Interactions of the fishery of the spider crab Maja squinado with mating, reproductive biology and migrations
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Interactions of the fishery of the spider crab Maja squinado with mating, reproductive biology and migrationsDate
1998Abstract
[Abstract] In this paper different aspects of the fishery and life history of the spider crab Maja squinado in southern Galicia (NW Spain) are analyzed to evaluate the potential effects of the fishery on the sperm limitation of the reproductive effort (egg production) of the population.
Juveniles of the spider crab inhabit shallow waters, where they carry out a terminal
moult in August-September, attaining sexual maturity when they are 2+ years old. A short
time after the terminal moult (October-November), adults migrate to deeper waters (up to
100 m), where mating occurs (January-February). Field and laboratory data show that
multiple matings and sperm storage in female seminal receptacles occur, indicating that
females are able to fertilize multiple broods during the annual breeding cycle using stored
sperm.
The spider crab is the target of a tangle-net fishery, characterized by a very high fishing
effort similar for both sexes. The fishing season is from November-December until May-June
and is mostly dependent on migrating animals. Data from catch composition (percentage of
recent recruits at the beginning of the season), recaptures from the fishery of females
tagged with ultrasonic transmitters and electronic archival tags, and CPUE trends over the
course of the fishing season (Leslie analyses of stock depletion) indicate that more than
90% of postpubertal (primiparous) adults are caught during the fishing season. The fishery
is almost exclusively dependent on the autumn recruitment of the annual cohort of
primiparous adults. Most of the catches are made in autumn and early winter, before or
during the mating season (for 4 fishing seasons an average of 45 and 66% of the catches
are made before January and February respectively).
The volume of sperm stored in the seminal receptacles and the percentage of females with
sperm is lower for females caught in the field during or immediately after the mating season
than for females kept in laboratory with a high density of males, and decreases throughout
the annual breeding cycle. These two facts may be brought about the low density of both
sexes in the mating grounds due to fishery exploitation. We hypothesized that, although
sperm limitation probably does occur, the main factor in the severe fishery induced
limitation of the reproductive effort of the Galician spider crab populations, as opposed to
other crab fisheries targeting only males, is the mortality imposed on females before or
during breeding. More information about mating habitat, seasonality and behaviour would be
needed for an accurate evaluation of the potential effects of the fishery (and of different
management strategies) on sperm limitation.
Keywords
Life history
Maja squinado
Mating
Migrations
Mortality
Reproductive effort
Seasonality
Spider crab
Tangle-net fishery
Maja squinado
Mating
Migrations
Mortality
Reproductive effort
Seasonality
Spider crab
Tangle-net fishery