Species and size selectivity in a Portuguese multispecies artisanal long-line fishery

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1 ICES Journal of Marine Science, 5: Species and size selectivity in a Portuguese multispecies artisanal long-line fishery Karim Erzini, Jorge M. S. Gonçalves, Luis Bentes, Pedro G. Lino, and João Cruz Erzini, K., Gonçalves, J. M. S., Bentes, L., Lino, P. G., and Cruz, J. 1. Species and size selectivity in a Portuguese multispecies artisanal long-line fishery. ICES Journal of Marine Science, 5: The species and size selectivity of long-lines using small hooks were studied off the south coast of Portugal using Mustad brand round bent, flatted sea hooks (Quality DT) numbers, 1, and 11 baited with razor shell clam (Ensis siliqua). Hook numbers 1 and 11 are 4 and 1% larger respectively than number hooks in terms of overall size (maximum width maximum length). A total of hooks were fished in 45 sets and 5 species of fish and cephalopods were caught. As a group, 1 species of sea breams (Sparidae) dominated the catch by numbers (58%) and weight (7%). Six species of sea breams, along with the greater weever fish (Trachinus draco) accounted for 81% of the total catch by weight, with the common or white sea bream (Diplodus sargus) being the most important (2%). Catch size distributions by hook size were, in general, highly overlapped for all species and hook size had little apparent effect on minimum size at capture. All hooks caught a wide range of sizes per species, but the catch rate (number of fish per 1 hooks) was significantly lower for the largest hook. Except for the black sea bream (Spondyliosoma cantharus), capture of illegally sized or immature fish was minimal. Small increases in average size with hook size were evident for four species: Diplodus sargus, D. vulgaris, Lithognathus mormyrus and Serranus cabrilla. No differences in size selectivity were detected for Boops boops, D. annularis, Spondyliosoma cantharus and Trachinus draco. A skew-normal model adequately described differences in size selectivity in five of six species. 1 International Council for the Exploration of the Sea Key words: selectivity, efficiency, hook, long-line, multispecies, artisanal, sea breams, Sparidae. Received 22 June ; accepted 25 January 1. K. Erzini: Unidade de Ciências e Tecnologias dos Recursos Aquáticos (UCTRA), Universidade do Algarve, 8 Faro, Portugal [ kerzini@ualg.pt]. Introduction Artisanal fisheries are of considerable importance in Portugal, involving 84% of the fishing fleet ( 4 of 14 8 boats (G.E.P.P., 12)) and employing a large number of fishermen. Along the south and south-west coasts small boats account for up to 5% by weight and % by value of the total landings. These boats capture high-value species using long-lines, gillnets, trammel nets, purse seines, traps, and pots. Long-lines with small hooks are widely used to capture a variety of species at depths ranging from 1 to more than 1 m. With hook numbers from 1 (largest) to 2 (smallest), the hooks used are at the lower end of the size range, with the number 1 being the most widely used. A long-line consists of a monofilament mainline (usually mm diameter) with.5 or. mm diameter monofilament gangions of variable length (.7 1. m) spaced 1.5 m apart. The long-line is coiled in round plastic tubs with cork rims for fixing the hooks. Each tub may contain or more hooks. Layers of damp beach sand are used to keep the long-line properly coiled. The most commonly used hook design on the south and south-west coast of Portugal are Mustad round bent, flatted sea hooks. The hooks are baited before the fishing operation with ghost shrimp, clam, squid, cuttlefish or sardine pieces/ strips and are left hanging loosely over the side of the tub. The long-line is fished on the bottom and is weighted at both ends with a rock or lead weight attached to a buoy. Depending on the length of the mainline, additional buoys and weights may be attached at intervals. Deployment of the gear involves raising the tub on a platform to avoid snagging the side of the boat or the engine, attaching the end of the long-line to the weight, sending the weight to the bottom, and then using 4 1//5811+ $./ 1 International Council for the Exploration of the Sea Downloaded from on 22 April 8

