Diet of the West Coast rock lobster Jasus lalandii: influence of lobster size,sex, capture depth,latitude and moult stage

Diets of male and female West Coast rock lobster Jasus lalandii in South Africa were compared across a large size range of 10–85 mm carapace length (CL). The diets of male rock lobsters were compared between two different depths, different seasons, across the moult cycle, and among eight sites along the South-Western Cape coast. There was no significant difference in diet between male and female rock lobsters for any of the size-classes examined. Male rock lobsters showed large differences in diet between small and large size-classes. The diet of small lobsters (<75mm CL) consisted of a wide range of species, which included, in order of importance, coralline algae, barnacles Notomegabalanus algicola, sponges and ribbed mussels Aulacomya ater. However, prey items rich in inorganic material were not dominant in their diet, as had been predicted. By contrast, large rock lobsters (>80mm CL) fed on few species, and fish and ribbed mussels were their most abundant prey items. There were some dietary differences between individuals captured at 20 m and those collected at 50 m, but these differences were less marked than between the two sampling sites (the Knol and Olifantsbos). There was seasonal variation in diet at the Dassen Island and Olifantsbos sites. Cannibalism was highest during the moulting periods. Gut fullness varied seasonally at Dassen Island, and was consistently high at Olifantsbos. However, the proportion of the population feeding showed marked seasonal trends at both sites, tracking the commercial catch per unit effort of rock lobster. Ribbed mussels were a ubiquitous and dominant component of the diet at the eight sites sampled. However, south of Dassen Island, black mussels Choromytilus meridionalis were scarce in the diet of rock lobster and sponges predominated. Gut fullness was lowest at the northernmost sites.     

North Cape — a ‘nursery area’ for the packhorse rock lobster,Jasus verreauxi (Deeapoda: Palinuridae)

In the North Cape area (34°26'S, 173°07'E) there appears to be a concentration of late juvenile packhorse rock lobsters, Jasus verreauxi (H. Milne Edwards'), which subsequently contributes significantly to the nearby fishery for adult J. verreauxi off Cape Reinga. Evidence for this is based on the overall smaller size and fewer mature rock lobsters at North Cape compared to areas nearby, and on the results of tagging experiments carried out during 1976–77. Rock lobsters tagged at North Cape moved 21–514 km, mainly west and south, before recapture at minimum rates of 0.03–2.00 krn.d^‐1. For females at least, the movement away from North Cape usually occurs at about the time that sexual maturity is attained. Rock lobsters tagged near Cape Reinga moved 3–34 km west at minimum rates of 0.04–0.35 km.d^‐1.

Although the closure of the North Cape grounds to rock lobster fishing restricts the taking of the small number of legal‐sized fish available in the area, the restriction ensures less mortality and damage to the undersized fish due to handling.     

A spatial- and age-structured assessment model to estimate the impact of illegal fishing and ecosystem change on the South African abalone Haliotis midae resource

The management of abalone stocks worldwide is complicated by factors such as illegal fishing combined with the difficulties of assessing a sedentary (but not immobile) resource that is often patchily distributed. The South African abalone Haliotis midae fishery is faced with an additional problem in the form of a relatively recent movement of rock lobsters Jasus lalandii into much of the range of the abalone. The lobsters have heavily reduced sea urchin Parechinus angulosus populations, thereby indirectly negatively impacting juvenile abalone which rely on the urchins for shelter. A model is developed for abalone that is an extension of more standard age-structured assessment models because it explicitly takes spatial effects into account, incorporates the ecosystem change effect described above and estimates the magnitude of substantial illegal (‘poached’) catches. The model is simultaneously fitted to catch per unit effort and Fishery-Independent Abalone Survey abundance data, as well as to several years of catch-at-age (cohort-sliced from catch-at-size) data for the various components of the fishery and different spatial strata. It constitutes the first quantitative approach applied to the management of this commercially valuable resource in South Africa and has provided a basis for management advice over recent years by projecting abundance trends under alternative future catch levels.     

