Stimulation of crusher claw development in cultured lobsters, Homarus gammarus (L.)

Abstract. During the culture of large numbers of lobsters, Homarus gammarus (L.), it was noticed that more than half the animals lacked a distinct crusher claw. The majority bore two morphologically similar cutter claws even though their ages ranged up to 3 years (92mm carapace length). The proportion of 3-month-old juveniles (11–13 mm carapace length) bearing clearly differentiated crusher claws was increased from approximately 30% to over 80% by adding live oyster spat to the rearing chambers. The differentiation of the crusher claws was completed within approximately 4 moults (71–83 days) and was morphologically more pronounced in lobsters grown in the presence of spat than in the 30% of control lobsters which developed crusher claws spontaneously.     

Survival and growth of juvenile lobster Homarus gammarus L. raised for stock enhancement within in situ cages

The growth of juvenile lobster Homarus gammarus L. reared on sandy sediments under laboratory conditions was compared with the growth of lobsters reared within in situ cages in the wild. The caged lobsters, left without any attention or care for 3 months, achieved an average size similar to that attained under optimal laboratory conditions. (8.8 mm carapace length; CL). Growth was positively correlated to cage size and depth. Overall average survival was 66%, ranging from 0% to 90% for clusters of 30 individually caged juveniles.     

Does Morning as Opposed to Night‐time Feeding Affect Growth in Juvenile Spiny Lobsters,Jasus edwardsh?

Previous research on juvenile lobsters has shown that they display a nocturnal rhythm in their oxygen consumption and ammonia excretion, such that lobsters that are fed in the morning have shorter specific dynamic action (SDA) response than those lobsters that are fed at night. It was therefore suggested that juvenile lobsters should be fed in the morning to maximize energy utilization. This research tested the hypothesis that the growth of juvenile rock lobsters would be improved by feeding in the morning rather at night. Juvenile spiny lobsters Jasus edwardsii were fed a squid meal (5% body weight) either in the morning or at night over a period of 80 d. Lobsters fed in the morning had a 108% weight gain, an increase of 4.6 mm in carapace length and a growth rate (SGR) of 0.92%. These were significantly higher than the 78% weight gain, carapace length increase of 3.8 mm, and growth rate of 0.76% recorded for lobsters fed at night. Abdomen muscle protein and mid-gut gland lipid and glycogen content were similar after 80 d. The digestive gland index (DGI) was the same in lobsters exposed to the different feeding regime but had decreased compared with control lobsters at the start of the experiment. Morning-fed lobsters outperformed night-fed lobsters in all aspects of growth and survival, and it is suggested that commercial farmers feed their lobsters in the morning rather than at night. Because these growth differences were predicted from specific dynamic action measurements, it is concluded here that this technique would be useful for the rapid evaluation of the effectiveness of natural and artificial diets on lobster growth.     

Variability in size at moult among individual broods of cultured juvenile lobsters, Homarus gammarus (L.)

Abstract. Information on carapace length (CL) and its variability at each instar from settlement (instar 4) to pre-recruit size (instar 24) is presented for 10 individually reared single parent broods and one mixed brood of European lobster, Homarus gammarus (L.). The lobsters grew from 5mm CL to 74mm CL in approximately 130 weeks at 20°± 2°C. There was some evidence that growth variability of the largest lobsters was influenced by the size of the rearing compartments used during the final growth period.     

Effects of marine reserve protection on spiny lobster (Jasus edwardsii) abundance and size at Tonga Island Marine Reserve,New Zealand

• 1. Diving surveys were undertaken to investigate the effects of marine reserve protection on spiny lobster (Jasus edwardsii) populations at Tonga Island Marine Reserve, northern South Island, New Zealand over a 2 year period from December 1998 to December 2000.
• 2. Spiny lobsters were 2.8 times more abundant overall, and mean size was 19 mm carapace length larger in shallow transects and 28 mm carapace length larger in deep transects, in the marine reserve than at adjacent fished sites. That pattern was evident despite very high variability within sites, and among sites within reserve and fished areas.
• 3. Large reproductive males were 10 times more abundant within the reserve compared to adjacent fished areas, suggesting that more eggs would be fertilized in the reserve than on the adjacent fished coast.
• 4. Estimates of size‐specific fecundity, combined with abundances of females, suggested that almost nine times more eggs would be produced in the reserve than in fished areas.
• 6. We estimate that the mean abundance of spiny lobster in the reserve has increased by 22%, 5 years after its establishment, indicating an annual population increase of 4.4%. Over the same period, abundance of spiny lobster outside the reserve has declined by 2.9% per annum.
• 7. Based on known spiny lobster movements, we suggest that marine reserves of more than 10 km length should be given priority over smaller reserves. Smaller reserves will, however, protect part of the population for at least a portion of their lifespan.
• 8. Previous studies of movement of J. edwardsii suggest that spillover from the reserve should occur, and as population density increases we predict that more spiny lobsters will move out from the reserve.

