Northern elephant seals have one of the most extreme breeding systems of any mammal, with massive males competing violently for harems, females crowded on beaches, and pups facing abandonment risks.
The elephant seal breeding system creates intense welfare costs as a consequence of their natural reproductive biology. Male-male competition causes severe wounds: deep lacerations to the face and neck from the canine teeth of rivals are characteristic. Losing males may die from their wounds or from exhaustion. Pups caught between competing bulls are crushed - a significant source of early mortality. The weaning cliff - where mothers abruptly abandon pups who have never swum - leaves bewildered, hungry pups to figure out survival alone. The fasting females lose approximately 40% of their body mass during lactation, a physiological stress that under poor prey conditions can be fatal.