Balanced exploitation and coexistence of interacting, size-structured, fish species

This paper examines some effects of exploitation on a simple ecosystem containing two interacting fish species, with life histories similar to mackerel (Scomber scombrus) and cod (Gadus morhua), using a dynamic, size-spectrum model. Such models internalize body growth and mortality from predation, allowing bookkeeping of biomass at a detailed level of individual predation and growth and enabling scaling up to the mass balance of the ecosystem. Exploitation set independently for each species with knife-edge, size-at-entry fishing can lead to collapse of cod. Exploitation to achieve a fixed ratio of yield to productivity across species can also lead to collapse of cod. However, harvesting balanced to the overall productivity of species in the exploited ecosystem exerts a strong force countering such collapse. If balancing across species is applied to a fishery with knife-edge selection, size distributions are truncated, changing the structure of the system and reducing its resilience to perturbations. If balancing is applied on the basis of productivity at each body size as well as across species, there is less disruption to size-structure, resilience is increased, and substantially greater biomass yields are possible. We note an identity between the body size at which productivity is maximized and the age at which cohort biomass is maximized. In our numerical results based on detailed bookkeeping of biomass, cohort biomass reaches its maximum at body masse

Tuning and Development of an Individual-Based Model of the Herring Spawning Migration

Norwegian spring spawning herring is a migratory pelagic fish stock that seasonally navigates between distant locations in the Norwegian Sea. The spawning migration takes place between late winter and early spring. In this article, we present an individual-based model that simulated the spawning migration, which was tuned and validated against observation data. Individuals were modelled on a continuous grid coupled to a physical oceanographic model. We explore the development of individual model states in relation to local environmental conditions and predict the distribution and abundance of individuals in the Norwegian Sea for selected years (2015–2020). Individuals moved position mainly according to the prevailing coastal current. A tuning procedure was used to minimize the deviations between model and survey estimates at specific time stamps. Furthermore, 4 separate scenarios were simulated to ascertain the sensitivity of the model to initial conditions. Subsequently, one scenario was evaluated and compared with catch data in 5 day periods within the model time frame. Agreement between model and catch data varies throughout the season and between years. Regardless, emergent properties of the migration are identifiable that match observations, particularly migration trajectories that run perpendicular to deep bathymetry and counter the prevailing current. The model developed is efficient to implement and can be extended to generate multiple realizations of the migration path. This model, in combination with various sources of fisheries-dependent data, can be applied to improve real-time estimates of fish distributions.publishedVersio

Exploring balanced harvesting by using an Atlantis ecosystem model for the Nordic and Barents seas

“Balanced Harvesting” (BH) has been suggested as a possible strategy to meet the objectives of the Ecosystem Approach to Fisheries, ensuring a high sustainable yield while maintaining ecosystem structure and function. BH proposes a moderate fishing mortality in proportion to productivity spread across the widest possible range of species, stocks, and sizes in an ecosystem producing a sustainable and overall non-selective harvest. The Norwegian and Barents Seas have been subjected to moderate fishing pressure on commercial species, and elements of an ecosystem-based approach to management for many years, but not the fishing pattern proposed by BH. By using an Atlantis ecosystem model of the Nordic and Barents Seas, we investigated the effects of applying a BH regime to a region with existing successful fisheries management. This was done by running simulations with combinations of historic fishing pressure and fishing mortality rates proportional to 25% of the productivity of most species and sizes. The simulations were then compared to a control run where the historical fisheries were applied. The model results showed that implementing a BH regime in the Norwegian and Barents Seas would only produce marginal increases in total yields of currently commercially exploited stocks, likely because the Norwegian fisheries are already mostly well-managed. However, expanding the fishery to include species that are not commercially exploited today did produce higher yields, especially on lower trophic levels. This study represents the first attempted examination of implementing BH based on productivity using an Atlantis ecosystem model, as well as the first investigation of BH in the Norwegian and Barents Seas. We use this model as a case study to identify the gains that species-based BH can be expected to give over well-implemented traditional fisheries management rather than simply comparing to an over-exploited system.publishedVersio

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

Fisheries in the Drylands of Sub-Saharan Africa – “Fish come with the rains”. Building resilience for fisheries-dependent livelihoods to enhance food security and nutrition in the drylands

