Sexual Maturity, Reproductive Pattern and Spawning Female Population of the Blue Swimming Crab, Portunus pelagicus (Brachyura: Portunidae) in East Lampung Coastal Waters, Indonesia

Little is known about the biology of the blue swimming crab, Portunus pelagicus in east Lampung coastal waters, Indonesia; despite in fishery point of view this species has valuable contribution to the country. We examined the gonad development and the occurrence of ovigerous females for determining the mean size at sexual maturity, reproductive pattern and spawning female population of the crab in East Lampung coastal waters. The mean size of males and females reached sexual maturity (Lm50) at 98-mm and 103-mm carapace width (CW), respectively. Reproductive pattern was partially spawners, seasonal-continuous throughout in the year with the peak spawning and breeding in April to June and October to November. Most female at the size >111-mm CW showed double breeding in a season. The relative percentage of all ovigerous females below the size of Lm50 was considerably low (±2%), spawning female population at 103–170.9-mm CW size range and the ratio of ovigerous to adult females above the average value found in 116-165.9-mm CW size range. Using 115-mm CW as minimum legal size would conserve ±21.38% spawning female as breeding population. *Author for correspondence Indian Journal of Science and Technology, Vol 8(7), 596–607, April 2015 ISSN (Print) : 0974-6846 ISSN (Online) : 0974-5645 Sexual Maturity, Reproductive Pattern and Spawning Female Population of the Blue Swimming Crab, Portunus pelagicus (Brachyura: Portunidae) in East Lampung Coastal Waters, Indonesia Zairion*, Yusli Wardiatno and Achmad Fahrudin Bogor Agricultural University, Indonesia; zairion.zai@gmail.com, yusli@ipb.ac.id, fahrudina@ipb.ac.id


Introduction
The blue swimming crab, Portunus pelagicus "sensu lato" occurs in shallow tropical and temperate coastal and estuarine waters throughout the Indo-West Pacific, while Portunus pelagicus (Linnaeus, 1758) "sensu stricto" is distributed across Southeast and East Asia 1 . The abundance of this species in nature combined with increasing demand renders it as valuable target in fishery sector throughout its distribution area. In Indonesia, P. pelagicus is exploited by small-scale fishery in most coastal waters and wild catch production tends to increase in the decade. Data in 2011 shows that the total capture was approximately 42,410 tons and P. pelagicus of the East Lampung coastal waters contributed approximately 21%. Most of catches are used in crab meat industry and then exported by the retailer 2 .
Philippines 18,19 and in Malaysia 20,21 . However, reproductive biology parameters seemed to have intra and interspecific variations, area-specific and regional differences. In most earlier studies, estimation of body size at sexual maturity of male and female in brachyuran crabs were usually determined by physiological maturity based on gonad condition 22 or functional maturity related to allometric changes in growth of the body parts 14,[23][24][25] or both [26][27][28][29][30] . A synchronous of physiological and functional maturity was found in females when studied by both approaches, but some asynchrony occured in males. Therefore, physiological maturity is often used to determine the size at sexual maturity of females portunid crabs, since there is an actual capacity to release gametes and correspond to functional maturity 22 . In addition, morphometric maturity does not always indicate functional maturity 31 or does not coincide with physiological sexual maturity 32 .
Brachyuran crabs are categorized as iteroparous species which have high variations of reproduction patterns 33, 34 . The reproductive periodicity of P. pelagicus follows a continuous pattern in tropical and subtropical region 18,35 . When duration, occurrence, and intensity of reproduction are taken into account, the reproduction periodicity may be subdivided into three categories 36 : (1) seasonal reproduction, either the presence of the females with mature gonad or the presence of ovigerous female are restricted to a certain months or seasons; (2) continuous, when ovigerous females occur during all months of the year with similar frequency; (3) seasonal-continuous, the presence of ovigerous female in all months of the year, but with distinguishable peak of high occurrence in some months or seasons.
Little is known about biology of P. pelagicus in East Lampung coastal waters and there have been no studies on its reproductive biology, although it supports substantial artisanal fisheries. The aims of this study were to determine sexual maturity in the term of the size at which 50% of the population is physiologically mature, reproductive pattern based on gonad condition (including ovigerous female and its occurrence) and spawning female population of P. pelagicus in East Lampung coastal waters. The use of those reproductive biology characters in fisheries management is highlighted.

