Life-history Variation and Age at Maturity in Eurasian Perch (Perca fluviatilis L.)

Heibo, E. 2003. Life-history variation and age at maturity in Eurasian Perch (Perca fluviatilis L.) This thesis deals with life-history variation in perch, with special focus on age at maturity. We conducted field studies to uncover the variation within short geographic distances and a literature review to study variation on a large geographic scale in order to reveal some factors affecting life-history. In two studies we discuss the relevance of predation risk and acidification, respectively, on age at maturity. With data from a large scale study (75 perch populations) covering a large range of the distribution area for perch we test life-history theory and optimality models. We found no effect of predation risk on age at maturity for five populations (3.6 – 4.5 years) in Northern Sweden, but predation risk was correlated with minimum size at maturity. There was no strong relationship between age at maturity in female perch and acidification in five lakes from southern Norway. However, age at maturity was lower for female perch from the most acidic lake (c. 2 years) compared with perch in the four other lakes (2.5 – 3.5 years). In the large scale study we found latitudinal effects on all life-history traits, except asymptotic body length. Generally, growth and mortality rates and reproductive investment decrease with latitude, whereas age and size at maturity and life span increased with latitude. There was a large variation in age at maturity with populations mean age at maturity span from 1 year in Lake Trasimeno in Italy southern Europe, to 6 years in Northern Yenisey in Siberia, Russia. Stunted (small-sized) populations had lower age and size at maturity and higher growth rate (K) compared to piscivorous populations. The life-history in southern populations with fast growth, high juvenile and adult mortality selects for early maturity and relatively large investment into reproduction. The opposite pattern was found for the northern populations. Roff's optimal age at maturity model gave good predictions for age at maturity in perch populations with data on growth and mortality rates. Mortality and age at maturity were negatively correlated, and growth coefficient (K) and age at maturity were also negatively correlated. In addition three other relationships showed invariance and all of them could therefore be termed as constants. Temperature differences, through latitude directly or indirectly, may to a large extent explain the variation found in life-history traits. In addition, different life-history trade-offs limit and constrains different …