«TRAMMEL NET SELECTIVITY STUDIES IN THE ALGARVE (SOUTHERN PORTUGAL), GULF OF CADIZ (SPAIN), BASQUE COUNTRY (SPAIN) AND CYCLADES ISLANDS (GREECE) REF. ...»
COMMISSION OF THE EUROPEAN COMMUNITIES
TRAMMEL NET SELECTIVITY STUDIES IN THE
ALGARVE (SOUTHERN PORTUGAL), GULF OF
CADIZ (SPAIN), BASQUE COUNTRY (SPAIN)
AND CYCLADES ISLANDS (GREECE)
REF. NO. 98/014
COMMISSION OF THE EUROPEAN COMMUNITIESDG XIV/C/1
TRAMMEL NET SELECTIVITY STUDIES IN THE ALGARVE
(SOUTHERN PORTUGAL), GULF OF CADIZ (SPAIN), BASQUE
COUNTRY (SPAIN) AND CYCLADES ISLANDS (GREECE)Ref. 98/014 FINAL REPORT – October 2001 Karim ERZINI 1
SCIENTIFIC COORDINATOR:Karim ERZINI 1
PORTUGUESE COORDINATOR:Kostas I. STERGIOU 2
GREEK COORDINATOR:Esteban PUENTE 3
SPANISH (BASQUE COUNTRY) COORDINATOR:José A. HERNANDO 4
SPANISH (GULF OF CÁDIZ) COORDINATOR:
Jesús ARAGONÉS 4, Luís BENTES 1, Ramón BRAVO 4, Rui COELHO 1, Carla CORREIA 1, Luis A. ERRAZKIN3, Jorge M.S. GONÇALVES 1, Paraskevi KARACHLE2, Vaso S. KARPUZI2, Menelaos KOULOURIS2, Pedro G. LINO 1, Pedro MONTEIRO 1, D. K. MOUTOPOULOS2, Joaquim RIBEIRO 1, Milagrosa C.
SORIGUER 4, César VILAS 4, Noelia VILLAR 4, Cristina ZABALA 4 * Names in alphabetical order 1 Centro de Ciências do Mar, Universidade do Algarve 2 Laboratory of Ichthyology, Aristotle University 3 AZTI (Instituto Tecnológico Pesquero y Alimentário) 4 Departamento de Biologia, Facultad de Ciencias del Mar, Universidad de Cádiz This study does not necessarily reflect the views of the European Commission and in no way anticipates any future opinion of the Commission.
Permission to copy, or reproduce the contents of this report is granted subject to citation of the source of this material.
This study has been carried out with the financial assistance of the European Commission.
SUMMARY FOR NON SPECIALISTS
1.1. Artisanal / small scale fisheries in the Basque country
1.2. Artisanal / small scale fisheries in the Algarve
1.3. Artisanal / small scale fisheries in the Gulf of Cádiz
1.4. Artisanal / small scale fisheries in the Cyclades
1.5. Static gearstudies in the Cantabrian Region
1.6. Static gear studies in the Algarve
1.7. Static gear studies in the Gulf of Cádiz
1.8. Static gear studies in the Cyclades
2. MATERIAL AND METHODS
2.1. Survey and characterization of trammel net métiers
2.1.1. Basque Country
2.1.3. Gulf of Cádiz
2.2. Experimental fishing and sampling
2.2.1. Basque Country
2.2.3. Gulf of Cádiz
2.3. Size selectivity
2.4. Diversity, dominance and multivariate analyses
2.5. Other analyses
3.1. Survey and characterization of trammel net métiers
3.1.1. Basque Country
3.1.3. Gulf of Cádiz
3.2. Species composition, catch rates and diversity
3.2.1. Overall and seasonal changes
188.8.131.52. Basque Country
184.108.40.206. Gulf of Cádiz
3.2.2. Depth related changes
220.127.116.11. Basque Country
18.104.22.168. Gulf of Cádiz
3.2.3. Discards and discarding practices
22.214.171.124. Basque Country
126.96.36.199. Gulf of Cádiz
3.3.1. Basque Country
188.8.131.52. Catch size frequency distributions
184.108.40.206. Size selectivity
220.127.116.11. Catch size frequency distributions
18.104.22.168. Size selectivity
3.3.3. Gulf of Cádiz
22.214.171.124. Catch size frequency distributions
126.96.36.199. Size selectivity
188.8.131.52. Catch size frequency distributions
184.108.40.206. Size selectivity
3.4. Method of capture
3.4.1. Basque Country
3.4.3. Gulf of Cádiz
3.5. Multivariate analyses
3.5.1. Basque Country
3.5.3. Gulf of Cádiz
3.5.5. Between- area comparisons
3.6. Length-girth relationships in Cyclades
ANNEX I ANNEX II ABSTRACT Trammel net fisheries were studied in four areas: the Cantabrian Sea (Basque Country, Spain), the Algarve (Southern Portugal), the Gulf of Cádiz (Spain) and the Cyclades Islands (Greece). Surveys were carried out in order to identify trammel net métiers and to characterise the gear used. Trammel nets were among the most important gears used in the small-scale fisheries, with up to 9 different métiers identified in each area. The most important métiers in the Algarve and the Gulf of Cádiz were those for cuttlefish (Sepia officinalis) and soles (Solea senegalensis, Microchirus azevia, Synaptura lusitanica). In the Cantabrian Sea, sole (Solea vulgaris), shellfish (several species) and scorpion fish (Scorpaena spp.) métiers dominated while a variety of species where targeted in the multi-species trammel net fishery in the Cyclades.
