ALARCON, Circuit Judge:
In Balelo v. Klutznick, 519 F.Supp. 573 (S.D.Cal.1981), plaintiffs-appellees, who are captains of tuna purse seiners (hereinafter the Captains), instituted this action against defendants-appellants (hereinafter the Secretary) seeking declaratory and injunctive relief.1 The district court granted a declaratory judgment invalidating subsection (f) of regulation 50 C.F.R. § 216.24 (1981) promulgated by the Secretary of Commerce2 pursuant to the Marine Mammal Protection Act (hereinafter MMPA), 16 U.S.C. § 1371.
Under the regulation, the Captains are permitted to take porpoise during commercial fishing operations only if they comply with certain conditions.3 They must allow government observers to board and accompany the vessel on regular fishing trips “for the purpose of research or observing operations.” 50 C.F.R. 216.24(f). The regulation further authorizes the collection of data which may be used in MMPA enforcement proceedings. Id. The district court ruled that the regulation was unconstitutional only insofar as it permitted the use of observer collected data in MMPA enforcement proceedings.
In United States v. $50,178.80, the Monetary Value of 57 Tons of Tuna and Gladiator Fishing, Inc., Cv. No. 79-4466-LEW (MX) (C.D.Cal. April 21,1982), a civil forfeiture proceeding, the district court denied a motion to suppress evidence of observer collected data.
We have taken these matters en banc to consider whether the regulation is valid under the MMPA, and if so, whether it violates the fourth amendment. For the reasons set forth below, we have concluded that: (1) the regulation was authorized under the broad rule-making power delegated by Congress to the Secretary; (2) the regulation is consistent with the policies and objectives of the MMPA; and (3) the regulation falls within the pervasively regulated industry exception to the warrant requirement of the fourth amendment.
FACTUAL AND STATUTORY BACKGROUND
The Captains utilize a method of fishing for yellow-fin tuna which results in the incidental taking4 of certain species of por[756]*756poise. Porpoise tend to swim in association with yellow-fin tuna in the eastern tropical Pacific. The porpoise is larger and more active on the ocean’s surface. Thus, the Captains can locate yellow-fin tuna by spotting porpoise. Purse seine nets are then set around schools of porpoises. The tuna swimming beneath them are encircled when the net is closed or “pursed” around them. During this operation, significant numbers of porpoise are injured or drowned. Their carcasses are discarded into the sea. In the two years preceding the enactment of the MMPA in 1972, the incidental taking resulted in more than 600,000 porpoise mortalities. Committee for Humane Legislation Inc. v. Richardson, 414 F.Supp. 297, 300 (D.D.C.), aff’d, 540 F.2d 1141 (D.C.Cir.1976).
Congress’ overriding purpose in enacting the MMPA was the protection of marine mammals. Congress declared the immediate goal of the MMPA to be “that the incidental kill or incidental serious injury of marine mammals permitted in the course of commercial fishing operations be reduced to insignificant levels approaching a zero mortality and serious injury rate.” 16 U.S.C. § 1371(a)(2) (1976-1982). To accomplish this goal, Congress imposed a moratorium on the taking and importing of marine mammals. 16 U.S.C. § 1371(a) (1976-1982). A two-year exemption from the moratorium for the taking of marine mammals incidental to commercial fishing operations was allowed. 16 U.S.C. § 1371(a)(2) (1976), amended by 16 U.S.C. § 1371(a)(2) (1982). The legislative history indicates that the exemption was provided “for the refinement of these fishing gear modifications” which industry representatives proffered as a solution to the porpoise mortality problem. Committee for Humane Legislation, 414 F.Supp. at 301.5 In addition, the Act directed the “immediate” undertaking of a research and development program to devise improved fishing methods and gear so as to reduce the incidental taking of marine mammals in connection with commercial fishing. 16 U.S.C. § 1381(a) (1976).
Although the commercial fishing industry was exempted for two years from the moratorium, the incidental taking of mammals during this time was conditioned on industry compliance with section 1381.6 See, [757]*757e.g., 16 U.S.C. § 1371(a)(2) (1976), amended by 16 U.S.C. § 1371(a)(2) (1982). Subsection (d) of section 1381 requires the industry to allow agents of the Secretary “to board and to accompany any commercial fishing vessel ... on a regular fishing trip for the purpose of conducting research or observing operations in regard to the development of improved fishing methods and gear as authorized by this section.” 16 U.S.C. § 1381(d) (1976-1982). Since expiration of this two-year exemption in 1974, the taking of marine mammals incidental to commercial fishing must be pursuant to a permit issued by the Secretary, 16 U.S.C. § 1371(a)(2), “subject to regulations prescribed by the Secretary in accordance with section 1373.” 16 U.S.C. § 1371(a)(2) (1976-1982).
