Arctic char (Salvelinus alpinus), the only freshwater native fish in Svalbard, is rather common (occurring in more than 100 lakes and watercourses) and is differentiated into two forms: stationary and anadromous (Overrein and Prestrud Reference Overrein, Prestrud, Kovacs and Lydersen2006).

In southern Spitsbergen (south of Van Keulenfjorden), the Arctic char ecology is well investigated and described. There are several papers on this fish in the water bodies of Wedel Jarlsberg Land, north of the Hornsund fjord (for example: Gullestad Reference Gullestad1975, Witkowski and others Reference Witkowski, Kotusz, Popiolek and Kusznierz2008).

The Svartvatnet lake (0.8 km²), connected with the sea by the Lisbetelva river 3,5 km long, is considered to be the only habitat of the Arctic char in Sørkapp Land, the southernmost peninsula of Spitsbergen (south of Hornsund). It was known to the trappers before the establishment of the South Spitsbergen National Park in 1973 as is evidenced by remains of their fishing activity found on the lake in 1982, and recognized by researchers (Gullestad and Klemsten Reference Gullestad and Klemsten1997, Kusznierz and others Reference Kusznierz, Kotusz, Kazak, Popiolek and Witkowski2008). However, apart from Svartvatnet, the fish was observed by the author in a small lake on the Sergeevskaret pass between the Sergeevfjellet and Lidfjellet mountains, with the water-table at an altitude of ca. 150 m, in the summer seasons 1983 and 1984. This fish does not exist in any other water body of Sørkapp Land, according to observations made during nine summer seasons in the period from 1982 to 2008.

Hence, it appeared extraordinary to discover, on 8 August 2008, that it was also present in the glacial Bungeelva river. A single fish was seen in a very shallow lateral bed and was caught by hand, after walking across this very muddy (silted up) and braided river 250 m from its mouth on the Greenland Sea during low tide. It was a male 46 cm long, completely dazed because of a huge amount of suspended material in the river water (Figs. 1–4). Two colleagues of the author, Justyna Dudek and Jan Niedzwiecki, were witnesses.

Fig. 1. Location of the site where the single Arctic char was caught by hand in the Bungeelva river on 8 August 2008 (marked with the arrow), and the Arctic char populations habitats in Sørkapp Land (lakes: Svartvatnet, and the small unnamed lake between Sergeevfjellet and Lidfjellet).

Fig. 2. Arctic char, male, 46 cm long, caught by hand in the Bungeelva river on 8 August 2008. Photo: J. Niedzwiecki.

Fig. 3. Lower course of the Bungeelva river from its mouth during the lowest tide, just after catching the fish on 8 August 2008. The Bungebreen glacier is in the background. The site of catching the fish is marked with the arrow. Photo: J. Niedzwiecki.

Fig. 4. One of the muddy lakes at the Bungebreen glacier's front, from which the Bungeeleva river flows out. Photo: J. Dudek.

Undoubtedly, the (anadromous) fish had mistaken its way to its maternal stream for spawning during a high tide because the thaw-lakes within the marginal zone of the Bungebreen glaciers (from which the Bungeelva exits) are extremely muddy and making fish life impossible.

According to opinions expressed by some biologists in my discussion, the event described above is a very interesting observation of a natural way of animal colonisation (expansion) to new potential habitats which can appear as a result of glaciers’ recession under climate warming. Of course, this unintended trial made by our fish was unsuccessful because the Bungebreen glacier still exists (in spite of shrinking) filling its valley and delivering a huge amount of the suspended material to the new water bodies in its marginal zone and fore-field.

However, even there, the situation could be changed in future, after transformation of today's extensive valley glacier into a smaller new cirque or slope glacier (or glaciers) and thus cleaning the river water. Such a transformation is very probable in the case of further climate warming or stabilising at the present temperature level during the next few decades (Ziaja Reference Ziaja2004, Reference Ziaja and Ziaja2011a, Reference Ziaja2011b).

A more difficult question is what a water body the fish wanted to swim into. According to the cited literature, the nearest habitat of the anadromous Arctic char is in the Revelva river basin (with the Revvatnet lake) north of Hornsund. However, the thesis that the Svartvatnet lake can not contain any anadromous form of the fish because the Listetelva river is ‘impassable to ascending fish’ due to ‘the steep rise in the lower part of the stream’ located ‘about 50 m before entering Hornsund’ (Gullestad and Klemsten Reference Gullestad and Klemsten1997) or ‘numerous waterfalls’ (Kusznierz and others Reference Kusznierz, Kotusz, Kazak, Popiolek and Witkowski2008) is rather doubtful in the light of the author's geomorphological and hydrological observations of the river. Moreover, the specimen from Bungeelva (Fig. 2) is very similar to specimens ‘from the landlocked population of (. . .) Svartvatnet’ and not to the anadromous ones from Revvatnet (Figs. 3 and 4 in: Kusznierz and others Reference Kusznierz, Kotusz, Kazak, Popiolek and Witkowski2008). In addition, the fish from Bungelva is practically identical with 7–8 male fish caught by the author in Svartvatnet during mid-August 1983, 1984, and 1986. Nevertheless, no fish have been observed in the lower part of Lisbetelva (which is very clean non-glacial river) despite careful explorations during six summer seasons (1982, 1983,1984, 1986, 2000, and 2008).