Dryland areas cover more than half of sub-Saharan Africa and are home to nearly 50 percent of its populations, who depend on agriculture (including livestock, crops and fisheries) as their main livelihood strategy. Sporadic and irregular rainfall patterns are the most important environmental driver for these regions and water, in particular surface water, is the primary element of scarcity in drylands. Generally, dryland water bodies are unstable and strongly pulsed ecosystems owing to intermittent and largely unpredictable precipitation. Such systems are characterized by very productive and highly resilient, small opportunistic fish species with “boom and bust” fluctuation adapted to strong environmental disturbances, and are therefore difficult to overfish. As a result of high productivity, they can sustain very high yields in years of good rains, but being largely short-lived they also respond rapidly to environmental changes in hydrological regimes, which means that alternating periods of low productivity are inevitable. The focus of this review is to both document the general resilience of many fish resources to climatic variability − including their underestimation in livelihood importance, particularly in protracted crisis situations − and to enhance the potential supply of fish from dryland areas through improved use of the available water bodies, and in particular small reservoirs. The important role that small water bodies play in supplying essential micronutrients and protein to rural communities has largely been overlooked since the termination of the FAO/ALCOM (Aquaculture for Local Community Development) programme in 1998, although they are more productive on a per unit area basis than the large lakes and reservoirs and, when pooled, constitute a much larger area of water. Most of the fish production, however, is consumed locally and goes unrecorded in official catch statistics. By refocusing attention on the fish productivity of small water bodies and reservoirs in drylands, and in particular by integrating fisheries with developments in water harvesting, irrigation and improved water storage facilities, the potential to increase the role played by fish in the diets of dryland people, and to provide improved livelihood opportunities is great. The overall conclusion is that the potential for increasing fish production in dryland areas is significant, that the resources are highly resilient and productive, but that the general and increased unpredictability of the rainfall required to sustain surface water bodies creates uncertainties in annual production. That must be counteracted by an adaptive and diversified livelihood strategy.publishedVersio

The Coastal Reference Fleet 2007-2019 - Fleet composition, fishing effort and contributions to science

Catch quotas are used for the sustainable management of fish stocks and are based on official catch statistics and research surveysSustainable management of the Norwegian fisheries depends on quota advice that is based on stock assessments, using scientific data from research surveys and official landings statistics. The official landings statistics are given in metric tons, and for vessels less than 15 meters only include rough information on fishing effort. The research cruises, on the other hand, only take place in certain areas and at certain times of the year. However, these methods provide only partial information, as the official catch data at best include rough measures of effort, and the survey data are only collected at certain times of the year. In 2005, the Norwegian Coastal Reference Fleet (CRF) was established by the Institute of Marine Research (IMR) ,to obtain data at-sea on in order to register catches in numbers per species including size- and age composition, discards, and bycatch, as well as data on fishing , gear, and effort. The vessels in the CRF were selected along the entire coast using criteria to ensure that they as represent able for the Norwegian coastal fishing fleet as closely as possible. These historic data and the development of the CRF are evaluated have been ccomprehensively visualisedin , and this report, using descriptive methods and provides a description and visual displaysanalysis of the CRF data. Between 2007-2019, a total of 64 fishing vessels particip ated in the CRF along the Norwegian coast collecting data from a cumulated total number of 287 taxa, and from 29 137 individual fishing operations. The most common species was cod (Gadus morhua), which occurred in 60.9% of the fishing operations. Throughout the study period gillnet was the most common gear in all years, but there were small shifts in the gear composition over time of the CRF shifted, however gillnet was the most common gear in all years. Catch per unit effort (CPUE) from fisheries standardises catch data for comparisons in both space and time and is often used as a proxy indices of for fish abundance, assuming constant catchability (the probability from 0 to 1 of a fish being caught per unit effort) over time. When collecting fisheries dependent data, however, fishers actively try to maximise catchability of their target species or species composition, by e.g., using different gears to handle natural variations in catchability dependent on season, and area. Broad coverage in space and time may reduce this human bias as well as providing information on the behaviour of the fishers and the effect of technological advancements. This report includes CPUE timeseries for cod, haddock (Melanogrammus aeglefinus), and golden redfish (Sebastes norvegicus) north of 62°N.publishedVersio

Putting small fish on the table: the underutilized potential of small indigenous fish to improve food and nutrition security in East Africa

Sub-Saharan Africa has a high prevalence of food insecurity. Small pelagic fish such as Silver cyprinid (Rastrineobola argentea) which is indigenous to Lake Victoria, can be a nutritious animal sourced food that contributes to a more nutrient dense diet. Potential sustainable catch of Silver cyprinid is estimated at 2 million tonnes yearly, which is four times the amount of the current catch. Whole sun-dried Silver cyprinid was purchased from several markets in Kenya and analysed for nutrient composition, microbial counts and metal content. The results show that utilizing the whole potential catch of Silver cyprinid would provide a significant daily source of vitamin B12, calcium, zinc and iron to the roughly 33 million people living in the Lake Victoria basin. Heavy metal concentration appears to be low, but other food safety aspects like microbial counts call for value chain improvements. We conclude that the underutilized potential of sun-dried Silver cyprinid could substantially contribute to fight malnutrition and food insecurity by providing an affordable nutrient dense animal sourced food to a large number of people. It also highlights the need to improve the value chains to increase the safety of these products.publishedVersio

