Non-commercial invertebrate discards in an experimental trammel net fishery

Non-commercial invertebrate discardsin an experimental trammel net fishery

J . M . S . G O N C A L V E S, L . B E N T E S, R . C O E L H O, P . M O N T E I R O,

J . R I B E I R O, C . C O R R E I A , P . G . L I N O & K . E R Z I N I

Centro de Ciencias do Mar – CCMAR/CIMAR, Universidade do Algarve, Faro, Portugal

Abstract Non-commercial invertebrate discards in an experimental trammel net fishery were studied in relationto selectivity of the gear, depth, soak time and season. Forty experimental fishing trials were carried out over a1-year period with six combinations of small mesh (100, 120 and 140 mm) inner and large mesh (600 and 800 mm)outer panels. On average, 43.8 ± 12.2 (SD) (individuals 1000 m)1 of net) of non-commercial invertebrates werediscarded, accounting for 48% and 65% of the total catch and total discards by numbers, respectively. Withinnon-commercial invertebrates discards, the six most abundant species by number were Phallusia mammillata(Cuvier) (27.5%), Cymbium olla (L.) (13.0%), Sphaerechinus granularis (Lamarck) (11.3%), Paracentrotus lividus(Lamarck) (10.9%), Astropartus mediterraneus (Risso) (8.2%) and Astropecten aranciacus (L.) (8.1%); Echino-derms (43.1%) particularly important. The highest and lowest discard ratios were found in autumn and winter,respectively. Discards generally decreased with depth, varied considerably in relation to soak time and were notrelated to mesh size combinations. Trammel nets seem to be the most important gear in terms of ecological impactson benthic invertebrates compared with other coastal fishing gears and at the depths studied (15–60 m).

KEYWORDS : biodiversity, by-catch, discards, fisheries, gear selectivity, invertebrates.

Introduction

The maintenance of marine biodiversity is an impor-tant priority for conservation, and fishing is one of theactivities that most impacts on marine communities,removing rare and abundant species, changing speciescomposition, modifying and even destroying habitats(e.g. Hall 1999). Discarding is a common practice infisheries worldwide, accounting for an estimated 8% ofthe annual commercial fish catches or 7.3 million tonof fish returned to the sea (Kelleher 2005). Asdiscarded organisms are often dead or in a poor state,their discarding represents a loss of diversity of marinecommunities (e.g. Hall 1996; Hall, Alverson & Metu-zals 2000).With the growing consciousness of the importance

of ecosystem functioning for sustainability of fisheriesresources (e.g. Gislason, Sinclair, Sainsbury & O�Boyle2000), a number of studies on the evaluation of theeffects of fishing on the environment have beenundertaken (e.g. Jennings & Kaiser 1998; Collie, Hall,Kaiser & Poiner 2000).

As trammel nets are one of the most widely usedgears in coastal waters worldwide, there have beensome studies on discards (e.g. Purbayanto, Tsunoda,Akiyama, Arimoto & Tokai 2001; Coelho, Erzini,Bentes, Correia, Lino, Monteiro, Ribeiro & Goncalves2005; Goncalves, Stergiou, Hernando, Puente, Mou-topoulos, Arregi, Soriguer, Vilas, Coelho & Erzini2007) but, as with discard studies for most gears, theemphasis was on vertebrates or commercially valuableor protected species.

In the Algarve (southern Portugal), 130 coastalfishing vessels were licensed to fish with trammel netsin 2002, accounting for 14.8% of all the licenses, withonly longline licenses more important (DGPA 2007).Given that the coastal vessels are allowed to fish up to9.0 km of trammel nets, the quantity of trammel netsused in Algarve waters (coastline of 160 km) couldeasily exceed 1000 km. Trammel netting takes place atdepths from 10 to 90 m, mostly within 6 nautical milesof the shore. The target species of this fishery aredemersal and benthic species, such as cuttlefish, seabreams, soles, red mullet, skates and spiny lobster and

Correspondence: Jorge M. S. Goncalves, Centro de Ciencias do Mar – CCMAR, Universidade do Algarve. FCMA Campus de Gambelas,

8005-139 Faro, Portugal (e-mail: [email protected])

Fisheries Management and Ecology, 2008, 15, 199–210

� 2008 The Authors. Journal compilation � 2008 Blackwell Publishing Ltd. doi: 10.1111/j.1365-2400.2008.00607.x

Fisheries Managementand Ecology

fish discards, consist mainly of pelagic species like chubmackerel and sardine (Goncalves et al. 2007).

