A great Tail of the Deep: Rattail Fish
The rattail fishes (also known as Grenadiers) of the family Macrouridae. Named from the Greek Makros, meaning “great” and oura meaning “tail”; is commonly known by its common name rattail due to its distinctive whip-like tapering form. Rattails are one of the oldest, most diverse fish families in the global oceans, with 34 genera and with more than 300 species. With sizes of these fish ranging from approximately twenty-five centimetres to greater than 1.5 metres. Representatives of the family can be found from the Southern Ocean to below the high Arctic, from tropical seas to the continental slopes. They are primarily benthopelagic (Fish that live beyond the shelf sea’s on the bottom of the ocean). But also bathypelagic,(occupying a wide depth range) residing from 200m to the abyssal plains > 2000m; some have even been found down at 7000m, due to the high diversity of species the family Macrouridae are thought to represent approximately 15 % of all deep-sea fish.
Rattail fish are long-lived. Estimates of longevity range from 70 years for some Pacific species, to 58 years for Atlantic species, with maturity, reached by 23 years. However, the life history of Macrouridae is poorly understood. Spawning happens upon the benthos, after which the lipid-filled eggs ascend into the seasonal thermocline where they hatch and metamorphose. After feeding mainly on pelagic copepods, the larvae descend towards the depths, performing diel vertical migrations from the benthos to the bathypelagic zone, feeding on small invertebrates. As they mature, they maintain their migratory habits but predate on larger pelagic species. As they reach adulthood, they take larger species including lanternfish, cephalopods and larger benthic crustaceans. They have even been observed feeding on chunks of decomposing whalebone extracting nutrition from the Osedax worms and their eggs that have bored within.
As these fish have such a distinctive look, it may be surprising that this fish is closely related to one of the most commercially fished species in history, the cod. This family connection could prove to be the rattail fishes’ downfall. A downfall that could be accelerated by an ever climbing human population draining food resources within coastal waters leading to further exploration and exploitation of some deep-sea fish species.
One species of Macrouridae already affected is Coryphaenoides rupestris (the roundhead rattail). This species occupies depths from 180 m to 2200 m; it can reach a size of about 1 m. Due to its affinity for shallower waters (600 to 900 m depth) during late summer and winter, and its preference to form dense schools, facilitated; it is quickly becoming a prime target species for commercial fishing in the Atlantic ocean during the 1960s. Peak landings of 83,964 tonnes in 1971, marked the highlight of this industry with the catch total falling to 3,843 tonnes by 2014. As a consequence of this decline, the British government listed the roundhead rattail as a UK priority species in 2010, after research demonstrated that it is a long-lived, late maturity species, which without protection would be extinct within the decade.
Another casualty of the fishing industry sometimes taken as bycatch by trawlers targeting Dover sole is Coryphaenoides acrolepis (the Pacific grenadier). C. acrolepis is the most common rattail in the North Pacific. Reaching just under a metre in size, it ranges from the seas of Japan to the Bering and Okhotsk seas of the western Pacific, Eastwards following the Aleutian Islands, along with the Western coast of North America and as far south as Baja California. This fish resides along the continental slope of the USA. During the 1980s it was landed within the United States and Japan, from longline fisheries off the West coast of the U.S. as a bycatch fish, when fishing between depths of 600 m to 1000 m for Anoplopoma fimbria (Sablefish or Black Cod). The Pacific grenadier is sold in the USA as fresh fillets and considered a high-quality food fish in Japan. Surveys during the mid-1980s conducted by the joint United States, Japan longline survey, reported a 13% decrease in catch rates over a one year period.
The third and final example of possible overexploitation for the foreseeable future of a deep sea rattail fish is Albatrossia pectoralis (the Giant grenadier). It occupies waters from between 140 m to 3500 m and can grow to a metre and a half. The Giant grenadier occupies the same geological areas as does the Pacific grenadier, although its range also includes the Bering Sea. The Giant grenadier is again, caught mainly as bycatch but was considered by the former USSR fisheries to be a valuable food fish, the flesh is watery, yet the liver and eggs contain up to 50 % vitamin enriched fats. Within the bearing sea between 1962 and 1965 catches reported were approximately 4 to 6 tonnes per haul. Although heavily fished during the sixties, it was shown during the joint Japanese USA longline survey within the North Pacific, that the giant grenadier showed a 37% increase in population from 1985 to 1986. However, this study was conducted using long lines. Catches from the Bering sea in 1962 to 1965 were completed using deep-sea trawls. This fishing ceased due to the depth and topography of the ground that the target fish occupied, being impractical to harvest, a lack of consumer demand, and absence of processing technologies at the time. In the present day, however, with population increase and new technologies becoming integrated into fishing fleets, such as advanced side-scan sonar that can pick out pathways across the seabed for a more efficient deep-sea trawl, and with processing equipment becoming cheaper and more attainable. How long will it be before this rattail fishes story becomes rooted in history?
(video credit Utube)