Effect of the El Niño–Southern Oscillation (ENSO) Cycle on the Catches and Habitat Patterns of Three Swimming Crabs in the Taiwan Strait

The swimming crabs is a crucial predator species in benthic habitats and a high value in commercial fishery industries in subtropical and tropical Asia. The climate variability caused by El Niño–Southern Oscillation (ENSO) events has substantial impacts on the catch and habitat of this species. In this study, a weighted habitat suitability index (HSI) model was constructed using logbooks and voyage data records from Taiwanese crab vessels (2013–2019) with the addition of environmental variables to examine the influence of ENSO events on catch rates (CRs) and habitat suitability for Charybdis feriatus, Portunus pelagicus, and Portunus sanguinolentus in the Taiwan Strait (TS). The autumn (September–October) is the major fishing season for catching these three swimming crab species in the TS. A high CR of P. sanguinolentus was observed across the TS, whereas high CRs of P. pelagicus and C. feriatus were recorded in areas in the southern and northern TS, respectively, during autumn. Moreover, the CRs for C. feriatus and P. pelagicus were higher (>7.0 and >8.0 kg/h) during La Niña events, with the increase being more than 40.0% compared with the CRs under normal and El Niño events in autumn. For P. sanguinolentus, the CRs were higher during both La Niña and El Niño events (>8.0 kg/h) compared with normal years. The high CRs for C. feriatus and P. sanguinolentus during autumn in La Niña years co-occurred with high sea temperature and low salinity, whereas the high CR of P. pelagicus co-occurred with high sea temperature and high salinity. Furthermore, the high CRs for C. feriatus and P. pelagicus were observed in areas with high HSI in the La Niña years but were distributed more widely with a lower HSI during normal and El Niño years. The low CRs for C. feriatus and P. pelagicus during normal and El Niño years and the low CR for P. sanguinolentus in normal years during autumn were highly consistent with substantial shrinkage of suitable habitats. Our findings suggest that ENSO events strongly affected the catch and habitat suitability of C. feriatus, P. pelagicus, and P. sanguinolentus during autumn in the TS.

Size selectivity and optimal soaking time of hoops and traps targeting the blue swimming crab Callinectes arcuatus in Cuyutlan Lagoon, Mexico

The selectivity of two types of commercial fishing gear (crab hoop/traditional gear and rigid rectangular cage traps) targeting blue crabs (Callinectes arcuatus) in Cuyutlan Lagoon, Mexico, was assessed. The effect of soak time on crab catches versus the retention and escape rate of organisms was also evaluated. Results suggested that traps captured larger individuals than hoops. The carapace width of crabs was significantly different between the fishing gears used: 63.9% of crabs caught with hoops were < 95 mm (sizes ranged from 40 to 113 mm) and 40.7% of crabs caught with traps were < 95 mm (range: 49 to 120 mm). Results also showed that catch rates were high during the first two hours and decreased after the third hour. The crabs tended to escape after several hours of soak time. The study found that the traps captured larger crabs than the hoops, suggesting that traps are a suitable fishing gear for catching blue swimming crabs in Cuyutlan Lagoon.

Kajian Tingkat Kerentanan Rajungan (Portunus pelagicus) di Perairan Desa Tunggulsari Kabupaten Rembang

