Research Proposal:
Marine Contamination Affects on
Young of Year Eastern Pacific White Shark Populations
Harsha Malavalli
Avyay Panchapakesan
Sam Hirsch
Nirupam Nigam
Kayla Sadwick
Kathleen McKeegan
Becca Gordon
Marine Contamination Affects on
Young of Year Eastern Pacific White Shark Populations
Abstract
The White Shark (Carcharodon carcharias) is an immensely powerful predator that has
evolved over millions of years. Fluctuations in the population and birthrate of white sharks can
severely impact the health of the ecosystems where they are present. Accidental catch through
gill net fishing and purse seining for other species of fish and poaching for fins are factors in the
decline of the white shark in the eastern Pacific. This proposal focuses on the affects of chemical
contamination on Young of Year White Sharks in the birthing and pupping areas of the Southern
California Bight. Young of Year (YOY) is the term that is used to refer to the first year of life of
the animal.
Introduction
Sharks are considered essential animals in the marine environment. Being the apex
predator of the world’s oceans, sharks maintain the populations of hundreds of different species
of animals, ranging from microscopic organisms to larger animals such as seals, sea lions, and
other marine mammals. The food pyramid in a marine environment consists of a top predator,
very often a shark, followed by different species below that predator on the food pyramid, and
the bottom being producers, such as phytoplankton. The removal of a top predator in a contained
ecosystem would lead to its primary prey starting to gain in numbers until they eat all of the
organisms that they prey on, leading to a surplus in an organism below that, until the organisms
that are in surplus can no longer find food, and starve to death. As sharks are most often the top
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predators of these environments, the reduction in numbers of a species would have a deleterious
affect on the marine ecosystem. Ecosystems rely on sharks to keep the levels of animals in
check, and a lack of sharks would cause serious problems that would easily upset the balance of
life in the sea. Since the oceans cover seventy percent of the planet and are responsible for most
of the world’s supply of oxygen (via phytoplankton) and also serve as a carbon sink, the decline
of sharks could have devastating affect to all life on Earth.
Unfortunately, due to a variety of reasons, shark populations have been in decline
throughout the world. Specifically, white shark (Carcharodon carcharias) populations have
quietly fallen away to below three thousand five hundred sharks (Platt). The white shark is
responsible for the control of the populations of many marine mammals, such as sea lions, seals,
and elephant seals, as well as a multitude of fish (Fishbase.org). White sharks play an especially
prominent role in the Southern Californian Bight, where their pups are born, and where the adult
sharks come to birth and to feed. A further reduction of the already dwindling population of the
Carcharodon carcharias will undoubtedly be catastrophic, particularly to this region, as the
populations of fish, seals, sea lions, elephant seals, and other animals could increase to numbers
that the ecosystem could not sustain.
An irony that exists is that one of the reasons that the White Shark population has been
reduced today is the fact that they are the top predators of this region. Their consumption of
many marine mammals and other species that are relatively higher on the food chain has led to
the increased levels of contaminants in sharks. Many contaminants, such as PCBs, DDT, and
more find a way to enter the bodies of organisms lower on the food chain. Organisms higher on
the food chain consume a lot of those organisms, increasing the concentration of these dangerous
contaminants. This accumulation process continues, magnifying the concentration until the top
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predator, the white shark, has high concentrations of these toxins (Mull, Blasius, O’Sullivan,
Lowe).
Many of these contaminants that enter the ocean come from runoff, spilling into the
Southern Californian Bight from nearby industries, urban regions, and more. Some
contaminants, such as PCBs and DDT, which are now banned from being used in the United
States, still remain in the sediments and in minute particles in the ocean from the periods when
they were used. These compounds build up in the organisms via the food chain. Other
contaminants continue to be dumped into this fragile ecosystem, and still cause problems in this
environment. A key effect that these contaminants have on White Sharks is the damaging of the
embryo, reducing the chance of survival of the pup (Mull, Blasius, O’Sullivan, Lowe). As the
female shark’s bodies accumulate chemicals, their body starts using more and more resources to
keep them contained, resources that don’t pass to the embryos, stunting their growth, and often
killing them. However, though this effect of contaminants is known to be possible, there is no
knowledge as to how often an embryo dies due to these contaminants. Therefore, a necessary
question to ask would be the following: What is the relationship between levels of contaminants
in runoff in the Southern California Bight, and the PCB accumulation in juvenile, Young Of
Year (YOY), white sharks in this region.
