a dedicated gis to estimate and map fishing effort and ... et al - gis to map fishing effort and...

GIS/Spatial Analyses in Fishery and Aquatic Sciences Afonso-Dias et al - GIS to map fishing effort and landings for the Portuguese trawl fleet (323-340) © Fishery and Aquatic GIS Research Group, 2004

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A dedicated GIS to estimate and map fishing effort and landings for the Portuguese crustacean trawl fleet

Manuel Afonso-Dias Faculdade de Ciências do Mar e do Ambiente (FCMA), Universidade do Algarve, Campus de Gambelas 8005-139, Faro Portugal Phone: 351(Portugal)-289-800929 Fax: 351(Portugal)-289-818353 E-mail: [email protected]

Joana Simões Center for Advanced Spatial Analysis (CASA), University College of London 1-19 Torrington Place, Gower Street London, WC1E 7HB, U.K.

Carlos Pinto Faculdade de Ciências do Mar e do Ambiente (FCMA), Universidade do Algarve, Campus de Gambelas 8005-139, Faro Portugal

Abstract A dedicated Geographical Information System (GIS), the GeoCrust 1.0, was developed to store, analyse and display Vessel Monitoring System (VMS) and landings data of the south-southwest Portuguese Crustacean trawl fleet. With this system, Global Positioning System (GPS) and vessel speed data transmitted via satellite by the Portuguese VMS (MONICAP) were used, for the first time, to estimate and map fishing effort and landings per unit effort (LPUE) for this fishery. This application, described in this paper, was developed in Visual Basic 6.0 using two ActiveX control: ADODB, to connect with the MsAccess 2000 database (DB) and MapObjects 2.0 Pro, to communicate with the maps and provide GIS facilities. The developed application comprises seven modules with the following objectives: Module 1- to map and edit the original VMS data for

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a single vessel or group of vessels, for different periods of time; Module 2- to analyse the trawl speed of each vessel; Module 3- to define the boundaries of all fishing trips performed by vessel throughout the year; Module 4- to identify and define the trawl hauls within each fishing trip; Module 5- to issue maps of fishing effort and LPUE; Module 6- for exploratory data analysis and to extract data from the DB for use in other computer packages, and Module 7- to recreate the activity of a single vessel, group of vessels or the total fleet, for a fixed period of time. This GIS application, fully developed by programming, has the advantage of being able to be used on its own without any need of external software support. It can be used from now on to analyse VMS and landings data for the Portuguese Crustacean Fishery on a routine basis. Key words crustacean, fisheries, fishing effort, GIS, Global Positioning System (GPS), trawl, Vessel Monitoring System (VMS).

1. Introduction The Portuguese crustacean trawl fleet operates with 55 mm codend mesh size nets mainly off the southwest (Alentejo) and south (Algarve) coasts of Portugal, between depths of 200 and 750 metres (ICES, 2001) (Map 1). The area supports an important multi-specific crustacean fishery (around 5500 tonnes in 1999) targeting three commercially important species, the Norway lobster (Nephrops norvegicus, NEP), the blue and red shrimp (Aristeus antennatus, ARA) and the deep water rose shrimp (Parapenaeus longirostris, DPS). During 1998 and 1999, only 25 out of 34 licensed trawlers operated monthly. Four of these operating vessels were freezer trawlers.

Although the crustacean trawlers land in many fishing ports along the southwest coast (from Lisbon to Vila Real de Santo António (VRSA), see Map 1), almost all the landings are transported in refrigerated vehicles from the landing port to the fish market in VRSA. Freezer trawlers sell their catches directly to fishmongers. The relative importance of the VRSA fish market is due to its geographic location, near Spain.

In this fishery each vessel reports landings by species and by fishing trip. Fishing trips extend from one to several days particularly in the case of the freezer trawlers. However, no information on the fishing location is recorded. The landing figures for each trawler are recorded by DOCAPESCA, the company which runs the fish markets in Portugal, and

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then sent to DGPA, the Portuguese Directorate-General of Fisheries. Information on geographical location is only available from logbooks in which they are referred to ICES (International Council for the Exploration of the Seas) statistical squares (0.5º latitude and 1º longitude or 30 x 30 miles squares), which cover very large areas. Therefore, these statistical squares are not suitable for providing the exact location of fishing activities. The number of fishing operations (trawl hauls) and their durations are also reported in the logbooks, along with catch data for each fishing trip, but this information is considered not reliable by the Portuguese fisheries researchers.

