Progress in Fishery Sciences (Oct 2023)
Body Condition and Reproductive Investment of Mature Male Argentinean Shortfin Squid Illex argentinus
Abstract
The Argentinean shortfin squid, Illex argentinus, is an oceanic cephalopod displaying characteristics of short lifespan, fast growth rate, and semelparous reproduction. Here, we aimed to comprehensively understand the squidxs life history strategy by investigating the body condition and gonadosomatic index of mature male squids collected from the high seas of the southwest Atlantic Ocean during the 2018-2021 fishing season. Our evaluations used residual index analysis and mixed-effects models to evaluate the relationships between body condition and gonadosomatic index and the key oceanic variables, including sea surface temperature (SST) and chlorophyll a concentration (Chla). The application of the mixed-effects models allowed us to explore the potential influences of habitat environment on somatic and reproductive growth. Our results showed that mature male I. argentinus had a measured mantle length (ML) between 143 mm and 291 mm and a body weight between 89 g and 559 g. We also noted that the largest individuals were collected in 2020, whereas the smallest were collected in 2018. The b values for individuals from 2018 to 2020, estimated using a power regression of body weight versus mantle length, were significantly different from the assumed isometric growth coefficient b value (equals to 3). The standardized residuals of BW-ML relationships indicated that the individuals collected in 2020 retained the best body condition, whereas the individuals from 2018 to 2021 displayed poor body condition. In contrast, mature male I. argentinus showed the lowest gonadosomatic index in 2020, followed by 2018 and 2021. Mixed-effects model evaluations revealed a significant correlation between body condition, SST, and Chla. The individuals displayed a decreasing trend in body condition in response to increasing sea surface temperature, from 9.0 ℃ to 12.5 ℃, and body conditions improved when the chlorophyll a concentration was around 1 mg/m3. Mixed-effects modeling also revealed that the gonadosomatic index was positively correlated with SST, demonstrating a relatively high value at approximately 15 ℃. Taken together, these findings indicate that there is a trade-off between body condition and reproductive investment, and that SST has a significant influence on body condition and reproductive investment for mature male I. argentinus. Additionally, chlorophyll a concentration also demonstrated a significant influence on the body condition of mature male I. argentines.
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