Occurrence of Pacific bluefin tuna Thunnus orientalis larvae off the Pacific coast of Tohoku area,northeastern Japan: Possibility of the discovery of the third spawning ground

Recently, based on the histological studies it is suggested that Pacific bluefin tuna (PBF) spawns in the Kuroshio–Oyashio transition, off the Pacific coast of northeastern Japan, in addition to the previously identified two spawning areas of the northwestern Pacific around the Nansei Islands and the Sea of Japan. Distributional surveys for PBF larvae have not been conducted in the Kuroshio–Oyashio transition, and thus, we conducted PBF larval surveys at twenty stations in this area in early August 2018 to obtain evidence for the spawning of PBF. Twelve PBF larvae (3.9–7.2 mm in body length) were collected at six stations where sea surface temperature ranged from 27.2 to 28.2°C. Otolith microstructure analysis indicated that age of these larvae ranged from 4 to 11 days after hatching and the larvae hatched in late July. Growth of the collected larvae was comparable to those in the other two spawning grounds. Therefore, PBF spawns, hatches, and at least survives to the postflexion stage, 11 days after hatching in the Kuroshio–Oyashio transition. This fact potentially has a large impact on recruitment processes of PBF if they survive to recruitment in this third spawning ground.     

Characteristics of pyrethroids for insect pest control in agriculture

Pyrethroid insecticides are characterised by high knockdown and lethal activity, a wide spectrum, good residual activity, together with repellent and antifeeding activity. With these characteristics, pyrethroid insecticides have become widely used for plant protection. Their major use has been for the control of bollworms and leafworms in cotton but they have also achieved widespread use for controlling various species of lepidopterous pests in fruits and vegetables, aphids in cereals, and many other minor outlets. Although the early synthetic pyrethroids suffered from a lack of activity against mites and soil pests, later additions, such as fenpropathrin, have combined high acaricidal activity with insecticidal activity and further pyrethroids are being introduced for use in soil. The extent of pyrethroid use has increased progressively since the first of the ‘photostable’ pyrethroids was registered. In 1986, the market share of pyrethroids reached 25 % of the total insecticide market for plant protection; this figure can be increased in the future.