Pakistan Journal of Marine Sciences, Vol. 13(1&2), 27-33, 2004.

OCCURRENCE AND ABUNDANCE OF JUVENILE PENAEIDPRAWNS IN SANDSPIT BACKWATERS OF KARACHI

Feroz A. Siddiqui, Nuruddin Mahmood and Farhana S. GhoryMarine Reference Collection and Resource Centre, Universityof Karachi, Karachi-75270, Pakistan (FAS, FSG); Institute ofMarine Sciences, University of Chittagong, Chittagong 4331,

Bangladesh (NM).

ABSTRACT: Juvenile penaeid prawns were collected frommangrove swamps of Sandspit backwaters to study theirseasonal occurrence and abundance round the year. Thespecimens were collected by a scissors net at fortnightlyintervals for a period of fifteen months between July 1995to October 1996. The results revealed presence of juvenilesof eight species, Metapenaeus affinis, M. monoceros, M. stebbingi,Metapenaeus sp. Fenneropenaeus indicus, Penaeus monodon, P. semisulcatusand Penaeus sp. This study indicated pronounced variations inoccurrence and abundance of different species. M. affinis(45.22%) and Metapenaeus monoceros (40.97%) were more commonlyfound in catches and constituted 86.19% of the population.These two species sustained their occurrence throughout theyear in the study area, whereas M. stebbingi constitute 8.94%of the population followed by Fenneropenaeus indicus (2.20%).Other species (P. monodon and P. semisulcatus) shared a verylittle percentage of the population (0.04%) both beingrepresented by a single specimen. Small individuals (5-19mm)of the genera Metapenaeus and Penaeus could not be identifiedto species level. They constituted 1.36% and 1.08%respectively of the population. It was also observed that M.affinis and M. monoceros occurred in abundance from Januarythrough July with occasional presence of M. stebbingi, whereasF. indicus occurred during August through December along with avery rare occurrence of P. monodon and P. semisulcatus. The singlespecimen of P. monodon, which was incidentally the largest inthe collection measured 99mm and the smallest specimen wasthe Metapenaeus sp., measured 5mm.

28 Pakistan Journal of Marine Sciences, Vol. 13(1&2), 2004.

Comparison with the previous study of Sultana, et al., 1991(site being located 5km away to the east) revealed absenceof Fenneropenaeus merguiensis and F. penicillatus.

KEY WORDS: Juvenile penaeid shrimp, Sandspit backwaters,occurrence and abundance.

INTRODUCTION

The present study deals with the occurrence and abundanceof juvenile penaeids in the Sandspit (24o50’ 24oN 66o54’24oE) backwaters (Fig. 1). The developmental cycle ofpenaeid prawns is completed in two phases: first is anoceanic phase, when they spawn and pass through a series oflarval stages to attain mysis and postlarval stages, andsecond is the estuarine phase in which the postlarvae moveinshore to estuarine backwaters of mangrove swamps andbecome demersal juveniles. The mangrove waterways and swampsare highly rich in nutrients, provides favourable habitatserve as nurseries and feeding grounds for juvenile penaeidprawns. These shallow estuarine backwaters enhance thesurvival and growth of the young prawns to adolescence. Thenthey move to offshore waters for spawning on being mature.

Previously a comprehensive study of juvenile penaeidprawns in backwaters of the Karachi coast was made bySultana et al (1991). The present work is another attempt tofurther the knowledge of this commercially importantresource, but based on observations in a differentcollection site, being 5km away from the area sampled by theprevious workers.

In addition to a comparison of the results of theprevious study, we provide an overview of the juvenilepenaeid prawn population, together with the seasonaloccurrence, abundance, and size distributions of thedifferent species.

Siddiqui et al.: Occurrence and abundance of juveniles penaeidprawns 29

Fig. 1. Map showing collection site at Sandspitbackwater (indicated by an arrow) for juvenile penaeidprawns.

MATERIALS AND METHODS

Juvenile penaeid prawns were collected from a tidalchannel in the mangrove swamp of Sandspit backwaters by ascissors net (4mm mesh size, 2.4m mouth area), atfortnightly intervals for a period of fifteen months (July1995 - October 1996). The water depth at the collection siteranged between 0.25 and 0.75m. Temperature, salinity and pHof water were recorded. Graphs and bargrams were made toexplain seasonal occurrence, abundance, and speciescomposition of the community. All the samples were preservedin alcohol, measured for length and housed at the MarineReference Collection and Resource Centre. Upgradation ofsubgenera to generic level in Farfante and Kensley (1997) isfollowed here.

30 Pakistan Journal of Marine Sciences, Vol. 13(1&2), 2004.

RESULTS

During the fifteen months (July 1995 - October 1996)sampling period, a total of 2494 juvenile penaeid prawnswere collected. The temperature, salinity and pH ranges were18oC - 34oC, 29-45‰ and 7.8 - 8.2 respectively.