Samples Collection and Environmental Regimes
In order to determine the size at sexual maturity and reproductive pattern, Portunus pelagicus samples were collected monthly from June 2011-May 2012 at two landing sites, i.e. Kuala Penet and Labuhan Maringgai, East Lampung District, Lampung Province, Indonesia ( Figure  1). Those samples represent different fishing ground (i.e. near shore and offshore), which captured by local fisher using set gill-net as main fishing gear, nets had mesh sizes of 3.0-4.5 in or 7.6-11.4 cm 37 . The proportion of landed crabs (males, ovigerous females and non-ovigerous females) from representative fishing ground was recorded daily during a week in each month. Sexes were determined by examining of morphological characteristics of species. Meanwhile, male and female non-ovigerous samples of representative size distributions were collected by stratified random sampling based on landing sited and fishing ground. This method provides wider size range of captured crabs and potentially less bias in estimating of size at sexual maturity. Collected samples were also represent small capture size and immature females, indicated by triangular shape of abdominal flap and tightly fix to the cephalothorax 38,39 . In addition, ovigerous females (egg bearing females) were also taken in various sizes for ovaries examinations. All samples were measured their carapace width (CW: the distance between tips of 9 th anterolateral teeth), carapace length (CL: distance between the frontal marginal to the posterior margin of the carapace), and body weight (W). Length measurement were done by using digital calliper to the nearest 0.01 mm, while W was measured to the nearest 0.1 g by using digital balance. Gonad examination was conducted after morphological characteristic measurements. In order to determine the spawning female population, the size distribution frequency data from independent monthly collection using the same type of fishing gear from March 2012-February 2013 was also included (Zairion et al. unpublished data). The East Lampung coastal land area is covered by approximately 60% of low land forest and protected as Way Kambas National Park (WKNP). There is no sea grass bed found in the shallow coastal waters, but this area is one among the blue swimming crab habitats and fishing ground of Indonesia. Based on water quality checking in February and August as a representative of rainy season (west and north west monsoon) and dry season (east and south east monsoon), there was no high variation of sea surface temperature (28-32 o C). Meanwhile, near bottom temperature for both season ranged between 28-29.5 o C. On the other hand, sea surface salinity ranged between 10-25 PSU from near shore to offshore at northern area in February due to high freshwater supply from Way Seputih River and 25-29 PSU at the bottom. At the same time, sea surface and bottom salinity were 29-30 PSU and 30-32 from near shore to offshore at southern area (close to Labuhan Maringgai). In contrast, salinity for both surface and bottom became 17-27 and 27-30 PSU at northern during dry season, and 28-32 and 29-32 PSU at southern, respectively.

Gonad Examination and Gonad Somatic Indices (GSI)
The female maturity stages in portunid crabs recognized by different researchers concerning the maturation of female ovaries in terms of morphological or histological feature show variation. Similar thing is shown in male vas differentia. In this study, maturity stages of female gonad were determined by classifying them into four categories, i.e. Stage I (immature), stage II (early development), stage III (late development or maturing), stage IV (fully mature). Whilst male gonad maturity stages were classified into three categories, i.e. Stage I (immature), Stage II (maturing), and Stage III (mature) 29,40,41 . In addition, three classifications were used for embryonic development stages, namely: (i) initial (yellow, orange-yellowish), (ii) intermediate (brownish-brown), and (iii) final (blackgrey black) 21,36 . Prior to measurement of gonad somatic indices (GSI), all part of individual gonad was taken carefully by blunt-nosed thumb forceps with serrated tips and the weight was measured to the nearest 0.001 g using electronic balance.

