1. What does it mean?
어장관리 literally means managing a fishing ground. In dating slang it accuses someone of giving several people enough hope to keep them attached while avoiding a clear relationship.
Also written or said as eojanggwalli
2. The nuance
It is an accusation about intent, not a fact established by friendliness alone. Dating nonexclusively with everyone's understanding is different from misleading someone about a commitment.
3. Examples
“친절하다는 이유만으로 어장관리라고 단정할 수는 없어.”
You can't conclude someone is stringing people along just because they're friendly.
“관계가 애매해서 어장관리인지 추측하기보다 직접 물어봤어.”
The relationship felt unclear, so I asked directly instead of guessing whether I was being strung along.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.