2 8 K. Erzini et al. the momentum of the moving boat to pay out the long-line. The fisherman is limited to rotating the tub, occasionally untangling hooks, linking the end of a long-line to the next tub and adding weights and buoys. In this way a typical artisanal inshore fishing boat (5 m with an outboard engine) with two fishermen may fish a long-line with 4 or more hooks, with one man handling the engine while the other sets the gear. However, some fishermen fish alone and can singlehandedly set and retrieve their long-line. The long-line is retrieved manually as the boat moves between buoys. It is placed in the tubs and is repaired and re-coiled properly on land. A landing net is used for the larger fish. The time of setting the long-line and the duration of the set depends on the species sought, area, depth and bait used. The target species are principally high value sea breams (Sparidae): Pagrus pagrus, Pagellus acarne, P. erythrinus, Diplodus sargus, D. vulgaris, D. cervinus, D. puntazzo, Sparus aurata, Lithognathus mormyrus and Spondyliosoma cantharus. Although long-lines using small hooks are widely used in many countries, there have been few studies to date concerning this gear. This work is part of an ongoing study on the artisanal, small scale fisheries of the south and south-west coast of Portugal which includes aspects of fisheries biology, ecology, gear selectivity and population dynamics of the more important species. The primary objective of this study was to evaluate species and size selectivity in a multispecies artisanal long-line fishery in Algarve waters (south of Portugal). Methods A preliminary survey of local (Algarve) artisanal fishing practices was carried out in order to select the hook sizes, bait type and gear specifications to be used in experimental fishing. The most commonly used hook size was number 1. It was decided to carry out the selectivity studies with hook numbers, 1, and 11 (i.e. two hook sizes above and below number 1). The dimensions of these round bent, flatted sea hooks ( Mustad brand Quality DT) are given in Figure 1. Using maximum width multiplied by maximum length to represent overall size (Otway and Craig, 1), hooks number 1 and 11 are 1.4 and 2. times the size of the number hook, respectively. The mainline and the gangions were 1.1 and.5 mm diameter monofilament and the bait chosen for the selectivity studies was razor shell clam (Ensis siliqua). A hook long-line was constructed (75 cm gangions, attached directly to the mainline, and spaced 1.5 m apart), with 2 hooks of each size in a series. After consultation with local fishermen it was decided to fish within a restricted area and depth range since species composition changes with depth. Consequently it was decided to concentrate on the white sea 8.74 ±.1 Hook 7. ± ±. 1.5 ±. 1. ±.17 Hook ±.. ±.4 breams (Sparidae), namely Diplodus sargus, D. vulgaris, D. cervinus, D. annularis, Spondyliosoma cantharus, Lithognathus mormyrus, and Sparus aurata which are fished year-round in relatively shallow water (less than m). At greater depths red sea breams such as Pagrus pagrus, Pagellus acarne, and P. erythrinus are the main species. The area selected was off the Praia de Faro ( 5 N, 8 W) and consists of a sandy bottom with patches of rocks and gravel at depths between 1 and 2 m. Fishing operations were carried out from a m boat with an outboard engine and two fishermen. The longline was baited with approximately equal sized pieces of razor shell (mean weight=4. g, S.D.=1.1, n=1) and fished in the morning between and 1 hours. The order in which the hooks were fished was alternated randomly every trial. Depending on the weather, the long-line was retrieved 2 4 h later. The fishermen were always accompanied by at least one member of the project team. The position of each set was recorded with a Global Positioning System (GPS). A total of 45 fishing trials were carried out from March 14 to March. After the first two trials the long-line was increased to hooks ( of each size) because catch rates were lower than expected. Thus a total of hooks were fished. Catches were separated by hook size and immediately transported to the laboratory. In the laboratory the fish were weighed, and measured (fork length (FL) and total length (TL) to the lower half cm). Prior to application of indirect methods for estimation of selectivity parameters an attempt was made to determine the appropriate selectivity model (bell-shaped or asymptotic with an inflection point) for each species by examining the plots of the ratios of the catches of different sized hooks against fish size (Ralston, 1; Kenchington, 1). Although results were generally inconclusive, there was more evidence supporting bellshaped selection or skew-normal selection, particularly in the cases where optimal lengths were very similar (Kenchington, 1), than for logistic or Gompertz selection. Consequently, the method of estimating 2.7 ±.5 1. ± ± ±.5 Figure 1. Shape and dimensions (mean in mm and standard errors based on a sample size of 1) of hooks used in the selectivity study ±. Downloaded from on 22 April 8

