm surface water then accumulates off the coasts of Peru and Ecuador. This reduces the east-west temperature gradients and hampers the trade wind pattern. The cold-water currents are displaced by warm water from the Central Pacific Ocean. This disrupts the upwelling of cold, nutrient-rich water at Galápagos and has a devastating effect on the marine food chain. When the supply of nutrients is cut off, the result is food shortages throughout the food chain, threatening many of the unique species in the ecosystem (Edgar & al. 2010).
Most important for the Galápagos sea lions is that El Niño events force the sardines to migrate into deeper water to avoid high surface temperatures or they simply die of starvation. This entails food shortages for the sea lions, with increased mortality due to hunger (Trillmich and Limberger 1985). It is still not well understood how global warming will influence the frequency and intensity of El Niño events (Wang & al. 2016), but this threat to the sea lions at Galápagos is still very real (Trillmich 2015; Edgar & al. 2010).
Endangered species
Based on a count in 1978, the population was estimated to about 40,000 sea lions at the Galápagos Islands (Trillmich 1979). Following a few strong El Niño events, a new count in 2001 showed a dramatic decline in numbers, and the population was estimated to 14-16,000 sea lions (Alva and Salazar 2006). The International Union for Conservation of Nature, IUCN, in 2008 therefore classified the species as endangered. After 2001, the population seems to have stabilized at this lower level (Trillmich 2015).
Copy to Galápagos
The preparations that Sivertsen (1953) used for his description of the Galápagos sea lion as a new, distinct species are now in the collections at the Natural History Museum in Oslo (Wiig and Bachmann 2013). These preparations are of great scientific value and must be well conserved and stored. As a funny wrap-up of this flashback, I can tell that Professor Øystein Wiig at the Natural History Museum gave a copy of the holotype skull as a present from the museum to the Charles Darwin Research Station in Galápagos in 2014, almost 90 years after the Norwegian Galápagos expedition and 61 years after Sivertsen’s scientific description of the species. The copy of the skull was made by the taxidermist Per K. Thorsland.
Acknowledgement
I am grateful to Dr Geir Ottersen, Institute of Marine Research, and Professor emeritus Øystein Wiig, Natural History Museum, University of Oslo, for very constructive comments to an earlier version of this manuscript. I will also thank the Museum of University History, University of Oslo, for encouraging me to write this flashback and to make it available on their webpage.
Refererences
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