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Explanation for answers to sea-urchin harvesting quiz:

Harvesting is more difficult at depth.  Yes.  Harvesting is done by divers with rakes, and deeper water means more air consumption (a logistical problem with SCUBA, but not with a surface supply), and possible decompression issues.

It is the sushi-trade that dictates harvest value.  Yes.  If gonad size relative to body size is less in deeper animals (which it seems to be from the authors’ data) and if overall gonad quality is poorer in the deep animals, then market acceptance for these gonads will be less.  The gonads, known as uni-zushi, are prized in the sushi market not just for their size, but also for their flavour, colour, and richness, all features likely to be superior in the better-fed, shallow populations.

Simple harvest-economics (“catch” of gonads per unit effort) will work against exploitation of the deeper population.  Yes.  This goes along with the previous points.  From the authors' data it would take 5 deep urchins to produce the gonad yield of one shallow urchin.

Removal of gonads is easier from short-spined (shallow) urchins than from long-spined (deeper) ones.  Possibly, but this is not likely to be of particular economic importance.

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