I just finished my research project on Pismo clams and thought since a community member helped me with it I should share the information. It's a long read, but if you are interested in the history of Pismo clams and the challenges they face you should find this interesting. I will add the pictures in as I upload them.
THE PISMO CLAM:
AN IN DEPTH LOOK INTO THE PAST AND PRESENT
San Jose State University
Environmental Studies 117
April 3, 2009
Last edited by spartafish; 03-12-2015 at 11:17 PM.
Reason: privacy concerns
Having experienced the beaches of California long before man traversed the Bering Strait, Pismo clams (Tivela stultorum) have proven to be more resilient than any population of humans to ever inhabit North America. However, since Pismo clams are one of the largest and meatiest clams found in California, inhabitants did not hesitate to utilize Pismo clams. Each group of human inhabitants that has called the California coast home has found a use for these clams. Pismo clams stand alone as a critical part of its natural trophic network while still being important to human consumption. Especially in the Monterey Bay area, Pismo clams are critical to apex, or near apex predators. Starting with predators found in the clam’s natural habitats and moving to human consumption, Pismo clams have proven to be a critical part of California’s coastal habitat.
There is little record of use, consumption and population of Pismo clams prior to their exploitation by the hands of Western settlers. Although there is little record of the use of Pismo clams, there is little doubt that California Native American populations incorporated these large clams into their daily lives. As settlers flooded the California coast, however, Pismo clams were quick to be introduced to the consumptive ways of non-indigenous Americans. Only after decades of overexploitation has the California Department of Fish and Game placed limits on the consumption of these slow-to-reproduce bivalves.
Populations of clams still exist throughout California. Some clam beds are dense with thousands of clams while others have proven to never have recovered from years of abuse. It is commonly believed and understandably assumed that it is because of human exploitation these mollusks are yet to reach their theorized historical populations. Despite the imbalance humans have caused on the Pismo clam’s trophic system, the fault does not solely fall into the hands of humans. Anything from rare, intense weather systems to predation have helped to suppress the revitalization of Pismo clams. In some areas these clams continue to thrive; they withstand recreational clam diggers, El Niño strength storms and predation. Why is it that clam populations on some beaches have nearly disappeared while populations at other beaches continue to sustain themselves? If this question can be answered, perhaps beaches with struggling populations can have management practices modeled after those beaches that are able to sustain thriving populations of Pismo clams.
PISMO CLAM BIOLGY
The Pismo clam is in the phylum mollusca. Like other clams, Pismo clams are bivalves. They consist of two symmetrical shells attached by a ligament at the hinge (Lampson 2007). With indeterminate growth patterns, the Pismo clam can grow upwards of seven inches in diameter. Because Pismo clams are slow growing, if they get up to six inches it is done in less than fifty years, which is the extent of the Pismo clam’s longevity.
As Pismo clams are stimulated to spawn by warm water, spawning may occur several times a year. Also, because different parts of the coast experience changing water temperatures at different times, clams in different geographic regions spawn at different times. More southern populations begin spawning in April while northern populations do not begin their spawn until September. Male clams stimulate female clams into spawning by releasing their gametes into the water. The female clams sense this and in turn release their eggs, an average of fifteen trillion per female clam (Shaw 1989). Generally, there are an equal number of female clams to male clams (Pattison 2001). Although rare, hermaphrodites do exist; in a study, three hermaphrodites were found of 289 clams examined (Shaw 1989).
When the egg is fertilized and the clam is in its initial phases of development, studies have found that the clams are hermaphrodites (Shaw 1989). During the larval stages of life the young Pismo clams have a high weight/volume ratio; therefore, they spend the majority of their larval stages in the bottom water column. Because of this, they are rarely redistributed to beaches other than the ones in which they were spawned (Lampson 2009). Being spawned in the summer, these new clams become sexually mature after their first winter. At this time they are only six tenths of an inch in diameter. During this time the clam develops a foot and attaches itself to the sand (Shaw 1989).
Studies have found that the Pismo clam’s “greatest increase in shell growth occurs in the spring, summer and fall seasons” (Shaw 1989, 5). Pismo clams grow slower as they grow older (Lampson 2007). In the first four years of a clam’s life, its average growth is a little less than eight tenths of an inch per year. At age ten, clams grow on an average of two tenths of an inch. Also contributing to growth rates is the location; the further north the clam lives the slower it grows (Fig. 1). Synonymous to the fact that clams grow faster during the warm water months, if a clam were to live where the water is comparatively warmer throughout the year then it make sense that the clam would grow faster and more often.
