Growth Of Lobsters Research Articles

Seawater ozonation and formalin disinfection for the larval culture of eastern rock lobster, Jasus ( Sagmariasus) verreauxi, phyllosoma

The effects of seawater disinfection with continuous ozonation or with daily formalin treatment during flow-through culture, on the survival, growth, bacteriology and histology of eastern rock lobster, Jasus ( Sagmariasus) verreauxi, phyllosoma were determined. Survival from hatch to Instar II was highest and bacterial abundance was least in low ozonated seawater (containing 5 ppb ionised bromine, Br). By contrast, at high ozonation (45 ppb Br) and medium ozonation (15 ppb Br), 77% and 69% of larvae, respectively, suffered deformities at the moult to Instar II and starved to death. Histological examination of phyllosoma showed no differences in cuticular epithelium thickness but the digestive gland tissue of moribund deformed phyllosoma had significantly thinner tubule epithelium, the lumen was dilated, B-cells were more abundant and there was greater separation between the cuticular epithelium and distal tip of digestive gland tubules. In unozonated (Control) water, 66% of larvae died during Instar II probably resulting from a possible Vibrio infection. In a second experiment, survival to Instar III was highest at low ozonation or no ozonation without addition of formalin (0 ppm). Bacterial numbers were lowest in low ozonation with 0 ppm formalin treatments, compared to daily treatment with formalin at 10 ppm or above. A concentration of 250 ppm formalin killed all larvae by Instar III. In a final experiment, larval survival between Instar III to VI in low ozonated seawater was approximately 80% at formalin levels of 0 to 80 ppm, whereas all larvae treated with 160 ppm formalin died shortly after Instar V. Disinfection improved survival by minimising bacterial disease for the culture of phyllosoma to Instar VI without interrupting growth and development. The present study established that the optimum treatment for the culture of phyllosoma to Instar VI appeared to be low ozonation (5 ppb Br) with 10 ppm formalin.

Effects of autotomy on long-term survival and growth of painted spiny lobster (Panulirus versicolor) on the Great Barrier Reef, Australia

The effects of autotomy (shedding of appendages) on survival and growth rates of painted spiny lobster were investigated at Northwest Island (23° 18′ S, 152° 43′ E) during the period 2003–2006. Adult lobsters were captured, tagged, and classified as either uninjured (n = 68), minimally injured (n = 39) or moderately injured (n = 19) depending on the number and type of appendages that were autotomized during capture and handling. Six to thirty-six months after release, 86 lobsters were recaptured (mean time at large = 305 days). Recapture rates of uninjured (64.7%), minimally injured (71.8%), and moderately injured lobsters (73.7%) were not significantly different. Similarly, mean annualized growth rates of uninjured, minimally injured, and moderately injured lobsters were not significantly different. This suggests that the energetic cost of a single episode of autotomy is either negligible or exists as a trade-off with some other life history trait, such as reduced reproductive performance. These results support the use of certain management tools (e.g., size limits) that prescribe release of non-legal lobsters, regardless of their injury status.

CARACTERIZACIÓN DE LOS SISTEMAS OPERACIONALES, MODALIDADES Y ARTES DE PESCA UTILIZADOS PARA LA CAPTURA DE LA LANGOSTA <i>PANULIRUS GRACILIS</i> (STREETS, 1871) EN GUANACASTE, COSTA RICA

Se describen las dos modalidades de pesca que se utilizan en la captura de la langosta del Pacífico Panulirus gracilis (Streets, 1871) en la región de Santa Cruz, Guanacaste, Costa Rica. Estas modalidades son el buceo a pulmón y el buceo con compresor, asociadas a un único arte de pesca llamado “bichero”, arte que tiene la singularidad de ser muy versátil y permite la captura de otras especies de interés comercial. Su uso, asociado a la modalidad de pesca del buceo con compresor, podría estar ocasionando una dispersión de la langosta y una alteración en sus parámetros de crecimiento; además, deja la selectividad en las tallas que se capturan a decisión del pescador. Asimismo, se describen los equipos que se utilizan en ambas modalidades de pesca, así como la forma en que operan, incluyendo los riesgos que representa el buceo con compresor para la integridad física de los pescadores. A partir del análisis realizado, se recomiendan otros tipos de artes de pesca selectivos, considerando que los sistemas tradicionales de pesca han impactado negativamente la disponibilidad de la langosta y demás especies a través de los años.

