Friday, March 2, 2012

Donation of South Bay Technology Saw for Ocean Sunfish Aging Research

Donation of Low Speed Wheel Saw for Ocean Sunfish Aging Research

NECWA would like to thank Mark E. Goodrich, President of E. McGrath Inc., for the very generous donation of a used Low Speed Wheel Saw. NECWA was in great need of this precision saw for our ocean sunfish aging research. This saw will be used to cut the vertebrae collected from dead ocean sunfish that wash ashore on our Cape Cod beaches each fall. It is hoped that once the vertebra are cut, the bands on the centrum surface can be used to determine the age of this very large and unusual looking fish.

Photo courtesy of Greg Skomal

Krill and her son Jamie went to meet Mark at E. McGrath Inc. in Salem and pick up the donated saw. Mark showed them around the buildings and discussed proper operation of the saw and possible blades that would be appropriate for cutting the bones of ocean sunfish. This donation is very important to the research that NECWA is attempting and we are sharing our results with other researchers in the United States and abroad.

Ocean sunfish migrate north each spring to feed in the cold waters of the Gulf of Maine. We typically start seeing young ocean sunfish move into our coastal waters in August as they move closer to shore to feed on jellyfish, ctenophores and other gelatinous critters. As fall approaches and water temperatures drop, the majority of ocean sunfish start migrating south to warmer, more tropical waters.

However, some individuals get caught in the arm of Cape Cod and become trapped by the physical features of the Cape itself. These unfortunate individuals are unable to continue their journey south and get stuck in our harbors and bay areas. As water temperatures continue to drop, these animals become cold-stunned and wash ashore on Cape beaches.

NECWA maintains a stranding response team that tries to rescue live animals that are coming ashore. If the animals wash ashore dead, then we perform a necropsy (animal autopsy) on the carcass and collect tissue samples for further analysis.

NECWA staff members Krill, Tammy, and Belinda have been working on an aging study for ocean sunfish. This research has been conducted in conjunction with Tracey Alleyne-Greene who is a student at Bridgewater State University and is working under Dr. John Jahoda.

Unlike other bony fish, ocean sunfish lack well-developed otoliths or "fish ear bones." These structures are consist of three pairs of small carbonate bodies found in the head of bony fish and function in hearing and gravity perception. These abilities are very important to any fish that moves throughout a three-dimensional water column. The image below shows one pair of otoliths that were collected from a cod.

Otoliths are typically used by fisheries biologists for aging purposes. Not only do ocean sunfish lack developed otoliths, but the skeleton of those animals that wash ashore on our Cape beaches each fall is reduced in complexity and is comprised of a porous bony material. Perhaps this is because the ocean sunfish in our area are young animals (as determined by size only) and therefore, their bones have not fully developed.

The images below show the entire otolith of an ocean sunfish. The second image is a close-up of the first image.

The image below shows a sectioned otolith that has been magnified and photographed.

Since we were not able to use otoliths to age ocean sunfish, the NECWA team decided to try an aging technique used by fisheries biologists who study cartilaginous fish, such as sharks, skates are rays. This aging technique involves examining and often sectioning the vertebrae to examine the banding pattern in the centrum or center face of the structure. It is assumed that each band pair, made-up of a light band/dark band combination, represents one year of growth for the individual.

We are still trying to work out a suitable protocol that will allow us age ocean sunfish using this vertebral banding pattern. And at present, we are not confident that this method will work for this pelagic species that seems to migrate to stay within a narrow temperature range. These types of ups and downs, curves and dead-ends, are all part of science and the scientific process of discovery. Although it can be frustrating at times, we are committed to this research and are loving the adventure.