When you think of fisheries, aquaculture, and the fish you eat, whether it be freshwater or marine, there are certain fishes that come to mind. You may think walleye, tilapia, and hake, or salmon, tuna, and cod. You may even be able to form images in your mind of what these fishes look like, and roughly, where they come from. But, there is another side, a deeper and spookier side to fisheries…
Over the last few decades there has been an increase in industrial fishing of the deep-sea. The deep-sea is usually categorized as depths below 200 m, where only minimal light can penetrate. Below 1,000 m, light from the surface of the ocean is completely absent and many of the fishes that live there have evolved unique adaptations to this extreme environment. Fishing these depths usually occurs in two forms, either via bottom trawls for benthic fishes that live on or near the ocean floor, or pelagic trawls for deep-sea fishes that swim in the open ocean. The push towards fishing in the deep sea, normally a difficult and expensive process, has come about for a variety of reasons. New refrigeration technologies enabled long term storage, the creation of Exclusive Economic Zones (200 nautical mile zone around countries) forced fishing vessels of various countries further away from the coast, and the ever depleting near-shore fisheries stocks drove fishing vessels to trawl deeper. Deep-sea industrial fishing began with only working the first few hundred meters of ocean depth, but has increased through time as humans make advancements in fishing gear. Many fishing vessels can now trawl at depths up to 2000 m.
Despite the reasons for the increase in deep-sea fisheries, many people don’t realize that some of the fishes they are eating come from these great depths. Not only are these fish unique for where they come from geographically, but many are peculiar in the way they look, behave, and grow. Below I highlight a few of the spooky and unique species that you may eventually find on your dinner plate, potentially unbeknownst to you.
Macrouridae – Coryphaenoides and allies
Macrourids, or rattails and grenadiers, include some of the deepest living boney fishes ever discovered. So-named because of their long and thin tails, the deepest living species, Coryphaenoides yaquinae, was recently discovered at 7,012 m deep. Most species of rattails can be found between 200 and 2,000 m deep and most live on or just above the ocean floor. Many different species are harvested by deep-sea fishing trawls worldwide. The fillets of the species targeted specifically for fisheries are white, and with a pleasant texture (e.g. Coryphaenoides rupestris). Other species are actively ignored, as they have evolved different adaptations for living in the deep sea, including watery muscles, which are unpleasant for human consumption.
Trichiuridae – Aphanopus
Black scabbardfish (Aphanopus carbo) are found in the Atlantic Ocean. They usually reside between 180 and 1,700 m deep. These fish migrate during their lifecycle, with some populations of adults spawning near the Madeira Islands in the fall/winter and larvae/juveniles moving north into cooler waters to grow. After becoming adults, they migrate to the area around Portugal until they reach sexual maturity. Although they aren’t known to get as old as some of the fishes highlighted in this post (~14 years), they are still thought to have a slow growth rate once they reach adulthood. Black scabbardfish have large fangs and long slender bodies. They are said have a similar taste and texture to cod, but with slightly softer flesh.
The Oreos (e.g. Allocyttus, Neocyttus, and Pseudocyttus) are a mostly Southern Hemisphere group of fishes that reside on continental slopes from 200 to 1,600 m deep. They are small and have long lifespans, with most species capable of living to 100 and some species living up to 210 years. Some species don’t reach sexual maturity until 30 years of age. Being such a slow growing fish, they are highly vulnerable to fishing pressure and overfishing. They provide rounded fillets and have a light, delicate flavor.
Trachichthyidae – Hoplostethus atlanticus
The orange roughy (Hoplostethus atlanticus), previously called ‘slime head,’ is a deep dwelling, bathypelagic fish species that occurs between 180 to 1,800 m in waters of the Pacific Ocean, Indo-Pacific, and eastern Atlantic Ocean. They are a long-lived fish that do not begin breeding until at least the age of 20 years. Orange roughy are also known to reach over 200 years of age. This species was fished excessively in the 1970’s, and their populations were dramatically depleted. Although some populations have bounced back, their slow growth and maturity is a leading factor in their slow recovery. They have a mild flavor and are usually sold as fresh or frozen fillets.
As humans push further into fishing the deep sea, it is highly likely that many deep-sea species, especially those with slow growth, later sexual maturity, and low fecundity, will be unable compensate for heavy fishing activity. Deep-sea fishing is also both ecologically and economically questionable. Over the years new deep-sea fish species are continually being considered for harvest, usually to replace species that were overfished. Many organizations are trying to put regulations in place for deep-sea fishing and others have been putting forth efforts to assign deep-sea marine protected areas (MPAs). These efforts will hopefully improve conservation and sustainable use of the deep-sea and its resources and ecosystems.