Midwater Trawl Research Articles

Hydrodynamic performance of a newly designed biplane-type hyper-lift trawl door for otter trawling

A biplane-type hyper-lift trawl door is newly designed to achieve stable handling while maneuvering, deploying, and stowing with excellent hydrodynamic performances for both bottom and midwater trawling. Flume-tank experiments were carried out to investigate the effect of the aspect ratio (λ, defined as the span b divided by chord c) on the hydrodynamic characteristics of the biplane-type hyper-lift trawl door with a camber ratio of 20% within a wide range of angles of attack (α). The maximum lift coefficients (CLmax) were 2.10 (λ = 1.0, α = 42°), 2.11 (λ = 1.6, α = 37°), and 2.06 (λ = 2.0, α = 28°). With a decreasing stall angle, the maximum lift coefficient remained constant (greater than 2). Considering the compactness and maneuverability of the biplane-type hyper-lift trawl door, an aspect ratio of 2 was adopted for the following experiments. The gap-chord ratio (G/c, G the gap between the fore and rear wings perpendicular to the chord direction) and stagger angle (θ, the included angle between the gap and the line connecting the leading edges of the fore and rear wings) expressing the positional relationship between the fore and rear wings of the biplane-type hyper-lift trawl door were set as 0.75, 0.9, and 1.0 and 20°, 30°, and 40°, respectively, to investigate the hydrodynamic characteristics further. The maximum lift coefficients and stall angles for the five biplane-type models were approximately 2.05 and 30°, respectively. Interestingly, these values were larger than the maximum lift coefficient and stall angle for a monoplane hyper-lift trawl door with the same aspect ratio (= 2) (CLmax = 1.78, α = 22°). This implies that the biplane-type structure contributes to enhancing the lift force and increasing the stall angle. The hydrodynamic forces of the fore and rear wings of the biplane-type hyper-lift trawl door were then calculated using a computational fluid dynamics approach. The lift coefficient for the rear wing was significantly higher than that for the fore wing before an angle of attack of 30° was reached. Nevertheless, the lift force distribution ratio for both the fore wing and the rear wing relative to the entire otter board approached 50%. On the other hand, the stall angle for the rear wing was approximately 30°, and that of the fore wing was around 38°. The fluid between the fore and rear wings tended to flow downstream and to successfully inhibit flow separation on the suction side of the fore wing.

Mathematical Models that Underlie Computer Simulation of the Trawl Doors for Mid-Water Trawls

Mathematical Models that Underlie Computer Simulation of the Trawl Doors for Mid-Water Trawls

Spatial and vertical bias in down-looking ship-based acoustic estimates of fish density in Lake Superior: Lessons learned from multi-directional acoustics

Hydroacoustic surveys using hull-mounted down-looking transducers are useful for estimating pelagic fish densities; however, this method may miss shallow fish owing to the acoustic surface dead zone and vessel avoidance. Our objective was to compare pelagic fish density estimates acquired by a traditional down-looking acoustic survey to estimates obtained by a new multi-directional-towed sled capable of sampling the entire water column using upward-, sideways-, and downward-aimed transducers simultaneously. We deployed both systems concurrently in the western arm of Lake Superior during a period of stable stratification. We found the two survey approaches provided significantly different estimates of fish density in the upper water column layer (~4–9 m below the lake surface) with the sled up-looking transducer providing 56 times higher densities compared to the traditional ship down-looking method. Densities also varied significantly in the 9–14 m layer where densities were 6.2 times higher in the sled survey. Midwater trawl sampling indicated that cisco (Coregonus artedi) and rainbow smelt (Osmerus mordax) were the predominant species occupying the uppermost 14 m of the water column. The two acoustic approaches provided similar results at water column depths >14 m where rainbow smelt and kiyi (Coregonus kiyi) were predominant. Overall, the sled-based method estimates were, on average, 2.5 times higher for the whole water column. Our findings show that the new sled can reduce bias by better sampling the surface dead zone leading to more accurate estimation of pelagic fish densities for both management and research.

