Use of nighttime visible images in the study of the spatial and temporal variability of fishing areas of jumbo flying squid (Dosidicus gigas) outside Peruvian EEZ 2004–2015

Abstract

We analyzed the temporal variability of the fishing fleet of Dosidicus gigas, located outside the exclusive economic zone of Peru (EEZ), with a spatial luminosity index. The nighttime satellite images were provided by the Operational Linescan System (DMSP-OLS) from 2004 to 2015. 2995 images were processed, selecting pixels in the range of 30–63 Digital Number (DN), to identify the presence of vessels in the image. The time series showed an extensive latitudinal distribution of the fishing fleet from 6◦S to 32◦S, with years of low (2005–2009) and high (2004, 2010–2015) presence, describing a recurrent seasonal pattern of latitudinal displacement measured from its center of gravity (CG). The CG reaches its southernmost position between February to April and its northernmost position between August to October. Some vessels were also detected within the Peruvian EEZ. The latitudinal inertia presented values of 0.3–1 indicating high fleet concentration between 12◦S to 17◦S and the longitudinal inertia presented values >2, showing the wide distribution of the resource. Luminous pixels showed high fishing occurrence (>18 times) on a single pixel, in front of Chimbote around 9◦51 S–82◦31 W from 2004 to 2011. From 2012 to 2015 areas of high fishing occurrence increased in front of Huarmey (10◦36 S/82◦41 W) and San Juan de Marcona (15◦53 S/80◦6 W). For both periods, high intensity pixels (DN >60) show extensive areas of fishing operation between 9◦S to 20◦S along 200 nautical miles from the coast, while values between 30 and 45 DN could be mostly associated with the search for fishing zones. Since 2012, pixels with DN >58 have increased, indicating a greater fishing activity likely related to a higher availability of the resource or a better knowledge of the fishing zones, associated with an increase of the fishing effort and a possible higher pressure on the resource.