The main objectives of this study, part of a projecton selectivity of trammel nets in southern Europeanwaters, were to quantify the discards of non-commer-cial invertebrates of trammel nets in Algarve waters(Northeastern Atlantic), in relation to gear/selectivitycharacteristics, depth, soak time and season.

Materials and methods

Experimental design and data collection

The trammel net fishery studied uses coastal cate-gory boats (vessels between 9 and 33 m in length),monofilament nets and targets cuttlefish/sole andassorted demersal fin-fish (Borges, Erzini, Bentes,Costa, Goncalves, Lino, Pais & Ribeiro 2001; Erzini,Goncalves, Bentes, Moutopoulos, Hernando-Casal,Soriguer, Puente, Errazkin & Stergiou 2006).

The experimental nets consisted of six differentcombinations, all of green monofilament netting. Thus,each net was constructed with one of two sizes of largemesh outer panels (600 or 800 mm stretched mesh) andone of three smaller mesh inner panels (100, 120,140 mm stretched mesh). Each combination was com-posed of five nets with the same mesh size for eachpanel. Overall, five groups of these combinations wereused giving a total of 150 nets. The six distinctcombinations were joined together by a footrope,leaving a 2-m gap between them so that fish are not ledfrom one combination to the adjacent combination,thereby causing biased catch rates. A total of 8900 mof trammel net, composed of 2500, 3000, 3400 m ofeach inner mesh size (100, 120 and 140, respectively)were used. For these inner mesh sizes, the calculatedhanging ratios were 0.49, 0.49 and 0.48, respectively(Erzini et al. 2006).

Normal fishing practices were followed, with thesetting of the gear in the afternoon or evening beforesunset and hauling after sunrise in the next day orseveral days later. As hauling usually took all morningand part of the afternoon, setting of the nets oftenoccurred after all the nets had been hauled. The soaktime was calculated as the time in minutes elapsedbetween the time of setting the nets (average betweenthe beginning and the end of the operation) and thetime of hauling (average between the beginning and theend of the operation).

Catches were sorted according to the six trammel nettypes and information recorded on fishing grounds,depth, number of fleets, times of setting and hauling,method of capture and discarding practices. All

organisms were identified and all fish, crustaceansand molluscs were measured (total length, disc widthor mantle length) to the nearest millimetre. When indoubt, organisms were taken to the laboratory foridentification. Before sorting, the catches were classi-fied by the fishermen as commercial or discard.

Experimental fishing trials were carried out on aseasonal basis, with 10 fishing trials per season with25 nets of each of the six combinations of inner andouter panels. Fishing took place in the same generalarea in Algarve waters between 10 and 90 m andthe exact position of each set was recorded with aGPS.

Data analysis

Abundances of each species, species diversity, richnessand evenness, and dominance curves were used toanalyse discard species composition per inner/outerpanel mesh combination of trammel nets. Diversitywas calculated using the Shannon–Wiener diversityindex H�, species richness using Margalef�s D index,and evenness using Pielou�s J measure (Magurran1988).

Matrices comprising the numbers of each species(discard numbers per 1000 m of net) from each inner/outer mesh combination per each season (i.e., averageof all trials per season) were constructed to study gearand season overlap [i.e. (all species) · (six inner/outermesh combinations) · (four seasons)]. From thesematrices, triangular matrices of similarities betweenall pairs of inner/outer mesh combinations werecomputed using the Bray–Curtis coefficient. Prior tothis computation, data were transformed using thedouble square root transformation to reduce theweighting of abundant species. Non-parametric per-mutation tests (ANOSIM with two crossed factors) wereused to test for differences between regions, seasonsand mesh sizes (Clarke & Warwick 2001). The contri-bution of each species to the average Bray–Curtisdissimilarity between groups of combinations as wellas to similarity within a group of combinations wasidentified using Similarity of Percentages (SIMPER)analysis (Clarke & Warwick 2001). All the above-mentioned analyses were carried out using PRIMER 6(Clarke & Warwick 2001).

