Length–weight relations for 19 freshwater fish species (Actinopterygii) from the lowland Elbe River, Germany

Monthly and mean length–weight relations (LWRs) were calculated for 19 freshwater fish species from the middle section of the lowland Elbe River (Germany): Abramis brama (Linnaeus, 1758); Alburnus alburnus (Linnaeus, 1758); Anguilla anguilla (Linnaeus, 1758); Ballerus ballerus (Linnaeus, 1758); Blicca bjoerkna (Linnaeus, 1758); Cobitis taenia Linnaeus, 1758; Esox lucius Linnaeus, 1758; Gobio gobio (Linnaeus, 1758); Gymnocephalus cernua (Linnaeus, 1758); Leuciscus aspius (Linnaeus, 1758); Leuciscus idus (Linnaeus, 1758); Leuciscus leuciscus (Linnaeus, 1758); Lota lota (Linnaeus, 1758); Perca fluviatilis Linnaeus, 1758; Romanogobio albipinnatus (Lukasch, 1933); Rutilus rutilus (Linnaeus, 1758); Sander lucioperca (Linnaeus, 1758); Scardinius erythrophthalmus (Linnaeus, 1758); and Squalius cephalus (Linnaeus, 1758). The values of the exponent b in the LWR W = aTLb ranged from 2.882 (Lota lota) to 3.517 (Cobitis taenia) and the correlation coefficient (r2) was greater than 0.96 for all species except for Cobitis taenia with 0.93. The relations allow for the accurate estimation of weight from length data with reduced handling times of fish in the field while enabling comparisons with other regions and future studies. The calculated LWRs together with species-specific abundance and catch data will be useful for fisheries modeling and estimating population status and related fish species protection, especially for the endangered species in the Elbe River

The impact of marine recreational fishing on key fish stocks in European waters

Marine recreational fishing (MRF) has been shown to substantially contribute to fishing mortality of marine fish. However, European MRF catches are only quantified for a small number of stocks, so it is unclear whether a significant part of fishing mortality is excluded from stock assessments. This study estimated: (i) European MRF removals, which were defined as landings plus dead releases; and (ii) impact at stock level by comparing the percentage contribution to total removal by MRF and commercial fishing. As MRF data were limited for some European countries, catches were reconstructed using a mixture of average release proportions, average fish weights, and extrapolation using the catch per fisher of the nearest country providing catch estimates. Where catch reconstructions exceeded 50%, data were excluded from further analysis. Furthermore, as MRF survey methodology can be variable, semi-quantitative estimates of bias and error were calculated for each stock. Only 10 of the 20 stocks assessed in this study had sufficient MRF data for full reliable estimates. Percentage contribution to total removals (MRF + commercial removals) by MRF ranged between 2% for Atlantic mackerel in the North Sea and Skagerrak and 43% for Atlantic pollack in the Celtic Seas and English Channel. The biomass removed ranged between 297 (± 116) tonnes (Atlantic cod in the western English Channel and southern Celtic seas) and 4820 (± 1889) tonnes (Atlantic mackerel in the North Sea and Skagerrak), but the errors were substantial. Additionally, the bias in the estimated removals was low for most stocks, with some positive biases found. The present study indicates that removals by MRF can represent a high proportion of the total removals for some European marine fish stocks, so inclusion in stock assessments should be routine. To achieve this, regular surveys of MRF are required to collect data essential for stock assessments

Atrial fibrillation genetic risk differentiates cardioembolic stroke from other stroke subtypes

