Data‐poor stock assessment of fish stocks co‐exploited by commercial and recreational fisheries: Applications to pike Esox lucius in the western Baltic Sea

Information on catch and effort of recreational angling in mixed‐use fisheries (co‐exploited by commercial and recreational fishers) is often scarce, preventing the application of data‐rich stock assessments typically performed for industrialised commercial fisheries. This study shows how data‐poor stock assessment methods developed for marine fisheries, particularly a model class labelled as “catch‐only” models (COMs), offer a possible solution. As a case study, COMs are used to assess a northern pike Esox lucius L. stock around the German Baltic island of Rügen. Multiple COMs were fitted to a time series of total pike removals, and their outputs were used as explanatory variables in ensemble models. The stock was found to be fully exploited and currently declining. This study highlights the potential for using COMs to determine status of previously unassessed coastal and freshwater stocks facing recreational fishing pressure and demonstrates how incorporating recreational removals is crucial for achieving reliable insights into the status of mixed‐use stocks.European Maritime Fisheries Fund (EMFF) of the EU and the State of Mecklenburg‐Vorpommern (Germany)Peer Reviewe

Data-poor stock assessment of fish stocks co-exploited by commercial and recreational fisheries: Applications to pike Esox lucius in the western Baltic Sea

Information on catch and effort of recreational angling in mixed-use fisheries (co-exploited by commercial and recreational fishers) is often scarce, preventing the application of data-rich stock assessments typically performed for industrialised commercial fisheries. This study shows how data-poor stock assessment methods developed for marine fisheries, particularly a model class labelled as "catch-only" models (COMs), offer a possible solution. As a case study, COMs are used to assess a northern pike Esox lucius L. stock around the German Baltic island of Rugen. Multiple COMs were fitted to a time series of total pike removals, and their outputs were used as explanatory variables in ensemble models. The stock was found to be fully exploited and currently declining. This study highlights the potential for using COMs to determine status of previously unassessed coastal and freshwater stocks facing recreational fishing pressure and demonstrates how incorporating recreational removals is crucial for achieving reliable insights into the status of mixed-use stocks

Challenges to fisheries advice and management due to stock recovery

AbstractDuring the 20th century, many large-bodied fish stocks suffered from unsustainable fishing pressure. Now, signs of recovery are appearing among previously overfished large-bodied fish stocks. This new situation raises the question of whether current fisheries advice and management procedures, which were devised and optimized for depleted stocks, are well-suited for the management of recovered stocks. We highlight two challenges for fisheries advice and management: First, recovered stocks are more likely to show density-dependent growth. We show how the appearance of density-dependent growth will make reference points calculated with current procedures inaccurate. Optimal exploitation of recovered large-bodied fish stocks will therefore require accounting for density-dependent growth. Second, we show how a biomass increase of large-bodied piscivorous fish will lead to a reverse trophic cascade, where their increased predation mortality on forage fish reduces forage fish productivity and abundance. The resulting decrease in maximum sustainable yield of forage fish stocks could lead to conflicts between forage and large-piscivore fisheries. Avoiding such conflicts requires that choices are made between the exploitation of interacting fish stocks. Failure to account for the changed ecological state of recovered stocks risks creating new obstacles to sustainable fisheries management.</jats:p

Implications of late-in-life density-dependent growth for fishery size-at-entry leading to maximum sustainable yield

AbstractCurrently applied fisheries models and stock assessments rely on the assumption that density-dependent regulation only affects processes early in life, as described by stock–recruitment relationships. However, many fish stocks also experience density-dependent processes late in life, such as density-dependent adult growth. Theoretical studies have found that, for stocks which experience strong late-in-life density dependence, maximum sustainable yield (MSY) is obtained with a small fishery size-at-entry that also targets juveniles. This goes against common fisheries advice, which dictates that primarily adults should be fished. This study aims to examine whether the strength of density-dependent growth in actual fish stocks is sufficiently strong to reduce optimal fishery size-at-entry to below size-at-maturity. A size-structured model is fitted to three stocks that have shown indications of late-in-life density-dependent growth: North Sea plaice (Pleuronectes platessa), Northeast Atlantic (NEA) mackerel (Scomber scombrus), and Baltic sprat (Sprattus sprattus balticus). For all stocks, the model predicts exploitation at MSY with a large size-at-entry into the fishery, indicating that late-in-life density dependence in fish stocks is generally not strong enough to warrant the targeting of juveniles. This result lends credibility to the practise of predominantly targeting adults in spite of the presence of late-in-life density-dependent growth.</jats:p

