Sample Case Study on Caspian Seals Trapped in Vast Waters


Caspian are the apex predators in the Caspian Sea ecosystem, and hence have a critical role in the control of the populations of other species, and the stability and sustainability of the ecosystem. However, the population of the seals has reduced drastically, with the current seal population being nearly a tenth of that of the beginning of the 20th century. Overfishing and encroachment of humans to seal habitats has led to the decline of the seal population to the historically low levels being witnessed, causing adverse effects on the delicate Caspian Sea ecosystem. The Caspian seal population is also facing a newer ecological problem of pollution, which has led to infertility and immune suppression, making the seals susceptible to epizootics, putting further pressure to a population that is already in decline. There needs to be an integrated approach to seal conservation efforts to ensure that the Caspian seal is not driven to extinction by the confluence of overfishing and pollution of the seal’s habitat

Caspian Seals Trapped in Vast Waters: No Room to Escape


The Caspian Sea is the world’s largest lake with an approximate surface area of 371,000 square kilometers. It is called a sea due to its extensive area. The vast water body is bordered by Russia, Kazakhstan, Turkmenistan, Iran, and Azerbaijan, which surround the water body making it an inland lake.

Fig. 1: Map showing the Caspian Sea

The Caspian Sea is home to a varied flora and fauna that coexists in a complex and delicate relationships of interdependence. The local marine mega fauna predator population consists of Caspian seals, (Pusa caspica) and the beluga sturgeon (Huso huso) that has been rapidly depleting in recent years (Harkonen et al., 2012). The depletion of the apex predators has a worrying impact on the delicate equilibrium of the ecosystem, and is likely to push the ecosystem’s equilibrium to a new level where it may never recover to return to the historical levels. The seals are part of a greater Caspian marine ecosystem where all biota is interdependent and the slightest perturbations in populations can have an adverse effect on the food chain, and the sustainability of the ecosystem. For example, depletion of the Caspian seal population led to a ten-fold increase of cod population, which was subsequently overfished, leading to an increase in herring population. This implied that a slight disequilibrium in any of the marine populations has an impact across the food chain (Harkonen et al., 2008). Such huge increases in the cod and herring populations are unsustainable for the marine ecosystem, and can lead to the degradation of the ecosystem in the long term.

The present presents many ecological challenges to the vulnerable Caspian seal population, with global warming projected to precipitate the fast melting of ice caps and warming of water bodies reducing the ice cover that is necessary for seal breeding. There has also been an increase in illegal fishing of the valuable Caspian seal further pressuring a declining species, pushing the population to unsustainably low levels. The Caspian Sea being an enclosed water body is susceptible to pollution. The waters have been polluted by agricultural and industrial activities in the hinterland, further exacerbating the pressure on the seals considering that the pollutants are responsible for some of the epidemics decimating the marine populations. The sharp decline in female breeding population, 245,000 in 1867 and 21,000 as of 2005, is an alarming sign (Harkonen et al., 2012). The numbers signify a downturn of at least 90%, which makes it our duty to alleviate the present situation for a brighter future. This research paper examines how the distribution of Caspian seals has been affected over time, as well as the anthropogenic and environmental causes linked to seals’ population decline (Kajiwara et al., 2007).

Decline of Caspian Seal Population Due to Pollutants/Viruses

The Caspian Sea is surrounded by countries with considerable industrial as well as mechanized agricultural activities, which extensively use chemicals in the form of fertilizers and pesticides for weed and pest control. These anthropogenic chemicals eventually end up in the Caspian Sea through the natural water cycle, where their concentration increased over time. According to Kajiwara et al. (2007), there have been increasing incidences of abnormalities in aquatic mammals all over the world, including reproductive failure, impaired immunity, tumors, and viral infections. In addition, there has been a general decline in marine populations and in some cases mass mortalities of mammals have been reported, with the  phocine distemper virus (PDV) outbreak in Northern Europe being responsible for the death of thousands of harbor seals (Phoca vitulina). It is necessary to note that most of the disease outbreaks and abnormal events recorded are prevalent in areas where human activities and industrial activities are high. This implies that there is a positive correlation between industrial and human activity and unusual aquatic events, hence the need to establish the linkages definitively.

