Both in the open ocean and the nearshore waters, spring is a busy time for marine mammals on the Central Coast. Some, including humpback whales, gray whales, and sea lions undertake long migrations at this time of year. Others, such as harbor seals, give birth locally, rearing their young on the small fish that are abundant in surface waters in April.

Humpback whales arrive to feed on krill larvae

A humpback whale, breaching. (Source: Cornelia Oedekoven - SWFSC/NOAA)

Many different animals feed on the young krill and anchovy that swarm in the near-surface waters in April. By far the largest of these krill-eaters are humpback whales, which typically begin to arrive in Central Coast waters in March or April (MBNMS 2006).

Note: Although humpback whales have historically been considered summer and fall visitors to the Central Coast of California, in recent years humpbacks have been in observed in Monterey Bay all year round, with a maximum in fall and a minimum in January and February (Ryan 2019).

Although humpbacks often begin arriving in March or April, their numbers will increase throughout the summer, as more and more whales swim northward from Central America and Baja California (where they feed on krill that mature earlier in the year) (NCCOS 2003). By August, both the humpbacks and the krill will reach peak abundance.

Humpbacks eat both krill and anchovies. If they are hunting krill, they are more likely to be out near the edge of the continental shelf or near the edge of Monterey Canyon (Kieckhefer 1992). If they are hunting anchovies however, you may see them relatively close to shore in areas such as Moss Landing, where Monterey Canyon comes close to the beach (Personal observation). Whether near shore or at sea, the humpbacks are often accompanied in their feeding frenzies by large numbers of pelicans, cormorants, and California sea lions.

Mother and baby gray whiles migrate north

If you see a whale near shore in April, chances are it is a gray whale. In fact, April is the best time of year to see female gray whales and their babies swimming north along the coast.

The baby whales that appear on the Central Coast in April were born during January or February in the warm, shallow waters of Scammon's Lagoon, about half way down the Baja California peninsula. These warm waters are the perfect nursery for the young whales, because they are born without an insulating layer of blubber (Miller 1975).

At birth, baby gray whale calves weigh about 1,500 pounds and are about fifteen feet long. Lolling in the warm waters of Scammon's Lagoon, the calves nurse like crazy, drinking up to 50 gallons of milk and putting on about 70 pounds a day (Tweit 1999). In this way they rapidly build up a layer of insulating blubber.

By the time they start their northward migration in March, the calves will weigh three times as much as they did at birth. However, their mothers will have lost a quarter of their body weight and will have eaten little or nothing since leaving their Arctic feeding grounds the previous October (Miller 1975).

By the time the mother and baby whales pass along the Central Coast in April, they will have been "on the road" for several weeks. But they still have a long way to go in their 7,000-mile trek north toward the Bering Sea.

From exposed coastal cliffs, you can often see the female whales swimming steadily northward, their babies close beside them. Although the journey may appear leisurely from shore, in reality, both the mother and the baby are likely to be hungry and tired. In fact, each year a number of young whales die during the long journey north, due to starvation or exhaustion. But their greatest risk is being attacked by killer whales (orcas).

The young whales face perhaps their greatest challenge of the entire trip when crossing the open waters of Monterey Bay. This thirty-mile stretch of open ocean, underlain by the deep water of the Monterey Submarine Canyon, is a favored gathering place for orcas. In fact, pods of orcas migrate to Monterey Bay in spring, specifically to hunt the baby gray whales (Tweit 1999).

Orcas gather in Monterey Bay to hunt young gray whales

Growing over 30 feet long, and capable of eating over 100 pounds of flesh a day, orcas are truly impressive predators. They are also extremely intelligent and social animals.

Like a pack of wolves, the basic orca family unit consists a matriarchal female, her calves, and one or more nonbreeding adults. Several families often band together to form a "pod" of up to 50 animals that travel, hunt, and socialize together. Different pods even use different sounds to communicate with each other as they hunt and travel (Tweit 1999).