Sexual Maturity and Gonad Somatic Indices
The proportion of matured gonad was used in determining size at sexual maturity and internal ovarian of ovigerous females were excluded 7 . The size at which 50% (Lm 50 ) of crabs were considered sexually matured by fitting a logistic regression curve to the proportion of mature gonad females for each sequential 5-mm CW size class, following the method as described by King 42 . Gonad somatic index (GSI) for males, females and ovigerous females was also analysed 6,40,41 . A trend analyses and one way ANOVA 43 were used to test differences of GSI for males, females, and ovigerous female by time and size.

Reproductive Pattern and Spawning Female Population
Reproductive pattern for both spawning and breeding season was determined by temporal distribution of mature female gonad, GSI, and the proportion of ovigerous to the adult females 6,25,29,44,45 . A trend analysis were used for the temporal GSI and the proportion of ovigerous and completed by the one way ANOVA test to describe any differences. Analysis of reproductive pattern was also completed by gonad condition of ovigerous female. Meanwhile, we propose the spawning female population by estimated the relative percentage of adult females and ovigerous in each 5-mm CW size class, as well as their ratio.

Crabs Size, Gonad Development and Sexual Maturity
TA total of 1297 specimens were collected during observation period, while the size of males was wider than females and ovigerous (

Gonad Somatic Indices
The gonad condition patterns is expressed by gonad somatic index (GSI). Mean monthly of all female GSI showed slightly cyclic pattern throughout the year, increase progressively from 1.60% in January to a maximum of 2.50% in May and subsequently decreased to minimum of 1.53% in July, and then became increased again to 2.30% in November ( Figure 6). The mean monthly GSI of matured females also exhibited cyclic pattern. It was prevalent during April to July (3.3%±0.5 to 3.6%±0.9SE) and September to December (3.3%±0.3 to 4.0%±0.3SE). There were significant difference (p<0.05) of females GSI in the observed period. However, the gonad index of males did not show significantly different; it would therefore not to be discussed further. The mean monthly GSI of all ovigerous females found more cyclic than non ovigerous ones, which the percentage was 0.82±0.18SE in June to 3.88±0.45SE in November and there were significant different (p<0.05) among ovigerous females GSI thorough observed month. The highest mean GSI of matured ovigerous females was found in July to August and October to December (Figure 7). Ovigerous female with gonad development at stage IV was found in the size class 111.0-115.9-mm CW and bigger, while the mean GSI was 1.2-4.8% in each size class which might indicate the ocurrence of double breeding.

Temporal Proportion of Ovigerous Females
Ovigerous females found in all sampling months and their monthly proportion to the adult females showed cyclic pattern with most prevalent in April to June and October to November, indicated as seasonal continuous reproduction pattern (Figure 8). These proportion for both by the number and weight ranged between 5.2-19.6%

Spawning Female Population
Female with gonad stage IV as well as the smallest size of ovigerous female were available since the size class 91-95.9-mm, pronounced spawning and breeding activity began at this size class to at least in the size class 166-170.9-mm CW. The relative percentage of ovigerous females in each 5-mm CW size class increased from the lowest of 0.28% in the size class 91-95.9-mm CW to the highest of 12.94% in the size class 126-130.9-mm CW, and then decreased again. Meanwhile, the relative percentage of all ovigerous female in the size below Lm 50 (i.e., 91-102.9-mm) was approximately 2%. The ratio between ovigerous females to the adult females was increasing from the lowest of 0.01 in the size class 91-95.9-mm to the highest of 0.36 in the size class 151-155.9-mm CW, and then decreased. The average ratio was 0.17±0.02SE and the ratio above of the average value found in the size between 115-165.9-mm CW (Figure 9), while the relative percentage of all ovigerous females less than 115-mm CW was approximately 21.38%.

