Catch-and-release of Atlantic cod (Gadus morhua) in recreational fisheries

The role of recreational fisheries in the exploitation pressure on fish resources is increasingly recognized. This has led to the introduction of new harvest regulations for several European marine recreational fisheries. Such regulations have been shown to increase the practice of regulatory catch-and-release (C&R). Additionally, anglers have been shown to practice voluntary C&R due to various personal motivations. Access-point surveys in two study areas in Northern and Southern Norway found that marine angling tourists release more than 60% of their catch for several species due to regulatory and voluntary C&R. For Atlantic cod (Gadus morhua) alone, this corresponds to more than one million individuals released annually by angling tourists in Norway. A review of published, unpublished and grey literature on C&R for nine European marine recreational fisheries found that C&R is a common practice in many European countries. Among the studied European marine species caught by recreational anglers, the highest absolute release numbers were found for Atlantic cod. Impacts of C&R on Atlantic cod under best practice conditions, and the effects of different capture depths on barotrauma symptoms and post-release mortality of cod were investigated in a telemetry study and a containment study, respectively. The telemetry study showed that some cod show behavioral alterations after C&R, but can recover quickly if they are caught in shallow waters (<20 m) and properly handled before release. The containment study showed that even though cod develop several barotrauma symptoms depending on capture depth, short-term mortality due to barotrauma is negligible (assuming minimal predation) if cod submerge quickly and are otherwise not substantially injured. Based on these results and other studies, a framework for the development of best practice C&R guidelines for cod is presented. To ensure that the study findings are understood and adopted by fisheries managers and anglers, efficient communication is essential, which requires a combination of several communication channels, including scientific publications, the media and information flyers. Even though emergent animal welfare concerns could not be resolved, a better understanding of C&R impacts on cod through this thesis will hopefully contribute to improving recreational fishing practices, which subsequently may minimize sublethal C&R effects and lead to decreased post-release mortality of cod in the future

The comeback of Atlantic bluefin tuna (Thunnus thynnus) to Norwegian waters

We document that Atlantic bluefin tuna (BFT) began making a comeback from 2012 onwards into Norwegian waters, after several decades of absence, in parallel with an overall increased abundance recorded for eastern BFT. This study explores the distribution, biology and ecology of BFT reestablishing in Norwegian waters. We analyzed commercial catch and bycatch data including biological data on weight, length and age of BFT from 2016–2018. Predominantly larger (overall range in catches: 120−465 kg in weight and 184−297 cm in straight fork length (SFL)) adult individuals between 6 and 14 years old have recently started to revisit Norwegian waters. Numerous recently documented BFT observations were reported in this study, and a significant increase was detected from 2012 (n = 1) to 2018 (n = 105) (p < 0.01). Schools of BFT were observed predominantly from June to December, including the northernmost registered observation in history recorded at 76.2 °N in September 2018. Atlantic bluefin tuna has now reestablished and has shown a positive comeback to its historical migration patterns in Norwegian waters, where it has expanded its feeding areas towards the north.publishedVersio

Development and evaluation of dynamic catch control devices in the demersal seine fisheries for cod (Gadus morhua)

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Targeted risk assessment of mercury exposure of recreational fishers: Are nephrops fishers in Norway at risk?

Recreational fishers often consume their catch, which may expose them to environmental contaminants. However, targeted risk assessment for exceeding the tolerable weekly intake (TWI) of a specific contaminant is often lacking, as specific data on the extent of fishing, consumption rates, and contamination of the caught seafood is needed. This study examined recreational fishing for nephrops (Nephrops norvegicus) at several different locations in Western Norway to identify important risk factors. The combination of a field survey to examine actual catches, interviews of recreational fishers about their seafood eating habits, and the analysis of total mercury (Hg, as a proxy for methylmercury (MeHg)) in recreationally captured nephrops allowed to conduct a targeted risk assessment. Recreational fishers consumed on average seven nephrops per meal, and 73% of the fishers ate nephrops once a month or more. The average Hg concentrations in nephrops were below the legal maximum level (100 ± 50 μg/kg wet weight (mean ± SD)). Hg concentrations in female nephrops were significantly higher than in males at the same size, and differed significantly between locations. The recreational fishers in this study were not at risk of exceeding the TWI for MeHg from consuming nephrops only; however, there is a general risk of exceeding TWI for MeHg as 70% of the fishers reported a frequent consumption of fish for dinner. Targeted risk assessments on recreational fishers may reveal particularly vulnerable populations where national dietary surveys may miss the highest seafood consumers.publishedVersio