Copyright © 2002 John Wiley & Sons, Ltd.     

The first returns of tagged juvenile lobsters [Homarus gammarus (L.)] after release to the wild

The success of re-stocking lobster fishing grounds has been difficult to assess given the problems of tagging juvenile lobsters. A system of tagging using a 1 mm long × 0.25 mm diameter stainless steel micro-tag has been used during a study of the feasibility of restocking fishing grounds with hatchery-reared juvenile lobsters. The first returns of juveniles tagged by this method are described.     

A comparison of techniques for the measurement of growth in adult lobsters

Four non-destructive measures of growth (wet weight in air, wet weight in water, displacement volume and carapace length) were correlated to two destructive measures of growth (dry weight and total body protein level) in adult American lobsters (Homarus americanus). All non-destructive parameters were significantly (P < 0.05) correlated to dry weight and protein for female lobsters. Only wet weight in water was significantly correlated to dry weight and total body protein level in male lobsters.     

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.     

Size at maturity for grooved Tanner crab (Chionoecetes tanneri) along the U.S. west coast (Washington to California)

We conducted a multiyear study to examine interannual variability in the mean size (carapace width, mm), maturity size (mm) and depth (m) for grooved Tanner crab (Chionoecetes tanneri (Rathbun, 1893)) along the U.S. west coast. An additional goal was to provide updated estimates of carapace width (mm) at 50% maturity (W₅₀) for male and female grooved Tanner crab and assess changes over time. Randomly selected samples came from trawl surveys undertaken annually by the Northwest Fisheries Science Center at depths of 55 to 1280 m. We used allometric relationships between carapace width (CW) and either abdominal width (AW) (females) or chela length (CL) (males) to determine functional maturity by sex. We evaluated maturity by fitting logistic regression models to proportion mature grooved Tanner crab. W₅₀ varied significantly between males (125.2 mm) and females (89.1 mm) but interannual differences were slight. The annual mean CW were greater for mature males (139.9–143.4 mm) relative to females (98.8–100.4 mm). The average sizes of immature grooved Tanner crab varied between sexes with males (75.7–84.6 mm) larger than females (66.7–71.9 mm). Size frequency distributions indicated little overlap in the size of mature male and female grooved Tanner crab but considerable overlap between immature grooved Tanner crab. The best model expressing complexity in growth incorporated width, sex and maturity stage. Depth ranged from 195–1254 m with the average depth of a mature grooved Tanner crab (females, 737 m; males, 767 m) significantly shallower than an immature (females, 949 m; males, 918 m) grooved Tanner crab.     

Exploitation of walleye in a Great Plains reservoir: harvest patterns and management scenarios

Abstract This study assessed exploitation and evaluated management options for walleye, Sander vitreus (Mitchill), in Glen Elder Reservoir, Kansas. A total of 2429 walleye varying from 240 to 687 mm was tagged with Carlin dangler tags during 2000–2003. After correcting for tag loss and non‐reporting, exploitation of walleye was estimated as 68.3%. More than 85% of the tagged walleye were harvested during April to June and 75% were harvested within 6 months after tagging. A Beverton‐Holt yield‐per‐recruit model was used to evaluate six minimum length limits varying from 250 to 610 mm. Given current exploitation rates, population demographics and harvest regulations (381‐mm minimum length limit), the walleye population is probably experiencing recruitment overfishing. Model results suggested that a 610‐mm minimum length limit would be required to prevent growth overfishing and a 533‐mm or longer minimum length limit would prevent recruitment overfishing.     

The Effect of Diet on Weight Gain,Shell Hardness,and Flavor of New-Shell American Lobster,Homarus americanus

Abstract

Harvested newly-shed American lobsters, Homants americanus, placed in pounds for long-term storage are prone to damage resulting from high-density confinement. It is beneficial for the new shell to harden as soon as possible after shedding. Artificial diets offer the potential for adding supplements to increase weight, muscle gain, and shell hardening. In this study, lobsters were fed 5 different diets: herring, fish racks, and prepared diets with three levels of vitamin D for a period of 38 days. After the feeding trial, lobsters were reweighed, and samples of the carapace and claw shell were removed and subjected to a compressive force/deformation test to measure shell strength. Results indicate a significant (P< 0.05) difference in weight gain, with the highest level of vitamin D actually inhibiting gain. Subsamples tested for compressive force yielded a positive correlation between the carapace measurement and feed type. Flavor tests on subsamples showed significant differences between all treatments; herring was the best, followed by pelleted feed and then fish racks. No off-flavors were detected in lobsters fed any of the three diet types.     

