Watching dolphins spring into the air and fall back into the water with a thunderous splash can be the highlight of the day for beachgoers or pleasure boaters. But what are they doing? Are they feeding? Are they playing?

Depending on the circumstances, they might be showing their annoyance at being disturbed.

Bottlenose dolphins are a common sight near the beaches and in the bays along the northern Gulf of Mexico coast. But it’s hard to get a good look at the graceful marine mammal without feeling a bit of wonder. And most people know very little about them.

Most people are aware they are an air-breathing mammal and not a fish. But throughout the northern Gulf they are frequently misidentified as porpoises. There are no porpoises in the Gulf of Mexico.

“We don’t have porpoises,” said Stacey Horstman, bottlenose dolphin conservation coordination for the southeastern region of NOAA Fisheries. “They are a colder water mammal, north of North Carolina.”

There are other species of dolphins in the Gulf of Mexico. But those seen from the shore and from boats near the shore are almost invariably common bottlenose dolphins with gray bodies, white underbellies and, as their name suggests, a pronounced snout.

(Photos/Robert DeWitt ) Typical dolphin behavior includes leaping out of the water and slapping the surface with their fluke.

(Photos/Robert DeWitt ) Typical dolphin behavior includes leaping out of the water and slapping the surface with their fluke.

Their ability to tolerate brackish water, unlike other species of dolphins, is probably what makes them the dominant nearshore species. Intelligent, sleek and nonthreatening, they are appealing to most people — enough so that many people pay to get a closer look at them.

“There are a couple of different groups,” said Nelson Box, who runs Surf’s Up Dolphin Cruises in Perdido Bay. “You can typically find one of them. They can be at the dock or they can be two hours away from you.”

Box starts taking groups of up to 49 people in 50-foot converted Navy utility boats out of Orange Beach in search of dolphins beginning at spring break. His busy season peaks when school is out for summer vacation and ramps down gradually to about the time of the National Shrimp Festival. But the season has nothing to do with the availability of dolphins to watch.

“The dolphins are here year-round,” he said. “We just run out of people.”

Box usually succeeds in finding dolphins to watch but it can take some time. And when he does find them, he has no idea how long they will hang around.

“From trip to trip, it’s different,” Box said. “You’re dealing with something on its terms. They don’t have a schedule. They have lots of different behaviors but there’s no telling when you’ll see what behavior.

“They kind of will get in patterns. But that will change. They can stay in an area for a month and then something changes — food, water temperature — and they’re gone.”

While their behavior might be a bit varied, their presence is fairly predictable. That’s because bottlenose dolphins come in two subspecies, coastal and offshore.

The coastal variety lives in the bays and nearshore waters along the coast. They are a resident population that stays here year-round. Offshore dolphins, as their name implies, live farther out into the Gulf and are migratory.

Dolphins vary from 6 feet to 9 feet long and weigh as much as 600 pounds. Both subspecies are gray with lighter underbellies but offshore dolphins tend to be darker and somewhat larger. The males are larger than females in both subspecies.

Both subspecies are large, powerful animals whose only natural enemies in the Gulf are sharks. And sharks are generally only a threat to unattended dolphin young or when a dolphin is injured or sick.

Inshore dolphins tend to be found in smaller groups of two to six. Offshore dolphins may gather in groups of up to 20.

Dolphin groups aren’t “pods” as they are often called. Pods are permanent groups. Dolphins are known to trade in and out of different social groups, Horstman said.

(Photos/Robert DeWitt ) Typical dolphin behavior includes leaping out of the water and slapping the surface with their fluke.

(Photos/Robert DeWitt ) Typical dolphin behavior includes leaping out of the water and slapping the surface with their fluke.

They do not pair off with mates, but breed indiscriminately, said Noel Wingers, who works at the Dauphin Island Sea Lab. But males may form pair bonds and stick together permanently.

Box might find it easier to locate dolphins if he fed them. That would make their behavior fairly predictable. But feeding wild dolphins is illegal. The Marine Mammal Protection Act, passed in 1972, forbids hunting and killing marine mammals. But it also forbids people to feed, attempt to feed or harass dolphins and other marine mammals.

Chasing dolphins in a boat, swimming toward them and trying to touch them can all be considered harassment. Prohibiting contact protects both dolphins and people, Horstman said.