Assessment of the eel stock in Sweden, spring 2024

For decades, the population of the European eel has been in severe decline. In 2007, the European Union decided on a Regulation establishing measures for the recovery of the stock, which obliged Member States to implement a national Eel Management Plan by 2009. Sweden submitted its plan in 2008. According to the Regulation, Member States shall report regularly to the EU-Commission, on the implementation of their Eel Management Plans and the progress achieved in protection and restoration. The current report provides an assessment of the eel stock in Sweden as of spring 2024, intending to feed into the national reporting to the EU in August this year. This report updates and extends previous evaluation reports by Dekker (2012, 2015) and Dekker et al. (2018, 2021). In this report, the impacts on the stock - of fishing, restocking and mortality related to hydropower generation - are assessed. Other anthropogenic impacts (climate change, pollution, increased impacts of predators, spread of parasites, disruption of migration due to disorientation after transport, and so forth) probably have an impact on the stock too, but these factors are hardly quantifiable, and no management targets have been set. For that reason, and because most factors were not included in the EU Eel Regulation, these other factors are not included in this report. Our focus is on the quantification of silver eel biomass escaping from continental waters towards the ocean (current, current potential and pristine) and mortality risks endured by those eels during their whole lifetime. The assessment is broken down on a geographical basis, with different impacts dominating in different areas (west coast, inland waters, Baltic coast). In the last decade, a break in the downward trend in glass eel recruitment has been observed, with recruitment no longer declining consistently. Whether that relates to recent protective actions, or is due to other factors, is yet unclear. Nevertheless, recruitment levels remain at historically low levels. This report contributes to the required international assessment, but does not discuss the causing factors behind the recent recruitment trend and the overall status of the stock across Europe. For the different assessment areas, results summarise as follows: On the west coast, a commercial fyke net fishery on yellow eel was exploiting the stock, until this fishery was completely closed in spring 2012. A fishery-based assessment no longer being achievable, we present trends from research surveys (fyke nets). Insufficient information is currently available to assess the recovery of the stock in absolute terms. Obviously, current fishing mortality is zero (disregarding the currently unquantifiable effect of illegal fishing), but none of the other requested stock indicators (current, current potential and pristine biomass) can be presented. The formerly exploited size-classes of the stock show a recovery in abundance after the closure of the commercial fishery, and the smaller size classes show a break in their decline in line with the recent global trend of glass eel recruitment. In order to support the recovery of the stock, or to compensate for anthropogenic mortality in inland waters, young eel has been restocked on the Swedish west coast since 2010. Noting the quantity of restocking involved, the expected effect (ca. 50 t silver eel) is relatively small, and hard to verify – in comparison to the potential natural stock on the west coast (an order of 1000 t). However, for the currently depleted stock, the contribution will likely constitute a larger share of silver eel escapement. For inland waters, this report updates the 2021 assessment, with substantial changes in methodology being the use of a new natural recruitment model, and the full separation of Trap & Transport catches from the fisheries statistics. The assessment for the inland waters relies on a reconstruction of the stock from information on the youngest eels in our waters (natural recruits, assisted migration, restocking). Based on 78 years of data on natural recruitment into 22 rivers, a statistical model is applied which relates the number of immigrating young eel caught in traps to the location and size of each river, the distance from the trap to the river mouth, and the year in which those eels recruited to continental waters as a glass eel (year class). The further into the Baltic, the larger and less numerous recruits generally are. Distance upstream comes with less numerous recruits. Using the results from the above recruitment analysis, in combination with historical