Section 1373 requires the Secretary to consider, in promulgating the regulations, the “existing and future levels of marine mammal species and population stocks,” 16 U.S.C. § 1373(b)(1) (1976-1982), and the “marine ecosystem and related environmental considerations,” 16 U.S.C. § 1373(b)(3) (1976-1982). The regulations may also restrict the taking of porpoise by species, number, age, sex, or other factors. 16 U.S.C. § 1373(c) (1976-1982). In addition to the rule-making authority conferred upon the Secretary, 16 U.S.C. § 1373, the MMPA provides for the imposition of civil and criminal penalties for violations of the provisions of the Act or the regulations or permits issued thereunder. 16 U.S.C. § 1375(a) (1982).
In 1974, the Secretary promulgated a regulation, 50 C.F.R. § 216.24(f) (1974), in language virtually identical to that set forth in section 1381,7 the statutory observer program, that required the placement of observers on vessels.
Pursuant to the powers granted under the MMPA, the Secretary promulgated the regulation at issue here. The challenged regulation, effective January 1, 1981, requires as a condition of engaging in fishing operations that vessel owners:
(1) ... [SJhall, upon the proper notification by the [NMFS], allow an observer duly authorized by the secretary to accompany the vessel on any or all regular fishing trips for the purpose of conducting research and observing operations, including collecting information which may be used in civil or criminal penalty proceedings, forfeiture actions, or permit or certificate sanctions.
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(4) The Secretary shall provide for the payment of all reasonable costs directly related to the quartering and maintaining of such observers on board such vessels. A vessel certificate holder who has been notified that the vessel is required to [758]*758carry an observer, via certified letter from the National Marine Fisheries Service, shall notify the office from whieh the letter was received at least five days in advance of the fishing voyage to facilitate observer placement. A vessel certificate holder who has failed to comply with the provisions of this section may not engage in fishing operations for which a general permit is required.
50 C.F.R. § 216.24(f) (1981) (emphasis added).8
The Captains appear to have no objection to the observers’ scientific role on board ship. Their objection is directed solely at those provisions of the 1981 regulation which authorize the use of observer collected data in enforcement proceedings. In the Captain’s opening brief we are told that: “The District Court’s injunction properly stripped the observer program of its unauthorized and impermissible search function and restored it to its pristine role of pure scientific fact-gathering.” Appellees’ opening brief at 9 (emphasis added).
IMPLIED CONGRESSIONAL AUTHORIZATION
The first issue we must address is whether the 1981 regulation is authorized by the rule-making power delegated by Congress to the Secretary. See FCC v. Schreiber, 381 U.S. 279, 290, 291, 85 S.Ct. 1459, 1467, 1468, 14 L.Ed.2d 383 (1965) (Court first addressed whether regulation promulgated by agency was authorized by statute); Haig v. Agee, 453 U.S. 280, 101 S.Ct. 2766, 69 L.Ed.2d 640 (1981) (same).
The Captains argue that the regulation prescribing the observer program is invalid because it was not expressly authorized by Congress. The Captains contend that the observer program is a constitutionally questionable method of enforcing regulatory schemes and that under Greene v. McElroy, 360 U.S. 474, 79 S.Ct. 1400, 3 L.Ed.2d 1377 (1959) authorization for such a rule cannot be found absent an explicit congressional grant. Greene does not stand for the proposition that Congress must expressly authorize any action which might be challenged on constitutional grounds. Rather, the case indicates that Congress will not be presumed to have authorized agency methods which depart radically from accepted norms. In the matter before us, we are being asked to decide whether a particular warrantless search is authorized by Congress and whether that search violates the fourth amendment. Merely because some warrantless searches may violate the fourth amendment, it does not follow that no war-rantless search may be undertaken pursuant to federal law absent express congressional authorization. Unlike the types of procedures at issue in Greene, certain types of warrantless searches have traditionally [759]*759been recognized as constitutionally valid. See Henderson v. United States, 390 F.2d 805 (9th Cir.1967) (border searches); United States v. Robinson, 414 U.S. 218, 94 S.Ct. 467, 38 L.Ed.2d 427 (1973) (search incident to arrest); South Dakota v. Opperman, 428 U.S. 364, 96 S.Ct. 3092, 49 L.Ed.2d 1000 (1976) (inventory searches); Warden v. Hayden, 387 U.S. 294, 87 S.Ct. 1642, 18 L.Ed.2d 782 (1967) (exigent circumstances); Donovan v. Dewey, 452 U.S. 594, 101 S.Ct. 2534, 69 L.Ed.2d 262 (1981) (regulated industry searches). Nothing in Greene prohibits us from determining whether Congress implicitly authorized the observer program. In our discussions below, we reject the contentions that the observer program substantially departs from accepted methods of enforcing regulatory schemes, and the Greene case is therefore inapplicable.
