Chub Squalius torgalensis and nase Chondrostoma lusitanicum, in a Mediterranean stream, showed important differences in life-history traits and population dynamics. Both species reached mean maturity at age 2 years. Chub lived up to age 5 years, spawned in March to June, grew at a maximum rate of 0·59 mm mm−1 year−1 and showed a low reproductive allocation, with fecundity and egg size increasing with body size. Nase lived up to age 4 years, spawned in January to April, grew at a maximum rate of 0·46 mm mm−1 year−1 and showed a high reproductive allocation, with egg size independent of body size. Both chub and nase showed moderate fluctuations in population size during 1991–1998, but differed in factors driving density at age. Density of age 1 year juvenile chub decreased following severe summer droughts and proportionate survival prevailed thereafter. Density of age 2 year adult nase decreased following severe spring floods, but neither environmental nor parental stock effects were detected for juveniles and older fishes. The results illustrated the interplay between life history and environmental variability in driving fish population dynamics, with impacts of both summer droughts and spring floods being contingent on species-specific patterns of spawning and reproductive investment.
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Document Type: Regular Paper
Centro de Biologia Ambiental, Departamento de Biologia Animal, Faculdade de Ciências de Lisboa, Campo Grande, Bloco C2, 3° Piso 1749-016 Lisboa, Portugal and
Department of Biology, Box 9019, University Station, Grand Forks, ND 58202, U.S.A.
Publication date: 2003-08-01