Разработка равнопрочной конструкции канатно-сетной части разноглубинного трала

The article implements the previously outlined proposal [1] on the feasibility of
 calculating the diameters of cables and threads of the cable-net part of a mid-water
 trawl based on ensuring their strength is equal to the cables in the first net piece.
 The case study was carried out regarding a commonly used trawl “Atlantic-1920
 m, Nizin” developed by the company “Fishering Service”.
 The calculation algorithm is described which includes determination of resistance
 forces of the cable-net part and tensions in the cables and threads of net pieces.
 The safety factor is determined on the basis of the permissible stresses for the
 respective materials of which cables and threads are manufactured.
 After that, the values of diameters for cables and threads are calculated so as to ensure
 that the safety factor in the net pieces is equal to the cables in the first net piece.
 As a result, the formula is derived, which is able to calculate the diameters
 of cables and threads of the cable-net part of a mid-water trawl based on
 ensuring their strength is equal to the cables in the first net piece.

Examining Retention-at-Length of Pelagic Fishes Caught in the Fall Midwater Trawl Survey

The Fall Midwater Trawl Survey has provided data on aquatic organisms in the San Francisco Estuary for over five decades. In 2014–2015, a study was conducted to investigate and quantify the efficiency of this trawl for catching the endangered fish species Delta Smelt (Hypomesus transpacificus). In an analysis based on that study, we calculated retention probability—the probability that a Delta Smelt is retained in the cod end of the trawl—as a function of fish length and fit a selectivity curve reflecting the relationship between size and retention. Here we return to the same gear efficiency study and further utilize the data set by (1) fitting selectivity curves for three additional pelagic fish species: Threadfin Shad (Dorosoma petenense), American Shad (Alosa sapidissima), and Mississippi Silverside (Menidia beryllina), (2) refitting the selectivity curve for Delta Smelt to incorporate between-haul variability, and (3) calculating the lengths of 50% and 95% retention in order to characterize and compare the resulting selectivity curves. We also present retention data on age-0 Striped Bass (Morone saxatilis), all of which were retained in the cod end. We found that Threadfin Shad, American Shad, and Delta Smelt are 95% retained at 45, 49, and 61 mm fork length, respectively. Because data were limited for Mississippi Silverside, American Shad, and age-0 Striped Bass, we used body shape, in conjunction with retention data, to develop hypotheses about selectivity based on whether each species’ body shape resembles that of Threadfin Shad, which are more deep-bodied and laterally compressed, or Delta Smelt, which are more fusiform. We also found that retention-at-length was more variable for Delta Smelt than for Threadfin Shad, potentially because length is a good predictor of retention in deep-bodied, laterally compressed fish whereas maximum girth is a better predictor of retention in fusiform fish.

Acoustic Characteristic of Sailfin Sandfish (Arctoscopus japonicus) in Dokdo, Republic of Korea

The aim of this study is to determine the acoustic characteristics of sailfin sandfish over a wide frequency range. The acoustic survey was conducted in February, May, and August 2015 off Dokdo, Republic of Korea using EK60 echosounder (18, 38, 70, 120, and 200 kHz) with the mid-water trawls. Target strength (TS) of sailfin sandfish as functions of frequency and tilt angle was modeled using the KRM (Kirchhoff-ray mode) backscatter model. The sailfin sandfish characteristics were examined by using the ΔMVBS (difference of mean volume backscattering strength) method and the net opening depth method, respectively. The acoustic signals were clearly concentrated at 20–100 m water depth. The MVBS tended to become lower as the frequency became higher. The MVBS of sailfin sandfish in the net opening depth was higher than that from the ΔMVBS method, yet both characteristics of frequency response were very similar. In comparison with the frequency response of the ΔMVBS method, that of the modeled TS was very similar in February and May. In particular, the sailfin sandfish were concentrated at 30.80 m depth and favored a temperature below 13°C. Lastly the greatest abundance of sailfin sandfish occurred in May. The highest distribution of sailfin sandfish was in the eastern part of Dokdo in February, in the west, northeastern, and southeastern areas in May, and in southeastern region in August.

A comparison of hydrodynamic forces in knotted and knotless netting, using both helix and conventional ropes for midwater trawls

This study evaluated the hydrodynamic forces produced by whole panels of hand-made (geometrically different) rope meshes typically found in midwater trawls. Experimental treatments included both knotted and knotless meshes constructed of helix composite ropes, conventional braided nylon (PA) ropes, and twisted polyethylene (PE) ropes. Direct measurement of lift (L) and drag (D) forces were conducted using controlled flume tank experiments on panels oriented at 21° relative to the flow. For knotted netting, our results showed that the hydrodynamic forces (L and D) were statistically higher for helix ropes compared to conventional ropes of the same diameter. For knotless netting constructed of helix ropes, our primary finding is that the arrangement of helix ropes (S and Z lay) in individual meshes significantly affects the resulting D and Cd of whole netting panels. Arranging the mesh bars in the S-Z-S-Z lay pattern exhibited 29% and 32% lower drag (D) compared to S–S–S–S and S–S-Z-Z lay meshes, respectively. We also use computational fluid dynamics (CFD) to characterize the fine-scale flow-field around helix and conventional ropes. The resulting streamlines and pressure contours provide a functional explanation for the empirical measurements collected in the flume tank. These results can be useful in informing the design of midwater trawls.

