Potential for cultured European spiny lobster juveniles to support fishery restoration

The European spiny lobster has traditionally been a primary target for fisheries off Ireland, the United Kingdom, France, Portugal, Spain, Italy, Greece, Tunisia and Morocco, as well as adjacent Mediterranean waters (Goñi & Latrouite, 2005). Poor biological knowledge and excessive fishing pressure, combined with weak management, have resulted in this valuable fishery undergoing a catastrophic population crash in the Atlantic.

Formerly one of the most important fisheries for the UK inshore sector it has long ceased to contribute to commercial fishery landings in some areas. There are signs of a slight recovery in parts of the UK, but in other former strongholds the species has been commercially extinct since the late 1970s. During 2021, fewer than 10 animals were caught in the Llŷn Peninsula, North Wales.

Despite the weakened status of the UK P. elephas fishery, the species is still targeted due to very high prices in both UK and international seafood markets, by destructive fishing techniques such as tangle nets (Cosgrove et al., 2016). P. elephas appears very sensitive to fishing pressure, with some overexploited populations taking several decades to show any signs of recovery. Even in those regions of Europe where the fishery is better managed some populations still show a steady decline. Despite its economic and ecological importance, limited information is available to perform stock assessments and make robust management decisions. There is also a global lack of knowledge about the basic life history and population parameters, like age, growth, and maturity, when compared to other commercial lobster species (Santos et al, 2022). As lobster fisheries decline fishermen may be encouraged to fish for longer periods and travel further to catch these valuable crustacea. This directly contributes to lobster being considered as one of the least sustainable seafood species captured due to related emission levels (Gephart et al., 2021).

UK P. elephas research has been limited to field surveys monitoring the steady decline of the species, while attempts to confer greater protection have been thwarted by arguments that show a poor understanding of species biology. Attempts to improve knowledge of the larval phases of P. elephas biology have been virtually non-existent since the early work of Kittaka et al. (2001). Meanwhile, decades of significant funding has focused on the clawed lobster (Homarus gammarus) – a species with exceptionally few characteristics to support economic large-scale juvenile production for either farming or restoration initiatives.

Following several years of research, RAS Aquaculture Research Ltd (RASAR) has generated some understanding of P. elephas phyllosoma biology, which resulted in the first juveniles being produced in Europe in 2019 and again in 2021. Juveniles were secured in a 2-3 month culture period, as opposed to the 7-9 month larval cycle in the wild. Subsequent data from ongoing growth studies, which took place in Anglesey, with P. elephas juveniles indicate that aquaculture could offer an additional management tool to help restore depleted fisheries in Europe. These trials were performed under communal conditions and some interesting data is summarised below:

1. P. elephas juveniles exhibit no serious aggression or cannibalism under communal culture conditions. This remains the situation even where newly settled pueruli are mixed with older feeding juveniles and subsequently when juveniles varying in size, age or moult status are grown together.
2. Only very brief skirmishes over preferred shelter sites have been observed, with juveniles occupying suitable refuges in close proximity while maintaining occasional antennal contact.
3. Juveniles will modify a suitable refuge – removing sand and gravel to enlarge a shelter.
4. Juveniles identify a range of natural prey items and quickly develop skills for capturing polychaete worms and opening bivalve shellfish.
5. Pelleted feeds with appropriate attractants are accepted.
6. Juveniles are strongly nocturnal for first 9 months after settlement, becoming more active at dusk.
7. Intermoult periods average 26 days, up to a total body length of 5.5-7.5 cm, at 9 months post-puerulus stage.
8. No mortality among juvenile lobsters has been recorded at the research scale, but this observation may not hold true at commercial production levels.

In the UK, P. elephas is considered a key component of biodiversity on Annex I reef habitat, essential for favourable conservation and good environmental status (GES) of these habitats. Recovery of the P. elephas population was considered vitally important in gaining GES under the EU Marine Strategy Framework Directive (Leslie & Shelmerdine, 2012). In 2014 concern over the lack of accurate assessments of its status led to the classification of P. elephas by the International Union for Conservation of Nature (IUCN) as “vulnerable”.

In contrast to H. gammarus culture, the larval cycle of P. elephas is more complex and settlement to the benthic phase takes longer. However, techniques to resolve the main obstacles to large-scale juvenile production are progressing. A particular focus during the 2022 season has been automating the cleaning of larval tanks and reducing costs of feed and labour. The principal advantage of P. elephas over H. gammarus culture is seen during the juvenile ongrowing phase. The aggressive behaviour of H. gammarus requires ongrowing juveniles in isolation, significantly increasing labour, maintenance and production costs. In contrast, ongrowing juvenile P. elephas is undertaken in communal tanks where the key requirement is well-controlled water quality supplying a tank system designed to maximise production. According to the optimal size required for restoration programmes, growth to a size suitable for tagging can be achieved within 4-6 months from egg hatch.

Apart from its ecological importance restoration of this high value seafood species is important to benefit small-scale inshore fisheries (SSF). Since 2000, the relative role that SSF play in regional European economies has dropped 20–30% and 30–50% in terms of employment and incomes respectively (Lloret et al., 2016). Where national capture fisheries can be properly managed, hatchery production of P. elephas juveniles for stocking Marine Protected Areas (MPAs) or suitable offshore energy structures may be of interest. Using culture techniques as a tool to support fishery restoration or improve management options for a spiny lobster fishery will still require financial support. However, the very high market value and the post-settlement characteristics of the species do present a number of possible options. Potential commercial projects have been identified and will be further explored with EU partners. These may include ongrowing P. elephas lobsters directly for the seafood market, where their very high market value may simultaneously support some juvenile production for restoration initiatives.

The involvement of regional fishery cooperatives in such programmes would be essential to ensure protection for recovering fisheries. Integration with RAS finfish farms, MPAs or cooperation with tourism and renewable energy projects could also assist in financing hatchery operations for restoration activities. Such an approach might support the concept of integrating mariculture with marine conservation i.e. supporting ecosystem services (Le Gouvello et al, 2022) and may even reduce the significant CO2 emissions associated specifically with this capture fishery (Parker et al., 2018).

A key area for further research relates to the need for improved feeds during the planktonic phyllosoma phase. High mortality (30 -100 percent) may be observed after the final phyllosoma stage which moults into a puerulus. Poor phyllosoma nutrition can result in weak pueruli with insufficient reserves to survive food deprivation until the juvenile stage. The puerulus is a resting stage before transitioning into a juvenile lobster in 2-3 weeks. A common characteristic of all spiny lobster species like P. elephas is that the puerulus stage does not feed. Further development at this stage requires adequate nutrient reserves stored during the earlier phyllosoma feeding period. These reserves may also be important for significant periods even after transition to the first juvenile lobster if feed supplies are inadequate or environmental conditions are unfavourable (Limbourn et al., 2008; Espinosa-Magaña et al., 2017).

Current work is also highlighting the potential for manipulation of juvenile growth rates, development of juvenile pelleted feeds and maximising production of 10 -15g juveniles in tiered tank systems. RASAR plans to expand current juvenile on-growing trials to determine performance of this species to larger sizes that might be acceptable to the seafood market.