Oil and gas exploration relies on seismic airguns that fire low‑frequency pulses up to ~200–260 dB re 1 µPa @ 1 m, and ambient ocean noise has risen ≈12 dB in some regions over 30 years. Regulators now mandate soft starts and shutdowns when animals are detected; the records show small but real delays—and mixed protection for wildlife.
Seismic airguns—arrays that map the seafloor—fire powerful, low‑frequency sound pulses every few seconds. The impulses can reach up to ~200–260 dB re 1 µPa @ 1 m (underwater decibels referenced to 1 microPascal; level at 1 meter from source), propagate for kilometers, and raise ambient noise levels (pubs.usgs.gov). Measurements indicate ambient ocean noise has risen dramatically—≈12 dB in some regions over 30 years (www.mdpi.com).
Concern has moved into policy. Indonesia now requires an environmental impact plan (UKL‑UPL) for marine seismic surveys, reflecting the fact that marine fauna—especially whales and dolphins—depend on sound for navigation, communication, and foraging (www.frontiersin.org). The result: a spectrum of effects, from acoustic masking and stress to behavioral disturbance and even hearing damage, with potential population‑level consequences.
Documented effects on marine mammals
For cetaceans and pinnipeds, seismic pulses can mask whale calls and echolocation, disrupt feeding or migration, and induce behavioral changes such as startle responses, avoidance, and altered dive patterns (www.frontiersin.org) (www.frontiersin.org). At high received levels, animals can suffer auditory injury—temporary or permanent threshold shifts (TTS/PTS) that reduce hearing sensitivity. Regulatory practice (e.g., U.S. NMFS) typically treats ~180 dB re 1 µPa (rms, a root‑mean‑square metric used by regulators) as the injury threshold for cetaceans (pubs.usgs.gov).
Many studies report behavioral effects (e.g., whales avoiding an area) but relatively few measure clear hearing loss. In one debated case, a 2002 3D seismic campaign off Brazil coincided with an unusual spike in humpback whale strandings, prompting Brazil’s regulator to ban seismic during the whales’ breeding season (www.researchgate.net) (www.researchgate.net). Causality remains contested: experts note seismic surveys may damage cetacean sonar organs but lack definitive proof of strandings (jakartaglobe.id) (jakartaglobe.id).
Observer records from the U.S. Gulf of Mexico illustrate how often animals and surveys intersect: of ~194,000 survey‑hours logged (2002–08), there were 3,963 cetacean sighting records (≈28,000 individual animals), dominated by sperm whales (1,136 records) and small dolphins; many animals swam within prescribed exclusion zones, causing operators to interrupt shooting (www.researchgate.net).
Baca juga:
Mengapa Sterilizer Horizontal & Kontrol Otomatis PLC/SCADA Jadi Pilihan Utama di Pabrik Kelapa Sawit
Fish and invertebrate exposure evidence
All teleost fish detect low frequencies (<500 Hz), so airgun pulses can startle them or disrupt schooling and spawning (www.mdpi.com). Early concerns led Norway (1980s–90s) to close fish spawning grounds to seismic surveys. Controlled experiments later found direct mortality only at very close range: for cod larvae, lethal effects were confined to ~2 m from the airgun, yielding a worst‑case 0.45% larval mortality per survey—far below natural daily mortality (5–15%) (www.mdpi.com). Norway lifted some restrictions, keeping only critical spawning/migration corridors closed (www.mdpi.com) (www.mdpi.com).
Reviews conclude seismic impacts on fish recruitment are negligible at population scale: lethal or sublethal effects occur only within a few meters of the source (www.mdpi.com) (www.mdpi.com). For invertebrates, experimental work on crustaceans (lobsters, crabs) and zooplankton similarly shows no widespread mortality beyond very close distances; one large review found no invertebrate deaths except larval krill very near the source (www.frontiersin.org).
Some field studies cite physiological stresses in lobsters (impaired righting reflex, sensory hair damage) when exposed at close range (www.frontiersin.org). Overall, review articles note that masking and disturbance occur at much greater distances than outright physical injury, but long‑term population effects are largely unmeasured (www.mdpi.com) (www.frontiersin.org). In short, seismic pulses generate masking and stress for many organisms and acute impacts if animals are very near the guns; marine mammals are the most studied group, showing avoidance and, rarely, injury at high levels, while fish and invertebrates generally suffer effects only within a few meters (www.mdpi.com) (www.frontiersin.org).