“They have a natural wariness of people and boats,” Horstman said. “When they have been illegally fed, they start associating people and boats with food. They start looking for that free handout.”

Too much interaction with humans often turns out bad for dolphins. They don’t know which boats will feed them so they approach all boats. That can lead to nasty injuries from boat props.

“It also puts people at risk,” Horstman said. “They get so conditioned to boats and people that they associate people with food. They have been known to actually bite people.”

Dolphins should forage naturally for their food, Horstman said. Those depending on boats for food can lose their foraging instincts. They also pass on the bad behavior to their young and run the risk of getting spoiled food that can make them sick.

Many fishermen, both commercial and recreational, consider dolphins a nuisance. Dolphins are efficient predators and when they show up, gamefish like speckled trout or red snapper often quickly disappear to avoid being eaten.

Fisherman-dolphin interaction can have tragic consequences for the dolphin. They’re artful at snatching fish off the lines of fishermen without getting hooked. But sometimes they get hooked in the mouth or even ingest a hook.

Fishing line can also be deadly for dolphins if they get tangled in it. It can cut into their bodies, tails and fins.

Fishermen should reel in their lines when a dolphin shows up, Horstman said. If they must release a fish while a dolphin is near, they should try to do so quietly on the opposite side of the boat from the dolphin. And if there’s a dolphin in the area that won’t leave, anglers should try to find another spot.

Dolphins naturally hang out near shrimp boats and other commercial fishing vessels. When shrimpers cull their bycatch, it’s an easy meal for dolphins. But it can also lead to dolphins becoming entangled in nets.

Some dolphin injuries aren’t accidental. In 2014, a juvenile was arrested for shooting a dolphin with a hunting arrow. The dolphin eventually died from an infection.

In 2012, a dolphin was found dead in Perdido Bay with a screwdriver sticking out of its head. In 2009, a Florida man was sentenced to two years in prison for throwing a pipe bomb at a dolphin. And charter boat captains from Panama City and Orange Beach were convicted of shooting at dolphins trying to steal fish from their clients’ lines.

Not all dead dolphins are the results of attacks.

“They have a normal life cycle so you have animals that die,” said Ruth Carmichael, senior marine scientist at the Dauphin Island Sea Lab and associate professor of marine science at the University of South Alabama. “And they die during the calving process.”

Sick or injured dolphins often strand or beach themselves. It is a behavior which might seem perplexing to people. Wingers, who serves as the marine mammal stranding coordinator for the Alabama Marine Mammal Network at the Dauphin Island Sea Lab, said most of the stranded animals she sees are dead.

But sometimes stranded marine mammals are still alive. They strand themselves when they are sick and injured so they don’t become weak and drown or fall prey to sharks. Dolphins can remain alive outside of the water, Wingers said, but a dolphin’s rib cage isn’t designed to support its internal organs out of water and being on land causes physical stress.

An unusually high number of strandings followed BP’s 2010 Deepwater Horizon oil spill. In 2011, a year after the spill, there was unusually high mortality among dolphins and particularly among calves. Many blamed the effects of the oil and the dispersants used on it for the dolphin deaths.

A paper Carmichael authored along with four other scientists suggests the spill might have been a contributing factor, along with extremely cold temperatures that year and an unusually high influx of cold freshwater coming into Mobile Bay.

A NOAA study of the health of dolphins in Barataria Bay, Louisiana, indicates they were in unusually poor health a year after the spill. Some of the symptoms were consistent with problems seen in marine mammals following other oil spills.

All samples and data have been passed along to NOAA, so local scientists have been unable to conduct any research.

“Studies into the effects of the Deepwater Horizon oil spill are ongoing,” Carmichael said. “NOAA is leading the assessment research. Several studies have been published on animals in the northern Gulf. They summarize the state of knowledge.”

For now, the dolphin population isn’t considered threatened or endangered. And the Gulf offers good opportunities to observe them in their natural habitat. Horstman suggests people who want to observe dolphins should approach no closer than 50 yards.

“Dolphins have natural curiosity in their normal behavior,” Horstman said. “They may approach and look and leave.”

“They will give you indicators of whether they want you around them or not,” Box said. “It just takes knowing it and seeing what kind of mood they are in.”