Catchability of the southern rock lobster Jasus edwardsii. II. Effects of size

Abstract

Abstract. For most of the year, the size-frequency distribution of trap-caught southern rock lobster, Jasus edwardsii, reflected size-specific catchability rather than the size-frequency distribution of the population in a scientific reserve in Tasmania, Australia. The size-frequency distributions of the population on the ground and of lobsters captured in traps were similar only during a few months, typically during moulting and mating. Small males and females were usually under-represented in traps. Catchability generally increased with size, but varied with sex and season. During moulting and mating, size-specific catchability and relative selectivity of larger animals were similar to or lower than for smaller animals. The relative pattern of catchability throughout the year was similar for most size classes within each sex. Negative associations between small and large lobsters in traps were stronger in winter than in summer, indicating strong behavioural interactions. These interactions could explain the lower catchability of smaller lobsters. Relative selectivity estimates using tag-recapture and size-specific catchability data provided generally similar results.

Spatial variation in size at onset of maturity of female southern rock lobster <i>Jasus edwardsii</i> around Tasmania, Australia

“…Estimated SOM from the Crayfish Point MPA was contrasted with that from Glenvar Point (147.397°E, 43.008°S), an area popular with recreational fishers. Diver transects at the Crayfish Point MPA in 2000 by Ziegler et al (2002) led to similar estimates of density to those from Maria Island MPA made by 4.75 per 100 m 2 and 5.6 per 100 m 2 respectively). No transect data are available from the fished site at Glenvar Point although density of legal-sized lobsters is clearly much reduced by recreational fishing; a 3 day survey by 4 divers at Glenvar Point in 2002 captured 615 lobsters, only 2 of which were above the minimum legal size, while over 50% of lobsters observed by Ziegler et al (2002) were above the minimum legal size at the nearby (5 km) Crayfish Point MPA.…”

“…This inability to produce reliable estimates of SOM occurred in some instances due to small sample sizes. In some of the southern sites, samples contained few immature animals due to their smaller SOM and selectivity of traps (Ziegler et al, 2002). Hence, despite large samples of several hundred animals, poor model fits were obtained on occasion as samples contained mainly mature females.…”

Trajectories of spiny lobster Jasus edwardsii recovery in New Zealand marine reserves: is settlement a driver?

“…Similarly, targeted fishing of lobster aggregations near the boundary of Cape Rodney to Okakari Point Marine Reserve has been suggested to have contributed to not only a reduction in population growth rate within the reserve, but also a reduction in the number of very large individuals in the reserve population (Kelly et al 2002;Kelly & MacDiarmid 2003). Mature lobsters undertaking offshore migrations as part of their reproductive behaviour crossed the boundary of the marine reserve, but larger lobsters would also have been more susceptible to fishing activity as a result of size-related catchability (Ziegler et al 2002). The decline in both legal-and sublegal-sized lobsters we recorded here coincided with this reported change in fishing effort.…”

Variabilidad ambiental y recursos pesqueros en el Pacifico suroriental: estado de la investigacion y desafios para el manejo pesquero

“…En el caso de J. frontalis, estas variaciones han sido atribuidas al desfase generado por la muda de los machos, la cual sería regulada, entre otros factores, por la temperatura (Ernst et al, 2010b). La temperatura afectaría también el nivel de actividad, influyendo de esta forma sobre la captura-bilidad del recurso (Ziegler et al, 2002(Ziegler et al, , 2003(Ziegler et al, , 2004. La época y duración del período de portación de huevos sería atribuido a factores ambientales (Larraín & Yáñez, 1985), donde la temperatura, que experimenta cambios intra-anuales de al menos 4ºC a una profundidad media de 80 m, podría modular estos procesos (Ernst et al, 2010b).…”