The discard/total catch ratio (D/T) in numbers wascalculated separately for each individual inner/outermesh size and season. Comparisons of mean diversityindices, numerical abundances and catch rates betweendifferent inner/outer panel mesh size combinations,seasons and geographic areas were carried out usingt-test or Mann–Whitney test and one-way analysis of

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� 2008 The Authors. Journal compilation � 2008 Blackwell Publishing Ltd.

variance (ANOVA) or Kruskal–Wallis ANOVA on ranks,according to the case (Zar 1999).

Results

The experimental fishing trials carried out betweenJanuary and December 2000 resulted in a total catch of29 844 individual organisms, with 8392 (28.1%) clas-sified as commercial, 13 220 (44.3%) as non-commer-cial invertebrate discards and 8232 (27.6%) as otherdiscards. These numbers illustrate the importance ofdiscards and in particular of invertebrates that accountfor the majority of trammel net catches. The averagetotal discard ratio of the trammel nets studied off theAlgarve coast was 0.74 ± 0.08 (SD). The overall meannumber of discarded invertebrates was 43.8 ± 12.2(SD) 1000 m)1, which corresponded to a mean D/T of0.48 ± 0.14 (SD), and accounted for almost 65% ofthe total discards in numbers.The commercial catch was dominated by Sepia

officinalis L. (cuttlefish) and Microchirus azevia (Cap-ello) (bastard sole), while Scomber japonicus Houttuyn(chub mackerel) and Sardina pilchardus (Walbaum)(sardine) were the most important discarded fishspecies. The most important discarded commercialinvertebrates were S. officinalis, Octopus vulgarisCuvier (common octopus), Loligo vulgaris Lamarck(common squid), Eledone cirrhosa (Lamarck) (hornedoctopus), Maja squinado (Herbst) (spiny spider crab)and Palinurus elephas (Fabricius) (spiny lobster).Individuals of these species were discarded largelybecause of poor condition and/or insufficient quanti-ties for sale in auction, and to a lesser extent for being

below the legal minimum landing size. For the lattertwo cases, the organisms are often taken by thefishermen for their own consumption, or returned tothe sea if very small and alive.

Fifty-five non-commercial discarded invertebratestaxa were recorded (Appendix 1) with the ClassEchinodermata represented by 15 species and 5690individuals (43.0% of all non-commercial inverte-brates, 26.5% of the total discards and 19.1% of thetotal catch). The most important echinoderm speciesdiscarded were the sea urchins Sphaerechinus granu-laris (Lamarck) (11.3%) and Paracentrotus lividus(Lamarck) (10.9%) and the starfish Astropartus med-iterraneus (Risso) (8.2%) and Astropecten aranciacus(L.) (8.1%) (Fig. 1). Nevertheless, the ascidian Phallu-sia mammillata (Cuvier) (27.5%) and to a lesser extentthe gastropod Cymbium olla (L.) (13.0%) were thedominant discarded species, together accounting for40.5% of the discarded non-commercial invertebrates(Fig. 1, Appendix 1). These six species plus Dardanusarrosor (Herbst) (4.7%), accounted for about 37.1 and83.7% of all discards and non-commercial invertebratediscards, respectively.

Overall, these important non-commercial inverte-brate species showed highly variable densities andseasonal differences. Discards were dominated byP. mammillata and A. mediterraneus in summer,P.mammillata in winter,P. lividus,C. olla,A. aranciacusand S. granularis in spring, and S. granularis and D.arrosor in autumn (Fig. 1).

In contrast to the catch of commercial species, totaldiscards (non-commercial invertebrates plus otherdiscards) were the lowest in winter, corresponding to

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Figure 1. Seasonal variation of the catch per unit effort (mean numbers per 1000 m of net, ±SD) of the seven most discarded non-commercial

invertebrate species (n = 11 062; 83.7% of the total).

TRAMMEL NET INVERTEBRATE DISCARDS 201


a D/T ratio of 0.63 (Fig. 2, Table 1). This ratio (D/T)was relatively constant in the other seasons, withvalues of approximately 0.78 (Table 1).

The numbers of discarded non-commercial inverte-brates were lowest in autumn and winter, around 36%of the total discards, increasing to approximately 60%in the spring and the summer (Fig. 2; Table 1).However, there was no statistically significant interac-tion between season and discarding practices in termsof quantities discarded (two-way ANOVA, P = 0.230).

