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A second assessment of the whelk fishery Buccinum undatum inthe southwest Irish Sea with particular reference to its history of management by size limit

Weitere Beteiligte (Hrsg. etc.): Fahy, Edward

Originalveröffentlichung: (2000) http://www.marine.ie/NR/rdonlyres/2B635751-B06C-491E-AC92-EAD52D1E254C/0/ns6.pdf
pdf-Format:
Dokument 1.pdf (1.253 KB)


BK - Klassifikation: 48.67
Sondersammelgebiete: 21.3 Küsten- und Hochseefischerei
DDC-Sachgruppe: Biowissenschaften, Biologie
Sonstige beteiligte Institution: Irish Marine Institute
Dokumentart: Bericht / Forschungsbericht / Abhandlung
Schriftenreihe: Irish Fisheries Investigations (Bd. 3-15, 17-20, 24)
Bandnummer: 6
Sprache: Englisch
Erstellungsjahr: 2000
Publikationsdatum: 14.05.2009
Kurzfassung auf : Whelk landings in the southwest Irish Sea increased from 56 t in 1990 to 6,575 t in 1996
after which they stabilized between 3,600 and 4,600 t annually. At its peak the fishery
supported approximately 80 vessels but this number has halved since. In 1994 a size limit
of 50 mm was introduced for conservation purposes. Age based assessments of the
landings were carried out in 1994, 1996, 1997 and 1999, for which purpose the fishery,
ranging from 52º10’ to 53º30’, is divided into four sectors. Landings to the four sectors
display biological characteristics which indicate the occurrence of a number of stocklets
rather than a single stock unit.
Whelk in the south west Irish Sea are relatively thin shelled and the fishery has a low
density of large crustacean predators. There is no evidence of contamination by TBT. The
northern and southern ends of the fishery have relatively lower densities of larger/older
animals; the centre sectors have smaller whelk of shorter life span at higher densities,
some of them showing symptoms of a Lee phenomenon and slower growth. A survey of
cpue places heaviest densities on the Codling and Rusk Banks, in strong tidal currents, at
depths of < 20 m. Growth and maturation rates vary among stocklets. L∞ ranges from
102 to 116 mm. Length at 50% male maturation is usually within the range of 63 – 68
mm and ages of 6.1-7.2 years although landings to one sector have a 50% male
maturation rate of 83 mm and 8.5 years of age. The existing size limit of 50 mm would, at
best, afford protection to 40% of spawning males. Compliance with the size limit has
been poor. From 20 to 33% of total landings in any of the assessed years have been less
than the legal limit and in 1994 51% of landings in one sector were below the acceptable
size. Trends in cpue have been monitored since 1990 and some areas do not show any
marked tendency. On the contrary, some fishermen in the centre sectors improved their
yield between 1994 and 1998. There are two explanations for this: the movement of pots
onto virgin ground and the fact that fewer fishermen are competing for landings in the
same areas. Whelk have responded to a reduction in fishing effort since 1996
immediately following which mortality coefficients (Z) were highest (0.79); they declined
to an average 0.61 in 1999. In terms of yield per recruit however they remain high. The
southern sector of the fishery is regarded as being most depleted although very few subsize
limit whelks were caught there.
The survival of the whelk fishery in the southwest Irish Sea is attributed to the instability
of the market which is dominated by a single customer, South Korea. A more effective
size limit for this fishery would be 68mm (83 mm in the northern sector) and this is
considered unrealistic, suggesting that alternative management measures will have to be
considered.


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Letzte Änderung: 12.10.2015