Abundance prediction and influence of environmental parameters in the abundance of Octopus (Octopus vulgaris Cuvier, 1797) in the Gulf of Cadiz

Understanding the processes that influence octopus abundance is important in order to manage the fishing grounds and offer advice on the exploitation of this important resource. Fluctuations in abundance of exploited stocks may be due to a great variety of factors. However, in short-lived animals such as cephalopods, in which abundance depends on strength of the recruitment, it is well known that population abundance is highly influenced by the environmental conditions. In this study we investigated the relationship between octopus (Octopus vulgaris) catches from the fishery located in the area off the Gulf of Cadiz (Spanish South Atlantic Region) and several hydrographic and oceanographic parameters such as sea surface temperature, surface chlorophyll-a, inorganic surface turbidity and climatic indicators such as the NAO index, rain, WeMoi Index, AMO index and or Guadalquivir River discharges. In addition, a recruitment index was obtained from fishery-independent surveys, which was also used to investigate its effect on annual catches. Results revealed that abundance of octopus showed a significant negative relationship with rain in the previous year as well as a positive effect of the recruitment index. We have obtained a model using the rain and the recruit index to forecast the catches. This model explained a high percentage of variation in annual catches and was used to forecast the next year’s catch providing results within the expected confidence intervals. This represents a potentially useful tool to guide fishery managers since no assessment of the species is currently conducted in the area.