One systematic review notes: “Seismic surveys did not result in invertebrate mortalities except larval krill,” and that any physiological effects varied by species and age (www.frontiersin.org). Precautionary assessments often assume zones of risk. (Note: Many regulatory analyses use thresholds like 160 dB re 1 µPa (rms) as behavioural harassment for cetaceans and 120 dB for fish, with injury assumed at 180–190 dB, although such criteria are coarse proxies.)
Ramp‑up (soft start) procedures
To reduce risk, operators use ramp‑up (“soft start”): turning on a single small gun and adding others over 20–40 minutes so sound levels climb slowly, giving animals a chance to move away before full power. In practice, ramp‑ups are legally mandated—typically 20–40 minutes—when beginning or resuming airgun firing (www.researchgate.net). Expert panels note, however, that effectiveness is uncertain (www.conservationevidence.com).
Controlled trials with humpback whales found ramp‑ups reduced peak received levels by only ~3 dB on average compared with an immediate blast, and only about half the whales reacted to move away (pmc.ncbi.nlm.nih.gov). Gulf of Mexico records suggest ramp‑ups slightly reduced dolphin sightings (9% fewer in ramp‑up vs silent periods) and pushed dolphins a few meters farther from the source (www.researchgate.net). Ramp‑ups inevitably extend total survey time, but observed downtime has been modest: over six years of U.S. surveys, 32 ramp‑up delays (mainly due to dolphins in exclusion zones) cost ~18.5 hours of airgun inactivity (www.researchgate.net). By contrast, reducing source levels gradually can reduce stress on responsive animals who depart early (pmc.ncbi.nlm.nih.gov); if animals do not respond to faint initial sound, ramp‑ups mainly prolong noise exposure.
Baca juga: Pengolahan Limbah Secara Kimia
Visual observers and exclusion zones
A primary mitigation is continuous monitoring by trained marine mammal observers (MMOs) who scan exclusion zones (often several hundred meters to over a kilometer in radius, set by expected sound levels). For example, one 1999 survey off California required three visual observers at all times (pubs.usgs.gov). If a protected species enters the safety zone (often where the received level would exceed ~180 dB or via a fixed radius), airguns must shut down.
In practice, MMOs frequently trigger delays. In the Gulf of Mexico dataset, observers logged 144 airgun shutdowns due to whales in the exclusion zone (97% were sperm whales), each averaging ~58 minutes, totaling ~125.7 hours over six years (www.researchgate.net). Observers also conduct pre‑shoot watches (typically 30 minutes) before any ramp‑up; the BOEM report found ~86% compliance with the 30‑minute pre‑survey check (www.researchgate.net). Other protocols commonly include no ramp‑ups at night or in poor visibility (to avoid undetected animals) and vessel maneuvering if protected species are nearby (www.researchgate.net).
Spatial and seasonal avoidance
Planning around biology may be the most effective tool. The MMO Observer Association emphasizes that the “single most important mitigation” is avoiding critical habitat and seasons (e.g., calving areas, migration corridors) (mmo-association.org). In practice, that means scheduling surveys outside known breeding periods and steering clear of marine protected areas. After the Brazilian whale strandings, seismic surveys were prohibited in the Abrolhos Bank during July–November (humpback whale season) (www.researchgate.net) (www.researchgate.net), and Indonesian scientists have urged limiting surveys in regions like the Savu Sea to outside peak cetacean migration periods (jakartaglobe.id). Such temporal controls can be more effective and cheaper than shutdowns.
Other “soft” mitigations include using repeated down‑detector systems (e.g., passive acoustics) to alert if whales vocalize at night, and maintaining wildlife exclusion corridors when mobilizing.
Additional mitigation practices
Guidelines often call for detection zones tailored to species (e.g., larger zones for baleen whales and smaller for dolphins, based on frequency sensitivity) (mmo-association.org). Observers may use binoculars, infrared, or night‑vision for nocturnal watches. In some countries, passive acoustic monitoring (PAM) supplements visual observers, though its use under seismic survey conditions is still developing. Nozzle or bubble barriers (used in construction) are not practical for commercial surveys.
