Seasonal changes in fish abundance, biomass and species richness in the littoral zone

Seasonal changein the abundance. biornass and species richness of fixh in the littoral zone of Lake Coustancc were examined. Electric fishing was conducted in three depth strata at six different sampling sitc« within the littoral zone from Novem­ ber ]991 to Fcbruar ]993 during daytime. Minimal abundance and biomaxs values were observed in February with 3.9 (SO ± ..\..2) ind· lOO Ill-" and 12.7 (SO ± LUI) g-wet· lOO III c. Maximal abundance value» were observed in August with 119.) (SO ± 88.)) ind· lOO m c. maximal hiom.i-,-, values in May with 9(n.9 (SO ± 1942.6) g-wet· 100 m c. The influence of indiv idual habitat variables on the littoral fish com­ munity was examined by canonical correlation analvxix. Seasonal chungcs in total fish abundance. biomass and species richuexx were muinl. explained by seasonal changes in water temperature followed by lake level. For the individual species. different sub­ xtratc characteristics such ~lS sediment type or the amount of large stones lying on the bottom providing shelter were also found to be important. However. these variables often influence fish abundance and biomas-, only within a range that is prcdcfincd by water temperature. Different patterns were found for the two bcnthic species. burbot iLota lota i and stone loaeh iNocnmchrilus burhatulusi. The distribution of both spe­ cies was mainly correlated with the availability of gravel substrate and shelter and mostly independent of littoral water temperature. Burhot larger than >5 cm TL cmi­ grated trom the littoral into deeper adjacent areas during summer when water temper­ ature increased above a certain threshold. indicating an upper thermal threshold for thi-, cold stenothermal species.