AbstractObjectiveWe sought to assess whether genetic risk factors for atrial fibrillation can explain cardioembolic stroke risk.MethodsWe evaluated genetic correlations between a prior genetic study of AF and AF in the presence of cardioembolic stroke using genome-wide genotypes from the Stroke Genetics Network (N = 3,190 AF cases, 3,000 cardioembolic stroke cases, and 28,026 referents). We tested whether a previously-validated AF polygenic risk score (PRS) associated with cardioembolic and other stroke subtypes after accounting for AF clinical risk factors.ResultsWe observed strong correlation between previously reported genetic risk for AF, AF in the presence of stroke, and cardioembolic stroke (Pearson’s r=0.77 and 0.76, respectively, across SNPs with p &lt; 4.4 × 10−4 in the prior AF meta-analysis). An AF PRS, adjusted for clinical AF risk factors, was associated with cardioembolic stroke (odds ratio (OR) per standard deviation (sd) = 1.40, p = 1.45×10−48), explaining ∼20% of the heritable component of cardioembolic stroke risk. The AF PRS was also associated with stroke of undetermined cause (OR per sd = 1.07, p = 0.004), but no other primary stroke subtypes (all p &gt; 0.1).ConclusionsGenetic risk for AF is associated with cardioembolic stroke, independent of clinical risk factors. Studies are warranted to determine whether AF genetic risk can serve as a biomarker for strokes caused by AF.</jats:sec

Ökologische, soziale und ökonomische Dimensionen des Meeresangelns in Deutschland

Research on the social and economic value of marine recreational fishing and its possible effects on marinefish stocks and ecosystems has been underrepresented in Germany in the past. This study should therefore collect and analyze representative data on (1) the number, fishing effort, and catches of German marine anglers in the North Sea and Baltic Sea (including the brackish lagoon Bodden waters), (2) the socio-economic importance,and (3) aspects of fisheries management.Therefore, a representative telephone screening survey was conducted with 50,000 randomly selected German households in the period from May to October 2014 to determine the incidence of marine anglers in the German population and to recruit participants for a one-year diary study. The telephone screening survey identified 562 households with marine anglers. The diary study involved 586 anglers who documented a total of 5,154 fishing days. The results showed that a total of around 200,000 German marine anglers fished approximately 1.8 million days per year in the German Northand Baltic Sea including the Bodden waters. In the Baltic Sea, about 161,000 anglers fished for approx. 1.2 million fishing days per year in 2014/2015. For the Bodden waters this resulted in about 49,000 persons and a fishing effort of about 332,000 fishing days per year in 2014/2015. At the North Sea there were about 32.000 anglers with about 147.000 fishing days per year in 2014/2015. While angling in the Baltic Sea and the Bodden waters was mainly carried out from boats, shore fishing was the most popular fishing method in the North Sea. German marine anglers were predominantly male (92%), on average 49 years old, and lived in households with two or three persons. Peace and relaxation, the experience of nature, and the capture of fish were the main motives for pursuing their hobby. On average, each angler spent about 900 Euro per year on marine recreational fishingin Germany, which corresponds to a total annual expenditure of 185 million Euro. The largest share of the expenditure was accounted for by costs for own boats, fishing tackle, travel/transportation, and accommodation. Marine anglers are thus an important source of income for coastal tourism in Germany, especially in the low season. The evaluation of the diary study showed that a total of 27 different fish species were caught in the Baltic Sea during the study period. The most important target species for Baltic Sea anglers were cod (Gadus morhua), sea trout (Salmo trutta), various flatfishes (Pleuronectoidei), and herring (Clupea harengus), with cod and herring being also the most commonly caught fish. Depending on the species, the importance of recreational fisheries harvests varied considerably compared to the German commercial fisheries landings in the Baltic Sea (ICES subdivisions 22 and 24). For example, the relative share of recreational fishing on the total harvest (sum of commercial and recreational harvest in tons) of sea trout (91%) and cod (53%) was high, while the shares of herring and flounder were each well below 10% of the total harvest. A total of 17 fish species were caught in the Bodden waters. Pike (Esox lucius), pikeperch (Sander lucioperca) and perch (Perca fluviatilis) were the most important target species. The most commonly caught species were herring, perch, pike, garfish (Belone belone), and pikeperch. Overall the results show that angling plays an important role for certain fish stocks in the Bodden waters. In the case of pike, angling is even the dominant form of exploitation. A total of 13 species of fish were caught in the North Sea. The most popular target fish species were sea bass (Dicentrarchus labrax), flatfish, cod and mackerel (Scomber scombrus). The most commonly caught species were mackerel, plaice (Pleuronectes platessa), and cod. Overall, it was found that angling in the North Sea is of rather minor importance compared to commercial fishing. About two thirds of the anglers were very or rather satisfied with their catches during marine recreational fishing, whereas about 22% were rather or very dissatisfied. The main reasons for being unsatisfied were overfishing and insufficient regulation of commercial fishing. Minimum landing sizes and closed seasons were judged as very good recreational fisheries management measures by about 80% of the marine anglers, whereas daily bag limits were assessed more critically. The results of this study may serve as basis for the development of a sustainable marine recreational fishery in Germany. Furthermore, social and economic aspects should be considered in future management decisions in order to ensure a sustainable, fair and, from an economic perspective, optimal allocation of the marine fish resources in Germany

