Drift Gillnet Research Articles

Environmental indicators to reduce loggerhead turtle bycatch offshore of Southern California

Extreme climatic events are expected to become more frequent under current conditions of increasing global temperatures and climate variability. A key challenge of fisheries management is understanding and planning for the effect of anomalous oceanic conditions on the distributions of protected species and their interactions with fishing gear. Atypical marine states can cause non-target species to shift outside of their normal distribution patterns, leading to unwanted bycatch events that threaten fisheries sustainability. Environmental indicators can serve as early warning signals that allow for proactive management responses before significant bycatch occurs. Marine heatwaves in the Pacific have caused shifts in the distributions of endangered loggerhead turtles (Caretta caretta), increasing overlap with California’s Drift Gillnet fishery and thereby the risk of turtle bycatch events. To reduce bycatch, a fishery closure offshore of Southern California – The Loggerhead Conservation Area – Is enacted when an El Niño event has been declared and local sea surface temperatures (SSTs) are warmer than normal. However, this regulation was based on qualitative assessment of bycatch that occurred during past El Niño events, and no explicit threshold for SST anomalies was defined. Additionally, closures enacted under the current regulation rely on structured expert decision-making. Providing a quantitative indicator could help to refine future decisions. We developed and evaluated potential new indicators to guide the Loggerhead Conservation Area closure timing based on thermal indices in three different regions: the equatorial Pacific, regional areas offshore of Southern California, and temperate pelagic areas off the US west coast. Our objectives were to: 1) quantify thermal indicators and their respective thresholds to guide closure timing, and 2) hindcast closure scenarios based on these indicator thresholds to evaluate efficacy in terms of opportunity costs to fishers and ability to avoid turtle interactions. The best indicator in terms of avoiding historical turtle interactions while minimizing opportunity cost to fishers was a six-month average local SST anomaly indicator with closures enacted above a threshold of 0.77 °C. This result can improve upon the current closure guidelines by providing a quantified and spatially-explicit indicator and threshold to supplement the structured decision-making process. Our analysis demonstrates a novel approach to developing fisheries management strategies for species with a paucity of data. Issues with data comprehensiveness are frequently present in fisheries management exercises, and precautionary approaches are needed to allow adherence with legislation while considering the best available science.

Length-weight relationships of three fish species from central China

Length-weight relationships were determined for three fish species (Culter oxycephaloides Kreyenberg & Pappenheim, 1908, Liobagrus marginatoides (Wu, 1930) and Pseudobagrus tenuis (Günther, 1873)) from central China. Specimens were collected using fishing gears [set nets (mesh: 1.5 cm × 2.0 cm), hook, drift gill nets (mesh: 1.0 cm × 2.0 cm × 3.0 cm) and electro fishing (depth: 30–60 cm; near the beach) quarterly from September 2016 to August 2017. For Liobagrus marginatoides the LWR estimate includes a new SLmax. Further, the estimate for Pseudobagrues tenuis yielded a relatively high coefficient of correlation despite the relatively small sample size.

Length–weight relationships of three carangid fish species Alepes vari (Cuvier, 1833), Uraspis uraspis (Günther, 1860) and Carangiodes oblongus (Cuvier, 1833) from the Bay of Bengal coast, Bangladesh

Length–weight relationships (LWRs) were determined for three Carangid fish, [Alepes vari (Cuvier, 1833), Uraspis uraspis (Günther, 1860) and Carangiodes oblongus (Cuvier, 1833)] inhabiting in the Bay of Bengal coast, Bangladesh. A total of 147 individuals of three species were sampled from four different sampling points of the Bay of Bengal coast, Bangladesh and examined from April 2017 to October 2017. Fishermen operated beach seine nets (mesh size BSN, 30 mm) and drift gillnet (10.5 cm) twice in each sampling campaign to catch the studied species. The calculated value for parameter “b” of LWRs were 3.003, 2.945 and 2.980 for A. vari, U.uraspis and C. oblongus, respectively.

