Chinese fishing boats have pierced deep into North Korean waters in recent weeks, ship tracking data shows, as China’s coast guard appeared to turn a blind eye to the likely illegal expeditions.

According to automatic identification system (AIS) data from MarineTraffic, Chinese fishing boats entered North Korea’s exclusive economic zone (EEZ) hundreds of times over the past several weeks, likely in search of high-quality seafood before China’s annual summer fishing ban goes into effect.

AIS refers to a collection of ship-based radios, ground stations and satellites that provide vessel locations and other