Year-round energy dynamics of sardine and anchovy in the north-western Mediterranean Sea

Abstract

Variability in body condition and energy storage has important implications for fish recruitment and ecosystem structure. Understanding strategies for energy allocation to maintenance, reproduction and growth is essential to evaluate the state of the fish stocks. In this study, we address the energetics dynamics of the annual cycle of anchovies (Engraulis encrasicolus) and sardines (Sardina pilchardus) in the northwestern Mediterranean Sea using indirect and direct condition indices. We assessed and validated the use of morphometric, biochemical and energetic indices for both species. Annual patterns of the relative condition index (Kn), gonadosomatic index (GSI), lipid content (% lipids) and energy density (ED) were linked to the energy allocation strategy. Our results highlight that anchovy mainly rely on income energy to reproduce, while sardine accumulate the energy during the resting period to be used in the reproduction period. Consequently, variability in the lipid content and ED between seasons was lower in anchovy than in sardine. In both species, we observed an early decline in energy reserves in late summer-early fall, which may be related to unfavourable environmental conditions during spring and summer. Regarding the use of different condition indices, both direct indices, lipid content and ED, were highly correlated with Kn for sardine. ED was better correlated with Kn than lipid content for anchovy. For the first time, a relationship between ED of gonads and GSI for sardine and anchovy was provided, highlighting the importance of the energy invested in reproduction. This work provides new insights into the energy dynamics of sardine and anchovy. We also demonstrate which are the most suitable indices to measure changes in the physiological condition of both species, providing tools for the future monitoring of the populations of these two commercially and ecologically important fish species.

Changes in Life History Traits of Small Pelagic Fish in the Western Mediterranean Sea

“…Anchovy reproduces in spring and summer and obtains energy from feeding that is directly used for reproduction (Ganias, 2009;Giráldez, 2009). Seasonal variability in the body condition of anchovy tends to be less marked than in sardine (Albo-Puigserver et al, 2020), but the marked seasonality of the body condition of anchovy observed in the north suggest potential food limitations and the use of reserves for reproduction. Seasonal environmental patterns could partially explain differences in the phenology of life history traits.…”

“…Similar to our results, Giráldez and Abad (1995) also described different seasonal peaks of body condition in the south for anchovy. These differences in the seasonal pattern of body condition might play a key role in the dynamics of the reproduction of sardine, as this species accumulates energy during spring and summer for reproduction in autumn and winter (Albo-Puigserver et al, 2020). Low body condition before the start of the reproduction in October could have affected the quality of the spawning and ultimately the recruitment success in the northern area, as has been suggested for sardine off the coast of Portugal (Garrido et al, 2007).…”

“…In recent decades, the discharges of the main rivers, such as the Ebro River, in the western Mediterranean basin, have decreased which could have been a driver of the altered NPP and plankton dynamics in the north, reducing energy availability for higher trophic levels (Lloret et al, 2004;Ludwig et al, 2009). This could explain the lower body conditions observed in the north before the reproduction period in the case of sardine (Brosset et al, 2016b;Albo-Puigserver et al, 2020).…”

Energy content of anchovy and sardine using surrogate calorimetry methods

“…Being low-cost, quick, and usually non-disruptive, these morphometric indices are used in many fields. Although their use have been validated for sardine and anchovy (Albo-Puigserver et al, 2020;Brosset et al, 2015a;Gatti et al, 2018a;McPherson et al, 2011), their utilization to infer energy content is still controversial (Davidson and Marshall, 2010;McPherson et al, 2011;Sardenne et al, 2016;Stevenson and Woods Jr, 2006).…”

Zooplankton Biomass Depletion Event Reveals the Importance of Small Pelagic Fish Top-Down Control in the Western Mediterranean Coastal Waters

“…Moreover, changes in hydrology modifying the mesoscale dynamics in the western Mediterranean waters would affect the distribution and abundance of the zooplankton communities via direct effects on their metabolism and/or by affecting different trophic levels of the food web. Such variations may be responsible for the increased frequency of jellyfish blooms (Bernard et al, 2011;Brotz and Pauly, 2012;Falkenhaug, 2014) or the decrease in the small pelagic fish (SPF) stocks observed in the Alboran and NW Mediterranean (MED) basins (Van Beveren, 2015;Brosset et al, 2016Brosset et al, , 2017Albo-Puigserver et al, 2020), with notable socioeconomic impacts on tourism and fisheries. Despite the suspected importance of zooplankton in the Spanish Mediterranean (Mercado et al, 2007;Saraux et al, 2019;Yebra et al, 2019), studies focused on determining which specific factors drive the variability patterns of zooplankton biomass and metabolic rates in these coastal waters are scarce (Herrera et al, 2014;Yebra et al, 2017bYebra et al, , 2018.…”