PELAGIC DISPATCH
This just in:
Sharks and Orcas Thrive in Monterey Bay.
During the past nine weeks transient orcas have killed at least five gray whales and a number of sealions and porpoise over the Monterey marine canyon. Behaviorists Nancy Black (Moss Landing Marine Lab) and Sean Van Sommeran (Pelagic Shark Research Foundation) have been documenting these predatory events over the past several years and have seen a lot of action as of late. Every spring there is a noticeable increase in orca presence over the Monterey marine canyon. Orcas, (there are at least 3 distinct types) the largest member of the dolphin family, are believed to use the canyon as an ambush site to attack northerly migrating gray whale calf/cow pairs. This year researchers have seen the most action since spring of 1993, when orcas killed several gray and minke whales as well as a
number of seals and sealions.
"Once the orcas have had their way with the whale and have abandoned its carcass to drift, the site makes for an excellent shark research station as dozens of blue sharks and sometimes white sharks ascend to feed on the whale;" commented Van Sommeran who has witnessed many such incidents over the years.
Photos and video shot over the past decade can be compared year after year to ID individual orcas and orca pods. "This season we have seen several orcas that we know from years past" said Black as she and Van Sommeran inspected the badly battered and bitten carcass of a freshly killed gray whale calf that stranded near Ano Nuevo Island in early May.
Black has catalogued hundreds of dorsal profile shots of transient "rogue" type of orcas, a relatively rare, poorly understood sub-species of killer whale that has no known home range and has a reputation for killing other marine mammals. Aside from behavior and range, the transient orcas also differ physically from the typical 'fish eating' orcas that are often shown at marine parks. The fish eating orcas are called residents because they have very specific home ranges. Unlike the resident type of orcas (free willy) , the transient or rogue orcas appear to travel far and wide in smaller groups and have a very distinct pattern of vocalization.
"These orcas have been seen from Mexico to Alaska." adds Van Sommeran. "The orcas are given a numeric designation after the initial ID. CA 44 an alpha female, and CA 71, an alpha male have featured prominently in the
video taped attacks of this past season." CA stands for California and the
number indicates the order in which each animal was ID'd. It appears that more than one pod of transients may have been observed this season and researchers are eager to gain any insights they can as to inter-group behaviors. Orcas sometime gather into what has been called "super-pods" where several groups of orcas join forces and attack animals like blue whales or sperm whales.
Monterey Bay is visited by another orca variant during the fall, according to Black. "We've seen what are called the "off-shores" types
of orcas in the outer bay regions and way out on the open ocean." Last year
Black was able to observe an attack by orcas on sperm whales many miles offshore via aircraft while on an ATOC survey. "It was amazing to watch the sperm whales close ranks to fend off the charging attacks by the orcas."
While the orca season is winding down as the main pulse of the gray whale migration passes the Monterey bay heading north to Alaska, there have been orca sightings as recently as May 21.
Gustavo Richter
Davenport Ca (PD)
[ back to PSRF News Archive ]
|
|
