Shrimp Trawl Research Articles

Reducing catch efficiency of rabbitfish (Siganus oramin) in a shrimp beam trawl fishery of the South China Sea

The bycatch of unwanted fish species is a main concern in shrimp beam trawl fishery of the South China Sea. This study evaluated the effect of using combined square-mesh and diamond-mesh codends (CSDM codends) on catch efficiency of a shrimp trawl fishery with the catch comparison and catch ratio approach. The trouser trawl method was applied using the commercial 22-mm diamond mesh codend (D22) as the baseline. The target species, greasyback shrimp (Metapenaeus ensis), and main fish bycatch rabbitfish (Siganus oramin) were chosen as the referred species. The results demonstrated that there was no significant change for the target species but a significant reduction on the unwanted fish bycatch when the CSDM codends were used. Compared with the D22 codend, the CSDM codends would reduce the catch efficiency of greasyback shrimp by less than 18% on average, and the reduction was not statistically significant; whereas catch efficiency of rabbitfish would be significantly reduced by more than 45% and the reduction was length-dependent. The results also showed that the catch efficiency of fish bycatch would reduce as the mesh sizes of the diamond-section of the tested codends increased. These promising results demonstrate that the CSDM codends have a potential to be applied to fishery management for mitigating fish bycatch in the shrimp fishery of the studied area.

Decapod crustaceans associated with the shrimp fishery of the central-south portion of Veracruz, Mexico

The objective of this study was to analyze the brachyuran crab assemblages associated with shrimp fishing on the central-southern coast of Veracruz. Information was collected using 46 trawls organized within nine fishing quadrants. The total catch shrimp, bycatch, and discard were recorded and standardized (CPUE kg h-1). Value index by species, species richness, diversity using Shannon and Weaver index, and equitability were determined. A total of 3055 individuals were collected, which corresponded to nine families, 13 genera, and 14 species. Achelous spinicarpus species were identified at the greatest relative abundance (77.74%). Four new species records for the zone: Hepatus pudibundus, Iliacantha liodactylus, Leiolambrus punctatissimus, and Platylambrus granulatus. Species richness varied according to fishing quadrant and depth interval assessed. The highest value of species richness was eight, and observed Margalef species richness index values ranged from 0 to 2.23. The diversity values ranged from 0 to 2.41 bits ind-1; this may indicate that a few species share the greatest impact of trawling. The presence of lagoon systems was determined to define a portion of the composition of the assemblage. Understanding assemblage structure is important to improve knowledge on the impact of shrimp trawling activity on the ecosystem.

Age, growth, and reproductive parameters of four species of sea catfish (Siluriformes: Ariidae) from Kuwaiti waters

Age, growth, spawning season, and fecundity of four species of sea catfish inhabiting the northern Arabian (Persian) Gulf were investigated. These species constitute major bycatches of shrimp trawling and with lesser percentages in other fishing gears such as gill nets, gargoor traps, and hook and line setups, and most of these bycatches are eventually discarded. The most abundant catfish species found are Plicofollis tenuispinis and Netuma bilineata, while two other species, Netuma thalassina and Plicofollis dussumieri, are found in lower abundance. Length–otolith weight distribution showed a truncation in N. bilineata, which might indicate the presence of two sub-populations within Kuwait waters. Transverse sections of lapilli otoliths showed that annuli deposition occurs during the months of April and May. The von Bertalanffy parameters estimated for the four species showed that females of P. tenuispinis grow faster than males. Two presumptive sub-populations of N. bilineata inhabiting Kuwait waters showed a low growth rate population (K=0.27 y−1) and a higher growth rate population (K=0.35 y−1). The growth rate of N. thalassina was moderate (K=0.30 y−1), while the growth rate of P. dussumieri was relatively higher (K=0.34 y−1). The peak spawning season of the three major catfish species was from March to May, and data on fecundity and its relationship with body weight is presented. The fecundity of catfish species is low as is their market demand. However, the impact of shrimp trawling on the catfish population, as discarded bycatch, can have increasingly detrimental effects that on the overall population size and diversity of this population.