All mitigation practices raise operational costs (e.g., paying for observers and downtime). However, collected data show these costs are relatively small: in one large multi‑year survey program, downtime from all mitigation (pre‑survey delays + shutdowns) was only ~0.06% of total survey hours (www.researchgate.net).
Baca juga:
Measured performance and trends
Ramp‑ups: Out of ~32,939 documented ramp‑ups across many surveys, 90% complied with the mandated 20–40 minute duration. Individual vessels averaged about 2.5 ramp‑ups per day; 57% of ramp‑ups began in daylight, enabling effective pre‑ and during‑ramp monitoring (www.researchgate.net) (www.researchgate.net) (www.researchgate.net). Only ~3% of ramp‑ups lacked a full 30‑minute pre‑watch; when animals were present, ramp‑ups were delayed, totaling 18.5 hours over six years, and 75% of such delays were due to small cetaceans (www.researchgate.net) (www.researchgate.net).
Shutdowns: Whales in exclusion zones forced 144 seismic shutoffs in the Gulf of Mexico data; sperm whales alone accounted for 97% of triggers. Each shutdown averaged ~58 minutes, for a cumulative ~125.7 hours over six years (www.researchgate.net).
Behavioral responses: Dolphin sighting rates were 9% lower during ramp‑up than during silent periods, and dolphins kept a greater average distance during full‑power firing than during ramp‑up (and shortest distance during silent intervals), indicating animals may steer clear of the loudest pulses. Nevertheless, most dolphins remained visible near operating guns, and few made large avoidance moves—mitigation buys only incremental protection unless animals exit the zone entirely (www.researchgate.net).
Operational and regulatory takeaways
Quantitative impacts are small but real: mitigation (ramp‑ups, observers, shutdowns) imposes measurable delays—e.g., ~0.02–0.06% of total survey time in the cited Gulf of Mexico data. For a typical 3D survey (100+ days), this might mean several hours lost, which is usually acceptable versus ecological risk. Industry data show high compliance with mitigation protocols, though effectiveness varies by species catch rates (www.researchgate.net).
No single measure is foolproof: soft starts have limited efficacy unless animals respond, as shown by experimental trials (pmc.ncbi.nlm.nih.gov). Visual monitoring can fail at night or in poor conditions, which is why many guidelines disallow ramp‑ups in darkness (www.researchgate.net). Combining methods—observers plus avoiding high‑use periods—yields the best outcomes.
Site‑ and species‑specific planning is essential. Avoid surveys in whale calving areas (as in Brazil) or during mass migrations (as recommended in Indonesia’s Savu Sea) (www.researchgate.net) (jakartaglobe.id). Use of the latest research is advised: e.g., New Zealand and EU regulators incorporate acoustic data on local whale densities to set dynamic zone sizes.
Regulatory context is evolving. In Indonesia, seismic surveys must follow national environmental standards (BSILHK Form UKL‑UPL) that mandate management measures. International best practice (IAGP, IMOA) emphasizes avoidance of critical habitats and detailed monitoring plans (mmo-association.org) (mmo-association.org).
Baca juga:
Kondensat Sterilizer Sawit: Limbah Panas yang Bisa Diubah Jadi CPO dan Penghematan Energi
Bottom line for exploration teams
Loud airgun noise can disturb marine mammals via masking, stress, and behavioral change and, to a much lesser extent, fish and invertebrates. The worst‑case hearing injuries and mortalities occur very near the source; broad population effects remain unproven except via habitat exclusion or chronic stress. In industry practice, measures like ramp‑up and visual monitoring reduce the risk of incidental injury; operators typically delay or shut down if protected animals approach.
Watchdog reports from large offshore surveys show only minor fractions of time lost to mitigation—tens of hours over thousands of operating hours (www.researchgate.net). Even so, these procedures are critical for license compliance and social license to operate. Project planners should build in mitigation time and costs, apply site‑specific EIA guidance (as per Indonesian standards, and consider scheduling surveys to avoid peak marine mammal presence to minimize conflict.
