My first source would be the actual management plan that was set in place by the US Dept of Fish and Wildlife for the refuge - the relevant sections are below.
Second source would be the writing on the morning balls - DAY USE ONLY
Third source is the DPNR meeting that I attended in San Juan last month.

Culebrita, Luis Pena and the adjacent cays are all inside the refuge boundaries.


The Commonwealth will inspect and oversee development
and management activities on the lands conveyed to them on Culebrita. The Commonwealth agrees to enforce
the land use restrictions as outlined in this Cooperative Management Agreement.
III. OPERATIONAL PROCEDURES
The Commonwealth will comply with the following opera
tional procedures:
1. Only daytime use (1/2 hour before sunrise to
1/2 hour after sunset) shall be permitted on
beachfront areas and use will be restricted to
hiking, picnicking, swimming, and similar recre
ational activities. These beachfronts have been
identified as essential habitat for the hawksbill
turtle and as such must receive full and absolute
protection in accordance with the provisions of
the Endangered Species Act of 1973, as amended,
and the laws of Puerto Rico. Human disturbance
such as, but not limited to, nest robbing, inter
ference with the progress of the young in reaching
to such an extent as to significantly disrupt
essential behavioral patterns, which include,
but are not limited to, breeding, feeding, or
sheltering; significant environmental modifica
tion or degradation which has such effects is
included within the meaning of "harm;" (CFR 50,
Chapter I. Part 17.3).

2. Boats shall not be anchored in the intertidal
zone or left on beachfronts during nighttime
hours (1/2 hour after sunset to 1/2 hour before
sunrise).