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Van Hoof L.,Institute for Marine Resources and Ecosystem Studies
ICES Journal of Marine Science | Year: 2013

Among the proposals for the 2012 revision of the EU Common Fisheries Policy, a strong case is made for the introduction of a system of rights-based management. The EU perceives individual fishing concessions as an important instrument for capacity management. We will use the introduction of individual tradable quotas in the management of the Dutch North Sea beam trawl fisheries as a case for exploring the effect of the introduction of such an instrument. The effect will be assessed in terms of reduction of fishing capacity in the Dutch beam trawl fleet and its economic and social impact. These Dutch experiences will be translated to the current debate on the reform of the EU Common Fisheries Policy. Especially, we will focus on the issues of "relative stability", the concentration of rights, and the effects on the small-scale fisheries sector. Some of the negative effects associated with individual tradable rights can be addressed through design. However, trying to maintain stability and counter perceived negative impacts on fishing communities will modify the effect of introducing individual fishing concessions. © 2013 International Council for the Exploration of the Sea. Source


De Boer M.N.,Institute for Marine Resources and Ecosystem Studies
Marine Ecology Progress Series | Year: 2010

Minke whales were recorded in the central North Sea in an area characterised by frontal features and high productivity northeast of the Dogger Bank (4677 km2). Survey efforts were carried out from 28 March to 2 July 2007, at a finer scale than in earlier studies in the region, using 2 vessels as platforms of opportunity and a dedicated line-transect survey vessel following distance sampling methods. The high density of whales indicated that this offshore bank slope is an important spring habitat for minke whales in the North Sea. In total, 77 sightings of minke whales comprising 130 individuals were recorded. The peak density of minke whales was estimated to be 0.029 whales km-2 (minimum estimate, 95% CI: 0.012 to 0.070) in May. During peak abundance, the minke whales temporarily congregated in the area, suggesting that the whales were taking advantage of the local spring abundance of sandeels. The density found was higher than previous studies have suggested for the central North Sea. The results correspond to recent observations of minke whale redistribution within the North Sea, and these may be related to a decline in sandeel availability elsewhere in the North Sea. Offshore banks that aggregate prey may therefore become increasingly important feeding habitats for minke whales and other top predators in the North Sea. The observed hab itat preference of minke whales along this offshore bank appeared to be similar to that observed in coastal areas, and this suggests some degree of generality regarding the preference for this type of habitat. © Inter-Research 2010 · www.int-res.com. Source


de Boer M.N.,Institute for Marine Resources and Ecosystem Studies
Journal of the Marine Biological Association of the United Kingdom | Year: 2010

Information on cetaceans off Gabon in tropical West Africa is summarized from boat-based surveys carried out between 7 March and 7 August 2009. Thirteen cetacean species were positively identified comprising two baleen whale species, one sperm whale species and ten species of delphinid. Bryde's whale (Balaenoptera brydei) and humpback whale (Megaptera novaeangliae) were the most frequently encountered species. Cetaceans were found throughout a range of sea surface temperature between 20.5°C and 27.5°C and a wide range of depths with the majority of effort and sightings occurring seaward of the shelf break. Of particular interest from the study were the following: (1) Gabonese waters have a broad cetacean diversity, especially with a large and diversified delphinid community in the northern part of the study area; (2) the variations in oceanographic conditions within Gabonese waters are likely to result in a temporal variation in species composition; (3) the sightings of Atlantic spotted dolphin (Stenella frontalis) are the first at-sea sightings confirmed for these waters, although not unexpected given their distribution and abundant presence in surrounding waters; and (4) the poorly known Clymene dolphin (Stenella clymene) was sighted on four occasions in deep oceanic waters and was the most abundant cetacean. These are the first confirmed records of Clymene dolphins in Gabonese waters. Source


Gislason H.,Technical University of Denmark | Daan N.,Institute for Marine Resources and Ecosystem Studies | Rice J.C.,Northwest Atlantic Fisheries Center | Pope J.G.,University of Tromso
Fish and Fisheries | Year: 2010

The natural mortality of exploited fish populations is often assumed to be a species-specific constant independent of body size. This assumption has important implications for size-based fish population models and for predicting the outcome of size-dependent fisheries management measures such as mesh-size regulations. To test the assumption, we critically review the empirical estimates of the natural mortality, M (year-1), of marine and brackish water fish stocks and model them as a function of von Bertalanffy growth parameters, L∞ (cm) and K (year-1), temperature (Kelvin) and length, L (cm). Using the Arrhenius equation to describe the relationship between M and temperature, we find M to be significantly related to length, L∞ and K, but not to temperature (R2 = 0.62, P < 0.0001, n = 168). Temperature and K are significantly correlated and when K is removed from the model the temperature term becomes significant, but the resulting model explains less of the total variance (R2 = 0.42, P < 0.0001, n = 168). The relationships between M, L, L∞, K and temperature are shown to be in general accordance with previous theoretical and empirical investigations. We conclude that natural mortality is significantly related to length and growth characteristics and recommend to use the empirical formula: ln(M) = 0.55 - 1.61ln(L) + 1.44ln(L∞) + ln(K), for estimating the natural mortality of marine and brackish water fish. © 2010 Blackwell Publishing Ltd. Source


Brunel T.,Institute for Marine Resources and Ecosystem Studies | Dickey-Collas M.,Institute for Marine Resources and Ecosystem Studies
Marine Ecology Progress Series | Year: 2010

The effect of temperature and population density on the growth of Atlantic herring Clupea harengus was studied using a comparative approach applied to 15 North Atlantic populations. The von Bertalanffy (VB) equation was applied to describe mean growth of individuals in each population, both averaged over the whole period studied and for each cohort. Water temperature was a determinant factor for herring growth at the species level: North Atlantic herring in cold water areas exhibited a lower growth coefficient (k), longer lifespan and a higher asymptotic weight (winf) than those living in warmer water. The average winf of herring was positively correlated to the density of biomass of that population. This relationship was most likely due to the negative correlation found between population density and mean temperature. At the within-population level, when looking at the temporal variability in growth parameters amongst cohorts, winf was still negatively correlated to temperature, but the positive correlation between k and temperature was no longer significant. In a single population, the temperature range is probably too narrow to have an identifiable effect on growth. The effect may be confounded by other factors such as density dependence. On the basis of this macroecological pattern, global warming should enhance growth of the youngest age-classes, but reduce the growth of older individuals and shorten the lifespan of herring. © Inter-Research 2010. Source

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