Academic literature on the topic 'Haliotis rubra'

Several Victorian populations of the abalone Haliotis rubra were studied. A comparison was made of relationships of the dependent variables, shell width, shell height, foot weight and total weight with shell length of abalone collected from several sites at different seasons. Male and female H. rubra were morphometrically similar. In contrast, the morphometrics for abalone collected from the same site at different times were significantly different, as were the morphometrics of abalone collected from different sites at the same time. Weight yields (foot weight relative to total weight) from Portsea and Apollo Bay were highest in winter and lowest in summer. This correlated with the known reproductive cycle in H. rubra, suggesting a relationship of gonad fullness and somatic tissue weight. Morphometric heterogeneity was attributed to differences in growth rates between sites. Growth rates were estimated at three sites and significant between-site variation was shown. At Mallacoota, H. rubra tagged with a threaded wire tag yielded lower estimates of growth rate than those to which tags were affixed with glue. Differences in growth rate, exclusive of tagging method, were attributed to difference of exposure between the study sites.

The results of tag-recapture studies on three Victorian populations of the abalone Haliotis rubra showed that the frequency of growth checks in the shells of individuals was not annual. The use of shell growth checks as a method for age determination of H. rubra is not reliable because of variation in the frequency of growth checks between populations and the inability to count growth checks in the shells of most individuals.

Results of a pilot study to assess the utility of settlement collectors for measuring settlement intensity of abalone in the field are presented. The collectors, consisting of transparent PVC sheeting, were conditioned in sea water before being deployed on the seabed in habitat containing adult and juvenile abalone. Collectors were recovered and replaced at intervals of between one and eight weeks over a 12-month period. The optimum period was found to be between two and four weeks. Two discrete peaks in settlement were recorded, coinciding with the annual spawning activity of two species, Haliotis rubra and Haliotis laevigata. Intensity of settlement in each peak was equivalent to 114 m-2 and 45 m2 respectively.

Marine derived drugs are emerging with promises to positively intervene in a range of diseases including viral, bacterial, fungal, and to even some forms of cancers. Hemolymph of several molluscs are of particular interest for their immunomodulatory properties that enhance their anti-microbial and anti-cancerous mechanisms. Our research aims to uncover the immunological effects of Haliotis rubra hemolymph, purified hemocyanin and hemolymph permeate. Their immunomodulatory properties can be key to treating Herpes Simplex Virus -1, HSV-1, infected patients and prostate cancer patients. In this study, we cultured HaCat cells and Human oral primary and prostate cancer cell line (PC-3) to observe immunomodulatory effects of the extracts on such form of cancer. Treatment with variable concentrations of abalone sera, purified hemocyanin and the sera/hemolymph were carried out. Results show a 50% inhibition in Interleukin-6 (IL-6) expression, 21% inhibition in Interleukin-8 (IL-8) . There is an observed inhibition of IL-6 expression in permeate, AH and sera treated PC-3. Additionally, the effects also extend to IL-8. The most significant results were obtained for primary oral keratinocytes treatment with the abalone sera yielding a sharp 35 fold increase in IL-8 concentration and 23 fold increase in IL-6 concentration as compared to the untreated control. To summarize: hemolymph, purified hemocyanin and hemolymph permeate targets IL-6 and IL-8 , that will potentially help HSV-1 infected and prostrate cancer patients. Whole hemolymph permeate induces highest degree of cytokine modulation in all cell types. The permeate is found to predominantly consist of hemocyanin fragments of various sizes . Therefore, broken hemocyanin fragments, rather than whole hemocyanin molecule, has greater immunomodulatory properties. HaCat cells do not fit as a model for IL-6 and IL-8 modulation studies, although targeted modulation of these cytokines are also exhibited here on hemolymph treatments.

