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Bay Nature magazineJul-Sep 2011

Safe Harbor

Welcoming Porpoises Back to San Francisco Bay

by on July 01, 2011

A harbor porpoise surfacing beneath the bridge gets the attention of a flock of western gulls and a Brandt’s cormorant looking for the chance to catch any fish the porpoise might drive to the surface.  (Photo by William Keener/GGCR.)
A harbor porpoise surfacing beneath the bridge gets the attention of a flock of western gulls and a Brandt’s cormorant looking for the chance to catch any fish the porpoise might drive to the surface. (Photo by William Keener/GGCR.)

Cavallo Point at Fort Baker is not just a place to watch sailboats go by as the morning sun illuminates the Golden Gate Bridge. It’s also a great place to watch the water surge in and out with the tides. And with a little patience, you might see a black dorsal fin cut the swirling water, followed by another, smaller fin. A mother harbor porpoise and her calf are rolling at the surface, entering the Bay. In the calm of a slack tide, if they come close enough, you can hear them breathe: two sharp chuffs.

The old sailors called them “puffing pigs.” Even the word “porpoise,” from the Latin porcus piscis, means “pig fish.” Of course, they are neither fish nor pig; they are marine mammals or, more precisely, cetaceans (the family that includes whales, dolphins, and porpoises). Blunt-snouted and stocky creatures, they have plenty of blubber to keep them warm. But they are agile in the water, with powerful flukes that propel them easily through swells and currents.

Standing on this rock at the southern tip of Marin County today, you can often see porpoises swimming past in groups of two or three. From the much higher vantage point of the Golden Gate Bridge, you might count as many as 20 or 30. Through the green water you can watch them traveling, or loafing, or spinning on their sides as they make a dash for a fish, then pop up beneath a flock of excited gulls.

Such sightings are all the more remarkable because for many decades porpoises weren’t seen inside the Bay. Now, however, the Bay Area is one of the few metropolitan areas in the world where you can see cetaceans every day.

More than a wildlife spectacle, the presence of these shy animals could be telling us something positive about the health of the Bay ecosystem. Big mammals, especially carnivores, are in decline everywhere. Unless humans intervene, as with the wolves reintroduced to Yellowstone, they rarely make a comeback. Yet it’s happened here–the porpoises have “reintroduced” themselves to San Francisco Bay.

Big mammals are in decline everywhere, and they rarely make a comeback. Yet it’s happened here.

No one predicted the return of the porpoises. Ever since I started whale-watching here in the 1970s, I had only seen them west of the Golden Gate, mostly as they fled our approaching boat. In the late 1980s, I was on a team of biologists hired to conduct a census of harbor porpoises in the Gulf of the Farallones National Marine Sanctuary. During three years of boat-based surveys, we never spotted a single porpoise east of the bridge.

Researcher photographing from Golden Gate Bridge
Focusing on a porpoise more than 200 feet below, Isidore Szczepaniak is a cofounder of Golden Gate Cetacean Research, a team of marine biologists studying the animals from their boat and the Golden Gate Bridge. Photo by William Keener/GGCR.

But we know they used to be here. Bones found in the Emeryville shellmound suggest the local Ohlone people consumed harbor porpoises in small quantities for some 2,000 years. In a mid-19th-century report, West Coast whaler Charles Scammon said of harbor porpoises, “They feed upon fish, and are occasionally taken in seines that are hauled along the shores of San Francisco Bay by the Italian fishermen.” And there are accounts from the 20th century, including one from the family that still operates the Tiburon-Angel Island ferry service. Its founder, the late Milt McDonogh, grew up around the docks in Tiburon and remembered seeing harbor porpoises there in the 1920s and 1930s.

Mother porpoise and calf
Following its mother’s lead, a porpoise calf surfaces to take a breath. Photo by William Keener/GGCR.

It’s unclear exactly when harbor porpoises abandoned the Bay, or why, but they seemed to have disappeared by the 1940s. Disturbance from ship traffic and environmental degradation likely played a role. The onset of World War II may have been the final stroke. To protect the harbor from submarine attacks, the navy stretched a steel net across the Bay from Sausalito to San Francisco. The net would have been a formidable obstacle to porpoises, an acoustic as well as physical barrier. The heavy mesh, straining against the currents, must have made an underwater racket. For animals that depend on their acute hearing to communicate and to locate prey, the noise might have been deterrent enough.