Artificial light improves size selection for northern shrimp (Pandalus borealis) in trawls

Size selection in the northern shrimp (Pandalus borealis) trawl fisheries is a widely studied topic. While the focus has largely been on codend and grid selectivity, studies have shown the importance of other design changes and the application of artificial light to evoke behavioural responses. LED lights of three different colours — green (∼470–580 nm), white (∼425–750 nm) and red (∼580–670 nm) — were mounted in the belly section of a shrimp trawl to investigate their influence on the overall selectivity of the trawl. The study was conducted using a twin-trawl setup, one with light and the other without light. For catch-comparison analysis, a polynomial regression with random effects was applied. The number of valid hauls with green, white and red lights were eleven, eight, and nine, respectively. All lights tested significantly affected the length-dependent retention of shrimp. Green light had the greatest effect, red the least. Significant loss was observed for shrimp below 17.5 mm carapace length (CL) for green light, 19.5 mm CL for white and 20.8 mm CL for red light.

FEEDING HABITS OF Paralonchurus brasiliensis (PERCIFORMES: SCIAENIDAE) FROM SOUTH OF BRAZIL

Shrimp trawling directly impacts target species and non-target species, altering micro-habitats and marine trophic webs. Thus, the objective of the present research was to analyze the feeding habits of Paralonchurus brasiliensis as a tool to evaluate the impact of trawling on the food chains in marine environments, in the South Atlantic of Brazil. One thousand and nineteen stomachs of P. brasiliensis were dissected after being captured as bycatch of shrimp Xiphopenaeus kroyeri, in Penha, on the north central coast of Santa Catarina, Brazil. The number of stomachs was enough to describe the feeding habits of P. brasiliensis, characterizing it as a carnivorous species and predominantly invertivorous. They also revealed that this species has a diversified and constant diet, with greater consumption of polychaetes, crustaceans, and ofiuroides, among other components of the macrobentos, all closely related to the sediment. It was also found that the target species X. kroyeri is not an important prey in the diet of P. brasiliensis, despite occupying the same habitat. According to the present study, P. brasiliensis can be characterized as a demersal-benthic species, predator, opportunistic and broad trophic spectrum. This work contributes to the understanding of trophic chains of the coastal ecosystems, using the P. brasiliensis as a model.

Invertebrates assemblage captured by a pink shrimp's fishery on Amazon continental shelf

Shrimp trawl fisheries constitute a major threat to continental shelves' biodiversity, given their profound impact on benthic communities. We investigated the composition of an invertebrate assemblage impacted by this type of fishery and possible correlations of the abundance and richness with specific environmental parameters. The activities of the industrial shrimp fleet on the north coast of Brazil were monitored over two years. We analyzed 20,303 specimens belonging to seven phyla (Porifera, Cnidaria, Mollusca, Sipuncula, Annelida, Arthropoda, Echinodermata) and 154 species. There was a predominance of generalist and rare species, given that most species (86) were sporadic. Taxonomic composition patterns were complex, dynamic, and were correlated mainly with the temperature and depth of the Amazon continental shelf, the largest in extension and low depth of the South Atlantic. The crustaceans were dominant in both abundance and taxonomic richness. The influence of environmental factors on the abundance of the main species is discussed. The invertebrates are a neglected component in studies of fisheries impact and important components of the ecological structure of the Amazon coast. They are an essential group for developing a holistic fisheries management approach, which will support the sustainability of the region's fisheries and preserve local aquatic communities.

Length–weight relationships of seven fish species in the Yangtze River Estuary and its adjacent waters, Eastern China

The length–weight relationships (LWRs) for seven fish species belonging to five families in the Yangtze River Estuary and its adjacent waters are presented. Cynoglossus gracilis, Cynoglossus macrolepidotus, Ctenotrypauchen chinensis, Collichthys niveatus, Ophichthus apicalis and Erisphex potti were collected monthly in 2009 using trammel nets (the size of smaller mesh net was 1.5 m × 15 m × 4 panels with mesh sizes of 2.5, 3.4, 4.3 and 5.8 cm; the size of larger-mesh net was 2.4 m × 30 m × 4 panels with mesh sizes of 5.0, 6.0, 7.0 and 8.0 cm; soaking overnight). Lophiogobius ocellicauda were collected December in 2020 using shrimp trawl nets (mesh size 2.0 cm). The precision of measurement for the fish specimens is 0.1 cm total length and 0.1 g total weight. The estimated ranges of the parameters a and b for the seven fish species were from 0.0001 to 0.0289 and 2.718 to 3.541, respectively. Two new maximum total length were recorded for Ctenotrypauchen chinensis and Ophichthus apicalis.