This thesis focussed on the effects of a range of trace metals on various stages of Haliotis rubra development. The trace metals assessed in this thesis were the essential metals Cu, Zn and Fe; and, the non-essential metals Hg, Cd and Pb. Copper and Hg proved to be the two most toxic metals to the life stages of H. rubra studied. The concentrations affecting normal development of the fertilised egg exposed for 48h showed a decreasing order of toxicity with 48hEC50 recorded at 7µg Cu/L, 20µg Hg/L, 42µg Zn/L, 4,102µg Fe/L, 4,515µg Cd/L, and 5,111µg Pb/L. Settlement and metamorphosis occur in normal larvae when aged 5 days, and exposure of the 5 day old larvae to the metals for 48h resulted in impaired crawling success at 128µg/L Cu and Hg, and 1250µg Cd/L. Settlement was inhibited after exposure to 128µg Cu/L, 32µg Hg/L, and 1250 Cd/L. Metamorphosis of larvae 96h after exposure was inhibited by 32µg Cu/L, 512µg Zn/L, 32µg Hg/L and 625µg Cd/L. The rate of meta morphosis was enhanced after exposure to Cu and Hg at 0.5µg/L and 64 - 256µg Zn/L. Exposure to Zn at concentrations 64, 128 and 256 µg Zn/L caused an increased rate of settlement and metamorphosis. Juvenile H. rubra exposed to the six metals for 96h were most sensitive to Cu, which produced a 96hLC50 of 87µg Cu/L compared to Hg with a 96hLC50 of 173µg Hg/L. Juvenile H. rubra were relatively insensitive to Zn and Cd with the 96h LC50 of 1730µg Zn/L and 3700µg Cd/L, respectively. Exposure to individual solutions of Cu, Zn, and Cd for 28 days resulted in juvenile H. rubra bioaccumulating significant concentrations of metals in the visceramantleedible foot muscle. Accumulation of Hg was greater in the mantle-viscera-edible foot muscle. Following exposure, depuration in clean seawater for 28 days produced varying decreases in metal concentrations for each tissue compartment. Sodium-potassium activated ATPase (Na+,K+-ATPase) activity in the gills of juvenile H. rubra was significantly affected following expos ure to the trace metals for 28 days, with a decreasing order of effect on enzyme activity of Hg-Cu-Cd-Zn. Depuration of H. rubra in clean seawater for 28 days resulted in the recovery of Na+,K+-ATPase activity to varying degrees. The recovery of ATPase activity was more efficient following exposure to Cd-Zn-Cu-Hg. The overall results of this thesis provide initial baseline information to evaluate the sensitivity of H. rubra to trace metal toxicants, and these results may be utilised by regulators for establishing marine water quality guidelines to protect H. rubra and other abalone species in their natural habitats.

Hemocyanin (HrH) has been shown to possess antiviral activity against HSV-1 by selectively binding to viral glycoproteins (gB, gC, gD). Its large size however precluded the application of this protein, which required identifying smaller structure with antiherpetic ability. Aiming to this goal, the amino acid sequences and theoretical 3D structure of two isoforms that constitute HrH were determined by this study for the first time. Eight of the smallest intrinsic structure of HrH, herein called functional units (FUs), were identified in each isoform. Subsequently, the gene encoding HrH was cloned and used to establish the first recombinant bacterial expression system of HrH. All 16 FUs were expressed individually at the optimised temperature (16°C) with a glutathione S-transferase (GST) fused at the N-termini, and were exploited to reveal direct protein-protein interaction between HrH and HSV-1 glycoproteins by the GST pull-down assay. Different degrees of binding amongst three HSV-1 glycoproteins (gB>gD>gC) were found implying that the antiviral activity of HrH was partially preserved in the recombinant FUs. Amongst 16 FUs, HrH2-FUb demonstrated the most consistent binding abilities. Therefore, it was hypothesised to be the prime candidate for future study. The investigation of exploiting E. coli to fabricate HrH2-FUb by a scale-upped system was also conducted in this study. The specific affinity between glutathione and the fused GST tag was utilised to extract the GST-HrH2-FUb by affinity chromatography. Size-exclusion chromatography was employed to further purify the samples eluted from the affinity column. However, the generation of the low molecular weight GST-tagged HrH fragments revealed the limitations associated with the current bacterial system. Taken together, this study provided essential knowledge to facilitate the discovery of antiherpetic compounds from HrH, which could become novel treatment options, for HSV-1 infection in the future.

