Last Friday morning, James Powell from NOAA, and a grad school researcher named Nora Sturgeon arrived on the 10:00 boat with a cooler and a lot of equipment. A small crowd gathered at the North Beach to observe the necropsy. It was like CSI Dewees. In the group of Dewees observers, there were several people with professional interests in the experience: a dolphin researcher, an retired inhalation toxicologist, and an NIH researcher, as well as various students and people who poke dead things with sticks.
Between James and Nora, they were able to do their work and explain their procedures and some fascinating facts to us. SC gets 40-50 stranded marine mammals per year; 80% of which are bottlenose dolphins. Humans contribute to dolphin mortality– rope entanglements are a major cause of death, as well as boat collisions, net entanglements, and plastic ingestion.
It turns out that there are two distinct populations of Atlantic Bottlenose dolphins in our area; resident river dolphins who stay in our inland coastal waters and just offshore, and offshore migrants who regularly pass through our areas. The populations don’t really mix with one another, don’t mate with other or produce offspring, and don’t even eat the same food. For now, they are viewed as the same species, but since they are so different (and genetically separate) they may eventually be classified as different species. James takes some measurements and samples for further testing.
This was a fairly young dolphin, because the teeth are clean and sharp. James and Nora will take teeth back to the lab for samples. Because of the delay in being able to examine the carcass, any various toxins may not be able to be measured accurately, due to the fact that they begin to leach out of the body at death. An interesting toxin fact: Toxins bioaccumulate in the food chain, with greater concentrations occurring in top predators. In female dolphins, an interesting thing happens: once they have their first calf, their levels of toxins drop off sharply. It seems they “offload” toxins, mostly through breast milk, which is produced by using stores of fat in the body where toxins accumulate. This leads to higher mortality in firstborn offspring. While there is no official calving season in our local dolphins, there is a higher infant mortality rate in October and April, leading to a sense that there is a peak in calving activity during those times.
This is a male dolphin– with decomposition and bloating, the physiology is now visible. If it were a female, there would be mammary slits on either side of the genital area. The researchers insert a temperature probe to determine the internal body temperature, which will help gauge the level of decomposition they can expect inside.
After alerting observers to stay out of the “splash zone,” James and Nora began the real work of dissection, peeling away the ribs one by one to check for breakage and expose the thoracic cavity, obtaining a cross-section of the lungs and extracting several lungworms to take back as samples, collecting muscle tissue samples to check for viruses and skin samples for genetic analysis.
James was incredibly patient with all of our questions, working professionally and quickly with Nora and answering us with articulate, informative explanations. I think we all came away with an increased understanding of the threats facing dolphins in the ecosystem and the complex challenges scientists face as they try to understand and explain dolphin strandings in our area.