Sexual Maturity
Our results show that males and females were almost synchronous in gonad maturity and this strategy is believed as natural process of maintaining the population size, providing large numbers of adult crabs, and maximizing reproductive effort related to their habitat 36 . Based on gonad development, both sexes below 81-mm CW size were all immature and a priori as juvenile, whilst adolescent females in the size above 91-mm CW since they have capability in extruding egg 7 , while fully adult for males and females approximately in the size above 124-mm and 126-mm CW, respectively. This finding corresponds to the P. pelagicus in southwest coast of India where size <80-mm CW was categorized as juvenile 6 and in Moreton Bay of Australia where the sexually matured crab was considered above 90-mm CW 35 .
Our estimated for the Lm 50 of female P. pelagicus was slightly different with some estimates in some other coastal waters of Indonesia, i.e. 105-mm CW in northern West Java 46 , 48-mm CL or 101.40-mm CW in Central Java 47 as well as in Ragay Bay, Philippines, i.e. 105-mm CW 19 , but it was much different to many other areas ( Table 2). This discrepancy might reflect of disparate in biology of the species and genetic composition 33, 45 . The same species in the same area or in different area might also vary in the Lm 50 since pubertal occurred over wide size range 14 , which is related to variation in environmental conditions, i.e. food abundance, population density and parasitism 7,34,48 . Environments with abundant food allow individuals to grow faster and larger. By taking the maturity size of the crab, it can be said that East Lampung coastal waters might provide sufficient food and other favourable environments compared to coastal waters in northern West Java and Central Java of Indonesia.
Other factor which might influence in maturity size of the species was fishing intensity because it may diminish the density of the species [49][50] . Fishing ground or site of sampling (i.e. estuary versus offshore) may also influence the estimation of mean size at maturity of female P. pelagicus due to emigration habit of matured females from estuaries to offshore 29,45,51 . In addition, fishing gears may have also effect the differences in estimated Lm 50 related to their selectivity, i.e., traps catches are often biased for determining sexually matured crabs 39 . Fishing intensity in the study area is not known well yet; however, our samples were collected in representative of all fishing ground, as well as in all season. The crabs were also captured by the fisher using set gillnet with the mesh size of 7.6-11.4 cm and it seems to be a low selective fishing gear. Moreover, the Lm 50 may also vary as consequent of interspecific reproductive biology pattern 33 . In terms of reproductive biological characters, the crab in the study area might be different to the species in Karnataka, including in Persian Gulf and Bardawil lagoon of Egypt as well as the species in sub-tropical and temperate regions of Australia ( Table  2).
The estimated Lm 50 of female P. pelagicus was also comparable to the smallest size of ovigerous female since the proportion of ovigerous that has been used also to determine the size at functional sexual maturity in crabs 7,31 and lobster 52 . Other research reported that the female Lm 50 of P. pelagicus in Karnataka waters was 99-mm CW 6 , whiles the smallest ovigerous female has had carapace width 89-mm CW and it possibly occurred for few females to spawn under the size of Lm 50 . In particular, almost all of the small size ovigerous female below Lm 50 found in September to November, while this period represents late dry season in western part of Indonesia. During dry season, sea surface and bottom temperature were relatively high in East Lampung coastal waters (i.e. the average 29-32 o C and 28-29.5 o C), which might induce of early gonad maturation and spawning in the next consecutive month 29,44,49,53 .