Comparative study on Headless Shell-On (HLSO) Black Tiger Shrimp (Penaeus monodon) processing under on board and land based factory facilities

Shrimps is one of the main export commodities of the country and earns about more than 40 crores 47 lac US $in 2017. Black Tiger (BT) shrimp alone contributes about 67 % to the total shrimp export per year. Aquaculture shrimps are being processed in the land-based processing plant while wild catch is being processed onboard (fishing vessels) in the Bay of Bengal. A study was conducted to compare the yield and economic loss/gain of headless shell-on (HLSO) shrimp during processing by labor and crews at onboard (sea) and land based (land) factories. A total of twelve samples were examined; six for land and six for sea that was designated as “P” and “V”, respectively. After beheading to produce HLSO, individual shrimp weight was measured. The average weight of an individual BT was 50.25 ± 4.174 g for V and 51.13 ±3.66 g for P. Average yield from individual shrimp was 1.19 g higher in P compared to V. Found 23.10 g less production from 1 kg BT in V compare to P which is statistically significant (P=0.057). Our estimated results indicated that one vessel got 649.89 Kg less product valued BDT 1,381,016 compare to land based processing plants due to processing by crews on board. Whole scenario predicts that more economic loss if we consider for 37 shrimp trawlers in operation.
 Bangladesh J. Zool. 48(2): 393-398, 2020

Bycatch reduction in the deep-water shrimp (Pandalus borealis) trawl fishery with a large mesh top panel

In the Northeast Atlantic deep-water shrimp (Pandalus borealis) trawl fishery, the bycatch of juvenile fish and shrimp represents a problem. This study evaluated if inserting a 200 mm mesh size top-panel in the last three sections of the tapered upper belly section of the trawl could reduce bycatch of juveniles while maintaining the catch efficiency for deep-water shrimp. The bycatch species investigated were Greenland halibut (Reinhardtius hippoglossoides), redfish (Sebastes spp.) and polar cod (Boreogadus saida). The bycatch of Greenland halibut and the smallest polar cod was significantly reduced, while no effect was found for redfish. The large mesh panel did not lead to a significant loss of deep-water shrimp. The results of this study illustrate how a simple modification of a fishing gear can mitigate the bycatch problem in a shrimp fishery, without significant losses of the target species.

Development of Video Electronic Monitoring Systems to Record Smalltooth Sawfish, Pristis pectinata, Interactions in the Shrimp Trawl Fisheries of the Southeastern United States, with Application to Other Protected Species and Large Bycatches

Development of Video Electronic Monitoring Systems to Record Smalltooth Sawfish, Pristis pectinata, Interactions in the Shrimp Trawl Fisheries of the Southeastern United States, with Application to Other Protected Species and Large Bycatches

Can vertical separation of species in trawls be utilized to reduce bycatch in shrimp fisheries?

Several shrimp trawl fisheries use a Nordmöre sorting grid to avoid bycatch of fish. However, small fish can pass through the grid. Therefore, the retention of juvenile fish often remains an issue during shrimp trawling. We investigated the vertical distribution of deepwater shrimp (Pandalus borealis) and dominant bycatch species at the point where the Nordmöre grid section is installed. This was achieved using a separator frame which split the net vertically into three compartments of equal entry size. Our results showed that shrimp predominately follow the lower part of the trawl belly, whereas species such as redfish (Sebastes spp.), cod (Gadus morhua), polar cod (Boreogadus saida) and American plaice (Hippoglossoides platessoides) preferred the mid-section in the aft of the trawl. Haddock (Melanogrammus aeglefinus) primarily entered through the upper section of the trawl belly. Using these results, we predict that a vertical separation device installed forward of a 19 mm Nordmöre grid combined with a 35 mm codend would result in a significant reduction in bycatch with only minor loss of shrimp.