Survival, food consumption and growth of Norway lobster (Nephrops norvegicus) kept in laboratory conditions

Successful commercial aquaculture of crustacean species is dependent on satisfying their nutritional requirements and on producing rapidly growing and healthy animals. The results of the present study provide valuable information for feeding habits and growth of Nephrops norvegicus L., 1758) under laboratory conditions. The aim of the present study was to examine food consumption, growth and physiology of the Norway lobster N. norvegicus under laboratory conditions. N. norvegicus (15 g wet weight) were distributed into 1001 tanks consisting of five numbered compartments each. They were fed the experimental diets (frozen mussels and pellets) for a period of 6 months. A group of starved Nephrops was stocked and fasted for 8 months. Although Nephrops grew well when fed the frozen mussels diet, feeding on a dry pellet feed was unsatisfactory. The starvation group, despite the fact that showed the highest mortality (50%), exhibited a remarkable tolerance to the lack of food supply. The study offers further insight by correlating the amino acid profiles of Nephrops tail muscle with the two diets. The deviations from the mussel's diet for asparagine, alanine and glutamic acid suggest a deficiency of these amino acids in this diet. The results of the present study showed that the concentrations of free amino acids are lower in relative amount than those of protein-bound amino acids, except for arginine, proline and glycine. The present study contributes to the improvement of our knowledge on nutritional requirements of the above species.

Use of Herring Bait to Farm Lobsters in the Gulf of Maine

BackgroundEcologists, fisheries scientists, and coastal managers have all called for an ecosystem approach to fisheries management, yet many species such as the American lobster (Homarus americanus) are still largely managed individually. One hypothesis that has yet to be tested suggests that human augmentation of lobster diets via the use of Atlantic herring (Clupea harengus) as bait may contribute to recent increases in lobster landings. Currently 70% of Atlantic herring landings in the Gulf of Maine are used as bait to catch lobsters in traps throughout coastal New England.Methodology/Principal FindingsWe examined the effects of this herring bait on the diet composition and growth rate of lobsters at heavily baited vs. seasonally closed (i.e., bait free) sites in coastal Maine. Our results suggest that human use of herring bait may be subsidizing juvenile lobster diets, thereby enhancing lobster growth and the overall economic value and yield of one of the most valuable fisheries in the U.S.Conclusions/SignificanceOur study illustrates that shifting to an ecosystem approach to fisheries management should require consideration of cross-fishery interactions.

Growth rate of adult rock lobsters Jasus edwardsii increased through translocation

Growth rates of southern rock lobster, Jasus edwardsii, decrease from north to south of Tasmania and also decrease with depth. Slow-growing lobsters from deep-water regions were translocated to shallow-water, inshore areas to examine the potential of translocation to increase yield for the Tasmanian rock lobster industry. Within their first moult, translocated lobsters increased their growth rates, exceeding that of resident deep-water lobsters from the original site. Growth of translocated females increased to the extent that it exceeded resident shallow-water females in the first year post-release. The increased growth rate of deep-water southern rock lobsters after translocation and the magnitude of the growth increments achieved in a short period highlight the plasticity in growth of this species. Growth, and therefore size-at-age, are potentially determined by density effects, food availability or other unidentified environmental factors. Rapid increases in lobster growth achieved through translocation suggest that translocation could be applied to increase the productivity of the fishery.

