Transplant/release captive-bred or hatchery-reared species - Transplant/release crustaceans
Overall effectiveness category Likely to be beneficial
Number of studies: 5
Background information and definitions
Many populations of subtidal benthic invertebrate species have declined or been depleted due to the multiple threats they are under, such as habitat loss and overharvesting (Airoldi et al. 2008; Hobday et al. 2000). To counteract this phenomenon, captive-bred or hatchery-reared subtidal benthic invertebrates can be transplanted or released at a site, either to introduce a species to a new site (where they did not historically occur), to reintroduce a species to a site (where they used to occur), or to enhance the population at a site where the species is already present by increasing its abundance (Hansen & Gosselin 2013). As the outcomes of transplanting/releasing species can vary largely with the type of species, studies have been grouped by broader taxonomic group (e.g: crustaceans such as lobsters or prawns; or molluscs such as abalone, scallops, or mussels).
Here, only direct transplanting/releasing methods have been considered, without added interventions or changes to the methods to improve survival after release. However, when transplant/release was undertaken in predator exclusion cages, evidence has been summarised under “Species management – Transplant/release captive-bred or hatchery-reared species in predator exclusion cages”.
When transplanting hatchery-reared individuals is undertaken for a habitat-forming species, effects on the invertebrates associated with the habitat are reported in “Habitat restoration and creation – Transplant captive-bred or hatchery-reared habitat-forming (biogenic) species”. Evidence from translocation studies of naturally occurring species is summarised under “Species management – Translocate species” and “Habitat restoration and creation – Translocate habitat-forming (biogenic) species”.
Airoldi L., Balata D. & Beck M.W. (2008) The gray zone: relationships between habitat loss and marine diversity and their applications in conservation. Journal of Experimental Marine Biology and Ecology, 366, 8–15.
Hansen S.C. & Gosselin L.A. (2013) Do predators, handling stress or field acclimation periods influence the survivorship of hatchery-reared abalone Haliotis kamtschatkana outplanted into natural habitats? Aquatic Conservation: Marine and Freshwater Ecosystems, 23, 246–253.
Hobday A.J., Tegner M.J. & Haaker P.L. (2000) Over-exploitation of a broadcast spawning marine invertebrate: decline of the white abalone. Reviews in Fish Biology and Fisheries, 10, 493–514.
Supporting evidence from individual studies
A study in 1983–1992 in one seabed area off the east coast of England, North Sea, UK (Bannister et al. 1994) estimated that between 50–84% of the initial number of released hatchery-reared European lobsters Homarus gammarus survived and increased in size for up to eight years in the wild. Lobsters recaught reached 85 mm (legal catch size) within four to eight years after release. Between 1983 and 1988, hatchery-reared lobsters (49,000 in total) were tagged and released across an area of 30 x 8 km onto cobbles and boulders at 80 locations (10–15 m depth). At time of release, lobsters were three months old with carapaces measuring 15 mm in length. Between 1988 and 1992, a recapture programme caught a total of 56,700 lobsters, of which 621 were tagged lobsters previously released. The carapaces of recaptured tagged lobsters were measured. It is not known if the number of uncaught tagged lobsters was due to mortality or recapture effort. Percentage survival of the 49,000 released lobsters was estimated from the recapture programme catch-rate data.Study and other actions tested
A controlled study in 1998–2000 in one area off southwestern Norway, North Sea (Agnalt et al. 2007 - same experimental set up as Agnalt et al. 2008) found that hatchery-reared female European lobsters Homarus gammarus released into the wild had similar growth rate and movement patterns, compared to wild females. Regardless of carapace length, the growth rate of hatchery-reared females (7–10 mm between moults) was similar to that of wild females (3–8 mm). In total, 53% of hatchery-reared females remained within 500 m of their release sites, which was similar to wild females (41%). Between 1990 and 1994, hatchery-reared juvenile lobsters (approximately 128,000) were released as part of a restocking program. During the fishing season each year from 1998 to 2000, egg-bearing female lobsters caught by fishers were measured (total length, carapace length), weighed, and hatchery-reared females were differentiated from wild females by the presence of tags. All females were then retagged, kept in holding pens in the sea, and released after the end of the fishing season to potentially be recaptured by fishers the following fishing season (mark-recapture). A total of 81 hatchery-reared females and 231 wild females were recaptured at least once. Locations of release and recapture sites were recorded.Study and other actions tested
