Visual assessment of the reproductive condition of female western rock lobsters (Panulirus cygnus)

Abstract

An important issue when surveying the reproductive condition of large numbers of female Panulirus cygnus in the field is that each animal must be assessed quickly and accurately on the basis of only a few easily discernable criteria. The four biological criteria most commonly recorded for each lobster are: (1) ovigerous setae condition (not present, partially developed, and fully developed); (2) the presence (unused or eroded) of a spermatophore mass; (3) the presence and developmental stage of external ova; and (4) the visual appearance of the ovaries through the dorso-thoracic musculature. Using the above criteria each female can then be assigned to a reproductive state, i.e., immature, inactive breeder, single breeder, or double breeder. This study compared external assessments with internal cellular development of the ovary (via histology) and elucidated the shortcomings of the external technique. This has resulted in the production of a modified set of criteria that, if applied to samples collected during the peak of the breeding season, enables the breeding state of a female western rock lobster to be more accurately determined in the field without causing it any damage. The height of the breeding season is the optimum time for stock egg production assessment.

Interannual variation in the moult cycle and size at double breeding of mature female western rock lobster (Panulirus cygnus)

“…double) breeders. Recently, however, Melville-Smith and de Lestang (2005) showed that an ovary classified as ''developing'' in this situation is more likely a ''spent'' ovary containing residual atretic oocytes which make it appear yellow and developing, and so is only a single breeder. Furthermore, the DB 50 recorded by Chubb (1991) for Two Rocks, Dongara, and the Abrolhos Islands are the same as, or smaller than, the size at first maturity recorded by the same author for the same regions (Chubb, 1991), which casts doubt on the appropriateness of the criteria used to assign double breeding in this case.…”

“…It has not been possible to investigate whether DB 50 has decreased over the same period, because ovarian development has been recorded only since 1992. Moreover, establishing whether a female is a single or a double breeder is very sensitive to the time of year she is sampled (Melville-Smith and de Lestang, 2005), and suitable IBSS data are not available for this purpose in most years. However if, as we have suggested, DB 50 occurs on average two years after CL 50 , then it could be assumed that DB 50 has declined in a similar manner to CL 50 since the 1970s.…”

“…Clear identification of an individual female as a double breeder is only possible when they are sampled reasonably close to the middle of their spawning season (Melville-Smith and de Lestang, 2005). Small variations are likely to exist in the stimuli that initiate spawning between and within each location, resulting in spawning not being synchronous throughout the fishery.…”

“…Therefore, only females with undamaged appendages were used to determine the size at double breeding. A female P. cygnus was considered to be a double breeder (DB) if, at the peak of the breeding season, OctobereNovember, she had either an external ova and an unused spermatophore; or a late stage external ova, no spermatophore, and a developing ovary; or no external ova, a used spermatophore, and a developing ovary (MelvilleSmith and de Lestang, 2005).…”

Ovarian development and size at sexual maturity of the Mexican spiny lobsterPanulirus inflatus

“…Field studies of tropical palinurid lobsters have found that rapid and repetitive brood cycles are common, with up to 5 broods per annum (e.g., Juinio 1987;MacDiarmid 1989;Briones-Fourzán & Lozano-Álvarez 1992;Melville-Smith & de Lestang 2005;Senthil-Murugan et al 2005). Chittleborough (1976) reported that the sub-temperate species P. cygnus, when held in aquaria at a constant temperature of 25°C with abundant food, is capable of producing six broods a year.…”