| 1. |
- Vallin, Lars, et al.
(författare)
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Maternal effects on egg size and egg buoyancy of Baltic cod, Gadus morhua : Implications for stock structure effects on recruitment
- 2000
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Ingår i: Fisheries Research. - Amsterdam : Elsevier. - 0165-7836 .- 1872-6763. ; 49:1, s. 21-37
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Tidskriftsartikel (refereegranskat)abstract
- Successful spawning of cod in the Baltic is restricted to the deep basins: the Bornholm basin, the Gdansk Deep and the Gotland basin, at salinities varying between 11 and 20 psu. Due to oxygen-depletion commonly prevailing in these areas, neutral egg buoyancy above oxygen-critical levels is of substantial importance for egg and larval survival in the Baltic. In the present study, large females were found to produce larger eggs with neutral egg buoyancy at a lower salinity, implying egg development in more favourable oxygen conditions. An age- and batch-specific model of egg production, egg size and egg buoyancy showed a substantial increase in the probability of egg survival with female age. The relationship between egg production by old females and subsequent recruitment was tested in two separated periods with different conditions: 1967-1980 and 1981-1994. The number of recruited cod (age 2), in the Baltic Sea, was positively related to the fraction of eggs produced by old females ( greater than or equal to 5 years). That recruitment was positively related to the proportion of eggs spawned by old fish reveals that stock age structure should be seriously considered in stock-recruitment relationships and in the management of the cod stock in the Baltic.
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| 2. |
- Andersson, Anders, 1980-, et al.
(författare)
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Recreational trolling effort and catch of Atlantic salmon and brown trout in Vänern, the EU's largest lake
- 2020
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Ingår i: Fisheries Research. - : Elsevier. - 0165-7836 .- 1872-6763. ; 227
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Tidskriftsartikel (refereegranskat)abstract
- Recreational fishing has grown substantially worldwide; for some recreational fisheries both catch and economic value now exceeds that of commercial fisheries. Monitoring of recreational fisheries effort and catch is therefore important for sustainable fisheries management. We developed and implemented an angler survey to estimate effort and catch for the recreational trolling fishery for landlocked Atlantic salmon (Salmo salar) and brown trout (S. trutta) in Lake Vänern, Sweden. Major challenges were the large spatial scale and dispersed fishing effort, a lack of revenue from fishing licence sales, and a lack of catch reporting requirements. We developed a complemented roving/mail-in survey to estimate effort and catch during the main fishing periods, spring and fall, 2014. Instantaneous counts from major access sites were used for effort estimates, and mail-in surveys were used for catch rates. Our results show that Vänern supports a salmon and trout fishery of some 28.7 ± 3.3 tonnes per year. Fishing effort was higher in the spring than in the fall, and there were seasonal differences in catch rates for trout but not for salmon. Estimates show that the recreational trolling fishery now harvests more salmon and trout annually than do the commercial and subsistence fisheries combined. This highlights the importance of continuing an angler survey program for Vänern as a key element for sustainable fisheries management, and can serve as a model for other recreational fisheries at large spatial scales.
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| 3. |
- Andersson, Magnus, et al.
(författare)
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Short-term tagging mortality of Baltic cod (Gadus morhua)
- 2021
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Ingår i: Fisheries Research. - : Elsevier BV. - 0165-7836 .- 1872-6763. ; 234
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Tidskriftsartikel (refereegranskat)abstract
- Tagging-induced mortality experiments are an important component of mark-recapture studies, as they can be used to assess the appropriateness of the tagging methodology, and to improve the reliability of estimates of recapture rates used for calculations of mortality rates and population size. Here, short-term tagging mortality of Baltic cod was estimated through containment experiments in the southern Baltic Sea. Experimental cod were selected from trawl catches, and approximately half were tagged externally with T-bar tags and received an intraperitoneal injection of tetracycline-hydrochloride. The rest of the experimental cod formed the control group, and received neither tag nor injection. The tagged and control cod were mixed evenly within submersible cages, and held for 5-8 days. The experiments were conducted in different regions and during different months by different tagging teams. Overall mortality rate was 16 % (n = 324), with the mortality rate of the tagged group 19 %, and the mortality rate of the control group 13 %. A general linear mixed model was fit to assess the effect of tagging, month, experiment duration, fish length and tagging site (i.e. the combined effect of region and tagging team) on mortality. Tagging had no effect on mortality, indicating that mortality can be attributed mainly to the capture and handling procedure. There was a significantly negative relationship between fish length (range: 20-55 cm) and mortality. Mortality did not differ between the months tested, but there was a significant effect of tagging site on mortality. Tagging-related mortality should be accounted for in analyses of data from mark-recapture studies of Baltic cod, and some variability in mortality between tagging sites can be expected.
