Thursday, January 24, 2013

Cod are just like people:

They love to eat snow crabs!

You may remember meeting Laurinda Marcello through an interview last year as a student, but she's since graduated and published her results! Her paper looked at how snow crab recruitment is affected by water temperature and cold area extent, spawning stock biomass (how many crabs are out there makin' babies), and the biomass of crab predators (cod!). As a bonus, she compared these relationships between the Bering Sea and the Canadian North Atlantic.

What did she find out? Let's start with the predators! We know that cod like to eat snow crabs. I've had a cod puke little baby snow crabs on me (it had been through a lot, the poor cod, so I wasn't mad or anything). And check out this piece of knowledge:

snow crabs (in the orange square) make up a relatively large percentage
of both frequency of occurence (%FO, on the top half of the figure)
and stomach content weight (%W, on the bottom half) compared to
red king crabs and Tanner crabs in Pacific cod stomachs (from this paper)

Interestingly enough, Laurinda's study only saw an inverse relationship between predator abundance and snow crab recruitment in one study area! The rest of the areas had no real pattern. This could suggest that, while cod eat snow crab, there may not be enough predation on their part to be considered a top-down effect on snow crab recruitment. (That's a big statement up in here!) However, she warned us not to be too hasty with this conclusion as predator biomass may not mean direct predation pressure on the crabs.

Moving on, spawning stock biomass in both the Bering Sea and one portion of the North Atlantic study area was inversely related to recruitment. What? More baby-makers mean less babies? Crazy town sea, right? Laurinda posited that since snow crab reproduction relies on not only males and females to be present, but for them to be within each other's vicinity, simply looking at the number of adults may not accurately represent the number of mating adults. There's also the case of cannibalism in snow crabs: more adults mean more cannibalistic mouths to feed!

"Get into my belly!" - large snow crab

The big result was that the main factor associated with snow crab recruitment was the ocean climate. From her paper, "[t]his strongly supports our hypothesis... that cold conditions during early life history stages promote subsequent snow crab recruitment."

the colder the temperature (to a point), the more recruits to the fishery!

Cool! (Get it? wink.) Congratulations on the paper, Laurinda!

Read the full paper:
Marcello, L. A., F. J. Mueter, E. G. Dawe, and M. Moriyasu. 2012. Effects of temperature and gadid predation on snow crab recruitment: comparisons between the Bering Sea and Atlantic Canada. Marine Ecology Progress Series 469: 249 - 261. doi: 10.3354/meps09766

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