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The subtropical oceanic gyre in the North Pacific Ocean is currently covered with tens of thousands of tonnes of floating plastic debris, dispersed over millions of square kilometres. A large fraction is composed of fishing nets and ropes while the rest is mostly composed of hard plastic objects and fragments, sometimes carrying evidence on their origin. In 2019, an oceanographic mission conducted in the area, retrieved over 6000 hard plastic debris items > 5 cm. The debris was later sorted, counted, weighed, and analysed for evidence of origin and age. Our results, complemented with numerical model simulations and findings from a previous oceanographic mission, revealed that a majority of the floating material stems from fishing activities. While recent assessments for plastic inputs into the ocean point to coastal developing economies and rivers as major contributors into oceanic plastic pollution, here we show that most floating plastics in the North Pacific subtropical gyre can be traced back to five industrialised fishing nations, highlighting the important role the fishing industry plays in the solution to this global issue.

The dynamics of fishing nets can be estimated by modeling and numerically computing the forces acting on them. However, the dynamic models of fishing nets are highly nonlinear owing to the significant influence of hydrodynamic forces acting on the net. Therefore, if there are unknown parameters that define the state of motion in the model, it is often difficult to achieve high accuracy in the numerical simulations of fishing gear and evaluate its dynamics. To address this issue, a method is proposed for estimating these unknown parameters by integrating a nonlinear Kalman filter into a fishing net dynamics model. This study aimed to estimate the hauling velocity of large- and medium-sized purse seine fishing nets, which can be a challenging parameter to measure. The calculations are based on the data obtained from a research operation conducted by the Marine Fisheries Research and Development Center in 2019 using the purse seine fishing vessel “Taikei Maru No. 1”. The time series of the hauling-net velocity was estimated based on the results of the estimation experiment. These results allowed the estimation of the hauling velocity and calculation of the net dynamics during the hauling process. This shows that net dynamics simulation is possible even with unknown parameters.

Polyethylene terephthalate (PET) is one of the most widely used materials for food packaging and fishing nets. After use it become waste and, due to poor collection, most will be found floating in marine waters. This paper presents the results of a study of PET depolymerization by hydrolysis. We observed that marine water is a perfect reactant because it contains a multitude of metal ions that act as catalysts. A first-order kinetic model was developed and experimental data fitted to it. An activation energy of 73.5 kJ/mole and a pre-exponential factor of 5.33 × 10 7  h –1 were obtained. Considering that the global ocean is a huge batch reactor operating under isothermal conditions, the solution of the mathematical model shows that in tropical regions only 72 years is needed for total and only 4.5 years for 50% PET conversion.

Malaria remains a major health problem in many parts of the world, including Sub-Saharan Africa. Insecticide-treated nets, in combination with other control measures, have been effective in reducing malaria incidence over the past two decades. Nevertheless, there are concerns about improper handling and misuse of nets, producing possible health effects from intoxication and collateral environmental damage. The latter is caused, for instance, from artisanal fishing. We formulate a model of impulsive differential equations to describe the interplay between malaria dynamics, human intoxication, and ecosystem damage; affected by human awareness to these risks and levels of net usage. Our results show that an increase in mosquito net coverage reduces malaria prevalence and increases human intoxications. In addition, a high net coverage significantly reduces the risk perception to disease, naturally increases the awareness for intoxications from net handling, and scarcely increases the risk perception to collateral damage from net fishing. According to our model, campaigns aiming at reducing disease prevalence or intoxications are much more successful than those creating awareness to ecosystem damage. Furthermore, we can observe from our results that introducing closed fishing periods reduces environmental damage more significantly than strategies directed towards increasing the risk perception for net fishing.

Bycatch is one of the main causes of mortality among marine megafauna around the world. In the coastal waters of southern Brazil, bycatch in gillnet fisheries affects threatened species that use this region as a breeding and feeding area. The identification of hotspot areas of bycatch is necessary to design and prioritize efficient spatial–temporal closures that protect the largest possible number of threatened species of marine megafauna. In this context, the use of a multispecies approach is an important step towards planning effective fisheries management measures. This study has two main objectives: (1) to identify hotspot areas of bycatch in gillnet fisheries for the most threatened marine megafauna species on the continental shelf of Rio Grande do Sul (RS); (2) compare single species and multispecies mapping methods for the identification of these areas. To meet these objectives, data collected by onboard observers during fishing trips in the coastal commercial RS-based gillnet fleet between 2013 and 2015 and between 2018 and 2020 were analyzed. For the identification of the areas, hierarchical Bayesian spatio-temporal models were implemented, using monospecific and multispecific approaches and a weighting system for the conservation status of the species. Both approaches provide similar results, identifying three bycatch hotspots according to the time frame analysed. Based on our findings, we propose these areas as the top candidates for fishing exclusion zones, based on their biodiversity value. The suggested spatio-temporal closures would benefit several endangered species while also contributing to the recovery of fish populations.

