Hatchery lobsters innately develop many behaviours which help them survive in the wild, even in captive rearing environments which lack the complexity of natural seabeds. However, these inherent qualities may well be complemented and enhanced by ecological conditioning targeted to promote traits that are likely to have a positive impact on the prospects of released lobsters settling and integrating into complex wild ecosystems. To this end, the Hatchery has investigated the shelter-seeking behaviours of lobsters following simulated release, finding that previous exposure to both tunnel structures and predator scents reduce the time taken to seek refuge on the seafloor. We have also identified ways in which sub-sea building materials can be modified to provide juvenile lobsters with burrows to inhabit, and developed release methods which improve settlement success.
Our research into sea-based container culture continues to show the promising potential of the method to provide a natural acclimation step for cultured lobsters ahead of their release. We are continuing to search for ways we can make our lobsters better prepared and adapted for life in the wild, and are currently examining whether aquaria colouration can be manipulated to reduce post-release predation vulnerability by stimulating shell pigmentations which provide better camouflage in natural environments.
Juvenile Settlement and Release Environments
2016-2017: Sara Mynott – University of Exeter, PhD research. ‘How rearing conditions influence camouflage in juvenile lobsters’.
Funded by NERC.
Many animals change colour for camouflage, but the applied benefits of this are only just being realised. Following crashes in the Scandinavian European lobster (Homarus gammarus) populations coupled with local declines across Europe, hatcheries were established to help enhance localised lobster stocks. Juvenile lobsters are reared through the most vulnerable stages before being released into the wild. Research has focussed on releasing healthy juveniles into suitable habitats, but little consideration has been given to matching individuals to their release site and how this could be enhanced through hatchery practices. Working with the National Lobster Hatchery, we have identified the potential for altered hatchery housing to enhance cryptic coloration in reared lobsters. By allocating individuals to different backgrounds and quantifying changes in their appearance through image analysis, lobster camouflage can be modelled to predator vision. Early results indicate that background-matching could be used to enhance juvenile survival on release, with the potential to benefit both lobster conservation and fisheries.
2016: Olivia Cole – University of Gloucestershire, BSc project. ‘The effects of rearing techniques on settling behaviour and substrate preference of early benthic phase European lobsters (Homarus gammarus) in the presence of chemical predator cues.’
This study looked at whether the behaviour of hatchery-reared juveniles when faced with predator cues was better suited to successful benthic settlement when rearing in a sea-based container culture system (‘sea-grown’), as opposed to traditional rearing in hatchery tanks relatively deficient in sensory stimuli (‘tank-grown’). For both sea- and tank-grown treatments, lobsters propensity to take shelter (the behaviour deemed least at risk of predation), freeze out of shelter, or locomote out of shelter (the behaviour deemed most at risk of predation) were assessed across four environment scenarios; the presence and absence of chemical odours from wild predators (‘predator cues’), each at 20% and 40% cobble coverage. Sea-grown lobsters were significantly more likely to take shelter compared with tank-grown equivalents when predator cues were present at 40% of cobble cover (p=0.004), although not at 20% cobble cover (p=0.936). Cobble coverage had no overall effect on likelihood of juveniles to take shelter (p=0.414). These results suggest that on-growing in containers at sea provides hatchery-reared juvenile lobsters with ecological stimuli that promotes behaviours likely to improve settlement success upon wild release.
2015-2016: Laura Bryans – Plymouth University, BSc project. ‘Substrate-specific preferences of juvenile Homarus gammarus in Cornwall.’
