With plenty of sunshine, nearly continuous supplies of nutrients from upwelling, diatoms often reach peak numbers during May and grow at their maximum rate of the year.
Note: Some research suggests that the year's densest populations of diatoms may not occur until upwelling and its associated currents begin to be die down, typically in June.
is one of the main diatoms that bloom in spring along the Central Coast (Source: Plankton Net)
These blooms typically consist of large, chain-forming diatoms such as Chaetoceros debilis
, which are adapted to the repeated cycles of strong upwelling and relaxation that occur between April and June. In May, however, at the height of the upwelling season, this diatom may share the stage with a northern species of diatom known variously as Chaetoceros venheurckii
or Chaetoceros constructus
The timing of the yearly peak in diatoms varies greatly depending on the distance from shore. During May, the biggest diatom blooms are typically found along exposed coastal areas, within about a dozen miles of shore. In these areas, northwest winds, upwelling, and chlorophyll concentrations also peak during late May or June.
In sheltered coastal areas such as the inner Gulf of the Farallons and the northeast corner of Monterey Bay, diatoms often reach peak densities earlier in the year, during March or April.
Farther offshore and north of Point Reyes, northwest winds, upwelling events, and diatom populations may not peak until late June. By this time, diatom populations near shore may have already begun to decline.
Note: The date of peak diatom blooms tends to be later the farther north you go. Off the coast of Oregon, the most dense blooms sometimes do not occur until July or August.
As diatom blooms shift from nearshore to offshore waters and from south to north, they are followed by schools of grazing animals, such as krill and sardines. The seasonal shift in diatoms away from shore may also provide food for some drifting larvae. Both larvae and diatoms are likely to be carried away from the coast by upwelling currents in May.
By May, the early spring crop of krill have developed from tiny, diatom-eating larvae to juveniles about half an inch long.
As the juvenile krill grow larger, they provide a more concentrated source of food and are easier for larger animals to catch. The net result is the krill become an increasingly important source of food for seabirds and fish at this time of year.
Krill will become even more important as a food source later in summer and fall, when most of the population will have developed into adults. Dense swarms of these adult krill (over an inch long) allow even huge animals such as humpback and blue whales to feed efficiently.
The juvenile krill are fairly strong swimmers, but they may still be carried far offshore by upwelling currents. Perhaps to avoid this fate, as well as to avoid visual predators, the juveniles of some species of krill swim to deep water in the daytime, then return to the surface at night to feed.
As diatoms bloom and summer-like weather starts to arrive on the Central Coast in May, so do vast schools of small migrating fishes. These fishes, including Pacific hake, Pacific sardine, and Northern Anchovy, are followed by hoards of hungry predators such as dolphins, porpoises, sea lions, and sea birds. They are also preyed upon by humans, and account for a large proportion of all the commercial fish caught in Central Coast waters.
Hake, sardines, and anchovies all spawn (release eggs) during spring or early summer in the warm coastal waters south of Point Conception. Within this relatively protected area, which extends from Santa Barbara to northern Baja, a slow counterclockwise gyre known as the Southern California Eddy helps retain warm water, algal blooms, zooplankton, and fish eggs relatively close to shore. This region also harbors an abundance of tiny swimming algae known as dinoflagellates, which provide food for fish larvae.
Note: The Southern California bight is like a giant version of the "upwelling shadow" areas found in northeastern Monterey Bay and in the inner Gulf of the Farallones.
As the young schooling fishes develop from larvae to juveniles, they begin to eat copepods and larger diatoms. To find this food, they must migrate northward along the coast, moving from one upwelling center to another as the diatom blooms themselves progress up the coast.
These waves of migrating juvenile and adult fish follow the seasonal peak in upwelling and diatom blooms, which occurs later the farther north you go. The net result is that older, larger fish are often found farther north (and later in summer).
This seasonal parade of animals from south to north includes not only hake, anchovies, and sardines, but also by their prey (krill) and their predators (sea lions, pelicans, some dolphins, and humpback whales). In many cases, the predators must not only find prey that are in dense enough patches, but also in which the individual animals are large enough to provide an efficient food source.
Both predators and prey tend to congregate along certain "feeding stops" along the coast. Many of these "oceanic truck stops" are in upwelling shadow areas such as northeastern Monterey Bay, as well as areas in the lee (south) of Point Reyes, Point Arena, and Cape Blanco, Oregon. Although some schooling fish and mammals finish their migrations in prime feeding areas such as Monterey Bay and the Gulf of the Farralones, others end up as far north as British Columbia.