In each area, experimental trammel nets of six different types (combinations of 2 large mesh outer panel sizes and 3 small mesh outer panels) corresponding to the most common métier, were constructed and fishing trials carried out on a seasonal basis (4 seasons in the Cantabrian Sea, Algarve and Cyclades and 2 in the Gulf of Cádiz) using chartered commercial fishing vessels. Overall, 271, 360, 185 and 185 km of trammel nets were fished in the experimental fishing trials in the Cantabrian Sea, Algarve, Gulf of Cádiz and Cyclades Islands respectively.
The trammel nets caught a large number of species: 79, 128, 63 and 79 in the Cantabrian Sea, the Algarve, the Gulf of Cádiz and the Cyclades Islands respectively. In the Cantabrian Sea trials Solea vulgaris (19%), Trisopterus luscus (12%), Scomber scombrus (9%) and Trachinus draco (8%) dominated the catches. In the Algarve, Scomber japonicus (21%), Sepia officinalis (17%), Microchirus azevia (12%) and Trachinus draco (6%) were the most important species in the trammel net catches. Sepia officinalis (43%), Solea senegalensis (8%), Sardina pilchardus (7%) and Torpedo torpedo (7%) accounted for most of the catch in the Gulf of Cádiz. In the Cyclades Islands, Mullus surmuletus (15%), Pagellus erythrinus (14%), Diplodus annularis (10%) and Scorpaena porcus (9%) were the four numerically most important species. Totals of 17041 (Cantabrian Sea), 16574 (Algarve), 8178 (Gulf of Cádiz) and 9619 (Cyclades Islands) individual fish, crustaceans and cephalopods were caught.
The multivariate analysis (cluster analysis and MDS) showed that there were significant differences in the species composition and relative abundance of the most important species between the seasons, especially in the cases of the Cantabrian Sea and the Algarve fisheries. Catch rates (numbers per 1000 m of trammel net) also showed depth related patterns for most of the dominant species. In general, catch rates increased with decreasing inner panel mesh sizes, whereas the mesh size of the outer panel had no significant effect.
Significant numbers of species and proportions of the catches were discarded in each area. Overall, 65, 105, 46 and 32 species were entirely or partly discarded in the Cantabrian Sea, Algarve, Gulf of Cádiz and Cyclades Islands respectively. The overall discard rate in terms of catch in numbers ranged from 15% for the Cyclades to 49% for the Algarve, with the high discard rate for the latter due largely to Scomber japonicus. The main reasons for discarding were as follows: 1) species of no or low commercial value (e.g. Scomber japonicus, Torpedo torpedo), 2) commercial species that were damaged or spoiled (e.g.
Merluccius merluccius), 3) undersized commercial species (e.g. Lophius piscatorius ) and 4) species of commercial value but not caught in sufficient quantities to warrant sale (e.g.
i Sardina pilchardus). The number of discarded species and discard rates generally decreased with increasing inner panel mesh size.
Trammel nets generally caught a wide size range of the most important species, with distributions that were skewed to the right and/or bimodal. In many cases the catch frequency distributions of the different nets were highly overlapped, indicating little or no size selectivity. In general, the Kolmogorov-Smirnov test showed that the large mesh outer panels had no effect in terms of size selectivity, while the opposite was true for the small mesh inner panels.