Integrating Dynamic Subsurface Habitat Metrics Into Species Distribution Models

Species distribution models (SDMs) have become key tools for describing and predicting species habitats. In the marine domain, environmental data used in modelling species distributions are often remotely sensed, and as such have limited capacity for interpreting the vertical structure of the water column, or are sampled in situ, offering minimal spatial and temporal coverage. Advances in ocean models have improved our capacity to explore subsurface ocean features, yet there has been limited integration of such features in SDMs. Using output from a data-assimilative configuration of the Regional Ocean Modeling System, we examine the effect of including dynamic subsurface variables in SDMs to describe the habitats of four pelagic predators in the California Current System (swordfish Xiphias gladius, blue sharks Prionace glauca, common thresher sharks Alopias vulpinus, and shortfin mako sharks Isurus oxyrinchus). Species data were obtained from the California Drift Gillnet observer program (1997-2017). We used boosted regression trees to explore the incremental improvement enabled by dynamic subsurface variables that quantify the structure and stability of the water column: isothermal layer depth and bulk buoyancy frequency. The inclusion of these dynamic subsurface variables significantly improved model explanatory power for most species. Model predictive performance also significantly improved, but only for species that had strong affiliations with dynamic variables (swordfish and shortfin mako sharks) rather than static variables (blue sharks and common thresher sharks). Geospatial predictions for all species showed the integration of isothermal layer depth and bulk buoyancy frequency contributed value at the mesoscale level (<100 km) and varied spatially throughout the study domain. These results highlight the utility of including dynamic subsurface variables in SDM development and support the continuing ecological use of biophysical output from ocean circulation models.

Reducing bycatch while sustaining harvests

Ecology Reducing bycatch—the capture of nontarget marine species—remains challenging for global fisheries, which provide essential sources of protein for billions of people. Even in well-managed fisheries, the ensnaring of species such as turtles, seabirds, and sharks is a problem. For many species, the solutions used to mitigate bycatch have not been successful. Focusing on the California drift gillnet fishery, Hazen et al. developed a multispecies ocean management approach that combines several types of historical data on multiple species' movement to predict daily catch. With this tool, they discovered that operating the California drift gillnet fishery on the basis of daily oceanographic conditions, instead of more static approaches based on rigid boundaries, could greatly reduce bycatch while maintaining fish harvests. Sci. Adv. 10.1126/sciadv.aar3001 (2018).

Length-weight relationships of four fish species from the Yellow River, China

Length-weight relationships (LWRs) were estimated for four fish species [Schizopygopsis anteroventris Wu & Tsao, 1989, Schizothorax lissolabiatus Tsao, 1964, Triplophysa markehenensis (Zhu & Wu, 1981) and Triplophysa siluroides (Herzenstein, 1888)] from the Yellow River. Samples were collected seasonally from August 2016 to October 2017, using various fishing gears [set nets (mesh: 1.5 cm × 2.0 cm), hook, drift gill nets (mesh: 1.0 cm × 2.0 cm × 3.0 cm) and electro fishing]. Four new maximum standard length were recorded for S. anteroventris, S. lissolabiatus, T. markehenensis and T. siluroides.

Length-weight relationships for three fish species from the middle and lower reaches of the Jinsha River, China

This paper provides the length–weight relationships of three fish species from the middle and lower reaches of the Jinsha River, China. Samples were obtained seasonally during 2013~2016 using fishing gear (drift gillnets and di long) and electroshock fishing techniques (backpack electrofishing control unit powered by 12 V). For each species, the sample size, length range, weight range, LWR, 95% confidence intervals of a and b, and coefficient of correlation were determined. Length–weight relationship (LWR) for one species was unknown to FishBase and new maximum lengths were recorded for two species.