Effect of lure and bait type on catch, size, hooking location, injury and bycatch in the western Baltic Sea recreational cod fishery

Atlantic cod (Gadus morhua) is an important recreational and commercial fisheries target species in the Northern hemisphere. Release rates are high in the recreational fishery due to regulatory and voluntary catch-and-release practice. Although post-release mortality of cod is relatively low, there is potential for further reductions. The most effective way to reduce post-release mortality is to minimize the catch of sublegal fish or non-target species and to reduce hooking injuries by using more selective fishing methods. This study investigated the influence of the lure/bait type on: (1) size of fish, (2) catch and harvest, (3) proportion of bycatch, (4) hooking location, and (5) injury (bleeding) in the western Baltic Sea recreational cod fishery. Data were collected via random onboard sampling of 35 charter vessel angling trips (778 anglers) and during two supplementary studies in the western Baltic Sea. Overall, the median total length was significantly higher for cod caught on artificial lures (39 cm) than for cod caught on natural bait (28 cm), leading to a 43% higher proportion of sublegal (<38 cm) cod for bait than for lure. Median catch-per-unit-efforts (number of captured cod per angling hour) did not differ significantly between lure and bait angling (both: 0.49 cod per hour), whereas the median harvest-per-unit-effort (number of captured cod ≥ minimum landing size (38 cm) per angling hour) was significantly higher for lure (0.24 cod ≥38 cm per hour) than for bait angling (0.06 cod ≥38 cm per hour). The incidence of deep hooking and severe bleeding was significantly higher for bait angling. Furthermore, bait angling significantly increased bycatch of other species dominated by whiting (Merlangius merlangus) and European flounder (Platichthys flesus). Cod anglers can reduce the catch of sublegal cod and non-target species and minimize hooking injuries of released fish by using lures instead of bait in the western Baltic Sea. Thus, voluntary terminal gear recommendations may be an effective tool for anglers and managers to increase selectivity in recreational cod fisheries

Post-release effects of catch and release angling for sea trout: Mortality, growth and wound healing

Sea trout (anadromous brown trout, Salmo trutta L.) is a popular recreational angling target species in the Baltic Sea region and beyond. Across countries, a substantial part of angled sea trout is released after capture either due to management regulations or due to voluntary decisions by the anglers. However, information about post-release impacts of catch and release (C&R) on survival and growth in saline waters is largely missing. We used a flow-through seawater raceway (4–10 °C) to investigate impacts on survival and growth of angled and released sea trout (< 40 cm) up to 29 days post release. Bleeding was common among angled sea trout, but differed between angling treatments, i.e., lure fishing with treble hook (size 4), lure fishing with single hook (size 1/0) and fly fishing with single hook (size 12). However, no mortality and no significant differences in growth were found after a 26–29 days monitoring period among a control group and the three treatment groups, but a small subset (6%) of the angled fish caught on lure had unhealed/infected hooking wounds at the end of the experiment. The results infer that adverse effects of C&R on coastal sea trout due to high post-release mortality or reduced growth can be limited and may not pose a significant problem for sea trout stocks. Nevertheless, further studies are required to corroborate these results under more natural field conditions and at higher water temperatures. In addition, further studies on long-term sublethal impacts of C&R on sea trout are needed.publishedVersio