The use of an incorrect growth model in fisheries management may lead to inaccurate predictions about stock productivity. In Australia, three non-nested size-based growth models are generally used to describe the growth of abalone populations: the von Bertalanffy, Gompertz and inverse logistic. The models differ in their description of growth, especially in the juvenile phase. However, while data on juveniles has the greatest discriminating power between models, in reality good data on size distributions and growth of juveniles is uncommon, and this leads to ambiguity in model selection. I use a large dataset (from the Tasmanian Aquaculture and Fisheries Institute) describing sizes and growth of juvenile and adult size classes to systematically resolve model ambiguity for blacklip abalone (Haliotis rubra) populations in Tasmania. Modal progression analysis of bimonthly data collected over two years from the same site identified two cohorts of juveniles between 10 – 75 mm shell lengths. The best statistical model was selected using standard statistical model selection procedures, i.e. Akaike’s Information Criteria and likelihood ratio tests. Despite the large data set of 4,259 specimens, model selection remained statistically ambiguous. The Gompertz was selected as the best statistical model for one cohort and the linear model for the other. Interestingly, the biological implications of the best fitting Gompertz curve were not consistent with observations from aquaculture. The study revealed that slight differences in data quality may contribute to ambiguity in statistical model selection and that biological realism is also needed as a criterion for model selection. The robustness of different growth models to sampling error that is inconsistent between samples was explored using Monte Carlo simulation and cross model simulation. The focus was on simulated length increment data largely from adult size classes (55 – 170 mm shell length) as these data are more commonplace than data from juveniles. Results confirm that the two main shortcomings in length increment data contributing to model misspecification were (i) poor representation of juvenile size classes (< 80 mm) and (ii) low sample size (n<150). Results indicate that when negative growth data are included in the von Bertalanffy model, K increases and L∞ decreases. In reality the true description of growth remains unknown. Given realistic length increment data, there is a reasonable probability that an incorrect growth model may be selected as the best statistical model. This is particularly important, because this study indicates there is a different magnitude of error associated with each growth model. The important overall finding is that while it is possible to make incorrect model selections using customary statistical fitting procedures, departures from biological reality are lower if the incorrect inverse logistic model is selected over the incorrect von Bertalanffy or Gompertz model. The selection of the most appropriate growth model was further tested by fitting each of the three growth models to length increment data from a total 30 wild populations. The inverse logistic was the best statistically fitting model in 23 populations. The combined results from data on the growth of juveniles, cross model simulation, and fitting to data from numerous wild populations systematically revealed that the inverse logistic model was the most robust empirical representation of blacklip abalone growth in Tasmania. With this confidence in the selected model, it was then possible to address two urgent ecological and management issues related to stock productivity; the effect of climate change on growth rates and the success of broad-scale management controls in the presence of fine-scale variability in growth rates. The effect of ocean warming on the growth rates of blacklip abalone populations was explored from the analysis of length increment data from 30 populations across a range of water temperatures. Measurements based on the growth rates of juveniles did not reveal a clear negative relationship between temperature on growth. A decrease in growth rate was observed however it may not be directly attributable to temperature but may be forced by the onset of maturity, which does appear to be directly influenced by temperature. Fine-scale estimates of growth rate are an implicit aspect of evaluating the success of broad-scale management control such as Legal Minimum Length (LML) for harvesting. In reality, it is not possible to obtain fine-scale growth rates given the expense of obtaining empirical length increment data at fine spatial scales. Therefore, an alternative approach was developed that exploited the correlation between the parameters of the inverse logistic model and size at maturity. The approach generated theoretical, fine scale growth parameters and population-specific LMLs for 252 populations around Tasmania. Using population specific size limits, results revealed that 46 populations were unprotected by the current Legal Minimum Length (LML) settings, potentially exposing those populations to overexploitation. The majority of unprotected populations were located in the south west, a region that is economically valuable. An important recommendation from this thesis is that the LML of the economically valuable south-west region should be increased in order to achieve the management goals of the fishery.

