Viability Of Fisheries Research Articles

Marine heatwaves and commercial fishing in New Zealand

A marine heatwave (MHW) is an atypical and relatively short period of warmer Sea Surface Temperature (SST) which may be disruptive to marine life. Changes brought about by MHWs can reshape marine ecosystems in ways that have an economic impact on their users. MHWs are expected to become more frequent, longer, and more intense due to anthropogenic climate change. We leverage high-resolution SST data, and spatially and temporally detailed fish catch data, for an analysis of the impact of MHW events on fish catch in Aotearoa New Zealand's large marine Exclusive Economic Zone (EEZ). We use Geographically and Temporally Weighted Regression to assess the spatially heterogenous impact of MHWs on fish catch across different areas within the EEZ. We find that moderate MHWs correlate with increased fish catches; but, as the intensity of MHWs increase, their impact becomes predominantly negative. Intense MHWs are associated with substantial decreases in fish catch, suggesting significant disruptions to fish populations and their habitats. This pattern underscores the vulnerability of marine ecosystems and consequently commercial fisheries to the increasing frequency and severity of MHWs caused by climate change. As MHWs become more frequent and intense, better informed management approaches will be required to ensure the sustainability and viability of fisheries.

Trade-offs between spatial temporal closures and effort reduction measures to ensure fisheries sustainability

Overexploitation has led to large scale declines in many fish stocks around the world with the 2030 United Nations agenda calling for more spatial management tools to achieve sustainability targets. However, without spatially explicit consideration of fisheries dynamics, assessment of management measures combining spatial temporal closures and effort reduction measures remain limited. This is particularly true when balancing population biomass recovery goals and their socioeconomic consequences. Using ISIS-Fish, the first spatially explicit bioeconomic model describing hake (Merluccius merluccius) fisheries in the Gulf of Lion, Mediterranean Sea, we investigated the consequences of individual spatial temporal closures and spatial closure network effects with all-at-one and gradual effort reduction measures. Their effectiveness in restoring the collapsed population and economic objectives were quantified to identify measures best suited for rebuilding population biomass, increasing catch weight, and maintaining revenue levels. While severe effort reduction was more effective in achieving population recovery goals than spatial temporal closures, these scenarios did not lead to an increase in catches until after five years. In contrast, spatial temporal closures failed to reach population recovery goals at any point during the simulation period, but impacted revenues the least. Simulated effort redistribution also led to greater depletion of juvenile hake, a pattern common elsewhere in the world. The present study illustrates how robust spatially explicit models may be used to evaluate the impacts of complex alternative management scenarios and to identify tradeoffs between biomass recovery, fishery viability, and the management equitability (and acceptability) between fishing fleets.

When large marine predators feed on fisheries catches: Global patterns of the depredation conflict and directions for coexistence

AbstractThe sustainable mitigation of human–wildlife conflicts has become a major societal and environmental challenge globally. Among these conflicts, large marine predators feeding on fisheries catches, a behaviour termed “depredation,” has emerged concomitantly with the expansion of the world’s fisheries. Depredation poses threats to both the socio‐economic viability of fisheries and species conservation, stressing the need for mitigation. This review synthesizes the extent and socio‐ecological impacts of depredation by sharks and marine mammals across the world, and the various approaches used to minimize it. Depredation was reported in 214 fisheries between 1979 and 2019 (70% post‐2000) and affected fleets from 44 countries, in all sectors (commercial, artisanal and recreational), and in all major fishing techniques (nets, traps and hook‐and‐lines). A total of 68 predator species were involved in depredation (20 odontocetes, 21 pinnipeds and 27 sharks), and most (73%) were subject to either by‐catch and/or retaliatory killing from fishers when interacting with gear. Impacts on fishers were primarily associated with catch losses and gear damage but often lacked assessments. Deterrence was a major mitigation approach but also the least effective. Gear modifications or behavioural adaptation by fishers were more promising. This review highlights the need for improved monitoring, and interdisciplinary and integrated research to quantify the determinants and impacts of depredation in the socio‐ecological dimension. More importantly, as the conflict is likely to escalate, efforts directed towards changing perceptions and integrating knowledge through adaptive co‐management are raised as key directions towards coexistence between fisheries and large marine predators.

Estimating maturity from size-at-age data: Are real-world fisheries datasets up to the task?

The size and age at which individuals mature is rapidly changing due to plastic and evolved responses to fisheries harvest and global warming. Understanding the nature of these changes is essential because maturity schedules are critical in determining population demography and ultimately, the economic value and viability of fisheries. Detecting maturity changes is, however, practically difficult and costly. A recently proposed biphasic growth modelling likelihood profiling method offers great potential as it can statistically estimate age-at-maturity from population-level size-at-age data, using the change-point in growth that occurs at maturity. Yet, the performance of the method on typical marine fisheries datasets remains untested. Here, we assessed the suitability of 12 North Sea and Australian species’ datasets for the likelihood profiling approach. The majority of the fisheries datasets were unsuitable as they had too small sample sizes or too large size-at-age variation. Further, datasets that did satisfy data requirements generally showed no correlation between empirical and model-derived maturity estimates. To understand why the biphasic approach had low performance we explored its sensitivity using simulated datasets. We found that method performance for marine fisheries datasets is likely to be low because of: (1) truncated age structures due to intensive fishing, (2) an under-representation of young individuals in datasets due to common fisheries-sampling protocols, and (3) large intrapopulation variability in growth curves. To improve our ability to detect maturation changes from population level size-at-age data we need to improve data collection protocols for fisheries monitoring.