Analysis of the collected material revealed the presenceof eight species: (2 undetermined)Metapenaeus affinis, M. monoceros, M. stebbingi, Fenneropenaeus indicus,Penaeus semisulcatus and P. monodon. There were some smaller (5-19 mm) specimens of the genera Metapenaeus and Penaeus thatcould not be identified to specific level.

Species composition and their seasonal abundance:The present investigation indicated a pronounced

variation in the composition and abundance of (Figs. 2,3),Metapenaeus affinis (45.22%) and M. monoceros (40.97%) were foundto be very common in the samples of July 1995 to October1996, where they constituted 86.19% of the population,whereas M. stebbingi represented 8.94% of the populationfollowed by Fenneropenaeus indicus (2.20%). Other species,Penaeus monodon and P. semisulcatus shared very little percentageof population (0.04%). The unidentified species ofMetapenaeus and Penaeus are represented by 1.36% and 1.08%respectively of the total population.

Both M. affinis and M. monoceros showed their peak abundancein different months. M. affinis reached peak in October of1995, with a second and higher peak in January 1996.Thereafter, the population declined sharply until July 1996,recovered with another, peak in August 1996. M. monocerosreached peak in August 1995, second smaller peak inNovember, 1995. In 1996 higher peak in June and August,another smaller peak in October. M. stebbingi attained itshigher peak in December 1995 and sustained occurrence duringother months in fewer individuals. In case of F. indicus thepeak of abundance were observed in September 1995 andSeptember 1996 whereas in other months either it disappearedor reappeared through fewer individuals, during November to

Siddiqui et al.: Occurrence and abundance of juveniles penaeidprawns 31

July. P. monodon and P. semisulcatus showed their presence inSeptember and October 1996 respectively by a singleindividual of each. Smaller specimens of Metapenaeus sp.showed their peak abundance in July and August 1995 andanother smaller peak in September and October 1996. In caseof Penaeus sp. showed abundance in only August 1995.

Size Distribution:Size distribution of juveniles of different penaeid

species collected from the study area were as follows: Thesmallest specimen was a Metapenaeus sp. measuring 5 mm intotal length; whereas the largest individual was P. monodon,measuring 99 mm in total length. Length frequencies ofoccurring species have been plotted in Figure 4. It appearsthat M. affinis ranged from 15 to 74 mm, 15 to 69 mm for M.monoceros and M. stebbingi was also in the same size range (15-69 mm). F. indicus had a size range of 20-59 mm, a singleindividual of P. semisulcatus measuring 59 mm in total lengthand Penaeus sp. ranged from 10-14mm.

32 Pakistan Journal of Marine Sciences, Vol. 13(1&2), 2004.

Siddiqui et al.: Occurrence and abundance of juveniles penaeidprawns 33

Fig. 2. Showing percentage composition of juveniles ofdifferent penaeid species, collected during July 1995to October 1996.

Fig. 3. Seasonal abundance of juvenile of differentpenaeid species, during July 1995 to October 1996.

REMARKS

The present study conducted in the mangrove swaps ofSandspit backwaters, gives very interesting results whencompared to the studies done by Sultana et al. (1991). Theyreported seven species of penaeid prawn juveniles, includingFenneropenaeus merguiensis and F. penicillatus complex whereas in the

34 Pakistan Journal of Marine Sciences, Vol. 13(1&2), 2004.

present study Penaeus semisulcatus was sampled. Metapenaeusmonoceros was the common species in both the studies (presentand previous) which occurred throughout the year.

Ahmed (1985) and Hassan (1989), reported juveniles of M.affinis and F. indicus from Indus delta, however these two studieswere limited to only three months samples. According tothese reports M. affinis and F. indicus can be sampled from Indusdelta as seed for aquaculture. The occurrence and abundanceof M. monoceros can be utilized as irrelevance seed foraquaculture. Further studies will be helpful to confirmingthis as an area collection ground of juveniles of commercialspecies.

Siddiqui et al.: Occurrence and abundance of juveniles penaeidprawns 35

Fig. 4. Size distribution of penaeid juveniles.

REFERENCES

Ahmed, M., 1985. Winter and spring abundances of juvenilepenaeid and caridean shrimps in the Indus delta(Pakistan: Northern Arabian Sea). Pakistan Journal of Zoology .17 (1): 67-70.

36 Pakistan Journal of Marine Sciences, Vol. 13(1&2), 2004.

Farfante, P., and B. F. Kensley, 1997. Penaeoid andsergestoid shrimps and prawns of the world. Key anddiagnoses for the families and genera. Memoires du Museum.National d Histoire Naturelle. Vol. 175 :1-233.

Hassan, H., 1989. Distribution and abundance of penaeidjuveniles on Makran and Sindh coast. Pakistan Journal ofZoology. 21(2): 147-152.

Sultana, R., and J. Mustaquim, 1991. On the occurrence andseasonal abundance of juvenile penaeid shrimps from thebackwaters of Karachi coast. In Proceeding of theNational Seminar on study and management in coastal zonesin Pakistan. MRC&RC and Pakistan National Commission forUNESCO (eds. N.M. Tirmizi and Q.B. Kazmi): 33-41.

(Received: 25 May, 2003)