Cabo San Lucas sits at the tip of a peninsula where two oceans collide. The cold, nutrient-rich California Current pushes down the Pacific side. The warm, enclosed Sea of Cortez opens to the east. Where they meet, you get one of the most productive fishing grounds on the planet. Jacques Cousteau called the Sea of Cortez "the world's aquarium." The fishing community calls it something simpler: wide open.
This region runs from Loreto south through La Paz, the East Cape, and down to Cabo, with Magdalena Bay on the Pacific side. It covers world-class marlin fishing on offshore banks, roosterfish on sandy beaches, yellowfin tuna on seamounts, and diving that ranges from schooling hammerheads to whale sharks to a marine park that's added 463% more biomass since fishing stopped. The water temperature difference between the Pacific side and the Cortez side can be 15 degrees on the same day. That's not trivia. That's why satellite data matters here more than almost anywhere.
Why Water Temperature Runs These Waters
Baja Sur is two fisheries in one, and temperature is what separates them.
The Pacific side runs 65-77°F depending on season, cooled by the California Current and coastal upwelling. The Cortez side runs 66-86°F, a semi-enclosed sea that bakes in summer and cools slowly in winter. At the tip of the peninsula, these two water masses collide. That boundary is visible on SST imagery, and it shifts daily.
Offshore, temperature breaks along seamounts and banks are where the money is. Striped marlin stack up along 1-2 degree breaks where Pacific cool water meets Cortez warm water. Yellowfin tuna at Gordo Banks concentrate where SST sits around 71-73°F with chlorophyll at 0.2-0.3 mg/m3. Research shows that combination produces 65-80% higher catch rates than surrounding water. Neither SST nor chlorophyll alone tells you that. You need both.
Inshore, temperature drives the seasonal rotation. Roosterfish at the East Cape want 75°F water and sandy beaches. Yellowtail show up at Loreto and the East Cape high spots when winter cooling drops water into the low 60s. Sierra mackerel stack along beaches when water stabilizes in the mid-70s. The species you target this week depends on what the water is doing right now.
For divers, temperature determines what shows up. Hammerheads school at El Bajo when water is warmest (peak September-October). Whale sharks aggregate in La Paz Bay when it cools (October-April). Mobula rays form massive schools July through November. The SST calendar is the marine life calendar.
Species and Seasons
Striped marlin: The year-round headliner. Cabo is the striped marlin capital of the world. Peak season runs November through May when they concentrate on the Pacific-side banks. Finger Bank, 50 miles from the marina, produces epic bites of 20+ releases per day. Golden Gate Bank, just 15 miles out, delivers double-digit release days during peak. Research shows highest catch rates at 72-75°F SST, with a strong correlation to elevated chlorophyll above 1 mg/m3. Average fish run 100-150 lbs in March.
Blue and black marlin: Summer and fall species, July through October. Blue marlin in the 300-500+ lb class show up when warmer currents move in and water hits the mid-to-upper 70s. Black marlin are less common but the ultimate trophy, peaking in October. These are the fish that drive Bisbee's Black & Blue, the world's richest fishing tournament, held every October with purses exceeding $11.6 million.
Yellowfin tuna: May through December, peaking in October. Gordo Banks is the tuna magnet. Trophy fish over 200 lbs come off these seamounts when conditions align. The inner bank is reachable by super pangas. The outer bank sits in deeper water 10 miles offshore. Also found at San Jaime Bank, Golden Gate Bank, and Santa Maria Canyon. They want 72-82°F water and feed most aggressively in the upper range.
Dorado (mahi-mahi): May through November with October bringing double-digit catches as the norm. Follow kelp paddies, debris, and temperature breaks. They want 75-85°F water and concentrate along 2-3 degree temperature seams where baitfish stack up.
Wahoo: Late spring through early winter. Found at Gordo Banks (inner bank especially) and the north end of Cerralvo Island after June when water warms. High-speed trolling along seamount ledges. Fish reaching world-record class (130+ lbs) have come off La Paz seamounts. They prefer 73-78°F and tend to work the edges of structure where depth changes fast.
