Reproductive dynamics of a swimming crab (Monomia haanii) in the world’s crab basket
Introduction
The global marine crab capture landings have grown dramatically over the past 40 years. The total annual production surpassed one million metric tons (mmt) in 1996 and 1.6 mmt in 2014 (http://www.fao.org) (Fig. 1). Collectively, China has contributed more than 40 % of the total global marine crab capture production since 2004. The category “swimming crabs” is the most important taxonomic group in global marine crab capture fisheries, and generally refers to the species from the family Portunidae. Swimming crabs collectively contributed to at least 80 % of the total national marine crab catches from 2003―2018. High-resolution statistical data for capture production of portunids in China are available from 1987 to present from Chinese Fishery Statistical Yearbooks, mainly coming from Zhejiang, Fujian, Jiangsu, and Guangdong Provinces (MOA, 1987–2018; MARA, 2019). Despite the importance of swimming crabs to domestic fisheries, there are only limited biological studies available, mainly focusing on the blue swimming crab Portunus pelagicus, the three-spot swimming crab P. sanguinolentus, the gazami crab P. trituberculatus and the sand crab Ovalipes punctatus (Dai et al., 1977; Song et al., 1988; Jiang and Yu, 2012; Liu et al., 2014; Yang et al., 2014). Further work on population dynamics and stock assessments is needed for effective management of these natural resources.
The red swimming crab Monomia haanii (Stimpson, 1858) (synonyms of Portunus haanii and P. gladiator) is widely distributed in the Indo-Pacific Oceans, and commonly found in the southern East China Sea and South China Sea (Dai et al., 1986; Zhang, 1997; Windsor et al., 2019). It inhabits sandy and rocky bottoms within the 10―100 m depth range (Dai et al., 1986; Zhang, 1997), and feeds on demersal invertebrates and fishes (Huang, 2004). Based on historical fishing catch reports, the southern Taiwan Strait, including the Taiwan Bank fishing ground and its adjacent waters, are the most important habitats for M. haanii (Zhang, 1997; Wang et al., 1998). Catches of M. haanii come mainly from bottom trawlers, baited crab traps, and gill nets. In the southern Taiwan Strait, the estimated annual capture production of M. haanii was 30,000―35,000 mt in the 1990s, ranking No. 1 in crab catches in the areas, and contributing 16–23 % of the total capture production in bottom trawl fisheries operated in these waters. The catches of M. haanii in China were mainly discarded before the 1990s due to its low value; however, this situation has changed (Zhang, 1997). With the growing demand in international trade, the processing industry for M. haanii meat products has developed since the 1990s, particularly in Fujian Province. More than 30 % of the total Chinese export volumes for processed crab products hail from Fujian, creating an international trade of millions of US dollars annually (Chinese Customs Datasets, 2008―2018). Of that, most are the lump crabmeat products from M. haanii. Dongshan County in Fujian is the most important area for M. haanii processing, contributing to approximate 80 % and 65 % of the provincial volume (20,646.28 t) and value (48.34 million US dollars) for M. haanii lump meat products, respectively (Liu and Lin, 2019; http://www.dongshandao.gov.cn).
As a commercially important crab species in China, the M. haanii fishery is indeed under intense fishing pressure. A detailed examination for its sustainable use is needed after over 20 years of heavy exploitation. This study examines the reproductive dynamics of M. haanii caught in its main habitat, i.e., the southern Taiwan Strait, China, based on monthly sampling from August 2018 to April 2019. Such data are essential for conducting fishery stock assessments. Creating an effective fisheries management strategy will be a big step towards a sustainable M. haanii fishery, jointly beneficial for fishers, processors, and managers (Boenish et al., 2020).