Myofascial trigger points in migraine and tension-type headache

Abstract Background A myofascial trigger point is defined as a hyperirritable spot in skeletal muscle that is associated with a hypersensitive palpable nodule in a taut band. It has been suggested that myofascial trigger points take part in chronic pain conditions including primary headache disorders. The aim of this narrative review is to present an overview of the current imaging modalities used for the detection of myofascial trigger points and to review studies of myofascial trigger points in migraine and tension-type headache. Findings Different modalities have been used to assess myofascial trigger points including ultrasound, microdialysis, electromyography, infrared thermography, and magnetic resonance imaging. Ultrasound is the most promising of these modalities and may be used to identify MTrPs if specific methods are used, but there is no precise description of a gold standard using these techniques, and they have yet to be evaluated in headache patients. Active myofascial trigger points are prevalent in migraine patients. Manual palpation can trigger migraine attacks. All intervention studies aiming at trigger points are positive, but this needs to be further verified in placebo-controlled environments. These findings may imply a causal bottom-up association, but studies of migraine patients with comorbid fibromyalgia syndrome suggest otherwise. Whether myofascial trigger points contribute to an increased migraine burden in terms of frequency and intensity is unclear. Active myofascial trigger points are prevalent in tension-type headache coherent with the hypothesis that peripheral mechanisms are involved in the pathophysiology of this headache disorder. Active myofascial trigger points in pericranial muscles in tension-type headache patients are correlated with generalized lower pain pressure thresholds indicating they may contribute to a central sensitization. However, the number of active myofascial trigger points is higher in adults compared with adolescents regardless of no significant association with headache parameters. This suggests myofascial trigger points are accumulated over time as a consequence of TTH rather than contributing to the pathophysiology. Conclusions Myofascial trigger points are prevalent in both migraine and tension-type headache, but the role they play in the pathophysiology of each disorder and to which degree is unclarified. In the future, ultrasound elastography may be an acceptable diagnostic test

Water level fluctuations and the ecosystem functioning of lakes

Hydrological regimes are key drivers of productivity and structure in freshwater ecosystems but are increasingly impacted by human activity. Using 17 published food web models of 13 African lakes as a case study, we explored relationships between seasonal and interannual water level fluctuations and 15 attributes related to ecosystem function. We interpreted our results in the context of Odum's ecosystem maturity hypothesis, as systems with higher magnitude fluctuations may be kept at an earlier maturity stage than those that are relatively stable. The data we compiled indicate that long-term changes in the hydrological regimes of African lakes have already taken place. We used Least Absolute Shrinkage and Selection Operator (LASSO) regression to examine relationships between ecosystem attributes and seven physical characteristics. Of these characteristics, interannual water level fluctuation magnitude was the most frequently retained predictor in the regression models. Our results indicate that interannual water level fluctuations are positively correlated with primary and overall production, but negatively correlated with fish diversity, transfer efficiency, and food chain length. These trends are opposite those expected with increasing ecosystem maturity. Interestingly, we found seasonal water level fluctuations to be positively correlated with biomass. An increase in standing biomass is generally associated with more mature ecosystems. However, we found that less production and biomass occurred at high trophic levels in highly fluctuating compared to relatively stable systems. This synthesis provides evidence that water level fluctuations are a key process influencing ecosystem structure and function in lakes.publishedVersio

Discards of cod (Gadus morhua) in the Norwegian coastal fisheries: improving past and future estimates

Discarding can be an unknown source of biases and uncertainties in stock assessments. Discarding patterns and quantities vary so a routine methodology for estimating discards is important to give a better picture of total catches, and potentially mortality, in fisheries. Using data from the Norwegian Reference Fleet between 2012 and 2018, this study presents a revised methodology for estimating discards of cod (Gadus morhua) in the Norwegian coastal gillnet fisheries, which accounts for variations in discarding between vessels and uncertainties in the conversion of numbers to weight discarded. The estimated average discard rate of cod (weight of cod discarded as percentage of total weight caught) is 0.55% (95% confidence interval: 0.45–0.70%), although discard rates in southern areas were an order of magnitude higher than in northern areas. We also present an exploratory analysis of the drivers behind discarding using a random forest regression model. Spatial variations and fishing intensity were identified as the most important drivers of discarding. Results from this study suggest ways in which self-sampled data can be used to estimate discards in Norwegian coastal fisheries, and where the accuracy of future estimates can be improved when a higher resolution data collection programme is established.publishedVersio