What Is Attracting Lagenorhynchus cruciger To The Antarctic?

A Little Bit Of Background

Early drawing of Lagenorhynchus cruciger from 1847 by Alcide Dessalines d’Orbigny.

The hourglass dolphin is an uncommonly known cetacean that is found in Antarctic waters.  This article is going to look into the possibilities as to why this dolphin has chosen Antarctica as a habitat. This dolphin is one of only seven species of dolphin that inhabits the Southern Ocean surrounding Antarctica. Lagenorhynchus cruciger (L. cruciger), first described in 1824 by Quoy and Gaimard with their characteristic black and white markings, that were seen to be in the shape of an hourglass (hence their name), with their length averaging around 1.5-2 meters. This striking animal has similar colour markings to none other than its cousin, Orcinus orca also known as the killer whale. The surprising thing is that there is very little known about this remarkable creature. Only a small number have been examined and they are rarely witnessed in their natural habitats. With such little knowledge of these animals, it is still unclear how they fit into their environment and what caused them to choose an extreme environment to call home. All this uncertainty is why they are becoming increasingly popular within the scientific community.

Where Are They Exactly?

As previously stated they are found in the Southern Ocean and have been seen around Antarctica. The map below shows the expanse that L. cruciger are believed to cover. However, with this vast area it is unclear whether this is exaggerated or possibly underestimated,  because there is very little physical evidence of L. cruciger and their migration patterns known.

Global distribution of Lagenorhynchus cruciger shown in blue by Achim Raschka

The distribution maps are based on witness accounts but also from information collected by surveys carried out. Jarrod A. Santora carried out 14 survey’s in Antarctica between January and March from 2003 to 2011 in order to map distribution and the abundance marine mammals. It was observed in this study that L. cruciger were observed in only 50% of the survey’s however. It was not understood why the were sparsely seen over the years. With this animal being of least concern regarding conservation status and with figures estimating around 144,000 they are not thought to be declining in numbers. 

Why Are They There?

Microscope image of the Antarctic krill (Euphausia superba) by Uwe Kils

In the paper published by Kasamatsu and Joyce in 1995 it was observed that there was a significant increase in L. cruciger in February, this increase was also seen by Jarrod A. Santora in 2011. Kasamatsu and Joyce stated a possible explanation to why L. cruciger are seen in higher numbers in February.  It was thought that it was due to warming sea surface temperatures and the seasonal increase in prey. Sea surface temperature in Antarctica is believed from previous data to increase from 1.04ºC to 1.37ºC between January and February.  It is believed by Kasamatsu and Joyce that this temperature is more favourable for their thermoregulatory, the process by which an animal retains its core internal temperature, in relation to their body shape and size. This sea surface temperature increase in February is not the only increase seen in the Antarctic. There is an increase in the Antarctic krill, Euphausia superba (E. superba)The reproduction cycle occurs between November and March with spawning and maturation occurring around late January into February. It believed that L. cruciger predates on fish, squid and crustaceans. With them feeding on the large amounts of E. superba themselves, E. superba also bring an increase of larger more valuable prey. These are just two factors that are thought to cause an increase however with still little known this may be occurring throughout the year and we are just not aware.

What Have We Got To Do Now?

With the Antarctic being one of the least researched areas in the world, which is due to the nature of the environment there. It is extremely difficult to carry out research and to gain valuable understanding about this part of our world. However, due to climate change and the effects it is having already. Antarctica is becoming yet more important because it is one of the environments where the change is seen and felt most prominently. Understanding how organisms are adapting to these sudden changes gives a greater insight as to whether or not they will be able to survive.

When an extreme environment that an organism depends upon is disappearing will they still be able survive? If the answer is yes how will one species effect the rest of the world?

Just something to think about.

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