The effect of abundance changes on a management strategy evaluation for the Atlantic surfclam (Spisula solidissima) using a spatially explicit, vessel-based fisheries model

Increased bottom water temperatures have caused a relocation and contraction of the range of the Atlantic surfclam, Spisula solidissima, in the Mid-Atlantic Bight (MAB). Consequences include declining stock abundance and landings per unit effort (LPUE) in southern portions of the range. A management strategy evaluation (MSE) assessed the potential of rotational closures to improve surfclam productivity and fishery viability under three levels of abundance. In simulations, fishing vessels harvest the stock under performance and quota constraints and captain behavioral proclivities. Management alternatives examined included the addition of area management to the current management plan using two closure location rules and three closure durations at two levels of incidental mortality. Simulations showed that area management increased stock abundance and fishery LPUE, particularly when surfclam abundance was low. Simulations suggest area management could help insulate the stock and commercial fishery from further shifts in range.

Cost structure and financial performance of marine commercial fisheries in the South Brazil Bight

In Brazil, economic data on fisheries are generally scarce, and difficult to interpret with respect to costs and fishery viability, thus making it difficult to practice consistent policy and industrial decision-making. Financial performance was assessed, as were the key factors affecting the fishing costs and profitability of the major fisheries fleets that operated in three Southeast and South regions. Through an unprecedented set of field survey data from 160 fishing vessels obtained during 2013–2014, we provide a cost-benefit comparison between different fleets and landing sites. Three generalized additive models (GAMLSS) were explored to identify major factors affecting gross profit. Fuel consumption, vessel repairs, revenue, and volume of catch were the most statistically significant factors explaining gross profit margin. For trawlers and purse-seiners, technical features such as vessel size and the number of fishing trips explained profitability, respectively, while the landing costs were significant to both types of fleet. Gross profits for trawlers also depend on ice cost and fleet type. Large pelagic fisheries showed the highest gross profit, while shrimp-trawlers, bottom-gillnetters and a purse-seining fleet showed the lowest profit, close to unviability. Indirectly, population size of target species may be influencing profitability. Labor wages increase when the financial performance of fleets improve; however, reduced yields and high operational cost levels may decrease the salaries. Specific policy advice and management strategies aiming to protect both financial performance and natural resources are highlighted, including the importance of cost-benefit analysis to help businessmen and vessel owners to identify factors that influence fleet profitability, thereby facilitating the creation of measures for increased efficiency. The approach presented may contribute to standardizing economic knowledge construction in data-poor fisheries, such as S/SE Brazil’s and in other jurisdictions of Brazil or elsewhere.

Effects of changes in stock productivity and mixing on sustainable fishing and economic viability

Within the new FMSY European paradigm, this paper shows how a combination of changes in fish stock mixing, non-stationarity in productivity, and constraints on unit stock concepts undermine the effective management of fisheries, especially when management reference points are not adjusted accordingly. Recent changes in stock structures, conditions and stock mixing between eastern and western Baltic cod can jeopardize the reliability of stock assessments and of the fishery economy. We modelled how different management, individual vessel decision-making, and stock growth and mixing scenarios have induced alternative individual vessel spatial effort allocation and economic performance by affecting fishing costs and by changing the relative stock abundance and size distribution. Stock mixing heavily influences profit and stock abundance for stocks that have experienced increased fishing mortality (F) levels. Western cod F has increased from a higher total allowed catches (TAC) advised in the medium-term due to the westward migration of eastern cod while eastern cod F has increased from reduced growth in the east. Greater pressures on western cod and decreased eastern cod growth and conditions greatly reduce the overall cod spawning stock biomass, thus changing the landing size composition and associated fishery profits. As a cumulative effect, fishing efforts are redirected towards western areas depending on management (quotas). However, total profits are less affected when traditional fishing opportunities and switching possibilities for other species and areas are maintained. Our evaluation indicates that current management mechanisms cannot correct for potential detrimental effects on cod fisheries when effort re-allocation changes landing origins. By investigating different economic starting conditions we further show that Baltic cod mis-management could have resulted in unintended unequal (skewed) impacts and serious consequences for certain fleets and fishing communities compared with others. Our management strategy evaluation is instrumental in capturing non-linear effects of different recommendations on sustainability and economic viability, and we show that fixed F-values management is likely not an attainable or sufficient goal in ensuring the sustainability and viability of fisheries and stocks given changing biological conditions.

Storage and Viability of a Fishery with Resource and Market Dephased Seasonalities

In this study we analyse the role of the storageregulation in a fishery's production process when theresource exploited and the market to which theproduction is exported are characterized by seasonaldephased oscillations. For this purpose we built up adynamic model drawn from the French Guyana shrimpfishery example. The underlying objective of the modelis not the maximisation of a given criterion (as wouldbe in the optimal control approach), but merely themaintenance of the fishery's economical viability. Thefundamental principle is here to try to preserve asmany as possible viable control options. Theconditions to achieve and maintain this viability arecaptured in a certain number of constraints. Theanalysis points out periods and situations within theseason where the fishermen must anticipate theevolution of their storage to avoid violating thoseviability constraints. The study also indicates howthe fishery's viability can be ensured even if theexploitation costs exceed the commercial value of thelandings for a finite part of the year. However, whenthe resource's and/or market's oscillations are toolarge, the fishery may be not viable any longer and itappears that the crisis can not be removed byinvesting in larger storage capacities.