Stock assessment in brown shrimp (Crangon crangon) part 1: Investigation of possible methods

Het Ministerie van LNV, de gezamenlijke Producentenorganisaties voor de garnalenvisserij in Nederland, en de natuurorganisaties Stichting de Noordzee en de Waddenvereniging hebben het belang onderschreven van een gezamenlijk traject naar een verduurzaming van de garnalenvisserij en het verkrijgen van een MSC (Marine Stewardship Councel) certificering voor de garnalenvisserij. Om voor een MSC label in aanmerking te komen moet er aangetoond worden dat de gewone garnaal, Crangon crangon, niet overbevist wordt. Momenteel wordt de garnalen visserij niet beheerd en is er geen officiële bestandschatting. Wel worden er door de ICES crangon werkgroep (WGCRAN, ICES working Group on crangon fisheries and life history) op een beschrijvende manier de fluctuaties in dichtheden van de gewone garnaal bijgehouden. Het is echter wenselijk om tot een meer kwantitatieve bestandschatting te komen

Case Study Sanwich Terns - a probabilistic analysis of the ecological effects of dreding

Every year, large amounts of sand are extracted from the North Sea to meet the demands for construction activities. Potential ecological effects of these sand mining activities have to be examined and reported in so called Environmental Impact Assessments (EIA’s). In the Netherlands, the potential impacts of sand mining activities on tern populations often form an important topic in these EIA’s. Sand mining causes an increase in silt concentrations. This increase will influence the turbidity of the water, which may affect populations of visual hunting birds, such as terns

Data availability for the evaluation of stock status of species without catch advice: Case study: turbot (Psetta maxima) and Brill (Scophthalmus rhombus)

Several commercially important demersal fish stocks for the North Sea fisheries are classified as “category 11” in the light of the EU policy paper on fisheries management (17 May 2010, COM(2010) 241). For stocks in this category, there is no STECF (Scientific, technical and economic committee for fisheries ) management advice, due to the unknown status of the stocks. The reason for this is that the data and information available to perform analytical stock assessments are highly uncertain or lacking. This document describes existing data and options for collecting new data for the evaluation of the state of category 11 stocks. We focus on turbot and brill in the North Sea. Existing data from logbooks and the market sampling program can be used to estimate LPUE series used in age-based stock assessment methods, similar to other commercially important flatfish species such as plaice and sole. Landings Per Unit of Effort (LPUE) data of the Dutch beam trawl fleet > 221 kW were standardised for engine power and corrected for targeting behaviour as described below and graphically shown in Figure 3.2.1. The methods are similar to those used to analyse commercial LPUE data for North Sea plaice, described in Quirijns and Poos (2010). Landing rates (LPUE) by market category were calculated for the period 2002-2010. The corrected LPUE series indicate an increase in commercial LPUE for both species during the period 2002-2006. For turbot, the LPUE stays stable in the first five years, increases between 2006 and 2008, and decreases afterwards. The increase in brill LPUE is larger, and occurs throughout the study period. Compared to other commercially important flatfish species relatively few brill and turbot market samples are taken. This reduces the ability to track the cohorts in the LPUE series of the older ages which is a prerequisite for reliable stock assessment estimates. Also, the time series currently spans only 9 years. Collection of additional data may therefore be desirable. Expanding the BTS survey will provide industry independent data and would therefore give easily interpretable results. The option of an industry survey is also a good option if the survey is already being executed for sole and plaice. However, both options are costly. Therefore, the option of increasing the samples of turbot and brill at the auction is relatively easy and relatively inexpensive and therefore at present the most promising. The methods used for this document will not per definition be applicable for all category 11 species. For dab, flounder, lemon sole and tub gurnard, samples at the auctions are taken to collect biological data. For these species it may be possible to raise the data in a similar way as was done in this report to estimate the age composition of the stock. For other species (witch flounder, horse mackerel, silver smelt, red mullet and squid) there is no market sampling. For these species, other methods will have to be developed

Palaeoecology of the neotropics: an overview of the state of affairs

An overview is given of the most important data on the palaeoecology of the Neotropics, with special emphasis on the Quaternary. Strong changes of temperature and rainfall affected tropical South (and Middle) America during the last few million of years. These changes are known in more detail from the last glacial-interglacial cycle. Relatively humid and cooler climates occurred in the period between >;50,000 and ca.25,000/30,000 years B.P.A cold and very dry climate occurred in the period of ca.21,000-c.14,000 B.P. Between 13,000 and 10.000 B.P. the climate became warmer and more humid, and from 10,000 B.P. to the present (the Holocene), the climate is more like the present, but there are still changes of temperature and especially of rainfall. While quantitative data of changes of temperature could be established beyond reasonable doubt in the high tropical Andes (6ºC-9ºC), ciphers for the tropical lowland are still uncertain (they might have been 2º to 6º lower than today). There is no doubt that the rainforest disappeared and was replaced by savanna or semidesert in some areas during certain climatic intervals. This was relatively well established on several sites in the southern part of the Amazon basin, in Bolivia and Brazil. In the northern savanna area of South America, large areas were changed in sand deserts