The total catch includes 178 species of which 85 werecommercial and 156 were partly or totally discarded,including 55 non-commercial invertebrates that werealways discarded. Non-commercial invertebrate dis-card diversity was lower in winter and summer,because of smaller numbers of species and dominanceof P. mammillata (Fig. 3). The greatest species richnesswas in autumn, with high equitability, for invertebratesas well as for the total catch.

There were no significant differences in the numbersof non-commercial invertebrates caught with thedifferent outer panel mesh size trammel nets (Mann–

Whitney Test, P = 0.622) or with the different smallmesh inner panel trammel nets (Kruskal–Wallis ANOVA

on ranks, P = 0.832), although there was an increasein catches with an increase in inner panel mesh size(Table 2). Season was a more important factor thanthe selectivity of the gear, for all inner and outer panelmesh size combinations, with autumn and winterhaving the highest and lowest values of the diversityindices used, respectively (Figs 3 & 4).

The multivariate analysis showed a clear separationby season, with autumn and above all winter differingfrom the other seasons (Fig. 4) (ANOSIM, r = 1.0,P = 0.001). The different proportions of the speciesP. mammillata, S. granularis, P. lividus andA. aranciacus are the main cause for the differencesbetween seasons, with autumn and winter associatedwith the greatest dissimilarity (SIMPER, averagedissimilarity: 70.4%), and the opposite for springand summer (SIMPER, average dissimilarity: 47.3%).Within each season, there was no clear pattern withregards to the different inner–outer panel mesh sizecombinations.

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Figure 2. Seasonal variation of the catch per unit effort (mean numbers per 1000 m of net, ±SD) of the commercial, non-commercial invertebrate

discards and other discards components of the trammel net catches (n = 29 844).

Table 1. Commercial catch, non-commercial (NC) invertebrate discards and other discards in numbers per 1000 m of net (n/1000 m) and

ratio of total and non-commercial invertebrate discards to total catch by season and annual mean plus standard deviation (SD) and coefficient

of variation (CV)

Autumn Winter Spring Summer Mean SD CV

Commercial catch (n/1000 m)1) 21.4 36.1 18.8 19.1 23.9 8.2 34.6

NC Invertebrate discards (n/1000 m)1) 31.5 35.3 56.4 51.9 43.8 12.2 27.9

Other discards (n/1000 m)1) 36.2 25.3 16.1 16.0 23.4 9.6 41.0

Total discards/total catch (D/T) 0.76 0.63 0.79 0.78 0.74 0.08 10.4

NC invertebrate discards/total catch 0.35 0.37 0.62 0.60 0.48 0.14 29.6

NC invertebrate discards/total discards 0.47 0.58 0.78 0.76 0.65 0.15 23.3



There was a decrease in non-commercialinvertebrate discards with an increase in depth(Fig. 5a), but not for other discards or for commer-cial catches (Figs 6a,b). For the latter, there were

large catches at depths between 30 and 40 m(Fig. 6b).

Although there was a slight increase in non-com-mercial invertebrate discards with increasing soak

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Figure 3. Non-commercial invertebrate discards species diversity by season and mesh size combination (n = 13 220; s = 56). A = autumn;

W = winter; Sp = spring; Su = summer; 600 and 800 mm = outer panels mesh size; 100, 120 and 140 mm = inner panels mesh size.

Table 2. Total catch, total discards and non-commercial (NC) invertebrate discards in numbers per 1000m of net and relative importance of

non-commercial invertebrate discards to total catch and total discards by inner/outer panel mesh size combination

Outer mesh size (mm): 600 800

Grand totalInner mesh size (mm): 100 120 140 Total 100 120 140 Total

Total catch (n) 54.4 57.9 52.6 164.9 58.7 55.7 54.1 168.6 333.5

Total discards (n) 37.2 41.4 39.7 118.3 40.7 39.4 41.3 121.4 239.7

NC invertebrate discards (n) 21.4 24.6 28.6 74.6 20.6 24.3 28.3 73.1 147.7

NC invertebrate discards/total catch (%) 39.3 42.5 54.4 45.2 35.1 43.6 52.2 43.4 44.3