So why are the porpoises back now? Are ocean conditions driving them into the Bay? Or are conditions in the Bay luring them in from the ocean? Perhaps it’s simply an increase in population coupled with an increase in available prey. Aerial surveys by the National Marine Fisheries Service do show a long-term trend of increasing abundance in harbor porpoises locally, helped by a mid-1980s ban on gill nets, which killed many porpoises as bycatch. The most recent estimate is that 9,000 harbor porpoises inhabit coastal waters between Pigeon Point in San Mateo County and Point Arena in Mendocino County.

Meanwhile, variations in the marine environment may have resulted in changes to the porpoises’ prey. Harbor porpoises along our coast are known to eat schooling marine fish, such as herring, anchovy, and jacksmelt, plus rockfish and squid. It’s possible that unusually low rainfall from 2007 to 2009 led to an influx of salt water into the Bay, which brought in fish species that attracted the porpoises. Also, thanks to modern sewage treatment systems and the regulation of industrial effluents, Bay water is less polluted than it was the last time the porpoises ventured inside the Golden Gate.

Larger-scale changes could also be having an effect. Marine scientists have recently correlated atmospheric conditions in the Pacific Ocean with winds and upwelling that can alter the habitat in estuaries, including San Francisco Bay. For the past several years, the Bay has been experiencing an ecological “regime shift” toward higher productivity of plankton and fish. We know the local herring population is bouncing back, and that’s a boon for porpoises.

Map of porpoise sightings
Areas where harbor porpoises and bottlenose dolphins are seen in the Bay. Porpoises are now in the Bay year-round, but their locations shift daily with the tides. Dolphins are seen mostly in the summer and fall. Map by Bay Nature, modified from William Keener/GGCR.

I was first tipped off to the porpoises’ return in 2008, when I got a call from San Francisco State University minke whale expert Jon Stern, who was surprised to see them from his boat off Sausalito. That spurred me to search the shorelines between the central Bay’s three main bridges. Everywhere I went, I found porpoises! In particular, deep trenches and steep peninsulas seemed to attract them, presumably because fish are concentrated there by strong tidal rips. Near Yellow Bluff, just north of Cavallo Point, up to a dozen porpoises at a time were congregating and diving, foraging for fish in ebb-tide feeding sessions.

Porpoises are now seen regularly at locations much farther inside the Bay, such as Raccoon Strait, and near Angel, Alcatraz, and Treasure islands. Passengers on the commuter ferries have seen them as far south as the San Francisco-Oakland Bay Bridge. There is a reliable report from July 2009 of harbor porpoises at East Brother Island off Richmond. A veteran skipper told me about a small cetacean, which he believed to be a harbor porpoise, in Suisun Bay in March 2009. If correct, this would be the farthest inland record in the San Francisco Bay-Delta Estuary.

Most of what we know about harbor porpoises is based on the examination of stranded animals–carcasses. With their regular appearance in the Bay, we now had a chance to learn how they live in their element. To organize the scientific endeavor, several colleagues and I put together a team called Golden Gate Cetacean Research and obtained a federal permit to approach the porpoises by boat. We also had an extraordinary resource: the Golden Gate Bridge. From its deck, 220 feet above sea level, we can observe behavior nearly impossible to see from a boat: underwater feeding, chasing, and nursing, or riding the wake of a passing tanker. We have even seen porpoises mating, something never before observed in the wild.

Porpoise mating attempt
Porpoises aren’t known for their acrobatics, but a male will often propel himself into the air as he attempts to mate with a female. (right) Recognizable scars help the researchers track individual porpoises. Photo by William Keener/GGCR.

The porpoises have a synchronized reproductive cycle, culminating in an early summer calving season quickly followed by a peak in mating behavior. Each spring the males’ hormones kick into overdrive. Undergoing tremendous growth, their “megatestes” reach up to 4 percent of their body weight–a ratio extraordinarily high for any mammal. Promiscuity is the rule in porpoise society, and males pursue females with persistence and vigor. As with almost all of their behaviors, mating is done on the move. Copulation lasts just a few seconds, complete with a splash as the pair seems to fly apart.

