ANCHORAGE, Alaska -- A veterinary pathologist worked Monday to determine what killed a juvenile fin whale discovered on the bow of a cruise ship entering an Alaska port.

The cause of death was not immediately apparent for the endangered whale spotted just after 5 a.m. Sunday on the bulbous bow of the Zaandam, a Holland America Line cruise ship, as it prepared to dock in Seward.

A spokeswoman with the Alaska Railroad confirmed a whale had been found on the boat, but would not comment further, CBS affiliate KTVA reported.

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The carcass was towed to a beach near Seward, a spokeswoman for the fisheries section of the National Oceanic and Atmospheric Administration, Julie Speegle, said Monday.

The veterinary pathologist, Kathy Burek, began a necropsy Sunday night and planned to continue Monday, with armed NOAA Fisheries law enforcement officers standing guard against bears, Speegle said.

The bulbous bow is an extension of the main bow. It rides under the water and is designed to avoid wave-making.

A whale on the bulbous bow may not be the result of a ship strike, Speegle said. It could have been already dead in the water and caught by the device.

"That's something, hopefully, the necropsy will determine," Speegle said.

The whale was not seen on the bulbous bow a half-hour earlier, Sally Andrews, a spokeswoman for Holland America, said in an email. An officer had been preparing the ship for arrival just after 4:30 a.m. and did not see a whale, she said.

The company is saddened by the event, Andrews said. Holland America has a comprehensive program to avoid striking whales and was not aware of whales in the area.

"Our ships have clear guidelines on how to operate if whales are sighted nearby, which include altering course and reducing speed as required," she said.

Fin whales feed on schooling fish and invertebrates by gulping large swarms of them while swimming on their sides, according to the Alaska Department of Fish and Game.

Fin whales were decimated by commercial whalers in the 1800s and early 1900s. The average adult male is 70 feet long and 45 tons. Adult females average 73 feet and 45 tons.

The dead male juvenile was considerably smaller, but Speegle did not have its dimensions.

Last year 10 fin whales were among 18 endangered whales whose carcasses were found floating near Alaska's Kodiak Island between Memorial Day Weekend and early July. The others were humpback whales.

Scientists speculated that the animals might have eaten something toxic in warmer-than-average water. That investigation was hampered because some of the whales had significantly decomposed before they were found.

The dead whale found on the cruise ship will be tested, Speegle said. "We are taking samples for harmful algal blooms," she said.