Mission: Shark Longline Survey
Geographical Area: Southern Atlantic/Gulf of Mexico
Date: August 3, 2011
Weather Data from the Bridge
Latitude: 32.50 N
Longitude: -079.22 W
Wind Speed: 17.75 kts
Surface Water Temperature: 28.60 C
Air Temperature: 29.90 C
Relative Humidity: 71%
Barometric Pressure: 1009.06 mb
Science and Technology Log
One reason the shark longline survey exists is because the populations of many types of sharks are in decline. There are several reasons for this – finning is one reason. “Finning” is the process where the shark’s fin is removed from the rest of its body. Since usually only the fin is desired, the rest of the body is discarded. Shark fins are used for things like shark fin soup – a delicacy in Asian cultures. When the fin is cut off and the rest of the body stays in the water, the shark can not swim upright and eventually dies. While some regulations have been passed to prevent this, shark finning still occurs. Sharks are also overfished for their meat. As a result many shark species have become vulnerable, threatened or endangered. Large sharks can take longer to reproduce. Therefore, they are more likely to be threatened or decline in their numbers.
Sharks are at the top of the food chain. They keep prey populations in control, without which the marine ecosystem would be unstable.
This is why the mission of the shark longline survey is important. The identification tags and roto tags used during this survey along with the data collected will help scientists assess the abundance of species in this area. They can then provide recommendations for shark management. On average, we are collecting data on 10 sharks per line (or 10%), although our catch rates are between 0% and around 50%. With 50 stations in all, that would be data on approximately 500 sharks (on average).
There are more than 360 species of known sharks. Below is a list of some that we have seen and measured during our survey. The IUCN red list (International Union for Conservation of Nature and Natural Resources) classify these sharks with a status:
Atlantic Sharpnose Shark – Least Concern
Blacknose Shark – Near Threatened
Silky Shark – Near Threatened
Tiger Shark – Near Threatened
Lemon Shark – Near Threatened
Dusky Shark – Vulnerable
Sandbar Shark – Vulnerable
Scalloped Hammerhead – Endangered
During my shift, we sometimes catch things we do not intend to catch. We might reel in fish or other sea creatures that get caught on the hooks. This is called “bycatch”. While everything is done to try to catch only the things we are interested in studying, bycatch occasionally happens. The fish are only on our line for 1 hour, so their survival rates are pretty good. Our bycatch data is a very important element and also contributes to management plans for a number of species like snappers and groupers.
Just the other day, we caught a remora (a suckerfish that attaches itself to a shark’s side). Remoras and sharks have a commensalism relationship – the remora gets leftover food bits after the shark eats, but the shark gets no benefit from the remora. We quickly took down its measurements in order to get it back into the water quickly. Other bycatch included an eel, and black sea bass.
We also caught a red snapper. Our chief scientist, Mark, showed me the two small, tiny ear bones called “otoliths” in the snapper’s head. These bones provide the fish with a sense of balance – kind of like the way our inner ear provides us with information on where we are in space (am I upside down, right side up, left, right?). You can tell the age of a snapper by counting the annual growth rings on the otoliths just like counting growth rings on a tree.
My experience aboard the Oregon II has given me a better understanding of the vulnerability of some shark species. While many of us may think that sharks can be threatening to humans, it is more accurate the other way around. Sharks are more threatened by humans than humans are threatened by sharks. This is due to our human behaviors (mentioned above).
Today I saw dolphins following our boat off the bow. There were about 6 or 7 of them all swimming together in a synchronized pattern (popping up for air all at the same time). It was really quite a treat to watch.
I’m also amazed by the amount of stars in the sky. With the lights off on the bow, you can really see a lot of stars. I was also able to see the milky way. There have been many storms off the horizon which are really cool to watch at night. The whole sky lights up with lightning in the distance, so I sat and watched for a while. With tropical storm Emily coming upon us, we may have to return to port earlier than planned, but nothing is set in stone just yet. I hope we don’t have to end the survey early.
Species Seen :
Black Sea Bass
Atlantic Spotted Dolphins