Roosterfish: The signature inshore species. The East Cape from Los Barriles to La Ribera is the roosterfish capital of the world. Peak May through November, best June through August. They hunt along sandy beaches, pushing baitfish into the sand. Fish grow to five feet and 110+ lbs. Sight-fished from pangas or even ATVs on the beach. They want 75°F water and rarely go deeper than 60 feet. Also found at Palmilla Point near San Jose del Cabo.
Yellowtail: Winter and spring species, peaking January through April when cooler water arrives. Found around pinnacles and inshore reefs near Loreto and East Cape high spots like La Reina and La Ribera Reef. Fish in the 20-35 lb class on jigs and live mackerel. They want 62-66°F water, so they show up when the Cortez side cools down.
Sierra mackerel, pargo, and cabrilla: The year-round inshore fishery. Sierra along beaches at dawn during winter and spring. Pargo (snapper) on rocky reefs, best April through July. Cabrilla (leopard grouper) consistent all months on bottom structure. These species keep the panga fleet busy when the big game isn't running.
Magdalena Bay inshore: Seventy miles of mangrove channels on the Pacific side. A completely different fishery: black snook ambushing near mangrove roots, orange-mouth corvina, bay bass, grouper, snapper, pompano. Light tackle, shallow water, year-round. The outer bay produces striped marlin during the sardine run (October-December) with bait balls so thick you can snorkel with feeding marlin.
The Spots You're Looking For
The offshore banks are what make Cabo. Golden Gate Bank, 15 miles northwest of El Arco, is perhaps the most iconic fishing spot in all of Baja. A flat coral bottom at 60-65 fathoms with consistently warmer currents filled with plankton. Finger Bank, 50 miles out, requires a bigger boat but rewards with the region's most concentrated striped marlin fishing. San Jaime Bank, three seamounts rising to 150 feet below the surface, sits closest to the 3,500-foot-deep Tinaje Trough and supports a complete food chain.
On the Cortez side, Gordo Banks dominates. Inner and Outer Gordo, 8-10 miles northeast of San Jose del Cabo, are the yellowfin tuna magnets. The 95 Spot southeast of Cabo, near the continental shelf, produces year-round billfish. The 1150 Bank between the two marinas mixes Cortez and Pacific water characteristics. Santa Maria Canyon connects these features and holds yellowfin, dorado, and wahoo throughout the season.
Inshore, the East Cape is a world unto itself. Sandy beaches where pangas launch through the surf, roosterfish cruising the shallows, and offshore high spots just a few miles out that hold striped marlin. Loreto further north has winter yellowtail around pinnacles and summer dorado of exceptional size.
Diving the Sea of Cortez
The diving here runs the full spectrum.
Cabo Pulmo National Marine Park, on the East Cape coast, is a no-take zone that's been protected since 1995. Biomass has increased 463% since fishing stopped. Over 800 marine species. Rocky reefs with walls of jacks, snappers, sea turtles, and rays. Visibility reaches 90 feet from August through December. No spearfishing, no gloves, no knives. It's a conservation success story, and its health radiates outward to benefit surrounding fishing grounds.
El Bajo seamount near La Paz is the hammerhead dive. Schools of scalloped hammerheads aggregate at cleaning stations from May through November, peaking September-October. It's the only deep structure for kilometers, so everything concentrates there.
Los Islotes at Espiritu Santo Island has a colony of roughly 900 sea lions. Juveniles are famously playful with divers and snorkelers, September through May. La Paz Bay hosts whale sharks from October through April, one of the world's most reliable encounters. And massive schools of mobula rays pass through July to November.
For spearfishermen, Cerralvo Island and Espiritu Santo offer pargo, grouper, amberjack, yellowtail, and wahoo (north end of Cerralvo after June). Only rubber band guns are permitted. Daily catch follows a point system by species. Fishing license and park permits required.