Maximum sustainable yield estimate for Brown shrimp, Metapenaeus monoceros (Fabricius 1798) in marine waters of Bangladesh using trawl catch log

Brown shrimp, Metapenaeus monoceros is a major contributor of shrimp trawling in Bangladesh marine waters. This is a key fisheries item owing of its fast growth and short life span. Though, stock assessment is need to be conducted annually, the present study is the maiden effort on the assessment of the stock of M. monoceros in marine waters of Bangladesh. Catch per unit effort (CPUE), the most common pieces of information was taken from trawl catch log between 1986 and 2017 for assessing the status of brown shrimp stock using Schaefer biomass model through MS-Excel and CMSY/BSM interfaces. The standing stock and fishing mortality were assessed to be around 5960 t and 43 %, respectively. The calculated reference points of maximum sustainable yield (MSY) with 95 % confidence interval are optimum biomass BMSY 5060 t (4190-6110 t) and optimum fishing mortality FMSY = 61 % (51-63 %). The average annual catch of last two decades was 2793 t, below assessed MSY of 3090 t (2920-3260 t). The stock is probably going to be of satisfactory size with sustainable exploitation close to MSY. Thus, management would be well advised not let to increase catches but to maintain them at the current level.

Finfish constituents of shrimp trawl low value by-catch off Visakhapatnam, India

With the increase in number of shrimp trawlers operating in Visakhapatnam waters at depths ranging from 20 to 100 m and occasionally even upto 200 m, the problem of by-catch also gradually increasing in this region. Thus it is important to know the finfish species composition in the trawl by-catches in order to develop appropriate management and conservation programs for juvenile finfishes. A total of 280 species of low value finfishes belonging to 80 families and 28 Orders were reported in the trawl by-catches off Visakhapatnam during the study period 2014-17. Moreover, two cardinalfishes namely Apogonichthyoides uninotatus is reported as a new record to the Indian waters and A. pseudotaeniatus has been recorded for the first time from east coast of India. The present paper also compares the constituents of finfish reported during early 90s thus reflecting the changes in species composition. About 112 species of finfishes belonging to 14 families viz . Rhinobatidae, Elopidae, Ophichthidae, Muraenesocidae, Kurtidae, Pomacentridae, Blenniidae, Acropomatidae, Cepolidae, Ephippidae, Datnioidae, Lactariidae, Citharidae and Plueronectidae were represented in by-catch of 1990, and now the representatives of these families have become very rare and could not be collected during the present study period. This study is useful in examining the factors influencing the structure of fish communities and fish species that are important indicators of ecological health.

Determining potential management strategies for the elasmobranchs bycatch of the Mexican shrimp trawl fishery of the Gulf of Mexico through a vulnerability analysis

Shrimp trawl fisheries capture several species of elasmobranchs as bycatch that are commonly unreported, this lack of data makes it difficult to assess their populations using quantitative stock assessment methods. Rapid evaluations like the productivity and susceptibility analysis (PSA), can help to determine species at risk of overexploitation and prioritize research, management and conservation efforts. The relative vulnerability (V) of 16 elasmobranch species associated to the Mexican shrimp trawl fishery in the Gulf of Mexico was determined using a PSA. The information of bycatch elasmobranch was collected by observer’s onboard shrimp fishing vessels in 55 fishing trips during the 2013–2017 period. Two hypothetical scenarios to test potential management strategies were developed to observe changes in V based on the current fishing practices. We determined that most elasmobranch species (n= 14) had low V (<1.8) related to this fishery, mostly as a result of the high productivity (P) of the coastal-demersal species and the low susceptibility (S) of the coastal-semioceanic ones. Only two species had a moderate V, Pseudobatos lentiginosus (1.87) and Squatina dumeril (1.85). The vulnerability of these two species could decrease through ensuring post-capture release practices and the protection of their aggregation, since both actions would lower their S and V. Post-capture release might be the most feasible potential strategy for both species, whereas protection of species aggregations would require further investigation to support its effect in the mitigation of mortality from bycatch.

