INTRODUCTION shrimps under decapods and given them the

  INTRODUCTION

 

            The shrimps and prawns which are
coming under Crustacea are known as  the
insects of  the sea (Poore, 2004). In the
Decapod Crustaceans  as the dominant
taxon is Brachyura  and the second
position is maintained by the Carideans (Fransen and De Grave,2009).  It was considered that there are about 2,500
species of  prawns and shrimps existing
throughout the world (Jayachandran, 2008), now the number of species reported
world wide have doubled into 4048 species according to De Grave and Fransen, 2011.
Burukovski (1982) categorised 
shrimps  under decapods and given
them the place of  higher forms of
crustaceans and the consistency of the number of  body segments as one of the major  important character. The body contains three sections: head, thorax and abdomen. In the gourmet’s choice
marine shrimps from capture as well as culture systems are highly important
as  the most valuable commodity (Diwan
and Modayil, 2007). Abello et al. in
1988 described that the spatial difference occurred in the decapods crustaceans
are variable according to different environmental and the oceanographic
conditions like characteristics of the particular water mass, depth, nature of
the bottom.

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            The term ‘shrimps’ and ‘prawns’ have
no definite references to known taxonomic groups. In some countries the term
‘shrimp’ is sometimes applied to small species and the term  ‘prawn’ is more  used for larger forms. The Food and
Agricultural Organisation says that there is  no clear distinction between the terms shrimps
and prawns and their usage is even reversed regionally and country wise(FAO,
1983). According to Kurian and Sebastin (1993) the term ‘prawn’ is used in
India is the same meaning   with the term used in western countries. The
standardization of the term was the subject of discussion at the Prawn
Symposium of the Indo-Pacific Fisheries Council held at Tokyo in 1955. The
discussion arrived at was that the word ‘prawn’ should be applied at the
Penaeids, Pandalids and Palemonids and shrimp to the smaller species belonging
to the other families. It was also noted that shrimps
look similar to prawns, but their gill structure is lamellar whereas it is
branching in prawns (www.wikianswers.com) Parihar (1994) stated that the
term prawns belong to the families Penaeidae, Hippolitidae, Pandalidae,
Sergastidae and Palemonidae. Commercial prawns of India can be grouped into
penaeid and non-penaeid ones, they can be easily have distinguished with an
important character that is the pleurae of the either side of the exoskeleton of
second abdominal segment overlap the pleurae of the first and third segments in
the non-penaeids, while in the penaids they overlaps only the third segment
(Kurian and Sebastian, 1993).

 

            Gulland and Rothschild (1984) reported
that in the waters of Indonesia, Thailand, India and in the Gulf of Mexico some
of the largest fisheries for shrimps occur. Further, these researchers reported
that the shrimp generally spawn offshore; the young shrimp then move to
estuaries which serve as a nursery area and the time spent by each species
before moving offshore vary among species. It was also reported that in the
cycle of shrimps, most of the shrimps mature and breed only in a marine
habitat, although there are a small number of freshwater species. The females
lay 50,000 to one million eggs, which hatch after some 24 hours into tiny
nauplii, these further enters into several larval stages and develops into
large shrimps (www.wikipedia.com).

 

            The phenomenon ‘chakara’ or mud bank
formation occuring along the Kerala coast in the monsoon season is a spurt in
the yield of prawns and it was reported by Kurian and Sebastian in  1993. Nandakumar and Maheswarudu, 2003 reports
that  penaeid shrimps are distributed
widely in the shallow tropical and subtropical waters and throughout the world
highly priced. They represent the back bone of seafood export industry as the
major foreign exchange earner as well as a source of livelihood for million of
fish workers. Frozen shrimp contributes about 70% of the total export value of
our country and the share of capture fisheries is 59% by the volume.

 

            In terms of population dynamics,
penaeid shrimps are fast growing and very generally live only about one year.
They thus have unusually high morality rates because of their determination of
the best sizes at which to capture shrimp are critically sensitive to
determination of mortality and growth rates (Gulland and Rothschild, 1984).
According to Nandakumar and Maheswarudu (2003) life span of penaeid shrimp is
around two years and 0-year group contributes more to the prawn fishery.
Penaeid shrimps are heterosexual, with females growing larger than males.