Length-weight relationship of selected elasmobranch species from north-eastern Arabian Sea, India

Length–weight relationship (LWR) was estimated for 12 elasmobranch species; five shark species, four species of rays and three species of guitar fishes from north-eastern Arabian Sea, India. Five major landing centres of Maharashtra were selected; Satpati (Lat. 19°43′15″N, Long. 72°42′00″E), Naigaon (Lat. 19°19′32″N, Long. 72°48′54″E), Versova (Lat. 19°08′33″N, Long. 72°48′11″E), New ferry Wharf (Lat. 18°57′29″N Long. 72°51′01″E) and Sassoon dock (Lat. 18°54′42″N, Long. 72°49′33″E). Samples were collected fortnightly during August 2016 to October 2017 from various gears; drift gill nets (Hung length 114–143 m and #100–270 mm) off Satpati coast at 35–50 m depth, dol nets (length 50–65 m and cod end # 30–69 mm) in Naigaon at 38–50 m depth and trawl (length 33–72 m and cod end # 17–32 mm) in Versova, New ferry Wharf and Sassoon dock operated at 20–50 m depth. Multiday fishing was carried out with 2–3 fishing trips in a month, each trip with duration of 7–13 days. Soaking time of gill net and dol net varied from 4 to 8 hr while each trawl haul lasted for 3–4 hr. Length–weight/Disc-width- weight relationship showed good fit with r2 values varying from 0.818 to 0.999. In addition to information on LWR, new maximum size for three species of elasmobranchs is reported in this paper.

Length-weight Relationships of four marine fish species in the Gulf of Oman (Konarak, Iran)

Length–weight relationships were estimated for four marine species, namely Pomadasys kaakan (Cuvier, 1829), Pampus argenteus (Euphrasen, 1788), Scomberoides commersonnianus Lacepède, 1801 and Euthynnus affinis (Cantor, 1849) in the Gulf of Oman (Konarak, Iran). During nine cruises, samples were collected at 20-miles distance from shoreline by 3 panel drift gill-nets with 120 mm mesh size, 8–9 m height and 0.5 hanging ratio in autumn and winter 2016.

Satellite tagging highlights the importance of productive Mozambican coastal waters to the ecology and conservation of whale sharks.

The whale shark Rhincodon typus is an endangered, highly migratory species with a wide, albeit patchy, distribution through tropical oceans. Ten aerial survey flights along the southern Mozambican coast, conducted between 2004–2008, documented a relatively high density of whale sharks along a 200 km stretch of the Inhambane Province, with a pronounced hotspot adjacent to Praia do Tofo. To examine the residency and movement of whale sharks in coastal areas around Praia do Tofo, where they may be more susceptible to gill net entanglement, we tagged 15 juveniles with SPOT5 satellite tags and tracked them for 2–88 days (mean = 27 days) as they dispersed from this area. Sharks travelled between 10 and 2,737 km (mean = 738 km) at a mean horizontal speed of 28 ± 17.1 SD km day−1. While several individuals left shelf waters and travelled across international boundaries, most sharks stayed in Mozambican coastal waters over the tracking period. We tested for whale shark habitat preferences, using sea surface temperature, chlorophyll-a concentration and water depth as variables, by computing 100 random model tracks for each real shark based on their empirical movement characteristics. Whale sharks spent significantly more time in cooler, shallower water with higher chlorophyll-a concentrations than model sharks, suggesting that feeding in productive coastal waters is an important driver of their movements. To investigate what this coastal habitat choice means for their conservation in Mozambique, we mapped gill nets during two dedicated aerial surveys along the Inhambane coast and counted gill nets in 1,323 boat-based surveys near Praia do Tofo. Our results show that, while whale sharks are capable of long-distance oceanic movements, they can spend a disproportionate amount of time in specific areas, such as along the southern Mozambique coast. The increasing use of drifting gill nets in this coastal hotspot for whale sharks is likely to be a threat to regional populations of this iconic species.