As in dendrochronology, Pismo clams can be aged by counting the rings on their shells. During winter months, when the clam is subject to the most amount of tidal disturbance rings form indicating the change in season. At seven and three-quarters of an inch, the largest clam ever found was dug up at Pismo Beach, a relatively cold water beach. The oldest clam, however, was not nearly as large. A fifty-three-year-old clam was unearthed at Zuma Beach, in southern California; this clam was a mere five and one-quarter inches across (Shaw 1989).
PISMO CLAM HABITAT
Like most organisms, Pismo clams require a special environment to survive and reproduce. Ranging from the Monterey Bay to the southern tip of Baja California, Pismo clams can be found on hundreds of miles of beaches in California (Fig. 2). Clams are only found on broad sandy beaches that are exposed to strong wave action. Beaches like Pismo Beach and Broad Beach are ideal habitats for Pismo clams (Fig. 3). Beyond broad beaches, however, Pismo clams can also be found at the openings of bays and estuaries (Shaw 1989). Mostly clams are found in the intertidal zone, but they have been found as deep as eighty feet. Usually buried between two and six inches of sand, Pismo clams use their foot to loosen the surrounding sand so they can move through it (Lampson 2007).
PREHISTORIC PISMO CLAMS
These impressive clams existed long before humans came into contact with them. Although it is impossible to gather data regarding prehistoric populations of Pismo clams, their fossil remains have been used in studies to help understand California’s changing coastal landscape. Pismo clams have been found in archeological sites dating back to the beginning of the Holocene era 10,000 years ago. The oldest Pismo clam shell ever found was dated to be more than 25,000 years old (Fitch 1961). Older clam populations have been carbon dated to help determine coastal development in California thousands of years ago. A study on the effect El Niño-Southern Oscillation had on the creation and destruction of beaches thousands of years ago may help understand why substantial clam populations exist where they do. Found near points and bays that had been sheltered from the battering El Niño wave action, Pismo clams have helped understand California’s coastal geographic history (Masters 2005).
Even though there is little information on the population of Pismo clams prior to human existence in California, mildly related studies have provided some useful information. Although numbers are not known or represented, it is known where clams representing the early Holocene era can be found. Also, by knowing the geographical location of these ancient populations, the geographic makeup of these places is also known, therefore, helping determine ideal clam habitat. The most ancient of populations were found in the Morro Bay area and relatively younger populations were found in the Santa Maria and Oceanside areas (Masters 2005). Ancient populations of Pismo clams seemed to have preferred shallow bays where the affect of storms is lessened and wide beaches where there is a similar protection.
PISMO CLAMS AND NATIVE AMERICANS
Not much written record of the use of the Pismo clam by California Native Americans exists. Why exactly, no one definitively knows. It is open to debate as to why clam gathering is rarely mentioned in Spanish writings (Landberg 1965). The common name does, however, come from the Chumash language. Derived from the Chumash word “Pismu,” meaning tar, Pismo clams were named thusly due to the naturally occurring tar deposits which occur on central and southern California beaches, Pismo Beach particularly (Lampson 2007).
Pismo Clams in Middens
Despite the fact that written record of Native American use is rare to nonexistent, archeological data has proved to be useful in determining the extent of Pismo clam exploitation by California’s numerous coastal tribes. With some radiocarbon dating placing some clams in Native American archeological sites up to 10,000 years ago, most occurred between 200 to 2,000 years ago (Pattison 2001). Without written record it is still apparent that Pismo clams played a substantial role in at least coastal Native American dietary lifestyles. “Remains of shellfish are abundant in most historic Chumash sites. The species that occur the most frequently are abalones and many of the larger southern California bivalves such as Pismo clams” (Landberg 1965, 72).
Although it is clear that Native American populations often consumed Pismo clams, some contend that they were not all that important to their sustenance. It is understandable that mollusks, clams in particular, were a mainstay in coastal Native American diets considering the content of the middens; however, when taken into consideration what else was available for food it is easy to be led to believe that other organisms played a much larger role (Moratto 1984). In terms of the biomass available consumption of Pismo clams did not provide a significant amount of food. Mollusks, which have a meat to shell ratio of one to one pale in comparison to large, edible fish. These fish, which range from leopard sharks to white sea bass, provided a meat to bone ratio of one to one-thousand. “In other words, the remains of a single ten kilogram fish might stand for as much edible meat as thousands of shells” (Moratto 1984, 236).