Based on their eating habits and distinctive markings, scientists have identified several different "populations" of orcas that hunt along the Central Coast. One population lives mostly in the Pacific Northwest, eats mostly salmon, and only occasionally makes forays down to the Central Coast. A second population lives farther offshore, tends to avoid the coast, and apparently eats mostly fish and squid (Tweit 1999).

The third population of orcas, known as "the transients," travels along the coast hunting marine mammals, including sea lions, elephant seals, dolphins, and baby gray whales. Unlike other orcas, those in "transient" pods don't communicate with sound very much (Tweit 1999). Presumably this helps them sneak up on their prey, most of whom have an excellent sense of hearing.

As described below, gangs of foolish young sea lions begin to arrive in the Central Coast waters during March or April. This is also when young, inexperienced elephant seal pups leave their nurseries and swim out to sea. Between the young sea lions, elephant seals, and baby gray whales, transient orcas find plenty to eat on the Central Coast (Lachman 2018).

The migrating female gray whales are apparently well aware of the danger to their young, and will go to great lengths to avoid orcas. Rather than swimming straight across Monterey Bay, some gray whales guide their babies close to the shoreline, following the perimeter of Monterey Bay (Tweit 1999). If orcas pursue a mother and baby whale toward shore, the mother may even herd her baby into the kelp beds to escape or hide from the orcas.

Other gray whale mothers and babies try to sneak across the bay, taking quiet, shallow breaths while swimming as fast as they can to minimize their time over the deep water of the canyon (Tweit 1999). You can sometimes see such mother-baby pairs swimming slowly just beyond the kelp beds near West Cliff Drive (Santa Cruz), apparently catching their breath after their sprint across they bay.

But not all gray whales are so lucky. The orcas swim silently, alone or in packs, often lurking just below the rim of the canyon, listening for the sound of gray whales spouting and breathing. When an orca hears a gray whale calf, it issues underwater sounds that attract others of its kind, who gather like wolves for a kill.

Like wolves, orcas can rarely kill their prey outright with their teeth, so they must encircle the whales and try to tire them out. They take turns charging toward the baby, trying to separate it from its mother. The mother, meanwhile, tries to block their attacks with her body and swat the attacking orcas with her powerful flukes (Tweit 1999).

As soon as the orcas see an opening between the mother and her baby, they attack, ramming and leaping on top of the baby like berserk water polo players. They try to knock the breath out of the young whale, crush its ribs, and eventually tire it out until it drowns (Tweit 1999).

When orcas do succeed in killing a calf, the entire pod may gather to dine on the animal for several days (Tweit 1999). If the whale carcass is still floating after the orcas have finished eating, blue sharks and a white sharks may come by to finish off the remains. Eventually the carcass of the baby whale washes ashore or sinks to the seafloor. There it provides a feast for scavengers such as crabs, snails, and worms.

Young California sea lions arrive on the Central Coast

A gaggle of young, enthusiastic seal lions can swim so fast that they leave a collective wake. (Source: Kim Fulton-Bennett)

During April, you may see lots of juvenile sea lions swimming along the shoreline or basking on rocks and jetties. However, you won't see many adult sea lions. The adults (mostly males) leave the Central Coast in February or March. By April these "big boys" are breeding on islands offshore of Southern California and Baja California (Nicholson 1986).

As the adult sea lions are leaving the Central Coast, groups of young sea lions begin arriving from down south. Some are just passing through to feeding areas such as Ano Nuevo or the Farallon Islands. Others will stay to feed in this area through the summer and fall.

The youngest sea lions in these migrating groups may only be a few feet long. Most of these pups were born off Southern California during the previous year's pupping season in June or July (Nicholson 1986).

Sea lions are extremely gregarious. By the time the young pups are two or three weeks old, they are already hanging out together in packs (MMC 1999). During spring, these gangs of young sea lions travel northward together, stopping to rest and feed at convenient haul-out spots along the California coast. For many sea lion pups, the spring trip northward is their first big outing, and it shows in their behavior.

