Translocate species - Translocate molluscs
Overall effectiveness category Likely to be beneficial
Number of studies: 7
Background information and definitions
Many populations of marine subtidal benthic invertebrate species have declined or been depleted due to the multiple threats they are under, such as habitat loss and overharvest (Airoldi et al. 2008; Hobday et al. 2000). To counteract this phenomenon, marine subtidal benthic invertebrates can be translocated from a site with a healthy population, 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 (Hughes et al. 2008; Swan et al. 2016). As the outcomes of translocating 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; molluscs such as abalone, scallops, or mussels; worms).
When translocation is undertaken for a habitat-forming (biogenic) species, effects on the invertebrates associated with the habitat are reported in “Habitat restoration and creation – Translocate habitat-forming (biogenic) species”. Evidence from transplantation studies of hatchery-reared species is summarised under “Species management – Transplant/release captive-bred or hatchery-reared species” and “Habitat restoration and creation – Transplant/release captive-bred or hatchery-reared 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.
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.
Hughes D.J., Poloczanska E.S. & Dodd J. (2008) Survivorship and tube growth of reef‐building Serpula vermicularis (Polychaeta: Serpulidae) in two Scottish sea lochs. Aquatic Conservation: Marine and Freshwater Ecosystems, 18, 117–129.
Swan K.D., McPherson J.M., Seddon P.J. & Moehrenschlager A. (2016) Managing marine biodiversity: the rising diversity and prevalence of marine conservation translocations. Conservation Letters, 9, 239–251.
Supporting evidence from individual studies
A replicated, before-and-after study in 1992 of four sites of seagrass bed in Bogue Sound estuary, Northern Carolina, North Atlantic Ocean, USA (Peterson et al. 1996a) found that up to six months after translocation, bay scallops Argopecten irradians concentricus survived at all sites. Following translocation, average scallop abundance (representative of survival) at the transplant sites did not significantly change (directly after: 8.0–10.3; 6 months after: 5.9–11.6/0.5 m2) and remained higher than before translocation (0.3–3.6/0.5 m2). In July 1992, adult bay scallops (135,000 in total) were translocated in coolers without water to sites with low scallop densities (0.7/m2). Scallops were deposited in one 30 x 40 m marked area at each site. Bay scallops were counted in 2 m2 quadrats (n=16–24) inside the marked area two weeks before and on five occasions after translocation ending in December.
A replicated, before-and-after, site comparison study in 1988–1994 of three to four seagrass bed sites in one to three estuarine locations in Northern Carolina, North Atlantic Ocean, USA (Peterson et al. 1996b) found that translocating bay scallops Argopecten irradians concentricus did not increase larval production but increased recruitment into the adult population compared to before translocation. Larval production was similar before (6–195/sample) and after (5–15) translocation, and remained lower than at sites in other estuaries (55–335). Larval recruitment (as abundance of settled spat) increased by on average 568% at translocation sites, while recruitment at sites without translocation increased (non-significantly) by 34%. In 1992–1994, adult bay scallops (100,000–150,000/year) were translocated in coolers without water to sites in Bogue Sound with low scallop abundance within seagrass beds. Larvae collectors (8–20) were deployed in 1988, 1989, 1992 and 1993 at one translocation site and at two sites without translocation in nearby estuaries (Core Sound; Back Sound). Settled scallop larvae were counted for each collector after two months. In 1988, 1989, 1992, 1993, and 1994 at two translocation sites and the same two sites without translocation, 0.5 m2 plots were dredged (35–61 plots/site) and scallops under 1-year old counted.Study and other actions tested
A replicated, site comparison study in 2001 of 12 sites across four areas of soft seabed in the Tasman Sea and South Pacific Ocean, New Zealand (Talman et al. 2011) found that, a week after translocation, >40% of translocated New Zealand scallop Pecten novaezelandiae had survived. In addition, mortality was lower in areas closed to commercial fishing compared to fished areas. Mortality in the two closed areas (15% and 24%) were lower compared to the two fished areas (39% and 59%) in three of four comparisons (24% not statistically different to 39%). In addition, across the two fished areas, mortality was significantly higher in the area also seeded with juvenile scallops (59%), than the area not seeded (39%). In 2001, scallops were translocated from nearby areas to two areas closed to commercial fishing (in February and April) and two fished areas (in April) (three sites/area). One of the fished areas had also been seeded with approximately 1.2 million juvenile scallops in February. At each site, a 4-m long chain was deployed, with 12 scallops attached at fixed intervals. The status (dead or alive) of all scallops was checked daily for three days and after a week, and mortality assessed.Study and other actions tested
A replicated study in 2001 of two sites of seagrass, coral rubbles, and sandy seabed in the Florida Keys, between the North Atlantic Ocean and the Gulf of Mexico, USA (Delgado & Glazer 2007) found that non-reproductive adult queen conch Strombus gigas translocated to aggregations of reproductive conch typically displayed similar behaviour to non-translocated resident conch, but effects varied with sites. At Looe Key, there were no differences between translocated and resident conch in total distances travelled (translocated: 203 vs resident: 270 m), movement rates (1.2 vs 1.1 m/day), migration patterns (reported as an index), home-range sizes (13,900 vs 13,200 m2), and conch-conch interactions (reported as a sociability coefficient). At Easter Sambo, there were no differences between translocated and resident conch in total distances travelled (186 vs 144 m), movement rates (1.2 vs 0.8 m/day), and migration patterns, but translocated conch had larger home-range sizes (30,300 m2) than resident conch (3,700 m2) and interacted more with other translocated conch than with resident conch. Authors suggested that differences in conch behaviour were associated with differences in habitats between sites. In 2001, non-reproductive adult queen conch were translocated from a near-shore site to two offshore sites in an enforced protected area with aggregations of reproductive adult queen conch (Eastern Sambo: 132 conch; Looe Key: 255 conch). Conch were tagged with acoustic transmitters and their movements followed bimonthly for 10 months (Eastern Sambo: six translocated, six resident; Looe Key: five translocated, five resident).Study and other actions tested