Whether or not Pismo clams played a large role in Native American diet, they still stand as a culturally important aspect of their existence. The fact that one fish largely provides more edible meat than a clam is not proof enough to say indigenous peoples of thousands of years ago did not share a particular affinity with Pismo clams. These unique clams could have easily represented a delicacy held in high esteem. Because there is no written record of the use of Pismo clams, it is likely that no one will ever know exactly to what extent these clams were used and for what purposes.
Beyond the obvious use for sustenance, Native Americans used Pismo clams for more cultural, aesthetically appealing reasons. After the initial consumption of the Pismo clams the shells were next used for a multitude of things. Mostly, the Native Americans used the shells to make ornaments. These ornaments included, but are not limited to, necklaces, bracelets, and ornate gifts. Likely due to their large size, the shells were also used as household aides and for digging and scraping (Frey 1971). Furthermore, for centuries Chumash Indians used the shells to make musical instruments (Anderson 2005).
Last edited by spartafish; 04-07-2009 at 12:43 AM.
A NEW ERA OF PISMO CLAMS
After Native Americans and their legacy disappeared from this land so did their sustainable management practices. Only exploiting resources to the extent of their direct needs, Native Americans were able to ensure a continuing harvest. Native Americans personally ate what they caught or gathered. These sustainable practices provide a stark contrast to practices ushered in by Western civilization.
Going far beyond their needs, Anglo-American settlers proved to be far more concerned with profit and consumption then ensuring prolonged populations for later generations. Going far beyond Pismo clams, the affects Anglo-Americans have inflicted on the clam’s food chain have greatly contributed to the fluctuating populations of these great clams.
Sea Otter Extermination
As the settlement of the California coastline by American migrants occurred, they ushered in a new era of natural resource exploitation never seen before. With large, expansive commercial takes of sea urchins and abalones in the Monterey Bay, the systematic extermination of sea otters quickly began. As a result of commercial fishing fleets trying to protect their catch, Pismo clams were protected, too (Lampson 2009). Sea otters had an incredible affect on Pismo clams; in the Monterey Bay alone sea otters were credited with having preyed on upwards of 700,000 Pismo clams. Others have cited sea otters as eating twenty-four clams in less than two-and-a-half hours (Pattison 2001). With sea otters not preying on the large clam beds the populations of clams exploded (Kalvass 2001). Although the clams had other predators, without sea otters they were able to exponentially increase their population size.
Larger clam populations. With the extermination of the sea otters and the explosion of clams, humans naturally noticed this and were quick to take advantage. Soon, where there had once been no market for Pismo clams, a commercial harvest began. Ploughs, drawn by horses, were used to comb the beaches in order to effectively harvest the clams. Initially, this harvest was used to feed livestock; however, by 1911 humans grew their own taste for Pismo clams. Because the clam fishery became so popular by this time, the California Department of Fish and Game began regulating fishermen’s take. Several years later, in 1916, the consumption grew so large that the Department of Fish and Game was forced into keeping records of commercial harvest of Pismo clams (Lampson 2007).
Dwindling clam population. As recreational and commercial clam diggers continued their reaping of the bounty, the population of Pismo clams began to take a nose dive. In 1947 the Department of Fish and Game closed the commercial harvest of Pismo clams due to their struggling population. In the twenty-nine years records were kept of the commercial harvest it is estimated that 6.25 million clams were harvested, averaging about 100,000 pounds a year and peaking at around 666,000 pounds in 1916 (Table 1). The number of clams harvested can be seen following certain patterns. As the numbers of clams harvested peaked, they slowly but surely crashed (Table 2). By this time the economic importance of Pismo clams ranked as the third most important mollusk in California, only beyond oysters and abalones (Lampson 2007).
Populations began to plummet with such large numbers of harvest. Because of this, and due to early thought of the idea of closing the domestic commercial harvest, commercial importation from Mexico began in 1935. These imports were increasingly important during the World War II era because the United States Coast Guard closed the majority of California’s beaches for security issues. When the import of clams from Mexico stopped in 1947 the Pismo clam market all but disappeared as it coincided with end of commercial harvests in the United States. Before these imports stopped, however, up to 54 million pounds of Pismo clams were shipped annually to California (Shaw 1989).
With a greater understanding of clam populations and exactly how fragile they are, limits on recreational take have been put in place. As mentioned before, the commercial harvest was closed in 1947, but it was not until 1985 that any limits of significance were placed on the take of Pismo clams. In 1911 any one individual could take up to 200 hundred Pismo clams regardless of their size. In 1985, the California Department of Fish and Game placed a ten clam limit on recreational clam diggers. Starting in the next year size limits were also set in place; south of the Monterey-San Luis Obispo County line clams must be larger than four and a half inches; north of the Monterey-San Luis Obispo County line clams must be larger than five inches (Shaw 1989).