The fishery for Haliotis rubra or blacklip abalone is Tasmania's most valuable fishery, with a landed value of approximately $50 million in 1988. Despite the fact that catch rates have remained relatively stable since 1970, commercial abalone divers in Tasmania are expressing grave doubts about the long term sustainability of this fishery. The aim of this study was to document the biology of H. rubra and the nature of the fishery in order to re-assess the fishery biology of this species, and current methods of stock assessment. For this purpose, a broad ranging study of the structure and dynamics of the pre-recruit, and recruited, abalone populations has been completed. The ramifications of the results of this study have been explored using a model which simulates the dynamics of a single unit stock of abalone. Finally, in the light of these results I have re-assessed historical trends in catch per unit effort within the Tasmanian abalone fishery. These results show that the structure of7-J. rub-ra-/populations is more dynamic than generally recognized, with high levels of recruitment and mortality amongst juveniles. Juveniles are cryptic, emerging onto the surface of the reef where they are vulnerable to commercial exploitation, as they mature. The emergent adult population is relatively stable being characterized by lower levels of growth and mortality. On a spatial scale of 10-100 m the adult population is relatively mobile, exhibiting patterns of movement which could lead to aggregation and dispersion in response to changes in population pressure. In contrast the scale of larval dispersal is apparently restricted to lO's of meters. These results suggest that the scale of a unit stock in this species can be measure on the scale of lOO's of meters and explain the spatial heterogeneity which is characteristic of abalone stocks. Commercial divers have a high degree of knowledge about the spatial distribution of abalone and target known aggregations of stock. Divers allocate their effort according to a range of priorities, one of which is the expected catch rate. When this characteristic of the fishery is combined with the biology of the species it is apparent that, on the spatial and temporal scale of commercial catch and effort data, catch rate is unlikely to be a reliable index of stock abundance. A re-assessment of the catch per unit effort data confirms the conclusion, that a wide range of factors determine catch rate trends in the commercial fishery. For this reason standard methods of stock assessment are not applicable to the fishery. Developing new techniques of stock assessment and management, based on survey data and detailed knowledge of the relationship between stock and recruitment offers the best long term hope for managing this fishery.

A study was initiated to determine the effect of selected factors on the reproductive development and early life history of blacklip (Haliotis rubra) and greenlip (H. laevigata) abalone relevant to their wild fisheries or aquaculture. In both species, the rate of gonadal and larval development was proportional to water temperature, but the relationship was not simply multiplicative, rather there was a critical minimum water temperature below which development was arrested, known as the Biological Zero Point (BZP). The BZP for gonadal development was 7.8 degrees C for H. rubra and 6.9 degrees C for H. laevigata. Corresponding BZP values for larval development were 7.8 degrees C and 7.2 degrees C, respectively. Observations of larval development relative to temperature enabled a description of the Effective Accumulative Temperature (EAT; the cumulative difference between the culture temperature and the BZP, calculated hourly) for prominent developmental stages. The difference between the EAT for metamorphic competence and that for hatchout (i.e. the interval during which the larvae remain in the water column) was 1120 and 1160 EAT degrees C-h for blacklip and greenlip abalone, respectively. These values, in combination with water temperature data, enable the prediction of the dispersal window for each species in situ. Spawning performance of blacklip and greenlip abalone was also affected by temperature, with both sexes of each species producing significantly more gametes when conditioned at 16 degrees C than 18 degrees C. Sperm production of H. rubra was an order of magnitude greater than that of equivalent sized H. laevigata. There was no apparent difference in the lipid or fatty acid composition of the ovary or testis between pre- and post-spawning animals of either species, presumably because of partial spawning and/or incomplete resorption of the gonad. Likewise, a 4 degrees C difference in conditioning temperature (i.e. 14 degrees C vs 18 degrees C) was insufficient to elicit changes in tissue biochemistry. There was a significant interaction between sperm density and contact time on the fertilisation success of eggs from both blacklip and greenlip abalone. Prolonged exposure (> 1200 s for H. rubra and > 480 s for H. laevigata) to concentrated sperm (i.e. 107 ml-1) resulted in egg destruction. Analysis of CoVariance of F50 values (i.e. the sperm concentration required for 50% fertilisation, derived from the linear regression of logit (proportion of eggs fertilised) versus sperm density) between species across a range of contact times demonstrated that contact time had a significant effect (p < 0.001) whereas species did not (p = 0.22). The lack of a species effect suggests that the fertilisation potential of blacklip and greenlip abalone eggs are similar, at least across the range of sperm densities and contact times used.