To determine whether the regulation was authorized by Congress, we must analyze the language of the statute. Haig v. Agee, 453 U.S. 280, 289-90, 101 S.Ct. 2766, 2773, 69 L.Ed.2d 640 (1981). Section 1371 of the MMPA provides in pertinent part:
There shall be a moratorium on the taking and importation of marine mammals .... Marine mammals may be taken incidentally in the course of commercial fishing operations and permits may be issued therefor under section 1374 ... subject to regulations prescribed by the Secretary in accordance with section 1373.... The Secretary ... is authorized and directed ... to determine when, to what extent, if at all, and by what means, it is compatible with this chapter to waive the requirements of this section so as to allow taking, or importing of any marine mammal, ... and to adopt suitable regulations, issue permits, and make determinations ... permitting and governing such taking and importing.
16 U.S.C. § 1371 (1976-1982) (emphasis added).
Section 1373 provides that the Secretary “shall prescribe such regulations with respect to the taking ... as he deems necessary and appropriate to insure that such taking will not be to the disadvantage of those species ... and will be consistent with the purposes and policies set forth in section 1361.” 16 U.S.C. § 1373(a) (1976-1982) (emphasis added). The Secretary is required to report to Congress every twelve months on the status of the species and “to describe those actions taken and those measures believed necessary, including where appropriate, the issuance of permits ... to assure the well being of such marine mammals.” 16 U.S.C. § 1373(f).
Section 1374 provides that the Secretary may issue permits and that he “shall prescribe such procedures as are necessary to carry out this section.” 16 U.S.C. § 1374(d)(1) (emphasis added). In addition, the applicant for any permit “must demonstrate to the Secretary that the taking . .. under such permit will be consistent with the purposes of this Chapter .. . and the applicable regulations established under section [1373].” Id. at § 1374 (emphasis added). The Secretary may issue general permits for the “taking of marine mammals” together with regulations to cover the use of such permits which are “[consistent with the regulations prescribed pursuant to section 1373 .. . and the requirements of section 1371.” 16 U.S.C. § 1374(h).
It is quite true that the MMPA does not expressly confer upon the Secretary a power to impose, as a condition of obtaining a permit, the stationing of an observer on a vessel. In our view, however, that power is implicit in the broad rule-making authority expressly delegated to the Secretary. See Haig v. Agee, 453 U.S. at 291, 101 S.Ct. at 2773-2774 (Secretary of State’s power to revoke passports is implicit in broad rule-making authority conferred upon the Secretary by the Passport Act).
The Supreme Court has admonished that even though a statute does not explicitly delegate a specific action, “particularly in light of the ‘broad rule-making authority granted’ ... a consistent administrative construction of that statute must be followed by the courts “ ‘unless there are compelling indications that it is wrong” ’ .... ” Haig v. Agee, 453 U.S. at 291, 101 S.Ct. at [760]*7602774. (citations omitted.) Accordingly, the specific content of the regulation need not be expressly authorized. The regulation is proper so long as it conforms to the fundamental objective of the Act, rationally complements its remedial scheme, Whirlpool Corp. v. Marshall, 445 U.S. 1, 11, 12, 100 S.Ct. 883, 890, 891, 63 L.Ed.2d 154 (1980), and “the policy [thereby] announced ... is ‘sufficiently substantial and consistent’ to compel the conclusion that Congress approved it.” Haig, 453 U.S. at 307, 101 S.Ct. at 2782 (quoting Zemel v. Rusk, 381 U.S. 1, 12, 85 S.Ct. 1271, 1279, 14 L.Ed.2d 179 (1965)). Accord Mourning v. Family Publications Service, Inc., 411 U.S. 356, 369, 93 S.Ct. 1652, 1660-61, 36 L.Ed.2d 318 (1973); United States v. Southwestern Cable Co., 392 U.S. 157, 177, 88 S.Ct. 1994, 2005, 20 L.Ed.2d 1001 (1968) (“We may not in the absence of compelling evidence that such was not Congress’ intention ... prohibit administrative action imperative for achievement of an agency’s ultimate purposes.”). (citation omitted); American Trucking Ass’n v. United States, 344 U.S. 298, 310, 73 S.Ct. 307, 314-15, 97 L.Ed. 337 (1953) (Congress creates regulatory agencies so that they will bring to their work the expert’s familiarity with industry conditions that delegating legislatures cannot be expected to possess).
