A Warming Ocean Brings the Tropics to the Farallones–But It's Not Fun in the Sun for Everyone
December 5, 2015
The month of October had something of a tropical feel at Southeast Farallon Island–no, its barren rocks and few Monterey Cypress were not suddenly replaced by white sand beaches and palm trees, but recently, wildlife more characteristic of tropical latitudes have been visiting the island. Throughout October, we witnessed species like Brown Boobies, Common Dolphins, and Ocean Sunfish in unprecedented numbers around the Farallon Islands. These animals are typically associated with warm-water marine environments and rarely occur this far north along the California coast in the fall. What could explain the abundances of unusual species? Not surprisingly, a recent spike in local sea surface temperatures may be contributing to this phenomenon.
|A handsome male Brown Booby visiting the Farallones. More typical in tropical regions, these birds have been showing up in increasing numbers in recent years around the islands. Photo: Jim Tietz.
Sea surface temperature (SST) from water samples obtained from shore is measured daily at Southeast Farallon Island, as part of Point Blue’s effort to monitor the surrounding oceanic conditions. The practice dates back to 1925, long before biologists had a presence on the island. The historic average daily SST for October is 13.6 degrees Celsius. This year, the month’s SST registered at 16.6 degrees! That makes it the warmest-ever October on the island, nearly 0.5 degrees higher than the previous warmest October.
|Historic average daily sea surface temperature (SST) for the month of October from Southeast Farallon Island. There is no SST from 1943-1954 and 1971.|
The marine ecosystem is heavily influenced by temperature–relatively minor temperature changes can alter nutrient availability, which has effects throughout the ocean food web. With such abnormally warm conditions, warm-water species are turning up in unprecedented numbers, likely in search of food that usually would not be available in the colder waters of the California Current around the Farallon Islands.
|Brown Boobies congregating on Sugar Loaf rock. Before recent years, seeing this many birds together on the island was unheard of. Photo: Jim Tietz.|
|Number of Brown Boobies seen on Southeast Farallon per year, 2000-present. There has been a notable increase in sightings since 2014. In 2015, 39 birds have been seen to date.|
Colorful and gregarious Common Dolphins, more typical in the waters offshore of Southern California, have also visited in exceptional numbers. They have been frequently seen near the island on our daily whale surveys, in fast-moving pods of several hundred individuals. In October alone, 2,900 Common Dolphins were seen. That’s nearly equal to the total number of dolphins seen between 2000 and 2014–about 3,300 were seen in that 15-year span. Additionally, this influx of warm-water Common Dolphins has corresponded with a decrease in sightings of cetacean species associated with colder waters, such as Pacific White-sided Dolphins and Northern Right-whale Dolphins. A typical fall may witness as many as a few hundred white-sided dolphins and several dozen right-whale dolphins, but neither species has been seen from the island this season.
|Number of Common Dolphins seen from Southeast Farallon Island per year, 2000-2015. Totals for 2015 are through November 15th. This year has seen substantially more Common Dolphins than previous years. Note the year-to-year trend since 2000 nearly mirrors Brown Booby sightings in that span.|
asted to peak this fall and winter, further warming the eastern Pacific. Early evidence indicates this years’ edition could be among the strongest on record, possibly surpassing the massive El Niño of 1997-98.
|Late-October El Niño status compared between 1997 and 2015 events. Images depict satellite-derived data of sea surface height anomalies, which correlate with relative upper ocean temperatures. The 1997 El Niño was the strongest on record. Image: NASA/JPL|
|A Common Dolphin adult and calf. While recent conditions around the Farallones have suited this warmer-water cetacean, other species have struggled from a disruption to their usual food resources. Photo: Protected Resources Division, Southwest Fisheries Science Center, La Jolla, California.|
On a broad scale, the ultimate consequences of this El Niño may be a mixed bag. If it turns out to be as strong as predicted, this El Niño may further exacerbate many of the ongoing stresses in the marine ecosystem. We may see more hardships for many animals if their food availability continues to be disrupted by warm conditions. There could be substantial economic impacts as well if fisheries struggle. On the other hand, El Niño is forecasted to bring much-needed rain to California over the winter, though this may come with damaging floods and mudslides.
Posted by Robert Snowden, Fall Intern