This thesis examines the release and long-term (>2 years) survival and growth of hatchery-reared larval and juvenile blacklip abalone (Haliotis rubra Leach), on natural coastal reefs in New South Wales (NSW), Australia. Abalone are demersal, relatively sedentary, marine molluscs, that support important commercial, recreational and indigenous fisheries in numerous locations around the world. This thesis was developed in response to substantial depletions of local populations of H. rubra along >250 km of the NSW coast and the ineffectiveness of traditional fisheries management strategies to arrest these declines. These failures stem from demographic processes, common to haliotids, that limit their ability to re-establish populations that have been subject to substantial decline. A series of laboratory and field experiments were designed and conducted to examine a range of factors, and their interactions, that can have substantial affects on the success of releasing hatchery-reared H. rubra to natural reefs. The principal finding was that successful stock enhancement of local populations can be achieved, and the greatest value of a stock enhancement strategy is likely to be gained where the primary management objective is rebuilding depleted natural populations. Methodology, baseline targets and other recommendations are provided that would aid implementation of a stock enhancement management strategy to complement current traditional fisheries management approaches. The objectives of the research in this thesis were to: 1) investigate factors affecting the settlement, metamorphosis and early growth of H. rubra larvae; 2) batch-tag larvae and juveniles to enable their identification when recaptured; 3) develop and test methods for the successful release of larvae and juveniles; 4) develop a monitoring strategy to estimate the abundance of released abalone through time; 5) quantify long-term survival and growth to provide minimum targets for stock enhancement; 6) determine the impact of releasing juveniles on wild populations; 7) provide a bio-economic analysis and; 8) provide recommendations for the implementation of a stock enhancement management strategy for H. rubra in NSW. The release of larvae to natural reefs requires them to be exposed to a number of handling and transport processes. In laboratory experiments conducted in this thesis, greater proportions (commonly >75%) of larvae settled, metamorphosed and grew to larger sizes when exposed to settlement substrata for longer periods of time (>24 hours). There was a lower settlement response in the presence of water flow, although the addition of gamma-aminobutyric acid (GABA) increased the proportion of larvae that settled within short periods of time, i.e. 25 - 100% more in ≤60 sec.. Larvae were resistant to simulated handling and transport processes, indicating their utility for stock enhancement. The tagging of larvae and juveniles is fundamental to assessing the success of an enhancement program. Hatchery-reared H. rubra larvae and juveniles were successfully batch-tagged. The tagging procedures provided an indelible mark, enabling the identification of individuals once recaptured, and unambiguous differentiation from wild conspecifics. Successful batch-tagging was also critical for the assessment of subsequent field experiments undertaken in this thesis. Larvae were batch-tagged with the epi-fluorescent dye, calcein. Laboratory experiments demonstrated that the tagged larval shell was clearly visible in the spire of juvenile shells after >250 days. The recapture of tagged and released larvae from natural reefs, >500 days after release, confirmed the persistence of this tag. A reliable and cost-effective method for batch-tagging juveniles was through the use of a commercial diet that resulted in the distinctive blue-green colouration of the shell. The presence of this blue-green colouration differentiated released juveniles from those in naturally occurring populations, could be observed with the naked eye, without the need for a UV light source, and persisted on the spire of individuals for >900 days. Methods of releasing H. rubra larvae and juveniles were developed and tested in a series of laboratory and field experiments. A deployment pump that included a pressurised container and hose, was used to successfully release larvae to natural reefs. The addition of GABA and refrigeration during simulated transport, and the stage of release from the deployment pump, significantly affected the number of larvae delivered through the pump. The release of larvae to physical shelters on the reef significantly increased the numbers that settled, and their survivorship. There was added complexity in the process of releasing juveniles than with that for larvae. The use of a deployment device (PVC tube, ~300 x 125 x 65 mm), that was securely placed onto the substratum, was integral to the successful release of juveniles. Use of these devices in a standard release protocol ensured the limited physical handling of juveniles and provided a simple, cost effective and efficient method for the release of large numbers to areas of natural reef. A monitoring strategy was developed and tested to enable accurate estimates of the abundance and therefore survival of released H. rubra ,of a variety of life history stages, to be measured. The abundance of H. rubra juveniles is difficult to accurately assess on natural reef because of their cryptic distribution among complex topography in rocky habitat. As a consequence, the precision and relative accuracy of methods to sample released abalone was examined in a series of field experiments, and included the dispersal of juveniles from deployment devices. The most accurate and precise estimates of the number of H. rubra surviving were detected using methods that disturbed the habitat, i.e. turning over boulders, within a release location, and multiple sampling approaches were required to measure the abundance of abalone of different sizes. For larvae, the collection of boulders provided more accurate estimates of abundance than samples taken using a venturi-lift. For juveniles, thorough searching of boulder substratum and more replicates provided more accurate estimates of abundance. Further, stratified sampling among habitats after natural disturbance revealed greater densities of H. rubra in 'solid habitat', and spatially stratified sampling indicated juveniles can disperse up to 10 m from their release point in <8 days. The success of a stock enhancement strategy is determined by the net value it adds to a population. This necessitates estimates of the long-term survival and growth of released individuals, the impact released individuals have on the extant population, and the bio-economic feasibility of an enhancement strategy. Rates of survival and growth varied substantially among releases and locations. However, the long-term survival of batch-tagged and released larvae and juveniles demonstrated that local populations of abalone could be enhanced with significantly greater numbers of juveniles surviving at multiple release locations than at control locations after >2 years. The release of juveniles had no detectable affect on the mean total number of wild conspecifics or wild recruits over these time scales. Long-term survival of released larvae and juveniles was generally low (<0.03%, range: 0 - 0.03% and; <4%, range: 0 - 10%, respectively). However, at three of the twelve juvenile release locations it exceeded that expected for wild abalone (range: 4 - 10%). Growth rates of released juveniles (range: 18 - 47 mm.yr-1) indicated that they would generally reach sexual maturity within 2 - 3 years and exceed the minimum legal length within 4.5 years. A deterministic, bio-economic model was used to analyse the net present value (NPV) of a stock enhancement strategy for H. rubra in NSW, against an alternate investment return of 10% p.a.. Positive NPV occurred where long-term survival was >4% and where growth rates were higher than average rates reported in this research, or beach price exceeded $AUD 34.kg-1. Low rates of long-term survival of larvae suggests their large-scale release is unlikely to provide a viable stand alone option to successfully enhance local populations of H. rubra. The survival and growth of released juveniles, to replicate locations, demonstrated that depleted local populations of H. rubra in NSW can be enhanced, and that a stock enhancement program can complement the NSW Abalone Fishery management strategy. The success of any large-scale stock enhancement program will be determined by the definition of its objectives. Outcomes from this thesis suggest that the greatest value of a stock enhancement strategy will be gained where its primary objective is to rebuild depleted populations, rather than optimise commercial yield through the release of individuals to overcome recruitment limitation or to harvest released individuals at a larger size. The decision to implement such a program, including explicit description of its primary objective, is required to be made among well-informed representatives of all stakeholders. Further, this decision needs to be made with a thorough understanding of the current biological structure of the populations, including the nature of population depletions, the economic status of the fishery and in light of current, complementary and alternative management arrangements that may provide comparative increases in net value.