In Mourning, the Supreme Court upheld the power of the Federal Reserve Board to promulgate regulation “Z” pursuant to the Board’s broad rule-making authority under the Truth and Lending Act. 15 U.S.C. § 1604. The Court emphasized that:
Where the empowering provision of a statute states simply that the agency may “make ... such rules and regulations as may be necessary to carry out the provisions of this Act,” ... a regulation promulgated thereunder will be sustained so long as it is “reasonably related to the purposes of the enabling legislation.”
411 U.S. at 369, 93 S.Ct. at 1660-1661. (citations omitted).
It appears to us that the regulation at issue here is consistent with the objective and directives of the MMPA. Requiring the Captains to consent to the placement of observers on their vessels as a condition of obtaining a fishing permit is reasonably related to the purposes of the enabling legislation. The paramount purpose of the Act is “the protection and conservation of marine mammals.” 16 U.S.C. § 1371.9 As the D.C. Circuit has observed, the MMPA is to be administered “for the benefit of protected species, rather than for the benefit of commercial exploitation.” Committee for Humane Legislation, 540 F.2d at 1148.
Effective implementation of the MMPA would be impossible without the use of observers for enforcement purposes. Under the MMPA, any incidental taking of marine mammals must be pursuant to a permit issued by the Secretary. 16 U.S.C. § 1371. The permits must specify such factors as the number, kind, age, sex, and location of the mammals to be taken. 16 U.S.C. § 1374(b). Such limitations are necessary to assure that the MMPA’s goal of reducing marine mammal mortality to the minimum practical is met.
The affidavit offered by the government on its motion for summary judgment discloses that the use of on-board observers is the only practicable method of enforcing the limitations in MMPA permits. The tuna vessels subject to the Secretary’s regulation operate over thousands of square miles of open ocean for months at a time. No independent surveillance program could [761]*761hope to be able to verify whether or not a particular vessel complied with its trip quota. Even if such a technically feasible surveillance program were available, its costs would be prohibitive. The observer program is thus “necessary and appropriate to insure that such taking will not be to the disadvantage of those species ... and will be consistent with the purposes and policies set forth in the [MMPA].” 16 U.S.C. § 1373(a). Because the observer program is necessary for the enforcement of the MMPA, it is within the authority granted to the Secretary by Congress. See Southwestern Cable, 392 U.S. 157, 88 S.Ct. 1994, 20 L.Ed.2d 1001 (authority normally presumed for regulations necessary to enforce its statutory mandate); cf. Mourning, 411 U.S. at 371-72, 93 S.Ct. at 1662 (“That some other remedial provision might be preferable is irrelevant. We have consistently held that where reasonable minds may differ as to which of several remedial measures should be chosen, courts should defer to the informed experience and judgment of the agency to whom Congress delegated appropriate authority.”). In addition, the Secretary could not fulfill his duty under the MMPA to make annual reports to Congress if the observer program were discontinued. See 16 U.S.C. § 1373(f); cf. FCC v. Schreiber, 381 U.S. at 294, 85 S.Ct. at 1469-1470 (rule promulgated by FCC necessary to execute its duty to make annual reports to Congress).
In upholding the regulation, we are impressed by the fact that Congress, through oversight hearings, was made aware of the continued existence of the observer program. Congress was informed through hearings conducted from 1976 to 1981 that information gathered by observers might be used in penalty proceedings.10 In 1981, Congress amended the MMPA and did not disturb the Secretary’s broad-rule making authority in spite of this regulation.11 See Haig v. Agee, 453 U.S. at 301 & n. 50, 101 S.Ct. at 2779 & n. 50 (quoting Zemel v. Rusk, 381 U.S. at 21, 85 S.Ct. at 1283 (fact that Congress left rule-making authority untouched while amending Act gives rise to presumption that Congress has adopted the construction)). Thus, as in Haig v. Agee, “the inference of congressional approval ‘is supported by more than mere congressional inaction.’ ” 453 U.S. at 301, 101 S.Ct. at [762]*7622779. (quoting Zemel v. Rusk, 381 U.S. 1, 11-12, 85 S.Ct. 1271, 1283, 14 L.Ed.2d 179 (1965)); cf. Fredericks v. Kreps, 578 F.2d 555, 563 (5th Cir.1978) (en banc) (congressional oversight committee’s awareness of regulations before they were put into effect reinforces determination that regulation is consistent with Congress’ intent). See also Andrus v. Allard, 444 U.S. 51, 57, 100 S.Ct. 318, 322, 62 L.Ed.2d 210 (1979) (Court upheld regulation noting that Congress twice reviewed and amended the Act without rejecting the Department’s view that it was authorized under the Eagle Protection Act, 16 U.S.C. § 688, to bar sale of preexisting artifacts); NLRB v. Bell Aerospace Co., 416 U.S. 267, 274-75, 94 S.Ct. 1757, 1761-62, 40 L.Ed.2d 134 (1974) (great weight may be accorded a long standing interpretation of a statute by an agency charged with its administration especially where Congress has reenacted the statute without pertinent change; failure to repeal or revise the agency’s interpretation is persuasive evidence that Congress intended the interpretation).