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| 4. |
- Appelberg, Magnus
(författare)
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What is left and what was achieved? A time perspective of a pioneering project 20 years after the European Fish Ageing Network
- 2022
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Ingår i: Fisheries Research. - : Elsevier BV. - 0165-7836 .- 1872-6763. ; 252
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Tidskriftsartikel (refereegranskat)abstract
- The European Fish Ageing Network (EFAN) funded by the European Union, is reviewed, and assessed after a 20 year hiatus. The large number of scientists and technicians involved in this independent and informal network, and the time invested (four years), provided a significant advance in fish age estimation and methodologies. The results presented are based on two survey questionnaires sent to EFAN members, specifically to those who had been most actively involved in the programme. Overall, EFAN can be considered as successful as it fulfilled the aim of the FAIR (Fostering Awareness Inclusion and Recognition) program in improving collaboration both at a national and European levels in the field of sclerochronology. Adding to the success was that many survey participants reported a positive impact on both their creativity and scientific careers, particularly participants from university environments and the female members, and around 50% of the participants continued in their age-related research careers. These factors, as well as the positive scientific impact EFAN has had in various European countries (n = 16), point to a very successful programme. The aim of improving what is an objective approach required to interpret growth increments in calcified structures (otoliths) in fishes, is reflected in the various tools developed by EFAN, all of which are found in the many reports produced by the Network. Examples are seen in the quality control approach by the International Council for the Exploration of the Sea (ICES), where tools developed by EFAN have been key to their fisheries management approach. Our general impression is that a project with a lifetime of around four years in principle provides a suitable time period to develop age estimation tools, quality control routines, and working procedures to improve the use of fish age data for fish stock assessments. We argue however, that developing a functioning network requires more time than a conventional project. Therefore, to fully meet the aims of projects such as EFAN, a period of between 10 and 15 years is a more appropriate time frame for these types of programmes to run. A longer time scale can help ensure recommendations are regularly followed, can provide more confidence in on-going routine age estimation data, and so achieve a significant improvement in the application of ageing methods. In turn a more accurate and robust scientific outcome would be available for European fish stock assessments.
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| 5. |
- Axenrot, Thomas, et al.
(författare)
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Year-class strength, physical fitness and recruitment cycles in vendace (Coregonus albula)
- 2016
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Ingår i: Fisheries Research. - : Elsevier BV. - 0165-7836 .- 1872-6763. ; 173, s. 61-69
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Tidskriftsartikel (refereegranskat)abstract
- Vendace, an obligate zoo-planktivore through all life stages, is a key-stone species in many large lakes in northern Eurasia. Vendace often produces strong year-classes in cycles of various length. To better understand the factors that determine the emergence of strong year-classes we analyzed long time-series hydroacoustic data on abundance of young-of-the-year and older vendace, and representative samples of vendace from trawl catches measured for length, weight and age. Data were collected in the three largest lakes in Sweden - Lakes Vanern, Vattern and Malaren - for 1995-2012, 1992-2012 and 2008-2012, respectively. The lakes range from ultra-oligotrophic to mesotrophic. In L. Vanern there is an extensive commercial fishery on vendace, whereas the fishery, at present, is small in L. Malaren and negligible in L. Vattern. Size of mature vendace, expressed as 90% of L-max, differed between the lakes and was positively correlated with lake nutrient levels. Strong year-classes did not occur in synchrony between lakes, not even between the two main basins within oligotrophic L. Vanern, and were less frequent in the ultra-oligotrophic and commercially unfished L. Vattern. Strong year-classes negatively affected physical fitness (Fulton's condition factor) of older fish. During years of low physical fitness in sexually mature fish no strong year-classes would appear. Recovery of physical fitness might take several years and depended on food availability, expressed as nutrient levels or population density. Not until fish had regained individual physical fitness and could allocate energy to gonads, other factors - as physical environmental conditions - might become important for the emergence of a strong year-class. (C) 2015 Elsevier B.V. All rights reserved.
