Kazakhstan's Emergency Agency said today that oil workers inspecting the shore in the country's western Mangistau region discovered the seal carcasses.
Authorities were conducting tests to determine what caused the deaths.
Environmentalist have long expressed concern about damage to the Caspian Sea as a result of increasing oil exploration there.
Similar cases of seals and other sea life dying have occurred regularly in recent years. In many cases, expert analysis has discovered large amounts of pesticides and toxic oil waste in animal carcasses.
Last year, 350 seals and thousands of sturgeon died due to a leak from Kazakhstan's Kashagan oil field.
Several epidemics of viral diseases have also killed thousands of seals in the Caspian since the late 1990s.
The Post-Soviet Environment
THE FRAGILE PLANET: Since the collapse of the Soviet Union, old environmental disasters have come to light and new ones have emerged. War, poverty, and weak central-government control have led to serious environmental problems from Eastern Europe to the Russian Far East. RFE/RL has provided extensive coverage of these important issues and of efforts to cope with them.