Deep Sea fishery and inventorying the deep sea mega fauna of Indian exclusive economic zone (EEZ) are rather neglected areas of research in the post-independent Indian context, probably due to lack of adequate infrastructural facilities. Our knowledge on the deep sea fishery resources of the Indian EEZ are mainly from the pioneering works carried out through the exploratory surveys of Her Majesties (HM) Royal Indian Marine Survey Ship (RIMS) Investigator 1 from 1879-80 to 1908, followed by the exploratory surveys of HM RIMS Investigator-II (1910 to 1914 and 1920 to 1925) in Burma and Andaman Sea, the John Murray Expedition (1933-34) onboard the Egyptian Research Vessel Mabahiss, the International Indian Ocean Expedition (IIOE) from 1959 to 1965, the deep-sea exploratory surveys of the Fishery Oceanographic Research Vessel (FORV) of the Ministry of Earth Sciences (MoES) from 1989 till date and exploratory surveys carried out by the Fishery Survey of India (FSI).
Captain A R S Anderson and Lt Col A W Alcock, British Surgeon Naturalists on board RIMS Investigator I were the pioneers to describe the deep sea fishery resources from the Indian Ocean. Investigator I carried out 113 successful hauls between depths 100 to 1997 fathoms (1 fathom equals 6 feet). Results of these exploratory surveys are published as monographs on deep sea fishes (Alcock, 1898; Alcock 1901). Lt Col R B S Sewell and Lt Col Francis Day, Surgeon Naturalists on board RIMS Investigator II, also made useful contributions to deep sea fishery resources of the Indian Ocean. The RIMS Investigator monographs documented 169 deep-sea fishes, 58 species of Brachuran crabs, 52 species of Anomuran crabs and 117 species of shrimps under Macura. The John Murray expedition surveyed 212 stations in the North West Indian Ocean between 29oN to 7oS and 32oE to 73oE, with collections from up to 4793 m depths. Detailed taxonomic reports on fishes (Norman, 1939) and Penaeidae (Ramdan, 1938) shed light to the deep-sea megafauna of the region.
Post colonial deep sea fishery explorations in the Indian EEZ were carried out by the vessels of Fishery Survey of India (FSI)—erstwhile Deep Sea Fishing Station later renamed as Exploratory Fisheries Project; Integrated Fisheries Project (IFP)—erstwhile Indo-Norwegian Project; and the MoES research vessel FORV Sagar Sampada. Valuable information on the diversity, distribution and abundance of demersal fishery resources in the Indian EEZ (up to 500 m isobaths) were generated through the surveys of FSI vessels (Joseph et al.,1987; Sajeevan et al., 2009). The IFP surveys, mostly in the 100-500 m depths revealed the existence of deep sea lobsters in the 180-270 m depths off Quilon (Kerala) and Mandapam (Tamil Nadu) and deep sea prawns and fish resources in the Quilon Bank (300-450 m depths) (Tholasilingam et al., 1964; Silas, 1969; Mohammed and Suseelan, 1973; and Oommen, 1985). Surveys of FORV Sagar Sampada have covered depths up to 1300 m of the Indian EEZ. Its major achievements include documentation of the biodiversity, distribution and abundance of deep sea fishes, identification of several new deep sea fishing grounds and identification of more than 50 new species of deep sea fishes from Indian Ocean (Karuppasamy et al. 2007,2011; Jacob 2017; Meera, 2018; Kumar, 2018).
Included in the new species of deep sea fishes from the Indian EEZ are the one foot long edible moray eel Gymnothorax indicus reported from 70 km off Medinipur, West Bengal (Mohapatra et al, 2016), the deep sea shark Mustelus manglorensis from 500 m depth off Mangalore (Cubelio et al, 2011), a new species of jaw fish, Opistognathusalbicaudatus from Andaman waters (Smith-Vaniz, 2011), a new species of toad-fish Colletteichthys flavipinnus (Greenfield et al,2012), a new Serranid species Liopropomarandalli (Akhileesh et al, 2012), a new species of Perciform fish from the Arabian Sea (Anderson and Bineesh, 2011) and seven new species of deep sea angler fishes reported by Kumar (2018).
Estimates on Deep Sea Fishery Biomass in the Indian EEZ
The Fishery Survey of India (2011) estimated a maximum sustainable yield (MSY) of 0.115 million tonnes (MT) of demersal fish within the 200 to 500 m depth zone of the Indian EEZ, which correspond to a standing stock of 0.23 MT. Though this appears to be an underestimate, it is to be noted that only demersal fishery is covered by this estimate and that the pelagic fishery resources which are abundant in the deep sea waters of Indian EEZ are not included. A reanalysis of the trophodynamic approach of Sanjeevan et al, 2011 using primary productivity (PP) and benthic productivity (BP) data indicates a standing stock of 3.81 MT of deep sea fish beyond the 200 m depths of the Indian EEZ. Sector wise, the South Eastern Arabian Sea (SEAS) account for 1.817 MT, the North Eastern Arabian Sea (NEAS) for 0.427 MT, the South Western Bay of Bengal (SW BoB) for 0.690 MT, the North Western Bay of Bengal (NWBoB) for 0.363 MT and the Andaman Sea (AS) for 0.511 MT (Table 1). Among the various fish groups that comprise the deep sea fishery of the Indian EEZ, lobsters and prawns, the lantern fishes (myctophids) and the purple back flying squids (Sthenoteuthis oualaniensis) are important in terms of their abundance, distributional range and potential to support commercial fishery.