Of the three methods of capture recorded, entangling was by far the most important, with combinations of entangling and wedging and entangling and gilling accounted for the greater part of the catches of all the species in the four different areas.
Six different selectivity models (normal scale, normal location, Gamma, log-normal, bi-modal and Gamma-Wileman) were fitted to data for the most abundant species in the four areas using the GillNet software (Constat, 1998). In general, the bi-modal model provided the best fits for a wide range of species, with the uni-modal models giving poor fits in most cases.
For some species, in particular Sepia officinalis, where entangling was the method of capture in 100% of the cases, none of the GillNet models fitted the data, whereas the logistic model fitted by maximum likelihood (Wulff, 1986) adequately described the selective properties of the trammel nets.
Key words: trammel nets, catch rates, discards, size selectivity, Cantabrian Sea, Algarve, Gulf of Cádiz, Cyclades Islands
Trammel nets are fixed gear, generally fished on the bottom, that are composed of a small mesh inner panel and two large mesh outer panels. The netting material can be of several types, with monofilament and multifilament trammel being the most widely used. The netting panels are hung loosely and the objective to catch fish, cephalopods and crustaceans primarily by entangling in the pocket formed when a fish/cephalopod/crustacean forces the small mesh inner panel through one of the meshes of the outer panel.
Trammel nets are widely used throughout the world, particularly in small-scale fisheries. Unlike gillnets, few studies have been carried out on trammel nets and little is known of their size-selective properties. The objectives of this study were the following: 1) to identify and characterise the main trammel net metiers in the Cantabrian Sea (Basque Country, Spain), the Algarve (southern Portugal), the Gulf of Cádiz (Spain) and the Cyclades Islands (Greece), 2) to construct experimental trammel nets based on the most important métier in each area and to carry out fishing trials with these nets, 3) to quantify species composition, catch rates, discard rates and method of capture on a seasonal and a depth basis, and 4) to estimate the size selectivity parameters for the most important species.
Questionnaire surveys were carried out in each of the four areas. These allowed us to identify up to 9 different métiers in each area and to identify the characteristics (material used to construct the nets and method of construction) as well as to obtain information on vessel and crew characteristics, fishing grounds and fishing strategies.
Experimental trammel nets using 3 mesh sizes for the inner panel and 2 mesh sizes for the outer panel were constructed in each area, giving a total of 6 trammel net types for each area. Commercial fishing vessels were chartered for carrying out fishing trials. Members of each team went on board each trip in order to sort the catch according to the six trammel net types and to record information on fishing grounds, depth, number of fleets, times of setting and hauling, method of capture and discarding practices. All organisms that were caught were identified, measured and weighed. At least 40 fishing trials were carried out in each area, over all four seasons in the case of the Cantabrian Sea, the Algarve and the Cyclades Islands. In the case of the Gulf of Cádiz, fishing took place in only two seasons because of the seasonal nature of the trammel net fishery.
A total of 271, 360, 185 and 185 km of trammel nets were fished in the Cantabrian Sea, the Algarve, the Gulf of Cádiz and the Cyclades Islands respectively. Species diversity was very high, with 79, 128, 63 and 79 different species caught in the Cantabrian Sea, the Algarve, the Gulf of Cádiz and the Cyclades Islands. Overall, 17041, 16574, 8178 and 9619 fish/crustanceans/cephalopods were caught in the four areas, with the great majority of the catch consisting of fish.
Relatively few species dominated the catches in numbers in all four areas. In the Cantabrian Sea trials Solea vulgaris (19%), Trisopterus luscus (12%), Scomber scombrus (9%) and Trachinus draco (8%) dominated the catches. In the Algarve, Scomber japonicus (21%), Sepia officinalis (17%), Microchirus azevia (12%) and Trachinus draco (6%) were the most important species in the trammel net catches. Sepia officinalis (43%), Solea senegalensis (8%), Sardina pilchardus (7%) and Torpedo torpedo (7%) accounted for most of the catch in the Gulf of Cádiz. In the Cyclades Islands, Mullus surmuletus (15%), Pagellus erythrinus iii (14%), Diplodus annularis (10%) and Scoraena porcus (9%) were the four numerically most important species.