The USCG's primary law enforcement authority is derived from 14 USC 89a (below) provided courtesy of the website of law.cornell.edu. I am not familiar with any laws that would require you to open hatches, or count a fish hold, BUT 18 USC 2237 (also below), and other laws, clearly distinguish what crossing the line is.
I monitor USCG very closely when they are aboard our boats - in the interest of damage mitigation from their gear and general inexperience with access on recreational boats. I refrain from further commentary except to say we have been boarded by USCG this year and in 2013.
Separately, what I find interesting is the fact that some STATES have gotten away from boating safety inspections and now require a higher threshold to be met before initiating a stop for an inspection (reasonable suspicion of a crime). Here is a link to some interesting case law:
I try to keep the mindset that the next boat stopped by any law enforcement agency might be the one that is prevented from hurting people/my loved ones because they are intoxicated or feloniously incompetent.
We do the majority of our boating hours in Canada and our enforcement experience there has been very professional.
The references are next :
14 USC 89a
(a) The Coast Guard may make inquiries, examinations, inspections, searches, seizures, and arrests upon the high seas and waters over which the United States has jurisdiction, for the prevention, detection, and suppression of violations of laws of the United States. For such purposes, commissioned, warrant, and petty officers may at any time go on board of any vessel subject to the jurisdiction, or to the operation of any law, of the United States, address inquiries to those on board, examine the ship’s documents and papers, and examine, inspect, and search the vessel and use all necessary force to compel compliance. When from such inquiries, examination, inspection, or search it appears that a breach of the laws of the United States rendering a person liable to arrest is being, or has been committed, by any person, such person shall be arrested or, if escaping to shore, shall be immediately pursued and arrested on shore, or other lawful and appropriate action shall be taken; or, if it shall appear that a breach of the laws of the United States has been committed so as to render such vessel, or the merchandise, or any part thereof, on board of, or brought into the United States by, such vessel, liable to forfeiture, or so as to render such vessel liable to a fine or penalty and if necessary to secure such fine or penalty, such vessel or such merchandise, or both, shall be seized.
(b) The officers of the Coast Guard insofar as they are engaged, pursuant to the authority contained in this section, in enforcing any law of the United States shall:
(1) be deemed to be acting as agents of the particular executive department or independent establishment charged with the administration of the particular law; and
(2) be subject to all the rules and regulations promulgated by such department or independent establishment with respect to the enforcement of that law.
(c) The provisions of this section are in addition to any powers conferred by law upon such officers, and not in limitation of any powers conferred by law upon such officers, or any other officers of the United States.
(Aug. 4, 1949, ch. 393, 63 Stat. 502; Aug. 3, 1950, ch. 536, § 1, 64 Stat. 406.)
18 USC 2237
(1) It shall be unlawful for the master, operator, or person in charge of a vessel of the United States, or a vessel subject to the jurisdiction of the United States, to knowingly fail to obey an order by an authorized Federal law enforcement officer to heave to that vessel.
(2) It shall be unlawful for any person on board a vessel of the United States, or a vessel subject to the jurisdiction of the United States, to—
(A) forcibly resist, oppose, prevent, impede, intimidate, or interfere with a boarding or other law enforcement action authorized by any Federal law or to resist a lawful arrest; or
(B) provide materially false information to a Federal law enforcement officer during a boarding of a vessel regarding the vessel’s destination, origin, ownership, registration, nationality, cargo, or crew.
(1) Except as otherwise provided in this subsection, whoever knowingly violates subsection (a) shall be fined under this title or imprisoned for not more than 5 years, or both.
(A) If the offense is one under paragraph (1) or (2)(A) of subsection (a) and has an aggravating factor set forth in subparagraph (B) of this paragraph, the offender shall be fined under this title or imprisoned for any term of years or life, or both.
(B) The aggravating factor referred to in subparagraph (A) is that the offense—
(i) results in death; or
(I) an attempt to kill;
(II) kidnapping or an attempt to kidnap; or
(III) an offense under section 2241.
(3) If the offense is one under paragraph (1) or (2)(A) of subsection (a) and results in serious bodily injury (as defined in section 1365), the offender shall be fined under this title or imprisoned for not more than 15 years, or both.
(4) If the offense is one under paragraph (1) or (2)(A) of subsection (a), involves knowing transportation under inhumane conditions, and is committed in the course of a violation of section 274 of the Immigration and Nationality Act, or chapter 77 or section 113 (other than under subsection (a)(4) or (a)(5) of such section) or 117 of this title, the offender shall be fined under this title or imprisoned for not more than 15 years, or both.
(c) This section does not limit the authority of a customs officer under section 581 of the Tariff Act of 1930 (19 U.S.C. 1581), or any other provision of law enforced or administered by the Secretary of the Treasury or the Secretary of Homeland Security, or the authority of any Federal law enforcement officer under any law of the United States, to order a vessel to stop or heave to.
(d) A foreign nation may consent or waive objection to the enforcement of United States law by the United States under this section by radio, telephone, or similar oral or electronic means. Consent or waiver may be proven by certification of the Secretary of State or the designee of the Secretary of State.
(e) In this section—
(1) the term “Federal law enforcement officer” has the meaning given the term in section 115(c);
(2) the term “heave to” means to cause a vessel to slow, come to a stop, or adjust its course or speed to account for the weather conditions and sea state to facilitate a law enforcement boarding;
(3) the term “vessel subject to the jurisdiction of the United States” has the meaning given the term in section 70502 of title 46;
(4) the term “vessel of the United States” has the meaning given the term in section 70502 of title 46; and
(5) the term “transportation under inhumane conditions” means—
(i) of one or more persons in an engine compartment, storage compartment, or other confined space;
(ii) at an excessive speed; or
(iii) of a number of persons in excess of the rated capacity of the vessel; or
(B) intentional grounding of a vessel in which persons are being transported.
(Added Pub. L. 109–177, title III, § 303(a), Mar. 9, 2006, 120 Stat. 233; amended Pub. L. 111–281, title IX, § 917, Oct. 15, 2010, 124 Stat. 3021.)