Spatio-temporal patterns of the crustacean demersal fishery discard from the south Humboldt Current System, based on scientific observer program (2014-2019)

Abstract

This study summarises six years of spatio-temporal patterns of the discarded demersal community fauna recorded by onboard scientific observer program for both artisanal and industrial crustacean fisheries between 2014 and 2019, from mesophotic to aphotic depths (96 to 650 m) along the southern Humboldt Current System (28-38°S). In this period, one cold and two warm climatic events were observed during the austral summer 2014, 2015-2016 (ENSO Godzilla), and 2016-2017 (coastal ENSO), respectively. Satellite information showed that Chlorophyll-a concentration varied seasonally and latitudinally, associated with upwelling centres, while equatorial wind stress decreased southward of 36°S. Discards were composed of 108 species, dominated by finfish and molluscs. The Chilean hake Merluccius gayi was dominant and ubiquitous (occurrence, 95% of 9104 hauls), being the most vulnerable species of the bycatch. Three assemblages were identified: assemblage 1 (~200 m deep), dominated by flounders Hippoglossina macrops and lemon crabs Platymera gaudichaudii, assemblage 2 (~260 m deep), dominated by squat lobsters Pleuroncodes monodon and Cervimunida johni and assemblage 3 (~320 m depth), dominated by grenadiers Coelorinchus aconcagua and cardinalfish Epigonus crassicaudus. These assemblages were segregated by depth, and varied by year, and geographic zone. The latter represented changes in the width of the continental shelf, increasing southward of 36°S. Alpha-diversity indexes (richness, Shannon, Simpson, and Pielou) also varied with depth and latitude, with higher diversity in deeper continental waters (>300 m), between 2018-2019. Finally, at a spatial scale of tens of kilometres, and a monthly basis, interannual variations of biodiversity occurred in the demersal community. Surface sea temperature, chlorophyll-a, or wind stress did not correlate with discarded demersal fauna diversity of the crustacean fishery operating along central Chile.

Fig 1. Spatio-temporal variation of the trawls (black dots) of the artisanal and industrial demersal crustacean fleet, obtained by the scientific onboard observers between 2014–2019.

Fig 2. Cumulative curves of species found as discards in the Chilean demersal crustacean fisheries, separated for each sampled year.

Dotted lines represent one standard deviation.

Fig 3

Multivariate analyses, a) beta-flexible clustering analysis and b) non-metric multidimensional scaling (nMDS) of the discarded demersal fauna from the crustacean fisheries operating off central Chile in 2014–2019. Code names are explained in Table 1.

Fig 4

Boxplots (mean, standard deviation, maximum and minimum) of depth distribution for each assemblage identified by the multivariate analyses and defined in Table 2, by latitude (a, b, c) and year (d, e, f).

Fig 5. Spatial variability (in latitude and depth) of alpha-biodiversity indices of the discarded demersal community off central Chile between 2014–2019.

Fig 6. Hovmöller diagram (latitude vs months between 2014–2019) of the alpha-diversity indices of the discarded faunal demersal community off central Chile.

Fig 7. Hovmöller diagram of coastal (first 100 nm) daily sea surface temperatures (SST) between 28°S and 40°S.

The black box indicates the spatio-temporal scale of the crustacean demersal fishery discard data. The right panel shows the mean latitudinal variation throughout the series.

Fig 8. Time series of multivariate ENSO index version 2 (https://psl.noaa.gov/enso/mei/) (MEI, upper panel), and Hovmöller diagram of the reconstructed sea surface temperature anomaly (SSTAr, medium panel) using the first three Empirical Orthogonal Function (EOF) modes.

The spatial EOFs (right panel), the temporal EOF (bottom panel) and their variability contribution are also shown. The black box indicates the spatio-temporal scale of the crustacean demersal fishery discards.

Fig 9. Hovmöller diagram of monthly coastal (first 100 nm) log-transformed Chlorophyll-a (Chl-a) between 28°S and 40°S.

The black box indicates the spatio-temporal scale of the discard data of the crustacean demersal fishery. The right panel shows latitudinal variation in the mean value throughout the series.

Fig 10. Hovmöller diagram of daily-averaged coastal (100 nm) northerly (red)-southerly (blue, upwelling-favourable) wind-stress (N m^-2) between 28°S and 40°S.

The black box indicates the spatio-temporal scale of the discard data of the crustacean demersal fishery. The right panel shows latitudinal variation in the mean value throughout the series.

Fig 11

Effects of the predictors Depth and Year on richness (a and b, respectively), fitted for a GAM model. Effects of predictor Year on the Shannon-Weiner diversity index (c), Simpson index (d) and Pielou’s evenness (e). Straight lines represent the mean and dotted lines represent the confidence interval (CI).