a boat sets a gillnet
NOAA Fisheries

Gillnets are large walls of netting that are set at the bottom of the ocean. When fish swim into the net webbing their heads become stuck—if they try to move forward the gap is too small to fit their full body, and if they try to move backward their gills get caught on the webbing. This type of net is usually used to catch salmon, ground fish, and tuna (among other fish). Large marine animals like seals are particularly susceptible to becoming caught in this type of fishing gear.

Tags: Fisheries