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.|
|Brown Boobies congregating on Sugar Loaf rock. Before recent years, seeing this many birds together on the island was unheard of. Photo: Jim Tietz.|
Brown Boobies have been one of the most apparent tropical visitors. Found throughout tropical oceans, this large seabird breeds as far north as the Coronados Islands in Mexican waters just south of the California border. Historically, Brown Boobies would only rarely venture further north up the California coast. Between 1968 and 1999, there were only 11 records from Southeast Farallon Island. Since 2000, a few individuals have been seen in most years, usually during the fall. But when a spell of relatively high water temperatures began late last year, booby numbers started to noticeably increased. That trend continued through this October, when we regularly saw dozens of birds roosting on Sugar Loaf rock, with as many as 30 in a single day.
|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.|
These unusual conditions are not confined to the Farallon Islands. Temperatures across the eastern Pacific Ocean have been markedly increasing over the past few years, with a well-documented impact on marine ecosystems along the west coast of North America. Since late 2013, a mass of warm water known as “The Blob” has persisted from Alaska to Mexico, raising regional sea surface temperatures several degrees Celsius above the norm. In addition to The Blob, however, an even larger phenomenon is looming--El Niño. Over the past year, scientists have observed the onset of an El Niño event that was forecasted 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.
Past El Niño events are readily apparent in long-term SST data from the Southeast Farallon Island. The historic 1997-98 El Niño coincided with some of the warmest average monthly temperatures around the island. The average SST from September of 1997, at 16.7 °C, was even higher than this October’s, while average temperatures from November of that year registered at a balmy 16.3 °C. The previous warmest October on record, in 1982, also corresponded with the start of a very strong El Niño. Thus, it appears this fall’s warm spell is a clear indicator of the arrival of this years’ much-heralded El Niño.
|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|
While it has been fascinating to see unusual wildlife around the Farallones, the El Niño may bring more serious consequences to the marine ecosystem. Abnormally warm temperatures can limit nutrient availability and thus disrupt ocean food webs. With the persistence of the Blob and the arriving El Niño, there have already been significant impacts on marine life in the region. The Blob was linked to a decline in krill abundances last year, which in turn led to massive die-offs of Cassin’s Auklets--a small, krill-eating seabird--along the coast in the winter. California sea lions in the southern part of the state have been strained of late, as their typical prey has been pushed hundreds of miles north by warm waters. Many sea lions are being forced to travel further north in search of food, or else starve, as indicated by reports of thousands of emaciated individuals stranded on beaches this year. Related to this trend, we have seen California sea lions in record numbers on the Southeast Farallon Island this fall (learn more about it in a previous blog post: http://www.losfarallones.blogspot.com/2015/10/zalophus-invade-farallones.html). Additionally, warm ocean conditions spurred a harmful algae bloom on an unprecedented scale in coastal waters this summer. Toxins produced by the algae have been linked to another wave of seabird mortalities and sea lion strandings, and have wreaked havoc on some fisheries, causing West Coast states to postpone the winter crabbing season.
|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.
In the end, it is hard to predict what the exact impacts of this El Niño will be. The context of climate change is important to consider, as rising global temperatures have already begun to alter marine ecosystems throughout the world. It remains to be seen how El Niño events and climate change may interact and influence each other, and whether that will further exacerbate stresses in marine systems. It is also possible the trends we have been observing on the Farallones will be more commonplace in the future if warming trends persist—perhaps Brown Boobies and other warm-water species will have a regular presence in years to come, while the island’s breeding seabirds may decline. Whatever this El Niño has in store, the continued observations of Farallon biologists are essential to better understand how environmental change will influence wildlife around the islands and throughout the region.
You can learn more about the recent changes in the ocean ecosystem and how Point Blue researchers are monitoring them through these articles:
Posted by Robert Snowden, Fall Intern
Posted by Robert Snowden, Fall Intern