Deep-Sea Lobsters and Shrimps
Surveys conducted so far have identified several grounds in the 200 to 1300 m depths, rich in deep sea lobsters and prawns. Among the deep sea lobsters the most abundant species is the spiny lobster—Puerulus sewelli found abundantly in the 200 to 500 m depths off west coast (7oN to 18oN), east coast (7oN to 14oN) and Andaman Sea (8oN to 12oN) followed by Nephropsis stewarti and Metanephropsisandamanicus. Sustainable yield from the southwest coast was estimated as 8000 tonnes and from the southeast coast as 1200 tonnes with peak abundance (200-300 kg per hour trawling) from the 180-360 m depths off Mandapam, followed by the Quilon Bank (Oommen and Philip, 1974). However, deep sea spiny lobsters have slow growth rates and therefore over exploitation can deplete the stock size rapidly (Kathirvel et al., 1989). In fact surveys conducted later (Anrose et al., 2010) have shown severe stock depletion with catch per unit effort (cpue) falling from 3.42 to 0.23 kg per hour along the east coast; 16.66 kg per hour along the west coast (1987) and from 60 in 1998 to 36 kg per hour in 2008 along the Andaman.
Similarly, deep sea shrimps are abundant in isolated pockets of Tamil Nadu, Kerala and Andaman waters. Dominant non-penaeid species include Plesionika spinipes, Heterocarpus gibbosus and H.woodmasoni distributed along the Quilon-Mangalore sector of the west coast and the Andaman. Abundant penaeid species in Indian waters are the red ring (Aristeus alcocki) in the 350-450 m depths of Quilon Bank, the scarlet shrimp Plesiopenaeus edwardsianus in the 900 m depths off Trivandrum, deep sea mud shrimp (Solenocera hextii) etc. Catch per unit effort recorded from landings at Sakthikulangara (Kerala) show a declining trend from 77 kg per hour in 2003-04 to 42.5 kg per hour in 2006-07.
Myctophid resources of Indian EEZ
Myctophids or Lantern fishes—typically inhabiting the 200 to 1000 m depth zones, make up 65 per cent of all global mesopelagic fishes. They undertake extensive dial (day/night) migrations and have rapid growth rates, a short life span of around one year and high mortality rates. The Arabian Sea has one of the world’s largest myctophid resource estimated to be around 100 MT (US GLOBEC, 1993) dominated by a single species; Benthosema pterotum. However, in 2001 the estimates have been revalidated to 48 MT. This species is most abundant along the western and northern parts of Arabian Sea, whereas in the Eastern Arabian Sea (west coast of India) the dominant species are Benthosema fibulatum, Diaphus watasei and Diaphus luetkeni. The myctophid biomass in the Indian EEZ of Arabian Sea is estimated to be around 17.90 MT (Meera, 2018) in which NEAS contribution is 9.21 MT and SEAS account for 8.69 MT. As most myctophids have a life span of one year, it is to be expected that this huge biomass is regenerated on an annual basis. Exploitation of even 10 per cent of the existing biomass is sufficient for India to meet the feed requirements of its aquaculture industry, which at present depend heavily on juveniles of several commercially important fish species. Since the cost benefit from myctophid fishing does not match, this fishery can only be sustained through government subsidies. Subsidised myctophid fishery need to be encouraged to stop large scale juvenile fishing that can deplete several stocks of high/medium value fishes from Indian waters in short time scales.
Indo-Pacific purple-back flying squid The large sized oceanic squid species Stenoteuthisoualaniensis are often called ‘Masters of the Arabian Sea’ as they completely monopolise the trophic niche of the top predators in the Arabian Sea (Mohamed et al., 2011). Studies indicate that this squid species dominates the oceanic epipelagic zone of Arabian Sea both in number and biomass and that their mean biomass is 4.5 tonne per sq km. Roper et al., 2010 have reported catches of more than 10 tonnes per sq km in the Arabian Sea. The fishable stock in Arabian Sea is estimated to be between 1 and 1.5 MT (Barratt & Allcock, 2014). In the Arabian Sea, this species exhibit three types of body forms—a giant form of 40-50cm mantle length found mostly in the northern sectors, a middle form with a 12 to 25 cm mantle length occurring throughout the Arabian Sea and a dwarf form (9 to 12 cm) mostly found in the equatorial waters. These squids are caught either by jigging or gill netting. The fishing season extends from October to March with peak abundance in December-Jsanuary. Major impediments in their commercial exploitation are their scattered occurrence and low market value. Since the quality of meat is relatively poor, value addition should be undertaken to promote fishing of this resource.
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