This study builds on previous work to try to establish the substrate preference of stage V European lobsters, to determine the areas in which hatcheries should release their juveniles into the sea. At stage V the European lobster is a truly benthic organism and therefore, substrate type will influence the survival of this species at this age. Forty stage V lobsters were given a choice between four substrates; pebbles, granules, coarse sand grains and medium sand grains. Juveniles were found to prefer the pebble substratum, spending the longest total period of time and longest individual period of time in this substrate during the experimental period. The results obtained may be because the pebbles provide pre-existing shelter in the form of interstitial spaces which can protect the lobsters from predation and cannibalism, as well as creating a darkened habitat which this species seems to prefer. However, a review of the current literature indicates that a combination of hard rocky substratum and finer substratum, in which the lobsters can construct burrows, may be the most beneficial habitat type for this species.
2015: Dan Sankey – Independent research funded by the National Lobster Hatchery. ‘Environment influences post-release competition and settlement in lobsters: comparing behaviours of aquaria-reared and maricultured hatchery juveniles’.
Findings of early benthic phase (EBP) European lobsters (Homarus gammarus) in the wild are scarce, which presents lobster hatcheries with a challenge in providing the environmental requirements for successful juvenile development. Attempts have been made to enrich hatchery-reared individuals with environmental cues, to try to understand and promote natural behavioural repertoire of lobsters released for stocking purposes. Studies of the American lobster (Homarus americanus) suggest that settling EBP individuals find, excavate and compete for shelter in which they will remain for one/two years, and their importance is demonstrated by trials which show that cultured individuals of both homarid species are usually predated within minutes of release if they fail to take shelter. We compared behaviours that are important to the immediate post-release survival of EBP lobsters in two groups of cultured juveniles; those on-grown in the wild (reared in sea-based containers providing a range of natural stimuli), and hatchery controls (reared in traditional mono-layered trays in shallow aquaria). Behavioural criteria assessed were: latency to shelter; sheltering duration; and the outcome of agonistic interactions in mesocosm environments. Compared to hatchery controls, total shelter duration was significantly higher among wild on-grown lobsters, while latency to shelter and shows of aggression during agonistic interactions were also more frequent among wild on-grown lobsters (although differences were non-significant). Our results suggest that rearing environment plays a significant part in the behavioural development of cultured lobsters, and that environmental enrichment is likely to have a positive effect on the post-release survival of hatchery-reared H. gammarus. We propose that on-growing in wild enclosures may be useful as an important ecological conditioning step for stocked lobsters that will improve settlement success following release.
2014-15: Joe Augier – Cornwall College, BSc project. ‘Predicting optimum release sites for stocked juvenile European lobster (Homarus gammarus) using ecogeographical data.’
The use of species distribution models has gained much momentum in recent years with a variety of statistical approaches being employed to better inform species management and conservation. In this study, the maximum entropy model was employed through the software MaxEnt (version 3.3.3k) by Phillips et al. (2006) to predict spatial distribution of juvenile lobster (Homarus gammarus) with the aim of providing suitable release sites for the National Lobster Hatchery. Juvenile lobster presence location was sampled from the Padstow Bay area and plotted within a GIS map encompassing the target areas of St Austell Bay and Falmouth. In addition to presence, plots within the GIS map were various environmental layers believed to have varying effects on species distribution. MaxEnt was then used to extrapolate environmental conditions located at lobster presence plots throughout the GIS map thereby predicting similar locations throughout the range of the whole area. Results showed a significant relationship between juvenile presence and depth (preferred 20m depth) with slope having the second greatest effect to the overall model. Aspect and terrain ruggedness also played a role in the generation of the model but ultimately had minimal contributions to the final output. While ultimately successful in producing habitat suitability maps the study suffered from severe sampling bias due to a change in the statistical approach. This had the effect of biasing predicted species distribution to the north coast Padstow Bay area and although the south coast area does show predicted habitats it is constrained by the lack of south coast sampling.
2014: Hazel Munt – University College Cork, MSc thesis. ‘Habitat suitability for stage IV European lobsters (Homarus gammarus (L.)) in Padstow, England, for long term stock enhancement.’