Hook shedding and post-release fate of deep-hooked European eel

-The European eel (Anguilla anguilla) is a commercially and recreationally important fishery target species. In the last decades, the eel has experienced dramatic stock declines and has been listed as critically endangered. To reduce fishing mortality, several European countries have closed the fishery or introduced stricter management measures which increase the likelihood of catch-and-release in the recreational fishery. This study investigated hook shedding mechanisms of deep-hooked, line-cut eels via radiography, and quantified hook shedding rates, post-release mortality and sub-lethal effects in captivity. Eels were caught with four different hook treatments, monitored in a tank for 23 weeks, and radiographed 0, 1, 3, 10, 24, 54, 115 and 163 days after capture. After 163 days, total hook shedding rate was significantly higher for smaller hooks (41.2%) compared to larger hooks (0.0%), and increased with fish length. Post-release mortality rates ranged between 27.3% and 50.0% after 23 weeks (not adjusted for handling and holding) and did not differ significantly between hook treatments. The majority of dead eels showed gastric perforations caused by the hooks leading to internal haemorrhaging and the intrusion of digestive fluids into the body cavity inducing lethal degradation and inflammation of vital organs. Anglers are encouraged to minimise bycatch of eel in countries where eel harvest is prohibited. Anglers targeting eel should use selective and appropriate fishing gears, baits and tactics (e.g. very large hooks, immediate hook setting after a bite) to reduce deep hooking and the catch of undersized eels, ultimately promoting the eel's conservation

Bærekraftig fisketurisme: Muligheter og utfordringer på Helgeland. En skisse til forskningsagenda.

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Catch and release angling for sea trout explored by citizen science: Angler behavior, hooking location and bleeding patterns

Sea trout (anadromous brown trout, Salmo trutta L.) is a popular target species for angling in Denmark and many other countries. In most regions, angling for sea trout is regulated by measures such as minimum landing sizes, bag limits or seasonal closures. This can lead to high catch and release (C&R) rates. However, information about angler behavior, C&R practices, hooking locations and level of injury and bleeding, as well as post-release impacts on survival and growth, is largely missing for this species. In this study, we used a citizen science approach to investigate C&R practices of Danish sea trout anglers and to explore drivers for hooking location and bleeding. During the study period from January 2016 to August 2021, 35,826 sea trout caught by angling were reported by users of the citizen science platform. Spin fishing was the most popular angling method (46 %), followed by fly fishing (35 %), bombarda fishing (19 %) and natural bait fishing (1 %). The results confirmed that C&R is a very widespread practice among Danish sea trout anglers, and ≥80 % of all sea trout captured are being released, the majority because they are below the minimum landing size. Twenty-five percent of the caught sea trout bled, and 2 % showed heavy bleeding. Bleeding was related to hooking location (deeply hooked fish bled the most) and to angling method (fly-caught sea trout bled less than fish caught on spin fishing gear), but the role of these two factors varied with fish length. When looking at fish above the legal minimum size, the share of bleeders among the released sea trout was significantly lower compared to harvested fish, suggesting that anglers were more prone to harvest fish that bled. Further studies on lethal and sublethal effects of C&R on coastal sea trout are needed, ultimately aiming to provide fishery managers and anglers with species- and fishery-specific best practice C&R guidelines.publishedVersio

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

Estimating and mitigating post-release mortality of European eel by combining citizen science with a catch-and-release angling experiment

Several anguillid eel species have experienced severe population declines over the past decades, particularly the European eel (Anguilla anguilla), which is listed as critically endangered by the International Union for Conservation of Nature. To reduce fishing mortality, many European countries have introduced strict recreational eel fishing regulations increasing regulatory catch-and-release (C&R) practice. Despite high release rates, only limited information exists on the potential consequences of C&R on eels. A field experiment was conducted with pre-tagged eels in a semi-natural environment to investigate lethal and sublethal impacts of C&R. The experiment was combined with a citizen science study evaluating the effects of different hooks on catch rates, fish size, and hooking location to develop best practice guidelines. Short-term mortality (≤72 h) ranged from 0.0–18.2%, and adjusted long-term mortality (>72 h) from 0.0–46.2% depending on treatments, resulting in adjusted total mortality rates between 8.4% and 64.4% at the end of the study period (≥43 d). The only significant predictor of mortality was the occurrence of bleeding from hooking injuries. Deep hooking was common, and only few deep-hooked eels for which the fishing line was cut and the hook left in place shed the hook after release. However, no significant effect of C&R on eel condition was found. The citizen science study showed that anglers can significantly decrease the catch of small eels, and thus release rates, by using large J-hooks. Furthermore, large J-hooks or circle hooks reduced the likelihood of deep hooking compared to small J-hooks. Post-release mortality of eels caught in recreational fisheries needs to be considered in future stock assessments and management plans to ensure conservation of the European eel. This study also highlights the strength of combining citizen science with experimental studies to develop best practice guidelines promoting fish conservation.publishedVersio