Regulations on the take of Pismo clams have seen numerous changes throughout the past century. Some of these regulations stand out more than others. In 1915 the allowable take of Pismo clams was reduced from 200 to fifty. By 1927, that number made its way down to fifteen. Four years later, in 1931 a fishing license was required in order to take Pismo clams (Table 3). The change in these regulations has likely contributed to the reduction in popularity of recreational clam digging. Where beaches once saw hundreds of clam diggers a day, they now see none (Ono 2009).
The implementation of these regulations was too late for some beaches, however. Even with the regulations in place the recreational take of Pismo clams reached staggering numbers. In one weekend alone in 1986, 150,000 diggers were surveyed at Pismo Beach. In this weekend, more than 75,000 pounds of clams were taken from Pismo beach. In a separate survey, over a ten week span, more than four million pounds of Pismo clams were taken in a four mile stretch of beach (Frey 1971). Although there has been clearly an irresponsible take of Pismo clams, today’s biologists hardly blame dwindling populations on recreational clam diggers. Much of the blame has transitioned to sea otters.
Recreational Take Today. Gone are the days of people hording hundreds of clams on one visit to the beach. Where horse drawn plows were, there are now pitchforks (Frey 1971). Instead of plows being dragged through the sand unearthing everything in its path, individual people use pitchforks to search for clams. Pitchforks are inserted into the sand, and when a tine hits something solid, the clam digger probes the sand in the hopes of unearthing a legal sized Pismo clam (Fig. 4).
Some have taken recreational clamming to a new level. Instead of exploiting the intertidal population, that is susceptible to greater amounts of predation, some clam diggers have taken to the water to harvest the clams found in the benthic zone (Lampson 2007). While some divers do free dive, the majority take advantage of available technologies such as SCUBA, or self contained underwater breather apparatus. Being able to stay submerged for extended periods of time allows the diver to thoroughly search a given area for Pismo clams. While clams can be found with their siphons exposed, clams are usually found by SCUBA divers similarly how beach-going clam diggers do so. Instead of using a pitch fork, divers use metal objects they insert in the sand; these are usually a dive knife or an abalone iron (Fig 5). When divers reach their limit, or run out of air, they emerge from the water and haul their catch onto shore (Fig. 6).
Reintroduction of Sea Otters. Pismo clams were able to flourish without the presence of their natural number one predator, the sea otter. Although human take of 200 clams per day may seem extraordinary, the sea otters’ ability to hunt and consume puts that of humans to shame. Needing to consume twenty-five percent of its weight in food per day as a minimum necessity to survive, it is easy to see how sea otters can quickly “denude a local clam bed of everything except for small individuals” (Pattison 2001, 7). As sea otters slowly reintroduced themselves down the coast of central California, it was easy to follow their path of destruction. In 1972 they reintroduced themselves in the Monterey Bay. By the following year they extended their range over one hundred miles to Morro Bay. And by 1979, the sea otter had extended its range to Pismo Beach. Each of these places saw their recreational Pismo clam fisheries all but disappear as the sea otters established themselves as permanent residents (Lampson 2007).
Understanding how sea otters feed is essential in understanding the immense amounts of food they consume. These marine animals have their places which they call home; populations have been established from the northern Monterey Bay area down to the Morro Bay/Pismo Beach area. In these areas sea otters easily suppress the extreme growth of any marine mollusk (Lampson 2009). Pismo clams are not the only mollusk affected by sea otters; abalones and sea urchins have felt the full effect of the sea otter’s immense appetite, but sea otters hold a special affinity for Pismo clams. Where viable populations of large Pismo clams are found, sea otters feed exclusively on Pismo clams (Lea 1986).
The consumption by sea otters extends far beyond their established homes. Every year groups of close to one hundred male sea otters go on feeding soirees that extend hundreds of miles beyond their homes. Like the affect seen on Pismo clam populations as they reestablished themselves along the coast in the 1970s, mass reductions in clam populations can be followed behind the sea otters feeding soirees (Lampson 2009).
HELPING PISMO CLAMS
Attaining a Non-measurable Goal
Several steps have been taken in order to resurrect Pismo clams to their prehistoric populations. The number one problem with doing this, however, is that there is little-to-no knowledge of the extent of prehistoric Pismo clam populations. Sufficient historical data of Pismo clam populations before the sea otter extermination does not exist (Lea 1986). But it is known that as sea otters have expanded more towards their historical range that clam populations have been reduced (Kalvass 2001).
