MARINE AND FISHERY SCIENCES 35 (2): 165-180 (2022)

https://doi.org/10.47193/mafis.3522022010501

ABSTRACT. Of particular concern in commercial fishing catch is 'size bycatch', i.e., the death

of early stages of resources that would reach a marketable value when they turn into adults. This

event is frequently associated with trawling because of the lower size selectivity of this gear as com-

pared to gillnets. However, this is expected when small-scale fisheries (SSF) employ gillnets simul-

taneously in setnets + driftnets that mix multiple mesh sizes. This work analyzes fishing captures

and compares characteristics of fish catch from gillnets and trawlers with respect to size at first mat-

uration, legal size of capture, and expected discards. Data were obtained from 2007-2021 for SSF

in Southern Brazil. A total of 112 fish species were represented in the data. Gillnets exploited fewer

species than trawlers; however, most of these constitute fishing resources in the study region. Of the

19 species whose maturation size is known, nine occurred in gillnets as juveniles, and of the 14

species for which the legal size of capture is established, seven occurred in gillnets in prohibited

sizes. Gillnets and trawlers presented size bycatch and affected different species between them, with

four resources that were present in bycatch from both gillnets and trawlers. The broad range of mesh

sizes employed by SSF warns of the discarding of undersized captures, and stresses the importance

of policies addressing gillnet management.

Key words: Artisanal fisheries, bycatch, fisheries management, Brazil.

Juveniles y peces pequeños en la pesca artesanal: las redes de enmalle no están menos impli-

cadas que la pesca de arrastre

RESUMEN. De particular preocupación en la pesca comercial es el tamaño de los organismos

en la captura incidental, es decir, la muerte de las primeras etapas de los recursos que alcanzarían

un valor comercial cuando se conviertan en adultos. Este evento se asocia frecuentemente con la

pesca de arrastre debido a la menor selectividad de tamaño de este arte en comparación con las redes

de enmalle. Sin embargo, esto es esperable cuando en las pesquerías de pequeña escala (PPE) se

emplean redes de enmalle simultáneamente en las redes de arrastre + redes de deriva que mezclan

varios tamaños de malla. Este trabajo analiza las capturas pesqueras y compara las características de

las capturas de peces en las redes de enmalle y en los arrastreros con respecto al tamaño de primera

madurez, el tamaño legal de la captura y los descartes esperados. Se obtuvieron datos de 2007-2021

para la PPE en el sur de Brasil. En los datos estuvieron representadas un total de 112 especies de

peces. Las redes de enmalle explotaron menos especies que los arrastreros; sin embargo, la mayoría

de estos constituyeron recursos pesqueros en la región de estudio. De las 19 especies cuyo tamaño

de maduración se conoce, nueve se encontraron en las redes de enmalle como juveniles, y de las 14

especies para las que se establece el tamaño legal de captura, siete se encontraron en redes de enma-

lle en tamaños prohibidos. Las redes de enmalle y los arrastreros presentaron captura incidental de

tamaño y afectaron a diferentes especies en forma conjunta, con cuatro recursos que estuvieron pre-

165

*Correspondence:

ptchaves@ufpr.br

Received: 10 August 2021

Accepted: 16 November 2021

ISSN 2683-7595 (print)

ISSN 2683-7951 (online)

https://ojs.inidep.edu.ar

Journal of the Instituto Nacional de

Investigación y Desarrollo Pesquero

(INIDEP)

This work is licensed under a Creative

Commons Attribution-

NonCommercial-ShareAlike 4.0

International License

Marine and

Fishery Sciences

MAFIS

ORIGINAL RESEARCH

Juveniles and undersized fish in small-scale fisheries: gillnets are not less

implied than trawling

PAULO DE TARSO DA CUNHA CHAVES*

Zoology Department, Federal University of Paraná, PO Box 19020, Code 81531-980 - Curitiba, Brazil.

ORCID Paulo de Tarso da Cunha Chaves https://orcid.org/0000-0001-6393-8256

INTRODUCTION

Small-scale fisheries (SSF) differ from large-

scale fisheries with respect to several technical,

economic, and social attributes. From a conserva-

tion perspective, fishing effort in SSF is often

more tolerable and catches are less focused on a

few stocks. By using passive gears such as hand

lines, fish traps, and gillnets, SSF tends to opti-

mize human work and reduce fuel consumption

(FAO 2016). These gears show higher capture

selectivity with respect to species and individual

size as compared to trawl nets (Armstrong et al.

1990; Wolff et al. 2015), another gear employed

by SSF fisheries as well as large-scale fisheries

(Misund et al. 2002; Santurtún et al. 2014). In

comparative studies between gillnets and trawl-

ing, Olin and Malinen (2003) found that in South

Finland fish smaller than 5 cm corresponded to

51% of trawler captures, while they corresponded

to only 1% of gillnet captures; and Huse et al.