Map 1. Map of the south-southwest coasts of Portugal showing the fishing area where the

Portuguese crustacean trawlers operated. Three Regions were considered in the study-area: Lisbon, Alentejo and Algarve. The depth strata are represented by a colour gradient, from 0-50m up to 1000-1100m. The triangles mark the main fishing ports visited by the crustacean trawlers (CAS – Cascais, LIS – Lisbon, SES – Sesimbra, SIN – Sines, SAG – Sagres, POR – Portimão, OLH – Olhão, TAV – Tavira and VRSA – Vila Real de Santo António), except Faro that is the capital city of Algarve.

The Portuguese crustacean trawlers are, however, controlled by MONICAP, the Portuguese Vessel Monitoring System (VMS). This system, created in 1987, was the first to be implemented in Europe (Vasconcelos, 2000) and it is fully operational. The GPS (Global Positioning System) positions of each vessel under VMS control are


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recorded every 10 minutes. These data are transmitted via satellite (every eight hours of data recorded) to Inspecção Geral das Pescas (IGP), the Portuguese monitoring authority responsible for marine surveillance. Since GPS data is geo-referenced with respect to longitude and latitude it is ideal for spatial analyses.

Until now, MONICAP data has been used, exclusively, by IGP

for fisheries control and marine surveillance, in particular to check whether trawlers are operating outside the six nautical miles line off the coast as required by law. However, the usefulness of MONICAP data for fisheries research purposes is obvious. The full analyses of data provided by this system makes it possible to measure and map the fishing effort either for a particular trawler, a selected number of trawlers or for the whole fleet within a time series (e.g. by month, quarter, semester or year). The cross analysis of landings (since real catches are not known) with fishing effort allows species landings to be mapped. As a consequence, landings per unit effort (LPUE) by species can be calculated and mapped.

To do this, a dedicated Geographical Information System (GIS),

the GeoCrust 1.0, was developed within a study conducted by the University of Algarve between 2000 and 2002 (GeoCrust project). In this project, GeoCrust 1.0 was used to analyse VMS and landings data for a two year period (1998 and 1999) (Afonso-Dias et al., 2002).

This paper aims to formally present GeoCrust 1.0 software. The results of the 1998 and 1999 data analysis will be published in a future paper. 2. GIS description GeoCrust 1.0 software is a GIS that stores, analyses, and displays both spatial and non-spatial fisheries data. It was developed to produce, visualize and analyse geo-referenced fishing effort and landings per unit effort (LPUE) exclusively for the Portuguese crustacean trawl fishery. GeoCrust 1.0 consists of a relational database (DB) system in which most data are spatially indexed and upon which a set of procedures is operated to answer queries about spatial entities of the database. Data manipulation is made in an oriented-purpose application with a set of menus (in Portuguese) to perform different tasks and a map control with a set of themes (or layers) to display the results.


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2.1 Relational database The DB was created and implemented with Ms Access 2000 to assemble three types of data: landings in weight by species, fishing vessels’ technical characteristics (source: DGPA DB) and MONICAP data for the crustacean trawl fishing fleet (source: IGP). Most of the DGPA tables were maintained in the GeoCrust DB to ensure compatibility between the two databases. The MONICAP data available for this study were GPS positions and speed in 10 minute intervals for each vessel using VMS. The technical characteristics of the active vessels in the study period included data on the overall length, gross registered tonnage, engine power, hull type and age. For most vessels landings by species correspond to vessel individual sales in the fish markets. For freezer trawlers, landings correspond to daily records in logbooks. Only data for 1998 and 1999 were included in the DB to be used in the GeoCrust project (Afonso-Dias et al., 2002).