Exploitation and length limit evaluation of Alabama bass in a South‐eastern USA reservoir

Alabama bass, Micropterus henshalli Hubbs & Bailey, are the dominant sportfish of Allatoona Reservoir, Georgia, USA, but no population assessment has been conducted. Thus, growth and total annual mortality were estimated in spring 2005, and a tagging study was conducted in 2006 and 2007 to estimate angler exploitation. These data were used with an age‐structured model to assess performance of a 356‐mm minimum length limit (MLL), a 406‐mm MLL and a 330‐ to 406‐mm protected slot length limit (SLL) compared to the present harvest regulation of no MLL. Mean annual exploitation varied from 12 to 22% each year and was generally highest for fish > 330 mm; total annual mortality was 44%. Models predicted a 49–153% increase in numbers of Alabama bass reaching 432 mm, a 22–66% decline in numbers harvested and only moderate declines in yield (5–25%) with the alternative harvest regulations compared to current conditions. The SLL may be an acceptable compromise to allow Allatoona Reservoir anglers to still harvest fish while also improving Alabama bass size structure.     

Estimates of heritability and genetic correlations for growth‐related traits in the tiger prawn Penaeus monodon

Heritabilities and genetic and phenotypic correlations were estimated for body weight (BW), body length (BL), carapace length (CL), carapace width (CW) and carapace height (CH) of the Penaeus monodon from measurements on progeny at 6 months of age resulting from a nested mating design. Estimation was made on data from 41 full‐sib and 10 half‐sib families. The estimated heritabilities for these traits were 0.13–0.24, and the significantly phenotypic and genetic correlations were 0.81–0.94 and 0.88–1.00, respectively. The present results indicate that genetic improvement through selective breeding conducted on P. monodon might be feasible and would be an efficient method to obtain a positive response to selection.     

Environmental factors influencing the reproduction of an estuarine penaeid population and implications for management

This study determined environmental factors influencing the reproductive dynamics of a recreationally fished penaeid Metapenaeus dalli Racek in the Swan–Canning Estuary, south‐western Australia, during a restocking programme. Prawns were collected from nearshore (<2 m deep) and offshore waters (>2 m deep) every lunar month from October 2013 to March 2016. Reproduction occurred between November and March, when water temperature was >17°C, salinity >25 and stratification (bottom–surface salinity) <3. Densities of gravid M. dalli were highest in November of each year when 0+ females matured (19 mm; ~56% asymptotic length) and were highest in the Lower Canning Estuary. Individual fecundity ranged from 34,000 (18.1 mm carapace length [CL]) to 132,000 ova (27.1 mm CL). Egg production peaked in December/January and differed among years, being greatest in 2015/2016. These results suggest that closing fishing between November and December would protect breeding aggregations of M. dalli in inshore waters.     

Estimation of temporal changes in the growth of green turtles <Emphasis Type="Italic">Chelonia mydas</Emphasis> in waters around the Ogasawara Islands

Biological and life-cycle information is essential to any fisheries management program. We have investigated temporal changes in growth parameters in the von Bertalanffy growth curve for green turtles, Chelonia mydas, in waters around the Ogasawara Islands. The variance model of individual variability of growth used in our study was one derived from the stochastic differential equation with the white noise of constant intensity. Maximum likelihood estimates of the parameters were made using the data of 102 recovery records of tagging experiments from 1974 to 1995. The estimations were carried out for each of two models of linear and sudden changes in the parameters, and the best model was selected using Akaike's information criterion. The selected model was that all of the parameters excepting asymptotic straight carapace length were linear functions of year and that the asymptotic length was constant over the years. The estimated values of the growth coefficient in 1974 and 1995 were 0.0317 and 0.192 per year, respectively, and the estimated value of the asymptotic straight carapace length was 97.2 cm. Implications of the results and future issues to be resolved in near future are discussed.     

