International Study Finds Species Migratory Highways Off San Diego Coast

Two new freeways may need to be added to Southern California maps, as a major scientific study released this week shows two distinct migratory routes in the Pacific Ocean that intersect off the San Diego coast.

The currents mix and cause upwellings of nutrient-rich water that draw marine life “like the savannah grasslands of the sea,” wrote study co-authors Barbara Block of Stanford University and Daniel Acosta of UC Santa Cruz.

The study points at two major highways for marine life—the California Current running south along the coast, and the North Pacific Transition Zone, a current that separates frigid Arctic waters from warm tropical waters, about halfway between Alaska and Hawaii. Those currents intersect along several hundred miles of California coast, including the local coastline and extending into Mexico.

The analysis is a result of a 12-year-long tagging study of predatory fish and sharks—and the fatty marine mammals that they prefer to eat, a total of 23 species—that “reveals how migrations and habitat preferences overlap,” giving scientists “a remarkable picture of critical marine life pathways and habitats,” according to a study summary.

Scientists and researchers from 80 different countries took part in the study, and it includes the combination of the findings of more than 100 published studies. Funded primarily by charitable foundations, part of the effort includes a near-real-time map of tagged animals as they munch their way along the Southern California coast, which can be found on the GTOPP website.

Several species—leatherback sea turtles, albatrosses, sooty shearwaters and salmon sharks—were observed to travel across the Pacific to gorge themselves in the California Current upwellings off the California coast.

The leatherback sea turtle travels from Indonesia and back to California and Mexico waters and beaches.

The upwelling is visible to Los Angeles residents in the form of the dozens of squid-fishing boats that sit off the coast each winter, harvesting the food that draws the predators.

Other predators make north-south commutes, including yellowfin tuna, blue whales, and white and salmon sharks, the study noted.

The study was the first to overlap tracking data from 23 ocean predators, like sharks, with food like anchovies, krill and squid.

Although such behavior has been noted for decades, the new study for the first time “linked the movements of tunas, sharks, and blue whales north and south along the southwestern U.S. coastline with seasonal changes in temperature and chlorophyll concentrations” in the Pacific, the study said.

The study also raised questions, like why a two-year-old bluefin tuna would “wake up in the light of the Japan Sea and decide to swim to Baja,” Block said.

City News Service contributed to this report.