Some aspects of the reproductive biology of albacore Thunnus alalunga from the western Mediterranean Sea

Abstract

Thunnus alalunga is an important commercial tuna species widely distributed in the three major oceans and the Mediterranean Sea. The Mediterranean population is currently classified as a data-poor stock and little is known about its basic life history parameters. This study provides the first detailed information on some aspects of the reproductive biology of T. alalunga from the western Mediterranean Sea. A total of 16 104 specimens were measured between 2005 and 2012. The overall sex ratio of females to males was 1.1:1, although the ratio was female biased in fish <70 cm fork length (LF) and male biased in those >75 cm LF. Histological analysis of the ovaries (N = 587) and the monthly variation of the gonadosomatic index for both sexes showed that spawning occurred from June to August, which is a much shorter period than the 7 months reported for T. alalunga in tropical oceanic waters. Thunnus alalunga caught during June and July are capable of spawning daily. The gonadosomatic index values for T. alalunga from the western Mediterranean were up to eight times higher than those of T. alalunga from other oceans. Histological examination of the ovaries showed that the minimum length at sexual maturity of females was 56 cm LF, which is considerably smaller than those estimated for other stocks.

Reproductive Biology of Albacore Tuna (Thunnus alalunga) in the Western Indian Ocean

“…The minimum size-at-maturity found was 83 cm L F which is slightly smaller than that reported for North and South Pacific albacore (78–90 cm L F ; [23,24,32,52] and previous estimates for the Indian Ocean albacore (90 cm L F ; [59,60]), but larger than in the Mediterranean Sea (56 cm L F ; [26]). The present study is the first to calculate the L 50 for albacore tuna in the Indian Ocean based on histological analyses, with estimates of the L 50 at 85.3 ± 0.7 cm based on a vitellogenic 3 maturity threshold.…”

Reproductive biology of little tunnyEuthynnus alletteratus(Rafinesque, 1810) in the southwest Gulf of Mexico

“…In the case of E. alletteratus in the southwest Gulf of Mexico, the population in global terms is in sex equilibrium (1:1), and the predominance of larger sized males is due to the fact that males reach greater lengths (Alcaráz-García, 2012). This finding is in agreement with other studies in tunids; for example, in albacore ( Thunnus alalunga ) fisheries in the western Mediterranean Sea, the number of females decreased for the greater sizes (Saber et al, 2015a).…”

Diet and feeding behaviour of albacore Thunnus alalunga in the western Mediterranean Sea during the spawning period

“…Macroscopic examination of gonads and GSI values of albacore from the western Mediterranean indicated that fish were able to spawn. The estimated high GSI values were similar to values observed in the same area (Saber et al, 2015), and in the eastern Mediterranean Sea for males (Akayli et al, 2013) and females (Karakulak et al, 2016).…”

“…Our data showed that females dominated in the small length classes (between 60 and 70 cm SFL) while a greater abundance of males of larger length classes (above 80 cm FL) were found. The predominance of males in larger length classes has been reported in the Mediterranean albacore stock (Karakulak et al, 2011;Saber et al, 2015) as well as in the oceanic stocks (Ashida et al, 2020;Dhurmeea et al, 2016;Farley et al, 2013). The difference in sex ratio among length classes has been related to differences in natural mortality and vulnerability to capture (Schaefer, 2001;Schaefer et al, 2005) and by the growth difference due to the discrepancy in reproductive investment, which is higher in females than in males (Chen et al, 2012;Farley et al, 2013).…”

“…In the present study, we have investigated the diet and feeding strategy of albacore through stomach content analysis of albacore caught by a recreational fishery in their major spawning ground in the western Mediterranean Sea during the spawning season (Saber et al, 2015). Our specific objectives were (a) to describe albacore's diet composition, (b) to explore the effect of biological traits (sex and fish size) on the diet and (c) to identify the feeding strategy (through the rate of feeding and condition index) during the spawning season.…”