Recovery of fish populations in Lake 223 from experimental acidification

The fish populations of Lake 223, a lake previously acidified to pH 5.1, we re monitored during 13 years of gradual pH recovery to preacidification pH 6.7. During acidification, recruitment ceased for all fish species in this lake and two were extirpated. During pH recovery, successful recruitment re sumed for all fish species that remained in the lake. One of the extirpated species, fathead minnow (Pimephales promelas), successfully colonized the lake. Lake trout (Salvelinus namaycush) abundance decreased during acidific ation and remained low during pH recovery due to very low recruitment. Grow th curves, condition factor, and annual survival of lake trout decreased du ring acidification and quickly increased to preacidification values during pH recovery. During the early years of pH recovery, white sucker (Catostomu s commersoni) abundance increased to almost 10 times the number at the star t of the experiment but decreased during the final years due to decreased a nnual survival and recruitment. Pearl dace (Margariscus margarita) became a bundant during acidification and their abundance decreased during pH recove ry as fathead minnow abundance increased. Other fish species that were caug ht infrequently prior to acidification, brook stickleback (Culaea inconstan s), lake chub (Couesius plumbeus), and finescale dace (Phoxinus neogaeus), were caught frequently during pH recovery.