data on assisted migration (young eels transported upstream within a drainage area, across barriers) and restocking (young eels imported into a river system), we have a complete overview of how many young eels recruited to Swedish inland waters. From this, the production of fully grown silver eel is estimated for every lake and year separately, based on best estimates of growth and natural mortality rates. Subtracting the catch made by the fishery (as recorded) and down-sizing for the mortality incurred when passing hydropower stations (percentwise, as recorded or using a default percentage), an estimate of the biomass of silver eel escaping from each river towards the sea is derived. Results indicate, that since 1960, the production of silver eel in inland waters has declined from over 700 to below 300 tonnes per year (t/yr). The production of naturally recruited eels is still falling; following the increase in restocking since 2010, an increase in restocking-based production is expected to be starting right around now. Gradually, restocking has replaced natural recruitment (assisted and fully natural), now making up over 90 % of the inland stock. Fisheries have taken 20-30 % of the silver eel (since the mid-1980s), while the impact of hydropower has ranged from 25 % to 60 %, depending on the year. Escapement is estimated to have varied from 72 t in the late 1990s, to 175 t in the early 2000s. The biomass of current escapement (including eels of restocked origin) is approximately 15 % of the pristine level (incl. restocked), or almost 30 % of the current potential biomass (incl. restocked). This is below the 40 % biomass limit of the Eel Regulation, and anthropogenic mortality (70 % over the entire life span in continental waters) exceeds the limit implied in the Eel Regulation (60 % mortality, the complement of 40 % survival). Mortality being that high, Swedish inland waters currently do not contribute to the recovery of the stock. The temporal variation (in production, impacts and escapement) is partly the consequence of a differential spatial distribution of the restocking of eel over the years. The original natural (not assisted) recruits were far less impacted by hydropower, since they could not climb the hydropower dams when immigrating. Since 2010, inland restocking is increasingly concentrated to drainage areas falling to the Kattegat-Skagerrak, also including obstructed lakes (primarily Lake Vänern, and many smaller ones). Even though Trap & Transport of silver eel - from above barriers towards the sea - has contributed to reducing the hydropower impact, hydropower mortality remains the largest estimated contributor to silver eel mortality in inland waters. Without restocking, the biomass affected by fishery and/or hydropower would be only 5-10 % of the currently impacted biomass, but the stock abundance would reduce from 15 % to less than 3 % of the pristine biomass. In summary: the inland eel stock biomass is below the minimum target, anthropogenic impacts exceed the minimum limit that would allow recovery, and those impacts have been increasing. It is therefore recommended to reconsider the current action plans on inland waters, taking into account the results of the current, comprehensive assessment. For the Baltic coast, the 2021 assessment has been updated without major changes in methodology. Results indicate that the impact of the fishery continues to decline over the decades. The current impact of the Swedish silver eel fishery on the escapement of silver eel along the Baltic Sea coast is estimated at 0.3 %. However, this fishery is just one of the anthropogenic impacts (in other areas/countries) affecting the eel stock in the Baltic, including all types of impacts, on all life stages and all habitats anywhere in the Baltic. Integration with the assessments in other countries has not been achieved. Current estimates of the abundance of silver eel (biomass) indicates an order of several thousand tonnes, but those estimates are extremely uncertain, due to the low impact of the fishery (near-zero statistics). Moreover, these do not take into account the origin of those silver eels, from other countries. An integrated assessment for the whole Baltic will be required to ground-truth these estimates. This would also bring the eel assessments in line with the policy to regionalise stock assessments for other (commercial) fish species (see https://ec.europa.eu/oceans-and-fisheries/fisheries/rules/multiannual-plans_en). It is recommended to develop an integrated assessment for the entire Baltic Sea eel stock, and to coordinate protective measures with other range states

