Changes in the spawning habitat of two small pelagic fish in the Northwestern Mediterranean

Abstract

We investigated the effects of three sea surface oceanographic variables (temperature, salinity, and chlorophyll a) on the abundance of eggs and larvae of two summer‐spawning species in the NW Mediterranean Sea, the anchovy Engraulis encrasicolus and the round sardinella Sardinella aurita, based on data from ichthyoplankton surveys carried out in the 1980s, 2000s, and 2010s. The environmental data showed an increase in seawater temperature and salinity along time, coupled with a decrease in chlorophyll a (proxy for primary production). These long‐term directional changes in environmental conditions helped explain the important reduction observed in the abundance of eggs and larvae of anchovy, as well as shrinking of spawning habitat in this species. At the same time, the probability of occurrence of round sardinella has increased from practically zero in the 1980s to probabilities near 1 along the coastal area of the study region in the two decades of the 21st century. Given that the trends observed in the environmental variables along the three decades of study are expected to continue during the 21st century, as a consequence of climate change, the spawning habitat of anchovy is expected to continue decreasing, while round sardinella habitat can expand. Considering that anchovy is of high commercial importance in NW Mediterranean fisheries, while round sardinella has very low commercial interest, our results show that the viability of small pelagic fisheries in the area may be compromised.

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

“…Due to the mid trophic level position of sardines and anchovies and their key roles in the ecosystem of the western Mediterranean Sea (Coll et al, 2008(Coll et al, , 2019, a reduction on their populations could impact the ecosystem dynamics across entire marine food web, from species that mainly prey on these forage fish to the dynamics of plankton (Tudela and Palomera, 1999;Navarro et al, 2017;Coll et al, 2019). For both species, optimal environmental values (SST and SSS) will be exceeded, first for sardine but eventually for anchovy, too, in combination with a reduction of eggs and larvae of anchovy in the last decades in GSA06 (Maynou et al, 2020) since the reproduction success of sardine and anchovy are highly influenced by SST and SSS condition (Palomera et al, 2007). The areas that will keep a probability of occurrence higher than 0.70 are around the Rhone River in the GSA07 and around the Ebro river in the GSA06 for both sardine and anchovy, and waters around the Gulf of Alicante for anchovy.…”

Future distribution of early life stages of small pelagic fishes in the northwestern Mediterranean

“…We estimated the future potential spatial distribution of the early life stages of the two summerspawning small pelagic fish (anchovy and round sardinella) based on a regression model parameterized with ichthyoplankton survey data and in situ environmental data (Maynou et al 2020) to delineate the habitat where the environmental conditions will be suitable for spawning (Fig. 2).…”

“…These variables are good descriptors of the spawning habitat and larval environment of both species in the study area (Palomera et al 1997;Maynou et al 2014). Briefly, Maynou et al (2020) estimated the spatial distribution of the early life stages of anchovy and round sardinella from the ichthyoplankton survey data obtained in three summer sampling programmes, which occurred in 1983, from 2003-2004 and from 2011-2012, where ichthyoplankton were sampled simultaneously with hydrographic data on a grid of stations (Fig. 1).…”

“…The latter two species show peak spawning activity during the summer months, when pelagic productivity is generally at the lowest levels, but their larvae can feed on high productivity patches on the surface in the vicinity of the major river outflow or at 50-60 m in depth, where the deep chlorophyll maximum (DCM) occurs (Olivar et al 2001;Sabatés et al 2013). In recent decades, good knowledge of the spawning habitats of E. encrasicolus and S. aurita and their variation over time has been gathered in the northwestern Mediterranean (Palomera et al 2007;Maynou et al 2020). Their spawning success and consequent recruitment are known to be threatened by hydrological changes caused primarily by increased temperature and decreased primary productivity (Sabatés et al 2013;Maynou et al 2014. Changes in the abundance and distribution of marine species in response to climate change in recent decades have been well documented.…”

The box-balance model: a new tool to assess fish larval survival, applied to field data on two small pelagic fish

“…Furthermore, recent studies have documented a decrease in biological productivity, likely due to a decrease in riverine runoff waters (Colella et al 2016, Cozzi et al 2019. Overall, these conditions would not be suitable for the development of S. aurita larvae (Maynou et al 2020).…”