NC invertebrate discards/total discards (%) 57.4 59.5 72.1 63.0 50.6 61.6 68.4 60.2 61.6

Figure 4. Multivariate analyses based on the matrices that comprise the discard numbers of each non-commercial invertebrate species from each

inner/outer mesh combination per season: dendrogram (cluster analysis). A = autumn; W = winter; Sp = spring; Su = summer; 6 = 600 and

8 = 800 mm outer panels mesh size; 10 = 100, 12 = 120 and 14 = 140 mm inner panels mesh size.



time, there was considerable variability in the data,with discard numbers probably stabilising around soaktimes of 72 h (Fig. 5b). Considerable variability wasalso characteristic of other discards, with highestdiscard values recorded for soak times of approxi-mately 24 h (Fig. 7a). There does not seem to be anyrelationship between catches in numbers of commercialspecies and soak time, except for low values for shortsoak times (2–6 h) (Fig. 7b).

Trammel nets were caught and torn on hardstructure (seven out of 40 fishing trips) and interactedwith other fishing gears, mainly octopus traps and potsin half of the trips.

Discussion

Non-commercial invertebrate discarded by-catcheswere dominated by six species, mainly echinoderms(S. granularis, P. lividus, A. mediterraneus andA. aranciacus), which are known for their voracity(e.g. Ruppert & Barnes 1994), and, together withC. olla and P. mammillata, are part of the mostimportant invertebrate top predators of the Algarve

coastal soft bottom communities (J.M.S. Goncalves,unpublished data). The latter species was the mostdiscarded non-commercial invertebrate and, in addi-tion to being a filter-feeding ascidian, is also avulnerable colonial sessile organism that provideshabitats for other species.

The seasonal pattern of non-commercial invertebratediscards followed the same patterns as those of com-mercial invertebrate and fish discards (Goncalves et al.2007), and the opposite to fish commercial catches,reaffirming winter as the most efficient season in termsof fishing and the D/T ratio. In addition to abundance,the diversity of discarded species is less in this season.Thus, there is a greater concern about the impact of thisfishery in the other seasons with the highest discardratios. The seasonal differences are probably associatedwith some spatial and fish recruitment variability,confounded in the case of the summer by shorter soaktimes and greater depths fished. This is reflected by thedifferent commercial species caught: cuttlefish, S. offi-cinalis, and soles,M. azevia and Solea spp., in autumn–winter–spring, and hake, Merluccius merluccius (L.)and forkbeard, Phycis phycis (L.), in summer.

non-commercial invertebrate discards

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Figure 5. Relationships between non-commercial invertebrate discards and depth (a) and soak time (b). The best fit regression with the respective

equation and coefficient of determination is presented.



The combination of small mesh inner panel andlarge mesh outer panel of the trammel nets did notinfluence the capture of non-commercial invertebrates;only small differences between the six combinationswere found. However, these differences were oppositeto those found for discards of fish and other commer-cial invertebrates (Goncalves et al. 2007).The decrease in non-commercial invertebrate discard

rates with increasing depth was because for thesefishing grounds, most of the rocky bottom is found atdepths of <30 m (J.M.S. Goncalves, unpublisheddata). It is not surprising that discards of commercialfish and cuttlefish do not follow the same pattern, asthey are relatively less dependent on rocky substrate.For depths >50 m, soak times of <6 h may havecontributed to the lower discard rates. The longerhauling time also may contribute to the lower discardrates as there is a greater probability of organismsescaping or falling from the net before reaching theboat.Although discards varied considerably in relation to

soak time, the general pattern was for an initialincrease of non-commercial invertebrate discards withsoak time, followed by a levelling off or even adecrease with longer soak times of up to around 40 h.

This pattern is probably caused by a tradeoff betweenthe increase in scavenging and predation over time andthe rise in by-catch of invertebrates in general and also,in part, of these very same opportunistic consumers.By comparison, discards of commercial species (fishand invertebrates) are relatively independent of soaktime, probably because these species are more mobileand catch rates are more constant over time (over atime period of 24 h or more), and the criteria for beingdiscarded does not depend entirely on fish conditions,but rather on factors such as minimum legal landingsizes.