Length-weight relationships of six fish species from the headstream region of the Dongjiang River, China

Dongjiang River, a main tributary of the Pearl River, is geographically situated in South China. The present study describes the length–weight relationships (LWRs) of six fish species (Acrossocheilus paradoxus, Barbodes semifasciolatus, Onychostoma elongatum, Microphysogobio fukiensis, Microphysogobio kiatingensis, Metzia lineata) from the headstream region of the river including five Chinese endemic species (A. paradoxus, B. semifasciolatu, O. elongatum, Mi. fukiensis, Mi. kiatingensis). Fish species of five genera of the same family were collected quarterly from April 2012 to October 2014 by using non-selective fishing gears: drag nets (5 m, mesh-size 3 cm), drift gillnets (30 × 15 m, mesh-size 5 mm), fish cages (4 m, mouth opening 40 × 40 cm), scoop nets (mesh-size 0.5-1 cm), and electro-fishing (12V, 200 Hz). The parameter a and b in the LWR equations (W = a Lb) ranged from 0.0014 to 0.0228, and 2.89 to 3.18, respectively. Compared with FishBase, this study provides the first LWR records for four cyprinids (A. paradoxus, B. semifasciolatu, O. elongatum, Me. lineata) and a new record of maximum body length for O. elongatum.

Length-weight relationships for seven fish species from the Nandujiang River in Hainan Island, China

Length–weight relationships (LWRs) were determined for seven fish species collected during 2014 and 2015 between January and July each year from Nandujiang River. The study used drift gillnet with 4 cm mesh (100 m long × 1.2 m high) as well as electrofishing. The parameter “b” of the LWR equations varied between 2.963 to 3.171 for the species studied.

Length-weight relationships for three freshwater fish species from the Pengxi River (a tributary of the Yangtze River, China)

This study determined the length–weight relationships of three freshwater fish species [Culter oxycephaloides (Kreyenberg & Pappenheim, 1908), Squalidus argentatus (Sauvage & Dabry de Thiersant, 1874), Rhodeus sinensis (Günther, 1868)] from Pengxi River, a tributariy of Yangtze River of China. Fish were collected during 2016 using drift gill nets (mesh size 1, 2 and 3 cm) and cage net (0.5 cm mesh size). For Culter oxycephaloides had no previous length–weight estimates were reported in the science literature. For Squalidus argentatus the present estimate includes a new maximum total length while for Rhodeus sinensis our study confirms the only existing LWR estimate quite well.

Length-weight relationships of four fish species from the Nujiang River, China

Length–weight relationships (LWRs) were determined for four fish species (Akrokolioplax bicornis [Wu, 1977], Barbodes wynaadensis [Day, 1873], Glyptothorax cavia [Hamilton, 1822] and Placocheilus cryptonemus [Cui & Li, 1984]) from the Nujiang River, China. Samples were collected from March 2008 to August 2016 (frequency of sampling during the study period: once per year), using various fishing gears (set nets [mesh: 1.5 cm × 2.0 cm], fish cages [0.5 cm mesh], hook, drift gill nets [mesh: 1.0 cm × 2.0 cm × 3.0 cm] and electro fishing). Two new maximum SL were recorded for B. wynaadensis and P. cryptonemus.

An adaptable agent-based model for guiding multi-species Pacific salmon fisheries management within a SES framework

Informing fishery management decisions using coupled socio-ecological systems (CSES) models requires model construction that captures the systems interactions with high precision. Ecological uncertainty in fishery models is easily reduced using existing scientific literature, but social drivers are often poorly defined or understood. The lack of knowledge about fishermen behavior results in inaccurate models of questionable utility for fishery managers. We designed and constructed a high fidelity agent based model (ABM) using the socio-ecological framework that reduces social system uncertainty by capturing complex behaviors using data-driven bounded rationality and feedback. The resulting generalized ABM of CSES dynamics was instantiated to Pacific salmon fisheries at Kenai river in Upper Cook Inlet, Alaska. The data-driven model construction fuses multiple data-sets for classification of social and ecological fishery regimes into stochastic distributions; the agent behaviors were generalized by evolving parametrized equations using data-driven machine learning; multiple non-trivial metrics on multiple scales verified model's accuracy and predictive capacity. The verified model of CSES dynamics at the Kenai river revealed recent instability in the dipnet fishery coupled dynamics, historic instability in the drift gillnet fishery coupled dynamics due to a compensatory and aggressive fishing strategy, and in the future the model will be used for scenario-based studies to understand the outcomes of alternative management strategies.

