Fishery and length based population parameters of little tuna, Euthynnus affinis (Cantor, 1849) from Gulf of Mannar, Southwestern Bay of Bengal.

1708-1714Little tuna is the third major tuna species landed along Tuticorin coast after Yellow fin and Skipjack tuna. The species is mostly harvested by large meshed drift gillnets where minor and seasonal catches comes from trawls and lines. Few months post fishing ban period are peak fishing season with high catch rates. There does exist, a seasonal shift in fishing ground in response to changing wind and current pattern. The species showed a positive allometric growth with ‘b’ estimated as 3.1989. Asymptotic length (L∞) and growth coefficient (K) were 79.0 cm and 0.63 yr-1, respectively. The natural, fishing and total mortality were calculated as 1.03 yr-1, 1.37 yr-1 and 2.40 yr-1, respectively. The current exploitation ratio of 0.57 is considerably lower than Emax indicating the possibility of enhancing the production from the capture fisheries

Length based population characteristics and fishery of skipjack tuna, <em>Katsuwonus pelamis</em> (Linnaeus, 1758) from Tuticorin waters, Tamil Nadu, India.

52-59Fishery and population characteristics of skipjack tuna (Katsuwonus pelamis) along Tuticorin coast were studied for the period of one year from June 2016 to May 2017. Population parameters of Katsuwonus pelamis based on the length frequency data collected from fish landing centers of Tuticorin. Lengths ranging from 25 to 80 cm total length were observed and analyzed in current study. The population parameters L∞, K, M, Z and F were estimated as 95.70 cm, 0.40 year-1, 0.73, 1.63 and 0.90 respectively. Virtual Population Analysis (VPA) indicated that noticeable fishing mortality starts from 35-39 cm class interval and continued increasing till 50-54 length class. Afterwards a general decline in fishing mortality was observed with a relatively heavy fishing pressure on penultimate length class. The exploitation ratio (E) of 0.55 was derived from present study which is less than the maximum exploitation ratio (Emax = 0.805) indicating a scope for potential increase in production

Morphological identification and occurrence of engraulid eggs off Gulf of Mannar, South east coast of India

1565-1570Sampling of eggs of species of family Engraulidae was investigated at three stations in the nearshore waters of Gulf of Mannar, for the period of January 2018 to December 2018. During sampling, the quantities and distributions of eggs of engraulids were determined. Horizontal tow was conducted from the surface (0-5 m), a plankton net of 45 cm in diameter and 150 &mu;m mesh. The eggs of engraulids sampled in plankton tows were found to be 542.92 ind./100 m3. A total of 1,075 eggs belonging to 8 species were identified during the sampling period. Eggs of Encrasicholina heteroloba, E. punctifer, Setipinna taty, Stolephorus baganensis, S. tri, Thryssa hamiltonii, T. dussumieri and T. mystax were identified. Engraulid eggs were found throughout the year in the nearshore waters of Punnakayal and Thoothukudi, but they were much abundant during the summer season. A significant positive correlation was found between environmental factors and the occurrence of eggs at Thoothukudi and Punnakayal stations. Thus Punnakayal region of Gulf of Mannar is identified as the spawning ground for the engraulid fishes

Reproductive traits of the obtuse barracuda Sphyraena obtusata Cuvier, 1829 in the Gulf of Mannar, south-east coast of India

The reproductive biology (sex ratio, maturity and fecundity) of the obtuse barracuda Sphyraena obtusata Cuvier, 1829 was investigated based on 698 specimens (323 females and 375 males) sampled along the Pamban Coast in the Gulf of Mannar during the years 2018 and 2019. The total length of the samples ranged from 11.8 to 41.6 cm and the overall sex ratio (male:female) was 1:0.86. The length at first maturity (Lm50) was estimated to be 31.26 cm for females and 31.12 cm for males. Monthly changes in the gonadosomatic index (GSI) values and reproductive phases revealed a protracted spawning, extending from September to February with a peak in January. However, the presence of mature females throughout the year indicated year-round spawning behaviour of the species in the region. Detailed histological studies of the ovary further confirmed that the species is a continuous batch spawner. The estimated absolute batch fecundity ranged between 20,520 and 2,22,422 oocytes and the relative batch fecundity ranged from 261 to 754, with an average of 505 ova per gram body weight of fish. The ova size ranged from 0.03 to 0.84 mm (Mean±SE: 0.43±0.04). Fecundity positively correlated with the total length and total weight of the fish, indicating larger females produced a greater number of ova compared to the smaller ones