It is difficult to understand past populations of Pismo clams directly, but indirectly one is able to ascertain a fairly good idea of how things may have been. It is known that sea otters did range clear down to Mexico. With this knowledge, and knowledge that sea otters heavily feed on Pismo clams, one can draw conclusions as to where Pismo clams occurred and to what extent. Even with this information, however, it is still impossible to definitively know the extent of clam populations on any given beach at any given time.
Ultimately, it may be impossible to know if today’s existing populations are similar to those of centuries past. Without knowing in what kind of numbers Pismo clams existed prior to human interaction a lot of room is left for debate. The current status of the Pismo clams may, in all actuality, be comparatively similar to that of its ancestral populations; conversely, the current status me be drastically different.
Pismo Clams Helping Themselves
Without the hand that has partly destroyed them, Pismo clams hold the ability to re-establish themselves. As humans have proved to be destructive and relentless, Pismo clams have proven themselves to be nearly as resilient. Pismo clams can re-establish viable populations after just three years of successful recruitment. When spawning occurs from July through November, each female clam releases fifteen million eggs that each have the opportunity to grow to maturity (Fitch 1961). Additionally, unlike other marine mollusk, like scallops, new generations of clams tend to repopulate the beaches in which they were spawned. Unlike scallops, who have the ability to swim and relocate themselves, Pismo clam larvae fall to the sea floor soon after fertilization (Lampson 2009).
Even though Pismo clams show the incredible ability to repopulate any given beach, it is by no means an easy life for young Pismo clams. Animals that reproduce by the millions tend to do so out of necessity; they do this because they have naturally been conditioned to do so because they inherently know that not many of their young will survive. This holds true to Pismo clams, too (Coe 1947). “Historic surveys have shown poor survival rates” (Lampson 2007, 5). In these surveys it had been found that 33,000 clams survived out of 120 trillion eggs released. That means that less than half of one/one thousandth of one percent of spawned eggs actually become mature clams (Lampson 2007). Furthermore, the 33,000 clams who do survive now must survive predation. Beyond sea otters, fish such as corbinas, leopard sharks and bat rays love to make meals of Pismo clams. Large depressions have been found in sand bottoms where bat rays have consumed Pismo clams. These depressions can get as large as six feet across (Lampson 2009). While sea otters dig for the clams, bat rays affix themselves to the sandy bottom and create suction with their wings. When the rays lift from the sand, they bring along with them all the sand and anything that may have been hidden underneath them (Lampson 2007). All in all, even though Pismo clams have the ability to release trillions of eggs, the natural cycle taken against these eggs makes the difference almost negligible.
Humans Helping Clams
Many steps have been taken in order to determine the cause of reduced populations and what can be done to lessen the affect these problems have on the existing Pismo clam populations. Beyond studies and surveys, the California Department of Fish and Game has conducted several experiments in order to re-establish viable clam populations where they are no longer found or not found in the numbers they once were.
Clam Plants. The Department of Fish and Game has planted clams at various beaches throughout the state. The planted clams did not help the population of clams beyond their initial stocking (Lampson 2007). The ultimate problem found with planting clams where wild populations are not able so sustainable seems obvious. If a beach was unable to sustain a healthy population of wild clams, planted, lab-created clams would not be able to survive for the same reasons (Lampson 2007). For example, 10,000 clams were transplanted from Pismo Beach to Huntington State Beach. The first survey after the initial plant only found 142 clams. The second only found fourteen (Pattison 2001). From 1900 to 1989 clams had been planted from as far north as Washington to the Mexican-California border. These plantings help definitively conclude one thing: that the range of Pismo clams today is the same as the range of Pismo clams centuries past. Clams planted north of Monterey Bay only survived for three years with an average of one year (Lampson 2007).
Well Meant, Bad Results
One of the negative effects of the planting of Pismo clams is that word of the stockings inevitably gets out to the public. Because public money was used to fund these projects, they required full disclosure of one kind or another (Ono 2009). Large clams were periodically planted to find if fully mature clams would have an increased positive effect, but with these large clams came large crowds. When news of these plantings reached the masses, abnormally large groups would come to search for these freshly planted clams. The problem created by this was doubly felt. Not only would the freshly planted clams be quickly located, but much of the native stock is also found (Lampson 2007).