Mass mortality and recolonization of Pyura stolonifera (Heller) on the south coast of South Africa

The fauna and flora of two sublittoral communities situated in close proximity on the west coast of South Africa are described and shown to be radically different, despite the fact that both experience similar physical conditions. One of these communities, at Marcus Island, has prolific beds of the black mussel Choromytilus meridionalis (35 954 g wet weight·m^?2) accompanied by a large number of other species, notably sea urchins, holothurians, brittle stars, whelks and barnacles. In contrast, the other site, Malgas Island, is dominated by a large population of rock lobsters Jasus lalandii together with a dense seaweed flora (3 866 and 4 402 g wet weight·m^?2 respectively). The numbers of species are similar at both sites (102 at Malgas Island and 107 at Marcus Island) but only 34 per cent are common to both localities. Although preliminary research indicates that the two sites have fairly similar physical conditions and bottom topography, they maintained their contrasting communities for the whole research period (1983–1986) and have probably done so for at least nine years, suggesting that they represent two stable alternative states of the same ecosystem. In the absence of rock lobsters at Marcus Island, wave action and inter/intraspecific competition are the main forces structuring the benthic community. Stability is maintained here by the resilience and rapid recovery of the mussel population after disturbance by storms. Where rock lobsters are abundant, as at Malgas Island, intense predation pressure is the main force controlling the structure of the benthos, and it is continually maintained because the rock lobsters are resistant to the effect of storms. Therefore, the presence or absence of high densities of rock lobsters is fundamental to the maintenance of these two contrasting communities.     

The potential for using acoustic tracking to monitor the movement of the West Coast rock lobster Jasus lalandii

Although acoustic tracking has been used to study the movement of several species of clawed and spiny lobsters, only recent technological advances have provided sufficiently small transmitters to examine the utility of using acoustic tracking as a means to analyse the movement of relatively small spiny lobsters, such as Jasus lalandii. The effect of the transmitter on the mobility of J. lalandii was tested in aquarium experiments and was shown to have no influence on movement in three separate experiments. Thereafter, adult male rock lobsters (86–98mm carapace length) were tracked in field trials for up to 32 days at Betty's Bay (n = 4) and Hermanus (n = 5) off the Western Cape, South Africa. Tracking J. lalandii in the field using acoustic tags was successful, even in areas with dense kelp beds and rocky outcrops. The signal from the transmitters was readily detectable from the surface and subsequent use of underwater tracking equipment enabled visual confirmation of the position of the rock lobsters. Lobsters moved significantly longer distances (>45m day^?1) in the first two days following tagging than during any subsequent time period (<10m day^?1). This suggests that transmitter attachment and/or handling altered the movement pattern for the first 72 hours after tagging. During the period of observation, J. lalandii displayed classical nomadic behaviour.     

Variations in fecundity and size at sexual maturity of female rock lobster Jasus lalandii in the Benguela ecosystem

Fecundity of female rock lobster Jasus lalandii was studied in order to examine whether regional differences existed along the west coast of South Africa, where growth rates (at least of males) were known to vary considerably. The study, in August/September 1985, included all major rock-lobster Fishing grounds from Port Nolloth in the north to Olifantsbos on the Cape Peninsula in the south. Earlier studies showed that growth rates of adult rock lobsters are fast in areas where per capita food availability is high (the south-central region of the West Coast), whereas growth rates were slower where food supplies are limited. The results presented indicate that fecundity of females is also higher in areas where growth rates of males are fast. Year-to-year variations in fecundity of females may possibly be an indicator of growth rates of adult rock lobsters.     

The artisanal fishery for East Coast rock lobsters Panulirus homarus along the Wild Coast,South Africa

East coast rock lobsters Panulirus homarus are collected by the indigenous people of the Wild Coast, in the Eastern Cape, South Africa, and are sold to coastal hotels and holidaymakers. The South African government has proposed a small-scale commercial fishery based on P. homarus to improve socio-economic conditions in that region. Catch data and information on fishery operations were collected for the artisanal fishery from Coffee Bay, Presley Bay, Port St Johns and Mbotyi, as well as from a commercial buying station near the Mdumbi Estuary, between March 2003 and October 2005. The catch per unit effort of rock lobster poling varied from 13.5 ± 7.7 fisher^–1 outing^–1 at Port St Johns to 5.9 ± 3.1 fisher^–1 outing^–1 at Coffee Bay, but the number of fishers or fishing frequency could not be verified. About two-thirds of the lobsters caught (69%) were smaller than the minimum legal size. Hotels and the buying station complied with size limits, but cottages and campers often bought undersized lobsters. Smaller lobsters (females) are caught by poling than by diving. Geographical variations in poling effort and lobster mean sizes could be indicators of heavy fishing pressure on shallow, inshore reefs. The implications of commercialising the fishery and its associated management are discussed.     

