Keywords

1 Introduction

Pisces constitute more than half of the vertebrates (Eschmeyer 2003). The number of valid species of fishes is nearing 31,000 with over 500 new species added in 2008 and it is expected that the final number will most likely exceed 35,000 (Eschmeyer and Fong 2009). Fish species new to science continued to describe at a rate of over 250 per year. The marine fishes constitute approximately 60 % of the estimated living fish species in the world (www.calacademy.org/research/ichthyology).

The first authentic record of the deep-sea fishes from India was made with the help of fishes collected during the explorations made by R.I.M.S. “Investigator” in the book “A Descriptive Catalogue of the Indian deep sea fishes in the Indian Museum” by Alcock in 1889. The R.I.M.S. “Investigator” had surveyed 711 stations in the Indian Ocean covering the range 5°–29° N., 46°–98° E during 1884–1914 and collected specimens up to a depth of 3652 m. “Valdivia” expedition (1898–1899) covered 12 stations in the Bay of Bengal in the geographical range 0°2′S–6° N, 73°–93° E and sampled between the sounding depths of 296–2,500 m. The John Murray expedition (1933–1934) surveyed 212 stations in the Indian Ocean within the range 29° N–7° S, 32°–73° E in the Arabian Sea in the depth 27–4,793 m (Misra 1962). Tholasilingam et al. (1964) gave some insight to the bathypelagic fishes from the continental slope of southwest coast of India. Other major studies during this period included those by Jones (1965), Rao (1965), Silas and Prasad (1966), Silas and Regunathan (1974), Silas and Selvaraj (1980).

A major contribution to the knowledge of demersal fishes of Indian EEZ was provided by Fishery Survey of India and their studies were mostly concentrated on the continental shelf and slope (Philip et al. 1984; Joseph 1984; Oommen 1985; John and Sudarsan 1988; Sudarsan and Somavanshi 1988; Sulochanan and John 1988; Vijayakumaran and Naik 1988; Philip and Mathew 1996). Recently, the exploratory fishing cruises onboard FORV Sagar Sampada have brought out many little known deep sea fishes from the Indian EEZ beyond 200 m depth. The major studies are those of James and Pillai (1989), Reuben et al. (1989), Sivakami (1990), Sudarsan (1993), Panicker et al. (1993), Khan et al. (1996), Sivakami et al. (1998), Venu and Kurup (2002a, b, c, 2006a, b), Thomas et al. (2003), Kurup et al. (2005, 2008), Jayaprakash et al. (2006), Deepu et al. (2007), Divya et al. (2007), Venu and Kurup (2009). The recent studies on deep sea fish taxonomy from Indian EEZ include the documentation and redescription of Glyptophidium oceanium from the west coast (Kurup et al. 2008), Dicrolene nigricaudis (Cubelio et al. 2008) deep sea eel Bassozetus robustus (Cubelio et al. 2009).

2 Methods

Materials for the present study were collected from the exploratory demersal trawling operations conducted onboard FORV Sagar Sampada along the southwest region of Indian EEZ during the periods 1998–2002 and 2005–2007. The upper continental slope region of 7o–15o N was surveyed as part of Cruise Nos. 174, 183, 189, 196, 197, 238, and 241 of FORV Sagar Sampada (Fig. 17.1). 38 m High Speed Demersal Trawl II (HSDT) and 45.6 m Expo-model Demersal Trawls were used for fishing in the above cruises in the depth from 200 to 1,100 m. Fish samplings were done at 164 stations. The catch composition and species wise catch in kg at each fishing station were recorded and the specimens were taken to the laboratory for detailed identification. The entire study area was divided into four transects based on the latitude and were each transect was divided into three depth zones. The transects so arrived at are 7°–9°, 9°–11°, 11°–13°, and 13°–15° N and depth zones were 201–500, 501–800, and 801–1,100 m (Panicker et al. 1993; Khan et al. 1996; Venu and Kurup 2002a). The fishes were identified up to species level with the help of authentic identification keys (Goode and Bean 1895; Alcock 1889; Fischer and Bianchi 1984; Smith and Heemstra 1986, www.fishbase.org).

Fig. 17.1
figure 1

Map showing the study area—South West coast of India

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3 Results

3.1 Species Composition

During the period of study, 149 species of fishes belonging to 123 genera, 70 families, and 24 orders were identified and recorded. The order Perciformes dominated with 26 species belongs to 17 families followed by the order Ophidiiformes with 17 species belonging to 2 families. The spatial and bathymetrical species composition and distribution of Deep-sea fishes along southwest coast of India is given in Table 17.1.

Table 17.1 Spatial and Bathymetrical species composition of deep sea fishes along southwest coast of India
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Fishes of the Order Ophidiiformes have shown maximum bathymetrical as well as spatial distribution in all transects and depth zones studied except in 501–800 and 801–1,100 m in the 7°–9° N latitude. Anguilliformes also showed a wider distribution with occurrence in all the transects and depth zones except in 501–800 and 801–1,100 m in the 7°–9° N transect and 801–1,100 m in the 9°–11° N transect. Fishes of the orders Carcharhiniformes, Aulopiformes, Beryciformes, Scorpaeniformes, Perciformes, and Pleuronectiformes have also shown a wide distribution in all transects.