3 Species and size selectivity in a long-line fishery 81 selectivity chosen for this study was that of Helser et al. (11) for the skew-normal probability density function: where s ij is the selectivity of overall hook size H i to fish of size class L j (TL), L o (TL) is estimated mean size of fish caught by H i, and σ i and q i are the standard deviation and the skewness coefficient of the catches of H i. Following Helser et al. (11), the mean, standard deviation and skewness coefficient were calculated for the three catch distributions of each species. L o, σ, and q were then modelled as simple linear and as second order polynomial functions of overall hook size (H i ). The estimated parameters of the most appropriate models were used as starting values for fitting the following model by weighted non-linear least-squares (SAS Institute, 8): where c ij are the observed catches and c i is the total catch for H i. In this model c i,h i, and L j are the independent variables. Depending on the choice of model for L o, σ, and q, the number of parameters to estimate ranges from six for all simple linear functions to nine for all second order polynomial functions of overall hook size. The selectivity curves were standardized to obtain maximal selectivity equal to unity for all hook sizes. Results The results of the experimental fishing are summarized in Table fish and cephalopods (5 species in total) were caught, weighing a total of kg. The majority of the species and of the total catch consisted of commercially important species, with high value sea breams accounting for a significant part of the catch. Catch rates (number of fish per 1 hooks) were generally low; rarely exceeding % for hook numbers 1 and or % for the number 11 hook. However, there was considerable variation in the catch rates and the percentage of hooks that were retrieved still with bait varied from 1 5% per set. Exceptional catches of 8 % were made during the first few days following a period of south-east wind, during the summer months. The smallest hook caught the most fish (2). The intermediate size caught 584 fish and was the most successful in terms of total weight (7.%). For most species there was a clear difference in terms of efficiency between the largest hook (number 11) and hooks 1 and. Overall, the number 11 hook caught fewer fish (7) and accounted for only 2.% of the total catch by weight. As a group, the 1 species of sea breams (Sparidae) were the most important with 44 fish (58%) caught weighing. kg (7%). Six species of sea breams (Boops boops, Diplodus sargus, D. vulgaris, D. annularis, Lithognathus mormyrus and Spondyliosoma cantharus) along with the greater weever fish Trachinus draco, contributed 81% of the total catch by weight. The common sea bream (D. sargus) accounted for 2% of the total catch with 177 fish weighing 8. kg. The greater weever fish was most abundant with fish weighing 41.7 kg (14% of total catch by weight). Conger eels (Conger conger), cuttlefish (Sepia officinalis) and some moray eels (Muraena helena) and octopi (Octopus vulgaris) which attacked hooked fish and not baited hooks were not included in Table 1. In general there was strong overlapping of the catch frequency distributions, with little evidence for an increase in mean size with hook size for most species. Hook size also did not appear to significantly affect the minimum size of fish caught per species. Of the more important species, there was little or no evidence for size selectivity for Boops boops, Spondyliosoma cantharus and Trachinus draco (Table 1). Small increases in mean size as a function of overall hook size were found in the case of Diplodus sargus, D. vulgaris, Lithognathus mormyrus, and Serranus cabrilla (Table 1, Figs 2 7). There were insufficient data for the other species. The catch size frequency distributions by hook size and the minimum legal size (MLS) for six species for which selectivity was modelled (Trachinus draco, Spondyliosoma cantharus, Diplodus sargus, D. vulgaris, Boobs boops and Serranus cabrilla) are given in Figures 2 7. Simple linear functions were in most cases adequate for describing the relationships between optimal length, standard deviation and skewness and overall hook size, and good fits were obtained for five of the six species modelled. The poorest fit was for Diplodus sargus, which is the species with the widest size range in the catch ( 4 cm) and for which the number 1 hook was the most efficient size. Clearly a much flatter curve or an asymptotic curve with decreasing selectivity at the upper end of the size range is probably more appropriate in this case. The parameters of these models are given in Table 2 and the catches predicted with the model are shown in Figures 2 7. The standardized selectivity curves are given in Figures 8a f. Discussion The long-lines used in this study cannot be considered to be highly species selective given the variety of species Downloaded from on 22 April 8