Stress hos europeisk ål under sumpning och transport

Fångst och transport används för att transportera fisk förbi hinder som blockerar dess vandringsväg. Den europeiska ålen, Anguilla anguilla, är en art där fångst och transport används som en bevarandeåtgärd. Fångst och transport av ål utförs genom att samla in vuxen ål, så kallad blankål, i sjöar och andra vattendrag, transportera dem förbi vattenkraftverk och dammar, och släppa ut dem i havet eller nedströms vandringshinder. Förhoppningen med denna åtgärd är att öka mängden blankål som kan fullborda sin vandring till Sargassohavet där de reproducerar sig. Under fångst och transport hanteras ålen i flera steg. Först fångas de med ett fiskeredskap eller samlas in med utvandringsfällor, därefter sumpas de en tid (i vissa fall sker transporten direkt efter insamling), för att sedan transporteras till platsen där de släpps ut. Dessa hanteringsmoment innebär en påverkan på ålen som kan leda till direkt dödlighet. Hanteringen kan även öka stress och orsaka skador på ålen, vilket i sin tur kan leda till förhöjd dödlighet senare.I den här studien har vi mätt hjärtrytm på ål med kirurgiskt implanterade elektroniska loggar, så kallade biologgers. Hjärtrytmen är en indikator på stress under sumpning och transport. Studien startade under 2023, men på grund av ovanligt kalla vattentemperaturer under de märkningsförsök som utfördes under sommaren 2023 samlades inget data in för normalt höga sommartemperaturer. I denna rapport redovisas resultat för kompletterande försök utförda under mer representativa temperaturer sommaren 2024. Vi har också analyserat ålder från hörselstenar (otoliter) från ål som ingick i försöket 2023 för att undersöka om ålarnas ålder skiljde sig åt mellan olika lokaler. En skillnad i ålder skulle kunna påverka hjärtfrekvensen och är därför viktig att ta reda på.Ingen ål dog under märkning eller den hantering som skedde i fångst- och transport-processen. Ålens hjärtfrekvens under fångst och transport ökade tydligt med ökande vattentemperatur. Detta var förväntat baserat på tidigare forskning och resultaten från försöken som utfördes under 2023. För att kontrollera för effekten av vattentemperatur på hjärtfrekvens undersöktes skillnaden mellan observerad (uppmätt hjärtfrekvens från denna studie) och predikterad hjärtfrekvens (baserat på tidigare utförda kontrollförsök). Vi fann att skillnaden mellan observerad och predikterad hjärtfrekvens var störst direkt efter märkningen, och att det även fanns en skillnad under transport, men inte under sumpning. Resultaten tyder på ökad hjärtfrekvens, och därmed ökad stress, direkt efter märkning och under transport, och det följer i stort sett resultaten från försöken utförda vid Vänern 2023, med skillnaden att differensen mellan observerad och predikterad hjärtfrekvens var högre under detta försök. Åldersanalysen av otoliter från ål som ingick i försöket 2023 visade att ålen i genomsnitt var 20 år gammal, och att det inte var någon skillnad i ålder mellan de undersökta lokalerna.Vår slutsats är att hjärtfrekvensnivåerna under fångst och transport inte var så höga att de orsakade någon direkt dödlighet vid de vattentemperaturer som uppmättes under de märkningsförsök som utförts under 2023 och 2024 (8–22°C). Vid höga vattentemperaturer var skillnaden mellan observerad och predikterad hjärtfrekvens generellt större, framför allt under transport. Sammantaget tyder resultaten på att fångst och transport som sker vid vattentemperaturer lägre än ~16°C under sumpning och ~19°C under transport inte leder till ökad mortalitet. Däremot tyder resultaten på ökad stress under transport då sumpningstemperaturen varit ~16°C jämfört med ~13°C

Stress hos europeisk ål under sumpning och transport : effekter av fångst and transport