Given that soak time is limited by law to a maximumof 12 consecutive hours in a 24-h period and that catchrates of commercial species are highest for soak timesof approximately 24 h, it is advisable to ensure propermonitoring and enforcement of current legislation. Asoak time of more than 24 h can be avoided byensuring that nets are not left to fish over the weekend,or for more days than permitted in the hope ofcatching spiny lobsters (P. elephas) and other highvalue crustacean species that are attracted by rottingfish in the net.

A limitation of this study was the underestimate ofsmall-sized species (<30 mm), because fishing trials

Other discards

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Figure 6. Relationships between depth and other discards (a) and commercial catch (b).



were carried out on a commercial fishing vessel whereconditions did not allow for adequate identification ofsuch species. However, megafauna are the best indica-tors of fishing effects because they are in general morevulnerable to fishing than smaller species and as slowergrowing organisms, they tend to take a longer time torecover from harvesting. Collie et al. (2000) concludedthat the removal of these species reduced the complex-ity and species diversity of the benthic community.

In the study area, coastal trammel nets are the maincause of by-catch and discarding of non-commercialinvertebrates at depths between 15 and 60 m. Atdepths <15 m, dredges for bivalves such as Donaxspp. and Spisula solida (L.), together with artisanaltrammel nets have a considerable impact (Borges et al.2001; Chicharo, Chicharo, Gaspar, Regala & Alves2002). With regards to other gears operating in thisarea, little is known of their impact on non-commercialinvertebrates. However, Erzini, Goncalves, Bentes,Lino & Cruz (1996) found that longlines fished atdepths between 10 and 50 m often caught starfish(A. aranciacus). At these depths, purse seines areresponsible for the discarding of relatively few inver-tebrate species, although at times in great quantities

(e.g. Polybius henslowi Leach), and at shallow depths(10–30 m) may scrape the bottom and have negativeimpacts on slow growing organisms such as gorgo-nians (Goncalves, Bentes, Monteiro, Coelho, Corado& Erzini 2008). Both gill netters and trawlers alsodiscard significant amounts of non-commercial inver-tebrates in these waters (Borges et al. 2001; Erzini,Costa, Bentes & Borges 2002; Erzini, Goncalves,Bentes, Lino, Ribeiro & Stergiou 2003). For example,for deep water crustacean trawls (300–700 m depth),non-commercial invertebrates accounted for 16.8%and 36.1% of the discards in weight and in number(Monteiro, Araujo, Erzini & Castro 2001). Garthe,Camphuysen & Furness (1996) reported that 19% ofthe total biomass of discards in the North Sea and NEAtlantic consisted of benthic invertebrates, while ahigher percentage was found for the southern NorthSea (40.3%).

As trammel nets are static gear, mortality ofinvertebrate megafauna is probably more associatedwith capture and subsequent discarding, rather thanthe impact of the gear on the bottom, although thisshould be incorporated in future research. By com-parison, only trawls could have a more direct physical

Other discards

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Figure 7. Relationships between soak time and other discards (a) and commercial catch (b).



impact on bottom invertebrates in addition to theircapture and discarding (e.g. Kaiser & Spencer 1996).Trammel nets are usually fished close to rocky

bottoms that typically have high diversity, as seen fromthe capture of fish species such as scorpaenids (rockfishes), and gorgonians, sponges and corals. The studyof variability of commercial to discard ratios as afunction of distance from rocky bottoms is importantas it could contribute to minimising discarding in thisfishery.With the exception of certain small, robust species

such as Scorpaena notata Rafinesque that are easilyuntangled from the trammel nets and discarded alive,the majority of discarded fish are either dead or in suchpoor condition that survival rates would be extremelylow. For non-commercial invertebrate discards, severaldifferent situations were identified: (1) asteroids andcrustacea: where loss of arms or appendages iscommon but survival is likely; (2) gastropod molluscsand echinoids: the shells of some species such as C. ollaand sea urchins like S. granularis and are often crushedby the fishermen in the process of removal from thenets, resulting in high mortality rates; and (3) ascidians– generally returned intact and likely to survive. Inaddition to the impact of the gear, the handling onboard and the condition and physical characteristics ofthe organism, survivorship after discarding is affectedby other factors such as, predation in the watercolumn, scavenging on the bottom, the resistance tochanges in pressure and the ability to re-colonise. Asdiscarding generally occurs while the fishing vessel isunderway and results in organisms being returned toareas, depths and habitats different from those wherethey were originally caught, the implications in termsof potential recolonisation are particularly importantfor organisms having poor mobility, such as molluscs(Malaquias, Bentes, Erzini & Borges 2006). However,an advantage of discarding taking place as the vessel isunderway is that there is no danger of concentration ofdiscards in a small area, which may have a negativeeffect on the equilibrium of benthic communities andlead to a loss in biodiversity. The quantification ofsurvivorship requires specific, carefully designed stud-ies that were beyond the scope of the present study.Of the discarded invertebrate species, none can be