Status of the major lobster fisheries in India

Commercial exploitation of lobsters from the Indian seas began in the 1950s. Annual landings have been declining from a peak of 4075 t in 1985 to 1364 t in 2002. Major fisheries were located on the north‐west, south‐west, and south‐east coasts. Among the 12 species recorded, only four species of spiny lobsters (three littoral and one deep sea) and one species of slipper lobster are commercially important. At Kayalpattinam and Tharuvaikulam, on the south‐east coast, lobster landings sharply declined for the gill‐net fishery. Of the two species that contributed to the fishery, Panulirus ornatus and Panulirus homarus, the latter has been more affected owing to high vulnerability to fishing activities. Catch composition analysis of the trammel‐net fishery showed that 35% of the landings consisted of P. homarus in the size range of 23–50 mm carapace length. On the north‐west coast, the spiny lobster Panulirus polyphagus and the slipper lobster Thenus orientalis are incidentally caught in trawl nets. However, the fishery for T. orientalis in the waters off Mumbai lasted only up to 1994. Large‐scale exploitation of spawning females, which formed 60% of the total catch, might have been detrimental to the recruitment process resulting in rapid decline and total collapse of the fishery. Abundance of P. polyphagus reached its maximum during September, constituting 23% of the average annual landing during 1988–2002. A high exploitation ratio (>0.7) indicated over‐fishing of the stock. Repeated spawning and high annual egg production are probably responsible for sustaining the stock, despite over‐exploitation. Major problems confronting the resource management of the multi‐gear and multi‐species lobster fisheries in India are discussed. An operational project, involving fisher community, has been taken up for creating awareness of the need for sustainable exploitation of the resource. Regulatory measures, such as closure of the fishery during the peak of the breeding season, ban on trammel‐net, mandatory release of egg‐bearing lobsters, and establishment of lobster sanctuaries are suggested to the State Governments for implementation.     

Assessing the impacts of trawling breeding lobsters (Panulirus ornatus) on the catch of the Torres Strait lobster fishery shared between Australia and Papua New Guinea

The shared Torres Strait rock lobster (Panulirus ornatus) fishery provides important income for commercial and traditional fishers in Australia and Papua New Guinea. The lobster stock is first fished in Torres Strait by divers from both countries and then becomes vulnerable to Australian prawn trawlers, followed by Papua New Guinea trawlers during its annual breeding migration. Lobster catch sharing arrangements are governed by the Torres Strait Treaty ratified in 1985, but the sequential trawling of breeding lobsters has been controlled by bilateral agreements. A trawl ban was implemented in 1984 in both countries to conserve the breeding stock, but some trawling has been conducted in the Gulf of Papua since then and there is renewed interest in Papua New Guinea to resume trawling. To evaluate the impact of trawling migratory breeding lobsters on the lobster fishery, a model that combines a cohort depletion model with a stock recruitment relationship was developed in this study. The model showed that when the fishery is fully or over‐exploited by the dive fishery, trawling breeding lobsters would reduce both the spawning stock and the total catch of the fishery. The reduction in catch would increase with increasing fishing mortality. If trawling occurred on the Papua New Guinea side only, a redistribution of catch between Australia and Papua New Guinea would result in a small gain in catch for Papua New Guinea at the expense of the Australian dive fishery. But when fishing mortality reaches a certain level, any trawling in any country will incur catch loss to both countries. For the long‐term sustainability and maximum production of the fishery, regulations should be implemented in both countries under a co‐management scheme of a shared fish stock.     

Predicting survival of western rock lobsters Panulirus cygnus using discriminant analysis of haemolymph parameters taken immediately following simulated handling treatments

Instances of morbidity amongst rock lobsters (Panulirus cygnus) arriving at factories in Western Australia (WA) have been attributed to stress during post‐harvest handling. This study used discriminant analysis to determine whether physiological correlates of stress following a period of simulated post‐harvest handling had any validity as predictors of future rejection or morbidity of western rock lobsters. Groups of 230 western rock lobsters were stored for 6 h in five environments (submerged/flowing sea water, submerged/recirculating sea water, humid air, flowing seawater spray, and recirculated seawater spray). The experiment was conducted in late spring (ambient sea water 22°C), and repeated again in early autumn (ambient sea water 26°C). After 6 h treatment, each lobster was graded for acceptability for live export, numbered, and its haemolymph was sampled. The samples were analysed for a number of physiological and health status parameters. The lobsters were then stored for a week in tanks in the live lobster factory to record mortality. The mortality of lobsters in the factory was associated with earlier deviations in haemolymph parameters as they emerged from the storage treatments. Discriminant analysis (DA) of the haemolymph assays enabled the fate of 80–90% of the lobsters to be correctly categorised within each experiment. However, functions derived from one experiment were less accurate at predicting mortality when applied to the other experiments. One of the reasons for this was the higher mortality and the more severe patho‐physiological changes observed in lobsters stored in humid air or sprays at the higher temperature. The analysis identified lactate accumulation during emersion and associated physiological and haemocyte‐related effects as a major correlate of mortality. Reducing these deviations, for example by submerged transport, is expected to ensure high levels of survival. None of the indicators tested predicted mortality with total accuracy. The simplest and most accurate means of comparing emersed treatments was to count the mortality afterwards.     