The Caspian seals are susceptible to interference from human and industrial activities considering that the sea is surrounded by countries that have a considerable human and industrial activity in addition to the sea being a closed ecosystem, with no likely escape for the aquatic animals. In the spring of 2002, an unusually high number of Caspian seals (Pusa caspica) died with analysis showing that the main cause of the high mortality was canine distemper virus (CDV), which had ravaged the seal population. The increasing susceptibility of aquatic mammals to epizootics raises the question as to what could be the triggering conditions that cause the decreased resistance to disease attacks. Prior research has shown that the presence of organochlorine compounds in an aquatic environment and in the body of marine mammals is positively correlated to greater susceptibility to viral attacks (Kajiwara et al., 2007). Organochlorine compounds that are usually associated with human farming activities are a major problem for the Caspian Sea because the soils surrounding the sea are suitable for farming and hence have attracted great human settlement and activity. The Caspian Sea loses water only through evaporation meaning that any pollutants that end up in the lake are likely to remain there, increase in concentration, and eventually enter the food chain.

In addition to farming activities and encroaching human settlement, the Caspian Sea has to contend with pollution from oil exploration. Oil exploration activities in and around the Caspian sea have been going on for over a century, and poses a serious pollution threat to the sea. In addition, the periodic rise and fall of the Caspian Sea level has on occasion led to the flooding of inland oil wells and seepage into capped oil wells leading to the spread of oil into the seawater. Despite the various forms of pollutants that enter the Caspian Sea ecosystem, persistent organic pollutants (POPs) are the most worrying, and have the most detrimental impact on the health of the seals; suppress the seals’ immunity, making them more susceptible to attacks from disease causing agents.

During breeding at the beginning of spring, mother seals give birth to pups on the surface of the ice, where they are fed by their mother for a period of approximately one month before moving into the sea. During this period, the mother seals lose nearly half of their blubber due to the lactation as well as the molting, which occurs afterwards. The blubber traps some of the organochlorine compounds, and hence the concentration of the compounds in the seals’ body tissues during autumn and winter is comparatively low. However, the lactation and molting process leads to the loss of fat and subsequent redistribution of the organochlorine compounds formerly trapped in the blabber into the body tissues (Kajiwara et al., 2007). The presence of organochlorine and other toxicants in the body tissues of the seals has a detrimental effect on the health of the seals, as they are involved in the immune suppression of the seals, making the seals vulnerable to attack from disease causing agents. Therefore, the spring – summer period is the period that seals are most susceptible to epizootics owing to the loss of blubber and the attendant redistribution of toxins from the blabber to body tissues.

The Caspian Sea seals have been found to have a significantly higher concentration of DDT, compared to seals from other areas despite the fact that a ban on the use of DDT since 1969 has been in force. The unusually high levels may be due to the formerly extensive use of the pesticide around the Caspian Sea as well as possible illegal use of the pesticide around the area recently. Persistent organic pollutants (POPs) like DDT remain in the ecosystem for a long time and are not easily broken down, presenting a continuous threat to the health of seals, as they are continuously recycled in the food chain. Other than DDT, Caspian seals also have an appreciable concentration of polychlorinated biphenyls (PCBs) in the blubber as well as other traces of organochlorine compounds. This potent mixture of chemicals is partly responsible for the immune suppression of seals during the spring – summer seasons, increasing the likelihood of epizootics. The presence of DDT in adult females has been shown to reduce the fertility of the females and in some cases cause infertility of the females. This causes an imbalance in the reproduction cycle, leading to the production of less pups’ yearly and hence consequently stunted growth of the seal population.

The Caspian Sea is a closed ecosystem with a complex and delicate web of relationships and interdependencies. Human encroachment on the sea shores, and farming activities around the sea’s catchment area have led to an increase in the level of pollutants that are seeping into the sea. The concentration of POPs in the sea, especially that of DDT remains above the averages from other areas; a consequence of not only human activity in the catchment area but also of the closed nature of the ecosystem that does not allow for the diffusion of pollutants. Toxic pollutants are a serious threat to the population of seals in the Caspian Sea as they are responsible for the emergence of abnormal occurrences in the seals. Organochlorine compounds that are in the bodies of the seals have significantly reduced the immunity of the seal population, making it susceptible to not only attack from disease causative agents but also leading to abnormalities in the normal bodily functions of the seals. With increasing encroachment around the sea, it is likely that more pollutants will enter the sea, putting the health of seals under pressure, and hence their population over time.

Decline of Seal Population Due to Fishing

The Caspian seal was formerly considered as a ‘harvested species’ in the former Soviet Union, and hence fishermen were at liberty to aggressively hunt for the seal and capture as much of the seals as they could. Both adult seals and baby seals were aggressively hunted during this period, and a vast number of seals and pups were killed. At the beginning of the twentieth century, the seal population was thriving, and numbered over one and a half million as seals colonized most of the areas around the Caspian Sea. However, by the end of the 20th century, this number had dropped precipitously to approximately a tenth of the population at the beginning of the century (Harkonen et al., 2008). This sharp decline in the population of the seals was mainly due to overexploitation of the seal resource by fishermen in the Soviet Union and other Caspian Sea surrounding countries. The population of the seal has currently reduced to levels that are low enough to warrant worries about the long-term prospects of the survival of Caspian seals.