Temporal fluctuations in abundance and size of the giant jellyfish Nemopilema nomurai medusae in the northern East China Sea, 2006–2017

The abundance and size of the giant jellyfish (Nemopilema nomurai) medusae collected by midwater trawl from 2006 to 2017 in the northern East China Sea (nECS) were investigated. While absent in 2008 and 2011, in other years, medusae were prevalent in June and July, rare in October, and not found from January to May. This seasonality in medusa abundance might be related to the life cycle characteristics of this species, with strobilation occurring near Chinese coast of the nECS from late March to early June but medusae dispersing in oceanic currents or dying by early autumn. Peak abundances in June and July varied from 0 to 62.1 × 106 medusa m−2 in the repeatedly observed area (30°30′ N–31 °N, 124°15′ E–126 °E). These annual fluctuations in medusae abundance in the nECS roughly coincide with patterns in the Sea of Japan (JS) in the autumn, which suggests that monitoring in nECS would be effective in predicting the occurrence of this species in the JS which undergoes massive occurrences of this species. The medusae sizes were comparable in June, but smaller in 2006, 2007, 2009, and 2010 than that in 2012–2017 in July. Hence, the existence of a large annual variation in the size of N. nomurai even in the same area and period was indicated.

Distribution, abundance and growth of early stages of the glass squid Galiteuthis glacialis (Cephalopoda: Cranchiidae) captured in Prydz Bay, Antarctica during austral summer

We describe the distribution, abundance and growth of the paralarvae and juveniles of the glass squid Galiteuthis glacialis which were collected from tows conducted at 500 m depth in Prydz Bay, Antarctica by using an Isaacs Kidd Midwater Trawl (IKMT). Paralarvae occurred in an area from 57° S to 65°30ʹ S and 57°–66° E. Early juveniles co-occurred with paralarvae at 57°–65°30′ S and 57°37′ E to 64°56′ E. Age of individuals was estimated based on statolith increment counts and ranged from 47 to 85 days with a daily growth rate ranging from 0.13 to 0.25 mm dorsal mantle length (DML)/day (mean 0.18 mm) for paralarvae. The early juveniles had an age of 85–103 days with a slightly faster growth rate ranging from 0.21 to 0.27 mm DML/day (mean 0.24 mm). The presence of paralarve of G. glacialis at the outer continental shelf edge of Prydz Bay during austral summer indicates a spawning site in this area.

Vertical and small-scale horizontal distribution of cephalopods in the Charlie-Gibbs Fracture Zone of the Mid-Atlantic Ridge

In summer 2009, NOAA surveyed the nekton fauna of the fracture zone on the Mid-Atlantic Ridge halfway between Iceland and the Azores as a small-scale follow-up to a previous large-scale Norwegian expedition. Midwater sampling with a Norwegian Krill Trawl resulted in 64 discrete-depth samples from 12 stations at depths from near-surface to 3000 m. Seven additional bottom samples were collected with a large trawl at depths of 2000–3500 m. The expedition collected 416 cephalopods in ca. 19 species in the vicinity of the fracture zone. Over 50 hrs of ROV video from the Norwegian expedition was also viewed to determine diel migratory patterns of the most common species of cephalopod in the region, Gonatus steenstrupi, for comparison with the NOAA trawl data. We found that trawl stations southeast of the Subpolar Front were generally most diverse. Cluster analysis showed that midwater trawls were more similar in species composition than bottom trawls. Unlike in the ROV observations, the small G. steenstrupi from trawl samples did not appear to participate in diel vertical migration, suggesting that trawl-caught juveniles are ecologically distinct from those visible in submersible videos.

