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.

Introduction

The Jumbo flying squid (Dosidicus gigas) is one of the main resources of the Peruvian sea, exploited by an important fishery composed of an artisanal Peruvian fleet and industrial fleets (Japanese, Korean and Taiwanese), as described by Paulino et al. (2015). This highly migratory resource is widely spread in the Eastern Pacific Ocean from 60°N to 60°S up to 125°W (Nesis, 1983, Roper et al., 1984).

In the southern hemisphere, the highest concentrations are located in the oceanic region off Peru, and in the northern hemisphere in the Gulf of California (Taipe et al., 2001), in areas characterized by a wide range of oceanographic regimes in oceanic and coastal waters, from tropical to temperate latitudes (Anderson and Rodhouse, 2001). One of the main characteristics of Dosidicus gigas is to be a mono-cyclical species (with only one reproduction during his life) with evidence of spawning throughout the year with a main concentration between October and January and a secondary one between July and August (Nigmatullin et al., 2001, Tafur et al., 2001).

The population support large multi-national fisheries in Mexico, Costa Rica, Peru, Chile and Argentina (Liu et al., 2013b, Waluda and Rodhouse, 2006, Yamashiro et al., 1998). In Peru the fishery of D. gigas is the second most important in volume (Ministerio de la Producción del Perú, 2014).

Squid jigging vessels operate at night using powerful lights (up to 300 kW per vessel) to attract squid (Rodhouse et al., 2001, Waluda and Rodhouse, 2005). The emission of light from these vessels can be observed using satellite-derived imagery obtained by the United States Defense Meteorological Satellite Program-Operational Linescan System DMSP-OLS (Waluda et al., 2004). These images are commonly used for the detection, tracking, quantification and identification of light-associated fishing spots and vessel trajectories (Kiyofuji and Saitoh, 2004, Waluda et al., 2008, Saitoh et al., 2010).

Waluda et al. (2004) found that the distribution of the fishery as derived from light signatures was closely related to those derived from direct vessels location data and that the fishing effort may be related to the ‘area illuminated’ by the fishing fleet. Spedicato et al. (2007) and Woillez et al. (2007) used spatial indicators as the center of gravity (CG) and inertia (I) to determine the spatial-temporal dynamic of the resource through the displacement of the fishing fleet.

Robinson et al. (2013) describes an increase in catches of the Jumbo flying squid associated with a period of prevailing cold temperatures followed by a decline in catches in 2005 as a result of warmer waters. Waluda et al. (2006) found that the abundance of squid is strongly influenced by the mesoscale variability linked to ENSO. We do not use catch data in this study, but only local luminosity levels from the DMSP-OLS imagery to study the spatial-temporal variability of the fishery outside the Exclusive Economic Zone (EEZ) of Peru for the period 2004–2015. We use the following indicators: center of gravity (CG), the inertia (I) and the recurrence and intensity of pixels of high luminosity detected.