The northern population was already almost lost before the 20th century.

The northern pike population has done quite well for the last six years.

Even the northern population's behavior and life history are remarkably little known.

The more northern population is on average slightly smaller than the southern.

By the middle of the 20th century, the northern population was effectively extinct.

The northern population is the larger of the two.

In some northern populations, no females lay more than one clutch per year.

The differentiation that is observed between the northern and southern populations should have occurred quite recently.

The southern and northern populations may be distinct species.

The same is true of northern populations in Iceland.