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Discarding of fish species in the Kattegat-Skagerrak Nephrops directed fisheries remains at high levels. In this work we have tested four sets of codends pair-wise with the catch comparison technique under full commercial conditions to assess their potential in reducing the catch of undersized commercial species, in particular cod. We investigate the position of a 90 mm square-mesh panel (SMP), the effect of increasing the mesh size from 90 to 120 mm in the SMP, the effect of inserting a 90 mm SMP in an 80 mm codend and the effect of increasing the codend mesh size from 90 to 120 mm in a total of 89 hauls. Inserting the SMP 3–6 m from the codline compared to 6–9 m from the codline, reduced catches of cod above the minimum landing size (MLS) and Nephrops above and below the MLS. Increasing the mesh size in the SMP from 90 to 120 mm increased the catch of cod above the MLS in weight with an overall increase of 12% in the revenue. The effect of installing a 90 mm SMP 6–9 m from the codline in a nominal 80 mm codend had no effect on the catch of cod. Increasing the nominal codend mesh size from 90 to 120 mm reduced the catch of all species below the MLS, except monkfish. Catches of Nephrops above the MLS were, however, reduced by approximately one third and the total loss in revenue was 21%. 相似文献
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Claus Reedtz Sparrevohn Martin Lindegren Brian R. Mackenzie 《Fisheries Oceanography》2013,22(5):400-408
The consequence of elevated ocean temperatures on commercial fish stocks is addressed using time series of commercial landings (1906–2004) and juvenile survey catch data (1904–2006) collected around Denmark. We analyze (i) whether warm‐water sole (Solea solea) has increased relative to Boreal plaice (Pleuronectes platessa) and (ii) whether two related warm‐water species (turbot, Psetta maxima and brill, Scophthalmus rhombus) show similar responses to increasing temperature or, alternatively, whether turbot (which has a broader juvenile diet) has been favored. Since the early 1980s, both sole and turbot have constituted an increasing part of the commercial landings and survey catches, as compared with plaice and brill, respectively. These changes in species composition were linked to sea surface temperatures, Northern Hemisphere temperature anomalies (NHA) and the North Atlantic Oscillation. NHA was closely related and explained 43% of the observed variation in sole survey catches relative to the plaice catches and almost 38% of the observed variation in the sole landings relative to the plaice landings. For the less common species, turbot and brill, none of the global change indicators explained more than 15% of the variation, although all showed a positive relationship. Survey catch per unit effort increased significantly for both sole and turbot around the early 1980s, whereas catch per unit effort for plaice and brill remained constant. The results indicate that the abundance of warm‐water species is likely to increase with increasing temperature but also that species with similar life histories might react differently according to degree of specialization. 相似文献
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Recent decline in cod stocks in the North Sea–Skagerrak–Kattegat shifts the sources of larval supply 
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下载免费PDF全文 Per R. Jonsson Hanna Corell Carl André Henrik Svedäng Per‐Olav Moksnes 《Fisheries Oceanography》2016,25(3):210-228
Cod stocks in the North Sea, including the Kattegat and the Skagerrak, have declined dramatically since the 1970s. Occasionally there is a high recruitment of juveniles in Kattegat/Skagerrak, without leading to the rebuilding of adult cod stocks despite reduced fishing mortality. In a biophysical model of egg and larval drift, we examined the potential importance of extant and historical spawning grounds for recruitment of cod in the Kattegat/Skagerrak seas using data of spawning stock biomass from the 1970s and from today's reduced stocks. The results suggest that Kattegat in the 1970s relied on largely locally retained (83%) larvae with little annual variation in recruitment. Kattegat also provided a substantial proportion of larvae recruiting in Swedish Skagerrak (72%). This is in contrast to present conditions where the Kattegat spawning stock has been reduced by 94%, and Kattegat only provides 34% of locally retained larvae and 30% to Swedish Skagerrak. Instead, the protected area in the Öresund and the Belt Sea are expected today to provide most larvae recruiting in Kattegat. Also, the inflow of larvae from the North Sea to Skagerrak and Kattegat can be significant although highly variable between years, with a positive correlation to the North‐Atlantic Oscillation index (NAO). The rebuilding of healthy spawning areas in the Kattegat may be key for restoring local cod stocks in both Kattegat and along the Skagerrak coast. This poses a management challenge if cod with local ‘Kattegat’ adaptations, e.g., in terms of egg density and migration patterns, are lost or reduced to non‐resilient densities. 相似文献