The creation of the GIS DB was a complex operation involving data capture, verification and structuring processes. The quality assessment of MONICAP data was difficult due to errors and missing data. The data to be introduced in the DB had to be submitted to a series of procedures, including the conversion to intermediate database structures, error checking, data validation and integrity. Only after going through these procedures was the structure design of the final database created and the relational integrity among tables checked. A substantial part of MONICAP data correction would not have been possible without a spatial platform, i.e., without the implementation of the GIS. The GIS implementation allowed the visual inspection of MONICAP data, making it easier for the user to detect and correct the errors. 2.2 Geo-referenced digital charts A digital chart for the Southwest and South coasts of Portugal (below 39º North) was prepared (Map 2) by assembling information from the available fishing charts AP5, AP6, AP7 and AP8, published by Instituto Hidrográfico (IH), the Portuguese Hydrographical Institute (map scale: 1:150 000). These charts were geo-referenced and vector converted in order to create the shapefiles correspondent to the following layers of information (themes): Coastline - Polygon theme; Depth contours (50, 100, 150 and 200-1000 meters, step by 100 meters) - Polygon theme; Toponymy - (names of the main cities, including all fishing ports visited by the crustacean trawl fleet) - Point theme; Six miles line off the coast (trawling is only allowed beyond this line) - Line theme; and the Sea bed sediments information available in the IH charts - Polygon theme.


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The original map data (digital charts of sea-bed sediments, depth contours, coast line and ports) were geo-referenced in Hayford Gauss Datum 73 projection. This projection is associated to Datum 73 geographic coordinate system. In this system the geographic coordinates origin is located in Melriça. Datum 73 is based on astronomic observations from 1964 and uses Hayford spheroid. The satellite constellation NAVSTAR/GPS uses World Geodetic System 84 (WGS84) spheroid to assure a global and geocentric position. It is defined by a set of reference stations spread all over the world. To overlay the charts with MONICAP information (not projected data, in WGS84) the maps were converted to WGS84 geographic coordinate system (with map and distance units in decimal degrees). However, to allow area and distance calculations in plane units, data were converted back to Hayford Gauss Datum73, but only for this purpose. This conversion was done by using the EsriSRProjCS_Datum73HayfordGaussIPCC’ method. The map units used during these calculations were meters but they were later converted to nautical miles.

Map 2. GeoCrust 1.0 software: digital and geo-referenced chart (originally

displayed in colour). All layers of information are shown. The depth contours are shown with different shades of blue; the black dashed line represents the six mile line off the coast; the sea bed sediments are marked with different colours depending on the nature of the sediment; the different landing places are marked with three or four characters.


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2.3 Fishing trip concept, regions and fishing grounds The Concept of Fishing trip was determinant in the development of GeoCrust 1.0 software. A true Fishing trip for a non-freezer trawler is defined as one departure and return to port that produces a single landing (a sale on the fishing market). In the case of the four freezer trawlers, the concept of Fishing trip is slightly different. The time spent off the harbour is considered as a Fishing trip and the landing of a Fishing trip corresponds to the sum of daily records from the logbooks.

Three large geographical areas, hereafter referred to as

Regions, were considered a priori: Lisbon, Alentejo and Algarve (Map 1), the last two corresponding to ICES Nephrops Functional Units 28 and 29, respectively. Within these three Regions, nine Fishing grounds were defined, which correspond to discrete areas where fishing activities were conducted. The boundaries of each Fishing ground were defined a posteriori, within ESRI ArcGIS software after defining and mapping the geographical distribution of the trawl hauls performed in 1998 and 1999 using GeoCrust 1.0.

2.4 GeoCrust 1.0: description and development Specific computer applications were developed in Visual Basic 6.0 and bundled with two ActiveX controls, the ADODB and Map Objects 2.0 Pro to communicate with the DB and to provide GIS functionalities respectively. This methodological option gave total freedom to create computer applications focused on the specific objectives of the study. Once finished, these applications had the advantage of being able to be used on its own without any need for external software support.