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| 6. |
- Bartolino, Valerio
(författare)
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First implementation of a Gadget model for the analysis of hake in the Mediterranean
- 2011
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Ingår i: Fisheries Research. - : Elsevier BV. - 0165-7836 .- 1872-6763. ; 107, s. 75-83
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Tidskriftsartikel (refereegranskat)abstract
- An age-length structured model was built for European hake Merluccius merluccius in the central Mediterranean Sea using Gadget. This analytical framework allowed to integrate multiple sources of information, including fisheries-dependent and fisheries-independent data, collected at different scales and aggregation levels. The model includes the two main fisheries targeting hake in the area, the trawl and the gillnet fisheries, and account for differences in their selectivity and effort. Alternative models were used for testing different assumptions on recruitment and growth. The model is then used to predict the main trajectory of the stock during the next years and to evaluate the potential effects of implementing closed areas management scenarios in the hake nurseries as a specific tool to reduce fishing mortality on recruits. The modelling framework presented performed successfully also in a commercial landing data limited context, common for the Mediterranean. Our results provide statistical support for fast growth and multiple recruitment events assumptions. Including both these key features represent an unprecedented improvement of modelling hake population dynamics in the Mediterranean. We found that the reduction in the fishing effort that characterized the fisheries in the study area during the last few years, coupled with fast recovery abilities of the hake stock, has the potentiality to allow a moderate increase of the stock during the next years. Interestingly, our simulations show that the positive effects which might be expected from protecting hake nursery grounds are only marginally related to a reduction in hake recruits fishing mortality. Although our model relies on assumptions and surely represents an over-simplification of the real world, it still contributed to improve our understanding of the temporal dynamics of one of the most valuable fish stocks in the central Mediterranean. (c) 2010 Elsevier B.V. All rights reserved.
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| 7. |
- Bergström, Ulf, et al.
(författare)
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Long-term decline in northern pike (Esox lucius L.) populations in the Baltic Sea revealed by recreational angling data
- 2022
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Ingår i: Fisheries Research. - : Elsevier BV. - 0165-7836 .- 1872-6763. ; 251
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Tidskriftsartikel (refereegranskat)abstract
- In the Baltic Sea, the large predatory fish northern pike (Esox lucius L.) is important for both recreational fisheries and ecosystem functioning. As existing fishery-independent surveys do not adequately monitor pike populations, a general lack of knowledge on population status and trends poses challenges for management. Here we use recreational angling data as an alternative method to describe pike population development along the Swedish Baltic Sea coast from 1938 onwards and assess the change over time in potential mortality factors by estimating harvest by fisheries and consumption by large predators. Data from a Swedish national register on trophy-sized pike (>12 kg) showed that numbers and maximum sizes peaked in 1990-1995, after which declines in both metrics are evident. In logbooks from a sport fishing club in the Stockholm archipelago, a simultaneous decrease in maximum sizes of pike was observed, together with a decrease in the total number of pike caught per fishing day. Jointly, these data indicate a decline in the abundance of large pike since around 1990. While commercial pike fisheries in the Baltic Sea have decreased continuously since the 1950s, recreational fishing increased after 1985, when Swedish coastal waters were made open access to anglers. The declines in large pike starting in the 1990s could, thus, have been driven by an increase in mortality from recreational fisheries, which at the time primarily practiced catch and kill. Since the 2000s, bag and slot length limits, spawning closures, and a general increase in catch-and-release fishing has reduced the landings of pike in recreational fisheries. Despite these fisheries regulations and higher release rates the decline in catches of large pike has continued, indicating an effect of other mortality factors. The strong growth of grey seal (Halichoerus grypus) and great cormorant (Phalacrocorax carbo sinensis) populations suggest that predation pressure on pike has increased over time. In the Stockholm archipelago these two predators were estimated to remove 5-18 times (range based on different diet composition estimates) more pike biomass than total fisheries landings in 2014-2017. To improve the situation for northern pike in the Baltic Sea managers need to consider both fisheries restrictions and measures to decrease predation pressure and increase recruitment. Catch data from recreational fisheries may be used to evaluate such management efforts by providing information on the population development of this keystone species.
