Depredation of purpleback flying squid (Sthenoteuthis oualaniensis) on tuna caught by gillnet fisheries in the Northern Arabian Sea: a major cause of concern for fishermen

Major concentrations of purpleback flying squid  (Sthenoteuthis oualaniensis) are known in the Arabian sea and other parts of the Indian Ocean. This squid is considered to be important part of the diet of  tuna species in the area especially in the mesopelagic zone it constitutes a  major part of the diet of tuna species. A very few cases of depredation by cetaceans and sharks were reported from tuna gillnet fisheries of the Arabian Sea, however, oceanic squid (Sthenoteuthis oualaniensis)  are  observed to be heavily depredating on tuna caught in the gillnets especially in the Pakistani offshore waters. Tuna fleet that operates in offshore waters during winter (December to March) reported heavy depredation by purpleback flying squid. Although depredation by squid is reported throughout the year but such instances are more frequent and intense during full moon period in winter months. In case of cloud overcast during full moon period the intensity of depredation is reduced which tends to indicate that the purpleback flying squid  (Sthenoteuthis oualaniensis) have diurnal vertical migration or visually attack the prey by locating them enmeshed on the gillnet. The paper present information about depredation of purpleback flying squid  as reported by observers under WWF-Pakistan’s Crew Based Observer Programme