Adult hake (about 16 inches long)
, otherwise known as Pacific whiting (Merlucus productus
), is a schooling fish that, because it is so abundant, provides vital food for ocean predators such as sea lions along the California Coast. Hake also provides food (if you can call it artificial crab "food") for humans as well. In fact, hake is currently the largest commercial "ground fish" on the West Coast (more on this later).
Each spring, hake migrate from southern California to north of Vancouver Island, feeding and growing as they go. Juveniles typically reach the Mendocino coast by March, adults are found off the Columbia River by April, and large adults (up to 20 inches long) appear off Vancouver Island in May.
By the end of May, adult hake are spread out along the entire West Coast, while juveniles (1-3 years old) often remain offshore of Central or Southern California. When winter comes, most of the adults will migrate back south of Point Conception. In early spring the adults will spawn in Southern California, starting the yearly cycle over again.
Like anchovies and sardines, hake form dense schools. Young hake are typically just a few inches long and look similar to young sardines and anchovies,. However, unlike anchovies or sardines, adult hake grow to over 20 inches long.
Another difference is that hake schools are often found dozens to hundreds of miles offshore and 500 to 1,000 feet below the surface. This is in contrast to schools of anchovies and (to a lesser extent) sardines, which are typically found within a few hundred feet of the surface and within a dozen miles of the coast.
Schools of hake often spread out horizontally at a particular depth, hunting smaller marine animals such as copepods and krill that also congregate at that depth. Both the hake and their prey migrate up toward the surface each night to feed. Hake are a favorite food of seals and sea lions, which sometimes forage offshore at night, when the hake are closest to the surface.
Although hake are one of the most profitable fisheries on the west coast, few people have heard of them. There are several reasons for this. First, most fishing for hake takes place 10 to 100 miles from shore, well out of sight of land. Second, most hake fishing is done by large factory ships that don't come to shore for months at a time, and even then deliver their catch only in large, commercial harbors. Third, you won't see hake in your grocery store because most of the catch is processed at sea--ground up to make fish meal and "krab" meat (surimi).
From April through August or September, factory ships follow the hake as the migrate up the coast from Northern California or Oregon to British Columbia. They are not allowed to catch the juvenile fish that frequent Central and Southern California waters, and which are less profitable.
Before the hake fishery was regulated, factory ships caught as many fish as did all the seals and sea lions on the entire coast. In fact, so many hake were caught near the Farallon Islands that sea lions in this area couldn't get enough to eat and were forced to hunt elsewhere during late summer and fall.
After the fishery closed in this area, more sea lions were seen foraging near the islands, and more adults stayed over the summer instead of migrating south. Even now, the giant ships typically catch more than 100,000 tons of hake--the entire allowable yearly quota--in just the first two to three weeks of the season.
School of medium-sized (6-inch-long) sardines in Monterey Bay.
Beginning in May or June and continuing through August or September, waves of young sardines migrate northward from their spawning grounds to feeding areas along Central and Northern California. Some continue as far north as British Columbia or even Southeast Alaska (during years when the water is particularly warm). However, by the following spring the adult sardines most head back south to warmer water in order to spawn.
Sardines don't usually spawn along the Central Coast, but prefer the warm waters offshore of Southern California and northern Baja. There they spawn from about April to August. During years with little upwelling (when water temperatures are warmer) sardines may spawn farther north, and spawn over a longer time period.
Sardines usually spawn out in the open ocean, within 100 to 200 feet of the sea surface. Like hake and anchovies, sardines are "broadcast spawners," sending millions of eggs and sperm into the water simultaneously. Those eggs that are fertilized and survive develop into larvae that live at or near the sea surface, feeding on young copepods and other tiny, drifting animals.
Pacific Sardines (Sardinops sagax) are often confused with anchovies because young sardines and anchovies are both small, finger-sized fish. However, sardines grow larger (over a foot long). Although they are larger, sardines actually feed lower on the food chain than anchovies, since adult sardines eat mostly diatoms and small zooplankton.
Another difference between sardines and anchovies is that sardines seem to prefer warm water, while anchovies are more common in cold water. In fact, one recent study showed that anchovies and sardines alternate in abundance over 25-year cycles of warmer or colder water in the northern Pacific Ocean. Such long-term cycles, compounded by overfishing, may account for the crash of the California's sardine fishery in the 1940s and 1950s.