We know that gestation lasts 10 to 11 months and the single calves remain with their mothers for about a year. In time, we should be able to determine their birthrate, which is critical to understanding how quickly a population can recover from a catastrophe such as an oil spill. Research in the Atlantic determined that harbor porpoises calve annually, and the females are often pregnant and lactating simultaneously. However, a 20-year-old study in California came to a different conclusion, with evidence in favor of calving every other year. We hope to shed light on this question by tracking females from year to year to see whether they are accompanied by calves.

Porpoises at the Bay's surface
The animal on the left (number 167 in the researchers’ catalog) displays a unique V-shaped scar whose source is unknown. She is presumed to be a female, based on her mating behavior. Photo by Isidore Szczepaniak/GGCR under NOAA Fisheries permit LOC #15477.

By photographing their markings, we can tell individual porpoises apart based on unique characteristics, such as body scars and skin pigmentation patterns. Porpoises give the impression of being all black from a distance, but high-resolution photos reveal more subtle colors, including pale blazes across their flanks. We’ve learned that a sizable percentage of the porpoises in the Bay sport scratches and scars. Some marks are obviously due to close encounters with fishing nets, while others are more enigmatic. They seem to be tough critters, and a few appear to be surviving, even thriving, despite apparently serious injuries.

In 2009, we started a Porpoise Catalog, linked to a database of sightings, which now has over 200 animals in it, a remarkable number for this hard-to-observe species. Each time we scan through a new batch of porpoise photos, whether taken from the bridge or the boat, we painstakingly compare them with prior images. The matches prove that several individuals are “regulars” in the Bay, sighted three or four times over the past year and a half.

But even with all this tracking, we still aren’t sure whether the porpoises form a resident community. Do they stay overnight in the Bay or come and go with the tides? One way to find out is to listen. We plan to place monitors, essentially three-foot-long plastic tubes crammed with electronic gear, on the seafloor to record the ultrasonic clicks porpoises emit for echolocation. After a couple of months, we’ll haul in the monitors and download the data, revealing every time porpoises passed by, day or night.

Dolphin spyhopping
Bottlenose dolphins emerge from the water much more frequently than harbor porpoises do, and they exhibit a wide range of aerial behaviors. This one is spyhopping off Fort Point at the southern end of the Golden Gate Bridge. Photo by William Keener/GGCR.

Porpoises aren’t the only small cetaceans that visit San Francisco Bay. At the northern end of their range, bottlenose dolphins sporadically enter the Bay, where they tend to hug the San Francisco shoreline. They normally travel only as far as Baker Beach or Crissy Field, but in fall 2009 a trio was spotted near Redwood City. Last year, pods of dolphins visited the cove between Fort Point and the Crissy Field fishing pier two or three times a week from June through October.

Our two Bay cetaceans are fairly easy to tell apart. Bottlenose dolphins are much heavier and twice as long as porpoises. Dolphins have a large curved dorsal fin, while porpoises show a short triangular fin during their brief surface rolls (see illustrations). Dolphins also tend to engage in more complex and acrobatic behavior. In the Bay, they can put on quite a show, and joggers along the breakwater have seen them slap their flukes, swim upside down, drive salmon into the air, and spyhop (stick their heads out to look around). Porpoises, on the other hand, seldom emerge fully from the water.

Harbor porpoise illustration
Harbor porpoises (Phocoena phocoena), with a small triangular dorsal fin and a blunt snout, grow to about five feet long and live 10 to 12 years. Illustration by Uko Gorter, ukogorter.com.
Dolphin illustration
Bottlenose dolphins (Tursiops truncatus), with a large, curved dorsal fin and a distinct “beak,” grow to about seven to 10 feet and live 20 to 30 years. Illustration by Uko Gorter, ukogorter.com.

Compared to harbor porpoises, the dolphin population is small, perhaps 400 for all of California. Whenever we see dolphins in the Bay, we take “mug shots” to identify them because every individual is already well known. Exchanging photos with Okeanis, a marine conservation group in Moss Landing, we learned that at least 20 dolphins made the trip into the Bay in 2010. One of the dolphins we’ve seen several times is a female nearly 30 years old, first recorded in 1982 in San Diego, then spotted off Los Angeles, and later in Monterey Bay.

