Fifth International Crustacean Congress, 9-13 July 2001, University of Melbourne, AustraliaXunta de Galicia; XUGA10301B97Ministerio  de Ciencia y Tecnología; REN2000-0446/MA

Bernárdez Martí, Cristina

Corgos López-Prado, Antonio

Fernández, Luis

Freire, Juan

Verísimo Amor, Patricia

Repositorio da Universidade da Coruña

5th International Crustacean Congress, July 2001 (Melbourne, Australia) 1 Timing and seasonality of the onset of maturity, gonad maturation and mating in the spider crab Maja squinado: Relationships with habitat use and social structure  Antonio Corgos, Juan Freire, Cristina Bernárdez, Luis Fernández & Patricia Verísimo Departamento de Bioloxía Animal, Bioloxía Vexetal e Ecoloxía, Universidade da Coruña, Campus da Zapateira s/n, E-15071 A Coruña, Spain   INTRODUCTION: Juveniles of Maja squinado inhabit shallow waters. During their second or third summer of life (depending on the recruitment season), they undergo the terminal moult, attaining sexual maturity (González-Gurriarán et al., 1995; Sampedro et al.,1999). During late summer and early autumn adults start a reproductive migration towards deep waters (Freire et al., 1999; González-Gurriarán & Freire, 1994). The present study analyzes in detail the timing of morphometric and gonad maturity, and the onset of migration, and the reproductive status and body condition during this period, trying to define reproductive strategies including their individual and intersexual variability and the relationships with habitat use and social structure.  METHODOLOGY: Monthly samplings were carried out between December 1997 and November 1999 using experimental traps (Fig. 1). The sampling area was the Ría de A Coruña (NW Spain) (Fig. 2). Three shallow water (5-15 m) sampling stations were selected along the ría and another one in deeper waters (25-30 m) in the central channel of the ría, that constitutes the migration corridor for postpubertal adults. In the inner area of the ría (Bastiagueiro), where the abundance is higher, sampling was done along a transect in the longitudinal axis of the ría where seven tows were carried out disposing the traps parallel to the coast, and each tow was separated approx. 180 m from each other.   Reproductive status and body condition: Monthly samples were taken between May 1998 and June 1999. Crabs were dissected in order to determine gonad maturation stage, gonad dry weight, dry weight of hepatopanchreas and muscle of the second pereiopod, presence and fullness of spermathecae in females, and presence of spermatophores in males. The condition indexes of hepatopanchreas, gonad and muscle were estimated from the residuals of a linear regression of the dry weight of each tissue against the carapace length (CL).    Terminal moult: Adult males inhabiting shallow waters in May and June were in a large percentage in soft-shell condition, while soft adult females were found mainly between June and August. As showed in the Figure 3, the terminal moult period was longer and took place one month before for males than for females. SPAIN43ºN42º8º W 7º50 kmA CORUÑAPORTUGAL% posmoult adults0102030405060Dec 97Jan 98 FebMarAprMayJunJulAugSepOctNov DecJan 99 FebMarAprMayJunJulAugSepOctNovMales Females Figure 2. Sampling areas in the Ría de A Coruña. Figure 1.  Experimental traps used in the study. Figure 3. Percentage of soft adults in the shallow area 5th International Crustacean Congress, July 2001 (Melbourne, Australia) 2  Gonad development: Females started their gonad development in November, 2-3 months after the terminal moult (Fig. 4). Males developed their gonads before they attained morphometric maturity. More than the 76 % of the juvenile males larger than 96 mm (CL) and all morphometrically mature males had spermatophores.  Spatial and social structure and timing of the migration: Juvenile crabs showed a very clear aggregative behaviour in shallow areas (Fig. 5), probably to avoid predation risk in these kind of sandy areas without refuges. Between June and November the aggregative pattern is broken by the presence of recently moulted adults, and both juveniles and adults are dispersed along the area. Adults move progressively to the outer part of the shallow area (Fig. 6), leaving it coordinately in September (males) and October (females) (Fig. 7). The coordination of the migration within each sex (regardless of body condition, see below) seems to indicate that the migration is triggered by oceanographic signals (Freire et al., 1999).   Body condition: From July to December, adult males in the shallow water area gradually increased their gonad, muscle and hepatopanchreas condition (Fig 8). Crabs captured in November in the migration corridor showed a similar body condition to those captured in the shallow area, so the hypothesis of the acquisition of a minimum body condition level as a condition for the start of migration seems not to be supported by the data.  