Kritiske elementer i bestandsvurderingsmodeller for ål og havørred

Denne rapport omfatter resultaterne af tre delprojekter, der blev gennemført med støtte fra European Maritime and Fisheries Fund (EMFF) i perioden 2019-2022. Projektet omhandler arterne ål (Anguilla anguilla) og havørred (Salmo trutta). For åls vedkommende forsøges der at svare på spørgsmål vedrørende udvandringen af blankål fra Østersøen og risikoen for at blive fanget i det danske fiskeri. For havørred ønskes viden om omfanget af skarvprædation på unge ørreder på kysten samt viden om omfanget af såkaldt Catch and Release (C&amp;R) lystfiskeri på havørreder på kysten, og hvordan C&amp;R påvirker fiskene efter genudsætning.Udvandring og fangst af blankål i dansk farvand blev undersøgt i fællesskab med øvrige forskningsinstitutioner i Østersøområdet via et samarbejde, som blev indledt i 2019. Nærværende rapport omhandler de af EMFF-finansierede mærkninger, hvor blankål mærket af DTU Aqua og svenske SLU Aqua i 2019, kan anvendes til at estimere fiskeritrykket på blankål i danske farvande. I alt 248 ål blev mærket med elektroniske (akustik) mærker på hhv. Yxlö (103 ål), Svartö (72 ål) og Utlängän (73 ål) langs den svenske Østersøkyst i august-oktober 2019. Det elektroniske mærke udsender et unikt, kodet signal hvert minut, som kan registreres af hydrofoner. Ved at opstille hydrofoner, som kan monitere bundgarnsfiskeriers fangster af elektronisk mærkede ål og samtidig opstille rækker (arrays) af hydrofoner på tværs af Lillebælt, Storebælt og Øresund, kunne det registreres, hvor mange mærkede ål der hhv. fangedes af de overvågede bundgarnsfiskerier eller lykkedes med at vandre ud af Østersøen. Af de 103 mærkede ål fra Yxlö, som er det nordligste udsætningspunkt, blev ganske få (8 stk.) individer registreret på hydrofonerne i Øresund eller Bælterne, og derfor vil disse ål ikke indgå i analyserne. I alt 84 individer (58%) af de 145 øvrige mærkede ål trak ud af Østersøen, og 82 (98%) af disse vandrede ud af Østersøen gennem Øresund. Det tog i gennemsnit ålene tre måneder at svømme den relativt korte afstand fra udsætningsområderne til Øresund eller Bælterne, men med stor variation (13 – 412 dage). Fra Svartö er der ca. 350 km i direkte svømmeafstand, fra Utlängän er der ca. 240 km og fra Yxlö er der 600 km til hydrofonerne i Øresund.Ti individer blev fanget i Køge Bugt og Øresund, hvoraf syv blev fanget i de moniterede bundgarnsfiskerier, der ifølge landingsstatistikken stod for 32% af ålefangsterne med bundgarn i Køge Bugt og Øresund i 2019. Et usikkert estimat, baseret på disse tal viser, at ca. 20% af blankålene fra Østersøen kan ende i danske garn.Der er i perioden 2020-2022 også mærket ål i en række andre lande omkring Østersøen finansieret af midler fra kilder ud over EMFF. Disse resultater viser, at ål fra andre områder af Østersøen har andre vandringspræferencer og i højere grad trækker gennem Lillebælt og Storebælt end ålene, der blev mærket i Sverige. Indsamling af resultater fra disse ål er ikke afsluttet endnu.Havørred (anadrom ørred, Salmo trutta) er en populær art i det danske lystfiskeri, såvel som i mange andre lande omkring Østersøen. I de fleste lande er lystfiskeri efter havørreder reguleret gennem virkemidler såsom mindstemål, daglige fangstbegrænsninger og/eller fredningstider. Disse regler medfører i praksis, at mange havørreder genudsættes efter fangst. Samtidig genudsætter lystfiskere ofte havørreder af frivillige grunde, f.eks. fordi de ønsker at bevare en bestand af større havørreder. Oplysninger