The software developed contains seven modules: Module 1. ‘Preliminary Analysis’. This application was designed to assess the quality of MONICAP data (GPS and vessel speed). This module allows the visual inspection of the spatial distribution of each vessel activity (for different time units) and to correct errors (Figure 1). This analysis can be made for one or more selected quarters, groups of pre-defined fishing trips or just for a single one. The templates display automatically the distribution pattern of each vessel activity by quarter, making it easier to obtain visual information about each group of preliminary fishing trips (Figure 2). These preliminary fishing trips, only used in this module, are defined ad-hoc between two consecutive landings. For convenience, the cut-off was set at 6 a.m., since landings in VRSA, generally occurs by 6 a.m. True fishing trips are defined in Module 3.


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Figure 1. GeoCrust 1.0 software – Module 1 (Preliminary Analysis): screen display showing

the spatial distribution of a particular vessel trip performed in January 1999 off Faro. Several different tools (icons) were available to perform the preliminary analysis of the Portuguese Vessel Monitoring System (MONICAP) data. (Originally displayed in colour).

Figure 2. GeoCrust 1.0 – Module 1 (Preliminary Analysis): template showing the distribution pattern of one particular crustacean trawler’s activity (trawling and navigation data), by quarter, during 1999. (Originally displayed in colour).


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As recognized during the preparation of the 1998-99 database, MONICAP data had a large number of errors (e.g. different locations for the same vessel in a particular date and time, inconsistent location within a set of locations (track) and locations in the mainland) that needed correction. GIS facilities, within this Module, allow the detection and correction of MONICAP errors. This application allows the detection of outliers and duplication (the same or different locations at the same time) and makes it possible to correct and properly modify these records.

Module 2. ‘Trawl Speed Analysis’. This application was created to analyse the vessel speed frequency distribution for either one or more vessels for a given period of time. Differences in the trawling speed of one (in different periods of time) or many vessels are easily detected (Figure 3). The crustacean vessels’ trawling speed was set to be around three knots (nautical miles per hour), according to the information provided by some of the skippers of these vessels. However, in the field, that is not always the case. The trawling speed varied considerably between vessels.

Figure 3. GeoCrust 1.0 – Module 2 (Trawl Speed Analysis): speed frequency

distributions of five selected crustacean trawlers, in the period 1998-99. Two overall modes are shown in these distributions: the first mode corresponds to towing operations; the second mode corresponds to travelling speed. The peak of the first mode corresponds to the average towing speed. (Originally displayed in colour).

Module 3. ‘Fishing Trips Definition’. This application was created

as a tool to identify and define the limits (beginning and end) of each Fishing trip from a selected vessel. A map with the vessel track is plotted


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along with a graph of the vessel speed, for a selected number of days (Figure 4). This way the user is able to easily recognize the hauls (performed at lower and constant speed) and visualize the two most important variables used to define the limits of one Fishing trip: the speed near zero and the distance from the landing port. In some cases, the speed records given by the vessel GPS are wrong but the 10 minutes geographical positions are correct. In these cases, the average speed (in nautical miles per hour) between two consecutive positions is calculated by multiplying the distance between these two locations by 6 (=1/(10/60)).

A group of options was created with GIS tools (e.g. zoom) to analyse data in detail. The limits of one Fishing trip can be defined either by using an automatic or a semi-automatic procedure, depending on the quality of the data. A buffer around each fishing port, i.e. a circle with a fixed radius of 0.1 degree WGS84 (see Figure 4), was considered to set the beginning and the end of each Fishing trip, which results, by definition, in a sale. A manual procedure can be used to select the right landing record when sales do not take place in the morning (sales in the fish market are supposed to commence at 6 a.m.). In the case of freezer trawlers, the beginning and end of a Fishing trip coincides with the departure from and return to the fishing port.

Information regarding the beginning, the end, and the quality of each Fishing trip is recorded in the database. Fishing trips are considered to be valid or partially valid, depending on the information that is extracted from it. A Fishing trip is classified partially valid when it is possible to determine its limits but not the limits for all trawl hauls. The information extracted and inserted in the DB includes date, time (beginning and end of the trip) and the classification of each defined Fishing trip. The length (in nautical miles) and duration (in days) of each Fishing trip are calculated and inserted in the DB by running a routine procedure.

