The smoltification process — when juvenile salmon transition from fresh to salt water — is a physiologically demanding event. Welfare challenges during this period include transport stress, density, and the transition itself.
Smolt welfare is a concentrated welfare challenge period in the salmon production cycle. The transfer process — netting, crowding, pumping into transport vessels, and release into sea cages — involves multiple acute stressors compressed into a short period. Premature or delayed transfer catches fish at a physiologically vulnerable point, reducing their capacity to cope with additional stressors. The high disease susceptibility of newly transferred smolts, combined with immediate exposure to sea lice in open net pen environments, creates a welfare-perfect storm in the weeks following sea water entry. Mortality rates during and immediately after smolt transfer are a significant welfare indicator — elevated mortality reflects cumulative stress and physiological failure in fish unable to complete the transition successfully.