4 814 K. Erzini et al. Table 1. Catch by hook number from 45 long-line sets ( hooks). ML (cm) is mean TL and S.D. is the standard deviation. Hook no. 11 Hook no. 1 Hook no. Family and species n ML (cm) S.D. n ML (cm) S.D. n ML (cm) S.D. Total Balistidae Balistes carolinensis Batrachoididae Halobatrachus didactylus Belonidae Belone belone Callionymidae Callionymus lyra Carangidae Caranx rhonchus 1. 1 Trachinotus ovatus Trachurus trachurus Clupeidae Sardina pilchardus 1. 1 Gobiidae Labridae Coris julis Labrus bergylta Labrus merula Muraenidae Muraena helena Octopodidae Octopus vulgaris Pomatomidae Pomatus saltator Scombridae Scomber japonicus Scorpaenidae Scorpaena notata Soleidae Solea senegalensis Serranidae Serranus cabrilla Serranus hepatus Serranus scriba Sparidae Boops boops Dentex gibbosus Diplodus annularis Diplodus bellottii Diplodus cervinus Diplodus sargus Diplodus vulgaris Lithognathus mormyrus Pagellus bellottii Pagrus auriga Pagrus pagrus Sparus aurata Spondyliosoma cantharus Trachinidae Trachinus draco Total Total catch weight (kg) caught within a restricted depth range and area. For comparison, extensive experimental gillnetting along the entire Algarve coast from to 4 m depths with 4,, and 8 mm stretched mesh monofilament gillnets resulted in the capture of 45 species (Martins et al., 12), of which 2 were in common with this study. Although hook gear can be highly species selective through hook size and bait type (Bjordal, ), in this case lack of species selectivity can largely be attributed to the use of a bait which is readily consumed by the Downloaded from on 22 April 8

5 Species and size selectivity in a long-line fishery 8 Hook 1 Hook MLS Figure 2. Observed catch distributions (TL) and the predicted catches according to the skew-normal model for Boops boops (MLS is the minimum legal size). Hook 1 Hook MLS Figure 4. Observed catch distributions and the predicted catches according to the skew-normal model for Diplodus sargus (MLS is the minimum legal size). Hook 1 Hook 1 Hook MLS Hook Figure. Observed catch distributions (TL) and the predicted catches according to the skew-normal model for Diplodus vulgaris (MLS is the minimum legal size) Figure 5. Observed catch distributions (TL) and the predicted catches according to the skew-normal model for Serranus cabrilla (no minimum legal size exists). Downloaded from on 22 April 8

6 81 K. Erzini et al. Hook 1 Hook MLS Figure. Observed catch distributions (TL) and the predicted catches according to the skew-normal model for Spondyliosoma cantharus (MLS is the minimum legal size) Hook 1 Hook Figure 7. Observed catch distributions (TL) and the predicted catches according to the skew-normal model for Trachinus draco (no minimum legal size exists). majority of local demersal species. Other baits are used locally to target specific species such as the bass (Dicentrarchus labrax), caught with live swimming crabs and red sea breams (Pagrus pagrus and P. auriga) with green crabs. Since the fish had to be processed for biological studies within the same day, and because of considerable predation of hooked fish by cuttlefish, moray and conger eels, the duration of the long-line sets was shorter than we would have preferred. This was one of the main reasons for the relatively low catch rates. In this type of long-lining, catch rates of 1 % are typical (pers. obs.). Furthermore, while we fished independently of sea and atmospheric conditions, local artisanal fishermen who use a variety of gears such as gillnets, trammel nets and traps, tend to use long-lines only in specific circumstances (e.g. only after a period of east winds), thereby obtaining higher catch rates than in this study. For most species the size distributions of the catches overlapped considerably, with little or no significant increase in size with overall hook size. This can be seen in the estimated selectivity curves. Small differences in size distributions were apparent only for Diplodus sargus, D. vulgaris, Lithognathus mormyrus and Serranus cabrilla. However, there were significant changes in catch-per-unit-effort, with the largest hook generally being much