Fångst och transport, så kallad ’trap and transport’, används för att transportera fisk förbi hinder som blockerar dess vandringsväg. Metoden kan användas för att transportera fisk både uppströms och nedströms vandringshinder. Fångst och transport används ofta för att bevara fiskpopulationer och ekosystemfunktioner, men kan också användas för att förbättra möjligheterna till fiske i områden uppströms vandringshinder. Den europeiska ålen, Anguilla anguilla, är en art där fångst och transport används som en bevarandeåtgärd. Ålen har minskat kraftigt och är rödlistad som akut hotad av den internationella naturvårdsunionen (IUCN). Genom att samla in vuxen ål, så kallad blankål, i sjöar och andra vattendrag, transportera dem nedströms vattenkraftverk och dammar, och släppa ut dem i havet eller nedströms vandringshinder, är förhoppningen att öka mängden blankål som kan fullborda sin vandring till Sargassohavet där de reproducerar sig. Om metoden verkligen fungerar är i dagsläget okänt eftersom vi inte lyckats följa någon ål på hela dess vandring från Europas kuster till Sargassohavet. Det är däremot känt att passager genom turbiner medför dödlighet för den blankål som vandrar nedströms, varför det kan antas att fångst och transport åtminstone initialt minskar dödligheten. Under fångst och transport hanteras ålen i flera steg då de först fångas in med ett fångstredskap, därefter sumpas de en tid (i vissa fall sker transporten direkt efter insamling), för att sedan flyttas till en transporttank på en bil för att köras till platsen där de släpps ut. Dessa hanteringsmoment innebär en påverkan på ålen som kan leda till direkt dödlighet. Hanteringen kan även öka stress och orsaka skador på ålen, vilket i sin tur kan leda till förhöjd dödlighet senare, vilket har en negativ påverkan på ålens möjlighet att nå Sargassohavet och reproducera sig.I det här projektet har vi undersökt stressnivåer hos ål genom alla steg som ingår i fångst och transport inom ramen för den kompensatoriska åtgärd som finansieras av program Krafttag ål. Genom att kirurgiskt implantera elektroniska loggrar, så kallade biologgers, kunde vi mäta ålarnas hjärtrytm, vilket sedan användes som en indikator för att tolka stressnivå. Detta gjordes på två lokaler där fångst och transport normalt sett utförs, där metoden (utöver implantering av biologgers) efterliknade normal hantering under fångst och transport av ål. Försöken utfördes under vår, sommar och höst år 2023. För att samla in data över kontrollvärden, eller basnivåvärden, på ålens hjärtrytm under relativt ostörda förhållanden förvarades ål med biologgers i en miljö som var gjord för att minska stress så mycket som möjligt. Resultaten visade att överlevanden var hög under fångst och transport då ingen ål dog under hanteringsmomenten. Ålens respons på hantering under fångst och transport var tydligt påverkad av vattentemperatur, ålarnas hjärtfrekvens var generellt högre och ökade mer under hantering vid höga vattentemperaturer. Under tiden som ålen förvarades i sump var stressnivåerna relativt låga, för att sedan öka igen då de hanterades under transporten. Stressnivåerna var höga under hela transporttiden.Vår slutsats är att stressnivåerna under fångst och transport inte var så höga att de orsakade någon dödlighet vid de vattentemperaturer som uppmättes under märkningsförsöken (8–18° C). Vid höga vattentemperaturer var hjärtfrekvensen generellt högre, framför allt under transport. Om fångst och transport sker vid vattentemperaturer under 18–19° C så kan denna åtgärd öka möjligheterna för blankål att vandra mot Sargassohavet. Eftersom ålen utsätts för stress och hantering, samt att metoden kräver mänsklig inverkan, så bör det slutgiltiga målet vara att skapa fria vandringsvägar runt vandringshinder

A randomized physiotherapy trial in patients with fecal incontinence: design of the PhysioFIT-study

<p>Abstract</p> <p>Background</p> <p>Fecal incontinence (FI) is defined as the recurrent involuntary excretion of feces in inappropriate places or at inappropriate times. It is a major and highly embarrassing health care problem which affects about 2 to 24% of the adult population. The prevalence increases with age in both men and women.</p> <p>Physiotherapy interventions are often considered a first-line approach due to its safe and non-invasive nature when dietary and pharmaceutical treatment fails or in addition to this treatment regime. Two physiotherapy interventions, rectal balloon training (RBT) and pelvic floor muscle training (PFMT) are widely used in the management of FI. However, their effectiveness remains uncertain since well-designed trials on the effectiveness of RBT and PFMT versus PFMT alone in FI have never been published.</p> <p>Methods/Design</p> <p>A two-armed randomized controlled clinical trial will be conducted. One hundred and six patients are randomized to receive either PFMT combined with RBT or PFMT alone. Physicians in the University Hospital Maastricht include eligible participants. Inclusion criteria are (1) adults (aged ≥ 18 years), (2) with fecal incontinence complaints due to different etiologies persisting for at least six months, (3) having a Vaizey incontinence score of at least 12, (4) and failure of conservative treatment (including dietary adaptations and pharmacological agents). Baseline measurements consist of the Vaizey incontinence score, medical history, physical examination, medication use, anorectal manometry, rectal capacity measurement, anorectal sensation, anal endosonography, defecography, symptom diary, Fecal Incontinence Quality of Life scale (FIQL) and the PREFAB-score. Follow-up measurements are scheduled at three, six and 12 months after inclusion. Skilled and registered physiotherapists experienced in women's health perform physiotherapy treatment. Twelve sessions are administered during three months according to a standardized protocol.</p> <p>Discussion</p> <p>This section discusses the decision to publish a trial protocol, the actions taken to minimize bias and confounding in the design, explains the choice for two treatment groups, discusses the secondary goals of this study and indicates the impact of this trial on clinical practice.</p> <p>Trial registration</p> <p>The Netherlands Trial Register ISRCTN78640169.</p