(2000) found that the mean length of cod caught

in gillnets on the Norway coast was approximate-

ly 17 cm larger than those caught by trawl nets.

Trawling is known to generate bycatch (Silva-

Júnior et al. 2015; Cardoso et al. 2021). This pro-

motes design adaptations to reduce the capture

and consequent discarding of non-target species

and individuals (Alarcón Vélez et al. 2014;

Freiría et al. 2014), and strategies as in the

penaeid fisheries off Iran, where experiments are

being conducted to replace trawl nets with gill-

nets (Hout et al. 2021).

A particular concern regarding incidental cap-

tures is ‘size bycatch’, i.e., the death of juvenile

stages of fish, crustaceans, and cephalopods that

would reach a satisfactory price for selling as

adults. In Southern Brazil, size bycatch from

trawlers includes small individuals of marketable

species, such as Micropogonias furnieri (3% in

weight), Umbrina canosai (7%), and Cynoscion

guatucupa (14%) (Cardoso et al. 2021). Apart

from the economic loss, discarding resources that

are not targeted or are below the permitted cap-

ture size constitutes a sensitive problem because

of its ecological and ethical implications (San-

turtún et al. 2014).

Gillnets incidentally capture charismatic ani-

mals, such as turtles, birds, and mammals (Cheng

and Tien-Hsi 1997; Cardoso et al. 2011; FAO

2020). These captures do not produce discarding

of size bycatch origin (Santurtún et al. 2014),

probably because, as verified in the haddock and

the Arctic cod fisheries in Finland (Huse et al.

2000), rates of young-adults in catches are lower

with gillnets than with trawls and longlines.

However, gillnets also show size bycatch that

varies between mesh sizes, as observed in a fish

assemblage in a Brazilian lake (immature versus

mature individuals, Silvano et al. 2016), or with

depths of operation, as observed in the whiting

fisheries in the Black Sea (Kalayci and

Yeşilçiçek 2014).

Each mesh size is selective for a particular

morphology (Armstrong et al. 1990; Reis and

Pawson 1999). Gillnets mixing different meshes

are potentially efficient in capturing a larger spec-

trum of fish morphologies, widening the range of

vulnerable sizes for capture. The use of setnets

and driftnets is common in SSF, particularly in

tropical waters, where many target resources

share a common area (Alves et al. 2012; Wolff et

al. 2015). The present work investigates how the

employment of multiple mesh sizes in a restricted

166 MARINE AND FISHERY SCIENCES 35 (2): 165-180 (2022)

sentes en la captura incidental tanto de redes de enmalle como de arrastreros. La amplia gama de tamaños de malla empleados por la

PPE es una advertencia sobre el descarte de capturas de tamaño pequeño y enfatiza la importancia de políticas que aborden el manejo

de las redes de enmalle.

Palabras clave: Pesquería artesanal, captura incidental, manejo pesquero, Brasil.

area results in higher size diversity in the catch,

comparatively to trawling. If such heterogeneity

includes fish with no marketable value or prohib-

ited species and size classes, they are discarded

on board or after landing. Is it plausible to sup-

pose that, in such conditions, gillnets capture

juveniles and undersized fish at a not-smaller

scale than trawl, and are also harmful for fisheries

sustainability?

Along the littoral coast of Southern Brazil, in

shallow waters up to 30 m, gillnets and trawl nets

are the main fishing gears employed by SSF

(Chaves and Robert 2003). Gillnets are deployed

from the bottom to the surface and target several

teleosts and chondrichthyan species. Trawling is

performed on the bottom and targets shrimp.

Both gears register incidental captures, mainly

fish and invertebrates. While the small meshes

used for trawling (1-2 cm) catch an important

abundance of benthic fauna, including small fish

(Pina and Chaves 2009; Chaves and Silva 2019),

the larger meshes used for gillnets (5-20 cm)

retain a considerable number of non-target fish

(Chaves et al. 2019; Afonso and Chaves 2021).

This study analyzes the fish size in trawling and

gillnets captures, comparing the two gears with

respect to three parameters: legal size of capture,

size at first maturation, and expected discards.

Does trawling affect more undersized (legal cap-

ture and/or first maturation) species than gill-

nets? With respect to legal capture and first mat-

uration, what is the species performance of each

gear? What target resources occur as bycatch in

these gears?