One reason we keep close tabs on the dolphins is to look for any interactions they might have with the porpoises. Bottlenose dolphins have been known to act aggressively toward the smaller porpoises. Dead porpoises have washed up on shore with parallel rake marks that could have been made by the teeth of bottlenose dolphins. In September 2009 biologists in Monterey Bay witnessed a fatal attack on a harbor porpoise by male dolphins. So far, however, we haven’t observed such aggressive behavior here, even when groups of dolphins and porpoises come within a hundred yards of each other.

Over the next few years, our work to unravel the mystery of the porpoises’ return may also lead us to understand their social structure. It’s an open question whether they maintain long-term family bonds or form alliances, as other cetaceans do. One thing is certain: Observing these intriguing animals–as scientist or enthusiast–is a pleasure. We should all take the opportunity to get out and watch these porpoises once again making their home in our own briny “backyard,” San Francisco Bay.

Where to See Harbor Porpoises

Porpoises, which are in the Bay year-round, keep to a loose schedule based on the tides, but their whereabouts also depend on the interplay of currents and the presence of prey fish.

Cavallo Point, at Fort Baker in Marin, is a good place to observe porpoises at the beginning of the ebb tide, when porpoises may be as close as 30 feet off the rocks. In San Francisco, porpoises can sometimes be seen working the flood tide off the pier at Crissy Field. A knot of gulls on the water often means a seal, sea lion, or porpoise is actively feeding there, so watch carefully. And bring binoculars.

But the best place to watch for porpoises (if you don’t mind heights) is from the Golden Gate Bridge’s pedestrian walkway. Check the tide tables and time your visit to coincide with the currents running at maximum flood, an hour or two before a big high tide. There are two good zones–one near the north tower, and one near the south tower (see map for areas where porpoises concentrate). Walking slowly all the way across, taking time to scan below frequently, will almost always result in a few sightings.

Calling All Citizen Scientists

Information about your sightings of porpoises or dolphins in San Francisco Bay is valuable and adds to our knowledge of these species. Submit reports at ggcetacean.org. Send your photos for us to compare against our catalogs.

Most recent in Habitats: Freshwater, Bay, Marine

See all stories in Habitats: Freshwater, Bay, Marine


Mary Doshay on October 5th, 2012 at 9:24 pm

Hello, we were on cavallo point today, 10/5/2012, to watch the America’s cup trials and saw tow small set of 2-3 porpoises each. I think they were porpoises because they were smallish. They were about 30-50!feet from the shore facing southeast and gulls we circling the point like crazy. Then a few of them headed toward the Golden Gate Bridge but not too far, then came back. They were hanging out in one spot for a bit. There may have been a smaller one, it was hard to tell. My husband was shooting the boats and I don’t think got pics but if we come across any we’ll send them . There were also a couple of seals around. We see those often there, but haven’t seen porpoises before and go there a few times a month. Thanks!!

Ging Wang on January 26th, 2013 at 6:09 pm

Thanks for such an informative article. We had a great sighting today near Yellow Bluff, not far from Cavallo point. We were in our kayaks, and noticed seagulls congregating in the sky near us. Sure enough porpoises were sighted, presumably hunting. There were 6 or 7 animals, including a mother and a calf. We stopped paddling, and enjoyed the sounds of their quiet breathing for a while. They were a wonderful presence. I’m so glad they are back in the Bay!

Sally Jo Browne on March 16th, 2013 at 3:41 pm

great article. I was on the Alcatraz Ferry returning to Pier 33 on Wed Mar 13 in the afternoon and saw the fin of probably a porpoise near the side of the ferry. That was a nice surprise!

Dan Rademacher on March 16th, 2013 at 7:51 pm

Very cool, Sally Jo!

