This experiment’s purpose was to see the different types of harm caused by circle hooks versus straight hooks when catching blue fin tuna.
A third of the tuna were deep-hooked, resulting in horrendous injuries:
THIRD OF TUNA DEEP-HOOKED
"34% of the fifty bluefin tuna caught on straight hooks were deep-hooked."
HOOKS IN STOMACH, GILL ARCHES, PHARYNX, LIVER
"One age-4 fish had a circle hook protruding through the lumen of the anterior stomach. The exposed hook point ripped tissue that supports viscera in the abdominal cavity and caused internal bleeding."
"An age-1 fish had a circle hook that lodged between two gill arches in the pharynx and caused extensive bleeding from gill filament damage."
"In most instances where hooks penetrated the abdominal cavity, tissues and blood vessels supporting viscera were damaged. Hooks positioned close to the transverse septum with the point lacing anteriorly would often tear the septum and sever the hepatic¹ veins leading to the sinus venosus. Hooks positioned closer to the pylorus² were observed to damage the anterior liver lobe."
SCRAPING OF FACIAL TISSUE
"Large hooks embedded in the jaws of age-1 fish could result in scraping of facial tissue.... Nine of the 25 fish caught in the jaw with circle hooks larger than 10/0 had external damage caused by the hook point and barb."
HOOK IN EYES AND BLINDING
"In two of these cases, the hook point caused severe damage to the eye socket."
"It was observed that these relatively smaller tuna (2-5 kg) did not easily swallow the larger hooks, but could still experience extensive damage anterior to the gut (gill filaments and eye socket)."
"Eye socket damage found in three of the bluefin sampled (two circle, one straight), could cause blindness, thereby impacting feeding and potentially causing mortality."
¹ hepatic = pertaining to or affecting the liver
² pylorus = small circular opening between the stomach and the duodenum