By Guest Bloggers Cassie Pardee and Diona Drake
Here we present another update from project SE1503 aboard NOAA ship Oscar Elton Sette performing fisheries oceanographic research in the Mariana Islands (11-27 June 2015).
We have been trapping from the Sette with lobster pots, minnow traps, and a BIG trap around most of the archipelago, to supplement the trapping survey being done by the small boat team. Each morning we are never sure what we are going to pull out of the water. We are targeting relatively deep 50-125m soft-bottom areas using the best available mapping information, ship sounders, as well as a small Ponar bottom grab to assist in placing our gear in those areas with unconsolidated substrate (http://youtu.be/gfJqcSpTOSQ). Surprisingly, we are bringing up a more than a few sharks. We are surprised because the small openings in our traps would have seemed to be an effective deterrent to shark bycatch. The most common species being captured include white tip reef sharks (Triaenodon obesus), gray reef sharks (Carcharhinus amblyrynchos), and nurse sharks (Ginglymostoma cirratum). The gray reef and nurse sharks have all been brought up in the giant fish trap (Figure 1). Some of the sharks are so wide, we can hardly believe that they could fit through the trap opening. The white tip reef sharks really love the little, black lobster pots which have even smaller openings and less space. We have even brought up two sharks in one pot a few times (Figure 2), and once three white tips were jammed into a single lobster pot. All of the sharks are released alive once they have been quickly measured, photographed, and two non-invasive fin clips are taken from their dorsal fins for genetic analysis (Figure 3).
During our daytime BIG trap deployment we have been attaching GoPro and FlyWire cameras to the outside and the inside of the trap to see bottom type and what is really going on after we lose sight of the trap. The video footage has been very revealing. Sometimes we will bring up an empty trap and then watch video footage to see fish swim in and then back out of the trap, or watch as sharks and sting rays try repeatedly to enter the trap but are too big to fit through the opening. We have captured video images of garden eels (http://youtu.be/BuJmBKAVRO4), tiger sharks (https://youtu.be/HnirPxNu-Fk), huge sting rays (https://youtu.be/0Vh-oCiaqlU), giant hermit crabs (http://youtu.be/IxxN3InCGgQ), schools of juvenile fishes (https://youtu.be/3s_zIJvuWh0), and various other fish species (some cunning enough to swim in and out of the trap). The video footage exposes a whole new aspect to how the trapping process works and gives us the opportunity to see other species in the area that were too smart (or too big or too small) to get caught in our traps. We also tried collecting some video during the night (http://youtu.be/YZpHLdxJ2zo). While our trapping work is part of a broader ecosystem survey, the findings will feed into a better understanding of how fishing gear operates. The mechanics of the capture process are often overlooked, yet are a key component of fishing gear efficiency and fishery stock assessments that rely on data from fishing gear.
Figure 1. Nurse shark and gray reef shark brought up in the BIG trap.
Figure 2. Two white tip reef sharks being released from a lobster pot.
Figure 3. A white tip reef shark being released after measurement and fin-clips.