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- Kagervall, Anders, et al.
(författare)
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Expert opinion on using angler Smartphone apps to inform marine fisheries management: status, prospects, and needs
- 2021
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Ingår i: ICES Journal of Marine Science. - : Oxford University Press (OUP). - 1054-3139 .- 1095-9289. ; 78, s. 967-978
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Tidskriftsartikel (refereegranskat)abstract
- Smartphone applications (apps) that target recreational fishers are growing in abundance. These apps have the potential to provide data useful for management of recreational fisheries. We surveyed expert opinion in 20, mostly European, countries to assess the current and future status of app use in marine recreational fisheries. The survey revealed that a few countries already use app data to support existing data collection, and that this number is likely to increase within 5–10 years. The strongest barriers to use app data were a scarcity of useful apps and concern over data quality, especially biases due to the opt-in nature of app use. Experts generally agreed that apps were unlikely to be a “stand-alone” method, at least in the short term, but could be of immediate use as a novel approach to collect supporting data such as, fisheries-specific temporal and spatial distributions of fishing effort, and aspects of fisher behaviour. This survey highlighted the growing interest in app data among researchers and managers, but also the need for government agencies and other managers/researchers to coordinate their efforts with the support of survey statisticians to develop and assess apps in ways that will ensure standardisation, data quality, and utility.
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- Neuenfeldt, Stefan, et al.
(författare)
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Feeding and growth of Atlantic cod (Gadus morhua L.) in the eastern Baltic Sea under environmental change
- 2020
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Ingår i: ICES Journal of Marine Science. - : Oxford University Press (OUP). - 1054-3139 .- 1095-9289. ; 77:2, s. 624-632
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Tidskriftsartikel (refereegranskat)abstract
- Five decades of stomach content data allowed insight into the development of consumption, diet composition, and resulting somatic growth of Gadus morhua (Atlantic cod) in the eastern Baltic Sea. We show a recent reversal in feeding level over body length. Present feeding levels of small cod indicate severe growth limitation and increased starvation-related mortality. For young cod, the low growth rate and the high mortality rate are manifested through a reduction in size-at-age. The low feeding levels are likely the result of a decrease in benthic prey abundance due to increased hypoxic areas, while decreasing abundances of pelagic species in the area of cod distribution have prevented a compensatory shift in diet. Our study emphasizes that environmental forcing and the decline in pelagic prey caused changes in consumption and growth rates of small cod. The food reduction is amplified by stunted growth leading to high densities of cod of smaller size competing for the scarce resources. The average growth rate is negative, and only individuals with feeding levels well above average will survive, though growing slowly. These results suggest that the relation between consumption rate, somatic growth and predatorprey population densities is strongly environmentally mediated.
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- Palm, Stefan, et al.
(författare)
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Workshop on Baltic salmon management plan (WKBaltSalMP)
- 2020
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Rapport (refereegranskat)abstract
- This report contains the output of the International Council for the Exploration of the Seas (ICES) workshop on evaluating a draft Baltic salmon management plan (WKBaltSalMP). The main aim was to provide scientifically based responses to a special request received from the European Commission (EC). The process included two meetings attended by scientific experts, national managers and stakeholder representatives. As requested, information on river size and estimated potential productivity was compiled and updated following consultation with national experts within ICES WGBAST (Baltic Salmon and Trout Assessment Working Group). Existing and alternative reference points for assessment of stock status and fishing opportunities were also examined. The group concluded that the currently used targets (50% and 75% of the potential smolt production capacity, PSPC) are inconsistent with the overall objective in the draft plan of achieving maximum sustainable yield (MSY). As a precautionary reference point Rlim was evaluated, defined as the lowest level of smolt production from which the stock would be expected to recover to its specific MSY-level (RMSY) in one salmon generation, if all fishing was completely closed. Simulations developed specifically for the workshop allowed evaluation of requested recovery rates of individual wild salmon stocks under alternative commercial fishing scenarios. The simulations examined commercial harvest rates ranging from 0 to 0.9 (encompassing rates that gives maximum yield in the commercial sea fisheries, located between 0.2 and 0.3; Figure 5.1.1), with additional values examined below 0.1 to better illustrate impacts on less productive river stocks. Neither the EC request nor the draft multiannual plan specify criteria for when (i.e. with what probability) a target has been reached. Therefore, stock-specific tables with simulation-based probabilities of smolt production being above alternative targets for each fishing scenario are presented. These analyses only included river stocks currently assessed analytically by ICES. For remaining stocks, such river specific probabilities could not be determined. For river stocks not assessed analytically, correlative analyses between total estimated sea survival and recruitment over generations were performed. These results indicate that sea survival seem to play an important role in the development also for these stocks, similar to for those currently included in the ICES model. A simplified stable-state population dynamics model was constructed to study trade-offs between mixed (sea) and stock-specific (river) fisheries in terms of achievable catches and proportions of stocks above/below reference points. This analysis illustrated that when the mixed fishery harvest rate is low all river stocks can achieve MSY, whereas when this harvest rate increases, smaller (less resilient) stocks fall below this target. That some smaller stocks fall below MSY (or even goes towards extinction) does not make a noticeable difference to the total yield. Hence, there exists an inbuilt conflict between overall production aims and protection of weak stocks that can only be resolved if mixed-stock sea fisheries for Baltic salmon are kept at a low level. The report also contains requested comments on the draft management plan. The workshop identified that the draft has a strict focus on commercial sea fisheries, although the relative importance of recreational fisheries for Baltic salmon has increased significantly over time. The current two management units for EU commercial fisheries (subdivisions 22 to 31 and Subdivision 32) are further maintained in the draft, whereas evidence has accumulated that salmon are migrating between these areas more than previously recognized. The draft finally does not address management of hatchery-reared Baltic salmon more than marginally, despite large ongoing releases for various purposes in most countries.
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| 5. |
- Samson, Melvin A., et al.
(författare)
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Discrimination potential of otolith chemistry to distinguish two parapatric species of flounder (Platichthys) in the Baltic Sea
- 2022
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Ingår i: Journal of Sea Research. - : Elsevier. - 1385-1101 .- 1873-1414. ; 186
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Tidskriftsartikel (refereegranskat)abstract
- Baltic Sea flounder were recently split into two species, the offshore spawner Platichthys flesus and coastal spawner Platichthys solemdali. The two species can only be distinguished based on egg and sperm characteristics and via genetic analyses, which limits the species identification methods of larvae and juveniles to molecular techniques. We investigated whether otolith chemistry could be used as an additional tool to identify flounder to species level. We tested for species-specific differences in otolith multi-elemental signatures and spatial consistency of those differences for the early life stages of flounder in three areas of the central Baltic Sea (ICES SD 24-28), where the distribution of both species overlaps. Otolith chemistry signatures obtained through maternal transfer (i.e. core chemistry) and signatures that reflect the post-hatching phase were not significantly different between species. Species-specific differences at the sub-regional scale were only found for the Latvian coastal survey area for multiple elements (Ba, Cu, Mg, Pb, Sr and Zn), but were insufficiently distinct for reliable species discrimination. Geographic classification of age-0 juveniles to survey area was more successful than classification to species, which was reflected by a spatial trend in otolith Sr:Ca that followed the salinity gradient and higher Mn:Ca and I:Ca for Latvian individuals. Otolith chemistry of early life flounder from the Baltic Sea reflects spatial variability in environmental conditions but does not differentiate between the two flounder species in sympatric habitats.
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