Module 4. ‘Trawl Hauls Definition’. This module was created to define individual hauls within each Fishing trip. The definition of trawl haul limits through vessel speed analysis is more complex than the definition of Fishing trips limits. Consequently, it was not possible to develop an entirely automatic algorithm, as in the previous module. Therefore, a semi-automatic procedure was implemented to define the limits of each trawl haul (Figure 5). Upper and lower limits of trawling speed are automatically set from the analysis of each vessel monthly speed data (speed values corresponding to cut at the 4% level in the distribution of the speed frequencies)(Figure 3). This information is used to identify the trawl hauls because trawling speed is kept as constant as possible (between the two limits). Therefore, the beginning and end of each haul


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are set based on particular changes in the vessel speed (caused by setting and hauling) detected by the software.

The software developed makes it possible to display many types of information on the screen, namely the distance towed, the swept area (adopting a provisional constant value of 14.5 metres for the trawl opening width), duration, location (geographical areas) and depth of each detected haul. The records are generated and recorded in the DB. A similar procedure was adopted regarding each Fishing trip. For each Fishing trip analysed, it is possible to display the specific composition of the landings (on a table or pie chart format), fishing effort (number of hauls, number of trawling hours or the amount of swept area) and LPUE. The LPUE figures are calculated by dividing landings by the corresponding fishing effort (number of hauls, number of trawling hours or swept area).

Figure 4. GeoCrust 1.0 – Module 3 (Fishing Trip Definition): screen display showing a four day track for a selected vessel. The correspondent speed graph is also shown. The red triangles represent landings (sales in the fish market); the green and yellow triangles represent the beginning and the end of one fishing trip, respectively. The beginning (red cross) of a new fishing trip is being defined (green form). The blue circles, around each fishing port, are buffers used in the definition of the Fishing trips limits.


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Figure 5. GeoCrust 1.0 – Module 4 (Trawl Haul definition): screen display showing

six trawl hauls within a selected fishing trip for a particular vessel (map on the left side and speed graph at the bottom). In the map on the right side only a selected part of the first map is shown. Five hauls were already defined. The beginning of the last haul (red cross in the speed graph and white cross in the map) is being defined.

The length (in nautical miles), duration (in days) and depth range (taken from the digital chart) of each trawl haul are calculated and inserted in the DB by running a routine procedure. The names of the Fishing grounds (once defined) and Regions (Lisbon, Alentejo and Algarve) where each haul took place are also calculated and inserted in the DB using the same procedures. A routine was also included in this module in order to allocate each haul to the Region where it was performed since Fishing grounds boundaries were not known at the beginning of the GeoCrust project. The Fishing ground shapefile was prepared using ESRI ArcGIS software only after identifying the spatial distribution of trawl hauls from the 1998-99 data.

Module 5. ‘Cartography’. This application was developed to map fishing effort and LPUE by crossing landings with fishing effort. In this module, the user can select and extract information for a single vessel or set of vessels (e.g. all vessels with defined trawl hauls), a selected period


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of time, the whole area, a Region (Lisbon, Alentejo and Algarve) or a Fishing ground.

Two types of representation can be used to map the fishing effort. In the first, trawl hauls are defined as lines connecting all 10 minutes records for one haul, within the defined limits. This application allowed the user to overlay information from different queries, using different colours. However, with this type of representation, the differences between hauls for the area under consideration are hardly distinguished (Figure 6). In the second, densities of 10 minutes points corresponding to the defined trawl hauls, in a grid of 5 x 5 nm or 1 x 1 nm (Figure 6), are considered. To speed up the queries two shapefiles with the trawl haul positions (for 1998 and 1999), defined in Module 4 were prepared by using a routine procedure (also incorporated in Geocrust 1.0).

Figure 6. GeoCrust 1.0 – Module 5 (Cartography): screen displays showing (on the left) the spatial distribution of the trawl hauls (lines) conducted in 1999 by all vessels, from Fishing trips and (on the right) the spatial distribution (1 x 1 nautical mile grid of densities) of the trawl hauls conducted by a selected trawler in 1999. The legend key for densities is displayed on the screen. It corresponds to relative density frequency classes calculated in relation to the maximum value observed in a cell of the grid.

