Data from: Shorter juvenile telomere length is associated with higher survival to spawning in migratory Atlantic salmon

The risk of mortality associated with a long-distance migration will
depend on an animal's physiological state, as well as the prevailing
ecological conditions. Here we assess whether juvenile telomere length,
which in endotherms has been shown to be a biomarker of physiological
state and expected lifespan, predicts whether wild Atlantic salmon Salmo
salar successfully complete their marine migration. Over 1800 juvenile
fish were trapped, measured, PIT-tagged and a tissue biopsy taken when
migrating as juveniles down-river towards the sea. Survivors of the marine
phase of the life cycle were then re-trapped and re-sampled when returning
to the river to spawn as sexually mature adults, 1.5-2.5 years later. Most
individuals experienced a reduction in telomere length during the marine
migratory phase of their life cycle. While the relative rate of telomere
loss was greater in males than females, telomere loss was unrelated to
growth at sea. Contrary to expectations, salmon that had the shortest
telomeres at the time of the outward migration had the greatest
probability of surviving through to the return migration. This effect,
independent of body size, may indicate a trade-off between investment in
readiness for marine life (which favours high glucocorticoid levels, known
to increase telomere attrition in other vertebrate species) and investment
in telomere maintenance. Survival was also significantly influenced by the
seasonal timing of outward migration, with the fish migrating downstream
earliest in the spring having the highest probability of return. This
study reveals that telomere length is associated with survival, although
in ways that contrast with patterns seen in endotherms. This illustrates
that while telomeres may be universally important for chromosome
protection, the potential for telomere dynamics to predict performance may
vary across taxa.