A controlled study in 1996–1997 in one seabed area off southwestern Norway, North Sea (Agnalt et al. 2008 - same experimental set up as Agnalt et al. 2007) found that when comparing individuals of similar sizes, female hatchery-reared European lobsters Homarus gammarus released into the wild carried similar numbers of eggs and their eggs were of similar weight, diameter, and developmental stage, compared to wild lobsters. For further details of results see graphs in paper. Between 1990 and 1994, hatchery-reared juvenile lobsters (approximately 128,000) were released as part of a restocking program. During autumn 1996, and spring and autumn 1997, egg-bearing female lobsters were collected from commercial landings. Hatchery-reared females (104 individuals) were differentiated from wild females (111 individuals) by the presence of tags. All female lobsters were measured (carapace length), and the weight of their egg mass recorded. For each female, egg count and size were assessed from subsamples. A note was made of any developing embryos.Study and other actions tested
A study in 2000–2009 in one area of rocky seabed off Helgoland, German Bight, North Sea (Schmalenbach et al. 2011) found that after releasing one-year-old hatchery-reared European lobsters Homarus gammarus, they grew and survived in the wild, became reproductive, and appeared healthy. Recaptured lobsters had grown in the wild (females: 14.5–19.8; males: 16.8–21.8 mm/year) and reached 85 mm (legal catch size) within four to seven years after release. Survival rate of lobsters released in 2000 and 2001 was estimated at 32 and 39% respectively after up to five years. In addition, no recaptured lobsters displayed signs of “Black Spot” disease, 95% had developed a crusher-claw, and 16% of recaptured females carried eggs. Annually in 2000–2005, at two locations of 10 m water depth, tagged hatchery-reared lobsters were released at the surface (5,421 lobsters in total). Released lobsters weighed 1.5 g and had carapaces 15 mm long. Between 2000 and 2009, 488 of these were recaptured at least once, using lobster pots, traps, and divers. It is not known if the number of uncaught tagged lobsters was due to mortality, recapture effort, or migration outside the search zone. Recaptured lobsters were sexed, observed for signs of disease and presence of a crusher-claw, and their carapaces measured. Percentage survival was estimated from the mark-recapture programme data obtained between 2001 and 2005 for the 1,036 released in 2000 and 2001.Study and other actions tested
A study in 2013–2016 of 36 sites in the Swan-Canning Estuary, south-western Australia (Crisp et al. 2018) found that during the three years after yearly releases of hatchery-reared western school prawn larvae Metapenaeus dalli the abundance and size of egg-bearing females, as well as the overall population egg production, increased. Abundance of egg-baring females increased from 0.1–0.6/500 m2 in 2013–2014 and 0.6–1.4 in 2014–2015 to 1.1–1.6 in 2015–2016. The carapace length of egg-bearing females increased from 17–20 mm in 2014–2015 to 23-24 mm in 2015–2016. Egg production (fecundity) increased from 16,000 egg/500 m2 in 2013–2014, to 34,000 in 2014–2015 and 163,000 in 2015–2016. However, authors indicate that wild and hatchery-reared prawns could not be discerned, and therefore that the results cannot be solely attributable to the restocking programme. Yearly between December 2012 and March 2016, hatchery-reared juvenile prawns were released into the estuary (15,000 in 2012–2013; 635,000 in 2014–2015; 2 million in 2015–2016) as part of a restocking programme. Monthly in October 2013–March 2016, prawns were collected using a mix of hand nets (9 mm mesh; 570 m2) and otter trawls (9 mm at the codend; 650 m2) at 36 sites (two samples/site/month). Prawns were counted, sized, sexed, and egg-bearing females recorded.Study and other actions tested