A decade of illegal fishing in Table Mountain National Park (2000–2009): trends in the illicit harvest of abalone Haliotis midae and West Coast rock lobster Jasus lalandii

Illegal fishing activities are reported to be on the increase in South Africa, including in its marine protected areas (MPAs). Research is presented on the nature and the scale of illegal fishing in Table Mountain National Park (TMNP) by analysing the numbers of abalone Haliotis midae and West Coast rock lobster Jasus lalandii confiscated from fishers operating in the park's marine protected area between 2000 and 2009. Data were collected from offence logbooks maintained by South African National Parks rangers and managers, the South African Police Services, and interviews with alleged or self-confessed illegal fishers. The research findings indicate that the annual numbers of illegally fished abalone and rock lobsters have increased significantly over time. Spatial analysis suggests that confiscations of abalone occur predominantly on the east coast of the park, whereas higher confiscations of illegally fished rock lobsters occur on the west coast. It is clear from this research that new and more efficient approaches will need to be designed and implemented to minimise illegal fishing in the TMNP MPA. Context-specific conservation targets that acknowledge and integrate social as well as developmental needs are required, and may be essential for limiting biodiversity loss in the longer term, which will ultimately ensure the success of fisheries management and conservation in TMNP.     

Long-distance migration of the rock lobster Palinurus delagoae off South Africa and Moçambique

Long-distance migration patterns of deep-water rock lobster Palinurus delagoae were investigated using tagrecapture data obtained over a period of 6 years (1995–2000). Of 7 654 animals tagged, 363 (4.7%) were recovered from South African and seven (0.1%) from Moçambican waters. Lobsters remained at large for up to 3.2 years and migrated distances of up to 495 km. Some 48.3% of juvenile lobsters (carapace length <65 mm) but only 2.1% of larger lobsters migrated further than 20 km. Movements were mostly north-eastwards (91.7% of migrants), for both sexes, and the migration rate of the fastest 5% of migrants was 0.43 km day^?1. P. delagoae seems to have evolved long-distance, counter-current migrations as a retention mechanism to maintain its populations off both South Africa and Moçambique. The resource needs to be managed jointly between the two countries.     

Effect of reproductive state and sex on movement and food consumption of western rock lobster (Panulirus cygnus) in a tank environment

The catchability of western rock lobsters (Panulirus cygnus) during the spawning season (October and November) may be affected by their reproductive state. In this study, movement and food consumption of males and females of different reproductive states held in laboratory tanks were measured as proxies for catchability. Density of lobsters was found to influence both movement and food consumption. Solitary animals and, to a lesser extent, two lobsters per tank, were more sedentary and consumed significantly less food than animals at a density of three or four specimens per tank. Tests using three animals per tank confirmed that mature, unmated, and ovigerous females carrying early stage eggs moved more frequently away from their shelters than males or females carrying late stage eggs (P < 0.0001, d.f. = 3). Further, unmated females and females with early stage eggs recorded significantly higher food consumption (P < 0.0061, d.f. = 3) compared with males or females carrying late stage eggs. The greater time spent away from shelter and also food consumption make unmated females and females with early stage eggs likely to be more catchable than males or females with late stage eggs. As catchability is commonly used to obtain population estimates from survey data, these results have implications for surveys which use catch rates of breeding animals as indicators of egg production.     