An evaluation of the nutritional value of alternative lipid sources to juvenile southern rock lobster, Jasus edwardsii

Experimental lobster feeds are currently based on fish meal and fish oil formulations, and although survival and growth similar to that of lobsters fed fresh blue mussels has been achieved, varying the protein level in previous experimental feeds has not increased growth beyond that of lobsters fed natural food. This experiment assessed the growth performance of lobsters fed pelleted feeds containing constant amounts of protein, lipid and energy where the lipid was provided by a range of oil-rich ingredients (fish oil, FO; fish oil with added soybean lecithin, FOL; canola oil, CO; tuna oil, TO; mussel meal, MM; and squid meal, SQM). Feed performance was assessed by lobster growth rate, survival, final biochemical composition, nutrient retention and nutrient efficiency. Twenty tanks containing 15 post-larval lobsters each (1.5 ± 0.04 g) were randomly allocated one of six test feeds in triplicate, and the two remaining tanks were fed freshly opened blue mussels (FRM) as a reference feed. Lobsters were fed daily to excess for 10 weeks. Final individual weights of whole body and digestive gland were measured, and tissue chemical composition analysed. There were no significant differences in survival (88.4 ± 3.3%), or specific growth rate (1.3 ± 0.1%.day − 1 ) among the formulated feed fed lobsters, which were significantly lower than the survival (100 ± 0.0%) and SGR (2.2 ± 0.1%.day − 1 ) of FRM fed lobsters. The SQM fed lobsters had a significantly lower lipid efficiency ratio and lipid productivity value than lobsters fed TO, FOL and MM feeds. The digestive gland lipid content (g.100 g wet tissue − 1 ) of lobsters fed the feeds TO (3.7 ± 0.4), FO (3.5 ± 0.3) and SQM (2.2 ± 0.2) were significantly lower than lobsters fed feeds MM (9.9 ± 1.1), FOL (9.0 ± 2.3) and FRM fed lobsters contained most digestive gland lipid (12.3 ± 1.5).

Digestive enzyme response to natural and formulated diets in cultured juvenile spiny lobster, Jasus edwardsii

A better understanding of the nutritional requirements and digestive processes are essential for improving the consumption and growth of spiny lobsters on formulated diets used in commercial culture. Differences in the enzymatic digestive response (i.e., post-prandial changes in digestive enzyme activity, digestive fluid pH and digestive gland structure) of juvenile Jasus edwardsii fed either a natural (mussel flesh) or a formulated diet were investigated. Digestive enzyme activities (total protease, trypsin, α-amylase and α-glucosidase) and soluble protein concentration in the foregut after a single feeding event for the two dietary treatments displayed a common peak at 4 h, and a second peak at 18 h post-prandial for the mussel fed lobsters only. In lobsters fed the formulated diet, the lumen size of the digestive gland tubules was 88% larger, the number of B-cells per tubule at 18 h post-feeding was 269% higher, and the pH of the digestive gland was lower (6.20 versus 6.34) than in lobsters fed mussel flesh. These results indicated an intensified intracellular digestion in the digestive gland on the formulated diet that could have played a role in the poor appetite revival (>18 h) exhibited on this diet. Rearing of juvenile lobsters on the formulated diet for 6 months resulted in a marked decrease in the digestive capacity (i.e., total and specific enzyme activity of the foregut and digestive gland) and nutritional condition of lobsters. Overall, these results suggest that difficulty in the digestive processing of formulated feeds may help to explain the bottlenecks encountered in developing more effective formulated diets for juvenile spiny lobster culture. Improvements in the dissolution of dietary ingredients upon entering the foregut, and in the digestibility of dietary carbohydrate sources, may assist in further improving the performance of formulated diets for lobsters.