CURRENT CLAM POPULATIONS
Still stretching throughout their native range, Pismo clams have few places where they occur in great numbers. If not one limiting factor is suppressing the populations then it is another. Clams are finding beaches they once lived at inhospitable for different reason, and these reasons differ according to their location. It was written perfectly in a 1929 Division of Fish and Game of California Fish Bulletin: “If we expect to develop an intelligent program for the future conservation of the Pismo clam, it is necessary that we have an understanding of the agencies which have been responsible for the current condition” (Herrington 1929). Unfortunately, however, since this statement was so plainly and obviously stated, outside of changing take limits, not much work has been done in reversing the problems which are responsible for the current conditions (Ono 2009).
Predation. Outside of predation by sharks, rays, fish, birds and sea otters, not much is known as to why more than ninety-nine percent of Pismo clams face an early mortality (Weymouth 1923). Although it has not been documented, it is more than likely that these tiny clams are preyed upon by the numerous fish found in the surf (Ono 2009). The very young clams are far less protected; they have not developed their full outer shell by this time and they have not developed the ability to burry themselves in the sand (Herrington 1929).
The physical environment. Physical factors have also contributed to the death of young and old Pismo clams alike. Strong storms and frost have proven to be factors that efficiently kill large stocks of Pismo clams. During storms, clams can be washed up onto the beach where they become stranded. Here, they either die because they cannot get back to the water or because they are eaten by birds who take advantage of the easy meal. Not only do strong storms strand clams on the beach, but they also burry them. Shifting sands have been found to burry clams so deep that they were unable to dig themselves out. Also, because Pismo clams only burry themselves not much deeper than six inches in the sand, they are susceptible to frost. During extremely cold conditions clams can be frozen during low tide (Herrington 1929).
Human Suppression in Southern California
Beach development. Probably the greatest and most obvious change that Pismo clams are facing today is their changing environment. The most direct and visible change to Pismo clam habitat can be seen up and down much of the California coast. In Zuma and Malibu, for example, homes and businesses have been erected on what was once coastal habitat (Fig. 7). These developments have been placed right at the edge of the intertidal zone, where Pismo clams live. In northern California there is not as much coastal development as in southern California; however, because southern Californian beaches are more ideal grounds for Pismo clams, the affect on the total population is heavily felt (Lampson 2009).
As developments are placed at the ocean’s edge, humans have put barriers along with them. Roads had to be built to allow access to these new coastal developments. Many times roads have been placed such that they cut beaches in half; the ocean side of the beach is highly susceptible to ocean current because it is cut off from resedimentation (Fig. 8). Large boulders had been placed on the sea-side of roads in order to protect them from the sea (Fig. 9). Where waves would have once gently rolled up onto the sand, they are now refracted back into the sea (Fig. 10). This wave refraction causes the topography of the intertidal zone to drastically change (Lampson 2009). Also altering the topography of southern California beaches are sea walls. Populations in Malibu saw a steep decline in the late 1980s (Ono 2009). By no coincidence has southern California populations disappeared around the same time sea walls were constructed (Fig. 11). In many cases, both boulders and sea walls have been used further destroying beach habitat (Fig. 12). Where the beaches were once broad and shallow sloped, they are now narrow and steep (Fig. 13). Pismo clams find this habitat unsuitable and because of this populations have not been seen to populate beaches with any kind of intertidal development (Lampson 2009).
Choked rivers. Not only are beaches being eroded away by the change in the topographical dynamics, but they are also being withered away by the restriction of the natural supply of the beaches’ sediment. True to southern California beaches, the rivers that once fed them have now been dammed or diverted. Because of this, sediment is not being delivered to the beaches from inland sources via the rivers. Obsolete, out of date dams and culverts have been placed all along rivers in decades past to provide for irrigation and land reclamation. Now the affects of this are being felt at the beaches and by Pismo clams (Lampson 2009).
Polluted watersheds. Unlike beach developments and choked rivers, polluted watersheds apply to southern and northern Californian beaches. Especially true to the Oxnard Plains and Salinas Valley, where rivers drain onto beaches where Pismo clams have historically populated, agricultural runoff has proven to be a detriment to not only Pismo clams, but the coastal habitat throughout. Large scale irrigation systems are used to water crops that have been doused in petroleum based chemicals and pesticides (Fig. 14). After the crops are irrigated, the water runs into farm channels that eventually find their way to creeks or rivers that run to the ocean. Along with the chemicals, these channels also bring other unwanted items to the beach. Large amounts of trash are washed to the beach via this medium (Fig. 15). All of these factors combined provide a hostile environment for Pismo clams (Lampson 2009).
Recreational clam diggers. Because of all of the other limiting factors, much of the population has been suppressed. What was once a popular activity has now turned into an event that very few take part in. Recreational clam fisheries in places such as Pismo beach, which once saw hundreds of thousands of clam diggers in a single weekend, no longer see any (Pattison 2001). Because of this fact, the affect created by recreational clam diggers is negligible (Lampson 2009).
