Effect of tropical monsoon on fishery abundance of Indian squid (Uroteuthis (Photololigo) duvaucelii)

Indian squid, Uroteuthis (Photololigo) duvaucelii (Loliginidae) constitute an important component of the inshore cephalopod fisheries along the eastern Arabian Sea. Local environmental variation plays an important role in species–environment interactions in neritic squids, which inhabit nearshore/coastal waters. Such ‘active’ and ‘passive’ responses of squids to environmental changes is crucial in understanding their relationships and influence on the biological processes, distribution and abundance of the fast-growing shortlived coastal loliginids. The empirical relationship between squid abundance and the variability in rainfall and sea surface temperature (SST) were explored in a tropical monsoon fishery. Monthly catch rates (catch per fishing hour) of squids in commercial trawl during 1987–2009 were used as the abundance index. Linear regression models with ARIMA errors were fitted with catch per unit hour time series as dependent variable and rainfall and SST as exogenous variables. While rainfall was observed to have a negative effect on squid abundance, the SST recorded a positive impact. ARIMA models provided satisfactory fit to observed data and forecast of 22 months. Given that the squid life-cycle is a function of their environment, this result is relevant in forecasting squid biomass for themanagement of tropical monsoon fisheries

Rare double embryos in the egg capsule of Pharaoh Cuttlefish

The embryonic development of cephalopods is considered unique among molluscs. A recently spawned and deposited egg cluster of Pharaoh Cuttlefish Sepia pharaonis (Ehrenberg, 1831) was collected from the Arabian Sea off Kochi (10°01ʹ52ʹʹ N; 75°55ʹ09ʹʹ E) (40 m depth) on 25th November 2021. The egg stalks were attached to a moored coconut spadix and the colour of the egg cluster was white. Fertilized eggs were brought to the laboratory and allowed to develop in tanks with oxygenated seawater (28°C; pH 8.1-8.3; salinity 34-35 ppt) at the ICAR-Central Marine Fisheries Research Institute, Kochi, India

Experimental validation of periodicity of increment formation in the Statolith of bigfin reef squid Sepioteuthis lessoniana (Cephalopoda: Lolignidae) from tropical Indian waters

Sepioteuthis lessoniana (Lesson, 1830) is a neritic squid that inhabits coral, rocky reefs, seaweed and seagrass beds of the IndoPacific region. Increment validation or the periodicity of increment formation in squid statolith is fundamental for age determination, longevity estimation and life history traits, hence it is critical for fishery management and species conservation. Although studies have established one-increment-per-day hypothesis in neritic squids, it has never been validated for tropical Indian Seas. Squids are the dominant component of fauna in the Indian waters, hence an investigation on the statolith increment formation was undertaken for S. lessoniana, as a representative of Loliginid squids

Unusual landing of the giant form of Purpleback flying squid

According to the fishermen, this species is found in the Northeastern Arabian Sea but due to lack of domestic market demand, they are mostly discarded. Further studies on its reproductive biology, age, growth characteristics and identification of internal parasites are being carried out

Size and weight relationships of the purpleback flying squid, Sthenoteuthis oualaniensis (Cephalopoda: Ommastrephidae), from Arabian Sea

The size and weight relationships and morphometrics of 390 individuals of the purpleback flying squid, Sthenoteuthis oualaniensis, collected from the tropical Arabian Sea were studied. The lengthweight relationship was W = 0. 0320 DML3.0972 for females, W = 0.0318 DML3.1288 for males, and W = 0.0382 DML3.0395 when sexes were combined indicating an isometric growth pattern. Most of the morphometric characters showed a high degree of correlation among the compared characters. The relationships between ten morphometric characters against the dorsal mantle length of both the sexes were analysed and it indicated a very high degree of correlation in females compared to males. Females in the samples were twice the size of males, indicating sexual dimorphism in body siz

Genetic cataloguing of Octopus species from coastal waters of Kerala using molecular markers

Octopuses are one of the commercially important fishery resource form the Indian coast and there is a targeted fishery for octopus in many fish landing centres in Kerala. There are lot of taxonomic ambiguities within the octopus species and the accurate identification of species is of prior importance in conserving such vulnerable species. With a view to identify and genetically catalogue the octopus species of Kerala coast, specimens were collected from different landing centres of the region. Molecular characterization was done with partial sequence information of mitochondrial gene Cytochrome C oxidase-I (COI) gene. Total 17 specimens of 7 species were collected from 4 locations and COI sequences were generated (650 bp). 7 species included viz, three ocellate octopus, belonging to the genus Amphioctopus; (Amphioctopus neglectus. A. marginatus and A. rex), two from genus Cistopus: (Cistopus Indicus and C. taiwanicus), one each from Octopus vulgaris and Callistoctopus macropus. Both genus of Cistopus and Amphioctopus showed the intra and inter specific distance ranging from 0.0-1.0 % and 7.0-21.0 %, respectively. Phylogenetic analysis using maximum likelihood approach revealed that all the genera of the family Octopodidae are monophyletic

