Journal of Marine Science and Engineering Article The Role of Environmental Factors on the Fishery Catch of the Squid Uroteuthis chinensis in the Pearl River Estuary, China Dongliang Wang 1,2,†, Lijun Yao 3,†, Jing Yu 1,* and Pimao Chen 1 1 South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangdong Provincial Key Laboratory of Fishery Ecology and Environment China, Scientific Observing and Experimental Station of South China Sea Fishery Resources & Environment, Ministry of Agriculture and Rural Affairs, Guangzhou 510300, China; [email protected] (D.W.); [email protected] (P.C.) 2 College of Marine Science, Shanghai Ocean University, Shanghai 201306, China 3 Department of Optoelectronic Engineering, Jinan University, Guangzhou 510632, China; [email protected] * Correspondence: [email protected] † Authors contributed equally to this work. Abstract: The Pearl River Estuary (PRE) is one of the major fishing grounds for the squid Uroteuthis chinensis. Taking that into consideration, this study analyzes the environmental effects on the spatiotemporal variability of U. chinensis in the PRE, on the basis of the Generalized Additive Model (GAM) and Clustering Fishing Tactics (CFT), using satellite and in situ observations. Results show that 63.1% of the total variation in U. chinensis Catch Per Unit Effort (CPUE) in the PRE could be explained by looking into outside factors. The most important one was the interaction of sea surface temperature (SST) and month, with a contribution of 26.7%, followed by the interaction effect of depth and month, fishermen’s fishing tactics, sea surface salinity (SSS), chlorophyll a concentration (Chl a), and year, with contributions of 12.8%, 8.5%, 7.7%, 4.0%, and 3.1%, respectively. In summary, U. chinensis in the PRE was mainly distributed over areas with an SST of 22–29 ◦C, SSS of 32.5–34‰, Citation: Wang, D.; Yao, L.; Yu, J.; Chl a of 0–0.3 mg × m−3, and water depth of 40–140 m. The distribution of U. chinensis in the PRE Chen, P. The Role of Environmental was affected by the western Guangdong coastal current, distribution of marine primary productivity, Factors on the Fishery Catch of the and variation of habitat conditions. Lower stock of U. chinensis in the PRE was connected with La Squid Uroteuthis chinensis in the Pearl River Estuary, China. J. Mar. Sci. Eng. Niña in 2008. 2021, 9, 131. https://doi.org/ 10.3390/jmse9020131 Keywords: Uroteuthis chinensis; environmental factors; generalized additive model; remote sensing; Pearl River Estuary Academic Editors: Francesco Colloca and Francesco Tiralongo Received: 19 November 2020 Accepted: 22 January 2021 1. Introduction Published: 28 January 2021 Uroteuthis chinensis (Gray, 1849) (Cephalopoda: Loginidae), a species of squid, lives in warm continental shelf waters and is widely distributed in the South China Sea (SCS), Publisher’s Note: MDPI stays neutral East China Sea, and Japan [1]. It is a fast-growing and highly reproductive species with a with regard to jurisdictional claims in short life span (less than 7 months) and high yield (accounting for about 3/5 of the total published maps and institutional affil- production of the family Loliginidae) [2,3]. Because of these characteristics, the U. chinensis iations. is considered to be an ecological opportunist that can increase the population rapidly under a suitable environment [4]. For this reason, environmental factors play a critical role in the life cycle of U. chinensis. Studies showed that cephalopods are sensitive to water tempera- ture [5–9], marine primary productivity [10], and food supply [11], with temperature being Copyright: © 2021 by the authors. the key factor affecting the population biomass and the species’ distribution [12,13]. Such Licensee MDPI, Basel, Switzerland. conditions could impact the population dynamics by acting on the spawning activity and This article is an open access article recruitment [7,8,14]. In the east of the Ionian Sea, the population structure and distribution distributed under the terms and of Illex coindetii depend on temperature, salinity, and circulation [15]. Any change in water conditions of the Creative Commons temperature, chlorophyll a concentration, and salinity would affect the catch of Ommas- Attribution (CC BY) license (https:// trephes bartramii in the northwestern Pacific to a great extent [16,17]. The available studies creativecommons.org/licenses/by/ 4.0/). on the U. chinensis in the SCS are all focused on biological characteristics [18–20], migration J. Mar. Sci. Eng. 2021, 9, 131. https://doi.org/10.3390/jmse9020131 https://www.mdpi.com/journal/jmse J. Mar. Sci. Eng. 2021, 9 2 of 16 J. Mar. Sci. Eng. 2021, 9, 131 2 of 15 the catch of Ommastrephes bartramii in the northwestern Pacific to a great extent [16,17]. The available studies on the U. chinensis in the SCS are all focused on biological character- istics [18–20], migration characteristics [21], feeding behavior [22], and resource status characteristics[23]. Studies showed [21], feeding that U. behaviorchinensis did [22 ],not and migrate resource on a status large [scale,23]. Studies but moved showed in short that U.distances chinensis accordingdid not migrate to local on water a large temperatur scale, bute. moved It moved in shortnorthward distances from according the SCS toto localthe waterTaiwan temperature. bank and other It moved places, northward with the fromincrease the SCSof water to the temperature Taiwan bank every and spring, other places, and withmoved the southward increase of to water the SCS, temperature looking for every suitable spring, conditions and moved during southward winter [21,24]. to the These SCS, lookingstudies forhelped suitable to understand conditions more during about winter the [mi21,gration24]. These characters studies of helped the species, to understand but its morespatiotemporal about the distribution migration characters and quantitative of the relationship species, but with its spatiotemporal marine environment distribution in the andPearl quantitative River Estuary relationship (PRE) remains with marineunclear. environmentIt is still necessary in the to Pearl understand River Estuary the impact (PRE) remainsof environmental unclear. It variability is still necessary on U. chinensis to understand abundance the impact in the PRE. of environmental variability on U.Due chinensis to theabundance monsoon, inthe the PRE PRE. has two major currents: the Guangdong Coastal Cur- rent Due(GCC) to and the monsoon,the South theChina PRE Sea has Warm two majorCurrent currents: (SCSWC), the and Guangdong two coastal Coastal upwellings Current (GCC)(in the andeastern the SouthHainan China Island Sea and Warm the western Current Guangdong (SCSWC), andwaters) two [25–27]. coastal upwellingsIn addition, (ina thelarge eastern amount Hainan of fresh Island water and is thedischarged western from Guangdong the PRE waters) every year, [25– 27mixing]. In addition, with seawater a large amountto form ofthe fresh Pearl water River isplume discharged [28], which from radi theates PRE to every the coastal year, mixing waters with[29]. seawaterBecause of to formthese the dynamic Pearl Rivercharacteristics, plume [28 the], which PRE boasts radiates a high to the primary coastal productivity waters [29]. [22,30], Because making of these dynamicit one of the characteristics, major fishing the grounds PRE boasts for U. achinensis high primary in the world productivity [31]. Therefore, [22,30], the making status it oneof U. of chinensis the major stock fishing in the grounds PRE is of for greatU. chinensis researchin value. the world This study [31]. is Therefore, based on thesix years status ofof U.survey chinensis and satellitestock in remote the PRE sensing is of greatdata and research looks value.into the This relationship study is between based on the six yearsspatiotemporal of survey anddistribution satellite remoteof the U. sensing chinensis data and and some looks environmental into the relationship factors by between con- theducting spatiotemporal a quantitative distribution analysis. The of thepossibleU. chinensis mechanismand somedriving environmental the spatiotemporal factors dis- by conductingtribution of aU. quantitative chinensis in the analysis. PRE is Thealso possiblediscussed. mechanism Results of drivingthis research the spatiotemporal are helpful to distributionunderstand oftheU. migration chinensis characteristics,in the PRE is also to pr discussed.edict the Resultscenter of of the this fishing research ground, are helpful and toto understandprotect the key the migrationhabitat of the characteristics, species. to predict the center of the fishing ground, and to protect the key habitat of the species. 2. Materials and Methods 2. Materials and Methods 2.1.2.1. FisheryFishery Data TheThe researchresearch areaarea considered in this rese researcharch is located between between 19.15–22.15° 19.15–22.15◦ NN and and 111.12–115.37111.12–115.37°◦ E E (as (as shown shown in in Figure Figure1). 1). The TheU. U. chinensis chinensisdata data in thein the PRE PRE was was obtained obtained from thefrom monitoring the monitoring records records of light of falling-netlight falling-net fishing fishing vessels vessels from from August August 2005 2005 to May to May 2010, and2010, the and fishery the fishery data was data collected was collected at a spatial at a spatial resolution resolution of 0.25 of◦ 0.25°× 0.25 × 0.25°◦ and and summarized summa- inrized days. in Thedays. dataset The dataset is composed is composed by 359 by catch