Conservation of a unique bullhead population in Flanders, Belgium

Summary

The bullhead (Cottus perifretum), believed extinct from Belgium's Demer River basin since 1957, was rediscovered as a tiny relict population confined to a 200-meter stretch of the Dorpbronbeek stream in 2003, prompting the Research Institute for Nature and Forest and the Agency for Nature and Forests to launch a conservation program after genetic analysis confirmed the population held five private alleles worth protecting. A captive breeding program begun in 2004 using broodstock from the relict population became increasingly successful over time, while a 2007 habitat suitability assessment of seven candidate waters identified the Zevenbronnenbeek, a nearby tributary confirmed via electrofishing to be free of any existing bullhead, as the best reintroduction site. In October 2008, 1,220 cultured young-of-year bullhead averaging 5.5 cm were released along a 1,600-meter stretch, supplemented with 68 ceramic tiles as artificial spawning substrate and shelter. Follow-up electrofishing surveys through 2009 consistently recaptured released fish in good condition with healthy growth; territorial males defended nest tiles from February through April, 19 egg clutches were found by end of March, and young-of-year juveniles averaging 4.3 cm confirmed successful natural recruitment by late summer. Major difficulties included difficulty motivating authorities to implement habitat protections, securing consistent funding, and a scarcity of headstream sites with adequate water quality. The project rates itself Highly Successful, citing reliable captive breeding, strong post-release survival and growth, and confirmed natural reproduction at the new site.