<smarttagtype namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="PlaceType"><smarttagtype namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="PlaceName"><smarttagtype namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="country-region"><smarttagtype namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="place"> A new species of cuttlefish <i style="">Sepia ramani </i>sp. nov. (Class : Cephalopoda) from Tuticorin Bay, southeast coast of India </smarttagtype></smarttagtype></smarttagtype></smarttagtype>

81-86 A new cuttlefish Sepia ramani sp.nov. collected from Tuticorin Bay (8o48 N, 78o11 E), India, is described based on 50 specimens covering both-sexes with a comparison of the closely related species of the same genus, Sepia pharaonis. Sepia ramani sp.nov resembles S. pharaonis in morphological characters such as fins, funnel, head, buccal membrane and colour and in most of the morphometric characters. However, in S. ramani sp.nov, the tentacular club is long with 15-24 enlarged suckers and enlarged suckers are almost sub equal in size, in contrast to 6 enlarged medial suckers of which 3 to 4 suckers are greatly enlarged in S. pharaonis. Further, the left ventral arm in males of S. ramani.sp.nov is hectocotylised, with 14-16 basal series of quadriserially arranged normal suckers instead of 10-12 in S. pharaonis. Both the newly erected species and S. pharaonis belonging to Sepia sensu strico species complex as the inner cone of both the species are with plate like callosity and without any cavity. </smarttagtype

Population dynamics of siboga squid <i>D</i><i style="">oryteuthis sibogae </i>(Cephalopoda/Teuthoidea) in Thoothukkudi (Tuticorin) coast, southeast coast of India

213-217Study on the population dynamics of siboga squid Doryteuthis sibogae in Thoothukkudi coast revealed that the seasonal change has definite impact on the growth of this species. The growth parameters viz. L∞, K, t0, C, and φ were 39.5 cm, 0.4, -0.02, 0.5 and 2.9 respectively. Mortality parameters Z, M and F were estimated as 2.27 / year, 0.91 / year and 1.36 / year. Weight was more or less square function of length rather than in cubic function. This squid was found to have two recruitment seasons, one major season during December and a minor season during April. The length structured virtual population analysis revealed heavy fishing pressure on the length group 17 - 20 cm and hence the fishery of D. sibogae was not found to suffer due to recruitment overfishing in Thoothukkudi waters. Estimated total stock, average annual stock and maximum sustainable yield(MSY) were 529.47, 209.14 and 217.33 tonnes respectively. Present level of exploitation rate (U) and exploitation ratio (F/Z) was estimated to be 0.5372 and 0.6 respectively. The study infers that the cod end mesh size of the trawls of Thoothukkudi has to be increased from 10 to 25 mm to increase the yield per recruit. Further, the effort should be reduced and maintained at the exploitation ratio of 0.45 to get maximum yield per recruit. The study suggests reducing the present level of effort by 10 percent to sustain the stock of D.sibogae in Thoothukkudi waters

<i style="">Sepia prabahari</i> sp. nov. (Mollusca/Cephalopoda), a new species of Acanthosepion species complex from Tuticorin bay, southeast coast of India

45-51A new cuttlefish Sepia prabahari sp. nov. collected from Tuticorin bay(8o47’N, 78o9’E) is described with a comparison of the closely related species Sepia pharaonis. Sepia prabahari sp. nov. shows a clear-cut sexual dimorphism with respect to length and shape of arms. In males, first and fourth pair of arms distinctly extended and whip like. However, in females, first and fourth arms are neither distinctly extended nor whip like. Sepia prabahari sp. nov. closely resembles the juvenile of Sepia pharaonis as both of them have distinct tiger-stripe pattern on the dorsal side of the mantle. However, Sepia prabahari sp. nov. can easily be distinguished from the closely related species S.pharaonis based on the arrangement of suckers in the tentacular club. The tentacular club of S. prabahari sp. nov. is with minute suckers of equal size without any enlarged suckers, in contrast to that of S. pharaonis with big suckers, of which about 6 suckers in medial rows are much enlarged. In S .prabahari sp. nov. the left ventral arm of male is hectocotylised with 8 transverse series of normal basal suckers followed by 7 series of modified suckers, in contrast to 10-12 basal transverse series of normal suckers followed by 7 series of modified suckers in S.pharaonis. Further, S prabahari sp. nov belongs to Acanthosepion species complex (Rocheburne, 1884) as its inner cone of the cuttlebone is distinct, forming rounded and cap-like cavity in contrast to that of plate like callosity in S.pharaonis and hence belongs to Sepia sensu stricto species complex. The diagnostic characters of the species belong to the Acanthosepion species complex of the genus Sepia of Indian waters with that of S. prabahari sp. nov. are also discussed