The vaquita (Phocoena sinus) is the world's most endangered marine mammal with approximately 245 individuals remaining in 2008. This species of porpoise is endemic to the northern Gulf of California, Mexico, and historically the population has declined because of unsustainable bycatch in gillnets. An illegal gillnet fishery for an endangered fish, the totoaba (Totoaba macdonaldi), has recently resurged throughout the vaquita's range. The secretive but lucrative wildlife trade with China for totoaba swim bladders has probably increased vaquita bycatch mortality by an unknown amount. Precise population monitoring by visual surveys is difficult because vaquitas are inherently hard to see and have now become so rare that sighting rates are very low. However, their echolocation clicks can be identified readily on specialized acoustic detectors. Acoustic detections on an array of 46 moored detectors indicated vaquita acoustic activity declined by 80% between 2011 and 2015 in the central part of the species' range. Statistical models estimated an annual rate of decline of 34% (95% Bayesian credible interval -48% to -21%). Based on results from 2011 to 2014, the government of Mexico enacted and is enforcing an emergency 2-year ban on gillnets throughout the species' range to prevent extinction, at a cost of US$74 million to compensate fishers. Developing precise acoustic monitoring methods proved critical to exposing the severity of vaquitas' decline and emphasizes the need for continual monitoring to effectively manage critically endangered species. La vaquita (Phocoena sinus) es el mamífero marino en mayor peligro de extinción, con aproximadamente 245 individuos existentes en 2008. Esta especie de marsopa es endémica de la parte norte del Golfo de California, México, e históricamente su población ha declinado por causa de la captura accidental en redes agalleras. La pesca ilegal con redes agalleras de un pez en peligro, la totoaba (Totoaba mcdonaldi), ha resurgido recientemente en la zona de distribución de la vaquita. El lucrativo y oculto mercado de fauna con China, por la vejiga de la totoaba, probablemente ha incrementado la mortalidad por captura accidental de la vaquita en una cantidad desconocida. El monitoreo preciso de la población por medio de censos visuales es difícil porque las vaquitas son difíciles de ver por naturaleza y actualmente se han vuelto tan raras que las tasas de avistamiento son muy bajas. Sin embargo, sus chasquidos de eco-localización pueden ser identificados certeramente con detectores acústicos especializados. Las detecciones acústicas obtenidas en una malla de 46 detectores anclados al fondo indicaron que la actividad acústica de la vaquita declinó en un 80 % entre 2011 y 2015 en la parte central de la distribución de la especie. Dos modelos estadísticos estimaron una tasa anual de declive del 34 % (intervalo de credibilidad bayestano al 95% de-48 % a-21 %). Con base en los resultados del 2011 al 2014, el gobierno de México promulgó, y está haciendo cumplir, una prohibición de emergencia de 2 años para el uso de redes agalleras en toda la distribución de la especie para prevenir su extinción, con un costo de $74 millones de dólares para compensar a los pescadores. El desarrollo de métodos precisos de monitorización acústica resultó ser crítico para exponer la severidad del declive de la vaquita y enf atiza la necesidad de una monitorización continua para manejar efectivamente a especies críticamente amenzadas.

