[Morphological variations and discrimination of medium form of the purple flying squid Sthenoteuthis oualaniensis in the central and southern South China Sea]. / 南海中南部鸢乌贼中型群群体结构.

From 3177 specimens of purple flying squid Sthenoteuthis oualaniensis collected in 2012 and 2013 in the central and southern South China Sea, the morphological indicators including mantle length (ML), arm length-I (AL1), arm length-2 (AL2), arm length-3 (AL3), arm length-4 (AL4), tentacle length (TL), fin length (FL) and fin width (FW) were measured. The morphological variations among the squid species were analyzed using principal component analysis. Results showed that the medium form could be distinguished into cohort I and cohort II which accounted for 69% and 31% of the total, respectively. The percentage of females of the two cohorts decreased first with increasing ML, then increased and reached the ratio of 100% finally. Using Logistic regressing, the MLs at first maturity for females and males of cohort I were estimated to be 164 mm and 112 mm, respectively, and those for females and males of cohort II were 158 mm and 109 mm, respectively. The cohort I concentrated in the waters of Xisha Islands and Nansha Islands, whereas the cohort II was located in the waters of Nansha Islands. Significant differences in all the 8 morphological indicators between either males or females of cohort I and cohort II were found (P＜0.05). Significant differences between cohort I and cohort II in ML, AL1, AL2, AL4, TL and FW were identified in females (P＜0.05), while significant differences between cohort I and cohort II in ML, AL1, AL2, AL3, AL4 and FL were found in males (P＜0.01). The analysis of coefficients of difference indicated that the morphological variations between cohort I and cohort II suggested a clear division within the species.

[Risk assessment of coastal ecosystem in Beibu Gulf, Guangxi of South China].

Based on the marine ecological investigation in the coastal area of Beibu Gulf, Guangxi in September 2009, a GIS-based evaluation was conducted on the present status of ecological environment quality, including seawater quality, nutrient level, biomass, primary productivity, biodiversity, and ecological buffer capacity, in the area in autumn, and the integrated ecological risk index (ERI) was adopted to assess the risk of the coastal ecosystem in the Gulf. In September 2009, the study area had a better ecological environment quality. Most of the risk indicators were at medium or lower level, and the total area was overall at low ecological risk level. The ERI showed that there was an obvious spatial heterogeneity in the distribution of the ecological risk. The nearer to the harbors, the higher the risk was.

[Evaluation of sustainable utilization of fishery resources in Guangdong Province].

Sustainable utilization of fishery resources is the key for the sustainable development of fisheries, and its evaluation is a critical topic in the management of fisheries. Based on the theories of sustainable utilization, an index system suitable for the evaluation of the sustainable utilization of fishery resources in Guangdong Province was established, and a hierarchy and comprehensive grey evaluation model was adopted to evaluate this sustainable utilization in 1978-2007. In the study period, the utilization level of fishery resources in this province had an overall decrease, being the lowest in 1998, only 37.3% of that in 1978; but in the nearest 10 years, this utilization level had an increasing trend, with that in 2007 being 55.1% of 1978. The results of comprehensive evaluation were consistent with the observed facts, indicating that the model was feasible to evaluate the sustainable utilization of regional fishery resources.

[Variations of fish species diversity, faunal assemblage, and abundances in Daya Bay in 1980-2007].

Based on the 2004-2005 otter trawl survey data and the 1980-2007 relevant historical records, this paper analyzed the variations of fish species composition, faunal assemblage, diversity indices, dominant species, and abundance in Daya Bay. In the 2004-2005 trawl survey, a total of 107 fish species were recorded, belonging to 50 families and 13 orders, among which, meso-demersal fish were predominant, with 48 species recorded, and followed by pelagic and demersal fishes, with 37 and 21 species, respectively. The fishes in the Bay belonged to tropical and subtropical fauna, with the dominance of warm water fishes (97 species) and warm-temperate water fishes (10 species). The diversity index was the highest in summer (3.82), followed by in winter (3.37) and autumn (3.00), and the lowest in spring (2.40). The seasonal variation of Pielou evenness index mimicked that of diversity index. In 1980-2007, the characteristics of fish community in the Bay changed obviously. The species number reduced from 157 species in the 1980s to 110 species in the 1990s and to 107 species in 2004-2005, and the dominant species shifted from the high-value fishes such as hairtail and pomfret in the 1980s to low-value fishes such as sardine fish, anchovy, and juvenile porgy. A non-linear regression model composed of inter-annual trend and seasonal cycle was used to simulate the changes of fish stock density in 1980-1999 and 1990-2007, and the results indicated that in the two periods, the fish stock density in the Bay all showed a decreasing trend, but the decrement was larger in 1990-2007 than in 1980-1999. The seasonal variation of the stock density in 1980-1999 was relatively small, with an amplitude being 0.099, while that in 1990-2007 was relatively larger, with the amplitude being 0.420, illustrating that the fish abundance in the Bay had a larger seasonal fluctuation in 1990-2007.

[Effects of fishing on the marine ecosystem of Beibu Gulf].

By using Ecopath with Ecosim 5.1 software, the Ecosim model of Beibu Gulf marine ecosystem in 1959-1960 was constructed, which included about 20 functional groups such as fishery, marine mammals, sea-birds, sharks, pelagic fishes, demersal fishes, and benthic crustaceans, etc. Through the comparison with the investigation data in 1997-1999, the effects of fishing on the structure and function of Beibu Gulf marine ecosystem were analyzed. The results indicated that with the increasing fishing pressure in past forty years, the ecosystem structure and function shifted drastically, with the biomass of long-lived, high trophic level and piscivorous fishes declined while short-lived and small fishes and benthic invertebrates dominated gradually. The biomass of piscivorous species in 1999 was only 6% of that in 1960, while cephalopods increased 2.7 times or more. The trophic level of the catch declined from 3.2 in 1960 to 2.98 in 1999, which fitted the rule of "fishing down the food web" and suggested that the present exploitation patterns were unsustainable. Based on the data of the 1990s, the changes of the ecosystem under decreasing fishing pressure were predicted. This study validated the feasibility of Ecosim model in predicting the effects of fishing pressure on marine ecosystem.