The adult Caspian seal is hunted for two principal reasons. First, the seal is hunted for its blubber, which has many healthy oils that are beneficial to human health, and can be used to improve the health of people. The benefits of blubber to human health have been dramatically recorded in Greenland, where it is observed that individuals who take the local diet of whale and seal blubber have never suffered from cardiovascular diseases, and the arteries of 70-year-old adults on this diet have the same elasticity as those of a 20-year-old elsewhere. The blubber oil is also rich in omega-3 fatty acids that have been shown to improve cognitive development, and hence are used to make dietary supplements. In addition, the oil from the blubber is rich in vitamin D and hence can help to reduce the incidences of rickets in people living in temperate areas. Secondly, the seals are also hunted for their meat, which is one of the healthiest meats that have no negative impact on human health as observed by the health of Alaskans and Eskimos who live on this meat.

The Caspian pups are born with a fur coat that protects them from the extreme cold on the ice where they stay for up to one month. The fur coat is usually lost when the pups molt as they are weaned and enter the water, learning how to swim. The fur from the pups is used in making fur coats, and hence seal hunters will hunt the pups, which were skinned for their fur. The hunting of pups was more prevalent than that of adults in the 19760s and 70s, leading to a population that was skewed, with more adults than youngsters, creating the danger of a population implosion. The adult and pup hunting practices cumulatively led to an increase in pressure on the seal population, depleting the adults, which are essential for reproduction while killing the pups that could have grown to adults to replenish the killed stock creates a vicious cycle of continuous depletion of seal stock. The collapse of the Soviet union saw a reduction in the number of fishermen hunting seals as some countries like Kazakhstan stopped seal hunting. However, the Russian federation still hunts seals within specific quotas. The fishing methods used to catch seals for ‘scientific’ purposes in the Russian federation has been found to be indiscriminate in the catching of fish, causing entanglement and by-catches of other marine life.

Human activities, including hunting, encroachment on habitats, farming, and industrial activities have made the seals to abandon areas that were formerly used for breeding. In addition, the declining numbers of breeding females has led to the seals needing lesser areas for breeding hence the abandonment of some breeding sites. Illegal fishing of Caspian seals presents a challenge to any species conservation efforts as demand for the adult and pup seal products fuels the practice. The population of seals is at historically low levels and the current equilibrium may have shifted in an irreversible way, implying that the seal population in the Caspian may not recover to historic levels. In conclusion, the decimation of the Caspian seal population has been mainly due to overfishing, which targeted the pups, leading to an imbalance in the population structure where there were more adults than pups. This population structure was detrimental to the long-term growth and sustainability of the seal population considering that a healthy population should have more young members than adults.



Alternative Ways to Revive The Pura Caspica Population

The Caspian seal population can be revived by using a multidimensional approach that utilizes more than one approach to mitigate the population decline. First, there should be a moratorium in fishing of the seal because overfishing is the primary cause of the decline in the population of seals. Secondly, there should be a change in fishing methods to ensure that the incidences of seal by-catches are reduced. Although overfishing has been the main cause of population decline, other challenges to the seal population have emerged in the form of toxic pollutants that affect the health of seals. To address this problem, there should be tighter regulation in the use of chemicals around the sea’s catchment area. Additionally, seal nurseries can be established to increase the breeding and survival chances of the pups.




Harkonen, T., Harding, K. C., Wilson, S., Baimukanov, M., Dmitrieva, L., Svensson, C. J., & Goodman, S. J. (2012). Collapse of a marine mammal species driven by human impacts. PloS one7(9), e43130. Doi:10.1371/journal.pone.0043130-602.

Harkonen, T., Jüssi, M., Baimukanov, M., Bignert, A., Dmitrieva, L., Kasimbekov, Y., … & Goodman, S. J. (2008). Pup production and breeding distribution of the Caspian seal (Phoca caspica) in relation to human impacts.AMBIO: A Journal of the Human Environment37(5), 356-361.

Kajiwara, N., Watanabe, M., Wilson, S., Eybatov, T., Mitrofanov, I. V., Aubrey, D. G., … & Tanabe, S. (2008). Persistent organic pollutants (POPs) in Caspian seals of unusual mortality event during 2000 and 2001. Environm