John P. Mercer

Comparative studies on the nutrition of two species of abalone, Haliotis tuberculata L. and Haliotis discus hannai Ino. III. response of abalone to various levels of dietary lipid

This study was carried out to evaluate the effects of graded dietary lipid levels on the survival, growth and body composition of Haliotis tuberculata and H. discus hannai. Six purified diets were formulated to provide approximately 25% protein, and a series of graded lipid levels, from 0.63 to 11.58%, in the form of a mixture of corn oil and menhaden fish oil (1:1). The red alga, Palmaria palmata, was used as a control diet. Abalone juveniles of similar size (H. tuberculata, 588 mg; H. discus hannai, 389 mg) were distributed in a recirculating system using a completely randomized design with 7 treatments and 3 replicates per treatment (20 juveniles/replicate), and fed the appropriate diet every 3rd day for a 100-day period. P. palmata produced similar or better growth performance for both abalone species than the artificial diets. Among the artificial diets, significantly higher weight gains were observed for H. discus hannai at dietary lipid levels ranging from 3.11 to 7.09%, and for H. tuberculata at 3.11%. However, growth in terms of protein gain was best when both species of abalone were fed 3.11 and 5.15% dietary lipid. Soft-body lipid content positively correlated with dietary lipid levels. Inversely, soft-body protein concentrations decreased with the increase of dietary lipid. Overall, H. discus hannai deposited a slightly higher level of lipid, but a lower level of protein than H. tuberculata. There were no significant differences in survival of abalone fed the experimental diets.

Comparative studies on the nutrition of two species of abalone, Haliotis tuberculata Linnaeus and Haliotis discus hannai Ino. I: Effects of algal diets on growth and biochemical composition

Summary This study was conducted to examine the nutritional value of eight algal diets for two species of abalone, Haliotis tuberculata and Haliotis discus hannai, by measuring biochemical composition of the algae and relating this to feeding rate, growth and biochemical composition of the animals. Nutritional value of algal diets can be divided into three categories for each species of abalone. For H. tuberculata the best performance was on the mixed diet and Palmaria palmata intermediate was Alaria esculenta, Ulva lactuca and Laminaria digitata, and lowest growth was on Laminaria saccharina and Chondrus crispus. For H. discus hannai, best performance was on A. esculenta, P. palmata and the mixed diet; intermediate was on L. saccharina and L. digitata and lowest was on U. lactuca. It is generally accepted that high “balanced” levels of protein (>15%), lipid (3–5%) and carbohydrate (20–30%), with no detrimental substances in natural algae are essential for optimal growth performance of these abalone. The ...

The effects of size grading and stocking density on growth performance of juvenile abalone, Haliotis tuberculata Linnaeus

Abstract The effects of size grading and stocking density on the growth of juvenile European abalone, Haliotis tuberculata L. (Gastropoda: Haliotidae) were assessed in the hatchery. Animals were held in cages deployed in a flowtray with recirculating seawater maintained at 18 ± 2 °C, and fed ad libitum on the red alga Palmaria palmata (L.) Kuntze. In the grading experiment juvenile abalone were divided into four populations consisting of small (mean ± s.e; initial shell length = 15.3 ± 0.15 mm; n = 35), medium (initial shell length = 19.6 ± 0.16 mm; n = 35), large (initial shell length = 23.8 ± 0.17 mm; n = 35) and an ungraded control group (16.8 ± 0.41 mm; n = 35). Rearing was carried out over a period of 226 days, after which it could be concluded that an advantage in overall growth performance had been gained by grading the animals. There was evidence that growth of small abalone improved in the absence of larger conspecifics. In the stocking density experiment with two size grades and three stocking densities, a decreasing exponential relationship was found between growth (body weight and shell length) and stocking density, with a substantial amount of growth occurring at all densities. Final total biomass for both grades of abalone increased with density. For the smaller grade biomass gain increased as density increased. However, for the larger grade biomass gain declined at higher density. Overall mean survival (± s.e) was 98.3 ± 0.4% and was not influenced by density. It is suggested that the choice of stocking density is essentially a trade-off between maximum growth, optimal biomass gain, and economic considerations which may dictate densities that would result in a net reduction in overall production costs.

