Fishing triggers trophic cascade in terms of variation, not abundance in an allometric trophic network model

Trophic cascade studies often rely on linear food chains instead of complex food webs and are typically measured as biomass averages, not as biomass variation. We study trophic cascades propagating across a complex food web including a measure of biomass variation in addition to biomass average. We examined whether different fishing strategies induce trophic cascades and whether the cascades differ from each other. We utilized an allometric trophic network (ATN) model to mechanistically study fishing-induced changes in food-web dynamics. Different fishing strategies did not trigger traditional, reciprocal trophic cascades, as measured in biomass averages. Instead, fishing triggered a variation cascade that propagated across the food web including fish, zooplankton and phytoplankton species. In fisheries that removed a large amount of top-predatory and cannibalistic fish, the biomass oscillations started to decrease after fishing was started. In fisheries that mainly targeted large planktivorous fish, the biomass oscillations did not dampen, but slightly increased over time. Removing species with specific ecological functions might alter the food web dynamics and potentially affect the ecological resilience of aquatic ecosystems.

Dynamic Analysis of a Phytoplankton-Fish Model with the Impulsive Feedback Control Depending on the Fish Density and Its Changing Rate

This paper proposes a comprehensive fishing strategy that takes into consideration the population density of fish and its current growth rate, which provides new ideas for fishing strategies. Firstly, we establish a phytoplankton-fish model with the impulsive feedback control depending on the density and rate of change of the fish. Secondly, the complex phase and impulse sets of this model are divided into three cases, then the Poincar´e map for the model is defined, and analyzed the properties of Poincar´e map. In addition, the sufficient and necessary conditions for the global asymptotic stability of the order-1 periodic solution and existence condition of order- k ( k ≥ 2) periodic solution are discussed. The action threshold depends on the density and rate of change of the fish, which is reasonable than earlier studies. The analysis method proposed in this paper also plays an important role in the analysis of impulse models with complex phase sets or impulse sets.

PEMANFAATAN ALAT TANGKAP IKAN TRADISIONAL OLEH NELAYAN PULAU BAWEAN KABUPATEN GRESIK

Bawean Island is located in the middle of the Java Sea, about 150 km north of Gresik. The name Bawean was taken from the Sanskrit which means there is sunlight. The Bawean people are acculturation from several ethnic groups of Java, Madura, Kalimantan, Sulawesi and Sumatera including their culture and language. The majority of Bawean residents work as fishermen. Bawean Island fishermen utilize marine resources to meet the needs of their family by using knowledge that has been obtained from previous generations. The purpose of this study was to determine the use of traditional fishing gear and fishing strategies used by fishing communities in Bawean Island. The research method used was direct observation, and sampling using Purposive Sampling and Snowball Sampling. The results showed that the fishing gears used by Bawean Island fishermen were kareket (waring), pajeng (payang), jhering cursor (ring net), rompon (bubu), jhering pemhir (drift gill net), payimbek rentengan (drag fishing), gerany Panyimbek (drag fishing line), panceng (fishing line). These fishing gears are very environmentally friendly because the usage does not damage the seabed ecosystem. Each fishing gear has its own characteristics, so that different fishing gear will result in different fishing catch

Fish harvesting advice under climate change: A risk-equivalent empirical approach

The rate of climate change (CC) has accelerated to the point where it now affects the mid- to long-term sustainability of fishing strategies. Therefore, it is important to consider practical and effective ways to incorporate CC into fisheries advice so that the advice can be considered conditioned to CC. We developed a model to characterise the empirical relationship between a variable affected by climate and fish production. We then used model projections as a foundation for a risk analysis of CC effects on harvesting of Greenland halibut Reinhardtius hippoglossoides in the Gulf of St Lawrence, Canada. The risk-based approach quantified a) the relative change in risk of a status quo fishing strategy under various CC scenarios, and b) the change in fishery exploitation rates required to achieve a management objective over a specified time period at a level of risk considered acceptable (risk equivalent fishery exploitation advice). This empirical approach can be used to develop risk-based advice for any other external variable that affects stock production in addition to climate-related variables and it can be applied in most situations where there is an index of stock biomass and fisheries catch. Shifting the focus from process-based understanding of the responses of fish stocks to CC to quantification of how CC-contributed uncertainty can alter the risks associated with different fishing strategies and/or management options, can ensure timely delivery of robust scientific advice for fisheries under non-stationary environmental conditions.

Adaptive capacity of small pelagic fishing communities in coastal Tanga (Tanzania) to changes in climate-related phenomena

Studies examining the vulnerability, resilience and adaptation options of fisheries-dependent coastal communities have noted a decrease in viable options to respond effectively to the impacts of climate change. The extent of vulnerability is experienced in terms of varying capacity to respond to ecological changes through resource use practices. We analyzed the experiences of three coastal communities dependent on small pelagic fisheries in Tanga region, Tanzania, and their responses to the changing availability of fisheries resources. The study illustrates how conditions associated with upwelling, while not readily obvious to fishers, match some of their fishing strategies, with implications for fisheries-dependent livelihoods. Yet, the fishers’ perceptions are key determinants of the response options they adopt. Limited access to scientific knowledge also constrains the effectiveness of their response options. Our findings have important implications for the manner in which local and scientific knowledge systems can be integrated, particularly with regards to enhancing the adaptive capacities of coastal fishing communities through knowledge sharing.

Tuna Fisheries Fuel Consumption Reduction and Safer Operations

This chapter demonstrates the potential of tuna fishing fleets to reduce their fuel oil consumption. In the “Oceanic tuna fisheries, immediate operational choices” pilot, the data monitoring system on vessels periodically upload data to the server for shore analysis. The data analytics employs fuel oil consumption equations and propulsion engine fault detection models. The fuel consumption equations are being used to develop immediate operational decision models. The fault detection models are used to plan maintenance operations and to prevent unexpected engine malfunctions. The data-driven planning software allows probabilistic forecasting of tuna biomass distribution and analysing changes in fishing strategies leading to fuel consumption reduction. These changes in fishing strategies can be summarized as a transition from hunting to harvesting. Vessels do not search for fish, but instread take less risks and fish, where it is more likely that the fish can be found and is easier to capture. Buoy data are increasingly used to improve stock assessments and have the potential to allow better monitoring and planning of fish quotas fulfilment.

Fish harvesting advice under climate change: a risk-equivalent empirical approach

1AbstractThe rate of climate change (CC) has accelerated to the point where it now affects the mid-to long-term sustainability of fishing strategies. Therefore, it is important to consider practical and effective ways to incorporate CC into fisheries advice so that the advice can be considered conditioned to CC. We developed a quantitative model to characterise the empirical relationship between a variable affected by climate and fish production. We then used model projections as a foundation for a risk analysis of CC effects on harvesting of Greenland halibut Reinhardtius hippoglossoides in the Gulf of St Lawrence, Canada. The risk-based approach quantified a) the relative change in risk of a status quo fishing strategy under various CC scenarios, and b) the change in fishery exploitation rates required to achieve a management objective over a specified time period at a level of risk considered acceptable (risk equivalent fishery exploitation advice). This empirical approach can be used to develop risk-based advice for any other external variable that affects stock production in addition to climate-related variables and it can be applied in most situations where there is an index of stock biomass and fisheries catch. Shifting the focus from process-based understanding of the responses of fish stocks to CC to quantification of how CC-contributed uncertainty can alter the risks associated with different fishing strategies and/or management options, can ensure timely delivery of robust scientific advice for fisheries under non-stationary environmental conditions.