The Meso- and Bathypelagic Fishes in a Large Submarine Canyon: Assemblage Structure of the Principal Species in the Gully Marine Protected Area

Midwater trawl surveys were conducted during 2007–10 at meso- and bathypelagic depths in and near The Gully, a large submarine canyon off Nova Scotia that is also a Marine Protected Area. The fish assemblage in the canyon was highly diverse but 20 species together comprised more than 90% of the catch by number and 80% by weight. The most numerous was the gonostomatid Cyclothone microdon while the myctophid Benthosema glaciale was next in number and first in weight. Most of those principal species would be expected in catches taken in oceanic waters beyond the shelf break, only the bottom-spawning Melanostigma atlanticum being, in the surveyed area, distinctively a species of the canyon. Multivariate analyses showed that the primary variations in the assemblage were aligned with drivers that act in open ocean: depth, water mass and both diel and seasonal cycles. However, the effect of the canyon was evident in an up-canyon decline in the catches of most species. We hypothesize that the oceanic species are passively carried into The Gully by the known inflow and are there exposed to intense predation, depleting their numbers. We estimate that biomass flux as sufficient to support the Marine Protected Area’s signature species: northern bottlenose whales (Hyperoodon ampullatus).

DETERMINING OF OPERATIONAL PARAMETERS FOR TRAWL SYSTEM TAKING INTO ACCOUNT EXPERIMENTAL DATA ON SHAPE OF THE ROPE-NET SHELL OF MIDWATER TRAWLS

Calculating of horizontal opening for a trawl mouth using the mathematical model of midwater trawl system developed by V.I. Gabryuk gives the errors 25.4 and 32.9 %, on average, for the trawls RT 57/360 m and RT 80/396 m, respectively. The significant errors cause doubts about correctness of this model equations application for calculation of the catch zone that is necessary for assessment of abundance and biomass of marine biological resources. New empirical equations are proposed on the basis of experimental data on shape of the rope-net shell of a midwater trawl, which allow to calculate the horizontal opening for its certain sections. The errors of the horizontal opening calculation with these new equations are 13.7 and 6.1 %, on average, for the trawls RT 57/360 m and RT 80/396 m, respectively, that is satisfactory for using them for calculating operational parameters of a midwater trawl system. The operational parameters of the midwater trawls RT 57/360 m and RT 80/396 m are calculated using Baranov’s approach with these new empirical equations, and their good adequacy is shown in the experiment with hydroacoustic measurements of the trawls mouth horizontal opening and the distance between the trawl doors conducted aboard RV TINRO and RV Professor Kaganovsky in the Okhotsk Sea in 2012–2015.

Постановка задачи научного обоснования равнопрочной конструкции канатно-сетной части разноглубинного трала

The article outlined the R&D activities that would create a theory and methodology for designing the uniform strength cable-net mid-water trawls. To manage the mentioned problems a large volume of research is needed,
 however, the transition to cable-net design of trawls' parts will provide significant economic benefits. It therefore seems rather relevant and important.

Sonar imaging surveys fill data gaps in forage fish populations in shallow estuarine tributaries

Forage fish are economically and ecologically important to many coastal marine ecosystems, but most forage fish species are not targeted in species-specific abundance surveys. In the Chesapeake Bay, Atlantic menhaden (Brevoortia tyrannus), an important forage species for many upper-trophic level consumers, are sampled with beach seines and midwater trawls. There is evidence that these traditional fish sampling gears are insufficient for observing menhaden abundance and distribution, which may lead to biased and inaccurate indices of abundance. We suggest this is due to omitting or under-sampling shallow estuarine creeks and nearshore areas. We tested this hypothesis in the Patuxent River, Maryland and its surrounding shallow-water creeks, which are representative of many estuarine tributaries with varied bathymetry. Sonar imaging surveys were conducted using Adaptive Resolution Imaging Sonars (ARIS 1800 and 3000) and a generalized additive model was fit to the resulting data to model forage fish density. Results indicated that menhaden and other forage fish were present at significantly higher densities in shallow-water creeks than in deeper-water areas. Further, many forage fish were observed in creek habitats frequently omitted by both seines and trawls, suggesting that these survey designs may result in biased forage fish indices of abundance. Therefore, we recommend current forage fish surveys in the Chesapeake Bay, especially those with the intent of developing juvenile menhaden indices of abundance, be supplemented with hydroacoustic surveys in shallow waters to improve accuracy and reduce bias.

