Assessing the Impact of Temperature and Chlorophyll Variations on the Fluctuations of Sardine Abundance in Al-Hoceima (South Alboran Sea)

Abstract

Landings of small pelagic fish in Moroccan Mediterranean Sea show large fluctuations and trends, a fact that has a considerable socio-economic impact. These changes are often related to the impact of the environmental conditions on recruitment processes. We investigate fluctuations of the sardine's abundance at one of the most important fishing areas of the Moroccan Mediterranean Sea (i.e., Al-Hoceima region) and try to assess the impact of environmental changes on the availability of pelagic fish in this area. In these regards, we analyzed Seasonal and Trends Loess' (STL) decomposition of time series between 2008 and 2015 of catch-per-unit-effort (CPUE) data along with environmental parameters (i.e., sea surface temperature and chlorophyll-a) from remote sensing and we applied nonlinear models (GAM). Results show an inverse relationship between fluctuations of sardine CPUE and sea surface temperature. Nonlinear relationships confirm that the temperature is the most important parameter affecting abundance, whereas chlorophyll-a, is generally, weakly correlated to the CPUE data at monthly and seasonal level variations, except for annual trends. The analysis also shows positive trend of chlorophyll-a, from 2003 and a negative one starting from 2011, revealing an inter-annual variability that support fish landings fluctuations. Modeling based on the relationships between the CPUE and temperature/chlorophyll-a, allowed better prediction of the sardine abundance in the Al-Hoceima fishing area (South Alboran Sea)..

Surface Temperature Influences the Population of Limnothrissa miodon in Lake Kariba

“…In order to explore the infuence of global warming on Limnothrissa miodon population density, we projected lake surface water temperature for the next two decades and used data ftting and numerical simulations to predict the population density of Limnothrissa miodon in Lake Kariba. Our fndings show that the population density of Limnothrissa miodon declines as the lake warms and this is in agreement with Abdellaoui et al [33], who used a time series analysis and modelling approach on assessing the impact of temperature and chlorophyll variations on the fuctuations of sardine abundance in Al-Hoceima. Teir results showed an inverse relationship between fuctuations of sardine catch per unit efort and sea surface temperature and that sea surface temperature is the most important parameter affecting the abundance of small pelagic fsh in the Moroccan Mediterranean Sea.…”

Spatial pattern of sea surface temperature and chlorophyll-a trends in relation to hydrodynamic processes in the Alborán Sea

“…In additional to this increase of sea surface temperature affecting the development of phytoplankton in Alborán Sea, the decrease of precipitations as well as river runoff for the last 20 years, up to 40% in north Africa and south Europe (Schilling et al, 2012), are other factors that could enhance the decrease of chlorophyll-a in the coastal areas due the decrease of the continental organo-mineral inputs to the sea (e.g., Skliris et al, 2014;Richardson & Schoeman, 2004, Hernández-Almeida et al, 2011Schroeder et al, 2017;Abdellaoui et al, 2017).…”

“…Methodological approach For an appropriate assessment of the SST and Chl-a concentration trends, the time series were analyzed based on the method of decomposition of the signal into seasonal and annual components (trends without the effects of the seasons). The magnitude of positive or negative trends of each time series are validated by the Mann-Kendall (MK), which is a nonparametric estimation method (Wernand et al, 2013;Fu et al, 2016;Colella et al, 2016;Abdellaoui et al, 2017;Pisano et al, 2020;Moradi, 2020). This method is based on the computation of statistical test parameter (S) and its variance Var (S) defined as follows (Mann, 1945;Kendall, 1948):…”

“…For example, a change in water temperature may negatively impact the spawning and the feeding of larval survival (Miller et al, 1992, Moyle et al, 2004. Abdellaoui et al (2017) showed that higher temperatures combined with low productivity could lead to a gradual decline in pelagic fish yields over the sub-sequent years. According to Vargas-Yáñez et al (2020), who studied the inter-annual variability of sardine abundance, this abundance was strongly related to the wind intensity and chlorophyll-a (Chl-a) concentration during the previous year.…”