To better develop and protect the pelagic fishery in the northwest Indian Ocean, China’s fishing enterprises have been producing pelagic fisheries in the said area for a long time. Based on the fishing log data of light falling gear in the northwest Indian Ocean from 2016 to 2020, this study analyzed the impact of different time scales on the catch rate and fishing ground center of gravity of light falling gear fishing grounds. We also explored the relationship between different time scales and catch per unit effort (CPUE) by using the fishing ground center of gravity, the Random Forest model (RF), and the generalized additive model (GAM). The results were shown as follows: (1) From 2016 to 2020, 76,576 t were captured, and 16,496 nets were operated; (2) The gravity center of fishing ground in the Northwest Indian Ocean moved to the northeast as a whole, and the monthly fishing ground gravity center changed first to the Southern and then to the northern; (3) RF model (R² = 0.709, RMSE = 0.2034, and prediction accuracy is 55.8%), which is better than the GAM model (R² = 0.632, RMSE = 0.2242, and prediction accuracy is 37.3%). In the RF model, the importance of time variables on CPUE was in the order of week, year, operation time, and lunar phase; in the GAM model, it was week, year, lunar phase, and operation time. On the whole, the importance of the long time scale (year, week) is greater than that of the short time scale (lunar phase and operation time). (4) The RF model and GAM model show that the most critical environmental variables were SST, DO, SSS, and Chla, and the least important were SSH, Δ50, and CV50. SST, Chla, and DO significantly impact pelagic fishing and CPUE and are critical reference indexes for predicting the Northwest Indian Ocean light falling gear fishing ground. (5) The 95% confidence interval showed that the suitable interval of time, space, and environmental variables in the RF model was much smaller than in the GAM model.

Oceanic squids are typical species that sensitive to the environment change. Previous studies on oceanic squids mainly focus on its annually fluctuated abundance under the background of climate change. The changes of individual morphological sizes, including body and beak, have been observed in recent years. In this study, Ommastrephes bartramii, an important cephalopod species in North Pacific Ocean, has been selected to analyze the annual morphological changes of body and beak under different scales of climate events. Geometric morphometrics was used to analyze the shape variations of both upper beak and lower beak. The possible phenotypic plasticity of body and beak was also discussed in different aspects. Body size showed different variations among different climatic years. The size at the maturity stage in 2015 (El Niño year) was much smaller than that in other years for both sexes. The centroid size representing the beak size showed the significant difference between two types of Pacific Decadal Oscillation phases. The shapes of upper and lower beaks showed significant differences between small-scale climatic patterns in which El Niño or La Niña event occurred, displaying different growth patterns.

Investigating the ontogenetic variation of biological individuals helps us to fully understand the characteristics of evolution. In order to explore the ontogenetic variation and sexual dimorphism of the beak shape in Octopus minor, Uroteuthis edulis, Sepia esculenta and Sthenoteuthis oualaniensis of the China’s coastal waters, the differences between immature and mature stages and the sex-linked differences in the beak shape and size were analyzed with geometric morphometrics methods in this study. The results of Procrustes analysis of variance, principal component analysis and multivariate regression showed that the shapes of the upper beaks of O. minor, U. edulis and S. esculenta differed significantly among various ontogenetic stages (p < 0.05). The shapes of the lower beaks of U. edulis, S. esculenta and Sthenoteuthis oualaniensis were also significantly different among various ontogenetic stages (p < 0.05). The results of thin-plate spline deformation grids showed that the beaks of the four cephalopod species presented different variation patterns. This study gives us basic beak geometry morphology information for Octopus minor, Uroteuthis edulis, Sepia esculenta and Sthenoteuthis oualaniensis present in China’s coastal waters. The ontogenetic differences in beak shape might be related to extrinsic factors (diet difference and intra and interspecific competition) in habitat.