三疣梭子蟹微卫星标记与生长相关性状的相关性分析

选用35个多态性微卫星标记,对三疣梭子蟹人工选育快速生长自交家系F2代(以2008年莱州湾群体雄蟹为父本和海洲湾群体雌蟹为母本交配产生F1代,随机选取F1代后代进行交配产生F2代自交家系)的110个个体进行遗传多样性研究。结果表明:35个位点共检测出87个等位基因,各位点等位基因数为2~4个不等,平均有效等位基因数为2.2个,观测杂合度平均值为0.646 5,期望杂合度平均值0.513 0,多态信息含量平均值0.449 1。经卡方检验,多数位点显著(P<0.05)或极显著(P<0.01)偏离Hardy-Weinberg平衡。采用SAS 9.1中的一般线性模型(general linear model,GLM)对微卫星标记与生长相关性状(全甲宽、甲宽、甲长、体高、体质量、第Ⅱ侧齿间距、第Ⅰ步足长节长、大螯长节长)进行连锁分析。结果表明,Pot08位点与体质量、全甲宽、甲长、体高、第Ⅱ侧齿间距显著相关(P<0.05),Pot42位点与体质量、甲长、大螯长节长、第Ⅰ步足长节长显著相关(P<0.05),Pot53位点与全甲宽、甲宽、大螯长节长显著相关(P<0.05),与第Ⅱ侧齿间距极显著相关(P<0.01),Pot57位点与第Ⅰ步足长节长显著相关(P<0.05),PTR8a位点与第Ⅰ步足长节长、体高、甲长显著相关(P<0.05),与体质量、第Ⅱ侧齿间距、全甲宽、甲宽极显著相关(P<0.01),PTR30位点与体质量和甲长显著相关(P<0.05),PTR131位点与体质量、全甲宽、甲宽显著相关(P<0.05)。其中,位点PTR8a可作为以体质量为选育目标的首选标记。     

Growth rates and survival of western rock lobster (Panulirus cygnus) at two temperatures (ambient and 23 °C) and two feeding frequencies

Wild caught post-pueruli, year one and year two post settlement juvenile western rock lobster, Panulirus cygnus, were held at ambient temperatures (15.6 °C to 23.1 °C; mean 19.0 ± 0.07 °C) or at 23 °C, and fed the same ration of a formulated pellet diet either once per night, or 3 times per night, over 12 months, to determine whether elevated temperatures and multiple feeds per night would stimulate growth through increased metabolism and feed utilisation without significant negative impacts on survival. Survival of post-pueruli (mean 63%) did not differ between ambient and 23 °C. Survival of year 1 and 2 juveniles was higher at ambient temperatures (p < 0.01 ambient: year 1 juveniles, 68%; year 2 juveniles, 88%; 23 °C: 57% and 74%, respectively). Feeding frequency did not affect survival of post-pueruli and year 2 juveniles (mean 63%, 81% respectively), but survival was 9% higher for year 1 juveniles fed three times per night (58% versus 67%; p < 0.01). All lobsters grew faster at 23 °C than at ambient temperatures (p < 0.05), with the growth of post-pueruli almost doubled at 23 °C (weight gain at 23 °C versus ambient: post-pueruli, 18 438 % versus 9 915 %; year 1 juveniles 259% versus 165%; year 2 juveniles 23% versus 21%). Feed frequency did not influence the growth of year 1 and 2 juveniles. However, there was an interaction effect of temperature and feed frequency on post-pueruli where weight and carapace length were significantly higher at ambient temperatures when post-pueruli were fed three times a day, whereas at 23 °C weight and carapace length were significantly greater when fed once per day (p < 0.05). Feed intake (g pellet dry matter lobster^− 1 day^− 1) of pellet was higher at 23 °C for all lobsters (p < 0.05), but was the same between lobsters fed 3 times per night versus once per night. This study has shown that increasing temperatures to 23 °C significantly improved the growth of P. cygnus post-pueruli without any adverse effects on survival. The faster growth rates exhibited by year 1 and 2 juveniles at 23 °C may potentially offset their lower survival by significantly reducing culture period. There is no benefit of feeding P. cygnus multiple times at night in terms of growth and survival. The implications for P. cygnus culture are that temperatures should be maintained close to 23 °C during the entire growout period, with due care taken to minimise mortalities through adequate provision of food and shelter. Feeding P. cygnus once daily to excess just prior to dusk to co-incide with nocturnal feeding behaviour is recommended.     

