さあ！諸君！捕鯨問題だ！

（つづき）
The ability of scientists to detect trends in land-hauling pinniped
populations is considerably better. Although total population size
may be difficult to estimate, a segment of the population predictably
returns to land to breed, give birth, or molt, and this segment can be
counted accurately by ground-based observers or from aerial photographs.
Growth or decline in this segment is taken as an index of trend
for the entire population, so this kind of count is sometimes referred
to as an index count. Index counts may be based, for example,

on the number of pups born or the number of total seals hauled out
at the peak of the molting season. If index counts are used over a
wide range of population sizes, ancillary research is typically required
to ensure that the fraction of animals counted does not valy in a
density-dependent manner (e.g., as per capita resources become scarce,
the percentage of time spent foraging away from the beach might
increase). Another factor making positive trends in pinniped populations
easier to detect is that most are capable of growing at faster
rates than cetaceans and sirenians. Abundance and trends are much
harder to measure for pinnipeds that haul-out or pup on ice.


（執筆者：JAY BARLOW AND RANDALL R. REEVES）

要するに海洋哺乳類、特にクジラ、イルカ類はCV＝20％（0.20と書くのとおなじ）
より低い数、すなわち良い精度出すのが大変なのだけれど、
たとえ良い数字出しても、それをもとに操業してると気がつかないうちに
系群なぎ倒してる確率がかなり高いということなんだね。

よく管理された「持続的利用」というのが、技術的に難しすぎる生物だと
言えるわけです。

家畜や農作物でも、天候や伝染病で予測する収穫量や地域差の変動係数が
かなり大きいということはあるけれど、それで失敗して100年後の世代に
恨まれるということはないのですね。