Sunday, November 20, 2011

Northbrook Academy assists NECWA with an ocean sunfish necropsy.

On Saturday, November 5, 2011, Northbrook Academy parents and students helped staff from the New England Coastal Wildlife Alliance (NECWA) examine a dead ocean sunfish that stranded on the shores of Monument Beach. This carcass was recently reported to NECWA’s Ocean Sunfish Stranding Network and the carcass looked as if it was only a few days old.

This ocean fish carcass was missing the majority of its dorsal fin. Since the cut completely severed the top of the dorsal fin, we assume that the injury was the result of a collision with a large vessel. The tissue at the site of the injury was raw and red, indicating that the injury was relatively recent.

Ocean sunfish are the heaviest bony fish in the world and are common visitors to our New England waters, during the summer and fall. These large fish migrate great distances to feed in our cold waters on jellyfish, ctenophores and other gelatinous critters. As winter approaches, ocean sunfish begin their migrations south to spend their winters in warmer, more tropical waters.

Measuring the carcass.

But some individuals become trapped in the arm of Cape Cod. As water temperatures continue to drop, ocean sunfish become cold-stunned and are unable to swim or function normally. Many of these cold-stunned individuals will offshore and wash up on our local beaches.

The death of these beautiful giants is a sad occurrence, but the examination of each carcass provides insights into their biology and ecology. Last year, NECWA responded to over 18 ocean sunfish strandings and now has one of the largest databases on this species. Ocean sunfish that strand alive are pushed back into the water. Those that strand dead are studied and examined in order to further our knowledge of these unique coastal pelagic fish.

One piece of information that NECWA is now able to collect is the total body weight of each carcass. With the help of colleagues David Clapp and Sam McGee, NECWA created a portable weighing tripod that can be broken down and then re-assembled on a beach. Hanging from the center of the tripod is an electronic crane scale that provides an accurate body weight.

Northbrook parent, Chip, and Krill work to secure the carcass.

Northbrook parents and students were instrumental in helping NECWA examine and weigh this carcass. The team first weighed the carcass when it was partially submerged. Fearing that the water was interferring with the collection of an accurate weight measurement, it was decided to relocate the carcass to higher ground and re-weigh this fish.

Team effort in moving this carcass to a better location.

Northbrook Academy students and parents as well as local residents
helping NECWA staff relocate the carcass to higher ground.

After relocating the carcass, the teamed weighed this ocean sunfish once again and we were able to collect a weight of 650 pounds! This is the heaviest ocean sunfish carcass that NECWA has weighed so far using this portable tripod apparatus.

Northbrook Academy parent Chip, Krill and Foster
working on the tripod.

Foster and Jessica helping Krill with the tripod.

Northbrook Academy student Jessica and Lindsay helping out.

Northbrook parents Stuart and Chip helping rig the carcass.

Stuart adjusting the straps on the tripod.

As the team continued their efforts, Belinda experimented with tags in an attempt to find a tag that we could use in the future on live ocean sunfish that NECWA relocates to deeper water. Unfortunately, the dorsal fin of this animal was too thick for the tags that Belinda was using, but even failures like this provide valuable information that will allow us to determine the best tag for this species.

Krill and Belinda experimenting with tags.

Krill and Belinda then worked together to begin the internal examination of this animal. By cutting through the thin skin and then the thick reticulated collagen, they were able to access the reproductive tissues to determine that this individual was a female.

Cutting through the thick reticulated collagen.

Krill trying to locate the sex organ.

Ovary removed from this ocean sunfish.

Ocean sunfish have one gonad (reproductive organ) so they either have one ovary or one teste. The ovary of this fish was quite large and contained thousands of eggs.

Foster examining the whole ovary of this carcass.

Sections ovary.

Sectioned ovary of the ocean sunfish.

Next the team worked together to examine the animal’s internal structures and they determined that this animal was a female. The team also collected a series of tissues, including a section of the vertebra that will be used for aging studies.

As Krill continued examining the internal structures of this animal, Belinda and Foster worked together to remove the large and beautiful eye of this animal.

The eye of this beautiful species.

Belinda and her son Foster
working together to examine the eye.

Examining the eye of the ocean sunfish.

Krill, Belinda and Patty, all volunteer staff members with NECWA, want to thank Northbrook Academy parents and students for their amazing help and assistance. This was truly a team effort and it was one of the most successful necropsies NECWA has accomplished to date. Thanks to Patty from NECWA and Chip Warburton from Northbrook Academy for the amazing photos collected during the necropsy.

Dead ocean sunfish under tripod.
Krill lifting the sunfish with the chain lift.