Colour variation in the southern rock lobster Jasus edwardsii and its economic impact on the commercial industry

Southern rock lobster Jasus edwardsii varies in shell coloration throughout southern Australia. Predominantly exported as a live product to Asian markets, price is influenced by colour with prices higher for dark red than paler coloured lobsters, which are discounted. This paper explores spatial and depth variation in shell colour for the Tasmanian, South Australian and Victorian fisheries using catch sampling data. The proportion of red lobsters decreased with depth and was prevalent at depths less than 30 m, whereas paler coloured lobsters dominated the deeper depth ranges. The depth of transition where 50% of lobsters were classified as red showed a weak trend of increase with latitude from southern Tasmania to northern South Australia. Under quota management, lobster colour was a significant driver of fleet dynamics as fishers target areas of high price per unit. Consequently, catches of pale lobsters from greater depths remain low despite the high catch rates in these areas. The colour price differential varies seasonally (higher in summer) so fishers increase supply of pale lobsters during winter. Discounting on colour equates to AUS$6.67 million/year for the Tasmanian Fishery alone, which indicates value from management or marketina research to reduce discountina.     

Dietary change of the rock lobster Jasus lalandii after an ‘invasive’ geographic shift: Effects of size,density and food availability

During the 1990s the rock lobster Jasus lalandii shifted its focus of distribution south-eastwards along the coast of South Africa, to establish a dense population in an area where it was previously rare. This coincided with a marked decrease in the sea urchin Parechinus angulosus, a preferred prey item of J. lalandii and a vital source of shelter for juveniles of the abalone Haliotis midae. The range expansion of lobsters has thus economic and ecological ripple effects. We determined the diets of small (50–65 mm carapace length) and large (>69 mm CL) rock lobsters from gut content analyses, and compared them between three ‘lobster invaded’ sites and three adjacent ‘non-invaded’ sites where densities are still low. At the non-invaded sites, diets were collectively heterogeneous but the dietary breadth of individual lobsters was narrow (in contradiction to generally accepted ecological theory), and the lobsters fed mainly on large, individual, mobile, high-energy prey such as sea urchins and large winkles. Conversely, at invaded sites where lobster densities were high, they consumed predominantly small, colonial or sessile low-energy prey such as sponges, barnacles and foliar algae, and the diet was significantly more uniform among individuals, but broader within individuals. This was a direct result of the contrasting benthic community structure of the two areas, and consequent prey availability – itself caused by differences in intensity of rock-lobster predation. Cannibalism was unexpectedly greater at non-invaded sites, possibly as a result of lobsters being larger there. The diet of small and large lobsters also differed significantly. Large rock lobsters predominantly consumed large individual prey such as lobsters, urchins and crabs, while small rock lobsters ate mainly colonial, sessile prey such as sponges and barnacles, and small prey such as tiny winkles and crustaceans. Dietary selectivity indices revealed that algae and sponges were negatively selected (avoided) in non-invaded areas but positively or neutrally selected in invaded areas. These dietary differences have important ramifications not only for the lobster populations but also for the structure and functioning of the radically different communities that have developed in invaded areas, reflecting a regime shift induced by lobster predation.     

Direct impacts of commercial and recreational fishing on spiny lobster,Panulirus interruptus,populations at Santa Catalina Island,California, United States

The California spiny or red rock lobster, Panulirus interruptus, is an ecologically and economically important species that has been exploited since the 1800s. No previous study in California has assessed the impacts of the recreational or commercial lobster harvest. Before the 2003–04 commercial and recreational lobster seasons, we conducted a fishery‐independent trap survey at Santa Catalina Island to document the impact of the lobster fisheries on the size structure, abundance, and sex ratios of mature P. interruptus (>65 mm carapace length (CL)). We concurrently sampled a predominantly commercially fished area, a recreationally fished area, and a 23‐year‐old invertebrate no‐take (INT) reserve. Relative to the INT reserve, legal‐size lobsters in the recreational area were similar in CL, but 31% less abundant. Legal‐size lobsters in the commercial area were 8% smaller and 70% less abundant than those in the INT reserve. The sex ratio of legal‐size lobsters, although near 50:50 in the recreational and INT reserve areas, was male‐dominated (67:33) in the commercial area. Differences in CPUE and mean CL of sub‐legal lobsters in the recreational and commercial areas suggest that factors in addition to harvesting pressure may affect these populations. Total biomass of mature lobsters in the recreational and commercial areas was 92% and 45%, respectively, of biomass in the INT reserve. Fecundity in the recreational and commercial areas was 83% and 42%, respectively, of fecundity in the INT reserve. This study provides preliminary data for future ecological studies and fisheries management evaluations.     

