Collateral damage

Whoever eats fish and has tested some of the vibrant Madeiran cuisine has perhaps realised that highest amount of the fish comes from deeper waters. The most popular commercially exploited deep-sea fish is the Black scabbard fish (A.carbo) and, like other deep-sea fish, is caught using long-lines. Madeira was the first region in Portugal to fish for Black scabbards, a tradition that is thought to have began around the 17th century. These large, gruesome-looking deep-sea predators enter island’s waters to spawn, meaning that the majority of the animals caught are at a mature stage. 

Our own captain of the Ribeira Brava, Sr. Luis, who celebrated his 80th birthday this year remembers catching Black scabbards aboard traditional boats that were no different to our own Ribeira Brava. However, we all know fishing occurs at much higher levels today than it did back when Sr.Luis was in the business. The old school captain remembers releasing the 1km long-lines with 50 hooks to catch scabbards; fishermen today use long-lines with an average of 3000 hooks each containing a piece of squid for bait. The bait, however, also attracts a variety of other deep-sea fish, particularly sharks.

Madeira’s deep waters are home to a variety of deep-sea sharks, many of which used to be exploited commercially on the Portuguese archipelago. Ironically the black scabbard fishing industry was thought to begin as a result of fishing for deep-sea sharks including the Leafscale gulper shark (Centrophorus squamosus) and the Portuguese dogfish (Centroscymnus coelolepis), which are today both listed as endangered species in the Northeast Atlantic. Today the gulper sharks along with the Smooth lanternshark (Etmopterus pusillus) are the most frequently caught deep-sea shark species as bycatch according to report published in 2013 by MARE Portugal. 

Sharks are the top predators in different marine ecosystems and this also includes the abyss.  Deep-sea sharks are slow to grow and mature and have a low fecundity meaning even limited fishing activity can result in a serious risk to their conservation.  The cooccurrence of these predators in areas popular for Black scabbard fish has allowed the previously intended exploitation of these vulnerable animals to evolve into an unintentional collateral damage of commercial fishing. This is especially problematic if we consider that a large amount of bycatch isn’t documented or reported, making endangered shark populations around the archipelago very difficult to estimate. 

The Portuguese, however, have set certain regulations to help reduce bycatch on their long-lines with a maximum time of 36 hours per fishing set. The less time the long-lines are left in the water, the less likely bycatch will occur. Unfortunately, the stark decrease in the equally vulnerable Black scabbard populations around Madeira forces fishermen to increase their amount of sets during a fishing trip. Despite their increased efforts, the apparent decrease in scabbard landings is threatening the existence of these fishermen, who despite the low income and the decreasing reliability on their collapsed fishing grounds, still board their 14m fishing boats to make a living.

This just grows to show how complex the network of damage is that we have created for our oceans. Our overexploitation of certain species isn’t just claiming their existence and others they share their habitat with, it is also making the reliability on traditional and less exploitive fishing methods almost impossible.

By Paula Thake