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 26, 2017
Weather Data from the Bridge
13:00 hours
28°12.1’ N 89°23.8’W
Visibility 6 nm, Haze
Wind 15 kts 170°E
Sea wave height 4-5 ft.
Seawater temp 23.4°C
Science and Technology Log
The ship has completed our deep-water sampling and we are now headed to more shallow areas, where there are likely to be more sharks and hopefully even some that have been tagged in the past. With each shark we catch, we record in a database their measurements and exactly where they were caught. If things are going well with the shark out of water, we also take a fin clip, a blood sample, and attach a tag.
Tag-and-recapture is one way for wildlife biologists to estimate population size. You can compare the number of tagged sharks to newly caught sharks, and then extrapolate using that ratio to the total number of sharks in the area.
Recapturing a tagged shark also helps scientists determine the age of a shark, as well as its rate of growth. In bony fish, it is possible to examine the otoliths (bony structures in the ear) to determine the age of a fish. However, since sharks do not have bones, scientists must use other ways to determine their ages and track their growth. One of the scientists on board (my roommate) is collecting shark vertebrae so that her lab can use growth rings in the vertebrae to assess their age, sort of like counting the rings on a tree stump.
Personal Log
The past few days have put all my seasickness remedies to the test with waves over 6 feet and plenty of rolling on the ship. The good news is that they have been working pretty well for the most part – I’ve only lost my lunch once so far! One “cure” for seasickness is to stay busy, which has been difficult to do because the high winds and lightning have made it unsafe to do any sampling.
Fortunately, the crew’s lounge is well-stocked with movies, so I have watched quite a few while we wait for the waves to calm down and the thunderstorm to pass. The lounge has some cushioned benches long enough to stretch out on, which is key because being horizontal is the best way for me to minimize my seasickness.
Kids’ Questions
- How do you put the tag on?
Data collection sheet and shark tagging tool.
The tag for smaller sharks is a bit like a plastic earring, but on the shark’s dorsal fin. First you have to “pierce” the fin with a tool like a paper hole-punch, and then use another tool to snap in the tag — making sure that the ID numbers are facing out. If the shark is a species that will outgrow a plastic roto tag, they get a skinny floating tag inserted just under their dorsal fin.
- How does the tag stay on the shark?
The shark heals the wound made by the tag, and the scar tissue holds the tag in place. Because the tags are made of plastic and stainless steel, they do not rust or deteriorate in the ocean.
- How do they make the tags?
The NOAA fisheries lab orders tags from manufacturing companies, and are similar to tags used on domestic animals like cows. Each tag includes a phone number and the word “REWARD,” so that if fishermen catch a tagged shark they can report it.
- What are they doing with the shark tagging data?
Tagging the sharks in the Gulf of Mexico allows us to figure out how fast they are growing and how far they are traveling. Measuring all the sharks also helps scientists understand how the populations of different species might be changing. Some clues to changing populations include catching smaller or fewer sharks of one species.