Harvesting can induce rapid evolution in animal populations, yet the role of ecological change in buffering or enhancing that response is poorly understood. Here, we developed an ecogenetic model to examine how ecological changes brought about by two notorious invasive species, zebra and quagga mussels, influence harvest-induced evolution and resilience in a freshwater fish. Our study focused on lake whitefish (Coregonus clupeaformis) in the Laurentian Great Lakes, where the species supports valuable commercial and subsistence fisheries, and where the invasion of dreissenid (zebra and quagga) mussels caused drastic shifts in ecosystem productivity. Using our model system, we predicted faster rates of evolution of maturation reaction norms in lake whitefish under pre-invasion ecosystem conditions when growth and recruitment of young to the population were high. Slower growth rates that occurred under post-invasion conditions delayed when fish became vulnerable to the fishery, thus decreasing selection pressure and lessening the evolutionary response to harvest. Fishing with gill nets and traps nets generally selected for early maturation at small sizes, except when fishing at low levels with small mesh gill nets under pre-invasion conditions; in this latter case, evolution of delayed maturation was predicted. Overall, the invasion of dreissenid mussels lessened the evolutionary response to harvest, while also reducing the productivity and commercial yield potential of the stock. These results demonstrate how ecological conditions shape evolutionary outcomes and how invasive species can have a direct effect on evolutionary responses to harvest and sustainability.

The mechanical and hydrodynamic characteristics of single-piece nets are key to the design and optimization of offshore aquaculture net cages. A numerical approach for offshore submerged aquaculture net materials based on the Morison equations and finite element is proposed, simulating the hydrodynamic characteristics of single-piece nets under varying parameters such as wire diameter, mesh size, and flow velocity, and simulating the impact of marine organism attachment on nets by modifying the drag coefficient. The simulation results of nets made from materials such as Copper–Zinc Alloy (Cu-Zn), Zinc–Aluminum Alloy (Zn-Al), Semi-Rigid Polyethylene Terephthalate (PET), and Ultra-High Molecular Weight Polyethylene (UHMWPE) are compared, which provides a theoretical basis for optimizing design parameters and selecting materials for nets based on force conditions and hydrodynamic characteristics. The simulation results indicate that the current force on the net is positively correlated with flow velocity; the maximum displacement of the net is also positively correlated with the flow rate. Compared to other materials, the Cu-Zn net is subjected to the greatest water flow force, while the UHMWPE net experiences the greatest displacement; the larger the diameter of the netting twine, the greater the current force on the net; the mesh size is inversely related to the current force on the net. With increasing drag coefficient, both the maximum displacement of the net and the current force experiences increase, and UHMWPE material nets are more sensitive to increases in the drag coefficient, which indicates a greater impact from the attachment of marine organisms. The density and elastic modulus of the netting material affect the rate of increase in force on the net. The research results can provide a basis for further research on material selection and design of deep-sea aquaculture nets.

Every austral spring when Antarctic sea ice melts, favorable growing conditions lead to an intense phytoplankton bloom, which supports much of the local marine ecosystem. Recent studies have found that Antarctic sea ice is predictable several years in advance, suggesting that the spring bloom might exhibit similar predictability. Using a suite of perfect model predictability experiments, we find that November net primary production (NPP) is potentially predictable 7 to 10 years in advance in many Southern Ocean regions. Sea ice extent predictability peaks in late winter, followed by absorbed shortwave radiation and NPP with a 2 to 3 months lag. This seasonal progression of predictability supports our hypothesis that sea ice and light limitation control the inherent predictability of the spring bloom. Our results suggest skillful interannual predictions of NPP may be achievable, with implications for managing fisheries and the marine ecosystem, and guiding conservation policy in the Southern Ocean. Plain Language Summary In very much the same way as we do for the weather, we can make forecasts of many aspects of the earth system. For example, rather than trying to predict how much rain will fall next Tuesday, we can explore how much algal growth might take place in the oceans around Antarctica in several months time. Such predictions could be extremely useful for managing the fragile ecosystems of these regions, for example, informing fishing quotas in an upcoming season. However, just like for weather forecasts, there are upper limits for how far into the future we can expect to accurately make such predictions. It's this upper limit that we try to understand in this theoretical modeling study. We find that the upper limit is actually rather long (as much as 10 years!), and show that this is because of the close relationship between algal growth and sea ice (ice formed at the ocean surface) in this cold polar region. In turn, the extent of the sea ice can be predicted a long time in advance because there is a lot “memory” in this component of the earth system. Key Points Southern Ocean net primary production (NPP) is potentially predictable seven to 10 years in advance in a perfect model experiment The peak predictability of NPP in November lags the peak predictability of sea ice extent and net shortwave radiation by 2 to 3 months Seasonal progression of predictability suggests that sea ice and light limitation control the inherent predictability of the spring bloom