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

Abstract

The moult cycle of mature female Panulirus cygnus was examined from data recorded over 32 years at four sites along the coast of Western Australia. A repeating trend for mature females was inferred from samples taken between 15 November and 15 August. Setae were present on the endopodites of all large females from June until February–March; between March and June the proportions of females with setae declined sharply as about 80% moulted into a non-setose phase. Females that did not undergo this moult in February remained setose throughout the “normal” non-setose period before moulting and producing a new set of setae by midwinter. New or eroded spermatophores were present on most large females between November and January, but their presence declined sharply during the February–March moult, to be absent by May. The percentage of mature females that bypassed the non-setose moult varied markedly from 1% to 40%, and was well correlated with mean water temperatures in January and February. The proportion that did not undergo a moult increased when these months were cool but decreased when they were warm. The size (carapace width) at which females carry two batches of eggs in one breeding season (double breeder) declined progressively from 96.6 mm to 84.1 mm with decreasing latitude (32°S to 28°S), and further declined at the offshore Abrolhos Islands (29°S) to 78.7 mm. The implications of these findings are discussed in relation to management measures designed to protect females in a setose condition.

High levels of polyandry, but limited evidence for multiple paternity, in wild populations of the western rock lobster (Panulirus cygnus)

“…As we note above, in P. cygnus mating entails the attachment of the male's spermatophore (tar spot) to the underside of the female, which is partially eroded by the female during fertilization and is only sloughed off in the following molting. Subsequent matings within the same reproductive season (molt cycle) involve a male depositing a fresh spermatophoric mass on top of the previously eroded (used) spermatophore (de Lestang & Melville‐Smith, ). This can lead to the spermatophoric mass on a female being dominated by a single sire (by virtue of their positioning and numerical supremacy) while still containing the DNA from multiple sires.…”

“…This is reflected by the high incidence of multiple mating and low occurrence of multiple paternity. However, when double spawning has been observed, it is more likely to occur in the larger females (Chittleborough, ; Chubb, ; de Lestang & Melville‐Smith, ). This pattern of larger females spawning twice in a season has also been observed in other spiny lobsters (Briones‐Fourzán & Lozano‐Alvarez, ; Gomez, Junio, & Bermas, ; Macfarlane & Moore, ).…”

Population biology of the ghost shrimps, Trypaea australiensis and Biffarius arenosus (Decapoda: Thalassinidea), in Western Port, Victoria

“…Latitudinal or site differences in sizes of individuals of the same species have been found for a number of different organisms throughout Australia. For example the carapace width of western rock lobster (Panulirus cygnus) females that carry two broods of embryos, has been found to decline progressively with decreasing latitudes (de Lestang and Melville-Smith, 2006), the size of individuals and growth rate of near-shore tropical squids Loliolus noctiluca was found to decrease from northern Queensland to southern New South Wales (Jackson and Moltschaniwskyj, 2001) and the mangroves Avicenna marina, are found to be up to 15 metres taller in northern areas of Australia than in Western Port, Victoria (Edgar, 2001). Reasons for the differences in sizes of individuals between latitudes include increases in growth rate due to warmer temperatures (Lonsdale and Levinton, 1985), latitudinal changes in food availability (Dumbald et al, 1996) and limiting environmental properties such as temperature or salinity (Hanekom and Erasmus, 1988).…”

Spatial and temporal changes in egg production in the western rock lobster(Panulirus cygnus)fishery

“…This index, which is a catch rate measure of eggs per potlift, was derived by estimating the batch fecundity of each female sampled above size at maturity, using a Cl-fecundity relationship developed by Chubb (1991): F = 1.92Cl 2 . 69 , where F is the number of newly spawned eggs and taking into account spatial variations in size at maturity (Melville-Smith & de lestang 2006) and size at double breeding (de lestang & Melville-Smith 2006a). even though commercial length-frequency data were used to calculate egg production, it was necessary to assign maturity status based on Cl (Table 1) Size at maturity and size at double breeding estimates have previously been determined for deep water locations (40-80 m) at five coastal sites spanning the fishery (Fremantle, Lancelin, Jurien Bay, dongara, and Kalbarri) (Melville-Smith & de lestang 2006).…”

“…Research published since these reviews has provided evidence that some life-history features of western rock lobster have progressively changed over time. The size at first maturity of both sexes has decreased across the fishery over the last 30 years (Melville-Smith & de lestang 2006) and it is believed that the size at which female lobsters produce more than one batch of eggs per season has decreased similarly over time (de lestang & Melville-Smith 2006a). There is also evidence that the size at which juvenile western rock lobster undertake their offshore migration to the deep-water breeding grounds has decreased (N. Caputi pers.…”