MARAM_Tristan_2020_NOV_15.pdf (612.68 kB)
Further GLM analyses of Nightingale, Inaccessible and Gough CPUE data to incorporate trip length data
reportposted on 2021-01-29, 08:10 authored by Susan HollowaySusan Holloway
This document compares the original GLM analyses applied to Nightingale and Inaccessible data to a new GLM formulation that takes into account the sequential day number of each day’s fishing when this continues over a period of time. Results show that trip lengths have shortened over time at Inaccessible and Nightingale from historically 2 weeks or more, to around an average of 6 days in length since around 2011. A decline in fishing effectiveness is shown for all three islands as trip length increases – the effect is most appreciable at Nightingale with a 40% decline in catch rates by day 14. The overall impact of including sequential days as a factor in the GLM analyses is fairly small in the main, but the standardised CPUE for both Inaccessible and Nightingale becomes somewhat less for the last two years. It is recommended that in future the GLMs which take sequential fishing days into account should be used for the management of these fisheries.