MATERIALS AND METHODS

The study area is located in Southern Brazil,

on the coasts of Parana and Santa Catarina states,

25° 30'S-26° 10'S; 48° 10'S-48° 40'W. This

corresponds to the fishing area of three SSF com-

munities: Matinhos, Itapoa, and São Francisco

do Sul (Figure 1). The fishing fleet consists of

between 30 and 50 fiberglass canoes in each

167

CHAVES: JUVENILES AND UNDERSIZED FISH CAUGHT BY GILLNETS

Figure 1. Study area (small square) on Southern Brazilian coast and location of fishing communities of Matinhos, Itapoa, and

São Francisco do Sul (arrows).

Brazil

Curitiba

Florianopolis

Matinhos

Itapoa

São Francisco de Sul

Southwestern Atlantic

Ocean

49° W 48° W

26° S 25'S

community, measuring 8-12 m, all motorized

with < 60 HP. They are equipped with a gillnet

and/or with bottom trawling gear. Fishers per-

form one-day trip, but gillnets fish for up to six

days continuously. In trawling, two nets are

simultaneously pulled by canoes at depths of 8-

15 m in successive hauls during 6-8 h per day.

The mesh size at the codend is 1-2 cm between

opposite knots, and the target resource is the

seabob shrimp Xiphopenaeus kroyeri. Gillnets

have a height of up to 20 m and a length of a few

hundred to four thousand meters. They are fixed

to the bottom or drifting at depths of 10-30 m.

Mesh sizes are diverse, typically 5, 7, 9, 11, 12,

and 20 cm between opposite knots, depending on

the target resource, sharks and teleosts. The latter

primarily belong to Mugilidae, Scombridae,

Pomatomidae, Sciaenidae, and Pleuronecti-

formes. Technical specifications of trawl nets

and gillnets used in the study area, target

resources, and modes of operation are described

by Chaves and Robert (2003), Nogueira et al.

(2011), Chaves et al. (2019), and Afonso and

Chaves (2021).

The range of total length (TL) by species and

the minimum and maximum TL values were

linked with gillnets or shrimp trawling. The

sources used were: (i) previous works carried out

in the study area from 2007-2016; fish were

obtained by monitoring landings in the cited com-

munities, or experimental cruises for academic

research using boats and fishing gears routinely

employed by them; and (ii) original data obtained

by monitoring landings of the Matinhos fleet dur-

ing 2020-2021. In experimental cruises, all indi-

viduals were measured, while in monitored land-

ings individuals were accessed by chance.

Because most of the sources did not discriminate

between the mesh size of gillnets, they were con-

sidered as a single entity.

For each species, the largest TL landed by

trawlers (Max. TL T) and/or the smallest TL land-

ed by gillnetters (Min. TL G) were identified.

These data were compared with two other specif-

ic TL values: the minimum size of legal capture

(TL C), and the average size at first maturation

(TL50), preferentially in this area or, when not

available, in Brazil. When TL50 differed between

sexes, the largest value was adopted. Values of

TL C came from federal rules MMA 53/05

(MMA 2005) and IBAMA 83/06 (MMA 2006),

while those of TL50 came from the literature.

Species of commercial interest in the study

area were recognized after the findings of Chaves

and Robert (2003), Chaves et al. (2019), and

Afonso and Chaves (2021), and designated as

fishing resources. Carcharhinus sp., Diplectrum

sp., Paralichthys sp., and Sphyrna sp. refer to two

or more species occurring in the study area and

are not always recognized at species level. To

simplify the representation of results, each genus

was considered a single species.

RESULTS

Values of Max. TL T were compiled from 100

species and those of Min. TL G from 32 species.

Overall, data on 112 species were compiled with

more than 30% (42) constituting fishing

resources in the study area (Table 1).

The number and weight of catches were not

quantified, but data indicate that, all species con-

sidered, individuals < 100 mm were vulnerable

almost exclusively to trawling, while those in the

range of 100-300 mm were vulnerable to both

trawling and gillnets. A few species were repre-

sented in trawl nets by individuals > 500 mm or

occur in gillnets with individuals not smaller than

500 mm (Figure 2). Gears partially shared the

ranges 36-940 mm for Max. TL T, and 110-720

mm for Min. TL G (Table 1). Most representative

size classes corresponding to > 10% of frequency

of occurrence confirmed significant captures by

both gears of species within TLs 100-300 mm:

Max. TL T at classes 110-230 mm, and Min. TL

G at classes 110-270 mm (Figure 2).

168 MARINE AND FISHERY SCIENCES 35 (2): 165-180 (2022)

169

CHAVES: JUVENILES AND UNDERSIZED FISH CAUGHT BY GILLNETS

Table 1. Fish species caught by small-scale fisheries in Parana and Santa Catarina littoral, Southern Brazil. Part of them (*) constitute fishing resources in

this area. Max. TL T, Min. TL G: maximum and minimum total length (TL) in trawling or gillnets, respectively. TL C: minimum TL of legal capture.