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The use of at‐sea‐sampling data to dissociate environmental variability in Norway lobster (Nephrops norvegicus) catches to improve resource exploitation efficiency within the Skagerrak/Kattegat trawl fishery 下载免费PDF全文
下载免费PDF全文 Jordan Feekings Asbjørn Christensen Patrik Jonsson Rikke Frandsen Mats Ulmestrand Sten Munch‐Petersen Bo Andersen 《Fisheries Oceanography》2015,24(4):383-392
Research into the influence of environmental variables on the behaviour of Norway lobster (Nephrops norvegicus), and hence catch rates, dates back to the 1960s (e.g., Höglund and Dybern, Diurnal and seasonal variations in the catch‐composition of Nephrops norvegicus (L.) at the Swedish west coast. ICES CM 1965/I46; Simpson, Variations in the catches of Nephrops norvegicus at different times of day and night. Rapport et Proés‐verbaux des Réunions Conseil permanent international pour 1'Exploration de la Mer 156:186). However, the use of fishery‐dependent data in identifying influential factors is relatively limited and only includes a number of papers on a limited dataset (e.g., Redant and De Clark, Diurnal variations in CPUE and length composition of the catches in a Nephrops directed fishery in the Central North Sea. ICES CM 1984/K:3; Maynou and Sardà, Influence of environmental factors on commercial trawl catches of Nephrops norvegicus (L.). ICES J. Mar. Sci. 58:1318). Here, we aimed to dissociate environmental variability in Norway lobster catches to improve resource exploitation efficiency within the Skagerrak and Kattegat trawl fisheries by utilising data collected as part of an extensive at‐sea‐sampling programme spanning 16 years. Catch rates were modelled using Generalized Additive Mixed Models (GAMMs) and considered a range of response variables, including depth, temperature, current speed, season, moon phase and time of day. The results obtained herein showed that time of day, season, depth, temperature, year, trawl type and location all significantly affect catch rates of Nephrops. 相似文献
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This paper presents a summary of all catch-comparison gear tests performed between 2002 and 2006 with Nordmøre-type sorting grids in the Swedish Nephrops trawl fishery in the Skagerrak and Kattegat. The overall aim was to minimise fish by-catch while maintaining catch rates for the target species, i.e. Nephrops. The results showed that a trawl fitted with a grid and a square-mesh cod-end, caught less small and marketable cod, haddock, whiting, hake and plaice than did a standard commercial trawl. For cod larger than 35 cm, the catch reduction was close to 100%. For marketable Nephrops no difference in catch amounts was detected. Results of three modified grid variants are also reported here. None of these showed convincing results in terms of better species-selectivity or superior handling characteristics than the standard grid. The results on fish by-catch reduction indicate that the Swedish grid may be a useful tool to reduce non-target mortality and to decouple Nephrops from cod and other demersal fish species under existing and future recovery plans. 相似文献
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Similar to many other commercial marine fish species, Atlantic cod (Gadus morhua L.) migrate towards specific sites at spawning. These temporal aggregations are generally the most targeted by the commercial fishery. The Kattegat cod has undergone a substantial reduction over the past 25 years and both stock size and spawning stock biomass have remained at very low levels since the end of the 1990s. There is, therefore, an urgent need to map and document spawning grounds still in use. In the present study, spawning sites of Atlantic cod were identified in the Kattegat using a combination of commercial and fishery independent data from 1996 to 2004. Moreover, putative spawning and non-spawning areas were also sampled before and during the reproductive season between 2002 and 2006, and the proportion of mature females together with the individual physiological status were used to validate and strengthen the spatial analyses.
The spatial analyses identified several spawning areas in the region and two areas in the southeastern part of the Kattegat which appeared to be the most important. The results showed the presence of cod spawning aggregations, although reduced in size, in areas that have been utilized for more than 25 years according to historical information. Some local spawning grounds may have also disappeared. The proportion of mature females was higher in putative spawning than in non-spawning areas (p < 0.001) and females from spawning areas had higher gonadosomatic (p < 0.05) and hepatosomatic (p < 0.001) indices than those from non-spawning areas.
Knowledge of stock spatial and temporal distribution is essential in designing recovery strategies for depleted fish populations. The unambiguous stability of the locations of spawning aggregations over time, as shown in this study, represents a useful aid in order to efficiently implement a recovery plan for the collapsing cod stock in this area. 相似文献
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