Time series analyses reveal transient relationships between abundance of larval anchovy and environmental variables in the coastal waters southwest of Taiwan

Abstract

We investigated environmental effects on larval anchovy fluctuations (based on CPUE from 1980 to 2000) in the waters off southwestern Taiwan using advanced time series analyses, including the statespace approach to remove seasonality, wavelet analysis to investigate transient relationships, and stationary bootstrap to test correlation between time series. For large-scale environmental effects, we used the Southern Oscillation Index (SOI) to represent the El Niñ o Southern Oscillation (ENSO); for local hydrographic conditions, we used sea surface temperature (SST), river runoff, and mixing conditions. Whereas the anchovy catch consisted of a northern species (Engraulis japonicus) and two southern species (Encrasicholina heteroloba and Encrasicholina punctifer), the magnitude of the anchovy catch appeared to be mainly determined by the strength of Eng. japonicus (Japanese anchovy). The main factor that caused the interannual variation of anchovy CPUE might change through time. The CPUE showed a negative correlation with combination of water temperature and river runoff before 1987 and a positive correlation with river runoff after 1988. Whereas a significant negative correlation between CPUE and ENSOs existed, this correlation was driven completely by the lowfrequency ENSO events and explained only 10% of the variance. Several previous studies on this population emphasized that the fluctuations of larval anchovy abundance were determined by local SST. Our analyses indicated that such a correlation was transient and simply reflected ENSO signals. Recent advances in physical oceanography around Taiwan showed that the ENSOs reduced the strength of the Asian monsoon and thus weakened the China Coastal Current toward Taiwan. The decline of larval anchovy during ENSO may be due to reduced China Coastal Current, which is important in facilitating the spawning migration of the Japanese anchovy.

Effects of climate variability and climate change on the fishing conditions for grey mullet (Mugil cephalus L.) in the Taiwan Strait

“…Climatic effects on the fluctuations of fish populations and fisheries have long been recognized and continue to be critical (Lehodey et al 2006;Hsieh et al 2009;Tzeng et al 2012a;Lan et al 2012). The most widely studied climatic events causing impacts on fishes include those on an inter-annual scale, such as the El Niño/Southern Oscillation (ENSO) (Lehodey et al 2006;Hsieh et al 2009), and on a decadal scale, such as the Pacific Decadal Oscillation (PDO) (Mantua et al 1997;Tzeng et al 2012a). In particular, large-scale climatic oscillations such as the ENSO can cause SST changes on an inter-annual scale (Tzeng et al 2012b;Kuo and Lee 2013).…”

“…Black bar: fishing effort of purse seiners; Grey bar: fishing effort of gill nets; Red line: CPUE of purse seiners; Blue bar: CPUE of gill nets Second, increasing sea surface temperatures (SSTs) and other climatic effects associated with global warming have contributed to reduce catches of grey mullet in Taiwan (Hung and Shaw 2006). Climatic effects on the fluctuations of fish populations and fisheries have long been recognized and continue to be critical (Lehodey et al 2006;Hsieh et al 2009;Tzeng et al 2012a;Lan et al 2012). The most widely studied climatic events causing impacts on fishes include those on an inter-annual scale, such as the El Niño/Southern Oscillation (ENSO) (Lehodey et al 2006;Hsieh et al 2009), and on a decadal scale, such as the Pacific Decadal Oscillation (PDO) (Mantua et al 1997;Tzeng et al 2012a).…”

Wavelet analysis of correlation among Canary Islands octopus captures per unit effort, sea-surface temperatures and the North Atlantic Oscillation

“…It is one of the best mother functions in terms of reproducing the frequency decomposition of the signal (Kirby, 2005). It has often been successfully used in the study of environmental variables, such as SST, NAO or ENSO (Torrence and Compo, 1998;Torrence and Webster, 1999;Maraun and Kurths, 2004) and ecological variables, such as tuna catches (Mènard et al, 2007;Rouyer et al, 2008), swordfish (Corbineau et al, 2008) or larval anchovy (Hsieh et al, 2009).…”

“…Recent evidence using wavelet analysis and other statistical tools indicates that climatic oscillations, such as the North Atlantic Oscillation (NAO), the Indian Oscillation (IOI), or the El Niño-Southern Oscillation (ENSO) have important effects on marine fish populations (Mantua et al, 1997;Mènard et al, 2007;Rouyer et al, 2008;Hsieh et al, 2009) far-reaching societal impacts (Jacobson et al, 2001;Hsieh et al, 2009). However, there are relatively few studies using cephalopod species, such as octopus, especially at the geographical locations around the Saharan bank (close to the Canary Islands and Northwestern African shelf) (Pierce et al, 2008).…”

Long-term AVHRR SST change analysis in the Taiwan Strait using the rotated EOF method

“…28, No. 1, 1-10, February 2017 larval anchovy catches (Hsieh et al 2009). In addition to the climate variability, ocean warming in the ECS and SCS areas has also been identified as a critical area of study.…”