Research Article: Response of Sthenoteuthis oualaniensis to marine environmental changes in the north-central South China Sea based on satellite and in situ observations

Date Published: January 29, 2019

Publisher: Public Library of Science

Author(s): Jing Yu, Qiwei Hu, Danling Tang, Hui Zhao, Pimao Chen, Ulrike Gertrud Munderloh.

http://doi.org/10.1371/journal.pone.0211474

Abstract

In the South China Sea (SCS), Sthenoteuthis oualaniensis (S. oualaniensis) generally has the highest stock density in spring and occupies an important position in fisheries. The responses of S. oualaniensis to marine environments in the north-central SCS in spring (March to May) from 2006 to 2010 were analyzed using satellite and in situ observations, with generalized additive models (GAMs). A high proportion variation in catch per unit effort (CPUE) was explained by environmental variables, including sea surface temperature (SST; explaining 13.8%) and the interaction between SST and chlorophyll a (Chl-a) concentration (explaining 16.9%). SSTs within the range of 24–28°C and Chl-a concentrations within 0.10–0.35 mg/m3 had positive effects on S. oualaniensis CPUE, and SST within 28–29.5°Cand Chl-a concentrations within 0.05–0.20 mg/m3 had negative effects. In addition, the response time of the maximum standardized catch per unit effort (SCPUE) in May to the maximum Chl-a in March was approximately six ten-day time step. The higher Chl-a and smaller stock size of S. oualaniensis in early March 2008 were partly associated with climatic anomalies caused by La Niña in spring and the limitation of S. oualaniensisby low temperature in 2008. The findings in this study can help better protect and manage S. oualaniensis resources in the SCS.

Partial Text

Sthenoteuthis oualaniensis (S. oualaniensis) is in the family Ommastrephidae [1], is widely distributed in the tropical and subtropical areas of the Pacific Ocean and Indian Ocean, exhibits strong phototropism and is one of the major target species of large-scale light falling-net fishing in the central South China Sea (SCS) [2]. Research has shown that S. oualaniensis habitat in the SCS is concentrated in the north-central area and contains the maximum stock density in spring [3,4]. This species migrates from offshore to coastal waters in spring to breed [5,6], primarily consumes fishes, cephalopods and crustaceans in the high trophic levels of 3 and 4, and breeds from March to May [7,8]. S. oualaniensis has a short lifecycle, a rapid growth rate, and high fecundity, thus occupying an important position in the marine ecosystem of the SCS [8].

The landing statistics of S. oualaniensis was used as a proxy for their abundance in the north-central SCS. The index of CPUE is generally assumed to be proportional to stock size [17]. However, CPUE data can be variable or compromised by environmental changes or management through time. In addition, changes in the abundance of pelagic species from commercial data were often difficult because of the high variability of these resources and their extremely aggregated geographical distribution [16]. However, as S. oualaniensis is the major target species of the north-central SCS and catches are not restricted by management strategy, the CPUE was considered as a proxy of their abundance in the resrarch area. By matching catch statistics with environmental factors, this study provided new insight into the response of S. oualaniensis to marine environmental changes in the north-central SCS.

 

Source:

http://doi.org/10.1371/journal.pone.0211474

 

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