I Analyzed 827,624 Fish Catches Over 4 Years — Here's What I Found About Yellowtail, White Sea Bass, and Halibut in San Diego

Peter Yee with a couple of solid yellowtail.

I've been diving San Diego for over 25 years. I've always had my own theories about what makes a good day — water temp, moon phase, tides, time of year. Every experienced diver does. But I wanted to actually test those theories against real numbers, not just gut feel.

So I pulled every commercial passenger fishing vessel (CPFV) dock report filed in San Diego from 2021 through 2024 — four full years of data. Then I cross-referenced every single day against NOAA sea surface temperature readings and lunar cycles.

The final dataset: 827,624 fish. 302,179 angler-trips. 1,461 days.

Some of what I found confirmed what I already knew from decades in the water. Some of it genuinely surprised me. And a couple of findings flat-out contradicted things I'd believed for years.

I want to share all of it.

Quick Note on the Data

This is all from party boat dock totals — hook-and-line catches, not spearfishing. For yellowtail and halibut, the patterns translate pretty directly to diving. For white sea bass, party boats barely catch them (WSB is really a diver's fish), but the data still tells us a lot about when they're active and feeding.

I measured everything as fish per angler-trip. A rate of 1.0 means every angler on the boat averaged one fish. It normalizes for boat size and how many trips went out, so we're comparing apples to apples.

Yellowtail: Way More Flexible Than I Thought

The yellowtail dataset was massive — 44,279 fish across 52,915 angler-trips. With that kind of volume, the patterns are solid.

The biggest surprise was temperature. I always figured yellowtail wanted water in the upper 60s to low 70s. Turns out, every SST reading from 63°F to 75°F produced catch rates above 1.0 fish per angler. That's a 12-degree window. The peak was actually 65°F at 1.19 fish/angler — not 72 or 73 like most people assume. Some of the best catch rates in the entire dataset came when the water was 63°F.

If you're sitting at home because the water is "too cold" at 64 degrees, you're missing good yellowtail fishing.

The season turned out to be bimodal. Everyone knows about the spring run — March through May, peaking in May at 1.11 fish/angler. But there's a second peak from July through November that most people wind down too early on.

And here's the one that really got me: November had the highest catch rate of any month for any species in the entire four-year dataset — 1.41 fish per angler. November. When most people have put their gear away. The late-season fish are bigger, there's almost no boat pressure, and the yellows are feeding hard before winter. If you're only diving for yellowtail June through August, you're missing the best month of the year.

Moon and Weekday Effects

Full moons were best for yellowtail (0.92 fish/angler), quarter moons close behind (0.87), new moons worst (0.79). About a 16% spread — worth paying attention to, but not the biggest factor.

The weekday effect was bigger than the moon. Tuesday averaged 1.04 fish per angler. Saturday averaged 0.75. That's 38% better midweek. Consistent across all four years. More boats on weekends means more noise over the kelp edges and high spots. The fish don't leave — they just get harder to approach. For divers, that effect is probably even stronger than it is for the guys dropping bait from a boat.

White Sea Bass: New Moon Changes Everything

WSB are rare on party boats — only 179 fish in four years across 2,831 angler-trips. But when you have sparse data, only the strongest signals show up. And the signal here was unmistakable.

New moon catch rates for white sea bass: 0.152 fish per angler. Full moon: 0.031. That's nearly five times better in the dark.

This was the single strongest correlation in the entire dataset, any species, any factor. Nothing else came close.

Jon Stenstrom with a 65lb WSB.

It makes sense when you think about how white sea bass hunt. They're lateral line predators — they feel vibration and pressure waves in the water. They don't need to see their prey. Darkness actually gives them an edge because the baitfish they're hunting rely more on vision. Take away the light, and the WSB owns the encounter.

Research backs this up. Aalbers and Sepulveda (2015) tagged 173 white sea bass off Southern California with depth/temperature sensors and found they're crepuscular feeders — their movement rates jump 24% during twilight. They live in a narrow thermal band of 55-61°F at depth and 95% of catches happen between April and October.

Our temperature data lined up: best catch rates at 63°F (0.19 fish/angler) and 65°F (0.12). WSB want cooler water than yellowtail. Peak month was June.

I'll be honest — I've seen white sea bass on full moons, and friends of mine have shot some nice ones under a full moon too. It definitely happens. But the data across four years is pretty clear — new moon is where it's at for WSB overall. The darkness combined with the spring tide current flowing through the kelp beds — that's the setup. Full moons can still produce, but if you're picking your days, the numbers say go dark.

