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It is standard practice when conducting a census of any given species that the 'captive' and wild populations are tallied separately. This is done because there is seldom any guarantee that the 'captive' population can sustain itself once released into the wild.

Two useful examples to illustrate this point are the scimitar-horned oryx of northern Africa and the Waldrapp Ibis of Africa, Europe and Asia Minor. The Scimitar-horned oryx is considered extinct, as no population is known to exist in the wild, despite healthy populations existing in zoos worldwide. A reintroduction program is underway but until the reintroduced population proves itself to be self sustaining in the wild this species will continue to be classified as extinct.

To the point of reintroduction: The Waldrapp ibis, a species once common across north Africa, Asia minor and into Europe, now only exists naturally in two known locations in north Africa and in a semi-wild state in Austria. The remainder of the population can be found in zoos around the world.

It has been noted in this and other species of bird that much of the behaviour recorded in the wild population is absent or diminished in the captive population. In order for the captive population to survive and thrive in the wild following reintroduction they do need to relearn those vital behaviours. It has been established that this does not happen automatically on reentering the wild and that the birds earmarked for reintroduction have to be encouraged through various enrichment activities to relearn the behaviours they have lost.

The reason I share these two examples is to justify why when conducting a census of endangered fish populations only the wild fish should be counted. No matter how well the hatcheries are doing (and they are critical to the longterm survival of many species) the net gain/loss from their reintroduced populations cannot be relied upon until they have proven themselves capable of survival in the wild.

Learn more about this author, Robert Wiggins.
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