Humpback whales in SF Bay-Delta
Mother and Calf Are 90 Miles From The Ocean, Injured and Lost
May 18, 2007
A mother and calf humpback whale (Megaptera novangliae) pair is wandering 90 miles inland from the Pacific Ocean through parts of the San Joaquin Delta near Sacramento. This is not the first time it has happened. In 1985, Humphrey the Humpback made his first appearance in San Francisco Bay, wandering up into the Delta for nearly a month. He returned in1990, this time stranding at low tide in the mudflats of San Francisco Bay. Grey whales (Eschrichtius robustus) have also stranded in these confined waters over the years. The use of whale songs helped to get Humphrey back on track but travelling under bridges seemed to confuse him.
Why do whales end up in the bay-delta complex?
For the grey whales this is not particularly unusual behavior. They are a coastal species and explore bays all along the Pacific coast as they migrate. This is especially true for young animals on their first migration. There is speculation that these whales once regularly spent time in the San Francisco Bay before human development reduced the amount of suitable habitat. Some believe that the humpback whales that enter the bay are descendants or a remnant of a population that once inhabited the bay regularly as well.
How do bridges affect the whales?
During the efforts to get Humphrey back to sea, it was noted that he often hesitated or turned around when he neared a bridge. And there are plenty of bridges in the San Francisco Bay-Delta complex. Each time he neared one he appeared disoriented. Researchers thought it was possible that the sound created by the bridge when Humphrey was echolocating may have confused him. Sounds overhead of a travelling whale are often things to avoid such as ships and predators. This may be creating a problem for the mother-calf humpback whales as well.
Whale Songs and Oikami
Both times that Humphrey was in the bay a combination of oikami- a Japanese drive fishing technique which uses the banging of steel pipes as an irritant sound to push the animals from behind- and whale songs played in front were used to get him back to the open ocean. Whale sounds are being used with the mother and calf but there may be a reluctance to use the oikami pipes because of concerns for keeping the pair together. In the next attempt, a flotilla of boats at the rear will likely be used and that may serve the same purpose without running as much risk of frightening them, which could cause them to separate.
This rescue effort will be closely watched by everyone involved in marine mammal conservation as new clues may be provided on how to safely move animals away from areas of danger, an ever increasing concern on our busy sea coasts.