Long-Term Trends in Calcifying Plankton and pH in the North Sea

Relationships between six calcifying plankton groups and pH are explored in a highly biologically productive and data-rich area of the central North Sea using time-series datasets. The long-term trends show that abundances of foraminiferans, coccolithophores, and echinoderm larvae have risen over the last few decades while the abundances of bivalves and pteropods have declined. Despite good coverage of pH data for the study area there is uncertainty over the quality of this historical dataset; pH appears to have been declining since the mid 1990s but there was no statistical connection between the abundance of the calcifying plankton and the pH trends. If there are any effects of pH on calcifying plankton in the North Sea they appear to be masked by the combined effects of other climatic (e.g. temperature), chemical (nutrient concentrations) and biotic (predation) drivers. Certain calcified plankton have proliferated in the central North Sea, and are tolerant of changes in pH that have occurred since the 1950s but bivalve larvae and pteropods have declined. An improved monitoring programme is required as ocean acidification may be occurring at a rate that will exceed the environmental niches of numerous planktonic taxa, testing their capacities for acclimation and genetic adaptation

Investigations of a stock assessment in brown shrimp (Crangon crangon) Part 2: Biomass model

The Ministry of Agriculture, Conservation and Food quality, Producer organisations of the Dutch shrimp fisheries and NGO’s (Stichting de Noordzee and Waddenvereniging) have underlined the importance of sustainable harvesting of brown shrimp in the North Sea and Wadden Sea. Also they would like the brown shrimp fishery to meet the conditions of an MSC (Marine Stewardship Council) certificate. The first principle that the shrimp fishery needs to fulfil in order to acquire an MSC-label states that the stock should not be overfished. The biomass dynamic model has been investigated. This model does not need demographic data and was used successfully in Northern shrimp (Pandalus borealis). The model only needs the total amount of shrimp landings and an index of catches per unit of effort (CPUE) to assess the stock. The main assumptions of the model are (1) the stock under study is a single stock and (2) the available index (CPUE, catch per unit of effort series) describes the trends in the population well. The main conclusion from the study is that the applicability of the biomass model for a reliable stock assessment of brown shrimp needs considerably more study and data collection

Vergelijkende studie naar alternatieve vormen van de boomkorvisserij

Als onderdeel van het VIP-project “Alternatief visplan duurzame platvisvisserij” is een vergelijkende studie uitgevoerd naar de traditionele boomkorvisserij en twee alternatieve vismethodes: outriggen en sumwing. Tijdens twee visreizen hebben onderzoekers gekeken naar verschillen in aanlandingen (maatse vis) en discards (benthos en (ondermaatse) vis) op drie verschillende schepen. De drie schepen die waren betrokken bij dit onderzoek zijn: de UK47 (outrig), de ST27 (boomkor) en de UK246 (sumwing). Daarnaast is de kwaliteit van schol van de verschillende vismethoden met elkaar vergeleken

Loodverlies en het gebruik van loodvervangers in de sportvisserij (2018-2019)

Met de Green Deal-aanpak wil de overheid vernieuwende, duurzame initiatieven uit de samenleving de ruimte geven. Binnen Green Deal is een programma opgestart met als doel het gebruik van loodgewichten door hengelaars te verminderen. De Green Deal Sportvisserij Loodvrij is een overeenkomst tussen diverse ministeries, de Unie van Waterschappen, Natuurmonumenten, Dibevo en Sportvisserij Nederland en heeft als doel de komende jaren het gebruik van lood binnen de sportvisserij volledig af te bouwen. Loodgewichten kunnen worden verloren, waarmee schade aan het ecosysteem kan worden aangericht (Klein & Vink 2013). Het gebruik van alternatieven voor een loodgewicht zoals ijzer, steen, glas of beton verminderen het gebruik & verlies van lood. In dit kader worden in deze korte rapportage de volgende vragen behandeld: - Hoe vaak wordt er door Nederlandse hengelaars met loodvervangers gevist? - Hoeveel lood wordt er door Nederlandse hengelaars verloren per jaar? Dit rapport is een vervolg op een eerdere rapportage (“Gebruik van alternatieven voor loodgewichten in de recreatieve visserij in 2017, CVO rapport: 18.006, T. van der Hammen”)