Performance of new hyper-lift trawl door for both mid-water and bottom trawling

A hyper-lift trawl door (HLTD) which is not heavily dependent on the bottom for its hydrodynamic performance was developed for both bottom and midwater trawling. Flume tank experiments were conducted on simplified HLTD models with an aspect ratio of 1.0 and camber ratios of 15%, 20%, and 25%. When the distance between the lower wing-end plate of the HLTD and the sea bottom approached 0.01c (where c is chord), the maximum lift coefficient decreased 32–39% compared with that in a free stream sufficiency off bottom. When a steel shoe was installed with a gap of 0.1c between the shoe and the lower wing-end plate, the maximum lift coefficient was greatly improved both in free stream and near the bottom. For HLTDs with camber ratios of 15%, 20%, and 25%, the lift coefficient was 2.14 at the attack angle (α) of 35°, 2.33 (α = 38°), and 2.45 (α = 40°) when in the free stream, and was 2.23 (α = 28°), 2.37 (α = 30°), and 2.46 (α = 32°) when near the bottom. Additionally, towing tank experiments with a 1/10 scale trawl model and four types of otter boards, including vertical V-type, biplane type, rectangular flat type, and the HLTD with a steel shoe, were carried out. It was found that the spread performance of the HLTD was best even though its wing area was only 70% of those of other doors. Furthermore, we compared the performance of the HLTD (with a steel shoe) with that of the vertical V-type door for bottom trawling at sea, and found that the HLTD had superior performance in spreading a trawl. Therefore, the HLTD with a steel shoe was verified as suitable for application in both mid-water and bottom trawling.

Marine Vertebrate Biodiversity and Distribution Within the Central California Current Using Environmental DNA (eDNA) Metabarcoding and Ecosystem Surveys

Environmental DNA (eDNA) metabarcoding is a new approach for assessing marine biodiversity that may overcome challenges of traditional monitoring and complement both existing surveys and biodiversity assessments. There are limited eDNA studies that evaluate vertebrate biodiversity in the marine environment or compare patterns of biodiversity with traditional methods. This study uses eDNA metabarcoding of the mitochondrial 12S rRNA genes present in seawater samples to characterize vertebrate biodiversity and distribution within National Marine Sanctuaries located in the California Current upwelling ecosystem. The epipelagic community in the study region has been monitored using traditional (mid-water trawl and marine mammal) survey methods since 1983. During 2016 and 2017, we concurrently sampled the epipelagic community using traditional survey methods and water for eDNA analysis to assess agreement among the methods. We collected replicate eDNA samples from 25 stations at depths of 10, 40, and 80 m, resulting in 131 small volume (1 L) environmental water samples to examine eDNA sequences. Across the eDNA and traditional survey methods, 80 taxa were identified. Taxa identified by eDNA partially overlapped with taxa through trawl and marine mammal surveys, but more taxa were identified by eDNA. Diversity and distribution patterns of marine vertebrates inferred from eDNA sequences reflected known spatial distribution patterns in species occurrence and community structure (e.g., cross-shelf and alongshore patterns). During both years we identified fishery taxa Sebastes (rockfish), Merluccius (hake), Citharichthys (sanddab), and Engraulis (anchovy) across the majority of the stations using eDNA metabarcoding. The marine vertebrate assemblage identified by eDNA in 2016 was statistically different from the 2017 assemblage and more marine mammals were identified in 2017 than in 2016. Differences in assemblages identified by eDNA were coincident with different oceanographic conditions (e.g., upwelling and stratification). In 2016 weak upwelling and warmer than average conditions were measured, and vertebrate assemblages were not different among ecological regions (Point Reyes, Pescadero, and Monterey Bay). While in 2017, average upwelling conditions returned, vertebrate assemblages differed at each region. This study illustrates that eDNA provides a new baseline for vertebrate assessments that can both augment traditional biomonitoring surveys and aid our understanding of changes in biodiversity.

A new Portholefish of the genus Diplophos (Stomiiformes: Gonostomatidae) from the western Pacific Ocean.

A new Portholefish, Diplophos vicinia sp. nov., is described on the basis of nine specimens collected from the western Pacific Ocean by commercial midwater trawl. The new species, currently known only from the South China Sea and north of Papua New Guinea, can be easily distinguished from six nominal congeners by the combination of the following characters: dorsal-fin origin closer to snout than caudal-fin base, distance between last two AC photophores half that between preceding photophores, gill rakers 4 + 10-11=14-15, abdominal vertebrae 30-32, caudal vertebrae 44-45, total vertebrae 74-76, and the following photophore counts: IP 13-14, PV 18-19, IV 31-32, VAV 12-13, AC 37-39 + 2, and IC 83-86.

