Interactions of the fishery of the spider crab Maja squinado with mating,reproductive biology and migrations

In this paper different aspects of the fishery and life history of the spider crab Maja squinadoin southern Galicia (NW Spain) are analyzed to evaluate the potential effects of the fisheryon 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 terminalmoult in August-September, attaining sexual maturity when they are 2+ years old. A shorttime after the terminal moult (October-November), adults migrate to deeper waters (up to100 m), where mating occurs (January-February). Field and laboratory data show thatmultiple matings and sperm storage in female seminal receptacles occur, indicating thatfemales are able to fertilize multiple broods during the annual breeding cycle using storedsperm.The spider crab is the target of a tangle-net fishery, characterized by a very high fishingeffort similar for both sexes. The fishing season is from November-December until May-Juneand is mostly dependent on migrating animals. Data from catch composition (percentage ofrecent recruits at the beginning of the season), recaptures from the fishery of femalestagged with ultrasonic transmitters and electronic archival tags, and CPUE trends over thecourse of the fishing season (Leslie analyses of stock depletion) indicate that more than90% of postpubertal (primiparous) adults are caught during the fishing season. The fisheryis almost exclusively dependent on the autumn recruitment of the annual cohort ofprimiparous adults. Most of the catches are made in autumn and early winter, before orduring the mating season (for 4 fishing seasons an average of 45 and 66% of the catchesare made before January and February respectively).The volume of sperm stored in the seminal receptacles and the percentage of females withsperm is lower for females caught in the field during or immediately after the mating seasonthan for females kept in laboratory with a high density of males, and decreases throughoutthe annual breeding cycle. These two facts may be brought about the low density of bothsexes in the mating grounds due to fishery exploitation. We hypothesized that, althoughsperm limitation probably does occur, the main factor in the severe fishery inducedlimitation of the reproductive effort of the Galician spider crab populations, as opposed toother crab fisheries targeting only males, is the mortality imposed on females before orduring breeding. More information about mating habitat, seasonality and behaviour would beneeded for an accurate evaluation of the potential effects of the fishery (and of differentmanagement strategies) on sperm limitation.