Acoustic sidescans have become a popular and useful tool to classify benthic habitats. Many Marine Conservation Zones (MCZ) were classified and managed using sidescans to understand the habitats and their changes over time. The coastal waters around the MCZ Padstow and Surrounds, in Southwest England, sustain a diversity of marine habitats and also support a wide range of anthropogenic activities. This area was deemed as a suitable site for one of the new MCZs. However, the information on the geomorphology and benthic habitats of the area was sparse. Such information was needed by the National Lobster Hatchery (NLH), who use the area to release hatchery reared juvenile lobsters. Acoustic sidescans were conducted using a SeaKing Towfish 675 kHz, and ground truthing of these scans were conducted using a GoPro HERO and a Bowtech colour inspection camera with 1 LED lamp. In total three data sets were collected: (i) Backscatter data; (ii) Video data and photographs and (iii) Ecological knowledge. Textural analyses of backscatter segmented the seafloor into geomorphological classes by identifying the grain size and reflectance texture. Ground truthing was then used to identify species and the two were used to classify habitat types according to European Nature Information System (EUNIS). In total, 3.677 km2 were identified as suitable for juvenile lobsters and 4.574 km2 were deemed completely unsuitable with an area of 2.274 km2 which could sustain small populations. By understanding the nature of both the geomorphology and the habitats, the NLH can locate suitable habitats and focus on releasing juveniles in these areas. With this in mind the NLH can, in theory, increase the survival rate of released juvenile lobsters. A sustainable lobster population would be clearly beneficial to the commercial lobster fishermen and the industry in general.
2011: Alex Ferguson – University of Exeter, MSc thesis. ‘The effect of experience on the settling behaviour of early benthic phase European lobsters (Homarus gammarus) in the presence of chemical predator cues.’
2011: Dan Brewer – Cornwall College, Marine Aquaculture FdSc dissertation. ‘Shelter preference in relation to juvenile European lobster (Homarus gammarus).’
2010: Phil Latto – University of Southampton, MSc thesis. ‘Early benthic phase habitat use by European lobsters (Homarus gammarus) along the southern coast of the United Kingdom.’
For many years it was believed that early benthic phase (EBP) European lobsters (Homarus gammarus) occupied a niche similar to its American relative (H. americanus) in the interstitial spaces between a cobble substratum. The lobster ecology and recruitment project, a trans-European study in 1997, raised doubts that this was the case, and the habitat preferences of newly settled lobsters have yet to be described accurately. The focus of this investigation was to determine the habitat preferences of hatchery reared EBP H. gammarus in experimental conditions, focusing on the sediment preferences and the shelter choices separately. The study used four substrata classes; mud, sand, gravel and a plastic control. Four shelter classes were investigated; no shelter, a plastic control, small rocks and shells as well as large rocks and shells. The sediment preference experiments found that the lobsters were observed significantly more on the mud substratum than any of the others. Gravel was occupied most often in the absence of mud and plastic was occupied least. The sediment experiment also showed that the act of sheltering was more important than the position of a shelter on the substrata. The shelter choice experiments showed that the occupation of an existing shelter is preferred over constructing a new one, and that natural materials of any size are preferred over synthetic surfaces. The results of this project aim to inform further studies and to assist in the construction of lobster friendly areas surrounding the proposed Wrecks-to-Reefs project in Dorset, UK, and are also important in the context of selecting optimum sites for the wild release of hatchery juveniles.
2009: Caroline Gates – Plymouth University, MRes thesis. ‘Investigating body size to shelter dimension relationships in hatchery reared stage IV Homarus gammarus using an artificial substrate.’
2007-2008 Charlie Ellis – Independent research funded by the Save Our Seas Foundation programme. ‘Developing stakeholder participation in lobster stock enhancement projects.’
Project to encourage fishing industry participation in NLH stock enhancement work.
2007: Charlie Ellis – Independent research funded by the DEFRA Fisheries Challenge Fund. ‘Developing stakeholder participation in lobster stock enhancement projects.’ Project to develop release mechanisms for the deployment of juvenile lobsters by the fishing industry.