Influence of Spatial-Temporal and Environmental Factors on Larimichthys polyactis, Octopus variabilis, and Species Aggregated Set-Net CPUEs in Haizhou Bay, China

Abstract

Set-nets are common alongshore fishing gear used in Haizhou Bay, which rely on flow to catch fish. The catch per unit effort (CPUE) of set-net is affected by spatial-temporal and environmental factors but no research has been conducted on this subject. In this study, we used generalized additive models (GAMs) to explore the influence of spatial-temporal and environmental factors on CPUEs of species aggregated, small yellow croaker (Larimichthys polyactis), and octopus (Octopus variabilis) based on logbooks investigations conducted at 4 stations in an alongshore area of Haizhou Bay from 2011 to 2012. The results showed that all CPUEs exhibited significant spatial-temporal differences at various scales. Aggregated CPUE was high when the sea surface temperature (SST) was 15–18°C and 20–23°C, which was mainly determined by life history traits of the octopus and small yellow croaker (optimal SSTs 14–17°C and 19–24°C, respectively). Chlorophyll-a concentration had significant influences on the aggregated, small yellow croaker and octopus CPUEs at optimal ranges of 3.8–6.2 mg m−3, 4.2–4.8 mg m−3 and 4.5–5.5 mg m−3, respectively. Flow through the net had positive relationships with CPUEs. The approximate logarithmic trends in regression curves had a critical point of 2.5 Mm3 d−1, which was the dividing point that differentiated whether the major factor affecting CPUEs was the flow velocity or the fishery resource. Our results from this study will help guide fishery production and improve catch rate of set-net fishing in Haizhou Bay.