Six people were arrested this week for capturing a Basking Shark off the coast of Cartagena.
The creature, which is harmless to humans, is protected under international conservation laws.
The action was taken against those involved after they subsequently tried to sell the meat to local hotels and restaurants in the area.
The investigation began in July when the authorities were made aware of illegal fishing activities around Cartagena.
Those arrested, all Spaniards and aged between 32 and 76, were brought before the courts in Cartagena.