considered threatened or had any kind of conservationstatus (IUCN 2007). However, this may be because fewspecies of invertebrates have such a status and alsobecause of the general lack of knowledge and studieson these species. Only one flag species, the red coral,Corallium rubrum (L.), an endemic species of valuableoctocoral from the Mediterranean and adjacent Atlan-tic rocky coasts that has been over-exploited for many

years (e.g. Santangelo, Maggi, Bramanti & Bongiorni2004), was discarded.

The highest non-commercial invertebrate discardrates observed were associated with greater fishingeffort on high complexity bottoms at low depths thatare rich in terms of biodiversity. Together with thepotentially disruptive removal of the most importantinvertebrate top predators of the coastal soft bottomcommunities, trammel netting on these types of bot-toms may have an impact in terms of reducing habitatcomplexity and consequently on the ecosystem as awhole.

Acknowledgments

We would like to thank all the people, institutions andorganizations who contributed directly or indirectly tothis study, with special thanks to Captain Julio Diogoand all the �Dois Alhinhos� crew for all of their supportand to our colleagues who took part in the laboratorysampling. Funds for this study were provided by theEuropean Commission, Directorate General of Fish-eries, DG XIV/C1 and the Portuguese NationalFoundation for Science and Technology (FCT) witha grant to J.M.S. Goncalves. We are also grateful totwo anonymous reviewers for the most valuablecomments.

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Appendix 1

Species list, mean abundances per 1000 m of net and percentage contribution of each species to the non-commercial invertebrates discards (NCID), total discards (TD) and total catch (TC).

Class Family Species n/1000 m % NCID % TD % TC

Anthozoa Actiniidae Actinia cari Chiaje 0.003 0.01 0.00 0.00

Anthozoa Aliciidae Alicia mirabilis Johnson 0.658 1.44 0.89 0.64

Anthozoa Actiniidae Anemonia viridis (Forskal) 0.003 0.01 0.00 0.00

Anthozoa Corallidae Corallium rubrum (L.) 0.079 0.17 0.11 0.08

Anthozoa Dendrophylliidae Dendrophyllia ramea (L.) 0.286 0.63 0.39 0.28

Anthozoa Plexauridae Eunicella verrucosa (Pallas) 0.048 0.11 0.07 0.05

Anthozoa Gorgoniidae Leptogorgia sarmentosa (Esper) 0.038 0.08 0.05 0.04

Anthozoa Gorgoniidae Leptogorgia viminalis (Pallas) 0.003 0.01 0.00 0.00

Anthozoa Veretillidae Veretillum cynomorium (Pallas) 0.255 0.56 0.34 0.25

Ascidiacea 0.007 0.02 0.01 0.01

Ascidiacea Ascidiidae Phallusia mammillata (Cuvier) 12.528 27.50 16.95 12.18

Asteroidea Astropectinidae Astropecten aranciacus (L.) 3.673 8.06 4.97 3.57

Asteroidea Echinasteridae Echinaster (Echinaster) sepositus (Retzius) 0.062 0.14 0.08 0.06