Initial validation of blubber cortisol and progesterone as indicators of stress response and maturity in an otariid; the California sea lion (Zalophus californianus)

Chronic stress can have detrimental effects on an individual’s health and reproductive success. The use of cortisol quantification as an indicator of stress in free-ranging cetaceans and phocids is increasing but no studies have applied this technique on blubber in otariids. We measured cortisol concentrations in blubber samples obtained from California sea lions, Zalophus californianus, stranded in San Diego County and those incidentally killed in the California drift gillnet fishery. We also measured progesterone concentrations to assess female reproductive status and, in males, as a potential secondary measure of adrenal steroid production. Blubber cortisol and progesterone values were compared across demographic groups (sex and maturity), season, and proportion blubber lipid extracted. Stranded animals (247.3±70.767SEng/gblubber) had significantly higher cortisol concentrations compared to fishery bycaught (8.1±2.108SEng/gblubber) animals. These findings are likely driven by inherent differences in the cause of death and associated nutritional state coupled with the mean duration of expiration for these two groups of animals (i.e., the duration from an animal’s initial perception of the threat-to-self until death). The duration of transition from healthy state to death in stranded animals is on the order of many hours to weeks while in fishery bycaught animals, this transition occurs much more rapidly (i.e., seconds to tens of minutes). The presumed longer duration of the mortality event in stranded animals gives sufficient time for elevated cortisol to diffuse into the blubber. No significant differences between demographic groups, or season were found. However, blubber cortisol declined inversely with proportion blubber lipid extracted, suggesting utility in assessing long-term nutritional status. Blubber progesterone was significantly higher in mature females than immature females (153.8±54.546SEng/gblubber and 9.7±3.60SEng/gblubber respectively), containing on average 15 times more progesterone, irrespective of pregnancy state. Additionally, a significant relationship between mean cortisol and progesterone was found in males with >35% blubber lipid (p<0.0001). This study is an initial step in validating blubber cortisol and progesterone concentrations as a potential marker of stress response and reproductive state, respectively, in otariids. Especially when paired with dart biopsying, this approach could represent a relatively rapid way to assess baseline stress, nutritional status and reproductive states in otariids while minimizing the effects of sampling.

From Sunrise to Sunset in the California Drift Gillnet Fishery: An Examination of the Effects of Time and Area Closures on the Catch and Catch Rates of Pelagic Species

From Sunrise to Sunset in the California Drift Gillnet Fishery: An Examination of the Effects of Time and Area Closures on the Catch and Catch Rates of Pelagic Species

Length-weight relationship of 12 fish species from the Lhasa River and surrounding area in Tibet, China

Presented are the relationship between standard length (SL) and weight (W) for 12 fish species in Tibet, China, representing three families and six genera from the Lhasa River. All fish samples were collected by either electro-shocker (12 V, 200 Hz), fish cages (mouth opening: 40 × 40 cm2, 5 m), or drift gillnets (3 × 1.5 m; mesh-size: 3 cm to 8 cm) from different areas in the Lhasa River Basin, August and September 2015. Parameter b ranged from 2.88 to 3.29, and all correlation coefficient (r2) values were higher than 0.95. Length–weight relationships (LWRs) for three of the species as well as one maximum length are first reports for FishBase.