The Captains advance two arguments against this construction. The first is that since Congress explicitly authorized funds for an observer program for only two years, 16 U.S.C. § 1381, the Secretary’s regulation adopting an observer program beyond this two-year period exceeds statutory authority. As noted earlier, the legislative history suggests, and the statute itself reflects, that this program was adopted to enable the Secretary to observe the industry’s utilization of advanced gear which purportedly would protect marine mammals.12 Moreover, the program was a condition to the industry’s incidental taking of porpoise during the exemption from the moratorium. 16 U.S.C. § 1371(a)(2) (1976), amended by 16 U.S.C. § 1371 (1982). Thereafter, the Secretary was authorized to waive the moratorium pursuant to regulations he deemed necessary and appropriate. Id.; 16 U.S.C. § 1373. Certainly, if Congress deemed the observer program a necessary condition to allowing the industry an exemption from the moratorium to ensure the protection of marine mammals, it is not unreasonable for the Secretary, in waiving the moratorium, to so condition the issuance of a permit for commercial fishing. The fact that funding for the statutory program was authorized by Congress only during the industry’s two-year exemption does not indicate to us that Congress intended to ban the use of observer programs.
Further, the expiration of the statutory observer program and the termination of the industry’s exemption from the moratorium on takings imposed by the MMPA coincided with the commencement of the rule-making authority delegated to the Secretary. 16 U.S.C. § 1371(a)(2) (1976), amended by 16 U.S.C. § 1371(a)(2) (1982). This suggests that Congress meant what the MMPA clearly states: The Secretary would have the broad authority to “determine when, to what extent, if at all, and by what means, it is compatable with ... [the MMPA] to allow taking ... of any marine mammal, ... and to adopt suitable regulations, issue permits, and make determinations . . . permitting and governing such taking.” 16 U.S.C. § 1371(a)(3)(A) (1976-1982) (emphasis added).
We believe that section 1381 of the MMPA, which expressly included an observer program, provided the Secretary with a model of Congress’ view as to what was necessary to carry out the purposes of the statute.
The Captains’ second argument is that since the House approved a bill in May of 197713 that explicitly authorized the use of observer data for enforcement purposes, but the Senate did not act upon it, congressional disapproval must be inferred. The House Oversight Committee, however, was well aware of the continued existence of the observer program and the fact that the [763]*763Senate might not act on the bill.14 The Committee was informed that existing funds were not adequate to staff all such vessels. Committee members expressed concern that the bill, which would have authorized additional funding for the observer program to staff all vessels with a capacity of four hundred or more tons,15 might not be acted upon by Congress. This concern stemmed from the discrepancy in numbers of porpoise mortalities reported by observed and unobserved vessels and the belief that the observer program was the only means of obtaining accurate information.16 We have found nothing in the 1977 or 1978 hearings of the Oversight Committee that suggests that the Committee disapproved of the collection of compliance data. When Congress amended the MMPA in 1981, it did nothing to alter Secretary’s power to continue the existence of the observer program. Thus, we conclude that the mere failure of the bill to be enacted does not demonstrate congressional disapproval of the observer program. Cf. American Trucking Association v. U.S., 344 U.S. 298, 309 n. 10, 73 S.Ct. 307, 314 n. 10, 97 L.Ed. 337 (1952) (fact that Act as originally drafted defined commerce to include leasing but lease terminology was stricken was of no consequence to Interstate Commerce Commission’s implied power to regulate leasing practices).