While surfing near Moss Landing in spring, I often see boisterous groups of up to 20 or 30 young sea lions swimming or floating around in "rafts" just outside the surf zone. Occasionally a group will suddenly take off down the coast, splashing, diving, porpoising, and even veering toward shore to ride a wave or two.

Several times, while sitting on my surfboard, packs of young sea lions have come swimming straight toward me at high speed. Each time they veered away at the last minute, the youngest animals looking over their shoulders at me as they dashed past. Sometimes older sea lions swim around these groups of rowdy youngsters, as if trying to riding herd on them and keep them from doing anything too foolish.

Most of the sea lions that we see on the Central Coast are males (the females tend to stay near the pupping areas in Southern California). In April or May, you can sometimes see large groups of juvenile male sea lions hanging out at places like the Monterey Breakwater, the Santa Cruz wharf, or San Francisco's Pier 39 (MMC 1999).

If you visit one of the sea-lion "hang outs," you will probably notice that most of the sea lions don't seem to be doing much of anything. Well-fed sea lions often sleep eight to twelve hours a day, and hunt only when prey are readily available. As one writer put it, sea lions are "binge eaters," who stuff themselves when food is abundant, then rest and conserve their strength when food is scarce (MMC 1999).

In the late afternoon or evening, packs of sea lions leave their haul-out areas and travel up to 10 or 20 miles away to hunt small, schooling fish and squid. Along the Central Coast, their prey include seasonally abundant animals such as anchovies, hake, young rockfish, and market squid (Nicholson 1986).

Sea Lions and Salmon

For better or worse, large numbers of juvenile sea lions arrive on the Central Coast just in time for the beginning of salmon fishing season. California sea lions are very fond of salmon, but even an adult sea lions has a hard time catching a 30-inch-long salmon. This is where humans come in handy.

Some sea lions have learned to follow salmon-fishing boats in hopes of snagging a free meal. These sea lions know that once a salmon is hooked on a line, it becomes easy prey. Fishermen, in turn, know that once they've hooked a salmon, they better get it out of the water as quickly as possible, or it will be picked from the hook by a "trained" sea lion.

More often than not, when a sea lion snags a salmon off a fishing line, it can't swallow the fish whole. So the sea lion surfaces with the fish in its mouth, then shakes the salmon back and forth, trying to break off bite-size pieces (Nicholson 1986).

Such behavior does not make fishermen feel very friendly toward these federally-protected marine mammals. In fact, commercial fishermen are allowed to throw small explosives called "seal bombs" into the water to scare sea lions away from their catch. However, some research suggests that sea lions learn to listen for seal bombs and head toward them--something known as the "dinner bell effect." (Simonis et al 2020)

Harbor Seals gather at nursery areas to give birth

While adult sea lions spend spring and early summer breeding in Southern California, harbor seals (Phoca vitulina), give birth right here on the Central Coast. In late March or April, females gather in warm, secluded coves and sand bars along the Central Coast, where they give birth and nurse their pups.

Note: Female harbor seals living around the Channel Islands of Southern California typically give birth in March, about a month earlier than those on the Central Coast. Farther north, along the Oregon and Washington coast, most harbor seals give birth in May (Baraff and Loughlin 2000).

In the greater Monterey Bay area, female harbor seals and their pups can usually be seen near Point Lobos, Carmel, Pebble Beach, Pacific Grove, Elkhorn Slough, Ano Nuevo, Bean Hollow State Beach, and Pescadero (among other places). Farther north, harbor seals give birth on sheltered beaches around Bolinas Lagoon, Drakes Estero, Double Point, Tomales Point, and Tomales Bay. At the largest birthing area, near Point Reyes, as many as 4,000 adult harbor seals will gather and give birth to up to 1,000 pups in a typical year (NCCOS 2003).

When on land, harbor seals are often skittish. Nursing females will panic and desert their babies if humans come too close. However, in a few areas, such as Pacific Grove, you can get close enough to watch the mothers and babies without disturbing them. In any case, the best way to get a close-up view of the young pups with is to bring a pair of binoculars.