This study revealed that Apristurus indicus, Coloconger raniceps, Gavialiceps taeniola, Chlorophthalmus bicornis, Hypopleuron caninum, Polymixia japonica, Priacanthus hamrur, Psenopsis cyanea, Bembrops caudimacula, Cubiceps squamiceps, Neoepinnula orientalis, and Chascanopsetta lugubris were distributed in all the transects. Altogether 15 species were found to have distribution in all transects except 7°–9° N latitude. Five species have shown distribution in all transects except in the 13°–15° N latitude. Whereas two species viz. Pterois russelii and Pterigotrigla hemisticta have shown their occurrence except in the 9°–11° N latitude. Cubiceps pauciradiatus was absent only in the catches in transect 11°–13° N latitude.

3.2 Latitude 7°–9° N

In general, the numerical strength of species was found to be very less when compared to other transects studied (Fig. 17.2). 35 species belonging to 26 families and 11 Orders were recorded from this transect. Altogether 8 families were recorded under the Order Perciformes. However, most of the families consisted of one or two species. Perciformes with 10 species followed by Scorpaenidae and Aulopiformes were the important orders found in this transect. Highest number of species (3 Nos.) was recorded under the family Chlorophthalmidae viz. Chlorophthalmus nigromarginatus, Chlorophthalmus agassizi, and Chlorophthalmus bicornis. The families Gempylidae, Centrolophidae, Ophidiidae, Nomeidae, and Triacanthodidae, Priacanthidae were represented with two species each. All the other families have only one species in this transect.

Fig. 17.2
figure 2

Bathymetrical distribution of deep sea fish species along South West coast of Indian EEZ

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3.3 Latitude 9°–11° N

The exploratory fishing surveys conducted in this transect have recorded 95 species from the depth between 201 and 1,100 m (Fig. 17.2). The depth zone 501–800 m recorded the highest of 52 species followed by 201–500 m depth zone (42 species) while only a single species was recorded from depth zone 801–1,100 m. Majority of the fish species comes under the order Perciformes in this transect with 13 in 201–500 m depth zone and 9 from 501 to 800 m depth zone. Order Gadiformes was represented by 9 species altogether of which 8 species were recorded in the depth zone 501–800 m. Six species under the Order Aulopiformes were recorded from 201 to 500 m depth zone.

Bathyclupea hoskynii, Bembrops caudimacula, Callionymus sagitta, Hoplostethus mediterraneus, Hypopleuron caninum, Physiculus roseus, Harriotta releighana, and Gavialiceps taeniola showed a wider distribution among the 95 species reported with occurrence between the depths 201 and 800 m. Lamprogrammus exutus of Ophidiidae family was one species recorded from 801 to 1,100 m depth zone.

3.4 Latitude 11°–13° N

In this transect, 121 species were recorded 70 families (Fig. 17.2). Highest of 61 species were recorded from the depth zone 501–800 m followed by 201–500 m (44 species) and least from 501 to 800 m (16 species). Members of the Order Ophidiiformes showed dominance in this transect with the representations in all the depth zones while higher number of species were encountered in the depth 501 and 1,100 m. Order Perciformes dominated in the depth zone 201–500 m with 10 species followed by Scorpaeniformes with 6 species. In the depth zone 501–800 m, Order Gadiformes was represented by 8 and Carcharhiniformes by 7 species in the catches. In the depth zone 801–1,100 m, Ophidiiformes dominated in the catches followed by Anguilliformes, Osmeriformes, Aulopiformes, Gadiformes, and Lophiiformes.

Members of the families Ophidiidae and Congridae were recorded with three species each in depth zone 201–500 m, followed by Proscylliidae, Lophiidae, Gempylidae, and Bothidae with two species each. In 501–800 m depth zone, Ophidiidae dominated with 9 species followed by Macrouridae (7 species). While 5 were recorded under Scyliorhinidae and 4 in Alepocephalidae. The families Stomiidae, Nemichthyidae, Congridae, Synaphobranchidae, Rhinochimaeridae, and Proscylliidae were represented with two species each. In the depth zone 801–1,100 m, four species under Ophidiidae family and two from Macrouridae were recorded.

Among the various species recorded, Gavialiceps taeniola was the lone species present in all the depth zones. Species like Echinorhinus brucus, Apristurus indicus, Eridacnis radcliffei, E. sinuans, Xenomystax trucidans, Physiculus roseus, Glyptophidium macropus, Hypopleuron caninum, Hoplostethus mediterraneus, and Psenopsis cyanea were found distributed between 201 and 800 m. Whereas, Bathyuroconger vicinus, Bathygadus melanobranchus, Coryphaenoides macrolophus, Dicrolene tristis, and Lamprogrammus exutus showed their presence in the higher depths between 501 and 1,100 m.