As described in March, anchovies living off the Southern and Central California coast mostly spawn from February to April. By May, those that spawned in Southern California are migrating northward, and have reached the Central Coast. Although young anchovies eat mostly phytoplankton, adult anchovies are carnivorous, feeding on zooplankton such as copepods and fish larvae.
Note: Like many other marine animals, anchovies living in northern waters spawn later than those in southern waters. For example, schools of anchovies living in San Francisco Bay typically spawn in May or June. Along the Oregon and Washington coast, anchovies spawn from June to August. These northern populations often spawn within or just offshore of major estuaries, which provide warmer water, abundant food, and some protection for larval and juvenile fish.
Despite their somewhat sinister sounding Latin name (Engraulis mordax) northern anchovies are small fish, rarely growing more than about six or seven inches long, and at vegetarians to boot. Anchovies often swim in large, dense schools within about 150 feet of the sea surface and sometimes very close to shore. This makes them a prime target for commercial fishers (who save on fuel for their boats), nearshore seabirds, and sea lions (who don't have to swim very far or dive very deep to get dinner).
Anchovies live for up to four years, with older individuals appearing farther from shore and farther north along the coast. Large schools are often found in the cold water associated with upwelling areas. This is not surprising because the anchovies feed on diatoms that bloom in response to the nutrients brought to the surface by upwelling events.
During years when upwelling is strong, large diatom blooms provide plenty of food for anchovies, and a much larger proportion of juvenile anchovies survive to adulthood and provide food for other animals. Conversely, during years when upwelling is weak, the seasonal "crop" of anchovies may be small, and animals such as seabirds, which depend on anchovies for food, may go hungry and may be unable to feed their own young.
Market squid spawning in Monterey Bay. Note masses of white eggs on the seafloor.
(Source: Roger Hanlon / SIMoN NOAA)
Starting in April or May of each year, millions of market squid gather in the sandy shallows of Monterey Bay, about a mile from shore, to mate and lay eggs. Spawning is most intense in May or June, but may continue through July or July. A second seasonal spawning event may also take place from November through January, providing an off-season bounty for seabirds and marine mammals that winter along the central coast.
Note: In a typical north-south progression, market squid in Southern California begin spawning in March, a month or two earlier than on those on the Central Coast. Off the coast of Washington, market squid spawn even later, from July through September.
Starting in April and May, millions of market squid gather to spawn in a few specific parts of Monterey Bay. These spawning areas are close to shore--typically less than a mile from the coast--where the water is about 60 to 180 feet deep.
One of the most important squid-spawning areas in Monterey Bay is a wide, flat, sandy area directly offshore of Monterey's Fisherman's Wharf. This area is a convenient fishing spot for the Monterey fishing fleet and a convenient feeding spot for the large packs of sea lions that hang out on Monterey Breakwater in May.
Some researchers suggest that the largest spawning events occur once a month, around the time of the new moon. SCUBA divers who have witnessed it say that the spawning of market squid is one of the most amazing things they have ever seen. Thousands of squid jet through the water in a frenzy, the males flashing red to attract the females, then passing sperm to the females using specialized tentacles.
Each female squid lays from 4,000 to 9,000 translucent, white, sausage-shaped eggs directly on the sandy seafloor. Sometimes the female squid lays her eggs near a seafloor feature such as a stick or small rock. Often she will lay eggs in an area where other squid have already laid their eggs. In favored parts of the bay, this can result in acres of seafloor being covered with anemone-like clusters of squid eggs. One observer has described the sight as looking like “a field of swaying pom poms."
Most or all of the adult market squid will die shortly after mating. These dead and dying squid provide easy pickings for gulls, shearwaters, sea lions, harbor seals. and even blue sharks. Squid carcasses that settle to the seafloor also provide a bounty for rockfish, sun stars, bat stars, sea urchins, and Dungeness crabs.
Although many animals eat dead and dying market squid, very few eat squid eggs (bat stars are one of the few exceptions). Perhaps the predators are so sated from gorging on adult squid that they don't have any need or desire to eat the squids' eggs. The newly laid market squid eggs will hatch after three to twelve weeks (depending on the water temperature), releasing tiny larval squid into the ocean currents. More on this in June.
Market squid - background info
If anchovies, sardines, and hake are the "bread and butter" of millions of birds and marine mammals, then market squid (Doryteuthis opalescens) may be the "peanut butter and jelly." During their spawning season, not only do market squid gather in huge numbers close to shore, but after spawning they are so weak that they can hardly swim, and can be picked off by any animal capable of swimming 50 feet below the surface.