If you're planning a white sea bass dive and you can only pick one variable to optimize, pick the new moon.

Halibut: 61 Degrees Is the Magic Number

Halibut had the tightest temperature response of any species. Out of 505 fish across 10,600 angler-trips, one temperature dominated.

At 61°F, halibut catch rates hit 0.24 fish per angler — four to five times higher than any other temperature. Drop to 59 or rise to 63 and the rate falls off a cliff. It's not "halibut like cooler water." It's a specific trigger. When the nearshore SST hits 61, the halibut bite turns on.

Seasonally, that maps to March (0.12 fish/angler) and April (0.11) — exactly when you'd expect San Diego water to be sitting in that low-60s range during the spring warm-up.

And there's a reason the timing is so tight: grunion. The grunion runs in San Diego peak from March through June, and they're the single biggest driver of the spring halibut bite. When grunion come up on the beach to spawn on those spring tide nights, halibut move into the shallows and absolutely gorge. If you've ever cut open a spring halibut, you know — their stomachs are stuffed with grunion. The 61°F water, the March-April peak, the shallow sandy flats — it all lines up because that's when and where the grunion are running. For divers, the days right after a confirmed grunion run are prime time. The halibut are still in tight to the beach, fat and aggressive, sitting in a few feet of water on the sand.

Quarter Moons Beat Spring Tides

This one challenged something I'd always assumed. A lot of us target halibut on spring tides — new and full moons — thinking the stronger current pushes bait and fires up the bite. The data says the opposite.

Quarter moons (neap tides) produced the best halibut catch rates across all four years. Not a one-year fluke. All four.

My theory: halibut are ambush predators that bury in the sand and wait. They need the bottom to be settled — good visibility at substrate level, clear contrast between their camouflage and the surrounding sand. Heavy tidal flow stirs everything up. Neap tides keep the bottom clean, and the halibut can do what they do best: sit still and strike.

For divers hunting halibut on the flats, this is immediately actionable. Plan around quarter moons, not spring tides.

The weekday effect was the biggest of any species. Wednesday: 0.087 fish per angler. Sunday: 0.036. Nearly 2.5 times better midweek. Halibut are in shallow, accessible water — the weekend pressure hits them hardest.

The Big Takeaways

After crunching every combination of temperature, moon, month, and day of week across three species over four years, a few things stand out:

Water temperature is the #1 predictor for every species. Before you check the tide chart or the moon phase, check the SST. Yellowtail: 63-75°F. White sea bass: 63-65°F. Halibut: 61°F. Each species has its range, and when the water is in that range, the other factors start to matter.

Moon phase is real, but it's species-specific. Full moon for yellowtail. New moon for white sea bass. Quarter moon for halibut. There's no universal "best moon" for diving. If someone tells you new moons are always best or full moons are always best, they're only thinking about one species.

Dive midweek if you can. Every species, every year, weekday catch rates beat weekends. The gap ranges from 38% (yellowtail) to 150% (halibut). Boat and diver pressure is real, and the fish know it.

Don't sleep on November yellowtail. 1.41 fish per angler. The best single-month number in the entire dataset. Bigger fish, less pressure, aggressive feeding. Get out there.

Quick Reference

Yellowtail: 63-75°F water, target November and May, full moon, Tuesday-Thursday

White Sea Bass: 63-65°F water, target June, new moon (5x better than full), dawn and dusk

Halibut: 61°F water, target March-April during grunion runs, quarter moons, Wednesday is your best day

Try the Live Conditions Tool

I built all of these findings into a free tool that scores current conditions for each species in real time. It pulls live CDIP buoy data, NOAA SST readings, swell forecasts, and tidal predictions, then runs them through the scoring model we developed from this four-year dataset. You can check conditions for eight San Diego dive sites — La Jolla, Point Loma, Coronado Islands, and more.

Check live conditions at spearfactor.com/conditions

The ocean has patterns. 827,624 fish over four years was enough data to finally see them clearly.

Data sourced from San Diego CPFV dock totals (sandiegofishreports.com), NOAA NCEI sea surface temperature records, and lunar phase calculations. White sea bass research: Aalbers, S.A. and Sepulveda, C.A. (2015), Seasonal movement patterns and temperature profiles of adult white seabass off California, Fishery Bulletin 113(1).

Photo 1 credit: Peter Yee with some nice yellowtail. Photo 2 credit: Jon Stenstrom with his 65lb White Seabass.