Current and Future Influence of Environmental Factors on Small Pelagic Fish Distributions in the Northwestern Mediterranean Sea

Marta Coll,José M Bellido,Ana Giráldez,Antonio Esteban,Marta Albo-Puigserver,Jeroen Steenbeek,Maria Grazia Pennino,Elena Fernández-Corredor,María González

doi:10.3389/fmars.2020.00622

Abstract

In the Northwestern Mediterranean Sea, the European sardine (Sardina pilchardus) and the European anchovy (Engraulis encrasicolus) are the most important small pelagic fish in terms of biomass and commercial interest. During the last years, these species have experimented changes in their abundance and biomass trends in the Northwestern Mediterranean Sea, in addition to changes in growth, reproduction and body condition. These species are particularly sensitive to environmental fluctuations with possible cascading effects as they play a key role in connecting the lower and upper trophic levels of marine food webs. It is therefore essential to understand the factors that most profoundly affect sardine and anchovy dynamics. This study used a two-step approach to understand how the environment influences the adult stages of these species in the Northwestern Mediterranean Sea. First, we explored the effects of environmental change over time using Random Forests and available datasets of species occurrence, abundance, biomass and landings. We then applied species distribution models to test the impact of the extreme pessimistic and optimistic Intergovernmental Panel on Climate Change (IPCC) pathway scenarios, and to identify possible climate refuges: areas where these species may be able to persist under future environmental change. Findings from the temporal modelling showed mixed effects between environmental variables and for anchovy and sardine datasets. Future pathway projections highlight that both anchovy and sardine will undergo a reduction in their spatial distributions due to future climate conditions. The future climate refuges are the waters around the Rhone River (France) and the Ebro River (Spain) for both species. This study also highlights important knowledge gaps in our understanding of the dynamics of small pelagic fish in the region, which is needed to progress towards an ecosystem approach to fisheries management.

Highlights

Small pelagic fish species (SPF) are sensitive to environmental fluctuations, which can be amplified from climate variability, with cascading effects up and down the food web, due to their high biomass at intermediate levels and their potential waspwaist control of the food web (Cury and Roy, 1989; Cury et al, 2000; Bakun, 2006; Checkley et al, 2009; Fauchald et al, 2011)
Temporal trends of sardine biomass in the acoustic datasets showed a negative trend for both GSA06 and GSA07 (Figure 2), which was significant in case of GSA07 (Figures 2, 3)
Regarding changes in sardine abundance and biomass, our results demonstrate a general decreasing temporal trend of biomass of sardine in both GSA06 and GSA07, which coincides with a significant decline in landings in both areas, likely reinforced by the depletion of the commercial stock (Quattrocchi et al, 2016; Coll and Bellido, 2018; Coll et al, 2019).The abundance and biomass of anchovy showed a general increase over time in both GSA06 and GSA07, which coincides with a significant increase of catches in GSA06

Summary

Introduction

Small pelagic fish species (SPF) are sensitive to environmental fluctuations, which can be amplified from climate variability, with cascading effects up and down the food web, due to their high biomass at intermediate levels and their potential waspwaist control of the food web (Cury and Roy, 1989; Cury et al, 2000; Bakun, 2006; Checkley et al, 2009; Fauchald et al, 2011). In the Mediterranean Sea, SPF species such as European sardine (Sardina pilchardus, Walbaum, 1792; hereafter sardine), and European anchovy (Engraulis encrasicolus, Linnaeus, 1758; hereafter anchovy) have been shown to be key elements in the transfer of energy from lower to higher trophic level organisms (Palomera et al, 2007; Coll et al, 2008; Albo-Puigserver et al, 2016). Changes in anchovy and sardine landings and abundances have been related with increases in fishing impact and recent high rates of exploitation (Palomera et al, 2007; Scientific Technical and Economic Committee for Fisheries [STECF], 2016; FAO, 2018; Ramirez et al, 2018)

Methods

Results

Conclusion