PELUANG PENGEMBANGAN PERIKANAN TANGKAP DI PROVINSI SUMATERA SELATAN

Provinsi Sumatera Selatan sejak tahun 2000 mulai mengelola sumberdaya perikanan secara terpisah dengan Provinsi Bangka Belitung. Kontribusi Bangka Belitung di sektor perikanan terhadap Provinsi Sumatera Selatan pada tahun 1999 sebesar 72%. Berdasarkan kondisi tersebut, maka dilakukan penelitian terhadap peluang pengembangan perikanan di sekitar perairan Sumatera Selatan. Penelitian ini dilakukan pada bulan Februari 2006 sampai Juli 2006 di dua kabupaten yaitu Kabupaten Ogan Komiring Ilir dan Kabupaten Banyuasin. Hasil penelitian menunjukkan bahwa komoditi unggulan di provinsi Sumatera Selatan adalah udang, kepiting, manyung dan golok-golok. Komoditi unggulan ini masih memiliki peluang yang besar untuk dikembangkan karena tingkat pemanfaatannya masih berkisar antara 58,42% – 66,77%. Jenis alat tangkap trammelnet, jarring insang hanyut dan bagan tancap merupakan alat tangkap prioritas terbaik untuk dikembangkan berdasarkan analisis dengan metode scoring dengan mempertimbangkan aspek biologi, teknis, sosial dan ekonomi

KAJIAN BIO-TEKNIK PEMANFAATAN SUMBERDAYA IKAN TENGGIRI DAN DISTRIBUSI PEMASARANNYA DI KABUPATEN BANGKA

Penelitian ini bertujuan untuk mengindentifikasi bangun, daerah, musim penangkapan ikan, produktivitas alat penangkapan ikan tenggiri, pemasaran hasil tangkapan serta menentukan pola pemanfaatan sumberdaya ikan ekor kuning yang berkelanjutan di Kabupaten Bangka. Metode penelitian yang digunakan adalah metode deskriptif survei yang bersifat studi kasus (case study) dan pengambilan sampel dilakukan secara purposive. Analisis data yang dilakukan mencakup analisis teknik dan bio-teknik. Analisis bio-teknik menggunakan pendekatan model CYP. Ikan tenggiri di perairan Kabupaten Bangka ditangkap dengan menggunakan alat tangkap gillnet dan pacing ulur. Jaring insang di Kabupaten Bangka termasuk dalam jaringi insang hanyut (drift gillnet) dan nelayan menyebut jaring ini dengan istilah jaring tenggiri. Kontruksi alat tangkap ini terdiri atas tali selambar, jaring, pelampung dan tali ris atas. Pancing ulur untuk penangkapan ikan tenggiri memiliki konstruksi yang terdiri atas reel (rooler), kili-kili (swivel), senar (line), pemberat (sinker) dan mata pancing (hook). Musim penangkapan ikan yang ada di Perairan Bangka pada bulan-bulan dimana terjadi musim ikan yaitu pada Bulan Maret, Mei dan Juni serta Agustus dan Oktober dengan IMP lebih dari 100%. Daerah penangkapan pemanfaatan fishing ground ikan tenggiri di Perairan Kabupaten Bangka yaitu pada jalur penangkapan 1 (pada perairan dari pantai sampai 6 mil). Pemanfaatan sumberdaya ikan tenggiri secara sustainable dapat dilakukan dengan mengetahui rejim pengelolaan sumberdaya ikan tenggiri secara optimal dimana secara biologi diduga telah terjadi biological overfishing dengan effort aktual sebesar 798 trip lebih besar dari pengelolaan sumberdaya ikan tenggiri secara optimal sebesar 379 trip. Pemasaran lokal ikan tenggiri dilakukan oleh pedagang pengumpul dan pedagang pengecer dan selanjutnya dijual ke konsumen, sedangkan pemasaran ekspor dilakukan oleh perusahaan. Harga jual, margin pemasaran dan keuntungan yang diperoleh dengan saluran makin pendek dengan fisherman share yang sama akan memberikan share bagi pedagang dan perusahaan perikanan lebih besar