Why do animals strand?

Animals can strand for a variety of reasons, both natural and anthropogenic (human-caused). Most often, the cause of the stranding is not known until a full investigation is done. Natural causes can include disease, illness, predation, maternal separation, poor navigation due to weather or other conditions, social cohesion within a group, and exposure to algal toxins (red tide).  Human-induced strandings can result from such things as entanglement (in fishing gear or marine debris), exposure to noise (seismic explorations, mid-frequency/low-frequency sonar, etc.), ingestion of marine debris, vessel strikes, and chemical/oil spills. The definitive cause of death or stranding is often difficult to establish. Often, multiple factors may contribute to the stranding event or mortality. It is important that when feasible and authorized, a necropsy (post-mortem examination/dissection) of the stranded specimen is conducted and appropriate samples are collected to improve our understanding of the species, identify causal factors for the stranding, and develop appropriate mitigation or conservation measures.

Melon-headed whales mass stranding. Credit NOAA