Studies of the sexual development and spawning of yellowfin tuna, Neothunnus macropterus, and skipjack, Katsuwonus pelamis, in three areas of the Eastern Pacific Ocean, by examination of gonads.

ENGLISH: Knowledge of the size and age at maturity, spawning seasons, and spawning areas of the tropical tunas supporting the fishery in the Eastern Pacific is an important part of the basic information required for understanding their life history, population structure, and fishery dynamics. Until a few years ago nothing was known of these matters. In 1947 the senior author and one of his colleagues (Schaefer and Marr 1948, Schaefer 1948) were able to demonstrate that both yellowfin tuna and skipjack spawn offshore from Central America at least during the late winter and spring months. During January to April many yellowfin tuna over about 70 cm. total length in commercial catches from that region were found to have gonads in advanced stages of maturity, and specimens caught during late June were found to be spent. Maturing skipjack were collected in late February, and spawned-out fish were observed in late March. Numerous very young juveniles of the yellowfin, down to 10 mm. in length, and two very young juvenile skipjack, were captured in this area between January and May. SPANISH: El conocimiento del tamaño y la edad que corresponden a la primera madurez sexual, así como de las estaciones y áreas de desove de los atunes tropicales que mantienen las pesquerías del Pacífico Oriental, constituyen parte importante de la información que es menester para comprender la historia natural, la estructura de la población y la dinámica de la pesquería. Hasta hace pocos años nada se sabía sobre el particular. En 1947 el autor principal y uno de sus colegas (Schaefer y Marr, 1948; Schaefer, 1948) pudieron demostrar que tanto el atún aleta amarilla como el barrilete desovan en el mar abierto, frente a América Central, por lo menos durante la última parte del invierno y en la primavera. De enero a abril encontraron que muchos de los atunes aleta amarilla de más de 70 cm. de longitud total, procedentes de las pescas comerciales de dicha región; tenían gónadas en avanzados estados de madurez, mientras que ejemplares pescados hacia fines de junio ya habían desovado. Se recolectaron barriletes en vías de maduración a fines de febrero, al paso que en los últimos días de marzo se encontraron especímenes que ya habían desovado. Numerosos ejemplares muy juveniles del atún aleta amarilla, tan pequeños como 10 mm., y dos barriletes también muy juveniles, fueron pescados en esta región entre enero y mayo. (PDF contains 65 pages.)

Reproductive biology of the blue swimmer crab (Portunus pelagicus, Decapoda: Portunidae) in five bodies of water on the west coast of Australia

Portunus pelagicus was collected at regular intervals from two marine embayments and two estuaries on the lower west coast of Australia and from a large embayment located approximately 800 km farther north. The samples were used to obtain data on the reproductive biology of this species in three very different environments. Unlike females, the males show a loosening of the attachment of the abdominal flap to the cephalothorax at a prepubertal rather than a pubertal molt. Males become gonadally mature (spermatophores and seminal fluid present in the medial region of the vas deferentia) at a very similar carapace width (CW) to that at which they achieve morphometric maturity, as reflected by a change in the relative size of the largest cheliped. Logistic curves, derived from the prevalence of mature male P. pelagicus, generally had wider confidence limits with morphometric than with gonadal data. This presumably reflects the fact that the morphometric (allometric) method of classifying a male P. pelagicus as mature employs probabilities and is thus indirect, whereas gonadal structure allows a mature male to be readily identified. However, the very close correspondence between the CW50’s derived for P. pelagicus by the two methods implies that either method can be used for management purposes. Portunus pelagicus attained maturity at a significantly greater size in the large embayment than in the four more southern bodies of water, where water temperatures were lower and the densities of crabs and fishing pressure were greater. As a result of the emigration of mature female P. pelagicus from estuaries, the CW50’s derived by using the prevalence of mature females in estuaries represent overestimates for those populations as a whole. Estimates of the number of egg batches produced in a spawning season ranged from one in small crabs to three in large crabs. These data, together with the batch fecundities of different size crabs, indicate that the estimated number of eggs produced by P. pelagicus during the spawning season ranges from about 78,000 in small crabs (CW=80 mm) to about 1,000,000 in large crabs (CW=180 mm).