I am so happy to know that some salmon get to retire from the whole “epic migration” thing.
In one species – the Dolly Varden char – the oldsters actually stop migrating and spend their golden years at home in freshwater feasting on salmon roe and sockeye tartare.
In an Alaskan population of Dolly Varden, the probability of seaward migration in any year starts to plummet after an individual’s fourth year, and it seems that no fish migrate after their eighth year. Dolly Varden can live 11 years or longer.
The researchers who documented this say that for young fish it’s worth migrating out to sea to gain access to more food to stoke rapid growth. But not so much for mature Dolly Varden char that are big enough to push around hordes of spawning sockeye to get at their freshly laid eggs. Larger body mass also allows these senior salmonids to go without eating for extended periods.
When the getting is good they binge – on sockeye eggs and spawned-out carcasses – and store enough energy in a few weeks to remain in the relative safety of fresh water streams until the next spawning season when the all-you-can-eat banquet returns.
Study: Beyond dichotomous life histories in partially migrating populations: Cessation of anadromy in a long-lived fish. Morgan Howard Bond, Jessica A. Miller, and Thomas P. Quinn, Ecology (2015)