Ocean Sunfish Necropsy on December 5, 2010

This afternoon, Krill, Leah and Nick traveled to the Cape to find a dead ocean sunfish that had stranded on Mants Beach in Brewster, MA. One of the local residents, Kathy, called the IFAW Marine Mammal Rescue Program to report this animal and they passed the information along to NEBShark, the community-sighting network for basking sharks and ocean sunfish that is maintained by NECWA.

Bob Prescott, Director of Wellfleet Bay Wildlife Sanctuary had also come across this carcass the night before as he was conducting night patrols for cold-stunned sea turtles. Bob reported back to Krill that this carcass was quite large, in fact, one of the largest he has seen. And he was right!

When the NECWA team arrived on site and found the carcass just below the high tide line, no one could believe just how big this animal really was. From tip of snout to tip of tail, this carcass was close to 8 feet in length. This is the largest ocean sunfish carcass that has been examined by NECWA staff since the NEBShark program began in 2005.

Not only was this a large ocean sunfish for the area, but the carcass was relatively fresh indicating that the animal had recently died in the waters of Cape Cod Bay. Hard to image that a more tropical-loving fish can continue to reside in our cold northern waters as winter approaches.

Many of the local residents came down to the beach and chatted with the NECWA team. Many had questions about the life history of this unique and unusual animal and its occurrence in our cold New England waters.

But we believe that the ocean sunfish stranding on our Cape beaches in the fall have missed the thermal cues that should have sent them migrating south to their warmer wintering grounds. Just like the sea turtles who become trapped inside Cape Cod Bay and become cold-stunned as Bay water temperatures continue to drop , these large fish can't seem to function in extreme cold waters.

This was Leah's first necropsy of an ocean sunfish and she was amazed at the size of the animal and the beauty of this marine creature. She helped Nick collect the external body measurements that will be included in the NEBShark database and she helped with the necropsy by focusing on the examination of the sex organ.

Because of the size and general health of this animal, it was very difficult cutting through the thick layer of reticulated collagen that measured over 10 cm in most areas. But when Krill and Leah extracted the ovary, they couldn't believe just how large in size it was.

It took the team almost 4 hours to conduct a Level A examination followed by a modified necropsy were the animal was sexed (female) and the vertebrae was collected for future age determination studies. Everyone was cold and hungry so off they headed to Hyannis for a quick meal before heading home.