An alternative stock management for snow crab, Chionoecetes opilio (Brachyura, Majidae), based on the presence of a terminal moult

1 Pages·1991·0.42 MB·

by  M Moriyasu

MEMOIRS OF THE QUEENSLAND MUSEUM 461
AN ALTERNATIVE STOCK MANAGEMENT of the spring and early summer fishing season, therefore only
FOR SNOW CRAB, CHIONOECETES OPILIO the males which reached the terminal moult one year earlier
(BRACHYURA, MAJIDAE), BASED ON THE can male efficiently. Management strategies were designed
PRESENCE OF A TERMINAL MOULT for avoiding the harvest of recent moulters, The catch would
The snow crab, Chionoecetes opilio, is the most important be optimised both in terms of yield per recruit and quality if
commercial crab in Canada. In the southern Gulf of St only the males which have reached the terminal moultat least
Lawrence, the landings decreased drastically from 32.0001 12months earlier were harvested. This can be achieved cither
in 1982 to 7880 1 in 1989, al which point the fishery was by using traps selectively inaccessible to the less aggressive
prematurely closed due toa high incidence of newly moulted non terminal moult males, or by introducing a gauge identi-
8white9 crabs in the commercial catch. fying terminal moult males asa function of allometry oft heir
The description of a terminal moult in male as well as larger claw size respective to carapace size.
female crabs (Conan and Comeau, 1986) has generated a Using geostatistical mapping techniques subareas likely to
new interpretation of the life cycle of the species, This. new contain high densities of recently moulted males can be
knowledge has important management implications for re- identified during a prefishing period survey, The geographic
building the commercial potential of the stack. concentrations of recently moulled males frequently differ
In the Gulf of St Lawrence, processors rely on hard shell from the concentrations of hard shell ones and specific zones
terminal moult males which moulted one year or more prior can be closed selectively prior to the fishing season in order
to the short ten week fishing season. At an early state of to protect the recent moulters.
exploitation, most individuals captured in the southern Gulf In order to rebuild the stock and stabilise the commercial
were inthe terminal moult phase. The catch resulted from the landings, the protection of the annual recruitment ofs oft shell
accumulation of 3 to 4 year classes of the terminal moult crabs as well.as catch limitations of hard-shell terminal moult
crabs. As the fishery developed, old terminal moult males crab are required, Tt appears that an age group reaches the
were fished out and the proportion of individuals which had terminal moull over a series of successive years, A major,
tecently moulted immediately prior lo the fishing season still unresolved issue is to determine whether a non terminal
increased in the commercial catch. These recently recruited C. opilio will opt for the terminal moult over a moult period.
(called 8whites9 by the fishermen) have a low commercial The answer would have major implications for management
value and are mostly discarded at sea with a subsequent high since many crabs reach terminal moult at a size smaller than
fishery induced mortality. The harvest became based almost the existing minimal legal size.
entirely on annual recruitment of newly moulted terminal
moult individuals, Such a catch would have beer ultimately Literature Cited
of low commercial processing quality and extremely sensi- Conan, G.¥. and Comeau, M. 1986. Functional maturity
tive to annual fluctuations of recruitment. and terminal moult of male snow crab Chionoecetes
The newly discovered patterns of life history are now opilio, Canadian Journal of Fisheries and Aquatic
being used for designing management strategies of the fish- Sciences 43(9): 1710-1719.
ery. Newly moulted mules have no chance to mate before a
complete hardening of their carapace. The matoif tnermgina l M. Moriyasu and G.Y. Conan, Science Branch,
moult males with hard shell multiparqus females takes place Department of Fisheries and Oceans, Monoton, NB.
shortly after the spring moulting season and at the beginning Canada,