Effects on short and medium term predictions of discard data inclussion into assessment. Southern megrim assessment as an example

TOR c of WGHMM 2004 encourages to “provide specific information on possible deficiencies in the 2004 assessments including, at least, any major inadequacies in the data”. This WD shows the discard data available to use in assessment from 1987 onwards. Data comprises hake, megrims and anglerfish both from northern and southern stocks assessed at WGHMM. The reliability of data is represented with a traffic light risk visual code. An example of how to integrate discard data into assessment is made with Southern Megrim (Lepidorhombus whiffiagonis) and comparisons of the assessment and predictions with and without discards are reported. Finally, conclusions state the necessity of an accurate sampling design as well as some advantages and disadvantages of using discard data in assessment. Obviously, it produces a more real picture of the fishing exploitation. However, on the other hand we might add another important source of uncertainty to the assessment model and increasing the parameterization of the model

Nuevo diseño de muestreo de alocación óptima para mejorar las estimaciones y los niveles de precisión de los descartes en dos unidades pesqueras de arratreros españoles en el Atlántico nororiental (subáreas VIIc,j,k del CIEM)

The present report discusses a new onboard sampling design for the Spanish trawlers in northeast Atlantic waters –International Council for the Exploration of the Sea (ICES) subareas VIIc,j,k–. This sampling design comprises three stages: i) number of vessels and trips per vessel to be sampled; ii) the minimum number of sampled hauls; and iii) a temporal distribution of those sampled hauls throughout the fishing trip to balance hauls sampling along the fishing trip. As a result, an optimal allocation sampling is suggested, comprising at least one vessel and one trip per vessel to be sampled monthly, between 30 to 50 sampled hauls within that fishing trip, and a time-division for hauls during the fishing trip, containing 8-15 sampled hauls at the beginning, middle and end of the trip.Nuevo diseño de muestreo de alocación óptima para mejorar las estimaciones y los niveles de precisión de los descartes en dos unidades pesqueras de arratreros españoles en el Atlántico nororiental (subáreas VIIc,j,k del CIEM). Se aporta un nuevo diseño de muestreo de aplicación a bordo para los arrastreros españoles que faenan en las suáreas VIIc,j,k establecidas en el Atlántico noreste por el Consejo Internacional para la Exploracion del Mar (CIEM), diseño en cuyo desarrollo en tres etapas intervienen las siguientes variables: i) número de barcos y de las respectivas mareas a muestrear; ii) número mínimo de lances a muestrear; iii) distribución temporal del muestreo de lances a lo largo de la marea. Como conclusión, se recomienda un muestreo de alocación óptima consistente en el muestreado mensual de un barco y una marea, la elección de entre 30 y 50 lances a muestrear y, por último, que éstos estén distribuidos a lo largo de la marea de forma que al menos de 8 a 15 lances correspondan a cada uno de los periodos inicial, intermedio y final de la misma.Instituto Español de Oceanografí

An optimal allocation hauls sampling in order to reduce bias within fishing trip in trawlers operating in the Grand Sole and Porcupine areas (NE Atlantic)

Spanish demersal trawlers which operate in the Grand Sole and Porcupine Areas usually make between 50 and 80 hauls in each fishing trip, lasting around 15 days where fishing is almost continuous. Since the observer is not able to sample every haul, it is crucial to define a robust number of hauls to be sampled by the observer. A bootstrap analysis was carried out to determine the minimum number of hauls to be sampled to reduce significantly intra-variance within a fishing trip. Additionally, number of vessels and trips per vessel to be sampled was also analysed. Taking account the multistage sampling design and partitioning the over-all variability over the various stages, optimum sample sizes was estimated. On the other hand, fishermen may vary its retained catch and discard patterns whilst fishing trip occurs. Particular targets, discarded fish length or proportion of discarded/retained may change according to weather, occasional presence/absence of main target, storage space, quota exceeded, etc... To look into these plausible differences, every fishing trip was divided in three periods, beginning of the trip, half period and ending period, containing each one the same number of hauls. Several statistical tests were applied to these three periods to look for differences as well as to fit a consistent division of hauls to every period. Finally, an optimal allocation sampling scheme is suggested, both in terms of minimum number of hauls to be sampled and temporal division of those hauls along the fishing trip

Composition, spatial distribution and sources of macro-marine litter on the Gulf of Alicante seafloor (Spanish Mediterranean)

The composition, spatial distribution and source of marine litter in the Spanish Southeast Mediterranean were assessed. The data proceed from a marine litter retention programme implemented by commercial trawlers and were analysed by GIS. By weight, 75.9% was plastic, metal and glass. Glass and plastics were mainly found close to the coast. A high concentration of metal was observed in some isolated zones of both open and coastal waters. Fishing activity was the source of 29.16% of the macro-marine litter, almost 68.1% of the plastics, and 25.1% of the metal. The source of the other 60.84% could not be directly identified, revealing the high degree of uncertainty regarding its specific origin. Indirectly however, a qualitative analysis of marine traffic shows that the likely sources were merchant ships mainly in open waters and recreational and fishing vessels in coastal waters.We are grateful for the support of the PESCAL Project by European funds through General Secretary of Fisheries of Spain, led by CETMAR with the participation of the Joint Research Unit between the Spanish Oceanography Institute (IEO) and the University of Alicante (UA). Santiago García-Rivera was supported by PESCAL Project and a PhD grant from the University of Alicante

