Bigeye Tuna — Full Transparency (v1)

Last updated: January 2026 Live URL: primetimefishing.app/bigeye

This page is designed to leave nothing out: the exact equations, every variable we use, the open-access URLs behind each driver, verbatim quotes (with page pointers where available), and a plain-English explanation of what is research-backed vs what is calibrated.

The exact math (Bigeye v1)

Bigeye is an offshore all-day rating built from “lifts” that map into a 1.0–5.0 rating.

L_ocean_raw = L_sst + L_chl
L_ocean     = clamp(L_ocean_raw, -0.02, +0.02)   // small ocean cap (modulate, don't dominate)

L_total_raw = L_phase + L_time_avg + L_ocean
L_total     = clamp(L_total_raw, 0, L_REF)       // global clamp

rating = 1 + 4 × (L_total / L_REF)               // where L_REF = 0.28

Important: Bigeye v1 is intentionally conservative, so it typically does not reach 1.0/5 or 5.0/5 in practice.

Calculation methodology (All‑day rating)

This section is the "how it's calculated" reference for Bigeye v1.

Step 1: Ocean block (SST required; CHL optional)
L_ocean_raw = L_sst + L_chl
L_ocean     = clamp(L_ocean_raw, -0.02, +0.02)
If SST missing → L_ocean = 0.00. If SST < 20°C → L_chl = 0.00 (cold gate).

Step 2: Total lift
L_total_raw = L_phase + L_time_avg + L_ocean
L_total     = clamp(L_total_raw, 0, L_REF)

Step 3: Lift → rating
rating = 1 + 4 × (L_total / L_REF)   // L_REF = 0.28

Variables (what’s research-backed vs calibrated)

Research-backed means the driver/pattern/mechanism is supported by open-access sources. Calibrated means we chose the exact curve shape/thresholds/weights/caps to produce a stable 1.0–5.0 score and to avoid overclaiming from region- or gear-specific studies.

Moon phase (L_phase)

Research-backed: Jatmiko et al. (2016) report significant differences among moon phases with the highest average catch rate at full moon in their dataset.

Source: Jatmiko et al. 2016 — ILMU KELAUTAN (open access)

“The result showed that the average catch rate of bigeye tuna differed significantly among the moon phases. Tukey post-hoc tests showed that the average catch rate at full moon was the highest among the groups with around 0.3/100 hooks.” (PDF p.1 / journal p.101)

Calibrated: the exact curve shape is a product choice (smoothness + stability). We implement a full-moon peak curve in code (moonPhaseBoostBigeyeFull) and scale it via:

L_phase = (phaseBoostValue × phaseWeight / 2.0) × 0.26
phaseWeight = 1.425

Night availability (L_time_avg)

Research-backed: tagging studies show strong diel vertical behavior (shallower at night).

Source (open PDF): Musyl et al. 2003 — Bigeye vertical movements

“At night, however, bigeye tuna generally restrict their vertical movements to the surface layer.” (PDF p.2)

Calibrated: we translate this into a small, fixed all-day-average lift:

nightAvailability = 0.38
timeBiasAvg       = nightAvailability × 0.5   // assume ~50% of a day is night
L_time_avg        = (timeBiasAvg / 0.4) × 0.03
               = 0.01425

Oceanography (SST + chlorophyll-a/SSC) (L_ocean)

Research-backed: regional studies support SST and chlorophyll (or SSC proxies) as predictors/covariates for Bigeye catchability/habitat.

Source (open PDF): Syamsuddin et al. 2013 — Fishery Bulletin (open access)

“SST was a more important oceanographic predictor of Bigeye Tuna catches than were the other environmental variables (SSHA and chlorophyll-a) in this region.” (PDF p.10)

Calibrated: we keep the ocean effect small and capped, and apply a cold-water gate:

• Ocean cap: L_ocean = clamp(L_sst + L_chl, -0.02, +0.02)
• Missing-data rule: ocean block only applies when SST is present; CHL optional
• Cold gate: if sstC < 20°C, we force L_chl = 0.00

Environmental variables (verification)

This section highlights the key open-access quotes behind the SST/CHL bands used in Bigeye v1.

SST anchors

Syamsuddin et al. 2013 (open PDF): PDF

“Our results indicate that Bigeye Tuna catches increased in areas with relatively low temperatures (24–27.5°C) and decreased at temperatures >27.5°C (Fig. 6B).” (PDF p.10)

Setiawati & Miura 2014 (ResearchGate landing page): Link

“Statistical analysis showed the optimum of SST for bigeye tuna is less than 29.1°C and more than 27.4°C.” (Abstract)

Chlorophyll / SSC anchors

“High probabilities of Bigeye Tuna presence were observed … for chlorophyll-a levels ranging from 0.04 to 0.16 mg m–3.” (Syamsuddin 2013, PDF p.8)

“In addition, the optimum value of SSC was 0.055 to 0.175 mg m-3.” (Setiawati & Miura 2014, Abstract)

Song et al. 2009 (open access PDF): PDF

“0.090–0.099μg·L−1” (PDF p.12, Table 5; units note: μg/L = mg/m³)

Worked examples (inputs → lifts → rating)

Best case (near full moon + favorable ocean)

Assume:
f = 0.50  (Full Moon peak)
SST = 27.5°C  → L_sst = +0.017
CHL = 0.12 mg/m³ → L_chl = +0.010

L_ocean_raw = 0.017 + 0.010 = 0.027 → capped to +0.020
L_phase     = (1.0 × 1.425 / 2.0) × 0.26 = 0.185
L_time_avg  = 0.014

L_total_raw = 0.185 + 0.014 + 0.020 = 0.219
rating      = 1 + 4 × (0.219 / 0.28) = 4.1/5

Low case (off-peak phase + cold water)

Assume:
f = 0.00  (far from full; curve floor ≈ 0.2)
SST = 17.0°C → L_sst = -0.010
CHL ignored (cold gate below 20°C) → L_chl = 0.000

L_ocean = -0.010
L_phase = (0.2 × 1.425 / 2.0) × 0.26 = 0.037
L_time_avg = 0.014

L_total_raw = 0.037 + 0.014 - 0.010 = 0.041
rating      = 1 + 4 × (0.041 / 0.28) = 1.6/5

Model changelog (Bigeye)

• 2026-01: Published full transparency page (this page). No changes to scoring logic.