Comparative studies on the nutrition of two species of abalone, Haliotis tuberculata L. and Haliotis discus hannai Ino. V. The role of polyunsaturated fatty acids of macroalgae in abalone nutrition

Abstract This study was undertaken to evaluate the nutritional role of polyunsaturated fatty acids (PUFA) in dietary macroalgae for the abalone, Haliotis tuberculata and Haliotis discus hannai . The effects of five species of macroalgae ( Alarla esculenta, Laminaria digitata, Laminaria saccharina, Palmaria palmata and Ulva lactuca ) on specific growth rates (SGR) of the abalone and, the relationship between abalone SGR and fatty acid profiles in the algae were investigated. The current study confirmed our previous findings. Based on SGR the dietary values of these macroalgae can be listed in a decreasing order as follows: P. palmata A. esculenta U. lactuca L. digitata and L. saccharina for H. tuberculata and, A. esculenta P. palmata L. digitata, L: saccharina and U. lactuca for H. discus hannai . Fatty acid analysis revealed that C 18 and C 20 PUFA, such as 18:4n − 3, 18:3n − 3, 20:4n − 6 and 20:5n − 3, were dominant in the brown algae, A. esculenta L. digitata and L. saccharina . The red alga, P. palmata , was characterised by the highest proportion of 20:5n − 3 among the selected algae. In the green alga, U. lactuca , however, the dominant PUFA were C 16 and C 18 fatty acids, while C 20 fatty acids were minimal. All the selected algae consistently contained very low levels of C 22 fatty acids. Statistical analyses demonstrated that (a) 20:5n − 3 played a prominent role in the nutrition of both abalone species; (b) 18:3n − 3 as well as other n − 3 PUFA, and 18:2n − 6 together with other n − 3,6 long-chained PUFA also contributed to the faster growth of H. tuberculata and H. discus hannai , respectively. The results suggest that the PUFA of both n − 3 and n − 6 families seem to be essential for growth of H. discus hannai ; for H. tuberculata , however, growth enhancement appeared to depend largely on n − 3 PUFA.

Comparative studies on the nutrition of two species of abalone, Haliotis tuberculata L. and Haliotis discus hannai Ino: II. Amino acid composition of abalone and six species of macroalgae with an assessment of their nutritional value

Abstract This study was conducted to evaluate the nutritional value of protein in natural feeds for the two species of abalone, Haliotis tuberculata L. and Haliotis discus hannai Ino. The amino acid compositions of 6 species of macroalgae (Ulva lactuca, Chondrus crispus, Palmaria palmata, Alaria esculenta, Laminaria digitata and Laminaria saccharina) and of the whole soft body of these abalone were determined and compared. The effects of these algal diets on the free amino acid (FAA) profiles in the viscera and muscle of animals were investigated. To find a suitable index to evaluate the protein quality of natural diets for algivores, several indices were computed and correlated to the growth performance of abalone using correlation analysis. These two species of abalone have a very similar amino acid composition, indicating that they may have similar amino acid requirements. In all the selected algae, arginine may be the limiting amino acid, and in some instances methionine, threonine or histidine may be also limiting. Judging from the results of feeding test and amino acid analysis, P. palmata and A. esculenta seem to have the better amino acid pattern and availability among the selected algae. On the other hand, U. lactuca and C. crispus appear to be poor in their amino acid availability and/or pattern. Dietary treatments significantly affected the FAA profiles in animal tissues. The essential amino acid index (EAAI) and the degree of similarity (DS) of EAA patterns may not be applicable to evaluating the nutritional value of protein in natural feeds for the algivorous molluscs. Among the indices examined, the newly proposed index—balance and adequacy of free EAA in viscera (BAEAAv)—seems to be suitable for estimation of protein quality of natural feeds for abalone, because it takes into account the balance, adequacy and availability of EAA in natural diets.

A comparison of methods for tagging juvenile lobsters (Homarus gammarus L.) reared for stock enhancement

The identification of cultured animals on recapture is an integral part of any modern stock enhancement programme. In lobster (Homarus sp.) release studies this is particularly taxing due to moulting, the small size of juveniles and costs. This work compares five tagging methods with respect to survival and tag retention over three moults. These consisted of internally placed tags, i.e., visible implant elastomer and coded microwire tags, two external marks, i.e., rostrum ablation and hot branding, and one external tag, i.e., the polyethylene streamer tag. A total of 1440 individuals were used in the study. Elastomer, microtags and rostrum ablations were applied to two age categories, i.e., 1.5 (5–8 mm carapace length (CL)) and 7 month (12–16 mm CL), brands were given to 7 and 9 month (16–19 mm CL) animals while streamer tags were given 9 month old individuals only. Older juveniles tagged abdominally with microtags and elastomer showed high survival (97%) and tag retention (99–100%). The younger age class also responded positively to microtags (83% survival and 96% tag retention) but survival was significantly reduced to 68%, with obvious tag migration, when this group were tagged with elastomer. To date, rostrum ablation proved to be a poor external mark with 100% of juveniles in both age classes successfully regenerating a rostrum within three moults. Survival of branded juveniles was size specific with levels of 57 and 90% for 7 and 9 month juveniles, respectively. Visibility of the mark faded with successive moults due to repigmentation in the exoskeleton. Lobsters tagged abdominally with streamer tags showed high survivorship (99%) and high tag retention (100%). Occasionally, this tag appeared to interfere with the moulting process and prolonged the time taken to shed the exoskeleton at ecdyses. Based on these findings, implantation of elastomer into juveniles less than 10 mm CL and branding of individuals less than 15 mm CL is not advised. Branding and ablation are not recommended for long term tagging studies. The internally placed tags, i.e., visible implant elastomer and microtags would appear to be more suitable options.