Discard Pattern of Hake Southern stock from the Spanish Trawl Fleet

Two exploitation units (North and South) of Hake (Merluccius merluccius) are assessed in the ICES Working Group of Hake, Monk and Megrim. In ICES Divisions VIIIc and IXa, Portuguese and Spanish ships captured this species mainly in mixed bottom trawl fisheries, but also in long-liners, gill net or in artesanal fleets. As far now, discard data are not used in the assessment of this species, though they are considered significantly high for younger ages. Discards data are available for Spanish trawlers for 1993, 1994, 1997, and the period from 1999 to 2001.This current paper shows available data of discards for Spanish Southern hake stock (Divisions VIIIc and IXa) as well as to present the sample level for the different periods. Some estimations on discard rate in number and in weight are also showed. Most of the results were obtained by different EU funded research projects. Several problems related to the raising method are discussed. Finally, the possibilities and difficulties to use discard data in stock assessment are numbered

Primeros resultados del proyecto para la evaluación preliminar de la merluza en determinadas zonas de la Plataforma Patagónica

Entre el 1 de enero de 2000 y el 31 de diciembre de 2001 se desarrolló el proyecto financiado por la DG PESCA de la UE titulado “Recogida de datos para la evaluación preliminar de los stocks de merluza en aguas de la Plataforma Patagónica”, en el que entre otros participantes estuvieron el Instituto Español de Oceanografía (IEO) y la Asociación Nacional de Armadores de Buques Congeladores de Pesca de Merluza (ANAMER). En este artículo se pretende exponer brevemente algunos de los principales resultados del proyectoDG PESCA CEPreprint0,000

Descartes: valor biológico y económico

Versión del editor0,000

Preliminary results of a Exploratory Fishing targeting deep-water species off Uruguay

A Pilot Action of Exploratory Fishing was carried out in the second half of 2001 by two Spanish bottom-longline commercial fishing vessels within the Uruguayan Economic Exclusive Zone (EEZ) targeting deep-water species. Trap fishing gears were also utilised as another alternative fishing gears.The main objective of the exploratory survey was to improve the knowledge of the distribution and the population structure of the species target of the survey: Groupers (Epinephelus spp.), Kingclip (Genypterus blacodes), Brazilian sandperch (Pinguipes spp.) and other accompanying species. Some preliminary results of this exploratory survey are shown in this current work. Fishery and biological data were collected by scientific observers on board of the two vessels which took part in the exploratory fishing. The collected data were date, time, position, depth, SST, SBT, weather condition, catches, discards, length distributions, sex, maturity, stomach fullness… among others. Length distributions, sex ratio and maturity stage of the most abundant species in the catch are also shown. Catch, effort and CPUE by area, gear and depth strata were analysed. Regarding bottom longline gear, the most abundant species were Dogfish shark (Squalus sp), Wreckfish (Polyprion americanus), Tope shark (Galeorhinus galeus) and Argentine hake (Merluccius hubbsi) in waters shallower than 200 m depth. Regarding Traps fishing gears, the most abundant species were crabs (Family Geryonidae) and Argentine conger (Conger orbignyanus)

Trends in the pattern of discarding in the hake (Merluccius hubbsi and Merluccius australis) fishery in the SW Atlantic.

This paper presents results from the EC Study Project 99/016 “Data collection for stock assessment of two hakes (Merluccius hubbsi and M. australis) in international and Falkland waters of the SW Atlantic”. Historical fishery and biological data series available from IEO (1988 onwards) were used to describe and quantify patterns and spatio-temporal changes in catches and discards in the hake fishery. Data were collected by scientific observers on board Spanish fishing vessels operating in the study area. Data collected on fishing activity included effort, catches and discards of target and non-target species on a haul-by-haul basis. Biological information (size, sex, maturity, etc) on target species was recorded on a daily basis, while biological data on non-target species was recorded periodically. The “discards ratio” was calculated by each haul, defined as the total weight of fish discarded divided by the total catch weight. The most important by-catch species are hoki or whiptailed hake (Macruronus magellanicus), red cod (Salilota australis), southern blue whiting (Micromesistius australis), Patagonian toothfish (Dissostichus eleginoides) and kingclip (Genypterus blacodes). Discards included both target and non-target species. The most commonly discarded species were Patagonotothen spp. (almost 100% of the catch is discarded), whiptailed hake (Macruronus magellanicus) (25% discarded), southern blue whiting (12%) and red cod (6%). These percentages vary with area, year and fishing season. The four target species (Merluccius hubbsi, Merluccius australis, Illex argentinus and Loligo gahi) have discard ratios below 5%. In recent years discard ratios for all species except Patagonotothen spp. have fallen below 15%