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| 8. |
- Blicharska, Malgorzata, 1979-, et al.
(författare)
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Recreational fishing for sea trout – Resource for whom and to what value?
- 2018
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Ingår i: Fisheries Research. - : Elsevier BV. - 0165-7836 .- 1872-6763. ; 204, s. 380-389
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Tidskriftsartikel (refereegranskat)abstract
- Recreational fishing is an important activity that delivers substantial social and economic values. Proper management of recreational fisheries relies on information about resource use and associated values by different fishers, but such information is rare, particularly for open access fisheries. In this study a survey of 471 fishers on the Swedish island of Gotland in the Baltic Sea, assessed catches, proportion of catch-and-release (C&R), and economic value (expenditures and willingness to pay, WTP) of sea trout fishing in 2015-2016. Data was analysed in relation to gear used (fly and spin angling, nets and mixed fishery) and fisher connection to fishing site (permanent and temporary residents, Swedish and international tourists). There were marginal differences in daily catch rates, but significant differences in effort and annual catches between different fishers, with resident fishers having the highest catches. Anglers had 86% C&R rates, and fly fishers (> 95%) differed significantly from other anglers. Anglers, particularly fly fishers and fishing tourists, had much higher expenditures per year, fish caught and fish kept compared to net fishers. WTP before refraining from fishing, for doubling of fish supply and for potential fishing license was also highest among anglers. Our findings are discussed in terms of distinguishing characteristics for different types of recreational fishers. Fishing efforts, economic values and the need for further studies are also outlined in the context of fisheries and tourism management.
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| 9. |
- Blyth, Samuel, et al.
(författare)
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To eat or not to eat, coastal sea trout anglers' motivations and perceptions of best practices for catch and release
- 2022
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Ingår i: Fisheries Research. - : Elsevier. - 0165-7836 .- 1872-6763. ; 254
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Tidskriftsartikel (refereegranskat)abstract
- The wide variety of perspectives and actions of individual anglers contribute greatly to success or failure when adopting and implementing fisheries management tools. Catch-and-release (C&R) is one such tool where success is influenced by both variation in human factors, but also species and fishery specific characteristics. In this study, an intercept survey of 94 sea trout anglers in a C&R dominated fishery on the Swedish island of Gotland investigated motivations to release or retain catches, self-assessment of anglers' own ability to release fish, and their rating of the importance of various factors influencing the successful outcomes of C&R. Retention of catches was most strongly motivated by situations where anglers deemed the fish unlikely to survive, however more than half of anglers acknowledged being unaware of delayed mortality in released fish. The spawning status of an individual fish was the primary motivation for release, particularly among anglers that prefer to keep at least some of their catches. The roles of water temperature, using single, and barbless hooks were scored as significantly less important than other components contributing to the success of a release. Anglers that gave a favourable rating to their ability to release sea trout also gave greater importance to various factors influencing the success of release, reported higher catch per unit effort, and released a greater proportion of their catches. These findings are discussed in the context of bridging knowledge and behavioural gaps around best practices for C&R in this fishery.
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| 10. |
- Bryhn, Andreas, et al.
(författare)
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Green lamps as visual stimuli affect the catch efficiency of floating cod (Gadus morhua) pots in the Baltic Sea
- 2014
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Ingår i: Fisheries Research. - : Elsevier BV. - 0165-7836 .- 1872-6763. ; 157, s. 187-192
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Tidskriftsartikel (refereegranskat)abstract
- This study compared catches in numbers (catch per unit effort, CPUE) and biomass (weight per unit effort, WPUE) of Atlantic cod (Gadus morhua) in two-chambered floating cod pots equipped with and without a green lamp as a form of visual stimuli in two areas. A green lamp inside the pot increased the CPUE and WPUE of cod above the maximum legal size (>38 cm) by 74 and 80%, respectively. There were no differences in CPUE and WPUE of small (<38 cm) cod caught in pots with and without a green lamp. By increasing the catch efficiency of cod green lamps could consequently be highly beneficial for the Baltic commercial cod pot fishery. (C) 2014 Elsevier B.V. All rights reserved.
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