Contribution of bait to lobster production in an oligotrophic marine ecosystem as determined using a mass balance model

The fishery for the western rock lobster ( Panulirus cygnus) in Western Australia is Australia's largest trap-based fishery, deploying 8.8 million pot lifts, landing on average 11,000 tonnes of lobster and using approximately 14,000 tonnes of bait annually. A mass balance model was constructed to determine the potential contribution of this bait to the diet of western rock lobsters. Bait is potentially a significant subsidy given the oligotrophic nature of Western Australia's marine environment. The mass balance model was constructed on the principle that the biomass of the lobster population reflects the difference between inputs (growth, immigration) and outputs (natural and fishing mortality and emigration). Biomass calculated using this approach was within 7% of biomass calculated from independent estimates based on depletion analysis, indicating the model is robust. The food required to explain observed growth was then calculated, allowing the potential contribution of bait to lobster diet to be assessed. The abundance of natural diet items on the benthos was sufficient to explain the observed growth of lobsters, with bait contributing a maximum of 13% of lobster food requirements over the whole ecosystem. This contribution of bait will differ spatially and temporally reflecting uneven distribution of fishing effort and may be as high as 35% during some months of the fishing season, a result consistent with dietary studies based on stable isotopes. Given observed effects of organic matter addition on ecosystem processes as observed in trawl fisheries and aquaculture operations, it is likely that the effects of bait addition on ecosystem function are more widespread than lobster production.

Identification of digestible carbohydrate sources for inclusion in formulated diets for juvenile spiny lobsters, Jasus edwardsii

Carbohydrates are a key ingredient in crustacean formulated diets because of their potential to greatly improve production efficiency. For the culture of spiny lobsters where daily food intake is limited, carbohydrates have the potential for delivering a low cost source of energy that could spare protein for growth. Therefore, the digestibility of different carbohydrate sources including refined sugars, mussel glycogen, algal polysaccharides, carboxymethyl cellulose (CMC) and starches (i.e., native, dextrinised, gelatinised) were assessed in juvenile spiny lobster (30–60 g). This was done by measuring the rate of carbohydrate hydrolysis in vitro using enzyme homogenates and postprandial haemolymph glucose concentrations following ingestion of semi-purified diets containing different carbohydrate levels and sources. Fresh mussel gonads and a practical formulated diet were also included for comparison. Storage polysaccharides (i.e., gelatinised starches, dextrin, mussel glycogen) and the structural polysaccharide CMC were the best digested carbohydrate sources in vitro. CMC was more digestible than the algal polysaccharides, agar and alginate, and therefore may have potential as a binding agent in formulated diets for J. edwardsii. The poor hydrolysis of sucrose and trehalose suggests that their use as an energy source might be limited in J. edwardsii. Native wheat starch was the best digested among the various plant starches tested. Gelatinisation of starches markedly improved their digestibility suggesting that pre-treatment of the dietary starch source would have a beneficial influence on the digestibility of diets for J. edwardsii. Consumption of the semi-purified diets (i.e., 1% BW) containing the digestible starch sources (i.e., 27% dry weight), as well as the practical diet, resulted in high haemolymph glucose concentrations (> 5 mmol l − 1 ) and a prolonged hyperglycaemic response (> 24 h) suggesting that these carbohydrate sources are well digested and absorbed, but possibly poorly utilised. In contrast, the fresh mussel gonad diet (i.e., 27% glycogen by dry weight) appeared to be better utilised (reduced glycaemia after 12 h). A lower inclusion level (i.e., 7%) of gelatinised maize starch reduced the peak (1.87 mmol l − 1 ) and extent (12 h) of the glycaemic response. Using lower inclusion levels (< 27%) of the rapidly digested starches (i.e., gelatinised, dextrinised) identified in this study, or incorporating digestible carbohydrate sources resulting in slower appearance of haemolymph glucose (i.e., native wheat starch, CMC), in formulated diets may have the potential to improve their utilisation for growth of juvenile spiny lobsters.

