Method and sources
Every number in this app and on this site, where it came from, and what it cannot tell you. Written for the sceptical reader.
This page exists because the audience for this product knows more about fishing than we do, and the only thing we can offer that a forum thread cannot is a chain of reasoning that can be checked.
What the model computes
Given a lure colour, a depth, a water type, a time of day and a target species, it estimates the apparent contrast of that lure against the water, in the species’ own visual channels, and the distance at which it plausibly becomes detectable.
- Sunlight at the surface, from a daylight standard modulated by Rayleigh extinction along the air mass.
- The air–water interface: Fresnel reflection (which throws away more than half the light at grazing sun) and refraction into Snell’s window.
- The water column: Beer–Lambert with the diffuse attenuation coefficient of the chosen water — Jerlov’s optical types for the sea, and a CDOM / sediment / chlorophyll parameterisation for fresh water.
- The lure surface: a smoothest-metamer reflectance reconstruction, plus a Stokes-shift term for fluorescent finishes.
- The sight line: Duntley’s contrast law, including the backscattered veiling light.
- The eye: Govardovskii pigment templates from measured cone λmax, integrated in photon units, with von Kries adaptation to the water background.
Where the numbers come from
- Jerlov, N.G. (1976). Marine Optics. Elsevier — the optical water types.
- Pope, R.M. & Fry, E.S. (1997). Applied Optics 36(33), 8710–8723 — pure water absorption.
- Duntley, S.Q. (1963). JOSA 53(2), 214–233 — the contrast transmittance law.
- Kirk, J.T.O. (2011). Light and Photosynthesis in Aquatic Ecosystems, 3rd ed. — inland water optics.
- Govardovskii, V.I. et al. (2000). Visual Neuroscience 17, 509–528 — the visual pigment template.
- Lythgoe, J.N. (1979). The Ecology of Vision. Clarendon Press — the foundational text.
- Aksnes, D.L. & Utne, A.C.W. (1997). Sarsia 82, 137–147 — the fish visual-range model.
- Hart, N.S. et al. (2011). Naturwissenschaften 98, 193–201 — cone monochromacy in sharks.
How confident each species is
Most fish have never had their visual pigments measured. Rather than invent a curve — which is what every lure-colour chart quietly does — every species carries a grade, and the grade is on the card, not in a footnote.
- Measured — direct microspectrophotometry, ERG or behavioural spectral sensitivity for this species.
- Close relative — measured in a congener with the same feeding ecology; the substitution is named.
- Same family — a coarser substitution. Reliable for which end of the spectrum, not for fine ranking.
- Estimated — no spectral data exists. The page says so in the strongest terms available.
What we found while building it
Two things worth reporting, because they changed the model and because nobody has to take our word for either.
First: Jerlov’s 1976 table of attenuation coefficients, taken literally, says clear ocean water is more transparent to red light than pure water is. At 700 nm his type-I value implies less attenuation than Pope & Fry’s measured pure-water absorption permits, which cannot be true. We keep the modern measurement, which makes this app up to 30 % more pessimistic about red penetration than the classic table — the conservative direction for our own headline claim.
Second: the published fixed-point solver for the standard fisheries visual-range equation is not a contraction in the regime that matters here — a big bright lure in clear water — where it oscillates and returns nonsense. We solve the same equation by bisection instead. The two independent range limits (contrast-limited and light-limited) then agree with each other, which is the check that says the formulation is right.
What it deliberately does not model
- Fish behaviour. It cannot tell you what a fish will do, only what it can distinguish.
- Polarisation, which many fish are sensitive to and many lure finishes produce.
- Motion, vibration and the lateral line — enormous in real fishing, and not optics.
- Individual variation: λmax shifts with age, season, temperature and the A1/A2 pigment ratio.
- Regulations. Size limits, closed seasons and quotas vary by region and change without notice. Ask your local authority.