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| United Kingdom Lobster Stock Enhancement ProgramRearing lobsters Homarus gammarus in hatcheries and releasing the progeny to the wild has a history going back over 100 years. Uncertainty about the outcome of restocking prevailed, as there was no method to confirm what proportion of the adult animals recovered was of hatchery origin. In the early 1980’s, scientists in the United Kingdom (UK) searched to find a long-lasting mark or tag, that would be retained through up to 26 moults and yet be suitable for the size of juveniles released; carapace length (CL) between 12-15 mm. Various systems were examined at the Fisheries Laboratory (MAFF), before deciding on the Coded Wire Tag (CWT). In the first release of the lobster stock enhancement programme (1983-1988), a standard 1 mm long tag was implanted in juvenile lobsters at moult stages X-XII (CL between 12-15 mm). Later small-scale trials at the North Western and North Wales Sea Fisheries Committee’s (NWNWSFC) hatchery tested the use of the 1 mm tag on juveniles as young as stage IV with some success. This was followed by the second release phase of the project, conducted in Scotland from 1990-1992, where half-length (0.5 mm long) CWTs were used on animals of stage V-VII (4-6 mm CL). An NMT MK IIa tagging machine was modified so the needle was in the “out” position. Head mold bases were supplied blank so that a custom support could be made with epoxy resins in order to ensure that each lobster could be accurately and quickly positioned for tagging. Later the machine was further modified to enable it to dispense half-length CWTs. Experiments established that tagging was best conducted when lobsters were at the midpoint of the intermoult phase of their moult cycle. Unfortunately, this is difficult to determine in a hatchery since moulting is not synchronous. Each tag was implanted ventrally in a muscle block at the base of one of the last pair of walking legs (either the 4th or 5th pereiodpod) parallel with the longitudinal axis of the animal. This position was chosen so that the tag would not be lost during moulting or if the limbs were shed. In the experiments conducted by MAFF and NWNWSFC, lobsters were released in the same areas in the spring and autumn of each year. The tags were implanted in either the left or right side of the cephalo-thorax to distinguish batches. In contrast, the Sea Fish Industry Authority (SEAFISH), with geographically separate release sites, used only the left side for tag location. Tagging mortality, measured by the three experimental groups in the laboratory, over 12 months, using the standard tag in stage X-XII animals, was usually less than 1%. Tag retention was in excess of 95%. Survival of the smaller animals, stage V-VII, tagged with the half-length CWT, averaged approximately 25% but often fell below this. The additional stress caused by handling and the large size of the puncture wound (in relation to lobster size) is thought to have contributed significantly to the higher mortality recorded with the smaller lobsters. Tag retention amongst survivors, measured under the same laboratory conditions as previously described, was 99%. The first release, by MAFF, took place in Bridlington Bay, Yorkshire in 1983 and by 1989, over 98,000 coded wire tagged juvenile lobsters had been released in the four areas around the UK (Bridlington Bay [MAFF]; Cardigan Bay, Wales [NWNWSFC]; Lock Ceann Traigh, Argyll and Scapa Flow, Orkney [both by Seafish]). During the second phase of the programme a further 10,000 animals were released between 1990-1992 into Lock Ceann Traigh, each marked with a half-length CWT. In Scotland, monitoring of the released animals began in 1985 with diver surveys and in 1986 target fishing using small-meshed creels (lobster traps) was also carried out. The other groups began creeling in 1988 and recovered juvenile lobsters which had grown large enough to be retained by commercial pots (>50 mm CL). As the animals grew, monitoring increased to include screening commercial fishery landings at the quayside or at merchants’ premises in order to detect lobsters which had reached the UK minimum landing size (MLS) of 85 mm CL. Coded wire tagged animals were detected using the NMT 6” diameter tubular detectors, either housed statically or in a trailer. So far as is known no mortalities were ever directly attributed to the tag screening process. Tags have been recovered up to ten years after implantation in a lobster and most were decoded almost at once with the code being clearly legible. Some tags had a ‘frosted’ appearance. These tags, after removal, were soaked in a potassium hydroxide (KOH) to remove any organic matter adhering to the tag. Some tags were found partially and in one case fully, enclosed in a melanized capsule. The degree of encapsulation did not appear to relate to the length of time since implantation. Immersion in KOH softened the capsule enough to enable its removal by careful dissection. Once clean, it was necessary to dry the tags to remove all traces of KOH because it was corrosive to the magnetic tips of the tag reading jig pencils. Determining the tag code was carried out using a low power binocular microscope and, with experience, became a speedy undertaking. The availability and use of the CWT technology has been crucial to the success of the research programme in the UK. Scientists have been able to demonstrate conclusively that hatchery reared juvenile lobsters, released to the wild onto natural habitats, survive and grow to reach market size. Where data on the position of recapture was available, there appeared to be a high degree of fidelity to the release sites and on some occasions up to 80% of the animals caught in individual pots strings have been of hatchery origin. The recovery of tagged, berried, females showed that the animals could reproduce normally and contribute further to stocks. Recaptures have so far totaled more than 1500 and recoveries from commercial landing have been an eloquent demonstration that fishermen can benefit directly from such introductions, and that no alteration to their gear or pattern of fishing is necessary. The next step in the UK is to extend the lobster restocking trials to a commercial level. Because of the costs of tagging and monitoring, coded wire tags may not be used in every animal released but it would be useful to tag sub-samples so that improvements in culture techniques and release strategies can be quantified, and ultimately, to enable the success of a stocking programme to be demonstrated. Authors: C.A. Burton, Sea Fish Industry Authority (Seafish), Marine Framing Unit, Ardtoe, Acharacle, Argyll PH36 4LD, UK. Tel + 1967 431213, Fax + 1967 431343 Beard, T.W., Wickins, J.F., Ministry of Agriculture, Fisheries and Food (MAFF) Fisheries Laboratory, Benarth Road, Conwy, Gwynedd, LL32 8UB Cook, W. North Western and North Wales Seat Fisheries Committee (NWNWSFS), University of Lancaster, Bailrigg, Lancaster, Lancashire, LA1 4XY Bannister, R.C.A. Ministry of Agriculture, Fisheries and Food (MAFF), Fisheries Laboratory, Pakefield Road, Lowestoft, Suffolk, NR33 0HT | ||
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Northwest Marine Technology, Inc. (360) 468 - 3375 | Last edited: 02 Dec 2008 | ||