Improvement of rearing conditions for juvenile lobsters ( Homarus gammarus) by co-culturing with juvenile isopods ( Idotea emarginata)

Growth conditions of the juvenile lobsters, Homarus gammarus, were optimized in view of a restocking project of the lobster population at Helgoland (German Bight, North Sea) aimed to produce more than ten thousand juvenile lobsters per year. Growth and survival rates of juvenile lobsters depend on diet, temperature and water quality. In the present study, diet at optimum temperature was considered, but special emphasis was placed on the optimization of cleaning and feeding methods from both an economical and ecological point of view. Six dietary treatments of juvenile lobsters (each n = 99) were tested in individual compartments in a semi-closed re-circulation system at around 20 °C. Lobsters were fed with combinations of two diets, newly hatched Artemia sp. nauplii and minced crabs Cancer pagurus (whole carcasses), every 2 or 4 days until a carapace length of 10 mm was reached. During the experiment (max. 105 d), juvenile isopods, Idotea emarginata, were constantly present in the lobster boxes. More frequent feeding significantly increased growth rates of the juvenile lobsters while different feeding combinations had no effect. The highest growth rate (0.091 ± 0.02 mm CL day − 1 ) was at a feeding frequency of every 2 days for each diet. At this rate the carapace length of 10 mm was reached in 68–71 days. The survival rate of the juvenile lobsters ranged from 90–97%. The diet consisting of C. pagurus was most cost-efficient and was obtained as discards from the crab fishery at Helgoland. The co-culture of juvenile lobsters with juvenile isopods I. emarginata as “cleaning organisms” was ideally suited for the rearing of lobsters and reduced the maintenance time by 50%. The isopods also served as supplementary diet.

Spatial and Temporal Variability in Growth of Hawaiian Spiny Lobsters in the Northwestern Hawaiian Islands

AbstractGrowth rates were estimated for recaptured Hawaiian spiny lobsters Panulirus marginatus tagged between 2002 and 2007 at Necker Island (23°30′N; 164°35′W), Gardner Pinnacles (25°00′N; 168°50′W), and Maro Reef (25°30′N; 170°45′W) in the Northwestern Hawaiian Islands (NWHI). The location and year‐specific nature of the tag–recapture cruises enabled investigation of spatial and temporal variability in growth. Mean growth rates, estimated by using the von Bertalanffy and Schnute growth models and fitted via a maximum likelihood technique, differed between sexes and particularly among locations and years. Male lobster growth rates at Necker Island were, in general, one‐third those at Gardner Pinnacles and one‐half those at Maro Reef. Female lobsters exhibited the same pattern with less‐pronounced differences. Maro Reef lobsters exhibited several abrupt, significant growth reductions among years, while Necker Island lobster growth rates increased significantly from 2004 to 2005. Model results also indicated substantial individual variability in growth. Neither density nor temperature could account for the differences in growth rates. No palinurid species studied to date has shown such spatial variability in growth, and only one panilurid species has exhibited similar variability on a temporal scale. Recognition of and accounting for the mean and individual variability in a life history trait of this endemic species will result in more accurate stock assessments and, ultimately, a better understanding of lobster dynamics and the NWHI coral reef ecosystem.

Spatial overlap and interaction between sub-adult American lobsters, Homarus americanus, and the invasive European green crab Carcinus maenas

Invasive species are considered one of the major threats to biological diversity, and they can negatively impact species of particular ecological and/or economic importance. In this study, we investigate the potential threat that the European green crab, Carcinus maenas, represents to sub-adult lobsters, Homarus americanus, in Passamaquoddy Bay, Canada, northwest Atlantic. We conducted transect surveys using SCUBA diving to evaluate spatial overlap between these species inside, and immediately adjacent to, a lobster nursery area, and ran two laboratory experiments to investigate interactions between them in conditions of limited food and shelter availability. We found marked spatial overlap between these species in nature, particularly between adult green crabs and sub-adult lobsters in the shallower parts of the nursery area. It was not uncommon to see green crabs and sub-adult lobsters less than 1-2 m from one another, and we estimated mean nearest-neighbor values as low as 0.5-1 m on certain transects and months, with a grand mean of 5.17 ± 1.62 m (SE). Monte Carlo randomization of positional data revealed that green crabs and lobsters were randomly distributed relative to one another; individuals of one species did not seem to aggregate or segregate relative to individuals of the other species. In the lab, green crabs did not negatively affect survival (one exception), growth, activity, feeding, or shelter use of sub-adult lobsters. In fact, sub-adult lobsters regularly preyed upon green crabs in the first lab experiment, where heterospecific individuals were matched for body mass. Our results suggest that green crabs do not pose a significant threat to sub-adult lobsters in Passamaquoddy Bay, and may in fact represent a food subsidy for them.

