People often think of ecosystems and the animals within them as separate from other ecosystems. The reality is that many ocean animals are migratory. Throughout the course of their lives, these migratory species will interact with a number of different ecosystems as they travel across the seas.
Sea turtles are migratory species that interact with a diverse array of marine plants and animals. There are seven species of sea turtle found all over the world, and females of all species return to the same beach that they hatched on to lay their own eggs.
One particular population of loggerhead sea turtles hatches their eggs on the coast of Japan. Although they are born in Japan, they don’t necessarily spend their whole lives there. A small group of the turtles rides a large ocean current that takes them to feeding grounds about 12,000 kilometers (7,456 miles) away, in Baja California, Mexico.
Loggerheads have adapted their diet to the long journey. They usually eat bottom-dwelling invertebrates such as clams, mussels, crabs, and shrimp. Because bottom-dwelling organisms are not readily available as loggerheads journey across the open ocean, the turtles shift their diet, eating jellies, squid, floating egg clusters, and other surface-dwelling invertebrates.
Loggerhead migrations can take them through the Great Pacific Garbage Patch, an area in the Pacific Ocean where debris collects near the ocean surface. The turtles frequently ingest plastic bags and popped balloons floating in the garbage patch—they mistake these materials for their gelatinous prey.
While in the open ocean, loggerheads are susceptible to predators such as sharks. However, humans are their greatest threat, says Jeffrey Seminoff, program leader at the NOAA Fisheries Science Center’s Marine Turtle and Assessment Program in La Jolla, California.
The turtles’ interactions with marine fisheries are particularly dangerous, Seminoff says, “whether it is longlines or drift nets.”
“Certainly with the loggerheads in the north Pacific, they are transitioning through a lot of habitats that have some pretty intense fishing pressures,” he says. “Once they get into coastal habitats, there are threats of direct harvest. There are a number of countries throughout the Pacific Rim nations that still do harvest sea turtles, whether it’s illegal or not.”
Longlines are fishing lines that can be kilometers long and include hundreds, if not thousands, of baited hooks. Large fisheries that use longlines and gill nets are located in the loggerheads’ migratory route off the west coast of North America. The sea turtles often become tangled in these gill nets, or mistake the longline bait for food. The fishing equipment is often unattended, and usually results in the drowning of trapped turtles.
Seminoff says fishermen and conservationists are attempting to reduce the unintentional capture of turtles in the Pacific. Strategies include changing the shape of hooks and attaching a device to the end of a trawl net that allows turtles to escape if they are caught.
“It’s important, I think, to note that while the fisheries’ bycatch is one of the biggest conservation challenges, there is also a cadre of scientists and conservation practitioners throughout the world that are trying to mitigate those impacts through creating these technological fixes to gear,” Seminoff says.
Along their journey, loggerheads interact with many other species and ecosystems. They travel through ocean habitats filled with large fish such as tuna and swordfish. They migrate past the coral reefs around the Hawaiian Islands, swimming alongside humpback whales and dolphins. As loggerheads continue their journey through the kelp forests off the coast of California, they may see sea otters feeding on urchins or gray whales making their own migration to the warm lagoons of Baja. Once in Baja, the sea turtles may feed off invertebrates that found refuge in mangrove swamps.
A closer look at the journey of the loggerhead sea turtle reveals just how many of the world’s ecosystems are connected. It also shows how nations must work together to conserve migrating species like the loggerhead.
“I think sea turtles in general, whether it’s a loggerhead or any of the other species, really underscore habitat connectivity in the oceans . . . and really, from a conservation standpoint, it underscores the need for multinational cooperation when we are trying to conserve sea turtles,” Seminoff says. “One nation can’t solve all the problems.”