The Caspian seal (Pusa caspica, syn. Phoca caspica)
Since the beginning of the 1900s, the population has dropped by over 90%. In 2022, a substantial die-off of the endangered species was reported, threatening the isolated population at an estimated number from fewer than 70,000 by the Caspian Seals Research and Rehabilitation Center
Description
Adults are about in length. Males are longer than females at an early age, but females experience more rapid growth until they reach ten years of age. Males can grow gradually until they reach an age of about 30 or 40 years. Their lifespan is around 40-50 years. The maximum reported size is in length and in weight. males are generally larger and bulkier.
The skull structure of the Caspian seal suggests it is closely related to the Baikal seal. In addition, the morphological structures in both species suggest they are descended from the ringed seal which migrated from larger bodies of water around two million years ago.
Diet
Caspian seals are primarily piscivorous. They eat a variety of food depending on season and availability. A typical diet for Caspian seals found in the northern Caspian sea consists of crustaceans and various fish species, such as Clupeonella engrauliformis, C. grimmi, C. caspia, Gobiidae, Rutilus caspicus, Atherina boyeri, and Sander lucioperca. Caspian seal adults eat about of fish a day and almost a metric ton of fish per year.
In autumn and winter, Caspian seals prey mostly on sculpins, gobies, and crustaceans while inhabiting shallow waters in the northern part of the sea. During the summer, in the southern part of the Caspian Sea, they eat herring, roach, carp, sprat, and smelt. When Caspian seals live in estuaries, they eat large amounts of the freshwater species, Sander lucioperca. Other prey include shrimp, crab, and silversides.
Being one of the top predators in the ecosystem, Caspian seals accumulate hazardous chemicals found inside their bodies such as heavy metals, organochlorine compounds, and radionuclides.
Behavior and ecology
Caspian seals are shallow divers, typically diving for about one minute, although scientists have recorded Caspian seals diving deeper and for longer periods of time. After foraging during a dive, they rest at the surface of the water.
In the summer and winter, during mating season, Caspian seals tend to live in large groups. At other times of the year, these seals are solitary. During the summer, however, they make aggressive snorts or use flipper waving to tell other seals to keep their distance. Little else is known about their behavior. The pups' white coats are molted at around three weeks to a month. Male pups become sexually mature after six to seven years, whereas female pups sexually mature after five to seven years. Newborn pups are not fully grown until 8 to 10 years after they are born. Breeding begins a few weeks after the birth of last year's pup around late February to mid March. Breeding usually occurs after weaning of a newborn pup, but can begin while the pup is still nursing. Caspian seals migrate back to the southern part of the Caspian Sea after the breeding season and molting in late April because the north begins to warm with constant ice melting. The southern region of the Caspian Sea has deep, colder waters where the seals spend the summer months.
Habitat
The seal is found exclusively in the Caspian Sea, which is nestled between 5 countries; Azerbaijan, Iran, Kazakhstan, Russia, and Turkmenistan. Caspian seals can be found not only along the shorelines, but also on the many rocky islands and floating blocks of ice that dot the Caspian Sea.
Clinical signs of infected seals included debilitation, muscle spasms, ocular and nasal exudation, and sneezing. Necropsies performed in June 2000 on eight Azerbaijan seals revealed microscopic lesions, including bronchointerstitial pneumonia, encephalitis, pancreatitis and lymphocytic depletion in lymphoid tissues. Similar lesions were also discovered on four seals from Kazakhstan. Morbillivirus antigen was also detected in multiple tissues, including lung, lymph nodes, spleen, brain, pancreas, liver, and epithelial tissue of the reproductive, urinary, and gastrointestinal tracts. Such tissue lesions are characteristic of distemper in both terrestrial and aquatic mammals.
Ecological threats
Caspian seals are monogamous and mate only once annually; however, their pregnancy rate has dropped to a historic low of just 30%.A century ago, their population was estimated at 1.5 million seals; in 2005, 104,000 remained, dropping by over 90% By 2022, the Caspian Seal Research and Rehabilitation Center (CSRRC) estimated the population at fewer than 70,000, and it is listed as endangered by the UICN.
Due to increased industrial production in the area, pollution has had an effect on the survival of the Caspian seal. From 1998 to 2000, the concentration of zinc and iron increased dramatically in the tissue of dead, diseased seals. This suggests these elements are causative agents in compromising the Caspian seal's immune system.
Sea eagles are known to hunt these seals, which results in a high number of fatalities for the juveniles. They are also hunted by humans for subsistence and commerce. , commercial icebreaker routes have passed through areas with high Caspian seal pup concentrations, which may contribute to loss of habitat.
For threats related to migration, high density seal aggregations were recorded in November 2009 and 2010 CISS helicopter surveys in Kenderli Bay, but the integrity of seal habitat in Kenderli Bay is currently threatened by an imminent large-scale coastal resort development. This resort development can be a serious disturbance for seals. The local authorities have been advised about the need to preserve the seal habitats in the bay, but it is not yet clear what steps are planned to achieve this. According to the present studies, Kenderli Spit plays an important role for the seasonal migration of the Caspian seals and is recommended to be a protection area.
In December 2022, a substantial die-off was reported, with initial reports of 700 corpses later revised upwards to 2,500. The cause is unknown.