Hadley Lake Benthic Threespine Stickleback
Scientific Name: Gasterosteus aculeatus
Other/Previous Names: Benthic Hadley Lake Stickleback ,Hadley Lake Benthic Stickleback ,Gasterosteus sp.
Taxonomy Group: Fishes
Range: British Columbia
Last COSEWIC Assessment: May 2000
Last COSEWIC Designation: Extinct
SARA Status: No Schedule, No Status
Image of Hadley Lake Benthic Threespine Stickleback
Threespine sticklebacks are small fish (35-55 mm) with a laterally compressed body and delicate pectoral and caudal fins. They are armoured with retractable pelvic and dorsal spines, and the body is protected by calcified lateral plates. Their body colour varies from silvery to mottled green and brown. Sexually mature males either develop bright red throats, or turn completely black. The Benthic Hadley Lake Stickleback was a freshwater species of stickleback which fed on benthic invertebrates in the littoral zone of only one lake. It had a robust body form, wide gape and few, short gill rakers, traits which were probably advantageous for benthic feeding.
Distribution and Population
This species formerly inhabited Hadley Lake on Lasqueti Island, British Columbia, in the Strait of Georgia. It was a unique BC endemic restricted to this single lake. It was first discovered in the late 1980s, but became extinct following an unauthorized introduction of catfish (Ameirus nebulosus) to the lake.
Hadley Lake is a small coastal lake on an island about 50 m above sea level. It is connected to the sea by about 1.2 km of stream. There is no permanent inlet stream for the lake, and the outlet creek flows through a culvert under a dam. The hydrology of the outlet stream has been substantially modified by road building and housing development. In the summer the littoral region is covered in dense beds of aquatic plants. There is a distinct pelagic zone in the lake, and in summer plankton productivity is high. Catfish are presently the only fish species in the lake, but there might have been cutthroat trout prior to alteration of the outlet stream.
Several lakes on Texada, Lasqueti and Vancouver islands in the Strait of Georgia contain distinct "pairs" of species of sticklebacks. In each case, one of the species is a limnetic feeder and one is a benthic feeder. Limnetics can be considered "live fast and die young" species, whereas benthics devote considerably more energy to growth and longevity. During the spring and summer months, Hadley Lake benthics were found in the littoral zone, where they fed on benthic invertebrates. During fall and winter they dispersed with the limnetics to deeper water. Benthics were bigger on average than limnetics, and may have lived longer, delaying reproduction for a year in order to attain a larger size. Both limnetics and benthics acquired territories in the littoral region, where they built nests and mated, sometimes with many females. Following fertilization, eggs took about 7-10 days to hatch. The males actively aerated the eggs by forward thrusts of their pectoral fins. They vigorously defended their nests and territories from invaders (most often other sticklebacks), and continued to defend their young for about a week after they hatched.
Reasons for extinction
Prior to the introduction of catfish to the lake, the primary limiting factor for this species was the capacity of the lake to produce benthos. There were no other fish-eating fish species, and predation from birds (herons, kingfishers and loons) was likely minimal. The extinction of the Hadley Lake pair might have been prevented, had anglers and other citizens been educated about the potential swift and irreversible catastrophic consequences of introductions.
PLEASE NOTE: Not all COSEWIC reports are currently available on the SARA Public Registry. Most of the reports not yet available are status reports for species assessed by COSEWIC prior to May 2002. Other COSEWIC reports not yet available may include those species assessed as Extinct, Data Deficient or Not at Risk. In the meantime, they are available on request from the COSEWIC Secretariat.
0 record(s) found.
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