Before you spearfish — this comes first
- Get proper instruction before you spearfish. A recognised freediving or spearfishing course teaches the things that actually kill people in this sport, and reading about them is not the same as being taught them.
- Dive with a buddy, and dive one up, one down — one diver in the water, one on the surface watching them, every dive. A breath-hold blackout is silent and gives no warning; a watching buddy is the difference between an incident and a fatality.
- Stay inside your own training and experience. Depth and breath-hold times are personal, they change day to day, and nobody else's numbers apply to you.
- Understand the conditions before you enter the water: visibility, current, swell, tide, boat traffic and your exit. Conditions decide whether a dive is reasonable far more often than skill does.
- Use equipment you have been shown how to use, check it before every session, and be visible — a marked float and line are how boat traffic knows you are there.
- Never extend a dive for a fish. No catch is worth pushing a breath-hold, and the urge to take one more second is exactly what a blackout feels like from the inside — which is to say, like nothing at all.
Spearfishing myths, and what is actually known
Explainer · Last reviewed 2026-08-27
Six claims that recur, set against what evidence establishes and what it does not — chosen because each one has a consequence, not because any of them is easy to knock down.
Safety
Shallow water blackout and breath-hold loss of consciousness — Can cause serious injury or death
Three of the beliefs on this page — that hyperventilation extends a safe breath-hold, that feeling well means being safe, and that a companion nearby constitutes a buddy — each remove one of the protections that make blackout survivable, and they are frequently held together.
What reduces it: No pre-dive hyperventilation; weighting for positive buoyancy at the surface; one-up-one-down with the watching diver observing the whole dive and the period after surfacing; and recognised training that teaches and assesses all three in the water.
Myth-busting is a genre with a bad habit: assembling weak claims nobody holds in order to correct them confidently. This record does the opposite. Every claim here is one that circulates widely among people who dive, several are held by experienced divers, and each is included because believing it changes what somebody does.
Each is treated the same way: what the claim is, what evidence establishes, what practitioners report, what remains uncertain, and why the claim persists. That last question matters — a belief that survives decades usually contains something true, and understanding what keeps it alive is more useful than declaring it wrong.
WHERE FISHINGHQ IS CONFIDENT it says so, and the confident ones are the safety-critical ones, because the physiology is settled. WHERE IT IS NOT — and two of these are genuinely unresolved — it says that instead.
The three where the evidence is settled
"HYPERVENTILATING BEFORE A DIVE GIVES YOU MORE TIME."
WHAT EVIDENCE ESTABLISHES: it does not add meaningful oxygen, and it removes the warning. The urge to breathe is driven mainly by rising carbon dioxide rather than by falling oxygen. Blowing off carbon dioxide before a dive therefore delays the urge to breathe without extending the oxygen supply — which means a diver can reach hypoxia and lose consciousness while still feeling comfortable. Diving medicine guidance is unambiguous, and describes hyperventilation as compromising the body's natural protection rather than improving performance.
WHY IT PERSISTS: because it works, in the sense people mean. Divers who hyperventilate genuinely do stay down longer. The extra time is borrowed from the warning system.
WHAT REMAINS UNCERTAIN: nothing that matters. This one is settled.
"IF YOU FEEL FINE, YOU ARE FINE."
WHAT EVIDENCE ESTABLISHES: hypoxic blackout gives no reliable warning the diver can detect, and occurs most often in the final part of the ascent or in the seconds after surfacing. There is no struggle and no call for help. Feeling fine is exactly what it feels like beforehand.
WHY IT PERSISTS: because subjective comfort is the only instrument a diver has, and it is a good guide to almost everything else in life.
"MORE WEIGHT MAKES DIVING EASIER."
WHAT EVIDENCE ESTABLISHES: overweighting is a recognised contributor to freediving fatalities. A wetsuit compresses with depth, so a diver weighted to feel comfortable deep is heavy at the surface — and the surface is where an unconscious diver needs to float. More weight does make descending easier, which is the whole trap.
WHY IT PERSISTS: because the benefit is felt immediately and on every dive, and the cost is only ever paid once.
Scientific evidence
Supported by peer-reviewed research or fisheries science. The sources are listed and can be checked.
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: That hyperventilation suppresses the urge to breathe without adding oxygen, that blackout occurs without usable warning and most often on ascent or after surfacing, and that these are the central hazards of breath-hold diving.States this directlyPassage read and verified
- AIDA International freediving education and safety standards — AIDA International (Water-safety or diver-training authority)Relied on for: That recognised freediving education addresses hyperventilation, weighting and supervision as safety fundamentals.Background and mechanism onlyCitation checked — the work exists and is described correctly
The one that is half true, and matters most
"HAVING A BUDDY NEARBY IS ENOUGH."
WHAT EVIDENCE ESTABLISHES: the buddy system works through direct one-to-one supervision — one diver down, one watching that diver, throughout the dive and for the period after surfacing. It is the mechanism that makes blackout survivable, and it depends on the watcher being in a position to get an unconscious person's airway out of the water within seconds.
WHAT THE CLAIM GETS RIGHT: a companion is better than nobody. They can raise an alarm.
WHAT IT GETS WRONG: two divers in the same bay are not buddying. Two divers descending together are two unsupervised divers. A companion who is hunting their own fish, or on the beach, or thirty metres away in three metres of visibility, is not performing the function the safety model assumes.
WHY IT PERSISTS: because it is nearly right, because most dives end uneventfully so the arrangement is never tested, and because proper alternating supervision is less fun — one diver is always not hunting.