Feeding and gut evacuation of cultured juvenile spiny lobsters, Jasus edwardsii

Low feed consumption has been suggested as a major impediment for the development of effective formulated diets for spiny lobsters. To seek an explanation for the low feed consumption, this study compared the feed consumption, appetite revival, foregut evacuation and fecal production of different sizes of spiny lobster Jasus edwardsii juveniles fed a fresh natural diet (i.e. mussel flesh) and a dry formulated diet. In addition, the effect of feeding frequency was determined by feeding juvenile lobsters the same ration of formulated diet at different time intervals. i.e., same ration delivered 3 week−1, 1 day−1, 2 day−1, 5 day−1 and 5 night−1. Lobster (10–15 g) growth and feed consumption (1.15% BW day−1) was maximized when receiving a single ration daily of the formulated diet. A slow appetite revival (AR>18 h) on the formulated diet was consistent with the negative effect of increasing feeding frequency on growth and consumption. In addition, there appeared to be no major advantage in dry matter intake by providing the nutrient dense dry formulated diet to Jasus edwardsii. Lobsters fed fresh mussel flesh (79.8% moisture) consumed similar levels of dry matter as those lobsters fed the dry formulated feed (7.3% moisture). This appears to be due to high moisture gain and expansion of the dry feed in the lobster foregut. Foregut evacuation lasted 10 h for the two diets but a delay in initial foregut evacuation and processing of the formulated diet was evident, and may have negatively affected feed consumption, appetite revival and dry matter digestibility (61.2%) of the dry formulated diet compared to the mussel flesh diet (89.2%). Appetite revival on mussel flesh was almost complete by 12 h after a satiation ration and was governed primarily by the rate of foregut evacuation. Differences in the timing of foregut evacuation and fecal production between the two diets suggested that a greater proportion of the formulated diet entered the midgut directly.The results indicate that J. edwardsii cannot achieve high levels of feed consumption on formulated diets because gut throughput is reduced due to a small foregut capacity, expansion of the feed post-ingestion, lengthy foregut filling time (1–2 h) and clearance time (10 h), combined with slow gut throughput time (34–42 h) and appetite revival (>18 h). A slow appetite revival and difficulties in processing and digestion of formulated diets appear as major issues to be resolved to improve the performance of formulated diets required for the commercial aquaculture of J. edwardsii and possibly other spiny lobsters.

On the growth of the European spiny lobster, Palinurus elephas from Sardinian waters (central western Mediterranean Sea)

Growth of spiny lobsters Palinurus elephas was investigated using tagging data. A total of 4044 lobsters were tagged and released between 1997 and 2004 in an area off central‐western Sardinia, Italy, where fishing is banned. The growth increments of 248 lobsters, recaptured inside the no‐take area and in the surrounding zones, were recorded and analysed with two different procedures, and von Bertalanffy growth parameters were estimated for each sex. Males showed a higher asymptotic carapace length than females (167.9 versus 120.2mm). Growth increments recorded inside and outside the no‐take area did not reveal any density‐dependent effects on females. Small but non‐significant differences were evident for males, showing faster growth in lobsters caught outside the no‐take area.

