Influence of sampling gear in assessment of reproductive parameters for bluefin tuna in the western Mediterranean

Comparative histological and stereological analysis of gonads from longline- and purse seine-caught Atlantic bluefin tuna Thunnus thynnus was undertaken to assess the reproductive potential of the population in the western Mediterranean breeding area. Bluefin tuna sampled by purse seine clearly had higher gonadosomatic index values (GSI) than those caught by longline. While no remarkable histological differences were found between purse seine- and longline-caught males, the ovarian histology indicated a higher level of maturity in females from purse-seine samples, where most specimens were found to be in active spawning (AS). Within the longline sample the pro- portion of active spawning females was considerably higher at the end of the fishing season (mid- June to mid-July) than earlier in May to mid-June (52.8 vs. 24%). Stereological analyses revealed that the samples collected by the 2 sampling gears differed primarily in the numbers of migratory- nucleus oocytes, which were overwhelmingly more abundant in purse-seine catches, with average relative fecundity: 59 oocytes g -1 vs. 1.2 oocytes g -1 (purse-seine vs. longline). The frequency of ovaries with postovulatory follicles (POFs) in purse seine-caught bluefin tuna was 83.7%, equivalent to a spawning interval of 1.2 d; in contrast, only 32.6% of the females in longline catches had POFs, representing a spawning interval of 3.1 d. Assuming an average individual duration of the spawning process of 14 d, and considering the estimates of fecundity and spawning interval obtained from purse-seine samples, the average annual fecundity of bluefin tuna in the Balearic spawning ground would be approximately 77 × 10 6 eggs (relative fecundity of 702 eggs g -1 BW (body weight)).

[1]  K. Schaefer.  Spawning time , frequency , and batch fecundity of yellowfin tuna , Thunnus albacares , near Clipperton Atoll in the eastern Pacific Ocean , 2008 .

[2]  S. Desantis,et al.  Size and age at sexual maturity of female bluefin tuna (Thunnus thynnus L. 1758) from the Mediterranean Sea , 2005 .

[3]  Jean-Marc Fromentin,et al.  Atlantic bluefin tuna: population dynamics, ecology, fisheries and management , 2005 .

[4]  F. Karakulak,et al.  Further evidence of spawning of bluefin tuna (Thunnus thynnus L., 1758) and the tuna species (Auxis rochei Ris., 1810, Euthynnus alletteratus Raf., 1810) in the eastern Mediterranean Sea: preliminary results of TUNALEV larval survey in 2004 , 2005 .

[5]  F. Abascal,et al.  Ultrastructure of oogenesis in the bluefin tuna, Thunnus thynnus , 2005, Journal of morphology.

[6]  Kevin C. Weng,et al.  Electronic tagging and population structure of Atlantic bluefin tuna , 2005, Nature.

[7]  D. Gunderson,et al.  Fecundity of shortspine thornyhead (Sebastolobus alascanus) and longspine thornyhead (S. altivelis) (Scorpaenidae) from the northeastern Pacific Ocean, determined by stereological and gravimetric techniques* , 2005 .

[8]  Andrew B. Cooper,et al.  Movements of bluefin tuna (Thunnus thynnus) in the northwestern Atlantic Ocean recorded by pop-up satellite archival tags , 2005 .

[9]  S. Desantis,et al.  Evidence of a spawning area for the bluefin tuna (Thunnus thynnus L.) in the eastern Mediterranean , 2004 .

[10]  M. Lutcavage,et al.  JOINT TURKISH-ITALIAN RESEARCH IN THE EASTERN MEDITERRANEAN: BLUEFIN TUNA TAGGING WITH POP-UP SATELLITE TAGS , 2004 .

[11]  F. Abascal,et al.  Testicular development in migrant and spawning bluefin tuna (Thunnus thynnus (L.)) from the eastern Atlantic and Mediterranean , 2004 .

[12]  Gerd Kraus,et al.  Procedures to estimate fecundity of marine fish species in relation to their reproductive strategy , 2003 .

[13]  S. Desantis,et al.  Histological investigation on the ovarian cycle of the bluefin tuna in the western and central Mediterranean , 2003 .

[14]  Kevin Coward,et al.  Stereological point-counting; an accurate method for assessing ovarian function in tilapia , 2002 .

[15]  K. Coward,et al.  Quantification of ovarian condition in fish: a safer, more precise alternative to established methodology , 2002 .

[16]  F. Abascal,et al.  Stereological assessment of the reproductive status of female Atlantic northern bluefin tuna during migration to Mediterranean spawning grounds through the Strait of Gibraltar , 2002 .

[17]  M. Cataldo,et al.  BEHAVIOUR OF POST-SPAWNING ATLANTIC BLUEFIN TUNA TAGGED WITH POP-UP SATELLITE TAGS IN THE MEDITERRANEAN AND EASTERN ATLANTIC , 2002 .

[18]  S. B. Blackwell,et al.  Migratory Movements, Depth Preferences, and Thermal Biology of Atlantic Bluefin Tuna , 2001, Science.

[19]  N. Bromage,et al.  Stereological validation of ovarian biopsy as a means of investigating ovarian condition in broodstock tilapia in vivo , 2001 .

[20]  A. Corriero,et al.  Study of the sexual maturity of female bluefin tuna : Purification and partial characterization of vitellogenin and its use in an enzyme-linked immunosorbent assay , 2001 .

[21]  K. Schaefer.  Reproductive biology of tunas , 2001 .

[22]  T. Davis,et al.  Size distribution of southern bluefi n tuna (Thunnus maccoyii) by depth on their spawning ground , 2001 .

[23]  B. Block,et al.  Advances in acoustic, archival, and satellite tagging of tunas , 2001 .

[24]  Richard W. Brill,et al.  Tracking adult North Atlantic bluefin tuna (Thunnus thynnus) in the northwestern Atlantic using ultrasonic telemetry , 2000 .

[25]  P. J. Bromley,et al.  The influence of feeding regime on sexual maturation, fecundity and atresia in first‐time spawning turbot , 2000 .

[26]  P. Howey,et al.  Results of pop-up satellite tagging of spawning size class fish in the Gulf of Maine: do North Atlantic bluefin tuna spawn in the mid-Atlantic? , 1999 .

[27]  K. Coward,et al.  Histological classification of oocyte growth and the dynamics of ovarian recrudescence in Tilapia zillii , 1998 .

[28]  D. Itano.  Reproductive biology of Yellowfin tuna (Thunnus albacares), in Hawaiian waters and the Western Tropical Pacific Ocean , 1995 .

[29]  I. Santos,et al.  Is the fecundity of the Atlantic mackerel (Scomber scombrus: Scombridae) determinate? , 1994 .

[30]  P. R. Witthames,et al.  A stereological method for estimating fish fecundity , 1990 .

[31]  R. E. Baglin.  REPRODUCTIVE BIOLOGY OF WESTERN ATLANTIC BLUEFIN TUNA l , 1982 .

[32]  P. Tomlinson,et al.  Population structure of Pacific yellowfin tuna , 1978 .

[33]  M. Gutiérrez.  Coloración histológica para ovarios de peces, crustáceos y moluscos , 1967 .

[34]  E. Weibel,et al.  PRACTICAL STEREOLOGICAL METHODS FOR MORPHOMETRIC CYTOLOGY , 1966, The Journal of cell biology.

[35]  E. Weibel,et al.  A principle for counting tissue structures on random sections. , 1962, Journal of applied physiology.