When alive, market squid are graceful, transparent creatures, typically between six to ten inches long. They spend most of their lives in scattered schools, cruising over the continental shelf and deeper waters just offshore. They live fast and die young, reaching adulthood in only four to six months. Adult market squid gather in immense schools in a few sheltered corners of Monterey Bay and elsewhere along the coast to spawn and die. A lucky few may survive spawning and live to the ripe old age of a year or two.
Market squid live all along the West Coast, from Baja California to Alaska, usually within 100 miles of shore. Those caught in Monterey Bay tend to be larger than those caught in Southern California. However, scientists still don't know if market squid migrate northward as they get older, as do hake and sardines.
Market squid are adaptable creatures, using different hunting strategies for different prey along different parts of the coast. In offshore waters, market squid eat small fish, calanoid copepods, and various shrimp-like creatures of the midwater.
While in Monterey Bay, market squid feed heavily on krill (which in May are just beginning to reach adult size). When spawning, however, market squid spend more time in shallow water, close to the seafloor. At this point, they may switch to eating crab larvae, worms, snails, and sometimes others of their own kind.
Primarily visual feeders, market squid hunt mostly within a few hours of noon, when the sunlight is brightest. Even cloudy days seem to reduce their hunting efficiency. At night they migrate seaward, off the continental shelf, to depths of over 1,500 feet. This is a "reverse commute" compared with the majority of deep-sea animals, such as hake, which spend the day in deep water and rise toward the surface at night to feed.
In addition to providing food for humans, spawning market squid are one of the most reliable and easily caught sources of food for many animals on the Central Coast, especially in key spawning areas such as Monterey Bay. At least 19 species of sea birds, 13 species of fishes, and seven species of marine mammals have been observed eating market squid within the bay. These include such key predators (and common summer visitors) as sooty shearwaters, California sea lions, harbor seals, dolphins, porpoises, salmon, mackerel, and bonito.
During the spring and summer months, you can often see the bright lights of squid boats floating offshore of Monterey Harbor. Although market squid were first caught by Chinese immigrants in the 1860s, there was relatively little demand for these animals until the 1980s.
Since the late 1990s, the yearly catch of market squid has been grown until it is the largest, most lucrative fishery on the California coast, (eclipsing even sardines, anchovies, and hake). During a typical year, more than 200 million pounds of market squid, worth more than 25 million dollars, are caught off Southern and Central California.
Most fishing for market squid occurs when the squid gather to spawn. In Central California the season typically begins in April or May and continues sporadically until the first winter storms arrive in November. After November, the schools of market squid schools along the Central Coast are too small and spread out to make fishing worthwhile. For this reason, many of the squid boats head down to Southern California in winter. As with some rockfish and intertidal animals, market squid in Southern California have two spawning seasons, in winter and in summer.
Squid fishing boats usually work at night, while the squid are spawning. In Monterey Bay, the boats typically fish the deeper parts of the spawning grounds, where the water is about 150 to 200 feet deep. A trawler with a purse seine (a large net with a draw-string at the top and bottom) is typically accompanied by one or more "light boats," each carrying high intensity lights drawing up to 30,000 watts. The lights attract the squid to the surface in tight schools.
Large nets are spread out around the schools (and the light boats). First the draw string at the bottom of the net is closed. Then a second draw string at the surface is hauled in, compressing the squid in the net. Sometimes other animals, such as sea lions or sharks have been feeding on the squid, and are trapped in the net, but they are generally released if possible. Finally the net is brought on board, along with ten to twenty tons of wriggling, inking squid. Most are shipped to markets in Asia.
END SIDEBAR on Market Squid fishery
The expanses of cold, dark, muddy seafloor of the continental shelf seem far removed from bright, teeming surface waters, yet animals on the deep seafloor rely on food from the spring bloom just as much as do the anchovies and animals at the sea surface. The main difference is that, by the time spring-bloom diatoms reach the seafloor, they have been eaten and excreted repeatedly, and have lost much of their original nutritive value.
By May, sinking debris from the spring blooms have awakened new life on the deep sea floor. In response, some rockfish are just giving birth. The larvae of other deep-seafloor rockfish, crabs, and octopus, which have been drifting around since January or February, are just beginning to mature and settle down to the seafloor just seaward of the kelp beds. These young animals, along with spawning market squid, attracts seafloor predators such as flatfish, which spend the winter in deeper water but migrate toward shore in spring.
