Geographic variability of sardine growth across the northeastern Atlantic and the Mediterranean Sea

Abstract

This study describes broad-scale spatial variations in sardine growth across the northeastern Atlantic and Mediterranean waters using opportunistic samples collected in recent years. More detailed information on spatial, decadal and seasonal growth variations is provided for the Iberian-Biscay region using data collected in acoustic surveys since the mid-1980s. Growth curves are fitted to annual or monthly length-at-age data using a robust Von Bertalanffy model; parameters for recent samples are compared with literature information using an auximetric plot while differences between areas within the Iberian-Biscay region are tested by log-likelihood ratio tests. Sardine growth performance is generally lower in the Mediterranean and declines across the northeastern Atlantic from the English Channel to north Morocco but increases sharply off Mauritania. Lower growth of Mediterranean sardines is possibly associated to the overall oligotrophy of this Sea while differentiation from the Atlantic is likely sustained by reproductive isolation between populations from the two areas. Within the northeastern Atlantic, size-and age related migrations may partly explain differences in maximum length/age and mean length-at-age between neighbouring areas but the broad-scale latitudinal decline in growth is consistent with adaptation to the north-south decline in seasonal temperature gradients and to the annual cycles of plankton production. Within the Atlantic Iberian waters, sardine grows and improves in condition during spring and summer when the allocation of energetic resources for gonad development cease, temperature is close to the annual maxima and plankton production is high. Variation in sardine length-at-age and growth within the Atlanto-Iberian stock area has implications for stock structure and needs to be taken into account in the calculation of weight and maturity-at-age for assessment purposes. No evidence of broad temporal changes in sardine growth within the Iberian-Biscay region is obtained.

Assessment of the sardine (Sardina pilchardus Walbaum, 1792) fishery in the eastern Mediterranean basin (North Aegean Sea)

“…Sardine landings as derived from the commercial purse seine fishery in the North Aegean Sea over the period 2000-2008 indicated a sharp decrease in 2002, oscillating since then around a mean value of 12420 t, although for the last two years landings have been low, around 9000 t. Based on the catch-at-age information derived from otolith reading, sardine in the North Aegean Sea presented an age range from 0 to 4 years. This age range is very narrow compared to that found in the Atlantic (SILVA et al, 2008), and also compared with other Mediterranean Sea sardine stocks SANTOJANNI et al, 2005;Silva et al, 2008). Age group-1 and age group-2 were dominant, ranging from 68 to 73% and from 17 to 26% of the total catch respectively.…”

“…They are short-lived species and unlike the Atlantic population of Sardina pilchardus (SILVA et al, 2008), sardine in the Mediterranean generally live up to 6 years (SAN-TOJANNI et al, 2005) and up to 5 years in the Greek Seas (TSERPES & TSI-MENIDES, 1991; current work). Their population level depends strongly on the incoming year-class strength, which is highly variable and largely dependent on environmental factors.…”

“…These age groups are also dominant in the fisheries of other sardine stocks from the western and the central Mediterranean, but make a strong contrast with the Atlantic and the Adriatic (SAN-TOJANNI et al, 2005;BELLIDO et al, 2008a, b;SILVA et al, 2008).…”

Evidence for microsatellite hitchhiking selection in European sardine (<i>Sardina pilchardus</i>) and implications in inferring stock structure

“…The genetic boundary between the Atlantic and the Mediterranean separates sardines with shallow but significant morphometric differences and substantial differences in growth performance, with individuals from Mediterranean showing a lower head-to-body ratio (Silva 2003, Silva et al 2008, lower length-at-age and lower maximum length (Silva et al 2008). Other morphological and life-history traits were reported to vary between the 2 regions, such as the number of gill rakers (Andreu 1969), relative fecundity and spawning frequency (Ganias et al 2003;Ganias et al 2004) and length at first maturity (Silva et al 2006): all of these showed lower values in the Mediterranean Sea, possibly reflecting a combination of poorer growth and lower global productivity in the area.…”

Otolith dimensions (length, width), otolith weight and fish length of Sardinella sindensis (Day, 1878), as index for environmental studies, Persian Gulf, Iran

“…In addition, sardines are consumed as fresh meal for humans and as commercial powder (Bennet et al 1992;Hill et al 2005;FAO, 2011). Many studies for sardine genus have been performed on the otolith structures, such as growth and mortality estimation, identification of fishes, determine the fish stock and trace migration pathway of fish (Nair, 1949;Krzeptowski, 1983;Cergole & Valentini 1994;Butler et al 1996;Watanabe & Nakamura, 1998;Gaughan & Mitchell, 2000, Silva et al 2008Mehanna & Salem 2011;Ward et al 2012;Dehghani et al 2015). According to FAO (2011), Sardinella sindensis is the most important commercial fish for Iran and Pakistan.…”