Objectives
This research proposal attempts to analyze the existence of a correlation between
populations of juvenile White Sharks (Carcharodon carcharias) in the Southern California Bight
and the change over time in water quality on specific shoreline sites; sites to examine include:
Venice Beach, Santa Monica, Surfrider Beach, Malibu, and Redondo Beach. The proposal will
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address variables including: populations of Young-of-the-Year (YOY) white sharks caught in the
vicinity of the listed sites, which will be analyzed in relation to the levels of common industrial
and residual pollutants such as Dichlorodiphenyltrichloroethane (DDT) and Polychlorinated
biphenyls (PCB).
Methods and Materials
This project will focus on analyzing trends in White Shark populations, comparing them
to trends in levels of pollution in urban runoff and shoreline water. The proposal is to utilize
various methods of tracking in order to monitor the populations of YOY white sharks each year,
and will employ a number of commonly used means to measure the data on water quality.
Two of the most commonly used technologies used to observe shark populations are the
PAT (Pop-off Archival Transmitting) and the Acoustic Tag, each of which has its benefits. The
PAT tag, which is designed to “pop off” the animal after a specific period of time for recovery at
a later point, uses satellite signals to determine the position, among other data, of the organism.
Unfortunately, this signal is received only when the shark surfaces near a receiver; however, if
the receivers are widely spread, it can be a valuable tool, especially due to the fact that sharks
frequently surface in order to catch air-breathing prey. The acoustic tag may provide a more
accurate count of specific populations of white sharks. These are more localized receivers, which
use sound wave receivers to record animal positions; however, this requires the creation of
acoustic receivers in several of the aforementioned congregation sites for White Sharks.
The research would ideally span 15 years. Over this period of time, researchers would use
a combination of aerial surveillance and encounters by fishermen in by-catch (although still an
inaccurate method of locating many sharks) to locate, capture, and tag YOY white sharks, re-
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releasing them into the wild. Tagging as many sharks as possible would allow population levels
of YOY to be observed in a given year, effectively measuring the birthrate of the animals.
The second part of the study is related to water quality. Many harmful chemicals from
industrial and urban processes have entered, through sewage and groundwater, into our oceans.
DDT and PCB, while banned from many industrial products for years, still have an enormous
impact on our oceans. However, the extent of this impact, or its relationship with the birth of
White Sharks is not fully understood. DDT, in fact, has been known to produce stillborn
newborn in White Sharks, a fact that could cripple white shark populations.
It is important that data is collected on shark populations as close to the beginning of their
term on the California coast; in other words, mid-summer, such as July or August. Pollution data
should be recorded in the same period, and regularly until January of the next year, which is
typically the extended end for the sharks’ time here near the shore. This data should be taken
both from samples from water samples near shore. There are a number of methods by which to
measure this pollution in the water. Measuring pH (Potential of Hydrogen) levels, or acidity
levels, can be a very good indicator of the presence of dangerous chemicals. The typical acidity
of water is 6.5-8.5, and the waters near shore show that they are becoming more acidic; an area
of concern that may not be related to urban runoff, but a concern nonetheless, as high acidity can
kill disrupt fish populations. Similarly, scientists can measure the health of water by measuring
its DO (dissolved oxygen) level, which indicates the oxygen available for fish to breathe. It is
believed that YOY sharks congregate near the surf to benefit from the highly oxygenated water.
Another reliable method for observation is specific conductance. This involves running an
electrical current through the water, measuring its conductivity. This is particularly indicative,
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because a high conductivity indicates the presence of high amounts of dissolved solids in the
water.
This data concerning wastewater and shoreline water can then be correlated, over a
period of several years, to data concerning the annual populations of YOY sharks. This could
provide a much-needed analysis on how industrial chemicals may be adversely affecting the
birthrates and sustainability of the white shark population in the Southern California Bight.
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