THE FUTURE: A PERSONAL REFLECTION
It has been proven almost impossible to fully understand the past of the Pismo clam. Especially in regards to its relationship with sea otters, a lot of space for assumption is left to debate. Clearly sea otters possess the power to decimate Pismo clam populations. But before human impact was felt all the way through the fragile trophic system in which both Pismo clams and sea otters share, perhaps the ecological balance made was such that both species were able to thrive together. Today there are two sea otters that live as far south as San Miguel Island; however, a Pismo clam is not likely to encounter sea otters further south than Santa Barbara (Lampson 2009). If sea otters still ranged as south as Mexico, would there be any Pismo clams at all? Probably.
Humans can only blame sea otters for the disappearance of Pismo clams to a certain level. That level ends where the sea otters’ current range ends. Past that point it is clear that what is suppressing clam populations are humanity’s impacts on the environment. Beaches have been destroyed for multi-million dollar homes; oceans have been polluted to feed not only the masses, but the cows, too. Rivers that once flowed at an incredible rate have been reduce to a trickle, often times less. All of these factors contribute to the reason why Pismo clams are hurting in southern California.
Taking a deeper look, it is highly plausible for sea otters to blame humans for forcing them to focus their diets on Pismo clams. With the commercial fishery for Pismo clams being closed, it would only be natural for otters to shift their focus to what is readily available. Abalones were harvested to near extinction in central and southern California; sea urchins continue to be harvested due to great international market demands. The sea otters’ diet has undoubtedly changed over centuries of marine exploitation by humans.
Take a short trip past the border, however, and one is given a picture of what California beaches once looked like. With little to no development on Mexico’s Baja peninsula beaches, clam populations have continued to thrive. Even with Mexican companies harvesting Pismo clams for exportation, sustainable populations have proven themselves to last (Lampson 2009). Pismo clams can survive in California, it is simply up to humans.
To get Pismo clams to repopulate the beaches the once inhabited a price would have to be paid. This price is largely one that the people will choose not to pay (Lampson 2009). Rivers will have to be restored to their natural state. Developments, entire cities for that matter, will have to be destroyed. Towns like Malibu, Zuma and Santa Monica will need to relinquish their power over the beach. Roads will have to be closed and removed. Asking the people to give up their property and then to destroy it would be futile.
Pollution would have to be greatly abated as well. Although organic agriculture has taken roots in the United States, big business farms still dominate the land. Chemical pesticides will continue to be sprayed on crops. And as that water makes its way to the ocean it will carry trash along with it. Cars will have to become cleaner. The amount of pollution washed from streets and into the waterways cannot be ignored. Although progress has been made in lessening the impact of pollution, it is negligible in terms of restoring the Pismo clam to its past luster.
Ultimately, old habits are going to have to die. Things that people are not willing to relinquish will have to be given up. Is California ready for such a big step? Probably not. However, Pismo clams will continue to exist. Unless if beach habitats are absolutely destroyed and sea otters extend their range back to Mexico, Pismo clams will find a way to survive; they have done just that for tens of thousands of years.
1. Growth rates at different beaches………………………………………………………16
2. Pismo clam range in California……...……………………………………………..…..17
3. Broad, shallow sloping beach, Pismo Beach, California……...…………………..……18
4. Pitch fork and clams……………………………………………………………….…...19
5. Abalone iron used by recreational clam divers, Oxnard, California...…………..……..20
6. Recreation clam divers emerging from their dive, Oxnard, California……...…………21
7. Coastal development in Malibu, California…………………………………………….22
8. Highway cutting beach in half, Pacific coast Highway, Point Mugu, California…...…23
9. Large boulders protecting the Pacific Coast Highway, Point Mugu, California……….24
10. Large boulders refracting waves, Point Mugu, California…………………………..…25
11. Sea wall built around the same time populations crashed, Malibu, California………...26
12. Sea wall and large boulders destroy more habitat, Malibu, California..……………….27
13. Steep beaches that were once shallow sloping, Malibu, California…………………....28
14. Mass irrigation contributing to agricultural pollution,
Oxnard Plains, Camarillo, California…………………………………………………..29
15. Farm channels taking trash to the beach, Oxnard Plains, Camarillo, California……….30
Figure 1. Growth rates at different beaches
Source: Data from William Herrington, The Pismo Clam Further Studies of its Life History and Depletion (Division of Fish and Game of California Fish Bulletin No. 18, 1929), figure 7.