Effects of dietary carbohydrate on growth of juvenile New Zealand rock lobsters, Jasus edwardsii

The commercial aquaculture of spiny lobsters is impeded by the development of effective practical diets, which is partly due to a lack of knowledge of the digestive capabilities and nutritional needs of these species. Carbohydrates have the potential to provide a low cost energy source in practical diets for spiny lobsters. This research investigated the effect of algal carbohydrates, on the growth of juvenile rock lobsters. Juvenile lobsters, Jasus edwardsii, (10–12 mm carapace length) were provided with one of five diets; blue mussel, squid (Nototodarus gouldii), or a mussel diet partially substituted with algal carbohydrates, either agar, carrageenan or alginate over 80 days in culture. In all treatments, diet consumption and lobster growth were maintained or increased over time. Growth was highest for the mussel diet followed by the agar diet. Similar lobster growth occurred on the carrageenan and alginate diets, with the least on the squid diet. After 80 d there were significant differences in the percent lipid and glycogen stored in the mid-gut gland with highest levels of glycogen in lobsters fed the mussel only diet. Percent protein in the tail muscle was greatest for mussel fed lobsters. The mid-gut index (mid-gut weight/whole wet weight) was highest for the mussel only diet and this was similar to control lobsters at the start of the experiment. The results indicate that glycogen from mussels and agar could be used as carbohydrate source in the future development of a practical diet for spiny lobsters.

The effect of different holding systems and diets on the performance of spiny lobster juveniles, Jasus edwardsii (Hutton, 1875)

This study evaluated the growth and survival of lobster juveniles over 8 months when fed fresh Perna canaliculus mussel and stocked at a density of 35 ind. m − 2 in one of three holding systems: a prototype sea-cage design, a commercial sea-cage design, and small experimental land-based holding tanks. At the same time the growth, survival and nutritional condition of lobsters fed fresh mussel in the prototype sea-cages were compared with lobsters feeding only on the biofouling of the sea-cages or fed two artificial diets (dry and moist) three times a week. Survival in the prototype sea-cages (83.3 ± 2.3%) was similar to the experimental flow-through tanks (87.9 ± 8.0%) but significantly higher than the commercial sea-cage (55.4 ± 1.8%). Furthermore, the prototype sea-cages resulted in significantly higher specific growth rate (SGR = 0.96% BW day − 1 ) than the other system designs (flow-through tank SGR = 0.86 BW day − 1 and commercial sea-cage SGR = 0.77% BW day − 1 ). The growth rate in the prototype sea-cages was one of the fastest ever recorded for this species, over this size range of juveniles (3–31 g) and at comparatively low seawater temperatures (15.2 °C). The survival of lobsters in the prototype sea-cages did not differ between the three experimental feeding regimes. However, growth when feeding on biofouling alone or with the addition of artificial diets was comparatively inferior to the lobsters fed mussels (SGR = 0.96% BW day − 1 ; survival = 83.3 ± 2.3%). Lobsters fed the dry formulated diet (SGR = 0.78% BW day − 1 ; survival = 79.3 ± 1.2%) grew significantly faster than on the moist formulated diet (0.60% BW day − 1 ; 59 ± 17.8%) or on the biofouling only (0.38% BW day − 1 ; 66.3 ± 4.9%). The growth of lobsters fed the dry formulated diet in the prototype sea-cage was better than in previous tank growth studies using experimental diets and was probably attributable to animals feeding on biofouling of the sea-cages. Digestive gland histology supported the growth trends, with lobsters fed fresh mussel and the dry formulated diet being in best nutritional condition at the end of the growth experiment. The results indicate that sea-cage culture of juvenile spiny lobsters can provide significant growth advantages over tank systems possibly due to supplementary nutrition from biofouling. However, sea-cage structural design, feeding and diet type are important factors influencing the performance of J. edwardsii juveniles in sea-cages.

Growth, reproductive cycle, and movement of berried European lobsters (Homarus gammarus) in a local stock off southwestern Norway