 

            Studies on penaeid shrimps are more
comprehensive and at present four families under 191 species are known to occur
in the Western Central Pacific, with the Penaeidae being the most important
family. Species of the penaeoid family Aristidae and Solenoceridae are mainly
deep water dwellers and largely unexploited. The fact that larger
representatives of these two families are often caught on the basis of
development of the deep-sea fishery in the area. In contrast, species for the
penaeoid family Sicyoniidae are generally small, abundant, and do not have any
commercial potential (FAO, 1983).

 

            Under the family Penaeidae a total
of 26 genera and 225 species (90 species commercially important) have been
reported. From India 14 genera have been reported due to the introduction of
species   for
farming purpose (Jayachandran, 2008). Some of the important penaeid shrimps
that support commercial fisheries along the Indian seas are Penaeus indicus (Indian white prawn), Penaeus semisulcatus (green tiger prawn),
Penaeus monodon (giant tiger prawn). Penaeus merguiensis (banana prawn), Marsupenaeus japonicus (Kuruma prawn), Penaeus penicillatus (red-tail prawn), Metapenaeus dobsoni (flower-tail prawn),
Metapenaeus monoceros (speckled
prawn), Metapenaeus affinis (Jinga
prawn), Metapenaeus kutchensis
(ginger prawn), Metapenaeus brevicornis
(Yellow prawn), Parapenaeopsis stylifera
(Kiddi prawn), Metapenaeopsis hardwickii (spider
prawn), Metapenaeus sculptilis
(rainbow prawn), Parapenaeopsis uncta (Uncta
prawn) Trachysalambria curvirostris
(rough prawn), Metapenaeopsis stridulans (fiddler
prawn), Parapenaeopsis longipes
(flamingo prawn),  Solenocera crassicornis (coastal mud prawn) and Solenocera choprai (coastal mud prawn)
(ICAR, 2006).

 

            Among commercial species
contributing to penaeid fishery, Penaeus semisulcatus,
P.indicus and P. monodon are larger in size and grow to a total length (TL) of
250, 270 and 300 mm, respectively. Length range of smaller species such as Parapenaeopsis stylifera,
Metapenaeusdobsoni and Solenoceracrassicormis are 46-145, 31-115 and 55-125mm
TL respectively (ICAR, 2006). Some of the penaeus species are used in
aquaculture including P. monodon and P. indicus did not receive priority in
aquaculture in India, in spite of the fact that this indigenous species  of shrimp fetches a higher price than the
more popular P.monodon or P.vannamei in the global market (Diwan and Modayil,
2007).

 

            Kurian and Sebastian (1993) reported
that the marine prawn fishery which supports the export industry is generally
confined to shallow coastal area within 40m depth and is constituted by P. indicus, P. merguensis, P.monodon,
P. semisulcatus, M.dobsoni, M.affinis, M. monoceros, M.brevicornis
and Parapenaeopsis stylifera though
individual species show variations in the breeding season, most of them spawn
throughout the year, with two peak periods – November to December and February
to April, the former being the most productive.

 

            Jayachandran (2008) reported about
50 species of penaeid shrimps from Indian waters. There are also two extinct
species Penaeus barmerensis and Penaeus glaessneri. The horizontal
distribution of species is in the Indo-West Pacific regions in the major marine
fishing zones Western Indian Ocean, Eastern Indian Ocean, Western Central
Pacific and North-west Pacific. All the 13 genera are seen distributed in these
regions. P.monodon, M. japonicus, P.indicus,
Trachysalambria curvirostris are distributed throughout the coasts of India
and Andaman Islands. Metapenaeus dobsoni,
Metapenaeus lysianassa, and Metapenaeopsis
sculptilis enjoy wide range of distribution. F. penicillatus, Metapenaeus brevicornis
and Parapenaeopsis hardwicki are
distributed from middle region of the coastline northwards. Metapenaeus mogiensis, Metapenaeus burkenroadi, and Pescadorensis are seen on Southern
regions of both coasts.