less efficient. It appears there is a narrow range in terms of effective hook size for the majority of the species in this fishery. This is largely due to the fact that these are mainly small species, which in most cases have maximum reported sizes of less than 45 cm SL (Whitehead et al., 4). Since individuals at the upper end of the size range are rare, the most common sizes are considerably less than the reported maximum sizes. Furthermore, many of the species caught are smallmouthed invertebrate feeders. Thus very small hooks such as number will catch even the largest individuals. In fact, some of the largest fish caught, including an exceptional Diplodus sargus of 4 cm TL and 2.2 kg, were caught on the smallest hook. In the case of species which do attain a large size such as Pagrus pagrus and Dentex gibbosus, only a few small individuals were caught. Large individuals are caught at greater depths with larger hooks and different baits than those used in this study. Previous studies of hook selectivity have used a wide range of sizes and types of hooks and have come to different conclusions. Clear and unambiguous size selectivity was demonstrated for the yellowfin tuna (Thunnus albacares) by Cortez-Zaragoza et al. () using a series of hook sizes with gapes ranging from 1.2 to 2. cm. Otway and Craig (1) used sizes of Mustad tuna hooks to evaluate selectivity in the sea bream Pagrus auratus. With overall hook size differences of only 2.5 and 5% they found that the smallest hook caught more illegally sized fish (<25 cm FL) while the largest hook caught relatively more bigger fish. All three hooks Downloaded from on 22 April 8

7 Species and size selectivity in a long-line fishery 817 Table 2. Parameters of the skew-normal probability density for seven species. H is the overall hook size (maximum width maximum length). Species Optimal length S.D. Skewness Weighted MSE d.f. Serranus cabrilla H 2.. H..8 H.5 2 Diplodus sargus H+.1 H H H Diplodus vulgaris.7+.1 H. H 2..2 H H.22 Boops boops H H H Spondyliosoma cantharus H H H Lithognathus mormyrus H H H Trachinus draco H H H caught fish ranging in size from less than 2 cm to more than cm, and efficiency decreased with increasing hook size. In other cases selectivity has only been demonstrated using hooks differing in overall size by more than 2%, with characteristically highly overlapped catch distributions. This is particularly true for small species with a relatively narrow size range such as spiny goby (Acanthogobius flavimanus) (Koike et al., ; Takeuchi and Koike, 1), pond smelt (Hypomesus olidus) (Koike and Kanda, 178), and chub mackerel (Scomber japonicus) (Kanda et al., 178). In general, these studies have shown that efficiency decreases with increasing hook size and all hook sizes catch a similar range of sizes. Some studies have concluded that there was no difference in selectivity (Ralston, 2; Bertrand, 8). In these two studies the largest hooks were 72% and % bigger than the smallest. Otway and Craig (1) suggested that the observed lack of selectivity differences in the latter study was due to the confounding effect of non-uniform bait sizes. Selectivity 1. (a) (b) (c) (d) (e) (f) Total length (cm) Figure 8. Estimated standardized selectivity curves for hook numbers ( ), 1 ( ), and 11 ( ) for: (a) Boops boops, (b) Diplodus vulgaris, (c) D. sargus, (d) Serranus cabrilla, (e) Spondyliosoma cantharus, and (f) Trachinus draco. 4 We believe that lack of strong evidence for differences in size selectivity may be a consequence of the size structure of the population. Thus, the apparent lack of a difference in size selectivity for some species in our study may be largely due to a small range in size of the individuals in the study area. For example, although the greater weever fish is known to reach 4 cm SL (Whitehead et al., 4), in our experience this size is not attained locally. Likewise, black sea bream (Spondyliosoma cantharus) can grow to cm SL (Whitehead et al., 4) but the largest individual found in a year of sampling of landings in the fishing ports of the south and south-west of Portugal was 8 cm TL, with 5% of the fish landed between and cm TL (Canário et al., 14). Given such limited size distributions, it is not surprising that little or no difference in selectivity were observed for some species. The reduced size range may be due to high fishing mortality in this area, primarily by inshore purse seiners and gillnetters. Unlike gillnets and bag-type gear such as trawls and seines, there is no clear consensus on the form of the selectivity curve for hooks on long-lines. Both logistic type models, typically