Abstract Agnatt, A-L., Kristiansen T. S., and Jorstad K. E. 2007. Growth, reproductive cycle, and movement of berried kuropean lobsters (Homarus gammarus) in a local stock off southwestern Norway. – ICES Journal of Marine Science, 64: 288–297. The Norwegian fishery for the European lobster (Homarus gammarus) collapsed between 1960 and 1980, to &lt;10% of its pre-1960 level, and since then the spawning stock seems to be too low to generate good recruitment. In 1998, a project to evaluate the feasibility and effect of protecting berried female lobsters as a management restriction was initiated. The study area selected was previously an important fishing ground in Kvitsøy off southwestern Norway, and 125 000 hatchery-reared juveniles were released between 1990 and 1994. From spring 1998 to spring 2000, a total of 942 wild and 480 cultured berried females was purchased from fishers, individually tagged with a streamer-tag, and released. The proportion of berried females in the landings varied annually from 19 to 58% for wild females, and from 22 to 44% for cultured females. By spring 2000, 23% of the tagged females had been recaptured at least once, and 3% twice or more. Average moult increment was 7 mm carapace length (CL), independent of pre-moult size in both wild and cultured females. Reproduction (spawning) and growth (moulting) alternated in a 2 y cycle for &gt;90% of the females. A small number moulted and spawned a few weeks after hatching. More than 95% of the recaptures were taken within a radius of 1 km of the release area. Egg production varied considerably between seasons. Reproductive potential (RP) of landed berried females underestimated egg production compared with what was actually produced (AE). For the entire period, RP was estimated to be about 15.0 million eggs, and AE to be 17.2 million eggs. Cultured females contributed 27% of AE. To reduce the fishing mortality in a heavily fished and depleted population is vital. A ban on landing berried females would be a valuable first step in attempting to increase the spawning biomass.

Modelling growth of rock lobsters, Jasus edwardsii, off Victoria, Australia using models that allow for individual variation in growth parameters

A method for modelling the growth of crustaceans, including rock lobsters, that assumes that all animals in a population grow differently, but that the individual variation in the parameters of the growth curve can be captured using a probability distribution, is developed. The method allows for the impact of selectivity on the probability of recapturing a tagged animal. The method is applied to rock lobsters, Jasus edwardsii, off Victoria, Australia. The results suggest that growth differs between males and females, as well as spatially. Ignoring the impact of selectivity on the probability of recapturing a tagged animal is shown to lead to over-estimation of growth rates, which could potentially lead to over-optimistic management advice.

Stocking density and shelter type for the optimal growth and survival of western rock lobster Panulirus cygnus (George)

The growth and survival of three size classes of wild caught western rock lobster, Panulirus cygnus (post-pueruli: mean 2.14 ± 0.07 g, 13.2 ± 0.1 mm CL; year 1: post-settlement juveniles, 57.1 ± 1.1 g, 38.7 ± 0.28 mm CL; and year 2 post-settlement juveniles, mean 138.2 ± 2.26 g, 51.9 ± 0.25 mm CL) were examined at combinations of two stocking densities (post-pueruli: 50 and 100 m − 2 ; year 1: 11 and 23 m − 2 ; year 2: 10 and 19 m − 2 ) and two shelter types (a novel rigid plastic mesh shelter or bricks) over a period of 6 months. Survival of lobsters held at the lower densities (90–95%) was significantly greater than for lobsters held at higher densities (post-pueruli = 78%, year 1 = 86%, year 2 = 88%). Post-pueruli survival was significantly higher in tanks with mesh shelters (91.7%) than brick shelters (75.8%) with a similar trend exhibited by year 1 and year 2 lobsters. Densities tested did not significantly affect lobster growth for any size class. Growth of post-pueruli was considerably higher in tanks with mesh shelters (641.7% weight gain; specific growth rate 1.07 BW day − 1 ) ( p < 0.05) but there was no difference in the growth of year 1 and year 2 lobsters between mesh and brick shelters. Feed intake (g pellet dry matter lobster − 1 day − 1 ) was not significantly different between densities. This study has shown that P. cygnus is well suited for aquaculture based on the collection and ongrowing of wild caught pueruli, as this species exhibits good survival at high densities (up to 100 m − 2 ) without adverse effects on growth, and shows no captivity-related health problems. We recommend mesh shelters, with stocking densities of 50 m − 2 for post-pueruli and between 20 and 25 m − 2 for year 1 and year 2 juveniles, to maximise survival and production.