A long-term mesocosm study on the settlement and survival of juvenile European lobster Homarus gammarus L. in four natural substrata.

To date, the natural substratum preferences of early benthic phase (EBP) European lobsters (Homarus gammarus) remain largely unknown. This study utilised a large scale mesocosm experiment to determine if the animal favours cobble ground, similar to its American counterpart (Homarus americanus), or has other substratum preferences. Postlarvae were provided with the choice of settling on four natural substrata: sand, coralline algae, mussel shell and cobble. Over a nine month period, the number and size of juveniles on each substratum was recorded, with loss of chelipeds used as an indication of social interaction. After a 30 day period, a non-random distribution of lobsters was observed on the four substrata. Juveniles were more abundant in substrata which provided pre-existing shelter in the form of interstitial spaces, i.e. cobble and mussel shell, than in sand or coralline algae. The survival of individuals from postlarvae to 30 day old juveniles ranged from 5 to 14% with surviving benthic recruits showing a clear mode at 6-8 mm carapace length (CL) in size distribution. The density of lobsters per m(2) of cobble remained relatively constant (18/m(2)) throughout the study period while the density of juveniles on mussel shell decreased significantly (35 to 5/m(2)). The size distribution of lobsters on each substratum also varied with time. By the conclusion of the trial, lobsters found in mussel shell had a mode of 8-10 mm CL within a range of 6-14 mm CL while those in cobble had a mode of 10-12 mm CL within a range of 8-24 mm CL. Overall, the results underline the importance of shelter-providing habitat such as cobble or crevice-type substrata to EBP European lobsters. They also confirm that for a shelter-dwelling animal such as a lobster, the physical structure of the habitat is a key factor in determining both the size and number of its inhabitants.

Genetic variation at three polymorphic loci in wild and hatchery stocks of the abalone, Haliotis tuberculata Linnaeus

Abstract The abalone, Haliotis tuberculata, is a gastropod mollusc of commercial importance in Europe with considerable potential for aquaculture. A wild population of H. tuberculata from Guernsey, Channel Islands was compared to two hatchery populations; one an F1 stock produced by a hatchery in Guernsey, the other an F3 stock cultured at the Shellfish Research Laboratory (SRL) at Carna, Ireland. The F1 and SRL stocks were each derived from the Guernsey wild population and reproductively isolated from this population for one and three generations, respectively. The three populations were screened for allozyme variation at three polymorphic loci, Gpi, Pgm and Mdh, using starch-gel electrophoresis. When compared with the wild population, both the F1 and SRL samples were very similar in terms of mean effective number of alleles per locus and levels of heterozygosity. However, the SRL stock did show a reduced number of rare alleles when compared to the F1 and Guernsey samples but without showing any evidence of inbreeding or reduction in levels of heterozygosity. Effective population size was calculated from direct census (Ne) and temporal changes in allelic frequencies ( N k ). Ne was estimated to be 48 and 54.5 for SRL and F1, respectively, whereas calculated N k was 21.4 and 23.9, respectively.

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.

An overview of the LEAR (Lobster Ecology and Recruitment) project: results of field and experimental studies on the juvenile ecology of Homarus gammarus in cobble

Field and experimental studies were undertaken in four European countries on clawed lobster (Homarus gammarus) ecology and recruitment. The aims were to assess: (a) abundance of early benthic phase (EBP) lobsters and other benthic species at cobble sites, (b) the effect of these species on EBP growth and survival, and (c) influence of these factors on recruitment and/or viability of restocking. Suction sampling of cobble sites revealed a wide diversity and abundance of potential competitors but no EBP lobsters. Hatchery-produced EBPs were therefore used for small-scale mesocosm experiments. In nature, predation on EBP was rapid without shelter, whereas in-vitro mortality, growth, and behaviour experiments showed that cover potentially increases survival. Scarcity per se may not completely explain the apparently absence of EBP, given that not a single EBP lobster was located either during this study or during any other of the extensive benthic investigations. The present paper discusses the implications of their apparent absence and whether it arises because EBPs are very scarce, cannot be captured by suction sampling, are not within lobster habitat, or occupy a specialized niche within adult habitat outside the range of current sampling methods.