Transplant/release captive-bred or hatchery-reared species in predator exclusion cages
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
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, captive-bred or hatchery-reared marine 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). Following transplantation or release, initial mortality can be high, for instance due to stress and predation. To potentially increase survival, animals can be transplanted/released in exclusion cages to reduce the initial predation while animals are acclimating to their new environment (Hansen & Gosselin 2013).
When species transplantation/release was undertaken without predator exclusion cage, evidence has been summarised under “Species management – Transplant/release captive-bred or hatchery-reared species”. Evidence for other related intervention is summarised under “Species management – Translocate species” and “Habitat restoration and creation – Translocate biogenic or 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 replicated, controlled study in 2009 in one area of seabed off Vancouver Island, North Pacific Ocean, Canada (Hansen & Gosselin 2013) found that hatchery-reared northern abalone Haliotis kamtschatkana transplanted into the wild in predator exclusion cages did not have higher survivorship following release compared to those transplanted directly onto the seabed. For the first seven days after transplantation, abalone in predator cages (not yet released) had higher survivorship (96%) than those not transplanted in cages (57%). However, seven days after being released from their cages, survivorship of abalone had decreased (42%) and was similar to those directly transplanted onto the seabed (34%). In addition, transplanting abalone in cages 1 m above the seabed or in cages onto the seabed led to similar survivorship, both before release (after 7 days; 96% vs 96%) and after release (after 14 days; 38% vs 46%). In 2009 a total of 1,680 hatchery-raised abalone (4.2–6.5 cm shell length) were used in a project assessing the survivorship of transplanted abalone. Three groups of 20 tagged abalone were transplanted at each of seven locations 10 m apart (9 m water depth). Each group corresponded to one of three treatments: 1) abalone placed in predator exclusion cages suspended 1 m above the seabed, 2) abalone placed in predator exclusion cages onto the seabed, 3) abalone transplanted directly onto the seabed (no cage). Seven days after transplanting, abalone in predator exclusion cages were released and allowed to disperse. On day 7 and 14 following transplanting, surviving abalone were searched for and counted inside all cages and during circular surveys (5 m radius around each of the transplantation locations).Study and other actions tested