What Chlorophyll Tells You That Temperature Can't
This is one of the few regions where peer-reviewed research has quantified exactly how SST and chlorophyll together predict catch rates.
Striped marlin catch rates off Baja Sur correlate with chlorophyll concentrations above 1 mg/m3 combined with SST of 79-82°F. The fish aren't in the warmest water or the coolest water. They're where productivity and temperature overlap.
Yellowfin tuna at the banks show the same pattern. Water at 71-73°F with chlorophyll of 0.2-0.3 mg/m3 outproduces surrounding water by 65-80%. A bank with the right temperature but dead-clear water won't fish as well as one where upwelling has kicked phytoplankton into gear.
For divers, chlorophyll is the visibility forecast. Low chlorophyll on the Cortez side from July through November means blue water and 60-90 foot visibility. High chlorophyll, especially on the Pacific side year-round, means green productive water. The same satellite data that tells a captain where to troll tells a diver where to find clear water.
Baja South Ocean Science in Plain English
The Sea of Cortez is a young ocean. It's still being pulled apart by the same tectonic forces that created the San Andreas Fault. That gives it dramatic bathymetry: the Guaymas Trench drops over 12,000 feet, with volcanic hydrothermal vents on the bottom.
More relevant to fishing, the Cortez has some of the strongest tidal ranges on Earth. The northern end sees 32-foot tides. That colossal water movement creates mixing down to 1,500 feet, pumping nutrients to the surface continuously. Half of Mexico's total fisheries production comes from this single body of water.
The banks and seamounts around Cabo work like underwater mountains catching the current. As water flows over them, it forces deep nutrient-rich water upward. That creates localized plankton blooms visible on chlorophyll imagery and temperature anomalies visible on SST. The combination of structure plus nutrients plus temperature breaks is why Gordo Banks, Golden Gate, and the other named spots produce so consistently.
El Nino years bring warmer water into the Cortez, pushing tropical species like dorado and blue marlin earlier and further north. La Nina years strengthen upwelling, cool the water, increase productivity, and often improve the striped marlin season. Knowing which phase you're in sets expectations for the whole year.
Fishing & Diving Calendar
January-February: Peak striped marlin on Pacific-side banks. Yellowtail at Loreto and East Cape high spots. Sierra mackerel along beaches at dawn. Whale sharks in La Paz Bay. Gray whales entering Magdalena Bay. Pacific 65-70°F, Cortez 66-72°F.
March-April: Striped marlin still strong. Best swordfish month is March. Yellowtail peak continues. Roosterfish begin appearing. Pargo season starts on the reefs. Pacific 67-72°F, Cortez 70-75°F.
May-June: The transition. Blue and black marlin season begins. Sailfish appear. Dorado numbers building. Roosterfish ramping up at East Cape. Wahoo arriving at Cerralvo. Yellowfin starting at Gordo Banks. Hammerheads begin at El Bajo. Pacific 70-75°F, Cortez 75-80°F.
July-August: Full summer. Everything offshore is in play: blue and black marlin, sailfish, dorado, yellowfin, wahoo. Peak roosterfish inshore. Mobula rays forming schools. Best dive visibility beginning. Pacific 73-77°F, Cortez 80-86°F.
September-October: Peak season across the board. Blue and black marlin at their strongest. Cow yellowfin over 200 lbs possible. Dorado numbers spectacular. Bisbee's Black & Blue in October. Hammerheads peak at El Bajo. Sardine run begins at Magdalena Bay. Whale sharks arriving in La Paz. Pacific 74-77°F, Cortez 80-85°F.
November-December: Striped marlin returning to dominance. Dorado and wahoo still around. Sierra mackerel arriving. Whale sharks peaking in La Paz. Sardine run continuing at Mag Bay. Tropical species winding down as water cools. Pacific 70-73°F, Cortez 72-80°F.
Fishing nearby waters too? Baja North and Southern California are the closest covered regions. See pricing for what a plan covering Baja South / Cortez costs.