Reproductive Pattern and Spawning Female Population
Analysis of P. pelagicus reproductive pattern in this study was furnished by the supplementary evidence concerning the occurrence of ovigerous female and their ovarian conditions. This method has additional advantages in of investigation of the spawning or breeding season 14,56 . Our result showed that P. pelagicus in East Lampung coastal waters was capable for continuous spawning throughout the year. However, the peak of spawning and breeding season seems to occur in April to June and October to November (Table 2). Indeed, the peak of breeding period also coincided with the period of high GSI's gonad stage IV for both females and ovigerous ( Figure 8). The occurence of high GSI of female gonad stage IV as well as ovigerous females GSI stage IV in certain months seems not to be overlapped to the high proportion of ovigerous females. They might spawn during our interval observation period or in the next consecutive month, or they migrate to deeper water for spawning. Reproduction period of P. pelagicus in the study area had two peak season (seasonal-continuous), which supports the other previous observations in tropical and subtropical region 18,35,55 . Various results in reproduction period was shown, i.e. thorough in the year and peaks season at the first and last quarters 18 , or in February to April and July to October19 (   (4-7); subtropical and temperate region (8)(9)(10)(11)(12)(13)(14) that peak of spawning or breeding season varied in different places and might relate to favourable environmental condition prevailing in that period, i.e., temperature, salinity, rainfall, food availability, and predators36. The other seasonal-continuous pattern in breeding season of other portunid crabs species in tropical and sub-tropical area were also found, i.e. Arenaeus cribrarius in Ubatuba SP, Brazil 36 and P. spinimanus in Ubatuba SP, Brazil 57 . The evidence in varieties of gonad stages of ovigerous females at all embryonic development stages make the females able to produce multiple spawning, and capable of producing more than one brood of eggs in the same season. Female blue crab (Callinectis sapidus) had "partially synchronous" in oocyte development stages in most ovarian lobe as well as inter ovarian lobe and individual female, make it became multiple spawning 58 . In addition, It was proved that this capability could be up to 3 broods of eggs and would be size-dependent within the species, i.e. above 110-mm CW 29,59 and above 55-mm CL 45 . Our finding exhibited that the double breeding in a season seemed to be occur in most female at the size above 111mm CW, since they had gonad at development stage IV.
Although, spawning is the process of releasing the eggs and sperm, while breeding is the process of releasing the offspring, however, the extrusion of eggs by female crabs could be referred also to the spawning 60 , since fertilization has occurred externally. Thus, the relative occurrence of ovigerous female over the size might notably as breeding population 6,18,25 . Despite of our study showed that spawning and breeding female population tended to start in the same size (i.e. above 91-mm CW), yet the relative percentage of ovigerous female was considerably the lowest in the size class 91-95.9-mm CW (i.e. 0.28%) as well as the ratio of ovigerous females to the adult females (i.e. 0.01). Similarly, all of ovigerous females in the size below Lm50 (i.e. 91.0-102.9-mm CW) was approximately 2% and their ratio value was 0.04 ( Figure 9). Therefore, the breeding female population was at 103-170.9-mm CW size range.

Recommendation for Crab Fishery Management
Management option by size-based limit to harvest strategy has been usually implemented in crustacean fishery 61 . Some protection may be given to the spawning potential and reproductive capacity of the stock to ensure that a few small adult crabs are caught, and permit them to spawn at least once before they become vulnerable to fishing. However, "spawn at least once policy" may crabs stock resilience become low and is easy to collapse 61,62 .The common policy in fishery management to protect a target population for its sustainable use is minimum legal size (MLS) 63 . MLS might be set up at the Lm 50 as limit reference point (LRP) in precautionary approach (PA) and the size could be increase 10% as target reference point (TRP) when fishing rate was increase. Figure 9 shows the ratio of all ovigerous females to adult female was low at the size class below the Lm 50 . Thus, MLS at the Lm 50 seems not to meet a properly sufficient protection to spawning female population for sustainable use of crab resource in the study area. In addition, regulation based on cut-off sizes (Lm 50 ) seems to be not an appropriate management strategy 64 . Therefore, recommended MLS for the P. pelagicus fishery in East Lampung coastal waters would be greater than Lm 50 and is proposed at the size 115-mm CW. At this size, the ratio of ovigerous females to adult females was in average value, meaning that the spawning female in population would become breeding population approximately 21.38% and would be an appropriate precautionary approach for spawning and breeding female population in maintaining stock productivity.

Conclusion
The mean size at which 50% of males and females reached physiological maturity (Lm 50 ) was 98±0.2-mm and 103±0.1-mm CW, respectively; thus, it is relatively different to those of the same species in other areas. Reproductive pattern was partially spawners, seasonalcontinuous throughout in the year. The peak of spawning and breeding season was in April to June and October to November. Double breeding in a season seemed to occur in most females at the size larger than 111-mm CW. The relative percentage of all ovigerous females below the size of Lm 50 was considerably low (±2%) and spawning female population in the size 103-170.9-mm CW. The spawning female under the size 115-mm CW would be approximately 21.38% of breeding population. The size is proposed to be the Minimum Legal Size for the crab fishery sustainable use.

Acknowledgement
This work is funded partially by the Directorate General