A study was initiated to determine the effect of selected factors on the reproductive development and early life history of blacklip (Haliotis rubra) and greenlip (H. laevigata) abalone relevant to their wild fisheries or aquaculture. In both species, the rate of gonadal and larval development was proportional to water temperature, but the relationship was not simply multiplicative, rather there was a critical minimum water temperature below which development was arrested, known as the Biological Zero Point (BZP). The BZP for gonadal development was 7.8 degrees C for H. rubra and 6.9 degrees C for H. laevigata. Corresponding BZP values for larval development were 7.8 degrees C and 7.2 degrees C, respectively. Observations of larval development relative to temperature enabled a description of the Effective Accumulative Temperature (EAT; the cumulative difference between the culture temperature and the BZP, calculated hourly) for prominent developmental stages. The difference between the EAT for metamorphic competence and that for hatchout (i.e. the interval during which the larvae remain in the water column) was 1120 and 1160 EAT degrees C-h for blacklip and greenlip abalone, respectively. These values, in combination with water temperature data, enable the prediction of the dispersal window for each species in situ. Spawning performance of blacklip and greenlip abalone was also affected by temperature, with both sexes of each species producing significantly more gametes when conditioned at 16 degrees C than 18 degrees C. Sperm production of H. rubra was an order of magnitude greater than that of equivalent sized H. laevigata. There was no apparent difference in the lipid or fatty acid composition of the ovary or testis between pre- and post-spawning animals of either species, presumably because of partial spawning and/or incomplete resorption of the gonad. Likewise, a 4 degrees C difference in conditioning temperature (i.e. 14 degrees C vs 18 degrees C) was insufficient to elicit changes in tissue biochemistry. There was a significant interaction between sperm density and contact time on the fertilisation success of eggs from both blacklip and greenlip abalone. Prolonged exposure (> 1200 s for H. rubra and > 480 s for H. laevigata) to concentrated sperm (i.e. 107 ml-1) resulted in egg destruction. Analysis of CoVariance of F50 values (i.e. the sperm concentration required for 50% fertilisation, derived from the linear regression of logit (proportion of eggs fertilised) versus sperm density) between species across a range of contact times demonstrated that contact time had a significant effect (p < 0.001) whereas species did not (p = 0.22). The lack of a species effect suggests that the fertilisation potential of blacklip and greenlip abalone eggs are similar, at least across the range of sperm densities and contact times used.