In May, several types of deep-water rockfish spawn, releasing microscopic larvae that float up toward the sea surface. These "spring-spawning rockfish" include Aurora rockfish (Sebastes aurora), stripetail rockfish, and cowcod, all of which tend to live in relatively deep water, near the edge of the continental shelf
Note: Aurora rockfish spawn from March through May offshore of northern and Central California, but they spawn a month later, in June, off British Columbia.
Some studies suggest that these spring-spawning rockfish release larvae when water temperatures drop rapidly during upwelling events. This strategy increases the chances that the larvae will disperse widely, as upwelling currents carry them tens to hundreds of miles along the coast (usually from north to south) or sweep them far offshore.
These larvae will they spend the next two to four months near the sea surface, first drifting as planktonic larvae and then swimming, as juveniles. These juvenile rockfish provide the single most important sources of food for seabirds, such as murres, which raise their young during the summer months. Between July and September, most of these juveniles will sink back down to the seafloor, where they will live out their adult lives.
Young vermillion rockfish hiding out in the kelp beds. Over the next year, as this fish gets older, it will lose its blotchy color, becoming solid red, and will move into deep water.
(Source: Steve Lonhart / SIMoN NOAA )
rockfish are releasing their young in April and May, the juveniles of winter-spawning rockfish
(which were born in January or February) are beginning to settle down to the seafloor. These “winter spawning” rockfish include: vermilion rockfish
, china rockfish
, blackgill rockfish
, yellowtail rockfish
, widow rockfish
, and bank rockfish
Some of these young rockfish settle onto deep reefs, such as the Cordell Banks off Point Reyes. Most, however, settle onto the seafloor at depths of 100 feet or less (often just offshore of the kelp beds).
Note: Marine biologists aren't sure how these young winter-spawning rockfish are able to return to shore in April and May, since strong upwelling currents at this time of year often flow away from shore. One possibility is that the juvenile rockfish sink down several hundred feet below the surface. This may put them below the strongest surface currents generated by upwelling, and may even allow them to "hitch a ride" on deep currents flowing toward shore.
Once they reach the seafloor, just beyond the kelp beds, the newly-settled young rockfish begin hunting small crustaceans such as bottom-dwelling copepods, shrimp, and young crabs. They may also eat other, smaller rockfish that settle later in the spring. They also congregate in fairly large schools, which will eventually disperse as the young are eaten or migrate away from shore.
Over the next six to twelve months, these young rockfish will grow larger and migrate away from their coastal nursery areas toward deeper water. Thus, larger, older rockfish are often found near the edge of the continental shelf or along the edges of submarine canyons, in water that is 300 to 400 feet deep. Many of these adult rockfish swim up above the seafloor to hunt swarms of krill, which also congregate in these "shelf break" areas.
Larvae of Dungeness crabs follow a similar reproduction pattern as do winter-spawning rockfish, giving up their drifting lifestyle and settling down to the seafloor from April through June. Like rockfish, the young Dungeness crabs initially settle out on the seafloor close to shore, then move into deeper water as they get older.
Note: As with winter-spawning rockfish, researchers aren't sure how the young Dungeness crabs (which are very weak swimmers) make their way toward shore in the face of upwelling currents. Sinking out of the surface waters may help them catch a ride on deeper currents flowing toward shore.
Newly settled juvenile Dungeness crabs eat mostly tiny bottom-dwelling animals such as worms, shrimp, and other crustaceans (amphipods and isopods). These mud dwellers may be particularly numerous in spring, when they feed on the seasonal pulses of debris ("marine snow") that sink down from the surface following spring blooms.
Young Dungeness crab also have an inordinate fondness for dining on others of their own kind. As one fisheries publication put it, "Cannibalism is prevalent among all age groups.”
If they survive their first year, the young Dungeness crabs will have grown to about one inch across. By the time they reach adulthood, the crabs will be omnivores, eating worms, mollusks, dead fish, drift algae, and other jetsam.
In April, schools of king salmon gathered just outside of the Golden Gate to feed on the larvae of krill and of Dungeness crabs. By May, Dungeness crab larvae are becoming scarce in the water column, so the salmon switch to eating a new type of prey--juvenile rockfish.
