Shipments of fresh fish, delicate flowers, fruits, vegetables and other perishables are among the most common types of perishable cargo shipped through U.S. airports, and that's not likely to change.
But transporting certain types of perishables by ocean has become a more viable option in recent years because of upgrades in maritime refrigeration technology and the relatively lofty rates for air-cargo service, among other factors.
"There are shipments that come in every month with flowers on them," said Christine Boldt, executive vice president of the Miami-based Association of Floral Importers of Florida, citing recent increases in airfreight rates. "I would say, with airfreight going up, that ocean is going to be a much more usable option for flowers in the future."
While roses and other delicate types of flowers generally go by air, the green ferns that serve as floral-bouquet filler material, known in the flower industry as "greens," come into Miami mainly aboard ocean freighters. "Ninety percent of that probably comes by ocean, and the biggest suppliers of that are Costa Rica and Guatemala," Boldt said.
One big motive for shippers to switch their transport mode from air to sea has been the disproportionately punishing impact of heightened jet fuel costs. For shippers of perishables who don't require overnight service, the lower cost per kilo of shipping by ocean can easily compensate for transit times to Miami of three days from Central America and a week or more from South America.
Fuel costs account for a larger share of the cost of air-cargo service than ocean service because ocean carriers can carry more volume, which permits them to spread their fuel costs over a greater volume of shipments. "Fuel is a big cost to a steamship line. But their capacity is so much greater to spread the fuel cost over," compared with air carriers, said Greg Weigel, executive vice president of global transportation for Houston-based forwarder EGL Inc.
"When you take it down to a customer's perspective, the cost of fuel per kilo is much higher for air shipments," Weigel said. And competitively priced ocean rates are readily available because "ocean capacity is growing significantly in a lot of trade lanes."
For some shippers of certain perishables, the time of year can determine the mode of transport, said Doug Tannehill, the Miami-based general manager of Southeast produce for forwarder C.H. Robinson.
"When we get into March and April, the California strawberries are at peak season and a quality suitable enough to ship by ocean," he said. "When you get into October and November, it's the end of the season for strawberries in California, and really the only way to ship is by air. They're very expensive, and the condition of the product doesn't hold as much shelf life."
Different fruits display a diversity of tolerance to transportation, Tannehill said. While raspberries and blueberries typically must be transported by air, apples from South America are hardy enough to go by ocean.
More sensitive items, including asparagus and cherries from South America, also have been moving more frequently on ocean freighters in recent years, said Tannehill, a 25-year veteran of the perishables shipping business.
Modern refrigeration technology for ocean containers not only cools perishable products but also restricts interior moisture levels and guards against product oxidation. "Oxygen and moisture create decay, so if you can eliminate moisture and oxygen to the point where the product can't oxidize, it actually allows the product to have a longer shelf life," Tannehill said.
However, not all ocean options are perfect. The freshness of perishables transported by ocean shows "very good consistency from shipping line to shipping line for short-haul freight in the Caribbean," he said. "When you're looking at three or four weeks' voyage, there are probably some lines that do a better job than others."
Shippers of fresh fish have a multimodal set of transportation choices. Central America's proximity to Miami has helped ocean carriers compete with air carriers for the region's exports of fresh tilapia. When properly stored, tilapia has a 28-day average shelf life from the day the fish is harvested, according to Tom O'Malley, Miami-based vice president for air cargo, Latin America, at UPS.
Among international shippers of tilapia and other hardy perishables, "we're seeing some tendencies to test ocean, or maritime, versus air," O'Malley said. "There are value seekers who are willing to accept products that are not quite as fresh at a price that's distinctly lower."
Farm-raised salmon from Chile must be moved by air, said Jose Carerra, Miami branch manager of Hellmann Perishable Logistics, a unit of Germany-based freight forwarder Hellmann Worldwide Logistics.
Hellmann has helped clients haul snow peas from Guatemala by ocean container, though. "I see more asparagus from Peru each day in containers," Carerra said. "The majority is going by air, but little by little, more is going by ocean. They have found the (container) technology to make it fast enough."
Ocean shipping is certainly cheap enough, compared to air-cargo service, and the ocean-air rate gap has widened, partly because of air carriers' tendency to pad their basic rates with surcharges for fuel and security costs. "Each day, it is more expensive to ship by air," Carerra said.
Perishable cargoes that must go by air, regardless of the rates, include shipments of aquarium fish and such live zoo animals as lions and zebras. But while some critters must be transported in planes, their embryonic counterparts may be seaworthy.
Baby chicks, for example, must be moved by air, while hatching eggs can be shipped in ocean containers, said Carlos Gonzalez, senior director of sales of Fort Lauderdale, Fla.-based air-cargo carrier, motor freight carrier and logistics provider Amerijet International.
Among other lively forms of cargo, fresh-cut asparagus from Peru can grow up to one inch over a period of seven to 10 days while in transit, Gonzalez said. It will turn brown or die, he said, unless stored at an air temperature "right above freezing and about 98 percent humidity."
In recent years, perhaps the biggest change favoring ocean freight at the expense of Miami airfreight has occurred at West Coast seaports, which no longer serve as a big source of trucked-in cargo, Gonzalez said. He said shippers that used to truck Asian imports from West Coast seaports to Miami International for air shipment to Latin America have started transshipping instead by loading the goods onto ships that reach the region through the Panama Canal.
"They would truck the freight into Miami in 96 hours and then try to deliver by air into Latin America within another 48 to 72 hours," Gonzalez said. "That business has pretty much gone away, and a lot of that has gone to ocean."