used to describe the selectivity of trawls, and the normal distribution used in gillnet selectivity studies have been proposed or used in hook selectivity studies (Clark, 1; Brock, 12; ICNAF, 1; Koike et al., ; Takeuchi and Koike, 1; Pope et al., 175; Kanda et al., 178; Koike and Kanda, 178; Ralston, 2, 1; Pavez and Oyarzún, 5; Cortez-Zaragoza et al., ). Since Ralston plots (Ralston, 1) were mostly inconclusive for the six species studied here, and given the characteristics of the observed catch distributions by hook size, we agree with other authors who have concluded that neither logistic or bell-shaped curves are entirely appropriate (Ralston, 1; Otway and Craig, 1). As reported by Leclerc and Power () who fished populations with known size structure, a flatter dome-shaped curve is more realistic than the normal curve. For small species such as the ones in this study, the hooks and bait used are capable of attracting and hooking all sizes above a certain minimum. However, as Downloaded from on 22 April 8

8 8 K. Erzini et al. we often observed, large fish were often lost close to the boat either because the hook straightened or came loose if the fish was lightly lip-hooked. Thus, a decrease in selectivity at larger sizes is to be expected. As a compromise a skew-normal selectivity model was used in this study. The Helser et al. (11) method is very flexible, allowing optimal length, the standard deviation and the skewness coefficient to be linear or polynomial functions of a measure of hook size. Other authors have also suggested that selectivity models allowing variations of parameters with mesh or hook size are more realistic (Wulff, ; Saila and Erzini, ). The non-linear fitting procedure proposed by Helser et al. (11) is considered superior to others since an overall response surface is fit to obtain selectivities as a function of both hook size and size of fish. The efficiency and species and size selectivity of longline gear are influenced by a number of factors. These include fish distribution, competition between fish, hook size, hook design, gangion length, gangion accessories such as floats and swivels, gangion diameter, colour and type (monofilament or braided), mainline diameter, colour and material, bait type, bait size, bait shape, bait combinations, time of fishing, and duration of soak (Takeuchi and Koike, 1; Forster, 17; Arimoto et al., 2; Anon., ; Bjordal, a,b,c, 4, 7a,b, ; Skeide et al., ; Løkkeborg, ; Løkkeborg and Bjordal, 12). In this initial study we focused on hook size because of the implications for management. Ongoing studies will focus on size selectivity for deeper water red sea breams as well as factors and combinations of factors such as hook design, hook size, bait type and bait size, which may affect size selectivity and catch rates. Acknowledgements Funding for this study was provided in part by EC DG XIV grant BIOECO//4 to K. Erzini and JNICT Programa PRAXIS XXI grant BD-8/4 to J. M. S. Gonçalves. We would like to thank Mr Francisco Matasete Soares and his sons Zé Maria and Vasco for the fishing and the many colleagues who helped with the sampling and biological studies, especially Paulo Vilia, Joaquim Ribeiro, Paulo Souto and Pedro Monteiro. We would also like to thank Dr Å. Bjordal and an anonymous referee for their suggestions which greatly improved the manuscript. References Anon.. Circle hooks outfish traditional halibut hooks. Marine Fisheries Review, 45: 1. Arimoto, T., Ogura, M., and Inoue, Y. 2. Catch variation with immersion time of gear in coastal set-line. Bulletin of the Japanese Society of Scientific Fisheries, 4: Bertrand, J. 8. Selectivity of hooks in the handline fishery of the Saya de Malha Banks (Indian Ocean). Fisheries Research, : 255. Bjordal, Å. a. Effect of different long-line baits (mackerel, squid) on catch rates and selectivity for tusk and ling. ICES CM /B:1. Bjordal, Å. b. Longline: full scale trials with new hook designs and reduced size of bait. ICES CM /B:2. Bjordal, Å. c. Long-line fishery of the future: mechanization, synthetic bait, and new hook types. Canadian Translation Fisheries and Aquatic Sciences, No Bjordal, Å. 4. The effect of gangion floats on bait-loss and catch rates in longlining. ICES CM 4/B:8. Bjordal, Å. 7a. Swivel connected gangions in mechanized longlining effect on catch rates and operation. ICES CM 7/B:. Bjordal, Å. 7b. Testing of a new hook design in the longline fishery for tusk (Brosme brosme) and ling (Molva molva). ICES CM 7/B:2. Bjordal, Å.. Longline gear catching performance, selectivity and conservation aspects. World Fishing (February) 4 8. Brock, V. E. 12. On the nature of the selective fishing action of longline gear. Pacific Science, 1: 14. Canário, A. V. M., Erzini, K., Castro, M., Gonçalves, J. M. S., Galhardo, C., Ribeiro, J., Bentes, L., Cruz, J., and Souto, P. 14. Estudos base para a conservação dos ictiopovoamentos e gestão da pesca costeira no litoral sudoeste. UCTRA, Universidade do Algarve e SNPRCN-APPSACV. Relatório Final. pp.