Each female harbor seal gives birth to just a single pup, usually on land, but sometimes in shallow water. At birth the pups are 18 to 24 inches long and weigh about 25 to 30 pounds (Trumble 1995). Because the pups are relatively large compared to their mothers, harbor seal births are sometimes long and difficult. If the pup is born in the water, the mother may have to help the pup hold its head above water for the first half hour or so, but after that, the young seal is usually able to swim and crawl more or less on its own. Fortunately, the pups are born with good eyesight and a thick coat of insulating fur.

The female harbor seals remain in close physical contact with their newborn pups for about four to six weeks, nursing, sleeping, and swimming together (Trumble 1995). Nursing female harbor seals typically spend the daylight hours on the beach with their pups. At night they may leave to hunt shallow-water fishes such as sculpin or sand dabs, which live just offshore of their nursery areas (Trumble 1995).

The young harbor seals grow very rapidly, nursing about once an hour and gaining more than a pound a day (the female's milk contains nearly 40% fat) (Tweit 1999). As their babies grow larger and demand more milk, female harbor seals must leave their babies on shore more often (even in the daytime) to find food. During this time, the baby harbor seals usually sleep happily. Every now and then, however, one will raise its head, look out to sea, and call to its mother, with a plaintive "ahhh" or "mahh." (Personal observation)

When human beings see a harbor seal pup without a mother nearby, they may think the pup has been abandoned. Some humans even try to approach such baby seals or "rescue" them. Unfortunately, such well-meaning efforts can have tragic results because the female harbor seal will not come ashore as long as a human is near her pup. In extreme cases, this can result in the pup's starving to death (Tweit 1999).

Young elephant seals leave their nurseries

Just as the harbor-seal nurseries are getting crowded in April, things are calming down at the elephant-seal nurseries. Without the huge, noisy males (who left the Central Coast in February), these beaches at Point Reyes, Ano Nuevo, and on the southern Big Sur coast seem almost quiet and peaceful. Instead of hosting gladiator battles, the beaches are covered with two- to three-month old "weaner" elephant seals lolling on the sand, fat and happy.

Note: Young elephant seal "weaners" are very similar in size and shape to adult harbor seals. Some even share the same beaches. Here are some ways to tell them apart: 1) Harbor seals tend to stay near the high-tide line, while young elephant seals often venture to the upper parts of a beach. 2) Sun-bathing elephant seals, with their thicker blubber, heat up more quickly than do harbor seals, so the elephant seals frequently cool off by flinging sand on their bodies using their flippers.

During late March or early April, these "weaners" teach themselves to swim. At first hesitant and awkward in the water, the young elephant seals spend increasing amounts of time in the shallow water near shore.

During the last weeks of April, these young elephant seals will swim, one by one, out to sea. There they will seek their fortune... or at least their dinner, which typically consists of squid and deep-water fish (Le Boeuf and Croker 2005).

Some weaners will travel hundreds of miles offshore, across the open Pacific. Others will head north along the coast as far north as Alaska (Le Boeuf 2004). But among the hundreds of young elephant seals making their way in the world, only about half will survive their first few months at sea (Le Boeuf 2004). Those that do survive will return to shore again in September.

One key factor that determines whether a young elephant seal will survive its first months at sea is the amount of milk it is able to obtain from its mother before it heads offshore (Le Boeuf and Croker 2005). During extended (multi-year) periods when the water along the Central Coast is relatively warm, fewer elephant seal pups survive, presumably because their mothers aren't able to find as much food to eat before coming ashore to give birth (Le Boeuf and Croker 2005). This suggests that such long-term ocean cycles affect even the cold, dark waters of the deep sea, hundreds of miles offshore, where adult elephant seals hunt squids and fish.

As the weaners leave the beaches of Ano Nuevo, the first adult female elephant seals return to the beach, where they will spend the next month molting (Ternullo 2000). This process is described in greater detail in the page on marine mammals in May.