Age and Growth of the Indian Squid, Uroteuthis duvaucelii: Analysis of Statolith Microstructure and Length Frequency Data.

Abstract

Understanding the age and development of a species provides knowledge about its longevity and growth, which are crucial in assessing its life history to maintain the sustainability of its fisheries. Over 3000 samples of Uroteuthis duvaucelii were collected from trawl catches off Concepcion, Iloilo, Western Visayas, Philippines, from April 2018 to September 2019. Daily rings in the statoliths were used to determine their age. The estimated age ranged from 73 to 154 days old, corresponding to sizes of 3.1 to 28.1 cm mantle length. The presence of small individuals (~4 cm) throughout the year indicate continuous spawning of this species. Growth curve patterns of U. duvaucelii were examined using two techniques: growth from sizeat-age data (statolith increments) and growth generated from length-frequency data using the ELEFAN software package. Both methods yielded results that were remarkably different from one another. The growth curve generated from length frequency analysis produced an asymptotic growth. In contrast, sizeat-age data (mantle length-age relationship) revealed that U. duvaucelii does not grow asymptotically. The growth of this tropical squid is best fitted with exponential growth, exhibiting a continuous rapid growth and short lifespan, a prominent characteristic observed in neritic species of squids. This work provides evidence that asymptotic growth is not applicable for the tropical squid species in the Visayan Sea, Philippines.