TL50: average TL at first maturation. Ref.: references see below. Code applies to species of Figure 6.

Max. TL Ref. Min. TL Ref. TL C Ref. TL50 Ref. Code

T (mm) G (mm) (mm) (mm)

Achirus declivis Chabanaud, 1940 190 1, 2, 3

Achirus lineatus (Linnaeus, 1758) 112 1

Anchoa januaria (Steindachner, 1879) 139 1 65 17 ANJA

Anchoa lyolepis (Evermann and Marsh, 1980) 87 3

Anchoa spinifera Valenciennes, 1840 177 1, 3

Anchoa tricolor Spix and Agassiz, 1829 113 1, 3

Anchovia clupeoides (Swaison, 1839) 156 3

Anchoviella brevirostris (Günther, 1868) 136 3

Anchoviella lepidentostole (Fowler, 1911) 119 2 94 17 ANLE

Anisotremus surinamensis (Bloch, 1791) 277 2

Aluterus monoceros (Linnaeus, 1758) 477 1

Aspistor luniscutis (Valenciennes, 1840) 256 2

Astroscopus y-graecum (Cuvier, 1829) 65 3

Bairdiella ronchus (Cuvier, 1830) 180 1, 2, 3 158 17 BARO

Carcharhinus sp.* 455 7 1,150

Cathorops spixii (Agassiz, 1829)* 273 1, 3

Centropomus parallelus Poey, 1860* 347 2, 3 210 8 300 10 200 11 CEPA

Centropomus undecimalis Bloch, 1792* 267 2, 3 500 10

Cetengraulis edentulus (Cuvier, 1829) 131 2 137 17 CEED

Chaetodipterus faber (Broussonet, 1782) 114 1, 3 305 7

Chilomycterus spinosus (Linnaeus, 1758) 80 1, 3

Chirocentrodon bleekerianus (Poey, 1867) 141 1, 3 76 17 CHBL

Chloroscombrus chrysurus (Linnaeus, 1766)* 159 1, 2, 3 200 7 120 10 124 17 CHCH

Citharichthys arenaceus Evermann and Marsh, 1900 186 1, 3

Citharichthys spilopterus Günther, 1862 173 1, 2, 3

Conodon nobilis (Linnaeus, 1758) 193 1, 2, 3

Ctenosciaena gracilicirrhus (Metzelaar, 1919) 148 2, 3

Cynoscion acoupa (Lacepède, 1801)* 300 8 427 17 CYAC

170 MARINE AND FISHERY SCIENCES 35 (2): 165-180 (2022)

Table 1. Continued.

Max. TL Ref. Min. TL Ref. TL C Ref. TL50 Ref. Code

T (mm) G (mm) (mm) (mm)

Cynoscion guatucupa (Cuvier, 1830)* 240 8 346 17 CYGU

Cynoscion leiarchus (Cuvier, 1830)* 200 7, 8

Cynoscion virescens (Cuvier, 1830)* 142 2

Dactylopterus volitans (Linnaeus, 1758) 230 1, 3

Dactylopterus auratus Ranzani, 1842* 171 3

Diapterus rhombeus (Cuvier, 1829)* 197 1, 2, 3 150 13 DIRH

Diplectrum radiale (Quoy and Gaimard, 1824) 184 1, 3

Diplectrum sp. (D. radiale or D. formosum) 190 8

Engraulis anchoita Hubbs and Marini, 1835 108 1

Etropus crossotus Jordan and Gilbert, 1822 174 1, 3 85 17 ETCR

Eucinostomus gula (Cuvier, 1830)* 180 3 150 13 110 17 EUGU

Eucinostomus. melanopterus (Bleeker, 1863)* 234 1, 3

Eugerres brasilianus (Cuvier, 1830)* 263 2 200 8 170 150 17 EUBR

Genidens barbus (Lacepède, 1830)* 171 1 410 7 400 10 415 17 GEBA

Genidens genidens (Cuvier, 1829)* 194 1 118 17 GEGE

Gempylus serpens Cuvier, 1829 106 1

Gobiesox barbatulus Starks, 1913 53 3

Gymnothorax ocellatus Agassiz, 1834 495 1, 3

Harengula clupeola (Cuvier, 1829) 166 2, 3

Hemicaranx amblyrhynchus (Cuvier, 1833) 210 2, 3

Isopisthus parvipinnis (Cuvier, 1830) * 194 1, 2, 3 180 8 159 12 ISPA

Lagocephalus laevigatus (Linnaeus, 1766) 173 2, 3

Larimus breviceps Cuvier, 1830* 256 1, 2 110 8 135 14 LABR

Lycengraulis grossidens (Agassiz, 1829) 150 1, 3

Macrodon ancylodon (Bloch and Schneider, 1891)* 224 1, 3 190 7, 8 250 10 237 17 MAAN

Menticirrhus americanus (Linnaeus, 1758)* 261 1, 2, 3, 4 177 17 MEAM

Menticirrhus littoralis (Holbrook, 1860)* 229 1 200 10 230 15 MELI

Micropogonias furnieri (Desmarest, 1823)* 274 1, 2, 3 190 7, 8 250 10 306 17 MIFU

Mugil liza Valenciennes, 1836* 450 7, 8 350 10 350 17 MULI

Myrophis punctatus Lütken, 1852 510 3

171

CHAVES: JUVENILES AND UNDERSIZED FISH CAUGHT BY GILLNETS

Table 1. Continued.

