Some lobster mothers produce offspring that are far more likely to survive - in findings that could help safeguard lobster diversity.
University of Exeter researchers, working in partnership with the National Lobster Hatchery (NLH) in Cornwall, studied European lobsters that survived the first few weeks of life.
Lobster larvae from different mixtures of females were hatched at the NLH research facility. Each batch of larvae contained offspring from multiple, naturally-mated mothers sourced from the wild. Using a combination of larval counts, sizing and genetic profiling of a subsample of the juveniles the study analysed 3,500 juvenile lobsters and explored their relatedness and differential survival within the rearing system.
While some groups of siblings survived in large numbers, others experienced a much lower survival rate - creating a genetic "bottleneck" with less diversity in the new generation.
Low diversity is bad for the health, resilience and adaptability potential of wild populations, so the findings raise questions about how release programmes should adapt to conserve fisheries.
The study also surveyed lobsters from nearby wild fisheries and found no clear evidence of "bottlenecking" in hatchery release areas, despite the hatchery releasing juvenile lobster into these areas for the last twenty-five years. However, the authors suggest that any significant upscaling of releases could threaten the genetic diversity of wild stocks unless delivered alongside improved culture protocols that can act to limit these survivability biases, combined with long-term monitoring.
Dr Charlie Ellis, from the University of Exeter, lead author of the study, said: "Current hatchery releases don't appear to be significantly reducing overall genetic diversity in wild lobster stocks, but our findings suggest that a major increase in the number of juveniles being released wouldn't necessarily be a good thing for the fishery due to the potential for unwanted genetic side effects." said.
"Overall, it just shows that rearing programmes alone aren't yet a silver bullet, but have a part to play in raising awareness and complementing sustainable, traditional fisheries management measures that conserve natural stocks, rather than replacing them."
Batches of lobster larvae in the study all came from mothers that released eggs on the same days, reducing but not eliminating the chance of cannibalism (as larger offspring will eat smaller ones).
Offspring of larger mothers generally had higher survival rates, while some smaller mothers also produced offspring with high survival rates (due to unknown fitness or genetic factors).
Due to this, surviving juveniles in the study had a genetic pool only about half that of their broodstock mothers.
To limit the "survival skew" of certain mothers' offspring, the team tested the effect of raising offspring of mothers of similar size together - and found this was expected to reduce the frequency of severe survival disparities by 22-52%.
This suggests hatcheries could reduce but not eliminate genetic bottlenecking effects by size-matching mothers for breeding batches.
After a "planktonic" stage lasting a few weeks, young hatchery lobsters are released into the sea - where they live on the seabed and remain largely unseen for two to three years, before emerging at about six inches in length.
Professor Jamie Stevens, a co-author of the study, added: "Our findings are challenging for hatcheries, but more research is needed to help understand both the survival of released juveniles and the stability of genetic diversity in wild stocks. It's also important to acknowledge the vital role hatcheries play in engaging the public and the fishing community."
The genetic methods used in this study were developed in Professor Stevens' lab at the University of Exeter, and are already being used elsewhere in Europe to monitor lobster populations.
Ben Marshall, Head of Production at NLH, says the research presents a vital first step, "As the National Lobster Hatchery, we are keen to further understand the genetics behind our stock enhancement work, and as such we partnered with the University of Exeter on the GEMALOR project.
"We hope to contribute to further investigation in this area that might enable us to expand the volume of our releases without eroding the natural genetic makeup of the wild stock."
The study was funded by the Fisheries Industry Science Partnerships scheme from the UK government's Department for Environment, Food & Rural Affairs.