Diet of elasmobranchs captured in the fishing of pink shrimp off souther of Brazil / Dieta de elasmobrânquios capturados na pesca de camarão-rosa no sudeste e sul do Brasil

Some fish species compose the so-called bycatch caught by pink shrimp trawling, including elasmobranchs (sharks and rays). The objective of the study was to analyze the stomach contents of the captured and compare the items identified in the literature. The material was requested to the commercial vessels that landed in Guarujá, São Paulo, being the study area between Rio de Janeiro and Santa Catarina, from 5 to 75 meters deep. In the laboratory, total length-TL and sexing (shark and ray), fork length-FL (shark), disk width- DW (ray) in centimeters, and total weight- TW in kilograms (shark and ray). For the stomach contents, the Degree of Repletion adjusted (empty and full), the Degree of Digestion (undigested and unidentified), frequency of occurrence (%FO) and the numerical frequency (%FN). Sixty-two specimens were analyzed: 20 rays (seven Atlantoraja castelnaui , five A. cyclophora , five Dasyatis hypostigma , one Myliobatis freminvillei , one Gymnura altavela and one Sympterygia bonapartii ); and 42 sharks (29 Squatina guggenheim and 13 S. occulta ), between June 12 to September 19, 2015 and June 15 to December 29, 2016. Most of the food items had been mentioned in the literature, however others only in this study as : Sycionia sp. and Dactylopterus volitans ( D. hypostigma ); Polydactylus sp., Pogonias cromis and Dactylopterus volitans ( S. guggenheim ); and Porichthys porosissimus ( S. occulta ).

Population structure of &lt;i&gt;Paralonchurus brasiliensis&lt;/i&gt; (Steindachner, 1875) (Perciformes: Sciaenidae) in the coast of Sergipe, northeastern Brazil

Paralonchurus brasiliensis is one of the most common fish species found in the bycatch of shrimp trawling in Sergipe. We analyzed its population structure through four sampling programs, two using hired shrimp trawlers (2013-2014 and 2017-2018) and two from the commercial shrimp fleet (2015-2016 and 2018-2019). The codend mesh size varied among programs (18, 20, and 21 mm). All specimens of P. brasiliensis were identified and had their standard and total lengths (SL and TL; cm) and their total weight (TW; g) measured. A total of 1509 specimens were collected measuring 4.7-22.9 cm TL and 0.4-114.8 g. About 67% of all specimens were below the length at first maturity (14.7 cm). The length-length and weight-length relationships estimated were TL=1.141+1.176×SL and TW=0.00270×TL3.391, respectively. The recruitment probably occurs in September-October and May. This species appeared to be more abundant at 15 m, and larger individuals were found at 5 m. Although P. brasiliensis is frequently caught in shrimp fisheries, it is not reported in catch statistics. Here, for the first time, we have documented its presence in Aracaju’s market under the categories ‘miunça’ and ‘pescadinha’ (97% adults), with the largest specimens landed and commercialized as ‘pescadinha’ together with other species. Smaller individuals are probably discarded by commercial fishers. The low selectivity of the fishing gear used leads to the capture of many juveniles, which may impact the population dynamics of this species as well as other species found in the same fishing ground.

Density-dependent condition of juvenile penaeid shrimps in seagrass-dominated aquatic vegetation beds located at different distance from a tidal inlet.

Seagrasses are critical habitats for the recruitment and growth of juvenile penaeid shrimps within estuaries and coastal lagoons. The location of a seagrass bed within the lagoon can determine the value of a particular bed for shrimp populations. Consequently, differences in the abundance of shrimp can be found in seagrasses depending on their location. As shrimp density increases, density-dependent effects on biological parameters are more likely to occur. However, knowledge about density-dependent processes on shrimp populations in nursery habitats remains limited. The present investigation was undertaken to examine the effects of population density on shrimp condition in two selected seagrass beds, located at different distance from a tidal inlet, one 25 km away (distant) and the other 1 km away (nearby), in a subtropical coastal lagoon. The study was based on monthly samplings during one year in Laguna Madre (Mexico), performing a total of 36 shrimp trawls (100 m2 each one) within each seagrass bed (n = 3 trawls per bed per month for 12 months). Shrimp density was related to the proximity to the tidal inlet (higher density was consistently observed in the nearby seagrass bed), which in turn adversely affected the condition of both species studied (Penaeus aztecus and P. duorarum). In this regard, the present study provides the first evidence of density-dependent effects on shrimp condition inhabiting a nursery habitat. Both shrimp species exhibited a negative relationship between condition and shrimp density. However, this pattern differed depending on the proximity to the tidal inlet, suggesting that shrimp populations inhabiting the nearby seagrass bed are exposed to density-dependent effects on condition; whereas, such effects were not detected in the distant seagrass bed. Shrimp density within the distant seagrass bed was probably below carrying capacity, which is suggested by the better shrimp condition observed in that area of the lagoon. Intra and interspecific competition for food items is surmised to occur, predominantly within seagrass beds near the tidal inlet. However, this hypothesis needs to be tested in future studies.