Max. TL Ref. Min. TL Ref. TL C Ref. TL50 Ref. Code

T (mm) G (mm) (mm) (mm)

Narcine brasiliensis (Olfers, 1831) 202 1, 2 288 17 NABR

Nebris microps Cuvier, 1830 331 1, 2 270 8

Ophichthus gomesii (Castelnau, 1855) 595 1, 3

Ophichthus parilis (Richardson, 1848) 471 3

Oligoplites saliens (Bloch, 1793) 270 7, 8

Oligoplites saurus (Bloch and Schneider, 1801) 213 1

Ophidium holbrooki (Putnam, 1874) 225 1, 3

Ophioscion punctatissimus 155 1, 3

Meek and Hildebrand, 1925

Opisthonema oglinum (Lesueur, 1817)* 185 1, 3 208 8 150 10 115 17 OPOG

Orthopristis ruber (Cuvier, 1830) 275 1, 2, 3 156 17 ORRU

Paralichthys sp. (P. brasiliensis or P. patagonicus)* 300 7 350 10

Paralonchurus brasiliensis (Steindachner, 1875)* 250 1, 2, 3, 5 160 8 149 14 PABR

Pellona harroweri (Fowler, 1917) 246 1, 2, 3

Peprilus paru (Linnaeus, 1758)* 185 1, 3 200 8 150 10 120 17 PEPA

Peprilus xanthurus (Quoy and Gaimard, 1825)* 210 7

Platanichthys platana (Regan, 1917) 124 3

Polydactylus oligodon (Günther, 1860) 214 1

Polydactylus virginicus (Linnaeus, 1758) 190 2, 3

Pomadasys corvinaeformis (Steindachner, 1868)* 214 1, 2, 3 175 8

Porichthys porosissimus (Cuvier, 1829) 265 1, 3

Priacanthus arenatus Cuvier, 1829 270 7

Prionotus punctatus (Bloch, 1797)* 272 1, 3 180 7 180 10 262 17 PRPU

Prionotus nudigula Ginsburg, 1950* 111 2

Pseudobatos percellens (Walbaum, 1792) 645 1, 2 430 7 583 17 PSPE

Rypticus randalli Courtenay, 1967 176 1, 3

Sardinella janeiro (Eigenmann, 1894) 149 3 192 17 SAJA

Scomberomorus brasiliensis 206 1 210 7, 9 370 446 9 SCBR

Collette, Russo and Zavala-Camin, 1978*

Selene setapinnis (Mitchill, 1815) * 195 1, 3 205 17 SESE

172 MARINE AND FISHERY SCIENCES 35 (2): 165-180 (2022)

Table 1. Continued.

Max. TL Ref. Min. TL Ref. TL C Ref. TL50 Ref. Code

T (mm) G (mm) (mm) (mm)

