The bottlenose dolphin is the largest of three species found in the western Mediterranean.
In the harbour, fishermen can often be seen mending nets they claim have been destroyed by a type of dolphin they have dubbed El Negro, or "the Black One" in Spanish.
Named after its dark grey -- almost black -- skin, the bottlenose dolphin is the largest of three species found in the western Mediterranean.
"He sees us coming and knows exactly when and how to attack the fishing net," said boat-owner Said Shaib, 44.
"When he attacks, we are sometimes left with only 10 to 20 sardine boxes" from a catch that can reach 400 boxes a day -- "and each time huge damage to the nets".
"It gets very expensive," said Shaib, with fuel expenses and time wasted on shore fixing nets.
In a long-neglected region still reeling from the gruesome death of a fishmonger crushed in a rubbish truck, the dolphin attacks have fuelled long-standing grievances.
Mouhcine Fikri, 31, was accidentally killed last year in Al-Hoceima as he tried to protest against authorities seizing and destroying swordfish caught out of season.
His death in the Rif region sparked outrage nationwide, but also ongoing protests in his hometown, including to demand state support for an economically devastated region that has long relied on fishing for income.
"In Al-Hoceima, the economy has always been based on fishing," Shaib said.
"We used to coexist with the dolphin. But from 2010, attacks by El Negro soared."
An expert on local fauna said it was not clear why bottlenose dolphins, which can measure up to four metres (13 feet) long and weigh 400 kilos (almost 900 pounds), were attacking nets.
"It's a very intelligent animal. It attacks to feed itself, but possibly also to free the sardines," the expert said, asking to remain anonymous.
Governor Mohamed El Yaakoubi agreed that bottlenose dolphins are a problem.
"Fishing has suffered a lot," he said.
Since 2011, catches in Al-Hoceima have dropped by half from 8,972 to 4,576 tons a year, according to official figures.
But Mohamed Jabran, an official with the water and forests authority, said dolphins may not be entirely at fault.
"With all the overfishing, there's less to catch and therefore more competition," he said.
The crisis has led many fishermen to flee Al-Hoceima on their boats in search of better catches operating from ports along the Atlantic coast.
Many others, like Shaib, have sold their boats and nets to convert to longline fishing, as dolphins tend not to attack fishing lines.
In the harbour, fishermen complain that the state has not done enough to protect their livelihoods, including to ward off the dolphins.
"The state has done nothing against El Negro," said fisherman Abdelhamid, who refused to give his second name.
It's "because dolphins are good for tourism", a former sardine catcher added, also asking not to be identified.
Like many of his colleagues, he accused Rabat of wanting to "kill fishing" to build a tourist marina in the area instead.
Local official Nourredine Boughdane rejected such accusations, however.
"It makes no sense. The economy here is based on two sectors: fishing and tourism," he said.
Governor Yaakoubi said the government would never do anything to harm the bottlenose dolphin, a species protected by a regional conservation agreement.
"Morocco scrupulously respects the protection of the species," he said.
The country is signatory to the Agreement on the Conservation of Cetaceans of the Black Sea, Mediterranean Sea and Contiguous Atlantic Area, or ACCOBAMS, he said.
Authorities tried to introduce ultra-sound emitting devices on fishing boats to scare away the dolphins, Yaakoubi said, but the cetaceans understood this meant fishing was under way and flocked to the nets in even greater numbers.
Instead, the state is now looking into compensating fishermen for lost nets, the governor said, and a sturdier French net is being tested for possible use.
Meanwhile, drift nets have made a comeback in Al-Hoceima, despite being banned since 2010 as they endanger dolphins and other protected marine species.
One activist, who asked to remain anonymous, said longline fishing boats along the coastline near Al-Hoceima were using the prohibited nets.
"Everybody is buying them at the moment," the activist said, suggesting authorities may be turning a blind eye to avoid further unrest in the region.
"They declare their catch as coming from longline fishing."