3.5 Latitude 13°–15° N

88 species belong to 60 families were encountered from this transect (Fig. 17.2). Depth zone 501–800 m was characterised by the highest number of species belonging to 40 families followed by 201–500 m with 34 while depth zone 801–1,100 m showed the least with 14 families. The order Perciformes dominated the depth zone 201–500 m in this transect also while 7 species were found in the depth zone 501–800 m. Ophidiiformes were having 10 species in this depth zone. In the depth zone 801–1,100 m, Osmeriformes dominated with 4 species followed by Ophidiiformes with 3 species.

4 Discussion

The exploratory surveys carried out in the southwest region of Indian EEZ between 7° and 15° N lat have revealed many new potential fishing grounds as well as unconventional fishery resources in the deeper waters beyond 200 m depth. Although the catches from these stations were fluctuating, the results were promising toward fulfilling the attempt of delineating the resource potential of the deep sea fishery resources of the area. The new grounds identified in the continental slope area now can be utilized by the deep sea fishing industry for the harvesting of unconventional resources for the enhancement of marine fish production from the country.

The results of the present study have shown that 149 fish species belonging to 123 genera, 70 families, and 24 orders embarked the entire study area with varying degrees of bathymetrical as well as spatial distribution. It is worth reporting that in many of the families very few species were found and majority of them were represented by a single species. Most of the genera are represented with single species and rarely, more than two species in a genus.

The pattern seen in the spatial distribution of deep-sea fishes revealed that there are greater aggregation of species in transect 11°–13° N latitude. Whereas bathymetrically the depth zone 501–800 m accounted for the maximum number of species. Results of previous studies also agree with the present findings. Prasad and Nair (1973) have shown high abundance of deep-sea fishes such as C. agassizi, N. orientalis, P. cyanea, and C. natalensis in the upper continental slope (180–450 m depth zone) in the Indian EEZ. Philip et al. (1984), Oomen (1985), Sivaprakasam (1986), Panicker et al. (1993), Khan et al. (1996), Sivakami (1990), Venu and Kurup (2002a), and Jayaprakash et al. (2006) identified certain pockets at depth of 200–500 m along the southwest region of Indian EEZ as target areas for exploitation of deep sea resources. Venu and Kurup (2006a) reported that the Neoepinnula orientalis and Psenes squamiceps are more abundant in the 7°–10° N latitude. Sivakami et al. (1998) reported a potential yield of Chlorophthalmus spp. as 81,328 t along this region.

The Centrolophid fish P. cyanea showed more distribution in the depth zone 201–500 m in the 7°–13° N latitude and was found to be an exploitable nonconventional resource with tremendous potential as a commercial species. Venu and Kurup (2002b, c) reported similar results from the south west region of Indian EEZ. Panicker et al. (1993) reported Centrolophus sp. and Chlorophthalmus spp. as dominant species in the depth zone 200–500 m in lat. 7°–17° N, off west coast of India. According to Khan et al. (1996), P. cyanea showed peak abundance in depth zone 301–400 m and moderate abundance both in zones 101–200 and 201–300 m. Sivakami (1990) observed a promising potential for Psenopsis spp., along with other resources in the south west zone in the depth range 151–398 m.

Out of 149 species recorded from the study area, 40 were found to have a circumglobal distribution, showing their presence in all the three major oceans viz. Atlantic, Pacific, and Indian Ocean. 6 species were exclusive to Atlantic Ocean and 4 species were distributed only in Pacific Ocean. 71 species among the total were reported previously from Atlantic Ocean, 88 from Pacific, and 133 from Indian Ocean including the species of shared distribution between these oceans (Alcock 1889; Goode and Been 1895; Misra 1947, 1952, 1953; Fischer and Bianchi 1984; Smith and Heemstra 1986; Eschmeyer and Fong 2009, www.fishbase.org, www.calacademy.org/research/ichthyology). 49 species were reported from both the Atlantic and Pacific Oceans while 56 species shared between Atlantic and Indian Oceans and 74 between Pacific and Indian Oceans. The previous reports from Indian Ocean have shown that there are 43 species of fishes exclusively distributed in this Ocean among the remaining 103. 9 species among the remaining 60 shared their geographical distribution between Atlantic and Pacific Oceans. Among the remaining 51 species, 16 are reported from both Atlantic and Indian Ocean. The rest of the 35 species were reported previously from the Pacific as well as Indian Oceans.

The bathymetric temperatures of the temperate and tropical zones tend to be more or less uniform, while the surface temperatures are fluctuating. The isotherms may serve as an indicator to the taxonomist in dealing with the relationships of the species and subspecies from the zoogeographical point of view (Misra 1962). According to Smith (1953), species common to the Indo-Pacific and the tropical Atlantic and the Mediterranean may be “relics of intermingling, for not very long ago in geological time conditions were different, and there was almost certainly a warm water connection between the Indian and Atlantic Oceans.” It has been proved that in the low latitudes, thermocline is between 200 and 1,000 m (Pickard and Emery 2003).

Many of the Families and Orders are represented in the study area with very few species. Many species were observed to share similar habitat as their counterparts in the other oceans. So it may also be concluded that there will be more species in the study area which could not be collected in the samplings carried out during this study. A much well organized and thorough study can unearth the real diversity of fishes inhabiting the deeper waters of southwest coast of India.