Friday, September 4, 2015

New Study Shows Female Blue Crabs Spawn in the Ocean in Southeast US

Long thought to spawn at the mouths of bays and rivers, we're now finding out that blue crabs spawn in the ocean in some places. My latest research, highlighted in Coastal and Estuarine Science News,  shows that many or even most female blue crabs spawn in oceans waters in the Southeast US. Off the coasts of Georgia and South Carolina, female sponge crabs like the ones in the photo are found at least as far as 8 nautical miles from shore. Other researchers in Louisiana have found female blue crabs even further from shore (read more here).

Why are they going to the ocean to spawn? It's most likely that they are just looking for the salty water (salinity >25) that their larvae need to survive and grow during the first month or two of life. In places like Chesapeake Bay and Delaware Bay, these salty conditions occur within the bay mouth. In much of the Southeast US and Gulf Coast, the same conditions occur mainly in the coastal ocean.

We've known for some time that blue crab larvae spend part of their first months in the ocean where temperature and salinity are relatively constant. Now that we know there are important spawning grounds in the ocean, we need to take a closer look at how many females are there and what they are doing.

The new study also notes a substantial decline in abundance of females in offshore areas since at least 1986. Understanding what this means will be important for ensuring sustainable crab fisheries throughout the Southeast US.

Here's a link to the scientific paper in Estuaries and Coasts.