The fishing effort is displayed on a map using a dynamic scale

of ten classes with a colour gradient to classify the different densities (percentages of points in each cell in relation to the maximum number of points in one cell). To do so, a correspondence is established between the number of points in each cell and the number of hours of fishing (e.g. 6 points = 1 hour of fishing).


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LPUE is also calculated in this module, for a particular vessel or group of vessels, and for a selected period of time. It is also possible to calculate LPUE by Region or Fishing ground and display it on a pie chart or histogram attached to the spatial entity (Figure 7). However, landings from a given Fishing trip may correspond to catches of several trawl hauls, performed in different Regions or, more often, in different Fishing grounds. Therefore, LPUE for a particular Fishing ground and Region are calculated with trawl haul records from Fishing trips exclusively performed in a particular Fishing ground or a Region.

Figure 7. GeoCrust 1.0 – Module 5 (Cartography): screen display showing pie charts of 1999

annual Landings per Unit Effort (kg/h), by Fishing ground. The dashed zones represent the different fishing grounds. Different colours are used to represent LPUE of the three crustacean target species (Parapenaeus longirostris, Aristeus antennatus and Nephrops norvegicus) and also LPUE of Finfish, Molluscs and Other Crustaceans. (Originally displayed in colour).

Module 6. ‘Statistics’. The access to the database can be made directly by running MsAccess, or through this module. Although data can be extracted for further analysis in other computer packages it is also possible to perform some exploratory analysis in this module. The user


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can compare landings by species, fishing effort and LPUE between vessels for a given period of time (by month, quarter, semester and year) (Figure 8) extract the number, speed, distance, duration and depth of a selected Fishing trip by vessel or group of vessels, landings by species or groups of species (target crustacean species, other crustacean, finfish, cephalopods and others) and LPUE (kg/nm, kg/hour or kg/nm2). It is also possible to display on a map the trawl hauls for selected Fishing trips.

Figure 8. GeoCrust 1.0 – Module 6 (Statistics): Screen display of histograms with

quarterly landings of Aristeus antennatus (1st), Parapenaeus longirostris (2nd), Nephrops norvegicus (3rd) and other crustaceans (4th), in 1998 and 1999, for three selected trawlers represented by different colours. (Originally displayed in colour).

Module 7. ‘Simulator’. This module is a complement application

capable of simulating the activity of selected vessels. The objective of this module was to show the fishing activity of the fleet during a selected period of time. During a simulation, daily landings and accumulated landings figures are displayed (histograms) automatically, for all selected vessels and, if required, for a single vessel. This module is particularly useful for demonstrations. However, it is also useful to understand some aspects of the dynamic of the crustacean trawl fleet (Figure 9).


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Figure 9. GeoCrust 1.0 – Module 7 (Simulator): Simulation of the activity of four trawlers (dots

in the sea) from 1.05.1998 to 30.11.1998. The screen display shows the activity of the vessels at 13 hours and 53 minutes on 20th July. The four small pie charts show the landings by species of these vessels, in the morning (sales at the fish market). The large pie chart on the top right side of the form is the total landings of the four selected vessels. The accumulated landings by species, for the four vessels, for the selected month are represented in the histogram on the middle right side. The histogram on the bottom right side displays the accumulated landings by species (for the crustacean target species Parapenaeus longirostris, Aristeus antennatus and Nephrops norvegicus, and also for Finfish, Moluscs and Other Crustaceans), for the four vessels, for the total period selected. (Originally displayed in colour).

A series of auxiliary routines were developed for updating the

database, i.e. to calculate several statistics related to the Fishing trips (duration and length), trawl hauls (duration, length and depth stratum – maximum and minimum depth contours, Region and Fishing ground where the hauls are located) and to obtain the shapefiles needed for mapping fishing effort in Module 5. 3. Discussion The GeoCrust 1.0 GIS software was developed and used to obtain and map fishing effort and LPUE for the Portuguese crustacean trawl fleet for the period of 1998 and 1999 (Afonso-Dias et al., 2002). For the first time,


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data from the Portuguese VMS (MONICAP) were used for scientific purposes. The software developed can be used, from now on, to analyse VMS data for the following years. However, further work is necessary to improve the GeoCrust 1.0.