The Captains also contend that the observer program exceeds the Secretary’s rule-making authority under the MMPA because section 1377 narrowly defines the acceptable enforcement procedures. The observer program is said to be in direct conflict with section 1377, which allows war-rantless searches if there exists reasonable cause to believe a vessel is in violation of the MMPA. We disagree.
Section 1377 provides that “the Secretary shall enforce the provisions” of the MMPA, 16 U.S.C. § 1377(a). The statute provides further that its provisions concerning enforcement by arrest, search and seizure, are “in addition to any other authority conferred by law[.]” 16 U.S.C. § 1377(d). Thus, section 1377 does not limit enforcement procedures to those expressly authorized in that section. The regulation prescribing the observer program comes within the meaning of “other authority conferred by law” as used in section 1377.
CONSTITUTIONALITY OF THE REGULATION
The Captains contend that the regulation authorizes a warrantless search in violation of the fourth amendment.
Whether the observer program constitutes a search is a question which is not free from doubt. This circuit has held that not every boarding of a vessel constitutes a search. United States v. Olander, 584 F.2d 876, 888 (9th Cir.1978). (boarding to serve process is not a search), vacated on other grounds sub nom. Harrington v. United States, 443 U.S. 914, 99 S.Ct. 3104, 61 L.Ed.2d 878 (1979). A search within the meaning of the fourth amendment involves governmental prying into hidden places for that which is concealed by persons exhibiting a “legitimate expectation of privacy.” See Rakas v. Illinois, 439 U.S. 128, 143, 99 S.Ct. 421, 430, 58 L.Ed.2d 387 (1978). The regulation does not authorize an inspection of private papers, nor a search of the person, or the personal effects of the Captains or their crews. Instead, the observers must confine their observations to the fishing operations of the vessel, which occur on the open sea or on deck. Thus, the information they may gather is restricted to evidence which is in plain view. “What a person knowingly exposes to the public, even in his own home or office, is not a subject of Fourth Amendment protection.” Katz v. [764]*764United States, 389 U.S. 347 at 351, 88 S.Ct. 507 at 511, 19 L.Ed.2d 576 (1967). See United States v. Whitmire, 595 F.2d 1303, 1312 (5th Cir.1979), (high levels of privacy -might.be accorded to crews living quarters on tanker that travels for months, but no crew member has legitimate claim of privacy on open deck of a fishing smack or in the hold of a cargo vessel available for hire), cert. denied, 448 U.S. 906, 100 S.Ct. 3048, 65 L.Ed.2d 1136 (1980).
It can be argued with equal force, however, that the observer’s constant surveillance of the activities of the Captains and their crews, for a prolonged period of time, constitutes an intrusion into liberty and privacy interests, protected by the fourth amendment, by exposing “what [a person] seeks to preserve as private, even in an area accessible to the public.” Katz, 389 U.S. at 351, 88 S.Ct. at 511.
We need not pause to resolve this nice question. Even if we assume that the regulation authorizes a warrantless search of the operations of a fishing vessel, it is our view that the regulation requiring the presence of observers on purse seiners does not violate the fourth amendment.
The fourth amendment prohibits unreasonable searches and seizures. Warrantless searches may be reasonable under certain circumstances. See, e.g., Weeks v. United States, 232 U.S. 383, 392, 34 S.Ct. 341, 344, 58 L.Ed. 652 (1914) (search incident to a lawful arrest); Carroll v. United States, 267 U.S. 132, 146, 45 S.Ct. 280, 282-83, 69 L.Ed. 543 (1925) (search of vehicles based on probable cause that contraband is being carried); South Dakota v. Opperman, 428 U.S. 364, 367-76, 96 S.Ct. 3092, 3096-3101, 49 L.Ed.2d 1000 (1976) (inventory search of impounded vehicles without a showing of probable cause); Illinois v. LaFayette, -U.S. -, -, 103 S.Ct. 2605, 2611, 77 L.Ed.2d 65 (1983) (booking search of a man’s purse-type shoulder bag); United States v. Villamonte-Marquez, - U.S. -,-, 103 S.Ct. 2573, 2582, 77 L.Ed.2d 22 (1983) (boarding of vessels without artic-ulable suspicion). In Carroll v. United States, 267 U.S. 132, 45 S.Ct. 280, 69 L.Ed. 543 (1924), the Supreme Court commented: “Under the common law and agreeably to the Constitution [a] search may in many cases be legally made without a warrant. The Constitution does not forbid search, as some parties contend, but it does forbid unreasonable search.” 267 U.S. at 146, 45 S.Ct. at 282.