Asteroidea Asteriidae Marthasterias glacialis (L.) 0.034 0.08 0.05 0.03

Asteroidea Ophidiasteridae Ophidiaster ophidianus (Lamarck) 0.231 0.51 0.31 0.22

Bivalvia Cardiidae Acanthocardia aculeata (L.) 0.014 0.03 0.02 0.01

Bivalvia 0.003 0.01 0.00 0.00

Bivalvia Pectinidae Chlamis varia (L.) 0.003 0.01 0.00 0.00

Bivalvia Pectinidae Pecten maximus (L.) 0.007 0.02 0.01 0.01

Crinoidea Antedonidae Antedon mediterranea (Lamarck) 0.048 0.11 0.07 0.05

Demospongiae Axinellidae Axinella polypoides Schmidt 0.059 0.13 0.08 0.06

Demospongiae Axinellidae 0.003 0.01 0.00 0.00

Demospongiae Spongiidae Spongia (Spongia) agaricina Pallas 0.003 0.01 0.00 0.00

Echinoidea Diadematidae Centrostephanus longispinus (Philippi) 0.045 0.10 0.06 0.04

Echinoidea Loveniidae Echinocardium cordatum (Pennant) 0.555 1.22 0.75 0.54

Echinoidea Echinidae Paracentrotus lividus (Lamarck) 4.972 10.92 6.73 4.84

Echinoidea Toxopneustidae Sphaerechinus granularis (Lamarck) 5.161 11.33 6.98 5.02

Gastropoda Aplysiidae Aplysina aerophoba Nardo 0.034 0.08 0.05 0.03

Gastropoda Turbinidae Bolma rugosa (L.) 0.951 2.09 1.29 0.92

Gastropoda Muricidae Bolinus brandaris (L.) 0.059 0.13 0.08 0.06

Gastropoda Cymatiidae Charonia lampas (L.) 0.121 0.26 0.16 0.12

Gastropoda Volutidae Cymbium olla (L.) 5.930 13.02 8.02 5.77

Gastropoda Muricidae Hexaplex trunculus (L.) 0.069 0.15 0.09 0.07

Gymnolaemata Adeonidae Aldeonella calveti (Canu & Bassler) 0.121 0.26 0.16 0.12

Gymnolaemata Myriozoidae Myriapora truncata (Pallas) 0.007 0.02 0.01 0.01

Gymnolaemata Hippoporinidae Pentapora fascialis (Pallas) 0.214 0.47 0.29 0.21

Holothuroidea Holothuriidae Holothuria (Panningothuria) forskali Delle Chiaje 0.365 0.80 0.49 0.36

Holothuroidea Holothuriidae Holothuria (Roweothuria) poli Delle Chiaje 0.007 0.02 0.01 0.01

Holothuroidea Holothuriidae Holothuria (Holothuria) tubulosa Gmelin 0.475 1.04 0.64 0.46

Holothuroidea Holothuriidae 0.124 0.27 0.17 0.12

Holothuroidea Stichopodidae Parastichopus regalis (Cuvier) 0.183 0.40 0.25 0.18

Malacostraca Calappidae Calappa granulata (L.) 0.331 0.73 0.45 0.32

Malacostraca Diogenidae Dardanus arrosor (Herbst) 2.136 4.69 2.89 2.08

Malacostraca Dromiidae Dromia personata (L.) 0.021 0.05 0.03 0.02

Malacostraca Galatheidae 0.003 0.01 0.00 0.00

Malacostraca Paguridae 0.562 1.23 0.76 0.55

Malacostraca Portunidae Polybius henslowi Leach 0.014 0.03 0.02 0.01

Malacostraca Portunidae 0.021 0.05 0.03 0.02

Octocorallia Pennatulidae Pennatula phosphorea L. 0.007 0.02 0.01 0.01

Ophiuroidea Gorgonocephalidae Astropartus mediterraneus (Risso) 3.714 8.15 5.03 3.61

Ophiuroidea Ophiurae 0.003 0.01 0.00 0.00

Polychaeta Serpulidae Filograna implexa Berkeley 0.699 1.54 0.95 0.68



Appendix 1. Continued

Class Family Species n/1000 m % NCID % TD % TC

Polyplacophora Ischnochitonidae Chaetopleura angulata (Spengler) 0.003 0.01 0.00 0.00

Scyphozoa Rhizostomae Rhizostoma pulmo (Macri) 0.558 1.23 0.76 0.54

Turbellaria Pseudocerotidae Pseudoceros maximus Lang 0.034 0.08 0.05 0.03

*Nomenclature from The European Register of Marine Species ERMS (http://www.marbef.org/data/) and MarineSpecies.org (http://

www.marinespecies.org/index.php).



Non-commercial invertebrate discards in an experimental trammel net fishery

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