Distribution of anguillid leptocephali and possible spawning areas in the South Pacific Ocean

Seven South Pacific anguillid eel species live from New Guinea to French Polynesia, but their spawning areas and life histories are mostly unknown despite previous sampling surveys. A July–October 2016 research cruise was conducted to study the spawning areas and times, and larval distributions of South Pacific anguillid eels, which included a short 155°E station-line northeast of New Guinea and five long transects (5–25°S, 160°E–140°W) crossing the South Equatorial (SEC) and other currents. This survey collected nearly 4000 anguilliform leptocephali at 179 stations using an Isaacs-Kidd Midwater Trawl accompanied by 104 CTD casts. Based on morphometric observations and DNA sequencing, 74 anguillid leptocephali were collected, which in the southern areas included 29 larvae of six species: Anguilla bicolor pacifica, A. marmorata, A. australis, A. reinhardtii, A. megastoma,and A. obscura (all anguillid species of the region were caught except A. dieffenbachii). Small A. australis (9.0–16.8 mm) and A. reinhardtii (12.4, 12.5 mm) leptocephali were collected south of the Solomon Islands, other A. australis (10.8–12.0 mm) larvae were caught northwest of Fiji along with an A. obscura (20.0 mm) larva, and an A. marmorata (7.8 mm) larva was collected near Samoa. Considering collection sites, larval ages from otolith analysis, and westward SEC drift, multiple spawning locations occurred from south of the Solomon Islands and the Fiji area (16–20 days old larvae) to near Samoa (19 days old larva) during June and July in areas where high-salinity Subtropical Underwater (STUW, ~150 m depth) and the warm, low-salinity surface Fresh Pool were present. Five long hydrographic sections showed the strong Fresh Pool in the west and the STUW formation area in the east.

Flume tank evaluation of the hydrodynamic lift and drag of helix ropes compared to conventional ropes used in midwater trawls

The hydrodynamic properties of ropes can significantly affect the underwater performance of midwater trawls, including their geometry, drag, fuel consumption, and rate of gear setting and hauling activities. In this study, we investigate the hydrodynamic properties of helix ropes compared to conventional polyethylene (PE) and nylon (PA) ropes. Flume tank tests were conducted using 17 different braided and twisted ropes of varying diameter (6 mm, 8 mm, 9 mm, and 14 mm). Samples of each rope type were subjected to a series of water velocities (0.5 m/s, 0.7 m/s, and 0.9 m/s) and angles of attack (0°, 12°, 20°, 45°, 61°, and 90°) in order to measure drag and lift forces. To understand how hydrodynamic coefficients vary with increasing Reynolds number (Re), we also evaluated a wider range of water velocities (0.3 m/s to 0.9 m/s) for 14 mm ropes. Our results showed that, when compared to conventional ropes of the same diameter, helix ropes produced increased lift force (L), verifying their description as self-spreading ropes. To our knowledge, these findings represent the first known evidence of its kind published in scientific literature with direct application to midwater trawling operations.

Length-Weight Relationships for Eight Caught Marine Fish Using Midwater Trawler in Chabahar Fishing Grounds, Sistan and Bluchestan (The Sea of Oman)

The present research provides length-weight relationship (LWR) of eight fish species included Pomadasys stridens (ForsskA¥l, 1775), Epinephelus areolatus (ForsskA¥l, 1775), Pristipomoides multidens (Day, 1871), Pomadasys maculatus (Bloch, 1793), Johnius borneensis (Bleeker, 1851), Diagrmma pictum (Thunberg, 1792), Epinephelus malabaricus (Bloch & Schneider, 1801) and Epinephelus coioides (Hamilton, 1822) from Chabahr fishing grounds (latitude 25° 11’ to 25° 12’ N; longitude 60° 04’ to 60° 13’ E) in the Sea of Oman. All fish specimens were caught using midwater trawl net, with 65 mm mesh size in the cod-end, from April to May 2016 during the spring season. The LWRs for fish species were W = 0.0127L2.874 for P. stridens, W = 0.0153L2.971 for E. areolatus, W = 0.0227L2.873 for P. multidens, W = 0.0534L2.689 for P. maculatus, W = 0.0023L3.157 for J. borneensis, W = 0.0164L2.807 for D. pictum, W = 0.0487L3.287 for E. malabaricus, and W = 0.0487L3.287 for E. coioides, respectively.