Windfield related light-trap catches of Nephotettix spp. (N. virescens Distant and N. nigropictus stål), vectors of rice tungro virus in West Bengal

ABSTRACT. Regular peak catches of rice green leafhoppers, Nephoteltix virescens (Distant) and N. nigropictus (Stal) are usually obtained in a light-trap 60 ± 14 days after the peak monsoon rains in August in West Bengal. In 1986, in addition to this peak catch, very high catches were obtained on two different dates, 17 September and 10 November. The high catch on 17 September was probably due to the increase of the effective trap radius caused by the overcast sky and by the presence of a resident population. The high catch on 10 November was due to the transport of the insects by cyclonic winds and deposition in a zone of light and variable winds (at a convergence) real the trapping site. Trajectory analysis indicates that these insects may have been brought from the north-east, upto about 280 km away from the trapping site.

Kootenay Lake kokanee (Oncorhynchus nerka) collapse into a predator pit

Kootenay Lake is a large, oligotrophic waterbody in southern British Columbia renowned for recreational fisheries for piscivorous rainbow trout (Oncorhynchus mykiss) and bull trout (Salvelinus confluentus). Long-term datasets showed a build-up of large-bodied (>2 kg) piscivore abundance followed by a collapse of the kokanee (Oncorhynchus nerka) prey population in 2013 and subsequent decline of large-bodied piscivores. An unprecedented post-collapse state formed in 2015-2018, characterized by low kokanee spawner abundance and biomass and high catch rates for small-bodied (<2 kg), slow growing piscivores. Bioenergetics model estimates of average historic (1961-2008) piscivore consumption was 29.3% of the average historic (1993-2008) kokanee prey supply (biomass and production), but increased to 78.7% in 2011, immediately preceding kokanee collapse. From 2015-2018, kokanee did not recover due to persistently poor juvenile survival; estimated piscivore consumption relative to prey supply remained high (73.0%), suggesting that kokanee were trapped in a predator pit. Although the ultimate and interacting causes of the initial predator build-up remain uncertain, overcoming current depensatory dynamics may be aided by kokanee stocking or increasing harvest on still-abundant, unsatiated piscivores.

Fishing for euros: how mapping applications can assist in maintaining revenues under the Landing Obligation

With the introduction of the Landing Obligation (LO) in EU fisheries, there is an increasing need for fishers to avoid unwanted catches while maximizing revenues. Improving understanding of the spatio-temporal dynamics of unwanted catches could assist the fishing industry optimize catches by altering where they fish. How following such advice relates to revenues and fishery dynamics requires more consideration. We take an existing hotspot mapping methodology and examine how it could be used to identify fishing opportunities under the LO in Irish (Celtic Sea) and Danish (North Sea and Skagerrak) demersal fisheries. We consider if fishing effort can be relocated to avoid unwanted catches while maintaining revenues. The value per unit effort of fishing activity in both areas was often linked to high catch rates of key demersal species (cod, haddock, hake, and whiting). Our analyses indicated, however, that there are options to fish in areas that could provide higher revenues while avoiding below minimum conservation reference size catches and choke species. This was evident across both case study areas demonstrating that hotspot mapping tools could have wide applicability. There does, however, remain a need to explore how the displacement of vessels may further alter species distributions and fleet economics.

Association of Environmental Factors in the Taiwan Strait with Distributions and Habitat Characteristics of Three Swimming Crabs

Information regarding the oceanic environment is crucial for determining species distributions and their habitat preferences. However, in studies on crustaceans, especially swimming crabs, such information remains poorly utilized, and its effects on crab communities in the Taiwan Strait (TS) has not been well documented. The purpose of this study was to understand the relationship between the catch rates of three swimming crab species and environmental factors in the TS. We fitted generalized additive models (GAMs) to logbooks and voyage data recorder data from Taiwanese crab vessels (2011–2015), developed a species distribution model, and predicted catch rates for these three swimming crab species based on the GAM output. The chlorophyll-a (Chl-a) concentration was related to the high catch rates of Chrybdis feriatus and Portunus sanguinolentus, whereas bottom temperature (BT) was related to high catch rates of Portunus pelagicus. The variance percentages for each crab species indicated that high catch rates of C. feriatus and P. sanguinolentus occurred in a Chl-a concentration > 0.5 mg/m3, whereas P. pelagicus catch rates exhibited negative correlations with BTs > 25 °C. The model predicted high catch rates of C. feriatus in the north of the TS during autumn and winter, whereas P. pelagicus was observed to the south during summer and autumn. P. sanguinolentus was predicted to be widely distributed around the TS and distributed further to the northern area during autumn and winter. These findings revealed that each species responds to spatiotemporal environmental variations. Understanding the distributions and habitats of these three crabs is vital in fisheries resource management and conservation planning.

