Monday, May 2, 2011

Baby boom

I can track the search words people use when coming to Snow Crab Love and saw the question:

How many babies can a snow crab mother have?

Ahahaha! I love this kid's expression!
(picture from here)

I feel bad that the reader didn't get the answer they were looking for, so here goes:

Conan et al. (1989) estimated that snow crab females can produce between 31,000 and 90,500 orange eggs in one clutch. The top number drops slightly, to 88,800, when considering brown eggs (embryos that are further along in development) due to egg loss. (Read about the different colors of development here.)

eyed snow crab emryos attached to their mom

Similarly, Comeau et al. (1999) estimated 88,500 brown eggs within a large (85 mm carapace width) female's clutch, and for smaller females (55 mm carapace width) they estimated 31,500 eggs. Their study showed that fecundity for female snow crabs is positively correlated with carapace width (or size), which isn't too shocking. The egg estimations were based off of subsamples of clutches that were back-calculated to get the full clutch number (using a ratio of dry weight of 250 sampled eggs to the dry weight of the full clutch). Their study differed in that they thought large females may start out with as many as 116,000 orange eggs! This difference suggests greater egg loss during development.

full uneyed snow crab clutch = THOUSANDS of potential baby crabs

Females may lose eggs within their clutch due to some eggs remaining unfertilized, developmental problems, predation, or parasitism. Loss due to unfertilized eggs is why I'm concerned with male snow crab gonads: we want to make sure each male is giving the females he mates with enough sperm to fertilize at least one whole clutch.

These estimates don't include loss after hatching due to predation, cannibalism, and other problems (which accounts for a huge proportion of snow crab mortality), but this should give you an idea of how many babies a female can produce.

Fecundity Findings:
Comeau, M., M. Starr, G. Y. Conan, G. Robichaud, and J.-C. Therriault. Fecundity and duration of egg incubation for multiparous female snow crabs (Chionoecetes opilio) in the fjord of Bonne Bay, Newfoundland. Canadian Journal of Fisheries and Aquatic Sciences 56: 1088 - 1095.

Conan, G. Y., M. Moriyasu, D. R. Maynard, and Y. Chiasson. 1989. Factors influencing egg production in decapod Crustacea with two case studies: Chionoecetes opilio and Homarus americanus in the Gulf of St. Lawrence. ICES CM 1989/Mini 04.

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