COMMON DOLPHINS IN MONTEREY BAY
Recent sea surface temperatures in Monterey Bay have been 2 to 5 degrees above normal. This appears to be caused by anomalous warm water conditions that may be a precursor to El Niño. According to recent oceanographic reports, true El Niño conditions have not yet arrived in Monterey Bay; however, we are seeing several species associated with warm water conditions. The most predominate dolphins in the Bay over the last month include both Long-Beaked and Short-Beaked Common Dolphins. Common Dolphins have recently been divided into two species based on morphological features. These two species do not appear to mix and occur in separate schools.
Common Dolphins are a spectacular sight as both species typically are found in schools of 500 to over 2,000 individuals. Within these schools are subgroups of mother/calf pairs, adult males, females without calves, and juveniles. Calves are born year-round so we frequently see newborn calves within these schools. These schools are easily sighted from a distance as they are tightly grouped, causing considerable disturbance in the water, and are often associated with large numbers of seabirds. The seabirds take advantage of the dolphins’ ability to herd fish toward the surface where the birds then capture many fish escaping from the dolphins.
Since September, these dolphins have been sighted nearly every day in the Bay or surrounding waters. The dolphins have been frequently associated with the edge of the Monterey Submarine Canyon, an area that is known to concentrate prey. An abundance of sardines and mackerel appears to be the primary prey of the dolphins.
Both species of Common Dolphins are normally seen farther to the south, off the Channel Islands and south to Baja California. In addition to common dolphins, both Pilot Whales and False Killer Whales have been reported in the Bay over the last month. Both of these species are also associated with warm water conditions and are normally rare to the area. As true El Niño conditions are expected to occur in the Bay in the coming months, we will be looking for and documenting the presence of these and other unusual species.