Immortal though they are, however, their birth rate is subject to mysterious annual fluctuations.

The researchers collected data from about 100 estates in northern England that showed similar annual fluctuations in numbers.

The temperature and salinity of this current show strong seasonal and annual fluctuations.

Quite apart from annual fluctuations brought on by changes in ocean water quality, officials and others say, there are fewer people visiting the beach these days.

Water levels are determined by seasonal and annual fluctuations, which may be quite significant.

Numbers migrating show marked annual fluctuations; no link with any particular food source has been established.

For Jack, the four annual fluctuations of the Twilight represented seasons.

So far this year, officials point out, the dollar has fallen only about 4 percent against the yen, well within its normal annual fluctuation in value.

In this way, they can estimate the population's annual fluctuations.

Strong winds, big waves, and annual fluctuations in the lake level also make fishing more difficult.