Tempo-spatial distribution characteristics of fish resources in Jiaozhou Bay

In order to understand the tempo-spatial distributions of fish resources in Jiaozhou Bay, we conducted four surveys on the fishery resources in Jiaozhou Bay by the underlying single trawl in 2016 and 2017. The surveyed results showed that there existed obvious differences in the seasonal variations in the density of fish resources. Individual density of fish resources was the highest in summer (233 427 ind/km²), followed by those in winter (40 746 ind/km²) and autumn (32 246 ind/km²), while that in spring was the lowest (18 080 ind/km²). Mass density of fish resources in winter was the highest (1 593.16 kg/km²), followed by those in summer (825.55 kg/km²) and spring (681.96 kg/km²), while that in autumn was the lowest (337.91 kg/km²). Among them, the average weight of fish in winter was the highest (39.10 g), followed by those in spring (37.72 g) and autumn (10.48 g), while that in summer (3.54 g) was the lowest. Compared with the historically surveyed data, the fish resources in Jiaozhou Bay have shown a significant downward trend during the past 30 years. The fish resource density (1 593.16 kg/km²) was lower than that in 1981—1982 (10 857.00 kg/km²) and 2008—2009 (2 196.00 kg/km²); the average individual mass of fish was 10.60 g, which was lower than that in 1981—1982 (37.70 g). There existed a trend of miniaturization and low-quality in the structure of fish community in Jiaozhou Bay. These changes may have been mainly caused by destruction of fish habitat and the deterioration of the ecological environment of the sea due to human activities.