Both international & inland a vessel is "engaged in fishing" when
select one:
a. she is using any type of gear, other than lines
b. she is using fishing apparatus which restricts her maneuverability
c. her gear extends more than 100 meters from the vessel
d. she has any fishing gear on board

(b) she is using fishing apparatus which restricts her manoeuvrability

Explanation:

The explanation is spelled out in Rule 3(d) of the inland and water ways  laws that state that: A vessel engage in fishing is one whose fishing apparatus restricts manoeuvrability. I f the fishing gear does not hamper her movements, then she is engage in fishing. The rules state categorically that a troller  with hook-spangled lines following in her wake is not restricted by her gear. Rule 3(d) might appear to be splitting hairs, but it has a point to make. Although a vessel might not be hampered as to be unable to keep clear of others, her fishing gear could still make following a script difficulty