The Northern spearnose poacher (Agonopsis vulsa, also known as the Window-tailed sea-poacher or the Windowtail poacher) is a fish in the family Agonidae (poachers). It was described by David Starr Jordan and Charles Henry Gilbert in 1880, originally under the genus Agonus. It is a marine, temperate water-dwelling fish which is known from the eastern Pacific Ocean, including southeastern Alaska to southern California, USA. It dwells at a depth range of 0 to 163 metres (0 to 535 ft). Males can reach a maximum total length of 20 centimetres (7.9 in).