Use of statoliths for age and growth studies of squids along southwest coast of India

Saji Kumar, K K (2021) Use of statoliths for age and growth studies of squids along southwest coast of India. Doctoral thesis, ICAR- Central Marine Fisheries Research Institute.

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    Abstract

    Squids support an important fishery component in the Arabian Sea. Because of this, efforts have been made during the last few decades to study the population characters of squids for an understanding of their population dynamics. Recent ageing studies interpret the growth rings in hard parts of cephalopods and it is now recognized worldwide as an accurate method. Therefore, this thesis aimed to study the age and growth of squids by using the hard part, “Statolith” of the different squid species from the Arabian Sea. A total of 15 squid species, including five species of Myopsida squids and ten species of Oegopsida squids, were successfully aged by counting the ring formed on statoliths. Validation studies on Sepioteuthis lessoniana confirmed the “one-increment = one-day” hypothesis in squids of the tropical Indian seas. The size of the adult statoliths ranged from 606 µm in the loliginid squid Loliolus hardwickei to 1926 µm in the mesopelagic squid Octopoteuthis sp. In all the species statolith increments were visible and they were laid outside the nucleus. Neritic myopsid squids have relatively faster growth rates when compared to oceanic oegopsid squids, except for pelagic Thysanoteuthis rhombus which had the fastest growth rate among the 15 squids studied. The statolith based age studies revealed that the lifespan of squids of the tropical Arabian Sea is short (less than 200 days) compared to temperate squids and fishes. This result proves that the currently adopted age estimation method (Length-frequency analysis) were not suitable for squids. Cohort-wise growth analysis proved that increased water temperature leads to faster growth and short lifespans. All pelagic squids have a faster growth rate and short lifespan than mesopelagic squids. Statolith ageing techniques are confirmed as an exceptionally useful life history tool for age and growth estimation of squids from the tropical Indian Ocean. In the light of the very fast growth rate and short lifespan, squid assessment models have to be fine-tuned to account for this unique life history. Fishery researchers and managers have to take into account the very short-lived nature of squid populations and consider in-season assessment and real-time management.

    Item Type: Thesis (Doctoral)
    Uncontrolled Keywords: statoliths; age and growth; squids; southwest coast of India
    Subjects: Fish and Fisheries > Fish biology > age and growth
    Molluscan Fisheries > Cephalopods
    Molluscan Fisheries
    Divisions: CMFRI-Kochi > Marine Capture > Molluscan Fisheries
    Subject Area > CMFRI > CMFRI-Kochi > Marine Capture > Molluscan Fisheries
    CMFRI-Kochi > Marine Capture > Molluscan Fisheries
    Subject Area > CMFRI-Kochi > Marine Capture > Molluscan Fisheries
    Depositing User: Arun Surendran
    Date Deposited: 07 Oct 2021 09:44
    Last Modified: 08 Oct 2021 06:32
    URI: http://eprints.cmfri.org.in/id/eprint/15398

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