Rajungan (Portunus pelagicus) adalah salah satu sumber daya hayati laut Indonesia. Rajungan merupakan komoditas utama perikanan di Indonesa, baik untuk lokal maupun ekspor. Nilai ekonomis rajungan yang tergolong tinggi mengakibatkan penangkapan rajungan dilakukan secara besar-besar dan dapat memicu terjadinya kepunahan. Penelitian bertujuan untuk mengetahui tingkat kerentanan rajungan di Perairan Desa Tunggulsari dan mengetahui karakteristik morfometri dari rajungan yang ditangkap pada lokasi tersebut. Metode yang digunakan dalam penelitian ini adalah metode Productivity and Susceptibility Analysis (PSA). Wawancara dilakukan kepada 60 nelayan di Desa Tunggulsari. Pengukuran parameter kualitas perairan meliputi suhu, oksigen terlarut, salinitas, dan pH. Pengukuran morfometri dilakukan pada salah satu pengepul di desa. Hasil dari wawancara diketahui bahwa nelayan di Desa Tunggulsari menggunakan 2 macam alat tangkap yaitu bubu lipat dan jaring insang dasar. Penilaian atribut produktivitas rajungan masuk dalam kategori tinggi, sedangkan penilaian atribut kerentanan tergolong pada resiko rendah untuk penggunaan kedua alat tersebut. Nilai MSC untuk alat tangkap bubu lipat adalah 96,0 dan 98,2 untuk alat tangkap jaring insang dasar. Nilai MSC > 80 menunjukkan bahwa tingkat kerentanan rajungan pada lokasi tersebut masuk pada kategori rendah. Selanjutnya, pola pertumbuhan rajungan di Desa Tunggulsari adalah allometrik negatif baik untuk rajungan jantan maupun betina. Hal ini menunjukkan pertumbuhan panjang dan lebar karapas lebih cepat dibandingkan penambahan berat rajungan. The blue swimming crab (Portunus pelagicus) is one of the Indonesian marine biological resources. The blue swimming crab is a main commodity of fisheries in Indonesia, both for local and export. Economic value of blue swimming crab classified as high involve over-exploitation of blue swimming crab and can lead to extinction. This research is aimed to determine level of vulnerability of blue swimming crab in Tunggulsari waters and to discover morphometry characteristic of blue swimming crab that caught at that location. The method used in this research is Productivity and Susceptibility (PSA) method. Interviews were conducted with 6 fishermen in the village of Tunggulsari. Measurement of water quality parameters including temperature, dissolved oxygen, salinity, and pH. Morphometry measurement was carried out in one of the collectors in the village. The results of the interview revealed that fishermen in the village of Tunggulsari used 2 fishing tools namely bubu lipat and bottom set gillnet. Assessment of blue swimming crab productivity attributes is included in the high category, while the assessment of vulnerability attributes is classified as low risk for the use of both tools. The MSC value for bubu lipat is 96,0 and 98,2 for bottom set gillnet. The MSC value is more than 80 indicates that the level of blue swimming crab vulnerability at that location is in the low category. Further, blue swimming crab growth pattern in the village of Tunggulsari are negative allometrics for both male and female blue swimming crabs. This shows the growth in length and width carapace is faster than the addition of blue swimming crab weight.

Morphometric Relationships in the Blue Swimming Crabs, (Portunus pelagicus) (Linnaeus, 1758) from the Palk Bay, Sri Lanka

The blue swimming crab (Portunus pelagicus) has become the focus of an important export-oriented fishery in Sri Lanka for a decade. The Palk Bay in the Northern coastal waters of Sri Lanka is one of the best-known fishing grounds for blue swimming crabs in Sri Lanka. This study was undertaken with the aim of establishing some morphometric relationships for P. pelagicus in the Palk Bay. Biological sampling was conducted for five consecutive days per month from November 2014 - October 2015 in the Northern landing sites in the Jaffna District where the catch of Palk Bay blue swimming crab fishery was landed. P. pelagicus specimens were also randomly collected for laboratory analysis. The morphometric measurements of the specimens for the following parameters were undertaken: CW - carapace width with the spine, CWW - carapace width without spine, MW – mouth width, TL - total length, LCPL - left chelar propodus length, LMOV - left movable part Length, RMOV - right movable part length, LCPH - left chelar propodus height, RCPH - right chelar propodus height, ABW - abdominal width, ABL - abdominal length and BW - body weight. The least squared method was used to obtain the Length-Length (L-L) and Length-Weight (L-W) relationships. Of the 65 L-L relationships obtained for P. pelagicus from the study, 34 relationships were correlated (r2>0.5). The estimated relationships between BW and CW for males and females were BW=0.0001 CW 3.01 (r2 =0.84) and BW= 0.0001 CW 2.90 (r2 =0.86), respectively. Positive allometric growth was observed for male P. pelagicus, whereas a negative allometric growth was observed for female P. pelagicus. Most of the morphometric relationships of P. pelagicus obtained in this study were not isometric.