Selene vomer (Linnaeus, 1758) * 110 1, 3 305 7,8

Serranus phoebe Poey, 1851 112 1

Sphoeroides greeleyi (Gilbert, 1900) 124 1, 3 70 17 SPGR

Sphoeroides testudineus (Linnaeus, 1758) 260 1, 3 108 17 SPTE

Sphyraena guachancho Cuvier, 1829 331 3

Sphyrna sp. (S. lewini or S. zygaena)* 720 7 600 10

Stellifer brasiliensis (Schultz, 1945)* 190 1, 2, 3 73 17 STBR

Stellifer rastrifer (Jordan, 1889)* 215 1, 2, 3 98 17 STRA

Stellifer sp. (species not described)* 124 1, 2, 3

Stellifer stellifer (Bloch, 1790)* 175 1, 2, 3 75 17 STST

Stephanolepis hispidus (Linnaeus, 1766) 202 3 139 17 STHI

Syacium micrurum Ranzani, 1842 175 3

Syacium papillosum (Linnaeus, 1758) 239 3

Symphurus jenynsi (Evermann, 1906) 158 3

Symphurus plagusia (Bloch and Schneider, 1801) 168 2

Symphurus tessellatus (Quoy and Gaimard, 1824) 200 1, 2, 3

Syngnathus folletti Herald, 1942 130 2

Synodus foetens (Linnaeus, 1766) 224 3

Thalassophryne nattereri Steindachner, 1876 36 1

Trichiurus lepturus Linnaeus, 1758* 940 1, 2, 3, 6 550 7, 8 700 10 506 17 TRLE

Trinectes microphthalmus (Chabanaud, 1928) 165 2, 3

Trinectes paulistanus (Ribeiro, 1915) 165 1, 3

Umbrina coroides Cuvier, 1830* 200 3

Urophycis brasiliensis (Kaup, 1858)* 265 1, 2, 3

Zapteryx brevirostris (Müller and Henle, 1841) 551 1, 2 380 7 506 16 ZABR

Ref.: 1: Pina and Chaves (2009); 2: Pinheiro (2016); 3: Souza and Chaves (2007); 4: Muniz and Chaves (2008); 5: Robert et al. (2007); 6: Del Puente and

Chaves (2009); 7: Afonso and Chaves (2021); 8: original data; 9: Chaves et al. (2021); 10: MMA (2005); 11: Chaves and Nogueira (2018); 12: Romero et

al. (2008); 13: MMA (2006); 14: Silva-Júnior et al. (2015); 15: Braun and Fontoura (2004); 16: Colonello and Menni (2011); 17: Froese and Pauly (2021).

Twenty species were common to both gears,

and 70% of them had Max. TL T > Min. TL G

(Figure 3). Species represented in trawling by

individuals < 200 mm only contained Min. TL G

> Max. TL T. Conversely, individuals > 200 mm

presented TL T > Min. TL G (Figure 3).

Among the 20 species common to trawling and

gillnets, 16 constitute fishing resources in the

study area (Figure 4). Thirteen species, ten of

which are fishing resources in the region, present-

ed the relationship ‘Max. TL T/Min. TL G’ > 1.0.

This reveals that trawling also acts on important

sizes that are larger than the smallest individuals

caught by gillnets. For five resources, Prionotus

punctatus, Paralonchurus brasiliensis, Centropo-

mus parallelus, Trichiurus lepturus, and Larimus

breviceps, trawling catches individuals up to 1.5-

2.3 times larger than the smallest ones caught by

gillnets (Figure 4). The other 26 fishing resources

were classified under trawling (18) or gillnets (8)

(Table 1).

The minimum size of legal capture (TL C) was

established for 18 fishing resources (Table 1).

Trawling exploits 13 of these species. Nearly

70% (9) presented the relationship ‘Max. TL

T/TL C’ > 1; however, it is expected that all 13

species have individuals caught with TL < TL C.

Gillnets exploited 14 resources; half of them pre-

sented the relationship ‘Min. TL G/TL C’ > 1, and

prohibited sizes were probably not caught by gill-

nets. The other 50% (seven resources) presented

Min. TL G < TL C and were vulnerable to being

captured at prohibited sizes (Figure 5).

The average size at first maturation is known

for 40 species (Table 1). Trawling exploited 37 of

them. Nearly 75% (29) presented the relationship

‘Max. TL T/TL50’ > 1; however, it is expected

that all 37 species caught individuals with TL <

TL50. Gillnets exploited 19 species. Nearly 55%

of them presented the relationship ‘Min TL

G/TL50’ > 1, and probably are not caught by gill-

nets before the first maturation. Conversely, 45%

(9 species) presented Min TL G < TL50 and were

vulnerable to gillnets as juveniles (Figure 6).

For trawling, nearly 75% (19/25) of fishing

resources analyzed for maturation size presented

the relationship ‘Max. TL T/TL50’ > 1, but it is

expected that all 25 resources caught individuals

173

CHAVES: JUVENILES AND UNDERSIZED FISH CAUGHT BY GILLNETS

Figure 2. Relative frequencies of species (N = 112) according to individual total length (TL) registered in small-scale fisheries

in Southern Brazil grouped in 40 mm size classes. Maximum TL in trawling: wide line, 100 species; minimum TL in

gillnets: narrow line, 32 species.

0

5

10

15

20

25

30

35

30 70 110 150 190 230 270 310 350 390 430 470 510 550 590 630670 710 750 790 830 870 910

TL (mm)

Relative frequency (%)

174 MARINE AND FISHERY SCIENCES 35 (2): 165-180 (2022)

Figure 4. Species of common occurrence in both fishing gears (trawl nets and gillnets) in Southern Brazilian small-scale fish-

eries, and values of the relationship between the maximum total length in trawling (Max. TL T) and the minimum TL in

gillnets (Min. TL G). *: species that constitute fishing resources in the study area.