Reproductive biology of the siboga squid <i style="">Doryteuthis sibogae </i>(Adam) from Thoothukkudi (Tuticorin) coast, southeast coast of India

257-260Studies on the seasonal occurrence of maturity stages of Doryteuthis sibogae revealed that it is a prolonged breeder as matured and spent specimens of both the sexes were recorded almost round the year. Two peak spawning periods, one from August to September and another from December to January were observed. Matured animals were represented by a wider length range inferring non semelparous nature of the species. However, dominance of males during peak spawning season as evidenced from sex ratio studies do confirm existence of a minor degree of post spawning mortality in females. The weight of gonad and nidamental glands increased during maturation and proved as good indices of maturation. Females attained maturity earlier than males. Fecundity showed a significant correlation with dorsal mantle length. Doryteuthis sibogae form regular fishery in Thoothukkudi coast on commercial scale. Since this species is a continuous spawner as evidenced in the present study and is intensively exploited at Thoothukkudi bay, an in depth study on stock assessment of this species is an urgent need to sustain the fishery

Pelagic Fish Eggs Diversity in the Nearshore Waters of Gulf of Mannar, South East Coast of India

Background: A study of the diversity, distribution and development of fish eggs and larvae as an integral part of a fishery research programme serves as a valuable aid in the proper management of fisheries. The study is also an essential prerequisite in understanding the spawning biomass of forecasting and trends of production. Information available on diversity of fish eggs from Indian waters is inadequate. The present study was conducted to understand the diversity and distribution of pelagic fish eggs in the nearshore waters of Gulf of Mannar. Methods: The present study conducted at three stations-Mandapam, Thoothukudi and Punnakayal in the waters of Gulf of Mannar, during 2017-2019. A total of 684 ichthyoplankton samples were collected. In the laboratory, the samples were sorted and identified. The diversity was calculated by Shannon-Weiner, Margalef richness index and Pielou’s evenness indices. All the diversity indices were done by using the PRIMER-E software. Result: Our investigation was taken up with objective to assess the status of pelagic fish eggs diversity in the nearshore waters of Gulf of Mannar and found to be more productive. From the diversity study, it is evident that the Punnakayal waters are habitat for a rich diversity of fish species and also a spawning and nursery ground for fishes. Fish eggs diversity is significant for management of fishery resources.</jats:p

<smarttagtype namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="country-region"><smarttagtype namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="place"> Gill net selectivity studies for fishing frigate tuna, <i style="">Auxis thazard</i> Lacepede (Perciformes/Scombridae) in Thoothukkudi(Tuticorin)waters, southeast coast of India^* </smarttagtype></smarttagtype>

329-333Auxis thazard form commercial fishery in Thoothukkudi coastal waters from June to October in big meshed drift gill nets with the mesh size ranging from 60 to 100 mm. The fishery is mainly constituted by the length group 275-500 mm. The present study deals with the estimation of mesh size to capture the commercially significant length group (326-400 mm) of A. thazard and its enmeshing pattern in gill nets with two different mesh sizes. The optimum mesh size for the exploitation of the commercial significant size group of A. thazard from Thoothukkudi coastal waters is estimated as 84 mm. As the length at first maturity of this species in Thoothukkudi coast varied from 300 to 310 mm, the nets with proposed mesh size would reduce growth and recruitment over fishing of A. thazard in this coast and allow for spawning before first capture. Though the big meshed drift gill net fishery of Thoothukkudi coast is multi species oriented, the study emphasises the need to regulate the mesh size of the nets based on the type of fishes that form fishery and fishing seasons. It is recommended to conduct big meshed gill net fishing from June to October with the nets having the mesh size of 84 mm,as A.thazard is the major contributor to the big meshed gill net catch during this season. The use of gill nets with the 60 mm-mesh size should be banned during this season, as this would result in capturing of juveniles of A.thazard leading to growth overfishing