WHAT REMAINS UNCERTAIN: nothing about the principle. What is genuinely unresolved is how much protection a partially-attentive buddy provides in practice, and it is not a question anybody can answer from the water.
This is the most consequential item on the page, because it is the belief that lets a diver think they are complying with the one rule that matters.
Authoritative guidance
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: That dedicated one-to-one buddy supervision is required, and that blackout is survivable when somebody competent is watching.States this directlyPassage read and verified
- BSAC diving safety guidance and annual incident report — British Sub-Aqua Club (Water-safety or diver-training authority)Relied on for: Buddy protocol and separation, and the requirement to observe throughout a dive.States this directlyCitation checked — the work exists and is described correctly
The two that are genuinely unresolved
"CAMOUFLAGE WETSUITS MAKE A REAL DIFFERENCE."
WHAT EVIDENCE ESTABLISHES: detection underwater is driven by contrast, movement and silhouette rather than by colour at the ranges that matter, and breaking up a large uniform outline against a structured background is a sound general principle of visual detection.
WHAT PRACTITIONERS REPORT: widely, that particular patterns help. Reports are not independent enough to constitute consensus under this platform's own definition, and the manufacturers are an interested party.
WHAT REMAINS UNCERTAIN: whether any pattern produces a measurable change in flight initiation distance in the field, and whether it is large relative to the variables that dominate — depth, distance, movement, silhouetting against the surface, and how heavily the population has been hunted. FishingHQ is not aware of published measurement.
WHY IT PERSISTS: the principle is sound, the product is visible, and every diver who wears one and has a good day has a confirming anecdote.
"SHARKS ARE THE MAIN DANGER."
WHAT EVIDENCE ESTABLISHES: hypoxic blackout is the leading cause of death in breath-hold diving by a wide margin. Most injuries to spearfishers come from handling spined fish and from equipment. Spearfishing does genuinely change the shark picture — a struggling bleeding fish is an attractant the diver created — so the management practice is worth following.
WHAT REMAINS UNCERTAIN: how much the practice reduces risk. It is plainly sensible and it has not been quantified.
WHY IT PERSISTS: because the consequence is vivid and the alternative is not. A blackout is silent and looks like nothing.
The cost of this myth is attention. A diver worried about sharks and casual about weighting and buddying has their concern pointed at the wrong thing entirely.
Unresolved
FishingHQ looked into this and could not settle it. The open question is recorded here rather than being papered over.
- The Ecology of Vision — Clarendon Press, Oxford, 1979 (Scientific literature)Relied on for: That underwater detection is contrast-limited and that background matching operates as a general principle of visual concealment.States this directlyCitation checked — the work exists and is described correctly
- Fear of fishers: human predation explains behavioral changes in coral reef fishes — PLoS ONE 6(8): e22761, 2011 (Scientific literature)Relied on for: That flight initiation distance is driven substantially by predation history, which is among the variables any concealment effect would have to be measured against.Background and mechanism onlyCitation checked — the work exists and is described correctly
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: The relative frequency of breath-hold diving fatality causes and the primacy of hypoxic blackout.States this directlyPassage read and verified
Where to go next
Where it matters
What these connections rest on (1)
Authoritative guidance — 1 connection
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Spearfishing
A membership assertion rather than a topical one: this record teaches the discipline or its equipment, so the discipline's mandatory safety posture applies to it.
- CMAS technical and sporting standards for underwater activities — Confédération Mondiale des Activités Subaquatiques (Standards body)Relied on for: Breath-hold spearfishing as a defined discipline with its own technical, equipment and safety standards, set out by the international underwater federation.States this directlyCitation checked — the work exists and is described correctly
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: That the safety requirements of breath-hold diving apply across the discipline rather than to particular equipment or techniques within it.States this directlyPassage read and verified
Recurring claims with consequences, rather than strawmen assembled to be corrected.
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: Diving medicine guidance on breath-hold physiology, hypoxic blackout, cold exposure and supervision.States this directlyPassage read and verified
Related reading
- Weighting, and the margin that keeps you at the surfaceMore weight does make descending easier, which is the whole trap: the benefit is felt on every dive and the cost is paid once.
- What a fish can see of you underwaterThe camouflage question answered from visual ecology: the principle is sound and the field effect is not measured.
What these connections rest on (2)
Authoritative guidance — 1 connection
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Weighting, and the margin that keeps you at the surface
The myth whose appeal is entirely real and whose consequence is not survivable.
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: Diving medicine guidance on breath-hold physiology, hypoxic blackout, cold exposure and supervision.States this directlyPassage read and verified
Scientific evidence — 1 connection
Supported by peer-reviewed research or fisheries science. The sources are listed and can be checked.
What a fish can see of you underwater
One of the two genuinely unresolved items, and the reason the record does not pretend otherwise.
- The Ecology of Vision — Clarendon Press, Oxford, 1979 (Scientific literature)Relied on for: Underwater visual ecology, contrast-limited detection and the attenuation of colour with depth and distance.States this directlyCitation checked — the work exists and is described correctly
Safety reading
What these connections rest on (1)
Authoritative guidance — 1 connection
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Breath-hold blackout
The record the three safety-critical myths all resolve to.
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: Diving medicine guidance on breath-hold physiology, hypoxic blackout, cold exposure and supervision.States this directlyPassage read and verified
Sources for this page
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: Breath-hold diving physiology, hyperventilation, blackout, weighting and supervision.States this directlyPassage read and verified
How FishingHQ labels evidence is explained in the evidence policy.