Status of Fisheries in Agusan Marsh: Lapaz and Talacogon, Agusan del Sur, Mindanao

In support to policy formulation of fisheries in Agusan Marsh, a stock assessment was conducted for the period of May 2014 to December 2016 using the data collected from Lapaz and Talacogon, Agusan del Sur within the Agusan Marsh. Results showed that Lapaz contributed 54% of the catch over Talacogon. A total of eighteen species, belonging to 13 genera and 11 families with 7 native and 11 introduced species were found in the marsh. Majority of the total catch consisted of Channa striata, Oreochromis niloticus, and Cyprinus carpio (35%, 27%, and 26%, respectively). Osphronemus laticlavius, Glossogobius celebius and Mugil cephalus were listed as seasonal species. An invasive janitor fish (Pterygoplichthys disjunctivus) was observed as by-catch. A strong pattern of high catch rates occurred during the rainy months of January, February, June, and December. Ten types of commonly used fishing gears were found, majority of which include fish pots, set gillnets, electrofishing and set long lines. Multivariate analysis showed similarity in species composition both in Lapaz and Talacogon. Exploitation of dominant species showed unsustainable level for O. niloticus, C. batrachus, C. caprio, andC. gariepinus, mainly due to excessive capture of immaturesized fishes by major fishing gears. The estimated exploitation rate is beyond the optimum level for O. niloticus and C. carpio in both years and followed by C. striata and C. gariepinus in 2016. Only C. bartachus is estimated to be exploited below the optimum level. Generally, the key species in Agusan Marsh are at risk of overfishing, hence, immediate policy measures must be given high attention.

EVALUASI SELEKTIVITAS JARING INSANG DI TELUK KOTANIA, SERAM BAGIAN BARAT

Jaring insang digolongkan sebagai alat tangkap yang ramah lingkungan mengingat ukuran ikan yang tertangkap dipengaruhi oleh ukuran mata jaring yang digunakan. Penelitian yang dilakukan selama 2013-2014 di perairan Kotania, Kabupaten Seram Bagian Barat bertujuan untuk menghitung kelimpahan ikan pada spektrum ukuran (abundance size-spectrum) berdasarkan habitat ikan pada waktu yang berbeda. Data dikumpulkan melalui logbook yang diisi oleh nelayan Dusun Pulau Osi dan Dusun Wael dengan daerah penangkapan di Teluk Kotania. Distribusi panjang ikan hasil tangkapan setiap mata jaring menunjukkan kisaran panjang yang tidak beraturan yang bisa menimbulkan selektivitas yang tidak konsisten. Ketidakpastian selektivitas jaring insang yang dioperasikan pada perairan dangkal disebabkan oleh perubahan pilihan habitat sebagai daerah penangkapan nelayan. Spektrum panjang menunjukkan distribusi panjang yang unimodal dengan jumlah ikan jenis ikan berukuran kecil tinggi dan menurun secara eksponensial untuk jenis ikan berukuran besar. Mengingat ikan besar mempunyai peranan penting dalam komunitas, dan kurang rentan terhadap jaring insang, kami menyimpulkan bahwa jaring insang adalah alat yang ramah lingkungan.EVALUATION OF GILLNET SELECTIVITY IN KOTANIA BAY, WEST PART OF SERAM. Gillnets are categorized as environmentally friendly fishing gear convinced by its selectivity. Study conducted at Kotania Bay, West Seram Regency, for two years (2012-2013) aimed to count the abundance size-spectrum on habitat for evaluating the catch of gillnets. Length distribution of catch for each mesh size showed irregular ranges, which may lead to selectivity uncertainties. Data was collected from logbooks filled by fishers from Osi Island and Wael. Uncertainty of gillnets selectivity which were operated in shallow waters was influenced by the fishers’ habitat preference that was distinct temporally. The size-spectra of exhibited unimodal length distribution with high catch of small-bodied species and lowered exponentially towards large-bodied species. As large- bodied species play important role in the community and they are less vulnerable to gillnets, we concluded that the practices of gillnet at Kotania Bay are environmentally friendly gear.