Figure2. Pismo clam range in California
Source: Data from William Shaw, Species Profile: Life Histories and Environmental Requirements of Coastal Fisheries and Invertebrates(Pacific Southwest)Pismo Clams (United States Fish and Wildlife Service, 1989), figure 2.
Figure 3. Broad, shallow sloping beach, Pismo Beach, California
Photograph by author
Figure 4. Pitch fork and clams
Photograph by Kai Lampson
Figure 5. Abalone iron used by recreational clam divers, Oxnard, California
Photograph by Gerard Strubeck
Figure 6. Recreation clam divers emerging from their dive, Oxnard, California
Photograph by Gerard Strubeck
Figure 7. Coastal development in Malibu, California
Photograph by author
Figure 8. Highway cutting beach in half, Pacific coast Highway,
Point Mugu, California
Photograph by author
Figure 9. Large boulders protecting the Pacific Coast Highway, Point Mugu, California
Photograph by author
Figure 10. Large boulders refracting waves, Point Mugu, California
Photograph by author
Figure 11. Sea wall built around the same time populations crashed, Malibu, California
Photograph by author
Figure 12. Sea wall and large boulders destroy more habitat, Malibu, California
Photograph by author
Figure 13. Steep beaches that were once shallow sloping, Malibu, California
Photograph by author
Figure 14. Mass irrigation contributing to agricultural pollution, Oxnard Plains, Camarillo, California
Photograph by author
Figure 15. Farm channels taking trash to the beach, Oxnard Plains,
Photograph by author
1. Commercial harvest and imports from 1916 to 1947……………………………..……32
2. Commercial harvest from 1916 to 1947………………………………………….….…32
3. Regulations through the years……………………………………………..…………...33
Table 1. Commercial harvest and imports from 1916 to 1947
Source: Data from Kai Lampson, Pismo Clam (California Department of Fish and Game, 2007), table 6.2.
Table 2. Commercial harvest from 1916 to 1947
Source: Data from Kai Lampson, Pismo Clam (California Department of Fish and Game, 2007), figure 6.1.
Table 3. Regulations through the years
Source: Data from Kai Lampson, Pismo Clam (California Department of Fish and Game, 2007), table 6.1.
Anderson, M. Kat. 2005. Tending the wild: Native American knowledge and the management of California’s natural resources. Berkeley: University of California Press.
Coe, Wesley R. 1947. Nutrition, growth and sexuality of the Pismo clam, Tivela stultorum. Journal of Experimental Zoology 104, no. 1: 1-24.
Fitch, John E. 1961. The Pismo clam. Sacramento: California Department of Fish and Game.
Frey, H. W. 1971. California marine resources and their utilization. Sacramento: California Department of Fish and Game.
Herrington, William C. 1929. The Pismo clam further studies of its life history and depletion. Sacramento: Division of Fish and Game of California.
Kalvass, Peter. 2001. Bay and estuary invertebrate resources: Overview. Sacramento: California Department of Fish and Game.
Lampson, Kai. 2007. Marine status report: Pismo clam. Sacramento: California Department of Fish and Game.
Lampson, Kai. 2009. Interviewed by author. Santa Barbara, CA. March 23.
Lea, Robert N. 1986. Temporal and spatial patterns in sea otter, Enhydra lutris, Range Expansion and in the loss of Pismo clam fisheries. California Department of Fish and Game Scientific Journal 72, no. 4: 197-212.
Masters, Patricia M. 2005. Holocene sand beaches of southern California: ENSO forcing and coastal processes on millennial scale. Journal of Paleogeography, Paleoclimetology, Paleoecology 232, no. 1: 73-95.
Ono, Dave. 2009. Interviewed by author. Santa Barbara, CA. March 23.
Pattison, Christine A. 2001. California’s living marine resources: A status report. Sacramento: California Department of Fish and Game.
Shaw, William N. 1989. Species profiles: life histories and environmental requirements of coastal fishes and invertebrates—Pismo clam. Washington D.C.: United States Fish and Wildlife Service.
Weymouth, Frank W. 1923. A case of the destruction of Pismo clams by oil. California Department of Fish and Game Scientific Journal 5, no. 4: 174-175.
Very Interesting and Detailed report Jared , I had no idea that the bigger pismos can live for so long . My older brother was scuba dv. for pismos at Zuma when I was just a little kid . Good job , now lets go get some Abalone , ha // steve
Very well done . I have been visiting pismo for twenty years and always looking for info on the clam history. Good stuff.
how come my college reports don't look like that. :(