The Supreme Court has recognized that warrantless searches in closely regulated industries can be reasonable. The Court has held that warrantless inspections are reasonable if they are reasonably necessary to further important federal interests and the federal regulatory presence is sufficiently comprehensive and predictable that “the assurance of regularity provided by a warrant is rendered unnecessary.” Donovan v. Dewey, 452 U.S. 594, 599-602, 101 S.Ct. 2534, 2538-40, 69 L.Ed.2d 262 (1981).17 The Court has applied the exception where the business premises searched are part of an industry “long subject to close supervision and inspection.” Colonnade Catering Corp. v. United States, 397 U.S. 72, 76-77, 90 S.Ct. 774, 776-77, 25 L.Ed.2d 60 (1970); see also United States v. Raub, 637 F.2d 1205, 1208 (9th Cir.1980) (“One of the recognized exceptions to the warrant requirement is for administrative searches of enterprises that traditionally have been closely regulated.”). In Marshall v. Barlow’s, Inc., 436 U.S. 307, 313, 98 S.Ct. 1816, 1820-21, 56 L.Ed.2d 305 (1978), the Court observed that certain industries have had such a history of close governmental supervision that no reasonable proprietor entering into them could have a justifiable expectation of privacy. In United States v. Biswell, 406 U.S. 311, 92 S.Ct. 1593, 32 L.Ed.2d 87 (1972), the Court extended the pervasively regulated industry [765]*765exception to industries without a long tradition of regulation where frequent unannounced inspections are essential to further an important governmental interest.
Where the regulation involves a comprehensive and predictable governmental presence, the owner “is not left to wonder about the purposes of the inspector or the limits of his task.” 406 U.S. at 316, 92 S.Ct. at 1596. The Court has also noted that where the industry is closely regulated, the owner cannot help but be aware that the government will conduct periodic inspections for specific purposes. Donovan v. Dewey, 452 U.S. 594, 600, 101 S.Ct. 2534, 2538-39, 69 L.Ed.2d 262 (1981). The reasonableness of a search in a closely regulated industry does not depend on the existence of probable cause but rather on the “pervasiveness and regularity of the federal regulations.” 452 U.S. at 606, 101 S.Ct. at 2542. When a person chooses to engage in a closely regulated industry and to accept a license which is conditioned upon such warrantless intrusion and inspection, he does so with full knowledge of the restrictions on his privacy. He is also free not to submit to such regulation and warrantless inspection by declining to seek a federal permit. Biswell, 406 U.S. at 315-16, 92 S.Ct. at 1596.
The Captains argue that the closely regulated industry exception does not apply to a warrantless administrative search unless it is expressly authorized by Congress. This argument was presented and rejected by the court in United States v. Rucinski, 658 F.2d 741 (10th Cir.1981), cert. denied, 455 U.S. 939, 102 S.Ct. 1430, 71 L.Ed.2d 649 (1982). It is quite true that in each of the cases cited above where the Supreme Court determined that a warrantless search of a closely regulated industry was reasonable under the fourth amendment, the entry was expressly authorized by statute. The Captains assume that since the Supreme Court has held that a warrantless search of a closely regulated industry is reasonable when expressly authorized by Congress, the search of such a business violates the fourth amendment if it is conducted pursuant to a regulation impliedly authorized by Congress. No authority is cited for this novel constitutional proposition. The law is to the contrary. Congress cannot authorize conduct which violates the fourth amendment. The proper inquiry when a warrant-less search is challenged is whether it is authorized by the fourth amendment — not by an act of Congress.
In Raub, this court noted that “[commercial fishing has a long history of being a closely regulated industry.” 637 F.2d at 1208 (footnote omitted). Regulation of the fishing industry began in 1793. Id. at 1209 n. 5. Since 1972, the tuna industry has been closely regulated by Congress because its fishing operations threatened the extinction of the porpoise. Congress’ interest in the protection of marine mammals was made known to all commercial fishermen in 1972 when Congress expressly authorized the placing of observers on purse seiners to protect the porpoise under the MMPA. As discussed above, in the MMPA, Congress authorized the Secretary to prescribe regulations and to issue a permit restricting the taking of marine mammals. Congress also authorized the Secretary to limit the issuance of permits to those persons who can demonstrate that any taking of marine mammals will be consistent with the MMPA, 16 U.S.C. § 1373. Thus, commercial fishermen have been made aware since 1972 that to take porpoise they must have a permit which is subject to conditions that will insure that marine mammals are given the protection required by Congress. The statutory observer program had been one such condition. Since 1974 commercial fishermen have also been aware of the regulation which prescribes the observer program. Any tuna boat Captain who does not wish to expose himself to the observation of his open deck activities is free not to submit to such an intrusion by refraining from seeking a permit. See Biswell, 406 U.S. at 315-16, 92 S.Ct. at 1596. See also Wyman v. James, 400 U.S. 309, 91 S.Ct. 381, 27 L.Ed.2d 408 (1971) (a welfare recipient may avoid an entry into his home by refusing to accept public assistance).