0

1

2

3

Max. TL T/Min. TL G

Species

Selene vomer*

Chaetodipterus faber

Genidens barbus*

Chloroscombrus chrysurus*

Opisthonema oglinum*

Peprilus paru*

Stellifer brasiliensis*

Isopisthus parvipinnis*

Macrodon ancylodon*

Pomadasys corvinaeformis*

Nebris microps

Eugerres brasilianus*

Micropogonias furnieri*

Zapteryx brevirostris

Pseudobatos percellens

Prionotus punctatus*

Paralonchurus brasiliensis*

Centropomus parallelus*

Trichiurus lepturus*

Larimus breviceps*

Figure 3. Distribution of values of maximum total length (TL) in trawling (dark circles) and/or of minimum total length in gill-

nets (white circles) of 112 species caught by small-scale fisheries in Southern Brazil.

0

100

200

300

400

500

600

700

800

900

1,000

0112

Species

TL (mm)

with TL < TL50. For gillnets, nearly 60% (10/17)

of the resources presented ‘Min TL G/TL50’ ≥ 1,

and probably were not caught before the first

maturation. However, 40% (7 resources) present-

ed Min TL G < TL50 and were vulnerable to gill-

nets in juvenile conditions (Figure 6).

175

CHAVES: JUVENILES AND UNDERSIZED FISH CAUGHT BY GILLNETS

Figure 6. Relationship between total length (TL) in catches and average TL of maturation (TL50) in species exploited by small-

scale fisheries in Southern Brazil. Dark circles indicate the maximum TL in trawling; white circles indicate the minimum

TL in gillnets. *: species that constitute fishing resources in the study area. Species code: Table 1.

Figure 5. Relationship between total length (TL) in catches and TL of legal capture in resources exploited by small-scale fish-

eries in Southern Brazil. Dark circles indicate the maximum TL in trawling; white circles indicate the minimum TL in

gillnets.

0

1

2

TL catches/legal capture

Resources

Genidens barbus

Centropomus undecimalis

Stellifer brasiliensis

Menticirrhus americanus

Micropogonias furnieri

Menticirrhus littoralis

Centropomus parallelus

Eucinostomus gula

Opisthonema oglinum

Chloroscombrus chrysurus

Trichiurus lepturus

Prionotus punctatus

Eugerres brasilianus

Carcharhinus sp.

Paralichthys sp.

Sphyrna sp.

Mugil liza

0

1

2

3

TL catches/TL

50

Species code

Fishing resources caught of undersized for

legal capture and/or before the first maturation

constitute incidental capture in such gear. In

trawling, size bycatch affects Genidens barbus,

Centropomus undecimalis, Scomberomorus

brasiliensis, Menticirrhus americanus, M. lit-

toralis, M. furnieri, and Selene setapinnis; in gill-

nets, S. brasiliensis M. americanus, M. furnieri,

Centropomus parallelus,Trichirus lepturus,Car-

charhinus sp., Paralichthys sp., Prionotus punc-

tatus, Larimus breviceps,Cynoscion guatucupa,

and C. acoupa are affected (Figures 5 and 6).

DISCUSSION

Data showed that trawlers catch thrice the

number of species than gillnetters, which reflects

different selectivity between the two gears (Arm-

strong et al. 1990; Alarcón Vélez et al. 2014), as

well as the mode and depth of operation. Active

fishing, which is independent of fish movements

and explores shallow waters, are the advantages

of shrimp trawling, which result in higher yields

than gillnets, which frequently work at the bottom

up to 30 m depth (Chaves and Robert 2003; Afon-

so and Chaves 2021). Previous studies have

pointed out a bathymetric heterogeneity in fish

size distribution, with smaller individuals occupy-

ing mostly shallower waters, while larger ones

occupy deeper waters. A similar trend was report-

ed by Macpherson and Duarte (1991), who

referred to demersal fish in the SE Atlantic (44

species) and the NW Mediterranean (31 species).

This was also observed in the pelagic tuna fishery

in Asia (FAO 2016). The size-depth relationship

associated with gear selectivity helps to explain

the size differences between captures from the

gears, the smallest TL of 36 mm was found for

trawling, and 100 mm for gillnets. Even so, the

range of minimum TL of species caught by gill-

nets reached 610 mm, which is an important value

in view of their high selectivity. This is due to the

multiple mesh sizes found in setnets plus drift-

nets, from 5 to 20 cm between opposite knots,

exceptionally up to 45 cm, operating simultane-

ously and/or alternately along the year (Chaves

and Robert 2003; Afonso and Chaves 2021).

