A Comparison of two CPUE calculation methods for longline fishing

Citation
Song L, Li J, Xu W, et al (2012) A Comparison of two CPUE calculation methods for longline fishing. IOTC, Mauritius
Abstract

The soak time of fishing gear influences the fishing efficiency, the catch rates (CPUE) and fishing mortality of target species in longline fishing. Based on the data collected in the tuna longline survey from September 2005 to December 2005 in Indian Ocean, the soak time calculation models of every branch line in each operation were built by both modes of hook retrieval. The fishing effort was calculated by soak time (10000 hours) and by the conventional number of hooks (1000 hooks). The respective CPUE of bigeye tuna (Thunnus obesus) for the entire water column and each water layer of each survey site were calculated, and the t-test was applied to test the significant differences between two CPUE calculation methods. The results showed that (1) Except to no. 1 and no. 25 hook, the total soak time of the different hook no. fluctuated in a small range at every operations (about 10h); (2) The soak time model can be used to estimate the soak time of each hook accurately; (3) There were significant differences between the CPUE of bigeye tuna calculated by soak time and by the conventional number of hooks in different survey sites; (4) Except to 200.0-239.9m and 280.0-319.9m water layers, there were significant differences between the CPUE of bigeye tuna calculated by soak time and by the conventional number of hooks in different water layers. We suggested that the soak time of fishing gear should be used to calculate the CPUE. The soak time of fishing gear included in the number of branch lines, the time of deployment, the period of waiting time and the mode of retrieval. The soak time of fishing gear reflected the effective fishing effort.
The accuracy of CPUE will be improved while the soak time of branch lines was taken as fishing effort.