Why do marine mammals strand?
Although there are numerous reasons why marine mammals strand, there are typically two types of stranding events – mass strandings and single strandings. In most stranding cases, the cause of stranding is unknown, but some identified causes have included disease, parasite infestation, harmful algal blooms, injuries due to ship strikes or fishery entanglements, pollution exposure, trauma, and starvation. In addition, strandings often occur after unusual weather or oceanographic events. In the past few years, increased efforts in examining carcasses and live stranded animals has increased our knowledge of mortality rates and causes, allowing us to better understand population threats and pressures.
Marine mammals may strand for any number of reasons. Marine mammals, like humans, get sick, tired, lost, or seperated from their mom when they are young. Pinnipeds, the seals and sea lions, often come to shore as part of their normal life history. Seals and sea lions will come ashore to rest, molt, and give birth. If you see a seal or sea lion on shore, it may not be stranded, it could simply be warming up in the sun. If you think the animal looks like it may be ill, entangled, or is a very young/small animal that may be separated it is best to REPORT the animal to the stranding network and a trained volunteer will evalute the animal to determine if it should be brought in for rehabilitation. Whales, dolphins, and porpoises (the cetaceans) also strand however if you see one on shore, it is always a stranding as these animals do not come to shore as part of their normal life history. If you see a whale, dolphin, or porpoise on the beach please REPORT this animal to the stranding network
Animals that die or become enfeebled at sea of course may be brought passively to shore by wind and wave action. More intriguing are those cases where marine mammals in distress purposely come ashore. A stranded animal when returned to the water may deliberately strand again. This is very frustrating to those who are trying to “rescue” it. It must be understood that an animal may have stranded because it has decided that it cannot keep itself afloat and survive at sea. Thus, deliberate stranding may represent an effort to keep breathing, whatever the ultimate cost. While this may not be adaptive behavior in evolutionary terms because nearly all stranded animals die if unassisted, given the alternative of equally certain but earlier death, the consideration may be moot. A will to survive is adaptive in general, even if not effective in this circumstance. The natural and unnatural causes of death and disablement leading to single strandings are many: environmental conditions such as anom