Gillnet selectivity of the Indian oil sardine Sardinella longiceps fished in the Sea of Oman

The size selectivity of drift gill-nets for Sardinella longiceps was investigated in the Sea of Oman using a range of nets between 3.3 and 5.7 cm stretched mesh size. All nets had a hanging ratio of 0.5. A total of 1 211 Indian oil sardines were caught in 5 experimental nets, the majority of which were retained by the 3.3, 3.8 and 4.5 cm mesh nets. Peak selectivity was reached at 14.9 cm FL for the 3.3 cm mesh size increasing to 16.9 cm for the 3.8 cm mesh size. The estimated and observed length frequency distributions were unimodal. A log-normal selection function indicated that the highest selectivity was obtained when the length class to mesh size (l:m ) ratio was 4.4. Sardinella longiceps's relative abundance was estimated to be the highest at 16.4 cm FL, with numbers decreasing beyond this peak. This would indicate that selectivity by gilling is optimal with a mesh size of 3.8 cm with nets having a hanging ratio of 0.5. This mesh size appears to satisfy two criteria: high catch efficiency and protection of juveniles.

Studi Variabilitas Produktivitas Primer Bersih Serta Hubungannya dengan El-Nino Southern Oscillasion (ENSO) dan Indian Ocean Dipole (IOD) di Laut Banda Berdasarkan Data Satelit Aqua MODIS

Banda Sea is one of the waters had rich of fish catch. The high catch of fish was related with primary productivity of these waters. Net Primary productivity in the Banda Sea was related with some oceanographic factors such as current, ARLINDO, upwelling and downwelling. The oceanographic factors are influenced by ENSO and IOD. The aim of this research to explained the variability of net primary productivity in Banda Sea and its relation with oceanography factor such as ENSO and monsoon. Data that used in this research were data from MODIS satellite and for analysis of net primary productivity data used Vertically Generalized Production Model (VGPM). The relation of net primary productivity with ENSO and IOD can used pearson correlation method. The result of net primary productivity value in Banda Sea was about 100 gCm-2day-1 - 1200 gCm-2day-1, with the highest apex net primary productivity in August precisely in the east season. The high value of net primary productivity due to upwelling in the season. The value of net primary productivity in west season was decreased. This condition caused by the downwelling of the season. The region with the highest net primary productivity value was the northeast of Banda Sea and the region with lowest net primary productivity value was the western of Banda Sea. The relationship between ENSO with net primary productivity in Banda Sea classified in medium correlation with value 0,556, while relationship between IOD and net primary productivity classified in weak correlation with value 0,23.

Environmental characteristics of mangrove forest in Mojo Village, Pemalang, Central Java as a reference to mud crab Scylla serrata aquasilviculture

Suryani I, Nirmala K, Hastuti YP. 2016. Environmental characteristics of mangrove forest in Mojo Village, Pemalang, Central Java as a reference to mud crab Scylla serrata aquasilviculture. Bonorowo Wetlands 6: 82-91. Mud carb is one of the fisheries commodity that has a high economical value. Production of mud carb still depends on the wild stock for the seed, while the production from aquaculture sector is not well established yet. Aquasilviculture is one of the option to develop aquaculture sector for this commodity. This research aimed to analyze environment characteristics of mangrove forest ecosystem in Mojo Village, Ulujami, Pemalang for aquasilviculture. This research was conducted based on the survey method. The results showed that the best environment characteristics were contained in station 3, with the mud crab production reached 4 kg/day when high catch, and 1.9 kg/day when low catch. From this result, the best environment characteristics of mangrove forests in Mojo village, Ulujami, Pemalang, for mud crab aquasilviculture is environment characteristics in station 3.