Panel discusses killer-whale interactions, stranding patterns and isotope diagnostics

The symposium audience raised whether killer-whale predation influences grey whale movement and stranding vulnerability and whether stable isotopes in baleen or skin can reliably indicate herring feeding.

Bob Pitman noted rake marks consistent with killer-whale interactions in photos and asked whether that plays a role in migrations to Baja and elsewhere. Panelists said killer whales have been implicated in some strandings and attacks, but they also reported many feeding aggregations have not seen targeted attacks. Panelists described field observations in Kodiak and other sites of killer-whale presence but not necessarily successful attacks on aggregations.

On isotopes, researchers said herring-egg signatures are distinct from benthic prey and can show up in skin within about a week of feeding; baleen (baleen plates) can retain isotopic records across longer time spans, but turnover rates and precise temporal interpretation in live animals remain uncertain and require careful sampling designs.