Sci­ence that should come as a sur­prise to no one

Annapolis Valley Register - - NEWS - Rus­sell Wanger­sky’s col­umn ap­pears in 36 SaltWire news­pa­pers and web­sites in At­lantic Canada. He can be reached at rus­sell.wanger­[email protected]­gram.com — Twit­ter: @wanger­sky.

I get dis­cour­aged some­times. Dis­cour­aged be­cause caught up in do­ing things the same way we al­ways have, we keep do­ing them, even though we should know bet­ter.

The source of my lat­est dis­cour­age­ment? Re­cent re­ports that fisheries sci­en­tists are see­ing a change in some At­lantic Cana­dian snow crab stocks. Sci­en­tists found male crabs have stopped grow­ing; more than 80 per cent of the stock in some zones is now too small to catch.

The prob­lem? The snow crab fish­ery tar­gets large crabs, and those are van­ish­ing, leav­ing only small crabs be­hind. What did we think would hap­pen?

Crab that would nor­mally be too small to win mat­ing battles are now the right size.

En­ter a con­cept known as “un­nat­u­ral se­lec­tion,” where an out­side force im­poses a new or­der in bi­o­log­i­cal se­lec­tion.

I first wrote about it in 1996, for a weekly news­pa­per called The Sun­day Ex­press, when I re­ported on a sci­en­tific study about the way suc­cess­fully spawn­ing male Dun­geness crabs in British Columbia were get­ting smaller and smaller. Keep in mind, that was 22 years ago.

I’ve kept track of it since. Here’s what I wrote when I re­turned to the same topic in the St. John’s Tele­gram in 2001.

“Fif­teen years ago, sci­en­tists work­ing in British Columbia did some fas­ci­nat­ing re­search on Dun­geness crab; they sug­gested that if the fish­ing in­dus­try took only the largest male crabs, that might have some ef­fect on the species as a whole. With the larger males out of the pic­ture, smaller males that might lose mat­ing battles had a chance to both mate, and pass on their ge­netic ma­te­rial.

“Not ev­ery­one agreed with the re­search, but most agreed with two points: that small male Dun­geness crab seemed to be mat­ing more often, and that smaller and smaller crabs seemed to be be­com­ing sex­u­ally ma­ture.

“Not only that; once they mate, a large pro­por­tion of the smaller males then stop grow­ing, and never reach mar­ketable size. But on the ge­netic front, like the En­er­gizer Bunny, the pygmy crabs just keep go­ing, and go­ing.

“In the great wide evo­lu­tion­ary world of the Dun­geness crab, smaller might sud­denly be bet­ter, which would be great news if you’re al­ready a small male Dun­geness crab.

“It’s an in­trigu­ing propo­si­tion for the New­found­land fish­ery, since we har­vest – you’ve got it – ex­clu­sively the large males of the snow crab species. And the snow crab fish­ery is such a huge part of what re­mains of our fish­ing in­dus­try.”

Fast for­ward to to­day, and fed­eral fisheries sci­en­tists are say­ing they hope large male crabs will re­turn – if left alone to grow – and that the change is, at this point, sit­u­a­tional rather than ge­netic. In other words, if enough big crabs are still around to be given a chance to sur­vive and mate, they re-es­tab­lish the nat­u­ral or­der.

It doesn’t al­ways work that way. In the Caribbean, the fish­ery for large conch changed that species’ en­tire ge­netic his­tory. Conches from 7,000 years ago had 66 per cent more meat in them but, as sci­en­tists from the Smith­so­nian Trop­i­cal Re­search In­sti­tute found in 2014, “Be­cause of per­sis­tent har­vest­ing of the largest conchs, it be­came advan- tageous for the an­i­mal to ma­ture at a smaller size, re­sult­ing in evo­lu­tion­ary change.”

Sci­en­tists from Woods Hole found sim­i­lar changes in cod, salmon and had­dock. When big fish are tar­geted, smaller vari­ants be­come more suc­cess­ful and pass on their ge­netic traits, in­clud­ing their smaller size.

The thing is, we’ve known for decades that se­lec­tively fish­ing large males skews species.

But there was lots of money in­volved. Snow crab is an im­por­tant and valu­able fish­ery in Nova Sco­tia, Prince Ed­ward Is­land, New Brunswick and New­found­land and Labrador.

So, of course, we did it any­way. Dis­cour­ag­ing, in­deed.

Rus­sell Wanger­sky Eastern Pas­sages

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