In determining whether warrantless searches in a closely regulated industry are [766]*766reasonable we must decide whether the regulatory scheme “in terms of the certainty and regularity of its application, provides a constitutionally adequate substitute for a warrant.” Dewey, 456 U.S. at 603, 101 S.Ct. at 2540. It is evident to us that the observer program regulation provides an adequate substitute for a warrant for several reasons.
First, the MMPA, the regulation, and the National Marine Fisheries Services’ (NMFS) Manual establish a predictable and guided federal presence and limit the scope of the data collection. The MMPA delegates to the Secretary the authority to waive the moratorium on porpoise takings only when he can determine that such takings will not disadvantage protected species. The MMPA specifically sets forth permissible restrictions on the takings of porpoises and authorizes the Secretary to impose additional ones. The Act also requires publication of proposed regulations, and clearly defines its objectives and purposes.
Under the observer program, vessel owners are sent advance calendars of scheduled observer trips. This notification includes a statement of the significant regulations promulgated by the Secretary. The regulation, 50 C.F.R. § 216.24(f), limits the scope of observer activities to data collection. The National Marine Fishery Service Field Manual further defines the data collection activities of individual observers. The 1979 Manual informs observers that they are not enforcement agents and they are not “to record extraneous comments, editorials, or personal opinions ... or evaluate or interpret data.” Observers are instructed simply to record the data called for in the form. The Manual, which is available to the industry, contains sections on the observer’s responsibilities, instructions to the observers, and standardized forms to record information. The 1981 Manual additionally establishes a predeparture conference between the owner, master, observer, and an agency official to ensure a common understanding of the scope of observers’ activities.
Second, the regulation requires that tuna vessel owners be given advance notice of the stationing of an observer on their vessel. Thus, the surprise element of many warrantless inspections is lacking here. See, e.g., Delaware v. Prouse, 440 U.S. 648, 657, 99 S.Ct. 1391, 1398, 59 L.Ed.2d 660 (1979). This advance notice also provides the Captains with an opportunity to seek judicial review of a particular scheduled observer trip. Cf. Dewey, 452 U.S. at 604-05, 101 S.Ct. at 2541 (opportunity for judicial review is factor important in reasonableness determination). They are also free to request a court order accommodating any privacy interests that may need protection. We conclude that the regulation as limited by the field manual provides a constitutionally adequate substitute for a warrant.
Use of observers advances the legitimate government interest of meaningful protection of the porpoise population, while the safeguards built into the observer program insure that there will be no significant intrusion on the Captains’ fourth amendment interests. Cf. Delaware v. Prouse, 440 U.S. at 654, 99 S.Ct. at 1396 (constitutionality of a law enforcement procedure is basically tested by balancing its intrusion on fourth amendment interests against its promotion of legitimate government interests).
The Captains ask us to invalidate the observer program on the ground that a less restrictive alternative for obtaining the information exists. The government’s affidavit, however, demonstrates that the suggested techniques — aerial surveillance and the like — are prohibitive in terms of cost and are ineffective in terms of data collection necessary for the Secretary to waive the moratorium on takings of porpoise and to issue permits. Cf. Wyman, 400 U.S. at 322, 91 S.Ct. at 388 (although secondary sources might be helpful, they would not always assure identification of information required for receipt of benefits).
In Vlllamonte-Marquez, the Court noted that the nature of water borne commerce in waters providing ready access to the open sea is sufficiently different from the nature of vehicular traffic on highways so as to make possible alternatives to the boarding of a vessel less likely to accomplish essential [767]*767governmental procedures. - U.S. at -, 103 S.Ct. at 2581.
CONCLUSION
We hold that the requirement that observers be permitted to board purse seiners on a scheduled basis as a condition of obtaining a permit to take porpoise is reasonable under the fourth amendment. The regulation and the field manual do not authorize the observers to conduct searches of the persons, personal effects, or living quarters of the Captains and their crews. Such a search would have to be justified independently under the fourth amendment.
The judgment in Balelo is reversed and remanded for further proceedings consistent with this opinion. The judgment in Gladiator is affirmed.