The European lobster - Using farmed produce to improve wild stocks
by Daniel Casbon, Alex H L Wan, Simon J Davies & Finnian Hartnett, National University of Ireland Galway, Ireland
The European lobster (Homarus gammarus) is a species of clawed lobster that is native to the Eastern Atlantic Ocean, as well as the Mediterranean and Black seas. Adults can typically found up to depths of 150m and reside on hard substrates, particularly on rough and rocky grounds. These lobsters can typically live up to 60 years, with an average life span being over 30 years for males and over 50 years for females.
Female lobsters become fertile after they have reached a carapace length of >120 mm. For this species, it displays an 'r-selection' life strategy, where females produce large clutches of eggs, up to 40,000 per breeding period depending on size and age.
However, estimations predict that only 1:20,000 of the offspring cohort survive and reach the juvenile stage. Eggs are held externally, attached to the female's abdomen, where they develop before hatching. The eggs will normally hatch into larvae after 9-11 months of post-fertilisation.
Shortly after hatching, the larvae become buoyant and float to the surface where they undergo three significant developmental/ morphological changes. Known as zoea stages, these typically last from six to eight weeks.
After developing past zoea stage 3, the larvae will descend to the seabed and adopt a benthic lifestyle to minimise predation risk in crevices and reefs, where the lobsters will develop into adulthood.
Current supply of lobsters to the seafood market
The European lobster is a high-value seafood species, with commercial fishing operations being undertaken throughout the species geographic range. The setting of 'pots' is the most typical and is the most successful fishing method.
However, other fishing techniques such as trammel nets and dredging are also used. Recent reports suggest, there has been significant growth in wild global capture in European lobsters over the last two decades (>220%), with an annual production now exceeding 4700 tonnes.
The main lobster fisheries of European lobsters are in United Kingdom, Ireland and France. Although, the largest lobster consuming markets are in southern EU states such as France, Spain, and Italy.
However, unlike the North American cousin species (Homarus americanus), the European lobster wild stocks are vulnerable
to over-exploitation, which raises concerns over whether future increases in consumer demand could be met. As such, this gives scope for potential intervention in the form of wild stock enhancements and farming to near market size.
Lobster larvae are typically fed with two species of live phytoplankton (Chatocerous muleri and Isochrysis galbana) and enriched artemia. Previous studies have shown that enriched Artemia can be critical in the early stages of larval development.
For instance, a trial using 5 Artemia mL-1 showed an increase in growth performance 72 hr post-hatching, compared to smaller concentrations of artemia. Although, recent work has shown that the larvae could be fed with formulated dry feeds that can also increase survival rates and reduce cannibalism incidences.
For settled juvenile lobsters, they are omnivorous and tend to feed nocturnally. When reared artificially, the lobsters are typically fed with a range of live foods, such as chopped fish and shellfish.
However, this can be costly, laboursome, and limit the lobster's nutritional intake potential. As such, formulated diets are needed for large scale rearing in research and in commercial farming.
The specific nutritional requirements of European lobsters are under-researched. However, reports have shown a progressive growth rate when protein levels have consisted of 40-45 percent, anything below this will result in lower performances and a smaller specific dynamic action response. Whilst wild sampled lobster have shown that eicosapentaenoic acid (7.7%) and docosahexaenoic acid (18%) are the two dominant fatty acids.
Similarly, essential amino acids also play a vital role in animal growth, supporting moulting, and improving the rate of protein synthesis. In particular, amino acids profiling in wild lobster gonads showed there was elevated valine, threonine, leucine, arginine, lysine and isoleucine concentrations. This suggests that diets for hatchery brood stock may require enrichment with these amino .
Commercial production of the European lobster
Hatcheries are considered a useful tool in the management of wild fisheries by facilitating stock enhancement through raising the survival rate during the larval stages and releasing the settled
juveniles back into the wild with higher chances of survival. Typically, hatcheries receive berried female lobsters from fisherman as it is less time consuming and more cost-effective.
Female lobsters can be left to hatch naturally on their own and are sometimes starved for a couple of weeks before hatching to ensure waste products do not contaminate the water. As well as this, some hatcheries bathe the females in iodine, 24 hours before hatching, to remove external parasites and potential pathogens which may pose a risk to larvae.
The post-hatching, offspring are collected and reared communally in incubation tanks, providing aeration and a high water turnover to help prevent premature settlement, biofouling and maintaining optimal water quality. European lobsters have a higher survival rate (10-15%) when reared in hatcheries due to the amount of available feed, reduced predation, accelerated metamorphism and controllable water quality and parameters. Certain stages can be time altered by increasing temperature or photoperiod, this allows eggs to develop at a faster rate.
The positive effect that commercial hatcheries can have on wild populations is significant and further research into the precise nutritional requirements of European lobster is required in order to improve hatchery efficiency and output. Furthermore, a better understanding of lobster husbandry will allow for increased survival and growth rates in hatcheries.
Creating a sustainable farm
There are significant knowledge gaps on the nutritional requirements of the early stages (larvae and juvenile) of European lobsters. There are multiple diets available for lobsters, however, the optimal nutritional intake is unknown, suggesting that these diets could not be meeting the demand of the lobster.
When a standard fishmeal inclusion was replaced with a by- product from the shrimp processing industry, results showed
that lobsters fed with either a wet shrimp or freeze-dried shrimp diet both showed improved performance, in terms of growth
and development parameters, as the intermoult period was significantly shorter and the specific growth rate was significantly higher when compared to the reference fishmeal diet.
The authors found that lobsters fed a shrimp feed-based diet containing 63% shrimp meal and 6% fishmeal, had a higher increase of body weight per day (3.67 ± 0.22) and specific growth rate (SGR, 2.30 ± 0.12), compared to a fishmeal-based diet with the percent growth/day being (3.06 ± 0.24) and an SGR of (2.01 ± 0.12). This was also confirmed through a wet shrimp reference diet, having an SGR of (2.49 ± 0.09) and percent growth/day of (4.09 ± 0.20).
There has been much difficulty in formulating a pelleted feed that contains all essential amino acids required by juvenile and adult lobsters alike, with no pelleted feed being able to yield the same growth as fresh or live feed to date. However, a formulated pelleted feed can be known to positively affect the thickness of a lobster's exoskeleton, increasing significantly with each ecdysis.
In particular, micronutrients such as astaxanthin, trace metals, vitamins, and glucosamine. Astaxanthin helps aid in colouration and glucosamine can be found in lobster shells. Studies suggest these functional ingredients have the potential to increase growth, lower moult death syndrome (MDS), and improve dietary carotenoids.
Another issue that is currently inhibiting the development of the industry is the cost associated with farming European lobsters in land-based hatcheries. A recent project at the Marine Institute of Ireland's Lehanagh Pool test sea cage facilities (west coast of Ireland), has validated the potential of farming Atlantic salmon (Salmo salar) with lumpfish (Cyclopertus lumpus), and European lobsters as an integrated multitrophic aquaculture system.
This kind of rearing system could increase the economic potential of European lobster aquaculture through reduced operating costs when compared to the running of a large-scale land-based hatchery including electricity, cost of land, running expenditure and capital equipment.
The current price of European lobster is ~£10,000 tonne-1 which is most likely not substantial enough to cover the expenses of the egg rearing stage (~10-11 months). However, recent advances in recirculating aquaculture system technologies such as tank designs, hides, more economical water treatment facilities, and better feed designs have allowed new sustainable on-land lobster production business models to appear in Europe.