From biomass mining to sustainable fishing — using abundance and size to define a spatial management framework for deep-water lobster

Based on the assumption that depleted stocks would have recovered during a six-year layoff from fishing, trapping for deep-water spiny lobster Palinurus delagoae and slipper lobster Scyllarides elisabethae off eastern South Africa resumed in 2004 until 2007. A generalised linear modelling approach was used to investigate the effects of year, sampling area, depth, month and trap soak-time on catch and lobster size, and to construct standardised abundance indices. The renewed trapping rapidly reversed partially restored nominal catch rates. Fishing strategy changed from targeting spiny lobsters during the first months of each fishing season to targeting slipper lobsters during later months. Small spiny lobsters were abundant in the southern area, identified as a recruitment hotspot. Spiny lobster abundance and size in this area increased over four years of fishing, but conversely, large adult spiny lobsters predominated in the central and northern areas, where trapping depleted their abundance over time. The adult populations in the central and northern areas are upstream from the recruitment hotspot, and are presumably a source of larvae. Slipper lobster abundance peaked in 2005, remained relatively constant across areas, and increased with depth. Trapping for deep-water lobster is unlikely to be sustainable in its present form. However, the clear gradients in spiny lobster size and abundance by sampling area and depth provide a good framework for spatial management planning.     

Temporal changes in kelp forest benthic communities following an invasion by the rock lobster Jasus lalandii

The rock lobster Jasus lalandii expanded its centre of distribution south-eastwards into an area known as ‘East of Cape Hangklip’ on the south-west coast of South Africa in the early 1990s. Using historical and present data, we analysed differences in the abundance of key species and functional groups between the pre- and post-rock lobster invasion periods at two sites along that coast: Cape Hangklip and Betty's Bay. Pre-1989, lobsters were absent, but after 1995 they reached densities approximating 0.4–0.8 m^?2. Benthic community composition also changed significantly with herbivores being abundant whereas macroalgae and sessile invertebrates were scarce pre-invasion. We attribute the decline of herbivores to the direct effects of lobster predation, in turn indirectly promoting macroalgae. Post-invasion sessile invertebrates and macroalgae increased by 2 600% and 453% respectively, whereas herbivores declined by 99.3%. The virtual elimination of the sea urchin Parechinus angulo-sus by rock lobsters has substantial implications for the commercial harvesting of the abalone Haliotis midae, because its juveniles are intimately associated with this urchin. The lobster invasion has thus not only led to a regime shift of the ecosystem but has also substantial economic consequences, which calls for an ecosystem approach to the management of the pool of commercially exploited resources in this region.     

Movement patterns of individual migrating western rock lobster,Panulirus cygnus,in Western Australia

Abstract

Migrating and pre‐migrating western rock lobster Panulirus cygnus were tagged with datastorage tags that recorded temperature and pressure, which was converted to depth (Pressure (kPa) — surface pressure (kPa)/10)) at Dongara and Jurien Bay in Western Australia between December 2005 and December 2007. All lobsters were fitted with tag flotation devices, and returns were made by either commercial fishers or beachcombers who located detached tags. A total of 135 lobsters were released with “backpack” flotation tags, but only 84 (62.2%) of the backpacks carried data‐storage tags. Depths of release ranged from 5 to 113 m. Of the tagged lobsters released, commercial fishers recaptured 52 (38.5%), whereas 11 tags (8.1%) were found by beachcombers. At least 33%, and possibly up to 63%, of animals identified by their pale coloration as pre‐migrating individuals, failed to migrate. Those that did migrate (n = 11) were at liberty from 1 to 94 days and showed generally similar movement patterns in that they migrated only at night from darkness (after 2000 h) until after moonrise. However, their movement patterns were less constrained by the rising of the moon in deep water. Only 27% migrated nightly, compared with 73% that skipped migrating on one or more nights, to restart some days later. This latter proportion would likely have been considerably greater, but some migrating animals were only at large for short periods before recapture, and therefore had little time to show any variation to the nocturnal migration pattern. Individual speeds of migration during periods of activity were estimated for nine lobsters as 0.20 to 0.68 km h^?1, with a mean speed of 0.44 km h^?1, or 7.4 m min^?1. Improved knowledge of daily movement patterns resulting from this study provides a potentially important input into technological improvements in bait and pot design.     

A technique for separating and counting rock lobster eggs

Eggs were separated from the setae of berried female rock lobsters (Jasus edwardsii) by soaking in 1 N KOH for 6–12 h. This technique separated almost all of the eggs from the setae and each other with minimal damage. An electronic egg‐counter incorporating a phototransistor was used to count the eggs suspended in water. It had a high degree of accuracy (C.V.= 1.5%) when eggs were counted at a rate of about 200 000 per hour.