By May the larvae of winter-spawning rockfish have turned into three-inch-long juvenile fish, and are almost ready to settle down to the seafloor. They provide an important source of food, not only for spawning salmon, but also for the immense colonies of nesting seabirds at the Farallon Islands, offshore of the Golden Gate.
During years when upwelling is weak or inconsistent, fewer rockfish larvae survive, so juvenile rockfish may be in relatively short supply. During these years, king salmon must stick to eating krill. However, this means that they may not be able to store up enough food reserves to complete their fall spawning run.
As the winter storms end in April and May, several seafloor predators begin to move from their winter habitats in deep water back toward shallower water (often just outside the kelp beds). These include giant octopus and several types of flatfish.
Like rockfish and Dungeness crabs, the young of another seafloor predator, the giant Pacific octopus, also begin settling down to the seafloor in April May. These young octopus hatched in February or March, and have been drifting around with the currents for a month or two.
By the time they settle down to the seafloor, the young octopus are about two inches long and weigh less than 1/4 ounce. Like juvenile rockfish and Dungeness crabs, young giant octopus initially settle down to the seafloor just offshore of kelp beds and other rocky areas, then move offshore as they grow older.
Like young rockfish and crabs, the newly settled octopus eat small shrimp, crabs, and other bottom dwellers. The young octopus eat so much that by the end of their first year they will have grown to several feet across and weigh as much as two pounds. Only a few years later, when they are full grown, their tentacles may stretch to 30 feet across and they may weigh up to 600 pounds (though 100 pounds is more typical).
Watching a giant octopus hunt is a fascinating experience. The octopus emerges from its rocky den at twilight, and flows across the seafloor with a cat-like stealth and sense of purpose. Changing color to match the surrounding the seafloor, the octopus hunts partly by sight, often hiding behind rocks and other seafloor objects. Feeling and tasting the water with its tentacles, the octopus seeks out crabs, shrimp, clams, scallops, abalone, and (inevitably) smaller octopus.
When it finds a possible prey, the octopus sneaks up close, then pounces, tentacles extended, to envelop its prey like a deadly umbrella. After trapping its prey beneath its tentacles, the octopus bites the animal with its parrot-like beak, which injects a paralyzing poison. For slower moving but better protected animals, they octopus can use its beak to drill through shells and inject enzymes to dissolve the tissue inside.
Once its prey is immobilized, the octopus carries the hapless animal back to its den to finish its meal. After digesting all of the soft parts of the animal, the octopus fastidiously deposits the hard parts on the seafloor just outside its den (a practice that brings a different, and more sinister meaning to the term "octopus' garden).
Though a fierce predator in its own right, a giant octopus falls prey to many animals, including sea otters, sharks, larger fish, seals, and sea lions. Sometimes the octopus can get away with just a lost tentacle. Since these tentacles grow back fairly rapidly, they provide a "renewable resource" for those deep-sea predators large enough to tackle an adult giant octopus.
If it survives for three to five years, a giant octopus will have its one and only chance to mate. After mating, the males die within a matter of days. The females die six months later, after their eggs hatch.
Central Coast fishermen know that some time in late spring the halibut will start moving into sandy areas just off the shoreline. California halibut (Paralichthys californicus) are active predators and pursue animals such as anchovies and market squid--fast-moving prey that become common in nearshore waters by May.
During spring and summer, halibut often frequent the sand-filled rock channels between kelp beds. With the rising tide, the halibut often move shoreward in these channels to hunt near shore. Halibut seem to be most active and feed closer to shore at full moon and new moon, perhaps because this is when market squid and other animals spawn.
Another type of flatfish, the English sole (Parophrys vetulus), mates and spawns on the outer continental shelf and slope during winter, then moves toward shore in spring. In early spring the sole congregate in the "mud belt" that covers the middle of the continental shelf off Monterey Bay, in water about 150 to 200 feet deep. As the spring progresses, they move ever closer to shore. This seasonal migration puts the sole within diving range of predators such as sea lions and harbor seals (who need the extra nutrition going into the spring pupping season).
As these adult halibut and sole are moving inshore from deep water in May, their year-old young are leaving coastal estuaries such as Elkhorn Slough. The young flatfish have spent the last few months in these protected waters gorging themselves on young fish that use estuaries as nurseries.
Once they reach the open ocean, the young flatfish begin to cruise the shallow seafloor hunting bottom-dwelling animals such as worms, shrimp, and crabs. They, in turn, provide relatively small, easily available prey for harbor seals and young sea lions (who also feed on readily available market squid and anchovies).