Rochelle Rosen on April 18th, 2013 at 3:07 pm

we were at Baker Beach this morning and saw a pod of 4 dolphins/porpoise. There were two larger and 2 smaller animals that surfaced as they moved to the south and after surfacing serveral times in one area we saw them going north 1 time. It is the first time I have seen marine mammals at Baker beach. The color seemed dark brown and they were to far away such a surprise I did not notice the dorsal shape. My friend felt they were dolphins. WAY COOL

Geoff Chin on May 24th, 2013 at 11:55 pm

Took my 4th graders across the bridge today. We spotted numerous porpoises near the north tower. Perhaps a dozen or the same six several times. Hard to say. Also sea lions, harbor seals, and jellyfish (brown sea nettles?). Seemed to be slack tide, just switching to ebb maybe. Think the kids were at least as excited by the marine life as the helicopter and tankers that passed underneath us.

Dan Rademacher on May 25th, 2013 at 8:55 am

Thanks for sharing, Geoff! That sounds like a great trip.

Mike H on June 1st, 2013 at 11:05 pm

June 1 2013- From about 11:00 a.m. to 12:00 noon, sailing slowly and silently between Alcatraz and the Oakland Bay Bridge at 3 to 4 knots through the water (maybe 1.5 knots Speed Over Ground) directly into a strong ebb current, I had a group of Harbor Porpoises with me for about an hour. They tracked the boat and zoomed to within about 2 feet of the hull, surfacing, chuffing and swimming past and under the boat. They seemed to like speeding past the bow and zooming in at a high rate of speed from a couple hundred yards behind me, to surface right along side. The smallest animals were about 2′ long and the largest about 4′. There could have been a lot of them but I suspect it was a small group that was just having fun buzzing the boat, and I never saw more than 3 at any one time, so there’s no way for me to guess if there were few or many. They stayed with me almost all they way to the Bay Bridge (about an hour), ending when a large noisy tug passed nearby and the animals went away.
Seeing them at VERY close range and many dozens of times, I am positive they were Harbor Porpoises. What a thrill that was for me!

Dan Rademacher on June 2nd, 2013 at 9:05 pm

Thanks for sharing, Mike! That sounds wonderful.

Nimmi on September 8th, 2013 at 9:11 am

Saw a bunch of these while out sailing yesterday. Even with all the America’s Cup boat traffic. They were mostly in pairs. We saw them mostly between Alcatraz and Sausalito.

Michael on September 9th, 2013 at 1:54 pm

saw one really close up Sept 7th just after 9am just south of the south tower. I was in an 2-man outrigger canoe, really great came with 10 feet of us and surface a couple times.

Mykala on September 12th, 2013 at 12:59 pm

Yeah Mike I think it was a dolphin. The nose was short but it was a longer shape, not rounded. It popped up a little to check us out, twice, and it had a darker tone. It looked young to me, but what do I know?

oni5150 on September 19th, 2013 at 1:19 pm

We saw a pair of harbor porpoises swimming with the boat on the way to Alcatraz yesterday, a great sight for my parents who are visiting from Boston for the week. They were very close and probably onle 2.5 to 3 feet long. It was incredible seeing them rolling, and the short dark dorsal risising out as they went confirmed they were porpoises.

Danny on January 20th, 2014 at 7:05 pm

January 19th 2014
Seen a pair of porpoises swimming just off baker beach this weekend, they were swimming out from the bay just past the golden gate.

Joe on July 9th, 2014 at 9:37 am

Saw 2 dolphins in the cove next to Ft. Point yesterday. Looked like they wanted to see what the fisherman off the shore had for bait.

krystal miller on October 29th, 2014 at 1:34 pm

i like the dolphins allot more!!!

MrUncomfortable on June 8th, 2015 at 3:37 pm

I frequently fish in the SF bay and ive been seeing what I think are smaller dolphins. I think this because they eventually come back up for air. They are very small maybe 3ft-ish long, and look like their are pitch black (or just very dark in general). I’ve been seeing them solo, not in groups. Ive mostly seen them in the central bay, and also as far as the south bay down towards San Mateo bridge. Is anyone familiar with what they are/what species they are?

William Keener on June 8th, 2015 at 4:21 pm

What you describe do sound like harbor porpoises. They are small and dark, and tend to be solo (or mother/calf pair) and they are in the central bay a lot. If you can get a picture, then we can figure out what it is for sure. Thanks for the comment!

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