Emily Sprowls: Shark Bait, March 28, 2017

NOAA Teacher at Sea

Emily Sprowls

Aboard NOAA Ship Oregon II

March 20 – April 3, 2017

 

Mission: Experimental Longline Survey

Geographic Area of Cruise: Gulf of Mexico

Date: March 28, 2017

 

Weather Data from the Bridge

RedSnapper

Red snapper (Lutjanus campechanus)

13:00 hours

29°09.3’ N 88°35.2’W

Visibility 10 nm, Scattered clouds

Wind 8 kts 170°E

Sea wave height <1 ft.

Seawater temp 22.9°C

 

Science and Technology Log

In addition to experimenting by sampling deeper, we are varying the fishing gear and using different kinds of bait. We have switched to hooks on a steel leader so that even a strong, big shark cannot bite through the line. We are rotating through squid and mackerel as bait in order to see which species are more attracted to different bait. In addition to many species of sharks, we have also caught and measured eels, large fish and rays.

Nick hooks

Nick prepares hooks for longline gangions.

One of the scientists on board specializes in fishing gear, and helps keep maintain all our gear after it gets twisted by eels or looped up on itself. He also works on turtle exclusion devices for trawling gear.

 

Personal Log

Last night the line pulled in a huge tangle of “ghost gear.” This was fishing line and hooks that had been lost and sunk. It would have been much easier to just cut the line and let the mess sink back to where it came from, but everybody worked together to haul it out so it won’t sit at the bottom tangling up other animals.

Ghost gear

Lost or “ghost” gear that tangled in our lines.

This is just one example of the dedication the scientists and crew have to ocean stewardship. I have been so impressed by the care and speed with which everybody handles the sharks in order to get them back in the water safely.

 

Kids’ Questions

  • Is there any bycatch of dolphins?
Deep seastar

A few seastars come up with uneaten bait as bycatch.

Today we saw dolphins for the first time! They were only a few of them pretty far from the boat, so they did not affect our sampling. Had they decided to come play by riding in our wake, we would have postponed our sampling to avoid any interactions between the dolphins and the gear. One of the reasons that we only deploy the fishing gear for one hour is in case an air-breathing turtle or mammal gets tangled (they can hold their breath for over an hour). However, since dolphins hunt live fish, they don’t try to eat the dead bait we are using.

  • Can sharks use echolocation? How do they find their food?

Sharks do not use echolocation like marine mammals, but they do have an “extra” sense to help them find their food. They can detect electrical current using special sense organs called ampullae of Lorenzini.

  • What are the chances of getting hurt? Why don’t they bite?

While there is a chance of the sharks accidentally biting us as we handle them, we are very careful to hold them on the backs of their heads and not to put our fingers near their mouths! “Shark burn” is a more likely injury, which occurs when a shark wiggles and their rough skin scrapes the person handling them. Sharks do not have scales, but are covered in tiny, abrasive denticles that feel like sandpaper.

 

 

 

Dena Deck, July 20, 2006

NOAA Teacher at Sea
Dena Deck
Onboard NOAA Ship Hi’ialakai
June 26 – July 30, 2006

Mission: Ecosystem Survey
Geographical Area: Central Pacific Ocean, Hawaii
Date: July 20, 2006

Science and Technology Log

Because of their remoteness, the largely uninhabited, and dynamic ecosystems of the Northwestern Hawaiian Islands are often thought of as pristine environments. A more accurate term is “near-pristine,” because this isolated archipelago acts as a giant filtering comb in the middle of the Pacific Ocean, picking up debris that float from afar. Signs of trouble are not immediately apparent to the casual observer, but a closer look reveals ghost nests (discarded or lost fishing nets) caught on the reefs, debris of all sorts on the beaches, and plastics inside the skeleton of albatrosses. Even here, pollution has left its mark. But it is not an indelible mark, and there are devoted groups working hard to erase it from the map of the Northwestern Hawaiian Islands.

The majority of the debris that accumulates on these islands is fishing gear, and lots of it. In addition to destroying the coral upon which it settles, derelict fishing gear can also cause entanglement for the highly endangered Hawaiian monk seal, the threatened green sea turtle, fish, invertebrates, and seabirds.

The Northwestern Hawaiian Islands are in the path of the North Pacific Subtropical Convergence Zone, which stretches from Japan to the West Coast of the US. This zone is a large, shifting line that is the product of ocean currents and wind interactions where areas of the surface waters meet. The convergence of different water masses result in the aggregation of trash, being carried by each water mass and deposited along this zone. The subtropical convergence zone can actually be observed from a thousand feet in the air as a semi-continuous line of trash, earning its nickname as “East Pacific Garbage Patch.”

The group charged with the removal of these pieces from these remote atolls and islands is the Marine Debris Project, part of the Coral Reef Ecosystem Division, under the NOAA Fisheries, Pacific Islands Fisheries Science Center. The group recently completed a large-scale project over the course of the last five years (which just ended in 2006) to remove as much of the derelict fishing gear in the Northwestern Hawaiian Islands as possible. Going out on missions stretching up to four months at a time, two liveaboard mother vessels would carry eight divers each. As the seasons change, the subtropical convergence zone can be observed performing an annual dance in the North Pacific Ocean ballroom. When in the winter this line shifts south and passes the Northwestern Hawaiian Islands around January and February, the large, fractured atolls become a giant comb, trapping these floating debris from all around the North Pacific rim. During the summer, this convergence zone shifts north again.

After reaching a predetermined location, the Marine Debris Project has two methods for covering an area. In shallow reef areas, they snorkel, with the boat nearby. In deeper areas, they do “towboarding,” which involves a small board attached to the boat, which is running on average of between 1-2 knots. Inhaling deeply, and with a quick maneuver of the board, the free diver pairs can then go to the bottom, covering it in a serpentine fashion. Each diver covers a transect of 7.5 meters apiece, checking both sides of this transect while staying within visual range of the divers on either side. The distance among divers varies according to the visibility, but it’s never more than 15 cumulative meters, or approximately 45 feet, between the combined diver pair.

One of the initial efforts undertaken in 1999 at Lisianski Island and Pearl & Hermes Atoll recovered 14 tons of derelict fishing gear. Most of this gear came from trawl netting, followed by mono-filament gillnet, and maritime line. This effort also showed this gear to affect the coral reef ecosystem of the Hawaiian Archipelago (Donnohue et al., 2001). To ensure that the whole swath is observed, divers take a daily visibility measurement by placing a small piece of net underwater, and determining from how far away this net can be seen. Surveys are then conducted, with a slight overlap among each swath to ensure full coverage. When derelict debris is found, they release the board, go to the surface, and raise their hand. At this point, the towing boat turns back, obtain latitude and longitude with a GPS unit, and help the diver retrieve the fishing gear.

The Marine Debris Project, having completed their focused clean up activities on the Northwestern Hawaiian Islands, has now entered into a maintenance phase. This will help them estimate the accumulation rates at repeated zones, which will allow them to determine the frequency of future clean up efforts, and the amount of funds needed. All of this to ensure that trash does not become constant stain in an otherwise vibrant and healthy environment. Since 2002, about 200,000 lbs of net have been recovered this way each year. Many of these pieces can be retrieved by one or two divers, but occasionally a particularly large net is found. One particular net had a weight in excess of 5,000 lbs, and took all divers working together to cut it into sections and pull it out of the water. Over the years, the group has found sharks, sea turtles and monk seals trapped in these nets. One even had a portion of a whale’s spine, apparently having caught the animal in the high seas.