My latest novel, Legacy, is set in Cadiz, a city in Andalucía that is almost entirely surrounded by sea. This is the view from my heroine Luna’s home at dusk:

The port of Puerto de Santa María glowed in the distance, accompanied by the steadfast wink of the lighthouse. Fishing boats were still out on the ocean and to the east, the faraway Sierra de Cádiz was edged with the fading sky, making los Pueblos Blancos dim to a soft violet.

The fishing boats are especially intriguing for Luna. Having come from New York, she is no stranger to fresh fish on a menu, but she has never had an opportunity to watch traditional fishermen at work, nor to sample some of the delicious fish available in Andalucía.

At the market, she sees stall after stall heaped with fresh, colourful local produce from land and sea:

Luna paused to admire the day’s catch of fish lying on slabs of ice, their silver scales glistening under the neon lights; some of which were specimens she had never heard of. She wondered how they were able to keep them looking still so appetizing in the heat.

‘We have the best red tuna in the world, fished locally in Tarifa,’ the fishmonger proudly told her.

Later, her new boss Ruy takes her out for a meal at a fish restaurant, and they enjoy a delicious meal of tuna Basquaise: tuna with tomatoes, onions and peppers cooked in herbs, fish stock, white wine and olive oil.

The tuna is caught, Ruy explains, through an age-old practice called the almadraba. The name is derived from the Arabic word meaning ‘a place to strike’, and the practice dates all the way back to the Phoenicians. Between February and July, the Andalucían fishermen trap tuna in a series of nets.

Eager to learn more about this ancient custom, Luna agrees to accompany Ruy on his yacht, the Vela Gitana (Sailing Gypsy), to the coastal town of Conil de la Frontera, where the fisherman are landing their catches.

En route, they stop off at an island and go snorkelling:

As they sank beneath the surface… the visibility was extraordinary, the water a crystalline blue with beds of coloured coral on the floor of the sea. They drifted further down into a magical underwater garden with an infinite variety of textures and shapes. Rainbow-hued fish cruised by, ignoring the newcomers, weaving themselves in and out of the fields of strange grasses that waved in the submarine currents, darting about and feeding off the fronds and ferns of the sea. Pretty variegated fish and other luminous ones came into vision from time to time…. A group of seahorses floated past and a large fish, which Luna couldn’t identify, chased a shoal of smaller fry, swimming only a foot away from her.

The sight of these sea creatures in their natural habitat is beautiful – and makes the sight to come all the more shocking for Luna.

When they reach Conil de la Frontera, Ruy explains to Luna how the almadraba works:

‘There’s a maze of fixed vertical nets stretching for several kilometres from the coast out to sea… They’re attached to floating barrels and corks, kept in place by very heavy anchors. As the blue-fin tuna migrate from the Atlantic to lay their eggs in the Mediterranean, they find their path blocked by the barrier net of the Almadraba. As they try to escape, they enter through a funnel into the cuadra, the holding net made up of several pens, to end up finally in the central pen, the copo, the only one with a horizontal net.’

Luna is intrigued, but when the next stage of the almadraba commences, it makes for difficult viewing:

Ruy led her to a good vantage point not far from the action. They could hear the fishermen’s excited shouts and laughter – ‘Anda! Vamonos!’ – as they hauled in their huge nets.

‘Look, the fish are trying to get away,’ Ruy pointed to the surface of the sea, which was turning white and frothing as though in ebullition, heaving with a multitude of enormous fish, their fins slicing through the water.

Men armed with sharp knives were jumping into the copo to hook the bluefin tuna, forcing them to the surface and hauling them into the boats, battling for supremacy with the fish, a couple of which looked as if they must be three times the fisherman’s body weight. The slaughter had begun.

Now the churning waters had turned blood red. In a frenzy, the huge fish were bucking and roiling, their slithery dark backs arching out of the water in the scarlet urgency of their death throes.

Should Luna have stayed to watch this part? Perhaps not. Ruy is certainly concerned that the sight has upset her. But this is history, right before them, an ancient custom. And history, whether beautiful or gruesome, is important. It has a certain pull. It can, if you let it, define you. So when, on the day of the almadraba, Luna crosses paths with a shadowy figure from her past, she must decide: be like the tuna, trapped and bleeding – or escape the net and swim free?