Reproductive characteristics of slipper lobster,cuttlefish and squid species taken as byproduct in a tropical prawn trawl fishery

Reproductive characteristics relevant to population sustainability were examined for eight abundant invertebrate species caught as byproduct by the Northern Prawn Fishery (NPF) in northern Australia. Slipper lobsters Thenus parindicus and Thenus australiensis differed in their size at maturity, with T. parindicus maturing at smaller size. Both species had similar reproductive seasonality, with most recruitment early in the year (January–March). Our estimates of carapace length (CL) at which 50% of females are mature (CL₅₀) suggest that current management regulations (minimum legal size 52 mm CL) for Thenus are probably adequate for T. parindicus, but suboptimal for T. australiensis. However, T. australiensis only contributes a small proportion to the NPF Thenus catch. This species is likely to be protected as its preferred habitat is coarse substrate and deeper water (>40 m), which does not overlap greatly with the current commercial trawl effort distribution. Uroteuthis squid and Sepia cuttlefishes also varied in size at maturity and reproductive seasonality. Squid and cuttlefish populations are likely to be underexploited based on historical catches. Under current fishing levels, squid stocks appear to be resilient to the opportunistic targeting of spawning aggregations in similar NPF regions over several years.     

Survival and growth of hatchery-reared individuals of the European lobster, Homarus gammarus (L.), in field-based nursery cages on the Irish west coat

At present, one of two strategies is employed by fisheries managers for enhancing wild stocks of homarid lobsters using hatchery-reared individuals. The first is repeated releases of large numbers (>5000 at a time) of postlarvae (stage IV and V; carapace length [CL]=5–7 mm) to selected bottom locations. This option exists primarily because these programs lack space, time, and/or the finances to rear animals to larger sizes that would most likely have initially higher survival rates. The second is to rear animals in the laboratory for 5–8 months to stage XII+ (CL=12–16 mm) and then release small numbers (<1000) of these relatively large juveniles. To date there has been no attempt to release large numbers of relatively large juveniles because the costs are too prohibitive.

We have developed a low-cost, low-maintenance, field-based nursery caging system for rearing cultured lobsters, Homarus gammarus (L). Individuals (780 and ranging in CL from 5.2 to 7.2 mm) were reared in pre-fouled and unfouled containers (360 cm³) fabricated from an extruded plastic netting (3.2 mm aperture) and in pre-fouled plastic petri dishes (200 cm³) that were deployed in five near-bottom cages for 10 months (September 2000 to June 2001) at two subtidal sites located in a shallow, relatively exposed embayment on the west coast of Ireland. Animals apparently were able to survive and grow by suspension feeding on the plankton and/or foraging on the fouling community that settled on and within individual containers. Mean recovery rate (±95% CI) was independent of a priori fouling treatments, but was site-specific (42.1±7.9% and 27.8±13.7%; n=5). These rates are minimal estimates of survival because we found that at least 20% of the animals were capable of escaping from the mesh containers. Mean recovery in petri dishes that prohibited emigration was 53.3±37.02% at one site and 75.0±23.1% (n=5) at the other. These recovery rates compare favorably with survival rates of fed conspecifics held in the laboratory over the same time (54/81=66.7%). At the end of the experiment, animals in field cages had mean CLs that were significantly smaller than the fed controls. Because of costs incurred with maintaining small lobsters under laboratory conditions, results of this short-term, manipulative field experiment indicate that field-based nurseries represent an economically viable, third option for managers of lobster stock enhancement programs.     

Laboratory experiment on survival,growth and tag retention following PIT injection into the body cavity of juvenile brown trout (Salmo trutta)

A laboratory study was conducted to assess the effect of PIT tagging on survival and growth of young-of-the-year brown trout (Salmo trutta) and evaluate PIT tag loss as a function of body size at tagging. Transponders (11.5 mm long and 2.1 mm in diameter) were injected into the peritoneal cavity of fish ranging from 41 to 70 mm fork length (FL) using hypodermic needles. A total of 145 tagged fish and 136 control fish of similar size were reared over 4 weeks. Logistic regressions show that survival rate reached 95% for fish ≥52 mm FL at tagging (with a tag retention rate >70%), and 99% for fish ≥57 mm FL (tag retention rate >80%). No significant effect of tagging on growth (fork length and weight) was detected at the end of the experiment. The specific growth rate varied markedly among PIT-tagged fish regardless of fork length, weight or tag-to-body-weight ratio at tagging. Results suggest that juvenile brown trout larger than 57 mm FL (tag-to-body weight ratio in water <3.4%) can be marked by injection of 11.5 mm PIT into the peritoneal cavity with negligible effects on survival and growth, but this leads to a relatively high tag rejection rate (up to 20%).