Abstract
Abstract. A group of small pelagic fish captured between 1981 and 2012 within El Niño area 1–2 by the Ecuadorian fleet was correlated with the oceanographic Multivariate ENSO Index (MEI), and the Oceanographic El Niño Index (ONI) referred to El Niño region 3–4. For the period 1981–2012, total landings correlated poorly with the indexes, but during 2000–2012 (cold PDO) they proved to have a 14–29 % association with both indexes; the negative slope of the curves suggested higher landing during cold events (La Niña) and also indicated a tendency to decrease at extreme values ( > 0.5 and < −1.0). Round herring (Etrumeus teres) fourth-quarter (Q4) landings were related to the MEI in a nonlinear analysis by up to 80 %. During moderate or strong La Niña events landings noticeably increased. Bullet tuna (Auxis spp.) catches showed a negative gradient from cold to warm episodes with an R2 of 0.149. For Chilean jack mackerel (Trachurus murphyi) irregular landings between 2003 and 2007 were observed and were poorly correlated (R2 < 0.1) with ONI or MEI. Anchovy (Engraulis ringens) captured in Ecuadorian waters since 2000 had an R2 of 0.302 and 0.156 for MEI and ONI, respectively, but showed a higher correlation with the cold Pacific Decadal Oscillation (PDO). South American pilchard (Sardinops sagax) was higher than −0.5 for the ONI and MEI, and landings dramatically decreased; however, Q4 landings correlated with ONI and MEI, with R2 of 0.109 and 0.225, respectively (n = 3). Linear correlation of Q4 indexes against the following year's Q1 landings had a linkage of up to 22 %; this species could therefore be considered a predictor of El Niño. Chub mackerel (Scomber japonicus) landings did not have a significant linear correlation with the indexes for 1981–2012 and therefore could not be considered a valid predictor. Chuhueco (Cetengraulis mysticetus) is a local species with high landings during El Niño years and, conversely, remarkably low landings during La Niña years. Additionally, chuhueco availability and landings were negatively affected by cold PDOs. Pacific thread herring (Opisthonema spp.) showed a 24 and 36 % relationship between landings (Q1) and the MEI and ONI (Q4). Therefore, results suggest that the South American pilchard and Pacific thread herring could be considered good species to use as predictors of El Niño in region 1–2 (Ecuador), especially when average Q4 MEI ∕ ONI is used against the next trimester Q1 landing. All species were prone to lower landings and/or fishing availability during strong–extreme events (ONI/MEI, > 1.0 and < −1.0), and were also shown to be affected by the PDO. In the long term, landings decreased under warm PDO and vice versa, and therefore PDO fluctuations could be used to help manage these fisheries and to help the industry in long-term planning.
Highlights
Oceanographic events of high and low frequencies such as El Niño and La Niña and Pacific Decadal Oscillation (PDO) have been studied for some decades, generating a huge amount of research literature
Results are presented for eight species whose landings were examined in time and against the indexes Oceanographic El Niño Index (ONI) and Multivariate ENSO Index (MEI) from 1981 until 2012; the series was split into 1981–1999 and 2000–21012
Most landings were registered between values from −0.5 to 0.5 of both indexes, showing that the highest registered peak was when the indexes were around −0.5, indicating that under cold conditions (La Niña) there was higher availability for fishing (Fig. 2)
Summary
Oceanographic events of high and low frequencies such as El Niño and La Niña and Pacific Decadal Oscillation (PDO) have been studied for some decades, generating a huge amount of research literature During El Niño the water bodies from Panama Bay move south; these have thermal anomalies as high as 6 ◦C (surface temperature > 27 ◦C, e.g., Trenberth, 1997), lower salinity (around 32 psu, D’Croz et al, 1991), nutrient concentration much lower and primary production productivity (Chávez et al, 2003), which in turn affects higher trophic levels (Ormaza-González et al, 2014a, b). De la Cuadra (2010) has found a strong relationship between the high- and low-frequency events with small pelagic-like round sardine, Chilean jack mackerel (Trachurus murphyi), South American pilchard (Sardinops sagax) and others using sea surface temperature (SST) anomalies in the region between the Ecuador coast and the Galapagos Islands
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