Assessment of dimorphic growth of the cuttlefish Sepia pharaonis (Cephalopoda: Sepiidae) using cuttlebone markings from the south-eastern Arabian Sea

The pharaoh cuttlefish Sepia pharaonis Ehrenberg, 1831, is one of the most important species exploited along the Eastern Arabian Sea. A study on the relationships between dorsal mantle length (DML) and number of cuttlebone septa (or chambers) and between total body weight and number of cuttlebone septa were carried out in S. pharaonis collected from the south-eastern Arabian Sea. The cuttlefish samples were collected from Cochin Fisheries Harbour (133 males and 67 females). Dorsal mantle length-at-chamber count and weight-at-chamber count were statistically higher in males than in females. The available literature suggests that females of S. pharaonis are heavier than males while males are found to attain greater ultimate lengths throughout the lifecycle. Literature also suggests that the rate of cuttlebone septum formation is the same in both sexes of Sepia species, however in the present study, S. pharaonis males have slightly higher growth rates than females (Fig. 1 & 2). The study indicates that there is considerable scope to use cuttlebone chamber counts as a means of determining actual age of cuttlefishe

Comparison of length-frequency versus statolith age analysis of Uroteuthis (Photololigo) singhalensis in eastern Arabian Sea

Loliginid squids are a commercially important group of neritic squids in the coastal marine waters in tropical and temperate regions around the world and are valuable resources in many areas. Uroteuthis (Photololigo) singhalensis is listed among the commercial species of loliginid squid exploited from the China Sea to the eastern Arabian Sea. Though this species is distributed from western Pacific to the Indian Ocean from the Andaman Sea, the Bay of Bengal to the Arabian Sea and the eastern African coasts, there is little information on the life cycle of this species throughout its distributional range. The objective of this study is to determine the length-weight relationship, age and growth of U. (P.) singhalensis off eastern Arabian Sea. Most earlier estimates of growth in tropical squids are derived from length frequency analysis. The accuracy and precision of squid growth estimates have been enhanced by using statolith increment analysis, hence statolith increment is used to determine age and individual growth rate of squid off the eastern Arabian Sea. Further, the comparison of the length frequency analysis with statolith ageing techniques is attempted

Mating In the Indian Squid Uroteuthis duvaucelii (cephalopoda: Loliginidae) From the Tropical Arabian Sea

The Indian squid Uroteuthis duvaucelii (D'Orbigny, 1835) is the most important commercial species of squid caught from the Indian Seas. Sperm transfer is a complex process in cephalopods, with males transferring intricate spermatophores to females during mating. However, nothing is known about the mating and sperm transfer behaviour of U. duvaucelii from the tropical Indian waters. Spermatangia implantations were tracked over the buccal membrane of 14 females and one male Indian squid Uroteuthis duvaucelii from the Arabian Sea during February and March 2021. The size of mated female individuals ranged from 110 to 160 mm dorsal mantle length (DML). The numbers of spermatangia in the buccal region range from 64 to 385 (mean=178). The length of the spermatangia ranged from 0.66 to 1.35 mm (average=0.89 mm) and the maximum width ranged from 0.14 to 0.23 mm (average=0.19 mm). Based on the statolith based age estimation, the age of the mated squid ranged from 98 to 148 days. Normally spermatophores are transferred to the buccal region of females by males during copulation, but strangely, a male buccal membrane was observed with spermatangium (n=254), which is evidence of same-sex (homosexual) mating behaviour in the Indian squid. Back-calculated hatching dates for the squids were from September 28th 2020 to 28th November 2020. The present observations give evidence for pre-monsoon mating for the species in the tropical Arabian Sea. Furthermore, we recommend a detailed study on reproductive biology for a complete understanding of the mating behaviour of loliginids in the Arabian Sea

Age and growth of the Indian squid Uroteuthis duvaucelii based on statolith microstructure analysis from the tropical Arabian Sea

The Indian squid Uroteuthis duvaucelii is distributed widely in the continental shelf waters of the Indo-West Pacific Seas and also contributes a major share of the annual squid landing from the Indian waters. Age and growth rate information is one of the most important set of variables for estimating population dynamics of the species. Earlier works on the age and growth of squids along the Indian subcontinent were mainly based on length-frequency analysis. Recent studies have proven that length-frequency analysis overestimate the life span and underestimate the growth rate of squids. Therefore, the aim of this study is to understand the age and growth of the Indian squid in the Arabian Sea based on analysis of the statolith growth increment, which has already been applied to growth studies in many squid species. A total of 432 (male: 235; female: 197) individuals of the Indian squid were sampled from the commercial trawlers operating along the southwest coast of India