 

            Jayachandran (2001) stated that
family Palemonidae is of great interest to fishery science as it contains true
prawns, quite a large number of which are important in the capture and culture
fisheries. The family includes two subfamilies namely Palemoninae and Pontoniinae.
The prawns belonging to the former inhabit and inland water bodies, from
brackish waters to hill streams, and are very rarely marine. The latter family
contains prawns which are exclusively marine. They generally live in
association with other organisms such as molluscs and echinoderms and are
frequently found along corals. Many of these species are brilliantly coloured
and hence are of great ornamental value. Tiwari (1955) reported that the genes
Palaemon has a marine origin, and has acquired fresh water habitat by
immigration from sea to interior of land through rivers. The process of
adaptation of freshwater is not complete because many species are found in
estuaries and still depend on brackish water for breeding.

 

            Non-penaeid prawn resources constitute
one of the important fishery resources contributing + 0.58% of total marine
fish production. The resource is characteristic of the North West coast, which
accounts for almost 90% of the total non-penaeid prawn production in the
country. In Maharashtra and Gujarat, the non-penaeidaccount for 10.8% and 12.6%
of marine fish landings (Deshmukh, 2003). According to him non-penaeid prawn
resource is multispecies, mainly supported by smaller species of the genus
Acetes (paste sharps) in addition to Nematopalaemontenuipes and
Exhippolysmataensirsotris.

 

            There are five species of Acete: A.indicus, A.johni, A. sibogae, A. erythraeus and A. japonicus reported
from India. Among these the first two species support commercially important
fisheries from marine waters, and the rest are exploited on a low key estuarine
and near shore coastal seas along both the north east and north west regions.
The non-penaeid shrimps in Maharashtra as well as in Gujarat show two peaks of
abundance, in October-November and in April-May, but in Andhra Pradesh only one
peak is noticed in July-September. Pandalid shrimps are the major contributors
to deep-sea shrimp fishery which consists mainly Heterocarpus woodmasoni, H. gibosus, Plesionika spinipes and P.martia (ICAR,
2006).

 

The
Alpheidae and Hippolitidea are families under caridians which are species with
less economic importance in the Western Indian Ocean. The family Hippolitidae
are mainly represented by species Exhippolysmata
ensirostris. The Alpheids are small sized shrimps. The significant
characters of them are the cylindrical carapace and small rostrum. (FAO, 1983).

 

            Nandakumar and Maheswarudu (2003)
reported that landings of penaeid shrimps from the country showed a phenomenal
growth in the last four decades with a seven-fold increase from 32,000 t in
1960 to 2,07,080 in 2000. This was mainly achieved by intense combing
operations of trawling to deeper waters, introduction of multiday fishing
operations, night trawling and introduction of innovative gear in the artisanal
sector. During 1991-2000, penaeid shrimps formed 47% of total circumstance
landings along both coasts. The all India annual shrimp production during this
period varied between 1,73,443t and 2,24,902t with an annual average catch of
1,95,059t. about three fourth (75%) of the catch was harvested along the west
coast (1,47,299t) and the rest (24.5%) from east coast (47,754t). Kerala,
Maharashtra, Gujarat, Tamil Nadu, Andhra Pradesh and Karnataka were the
important contributors to penaeid landings in the order of abundance.

 

            Among the maritime states, Gujarat
contributed maximum states, Gujarat contributed maximum (57.5%) followed by
Maharashtra (33.1%), West Bengal (3.9%), Andhra Pradesh (2.6%) and Kerala
(1.8%). Their catch in the other states was sporadic and in negligible
quantities. The marine fish landings of India during the year 2007 has been
estimated as 2.88 million tones, with the south-west coast region (Kerala,
Karnataka and Goa) contributing to about 35%; non-penaeid prawn landings during
the period was 1,39,052 t. The estimated marine fish landings of Kerala during
2007 was 6.19 lakh tones and compared to 2006 an increase of 5% (CMFRI, 2008).

