Dr. W. Brian McKillop, (Retired) Curator of Invertebrates

Actual Size

For many years, Museum volunteer Monty McKillop and I have been collecting invertebrates in the far north of the province. In 1996, while collecting at Nueltin Lake near the Northwest Territories, we found an unusual fish, a Threespine Stickleback, named for the three formidable spines on its back. This species usually lives in, or near, the sea but this one was found 400 km upriver from the coast. The specimen collected was a mature, fully plated or armoured, male. It was 41 mm long, or about the length of your little finger. It was taken at the base of a waterfall flowing from Bagg Lake into Nueltin Lake, in a sandy-bottomed backwater about one-half metre in depth with some aquatic plants growing in it.

The Threespine Stickleback has been reported from both coasts of North America and along the coast of Hudson Bay. The specimen from Nueltin Lake is the only one of this species in a Manitoba collection. It is of special interest because it not only extends the distribution of the species westward but also raises questions of migration and colonization from the coast. Researchers from the National Museum made a previous finding in this watershed in the Northwest Territories in 1966. They took a specimen from the Thlewiaza River, Nueltin Lake’s outflow to the coast, 330 km downstream from the lake but 70 km from Hudson Bay.

The obvious question is: how did this fish get into Nueltin Lake? They probably spread into Hudson Bay from the Atlantic Ocean shortly after the ice retreated along the Labrador coast some 8,000 years ago. The Stickleback normally lives in or near the ocean, moving into freshwater only to breed. But a few populations, including this one, are landlocked and thus physically restricted to freshwater. These fish cannot return to sea because of their great distance from Hudson Bay, and the waterfalls and rapids along the Thlewiaza River.

These barriers also prevent immigration into Nueltin Lake from the Bay. Therefore, any immigration would have had to occur before they were in place. It is likely that the species migrated up the Thlewiaza River shortly after deglaciation, some 7,000 years ago. Hudson Bay was much higher then, its waters extending much farther inland. The glaciers had just retreated northward and the land not yet begun to rebound from their weight. The difference in elevation between the Lake and the Bay was probably less than 30 m then, making it unlikely there were waterfalls in the Thlewiaza River. This suggests that the species gained entrance to Nueltin Lake about 7,000 years ago. It also implies that, while rarely collected, the Threespine Stickleback is probably more broadly
distributed in northern Manitoba than previously thought. In fact, I recorded a second specimen from Caribou Lake, 230 km to the southeast, in the summer of 1997.