Males mature, start gonad development and migrate earlier, arriving earlier than females to the mating grounds. Thus, we propose the hypothesis that males aggregate in deep waters (supported by fishers’ observations) and compete for the females, constituting probably a lek mating system.    Based in the above observations it could be hypothesized that intrasexual reproductive variability are due to the existence of different reproductive strategies within the male population:  024681012360 540 720 900 1080 1260 1440September 98Figure 4. Gonad developmental stage of females in the shallow area (see González-Gurriarán et al., 1998 for a definition of development stages).  048121620360 540 720 900 1080 1260 1440January 990481216360 540 720 900 1080 1260 1440MalesFemalesMarch 99Figure 5. Aggregative behaviour of the juveniles of the shallow area in the winter: catch per unit of effort (no. of crabs per trap ±95% confidence interval of the mean) along the transect sampledin the inner area of the Ría de A Coruña. The x axis represents the distance to the coastline. 02468360 540 720 900 1080 1260 1440MalesFemalesJuly 9802468360 540 720 900 1080 1260 1440August 9803691215360 540 720 900 1080 1260 1440 October 98 0246360 540 720 900 1080 1260 1440 November 98 0123360 540 720 900 1080 1260 1440 December 98 Distance to the coastline (m). Figure 6. Spatial structure of adults in the shallow area prior to migration: catch per unit of effort (no. of crabs per trap ±95% confidence interval of the mean) along the transect sampled in the inner area of the Ría de A Coruña The x axis represents the distance to the coastline. 5th International Crustacean Congress, July 2001 (Melbourne, Australia) 3 • The “early migrators” carry out the migration in “bad” body condition, which involves a higher risk due to the energetic cost of these large-scale movements, but has the advantage of arriving earlier to the mating grounds. • The “late migrators” carry out the migration in good body condition, but miss mating opportunities.   Adult females captured in the migration corridor also showed a similar body condition as that of their shallow water counterparts, although with larger gonad weights. They seem to have strategies similar to the males. However, females are in “bad” body condition until November. Females muscle condition is stable along the studied period, and this may indicate that they invest the energy in gonad development and energy accumulation rather than in muscle development, what might be due to a less intense mating competition than in the case of males (Fig. 8).    Aknowlwdgements: To Juan Otero for this help with the field work. This study was funded with grants XUGA10301B97 of the Xunta de Galicia and REN2000-0446/MAR of the Spanish Ministerio de Ciencia y Tecnología.  Literature cited:Freire, J., E.G. Gurriarán & C. Bernárdez (1999). ICES.CM.AA:14.pp. 11. González-Gurriarán, E. & J. Freire (1994). Journal of Experimental Marine Biology and Ecology 184: 269-291. González-Gurriarán, E., J. Freire, J. Parapar, M.P. Sampedro & M. Urcera (1995). Journal of Experimental Marine Biology and Ecology 189: 183-203. González-Gurriarán, E., L. Fernández, J. Freire & R. Muiño (1998). Journal of Experimental Marine Biology and Ecology 220: 269-285. Sampedro, M.P., E.G. Gurriarán, J. Freire & R. Muiño (1999). Journal of Crustacean Biology 19 (3): 578-592.  Fifth International Crustacean Congress, 9-13 July 2001.The University of Melbourne, Australia Residual dry weight (g)-6-4-20246810JUL 98 AUG SEP OCT NOV DECFemale gonad -2-10123SEP 98 OCT NOV DECFemale muscle-3-2-1012SEP OCT NOV DECFemale hepatopanchreas02468Mar 98AprMay JunJulAugSepOctNovDecJan 99FebMarFemalesMalesCentral ChannelFigure 7. Adult catches in the migration corridor (central channel) (no. of crabs per trap ±95% confidence interval of the mean). Figure 8. Body condition of adults in the shallow area and the migration corridor (central channel). Residual dry weight (g)-4-2024681012MAY 98 JUN JUL AUG SEP OCT NOV DECMale gonadShallow areaCentral channel-2.0-1.5-1.0-0.50.00.51.01.52.02.5SEP 98 OCT NOV DECMale muscle-3-2-10123SEP 98 OCT NOV DICMale hepatopanchreas

Timing and seasonality of the onset of maturity, gonad maturation and
mating in the spider crab "Maja squinado" : relationships with habitat use and social structure

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Timing and seasonality of the onset of maturity, gonad maturation and mating in the spider crab "Maja squinado" : relationships with habitat use and social structure

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