 

            Fishing crafts used for the prawn
fishery includes the traditional catamaran, canoes and plant built boats
(Kurian, 1993). In the reports of Setna (1955) Maharashtra is the first state
to introduce motorized boats in Indian fishery. According to Kurian (1972)
country or craft motorization was the first step in the introduction of
mechanized fishing. Introduction of trawling as part of Indo-Norwegian project
enhanced the landings of shrimps all along Indian Coast. According to
Nandakumar and Maheswarudu (2003) trawl net, which is the most efficient gear
to exploit demersal resources, is operated from medium sized mechanized boats
all along the Indian coasts, targeting mainly penaeid shrimps. During the last
decade trawlers contributed to about 80% of the penaeid landings of India. Ring
seines (smaller version of purse seines) are operated along Kerala-Karnataka coast
during monsoon for getting larger varieties of penaeids. Along Kerala coast
mini trawlers are used for harvesting shrimps. Trammel nets represent the other
type of gear operated in coastal waters to exploit penaeid shrimps. Juvenile
shrimps are exploited by stake nets from backwaters of both coasts.

 

            Rao (1973), Chandy (1970), and
Ramamurthy and Muthu (1969) reported that in the Kerala Coast
Kollivala/Paithavala are also used for fishing shrimps. According to Nair
(1958) Madivalas/Thattuvalas in Vizhinjam and Thanguvala (Kuriyan et al., 1962;
Kuriyan, 1965; Kurup and Rao 1974) are used in the central region of Kerala for
this purpose. Desmukh (2003) reported that along North-West coast traditionally
used bag nets, locally called dol nets, were used for shrimp harvesting.
However, after the introduction of shrimp trawlers the average annual catches
of shrimps in Gujarat increased from an average of 6,537 t during 1979-88 to
84, 156 t in 1996-2000.Trawling remains a controversial method of fishing due to
the perceived lack of selectivity of the trawl nets and the resultant capture
of a huge and diversity of non target species including endangered species
(Bijukumar, and Deepthi, 2006). Alverson et al. (1994) documented the quantity
of fisheries by-catch and discards in various oceans and seas around the world;
the report revealed that the commercial bottom trawling contributes about 27
million tones of discards. According to Andrew and Pepperell (1992) bycatch
from shrimp fisheries alone form 16.7 million tones on a global basis.

 

            Menon (1996) studies the by-catch
landings of trawlers in Karnataka, Kerala and Tamil Nadu during 1985-90 and
recorded 20 genera of fishes, 26 genera of crustaceans, 23 genera of
gastropods, 15 genera of bivalves, 10 genera of echinoderms, polychaetes,
anemones, sponges, gorgonids, ascidians besides a large number of juvenile
young fishes. According to Kurup et al. (2003), the discards of bottom trawlers
in Kerala coast were represented by 103 species of finfishes, 65 gastropods, 12
bivalves, 8 shrimps, 2 stomatopods, 12 crabs, 5 cephalopods, 3 echinoderms and
4 jelly fishes; the discards were represented mainly by epifaunal species and
juveniles of commercially valuable species. Bijukumar and Deepthi (2008)
studied the biodiversity associated with the trawl by-catch of Kerala coast and
recorded the presence of five species of reptiles, 262 species of fin fishes,
12 species of echinoderms, 140 species of molluscs, four species of prawns, 42
species of crabs, five species of stomatopods, many species of hermit crabs,
three species of lobsters, several species of annelids, one species of
sipunculid worm, one species of bryozoan, seven species of cnidarians, and
three species of sponges.

 

 

 

 

            The shrimp fishery of Kerala coast
began with the introduction of trawling through Indo-Norwegian Project. The
bottom trawlers operating from the Kerala coast primarily target shrimps. In
the race for economically valuable shrimps, the considerable by-catch hauled up
with it is, by and large, ignored in parts of the country. This by-catch also
includes economically less valuable shrimp species, which play an important
role in marine ecosystem and food web. Despite the economic and ecological
importance of shrimps and prawns, especially as the major target species of the
trawlers, very little information is available on the species diversity of non
commercial shrimps of  Kerala coast,
including the commercially important but less abundant species obtained. The
available studies focus mainly on commercially valuable species of prawns and
shrimps. This prompted the present study with major objective of documenting
the species diversity of shrimps along the coasts of Kerala –South-west coast
of   India.