om lystfiskeradfærd og omfanget af C&amp;R samt ikke mindst viden om skadesomfanget på havørred i saltvand efter genudsætning og dets konsekvenser på overlevelse og vækst er fåtallige. I denne undersøgelse anvendtes en kombination af borgervidenskab (citizen science) og standardiseret lystfiskeri i et større forsøgsbassin med havvand til at undersøge C&amp;R praksis hos danske havørredfiskere, og hvordan C&amp;R påvirker overlevelse og vækst af havørred op til 29 dage efter genudsætning i saltvand. Citizen science data bekræftede, at C&amp;R er meget almindeligt i det danske lystfiskeri, da omkring 80% af alle havørreder genudsættes, hovedsageligt fordi de er under mindste landingsstørrelse. En væsentlig del (68%) af havørreder over det lovpligtige mindstemål genudsættes også. Citizen science data indikerede, at 25% af de havørreder, der bliver fanget på kysten bløder, hvoraf 2% bløder kraftigt. Blødning var relateret til krogningssted (dybtkrogede fisk blødte mest) og fiskemetode (fluefangede havørreder blødte mindre end fisk fanget ved spinnefiskeri), men disse to faktorers rolle varierede med fiskens længde. Standardiseret lystfiskeri i saltvandsbassinet bekræftede, at blødning er almindelig blandt lystfiskerfangede havørreder, og også her var der forskelle mellem fiskemetoder. Da forsøget blev afsluttet 26-29 dage efter fangst og genudsætning, fandtes der ingen dødelighed og ingen forskelle i vækst mellem en kontrolgruppe og de tre behandlingsgrupper fanget under standardiseret eksperimentelt lystfiskeri. De fleste fisk havde ingen eller kun mindre krogskader ved den afsluttende inspektion. I alt 6% af havørrederne viste tegn på dårlig sårheling og infektioner, og denne gruppe viste også en tendens til nedsat vækst. Samlet set indikerer resultaterne, at negative effekter ved C&amp;R på kystnære havørreder generelt er få og derfor formentligt ikke udgør en begrænsende faktor for bestanden. Vi anbefaler supplerende undersøgelser, der kigger på, om dette også gør sig gældende ved højere vandtemperaturer.Skarvs prædation på små havørred blev undersøgt ved hjælp af radiotelemetri i Odense Fjord. I alt 51 havørreder (27-40 cm) blev fanget på stang og fik en radiosender implanteret og derefter udsat igen. Der blev pejlet jævnligt fra båd fra marts til maj, og der afsluttedes med pejling fra fly. Efter 4 måneder var mindst otte af disse ædt af skarver og mindst to fanget af sportsfiskere. Det vil sige, at der var en prædation på mindst 14% på de små havørreder i Odense Fjord. Denne prædation er betydelig, men noget mindre, end hvad man typisk finder i forhold til prædation på udvandrende ørredsmolt, der oftest er over 50%. De 7 sendere blev fundet på skarvers nat-rastepladser og kun én i kolonien på Vigelsø, hvilket tyder på, at prædationen mest fandt sted om vinteren.For at teste om udsætningstidspunkt og måde har betydning for prædationsrisiko fra skarv, blev i alt 2000 PIT-mærkede opdræts ørredsmolt udsat på Sydfyn, fordelt på 4 grupper 1) udsat om morgenen i åen, 2) udsat om morgenen spredt på kysten, 3) udsat om aftenen i åen og 4) udsat om aftenen spredt på kysten. Efterfølgende blev der skannet efter disse mærker i en skarvkoloni i området. I alt 411 af de 2000 mærker blev fundet og analyserne af disse viste, at de grupper af fisk, der blev udsat spredt på kysten, var udsat for lidt mindre prædation (17,6%) end de, der blev udsat samlet i å-mundingen (23,4%). Udsætning morgen eller aften gjorde derimod ikke nogen forskel for risikoen for at blive ædt af skarv