Life History Variation of Polymorphic Arctic Charr (Salvelinus alpinus) in Thingvallavatn, Iceland

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Abstract
The Arctic charr (Salvelinus alpinus) in Thingvallavatn, Iceland, exhibits four morphs. Small benthivorous charr grow slowly, have an asymptotic length of 13 cm, and mature at an age of 2–4 yr. Large benthivorous charr grow faster and almost rectilinearly with age. They mature at an age of 3–11 yr. Planktivorous and piscivorous charr have even higher initial growth rate, but planktivorous charr cease growing at 20 cm and piscivorous charr at a fork length of 30 cm. They mature at 3–5 yr and 5–10 yr of age, respectively. The gonadosomatic index and the annual allocation of energy into gonads relative to soma were higher for planktivorous and piscivorous than for benthivorous charr. The results indicate that piscivorous and planktivorous charr belong to the same gene pool; piscivorous charr are probably recruited from the most fast-growing planktivorous individuals and start feeding on fish at a length of 23 cm. The benthivorous morphs may belong to different stocks due to significant differences in several life history variables as well as genetics, spawning time, and feeding habitat. The four morphs seem to be differentiated within the lake through trophic radiation, but should be considered as conspecifics.