+appendices. Clark, J. R. 1. Report on selectivity of fishing gear. In Fishing effort, the effect of fishing on resources and the selectivity of fishing gear. ICNAF Special Publication, 2: 27. Cortez-Zaragoza, E., Dalzell, P., and Pauly, P.. Hook selectivity of yellowfin tuna (Thunnus albacares) caught off Darigayos Cove, La Union, Phillipines. Journal of Applied Ichthyology, 5: 17. Forster, G. R. 17. Line fishing on the continental slope: the selective effect of different hook patterns. Journal of the Marine Biological Association of the U.K., 5: G.E.P.P. 12. Embarcações de pesca: frota nacional Junho de 11. Gabinete de Estudos e Planeamento das Pescas, Direcção Geral das Pescas. 28 pp. Helser, T. E., Condrey, R. E., and Geaghan, J. P. 11. A new method of estimating gillnet selectivity, with an example for spotted seatrout, Cynocion nebulosus. Canadian Journal of Fisheries and Aquatic Sciences, 48: ICNAF, 1. The selectivity of fishing gear. Spec. Publ. No. 5. Int. Comm. Northwest Atl. Fish., Dartmouth, N.S., Canada. 225 pp. Kanda, K., Koike, A., Takeuchi, S., and Ogura, M Selectivity of the hook of mackerel, Scomber japonicus Journal of the Tokyo University of Fisheries, 4: Kenchington, T. J. 1. Estimation of the functional form of selectivity by baited hooks: a graphical approach. Canadian Journal of Fisheries and Aquatic Sciences, 5: Koike, A. and Kanda, K Selectivity of the hook of pond smelt, Hypomesus olidus. Journal of the Tokyo University of Fisheries, 55: Koike, A., Takeuchi, S., Ogura, M., Kanda, K., and Arihara, C.. Selection curve of the hook of long line. Journal of the Tokyo University of Fisheries, 4: 1. Leclerc, J. and Power, G.. Selectivity of fly fishing, spinning and gillnet for brook charr and ouaniche in a large northern Quebec river. Environmental Biology of Fisheries, 5: 1 4. Downloaded from on 22 April 8

9 Species and size selectivity in a long-line fishery 81 Løkkeborg, S.. Longline bait: fish behaviour and the influence of attractant release rate and bait appearance. Dr. Scient. Thesis, Univ. Bergen, Norway. Løkkeborg, S. and Bjordal, Å. 12. Species and size selectivity in longline fishing: a review. Fisheries Research, 1: Martins, R., Santos, M. N., Monteiro, C. C., and Paes da Franca, M. de L. 12. Contribuição para o estudo da selectividade das redes de emalhar de um pano fundeadas na costa Portuguesa no biénio INIP, Relatórios Técnicos e Científicos, No pp. Otway, N. M. and Craig, J. R. 1. Effects of hook size on the catches of undersized snapper Pagrus auratus. Marine Ecology Progren Series, :. Pavez, P. C. and Oyarzún, M. E. F. 5. Determinación de eficiencia relativa de espineles y parámetros de crecimiento del bacalao de Juan Fernández (Polyprion oxygeneios Bloch y Schneider, 1), en las islas Robinson Crusoe y Santa Clara. In Investigaciones Marinas en el Archipiélago de Juan Fernández, pp Ed. by P. Arana. Escuela de Ciencias de Mar, UCV, Valparaíso. Pope, J. A., Margetts, A. R., Hamley, J. M., and Aykuz, E. F Manual of methods for fish stock assessment. Part III. Selectivity of fishing gear. FAO Fish. Tech. Pap. No. 41 (Rev. 1). 4 pp. Ralston, S. 2. Influence of hook size in the Hawaiian deep-sea handline fishery. Canadian Journal of Fisheries and Aquatic Sciences, : Ralston, S. 1. Size selectivity of snappers (Lutjanidae) by hook and line gear. Canadian Journal of Fisheries and Aquatic Sciences, 47: 7. Saila, S. B. and Erzini, K.. An improved method of fitting gillnet selectivity curves to predetermined distributions. Fish. Stock Assess. CRSP Working Paper No pp. SAS Institute. 8. SAS/STAT User s Guide, Release. Edition. SAS Institute, Cary, NC. 128 pp. Skeide, R., Bjordal, Å., and Løkkeborg, S.. Testing of a new hook design (E-Z-Baiter) through comparative longline fishing trials. ICES CM /B:25. Takeuchi, S. and Koike, A. 1. The effect of size and shape of hook on the catching efficiency and selection curve of long-line. Journal of the Tokyo University of Fisheries, 55: Whitehead, P. J. P., Bauchot, M. L., Hureau, J. C., Nielsen, J., and Tortonese, E. 4. Fishes of the North-Eastern Atlantic and the Mediterranean. Vols I III, UNESCO. Wulff, A.. Mathematical model for selectivity of gill nets. Archiv für Fischereiwissenschaft, 7: Downloaded from on 22 April 8