Section snippets
Monomia haanii collection
Monthly portside sampling of M. haanii was conducted from August 2018 to April 2019. Due to the national fishing moratorium regulation (i.e., no bottom trawler fishing from 1st May to 15th August) in China, it was not possible to sample crabs in May―July of 2018 and 2019. A total of 205―575 crabs were randomly collected each month from 5―10 trawler catches at landing ports in Dongshan County, Fujian Province (Fig. 2). About 1 kg “feed-grade fish” from the same trawlers were collected for
Sex ratio
A total of 3222 individuals with 1560 males and 1662 females were used in the analysis. The overall male: female ratio was 1: 1.07, with no significant difference from the 1: 1 ratio (χ2 = 3.12, df = 1, p > 0.05). Monthly variation in sex ratio was significantly different from the 1: 1 ratio (p < 0.01), showing a significant male-bias in August, September and December 2018, and a significant female-bias in February and March 2019 (Fig. 4).
Size distributions of females and males
The sizes ranged from 2.4 to 13.1 cm CW (7.0 ± 1.2 cm
Sex ratio
A curious difference in M. haanii sex ratio over data from the past 20 years was identified. In this study, the overall male: female ratio of M. haanii (1: 1.07) was not different from 1: 1, although there was substantial monthly variation. Comparatively, an overall reported male: female ratio in 1992―1995 was nearly 2: 1 (Zhang, 1997). One possible explanation is the differences in fishing grounds over time and potential sexual segregation for parts of M. haanii life history. In 1992―1995, the
CRediT authorship contribution statement
Bai-an Lin: Formal analysis, Investigation, Methodology, Writing - original draft. Robert Boenish: Formal analysis, Data curation, Methodology, Writing - review & editing. Jacob P. Kritzer: Conceptualization, Writing - review & editing. Yan Jiang: Investigation, Methodology. Song-lin Wang: Funding acquisition, Writing - review & editing. Min Liu: Funding acquisition, Investigation, Methodology, Supervision, Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The study was funded by National Fisheries Institute’s (NFI) Red Crab Council and Ocean Outcomes (O2) of USA and Qingdao Marine Conservation Society (QMCS) of China. We thank technicians Qi-si Cai, Sheng-yao Sun, and Xin-ya Xu from Dongshan Swire Marine Station, Xiamen University (XMU) for facility and logistics support, Yi-yang Li, Jia-hao Song, Gui-hua Wang, Qing Xu and Lan-lan Zhang from Fish Biology Laboratory (XMU), and anonymous fishermen and traders for laboratory and field assist, and
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Cited by (4)
Advancing multispecies fishery management in China: Lessons from international experience
2023, Aquaculture and FisheriesCitation Excerpt :This strategy, which has been one important contributor to the success of the American lobster fishery in the United States and might help buffer that fishery from adverse effects of climate change (Le Bris et al., 2018), relies on high post-release survival. In China, the nationwide summer fishing moratorium currently provides protection from fishing mortality for egg-bearing females during that period, but at least M. haanii females bear eggs at many times of year outside of the moratorium (Lin et al., 2021). Crabs caught by gillnets and especially trawls, on the other hand, would likely experience lower survival rates, which would limit the effectiveness of management by multispecies TACs if management and market factors increased targeting, high-grading, and discarding from those gears.
A bioeconomic approach towards improved fishery management of Monomia haanii in the southern Taiwan Strait, China
2021, Fisheries ResearchCitation Excerpt :Because the ovigerous females and the egg developmental stages of M. haanii were recorded (Lin et al., 2021), we were able to capture monthly recruitment pulses in the model. We estimated relative monthly indices of egg production by multiplying the ratio of females with early-stage eggs (i.e., yellow, orange and brown coloration) over the overall number of surveyed M. haanii, times the commercial fishery CPUE for each month in the spawning season (January-April) (Lin and Liu, 2019; Lin et al., 2021). We could not find a published study with egg incubation time and larval duration for M. haanii, so we used estimates of other portunid crabs as proxies.
- 1
Contributed equally to this work.
- 2
Current affiliation: Northeastern Regional Association of Coastal Ocean Observing System, Portsmouth, New Hampshire, USA.