The minimum size of legal capture (TL C) is

normally determined based on the reproductive

condition, for example, the smallest mature fish,

the average size of maturation (TL50), or the size at

which 100% of fish are mature (Sunil Mohamed et

al. 2014). When TL C is larger than TL50, it

denotes caution in fisheries management. In the

present work, TL50 was estimated for some

species, and TL C was established for a lower

number of resources. The values of these parame-

ters are derived from various regions on the Brazil-

ian coast, and in certain species both TL C and

TL50 refer to two different stocks. Although not

definitive, results indicate undersized individuals

in bycatch that also occur in gillnets in the study

area. The size at first maturation exceeded the

maximum size caught by trawling in eight species,

as well as the minimum size caught by gillnets in

nine species. This means that undersized fish are

caught by trawling (as expected) as well as by gill-

nets. Both conditions simultaneously apply to four

species: G. barbus,S. brasiliensis, M. furnieri, and

Macrodon ancylodon. These species play an

important role in landings in Southern Brazil

(MMA 2005; Chaves and Silva 2019; Chaves et al.

2021), and juveniles are being exploited by both

trawling and gillnets. Because more species are

caught by trawling, this gear acts on more under-

sized species than gillnets. However, relative to

the number of species occurring in each gear, the

size bycatch from gillnets is significant.

Capture of resources smaller than TL50 by gill-

nets in Brazilian waters has long been reported.

Alves et al. (2012) studied mesh sizes of 7-13 cm

and found undersized individuals in five of six

species, including S. brasiliensis and M. furnieri.

The status of the other three species recognized in

the present work as occurring in gillnets is

unknown because of the lack of data on TL C or

176 MARINE AND FISHERY SCIENCES 35 (2): 165-180 (2022)

TL50. Indeed, there are resources (e.g., Centropo-

mus undecimalis and Menticirrhus littoralis) that

also occur in gillnets (Afonso and Chaves 2021),

but were not presented here because data on Min.

TL G were not available.

The number and biomass in captures were not

considered, nor were the discards accomplished on

board in the case of commercial samplings. It is

expected that in a single haul of trawling, a signif-

icant number of small fish were caught than with a

similar effort using gillnets. On the other hand,

considering the large area used to deploy gillnets

(thousands of meters), and their period of exposure

(up to six days fulltime), the total fishing effort of

gillnets is intense, and the impact of gillnets on

juveniles and undersized fish is not negligible. In

the study area, SSF is only managed with respect to

trawling; there are no policies on gillnet effort with

respect to extension, time of exposure, or manage-

ment by quotas. Only a few resources are subject to

local rules disposing on the non-capture of young

or of adults in the spawning period (Chaves and

Silva 2019), and on the capture of threatened elas-

mobranchs (Chaves et al. 2019). In view of the

occurrence of threatened teleost species in the

study area, Afonso and Chaves (2021) recom-

mended an effort reduction of gillnet with a mesh

size of 18 cm at the end of winter and spring. San-

turtún et al. (2014) stated that, for stocks that are

not managed by quota, the biggest problem was

discards due to minimum landing size, an alert that

highlights the relevance of the present findings

with respect to size bycatch in gillnets.

In the present work, gillnet captures were not

individualized by mesh size, an omission that pre-

vents an accurate analysis of the gear types most

implied in non-target captures. Measures to

reduce the capture of undersized fish, proposed

by Alarcón Vélez et al. (2014), include the

turnover of fishing areas and the extension of

close seasons for fishing, taking into account the

presence of juveniles. Alves et al. (2012) added

that gillnet management should consider the ear-

lier period of the reproductive cycle, since ovari-

an development increases the fish perimeter at the

first dorsal fin in M. furnieri and other teleosts.

The influence of the reproductive cycle on mesh

size selectivity, first described by McCombie and

Berst (1969), affects adult fish, but is usually

ignored in fishery rules.

This work highlights the suggestion of Car-

doso et al. (2021) with respect to catches, and the

partial discarding of fish that could be caught in

bigger sizes and provides higher yields. It applies

not only to fish and shrimp trawlings, but also to

gillnets. Furthermore, from a global conservation

perspective, gillnets affect vertebrates such as

sharks, turtles, mammals, and penguins and other

birds, when migrating in waters exposed to set-

nets and driftnets (Cheng and Tien-Hsi 1997;

FAO 2020), presenting a strong challenge for

monitoring and control. Following Santurtún et

al. (2014), in view of the size bycatch existing in

both trawling and gillnets, it is recommended to

implement landing obligations for all catches,

except for species with a high survival rate after

release. According to these authors, time can be

provided to fishers’ organizations to develop

innovative solutions to trade these undersized

fish, or to find processed products that use the

otherwise discarded fish as raw material.

ACKNOWLEDGMENTS

Author is grateful to three anonymous referees,

and to the MAFIS Editor, by the time they have

consecrated to the manuscript, and to the Matin-

hos fishers, by their assistance for data collection.

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