Demographic analysis reveals a population decline of the Longnose stingray Hypanus guttatus in Northeastern Brazil

High fishing pressure on elasmobranchs had caused declines in their populations worldwide, though these declines may not always be observed due to lack of monitoring. The Longnose stingray Hypanus guttatus is one of the most abundant and captured species in Northeast Brazil, mainly as bycatch by shrimp trawl. We aimed to estimate how the population of H. guttatus behaves in the face of different fishing pressures in the Northeast. For this purpose, we used a life matrix analysis from the metadata of three studies in the Northeast of Brazil (Bahia, Alagoas and Rio Grande do Norte). The average annual population growth rate estimated for the three states was strongly negative (−11.83%). However, there was considerable regional variation: data from Bahia showed in fact a low level of positive growth (3.24%) compared to the severe population decline (−29.47% per year) in Rio Grande do Norte, caused by the high mortality from shrimp trawling We conclude that the Longnose stingray has a high risk of long-term population decline in Northeastern Brazil, mainly caused by the high capture rate of juveniles.

Does a Trawl Ban Benefit Commercially Important Decapoda and Stomatopoda in Hong Kong?

Crustaceans were among the most valuable fishery resources in Hong Kong. However, the unrestricted and intensive use of different fishing gears, especially bottom trawling, has led to the depletion of commercially important crustaceans in Hong Kong since the 1980s. This study investigated whether commercial crustaceans recovered after the implementation of a permanent Hong Kong-wide trawl ban that began on December 31, 2012. Standardized field surveys were conducted using a commercial shrimp trawler at two sites in eastern and western waters of Hong Kong before (2004) and after the trawl ban (2013–2014 and 2015–2016) and two sites in southern waters after the trawl ban. Diversity, mean size, abundance, biomass and level of disturbance of commercial crustaceans from the three periods were investigated. The eastern waters exhibited an increased diversity of crustacean assemblages in Inner Tolo, and a higher abundance and biomass of crabs were detected in Outer Tolo after the trawl ban. Reduced disturbance, higher diversity in crustacean assemblages and greater abundance and biomass of predatory crabs were observed after the trawl ban in the outer estuary of western waters, and increased abundance and biomass of shrimp were detected in the inner estuary of western waters. No temporal or negative changes were detected in the southeast and southern waters of Lamma Island. The various responses of crustacean assemblages in Hong Kong waters revealed the critical role of complex interactions among multiple stresses, such as ongoing reclamation works, illegal trawling activities and increased fishing efforts using other (legal) fishing methods.

Spatial structure of the pink shrimp Penaeus (Farfantepenaeus) notialis (Pérez Farfante, 1967) (Decapoda, Penaeidae) in the Colombian Caribbean: implications for fisheries management

Abstract The objective of this study was to assess the patterns in the spatial distribution, size structure, morphometric relationships, and relationships of biomass and size to sampling depth and distance to the coast of Penaeus notialis in the Colombian Caribbean. The biological data were collected on board a shrimp trawler. The females were larger and heavier than the males, which indicated distinct sexual dimorphism in body size. The cephalothorax length at 50% maturity in females was 26.49 mm, and in males, it was 15.13 mm. Relatively high biomass values were found in the southern zone of the study area at depths between 25.6 and 49.3 m and between 3.94 and 7.80 nmi (= 7.29-14.45 km) from the coast. We found a clear spatial structure of biomass and size in relation to depth, so that the fishing effort can be directed to the locations of the adult population.