A replicated, site comparison study in 2003–2004 of two sites off the coast of Algarve, North Atlantic Ocean, southern Portugal (Joaquim et al. 2008) found that after translocation, clams Spisuloa solida were in similar condition to clams in the source site, and that despite increased mortality over time 45% survived up to a year. Before translocation, the condition of all clams was 6.3 (ratio without units). After three months, conditions were similar for translocated (6.4–6.5) and source site clams (7.4–7.8). Survival of translocated clams was 65-85% after two weeks, 52-60% after three months, and 45% after a year. Size of translocated clams did not affect survival or condition. In 2003, a total of 4,000 clams were translocated from a source site to two 50 m2 plots in a depleted site (1 clam/m2) inside an area closed to fishing. Each plot was sub-divided into fifty 1 m2 subplots. Clams, divided into sublegal (<25 mm shell length) and legal (>25 mm) size groups, were equally distributed to each subplot. After two weeks and three months, all clams/subplot were counted, and the condition index of 10 clams/subplot assessed. Clam condition was also assessed for the source site. After a year, all clams in the translocation site were counted.Study and other actions tested
A before-and-after study in 2009–2010 in one area of kelp forest, in the North Pacific Ocean, off the coast of San Diego, California, USA (Coates et al. 2013) found that 18 months after translocation of adult pink abalone Haliotis corrugata to existing patchy populations, total abalone (translocated and resident) abundance had decreased to similar levels as before translocation. Results were not statistically tested. Eighteen months after translocation, 35% of abalone at the site had been lost (due to mortality and emigration). Abalone abundance after 18 months was 0.11 abalone/m2, lower than immediately after translocation (0.18 abalone/m2) and more similar to before translocation (0.09 abalone/m2). Following translocation, translocated abalone displayed similar average home range (163 m2) and linear distance travelled (7 m) compared to resident abalone (home range: 145 m2; distance travelled: 8.6 m). The study site (254 m2) had 23 resident adult abalone. In September 2009, all were tagged with acoustic transmitters and returned to their original position. An additional 23 abalone from a nearby area (approximately 2.2 km north) were tagged and translocated to the study site in groups of 2–6. Divers monitored abalone for 18 months by counting dead tagged abalone and live untagged abalone. Home range and linear distance travelled by tagged abalone were assessed from their behaviour and movement patterns.Study and other actions tested
A replicated, site comparison study in 2010–2011 of 10 sites in Strangford Lough, Northern Ireland, UK (Fariñas-Franco et al. 2013) found that over a year after translocating habitat-forming horse mussel Modiolus modiolus, the abundance of mussel spat (young mussels) was higher in site with translocated mussels compared to both sites without translocated mussels and natural mussel reefs. Sites with translocated mussels had more spat (164/m2) compared to sites without (0/m2), and compared to natural reefs (6/m2). In 2010 divers translocated live adult horse mussels from nearby natural mussel patches within the Lough to four sites (1,000 mussels/sites). After 12 months, two quadrats (0.25 x 0.25 m) were deployed at each site with translocated mussels and at four adjacent natural sites without translocated mussels. Spat were counted from sediment and shell samples for each quadrat. Natural horse mussel communities from two nearby horse mussel reefs within the Lough were sampled in December 2010 using the same sampling methodology.Study and other actions tested
A study in 2006 of two sites of unspecified seabed in Lake Vouliagmeni, Gulf of Corinth, Greece (Katsanevakis 2016a) found that up to a year after translocation, most Mediterranean fan mussels Pinna nobilis survived in a deep site, but none in a shallow site. In the shallow site, all mussels were dead after 72 days, mostly due to poaching (90%). In the deep site 80% of mussels survived, 100% of mussel death was natural, and 75% of dead mussels were small (<6 cm). No statistical tests were performed. During a pilot study in July 2006, forty mussels were manually uprooted from a shallow area of the lake (4 m depth), their shell width measured, and translocated equally back to that same area or a deeper area (12 m). Translocated mussels in both areas were 1 m apart. Mussel survival was monitored by divers and mortality classed as “poaching” or “natural”, after 12 days, 72 days, and one year.
A study in 2007–2012 in one area of unspecified seabed in Lake Vouliagmeni, Gulf of Corinth, Greece (Katsanevakis 2016b) found that translocated Mediterranean fan mussels Pinna nobilis had similar survival and growth rate compared to naturally-occurring mussels. After five years, the survival of translocated mussels (96%) was similar to that of naturally-occurring mussels (95%). Size-specific growth was similar in translocated (smallest: 39%; largest: 1.5%) and naturally-occurring mussels (smallest: 47%; largest: 0%). Data for other size-classes were not provided. In 2007, forty-five mussels were manually uprooted from a shallow area of the lake (4 m depth) and translocated to a deeper area (12 m depth) in five groups (20 m apart) of 9 mussels (0.5 m apart). Yearly for five years, translocated mussels’ survival was monitored by divers and mortality classed as “poaching” or “natural”. Their shell width was measured, and mussels categorised in one of six size-classes. Twenty naturally-occurring mussels occurring at 12 m depth were also monitored.Study and other actions tested