The identification and definition of the limits of Fishing trips and trawl hauls, is based on the variation of vessel speed throughout the day, by running the different routines developed in GeoCrust 1.0. The whole process is very time-consuming, despite the reasonable degree of automation achieved. However, this seemed to be the only way to produce detailed and accurate information on the crustacean trawlers’ fishing operations using these data sets. By filtering data between two fixed speed limits, as performed by Marrs et al., (2002) in the study carried out in Clyde’s Nephrops fishery, it is not possible to obtain this type of information. Vessels trawl at different speeds and, in some situations, change their speed between hauls or even during the same haul. Considering the time required to perform some of the semi-automatic routines experienced during the analysis of the 1998-99 VMS data, it is desirable to develop automatic routines using techniques like the ‘Neuronal Networks’. However, this development may prove to be very difficult or even impossible to achieve, due to the high variability observed in the VMS data, particularly the definition of trawl haul limits. The development of these routines must, however, be preceded by experimental operations at sea in order to validate the criteria used to define trawl haul limits.

Another advantage of this software is its flexibility. The GeoCrust 1.0 can be easily adapted to incorporate and analyse data from the Portuguese finfish trawl fishery, the other trawl fishery that operates off the Portuguese coast (from north to south coast). These adaptations comprise the extension of the digital chart to the Northern coast of Portugal and small changes in some of the algorithms, particularly those used for the definition of trawl hauls limits (finfish trawls are performed at a higher speed than are crustacean trawls). This methodology can also be applied, with the necessary adaptations, to other European trawl fisheries. All European Union vessels exceeding 20 m between perpendiculars or 24 m overall length wherever they operate have, since the 1st January 2000, subjected to a VMS (Verborgh, 2000).

Confidentiality is required to manipulate the VMS data due to the location of fishing activities and respective landings of particular vessels. This confidentiality has been the justification for the difficulties experienced to access the MONICAP data for fishery research. It is clear that assembling, manipulating and analysing this kind of data, by routine, has to be centralized by a Portuguese institution with responsibilities in


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fisheries management. This institution would be responsible for quantifying and mapping fishing effort and LPUE. Subsequently, this information could be made available, in appropriate format, to scientists and also to the fishing industry, making use of Internet facilities. However, there is a need for further work to achieve this goal. Acknowledgments Thanks are due to Carlos Palma, for his help in the database design and data manipulation in the initial stages the GeoCrust project; Carla Paulo, for the preparation of the digital and geo-referred charts for GeoCrust 1.0; Isabel Afonso-Dias and two anonymous referees, for helping in the revision of this paper, and also to Pedro Sousa, Ana Carvalho, Rodrigo Santos, João Pinto and Jorge Candeias for their collaboration in the development of this project. This research was carried out with the financial support of the DGXIV of the European Commission (Study Contract number 99/059). References Afonso-Dias, M., Simões, J., Pinto, C. and Sousa, P. 2002. Use of satellite GPS data

to map effort and landings of the Portuguese crustacean fleet. Final Report EC-DGXIV/STUDY/99/059. Universidade do Algarve, Faro. 48 pp + Tables, Figures and Annexes.

ICES, 2001. Report of the Working Group on Nephrops Stocks. International Council

for the Exploration of the Sea, Report to the Advisory Committee on Fishery Management C.M. 2001/ACFM: 16 (mimeo).

Marrs, S.J., Tuck, I.D., Atkinson, R.J.A., Stevenson, T.D.I., and Hall, C. 2002.

Position data loggers and logbooks as tools in fisheries research: results of a pilot study and some recommendations. Fisheries Research, 58: 109-117.

Vasconcelos, M.S., 2000. The contribution of research to an improvement of fisheries

monitoring. Proceedings of the international conference on fisheries monitoring, control and surveillance. Brussels, 24-27 September 2000. 7 pp.

Verborgh, J., 2000. The European VMS. An illustration of the successful introduction

of advanced technologies for MCS. Proceedings of the international conference on fisheries monitoring, control and surveillance. Brussels, 24-27 September 2000. 15 pp.

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