Fishery Yields Research Articles

Interannual monsoon wind variability as a key driver of East African small pelagic fisheries

Small pelagic fisheries provide food security, livelihood support and economic stability for East African coastal communities—a region of least developed countries. Using remotely- sensed and field observations together with modelling, we address the biophysical drivers of this important resource. We show that annual variations of fisheries yield parallel those of chlorophyll-a (an index of phytoplankton biomass). While enhanced phytoplankton biomass during the Northeast monsoon is triggered by wind-driven upwelling, during the Southeast monsoon, it is driven by two current induced mechanisms: coastal “dynamic uplift” upwelling; and westward advection of nutrients. This biological response to the Southeast monsoon is greater than that to the Northeast monsoon. For years unaffected by strong El-Niño/La-Niña events, the Southeast monsoon wind strength over the south tropical Indian Ocean is the main driver of year-to-year variability. This has important implications for the predictability of fisheries yield, its response to climate change, policy and resource management.

An uncertain future: Effects of ocean acidification and elevated temperature on a New Zealand snapper (Chrysophrys auratus) population

Anthropogenic CO2 emissions are warming and acidifying Earth's oceans, which is likely to lead to a variety of effects on marine ecosystems. Fish populations will be vulnerable to this change, and there is now substantial evidence of the direct and indirect effects of climate change on fish. There is also a growing effort to conceptualise the effects of climate change on fish within population models. In the present study knowledge about the response of New Zealand snapper to warming and acidification was incorporated within a stock assessment model. Specifically, a previous tank experiment on larval snapper suggested both positive and negative effects, and otolith increment analysis on wild snapper indicated that growth may initially increase, followed by a potential decline as temperatures continue to warm. As a result of this uncertainty, sensitivity analysis was performed by varying average virgin recruitment (R0) by ±30%, adult growth by ±6%, but adjusting mean size at recruitment by +48% as we had better evidence for this increase. Overall adjustments to R0 had the biggest impact on the future yield (at a management target of 40% of an unfished population) of the Hauraki Gulf snapper fishery. The most negative scenario suggested a 29% decrease in fishery yield, while the most optimistic scenario suggested a 44% increase. While largely uncertain, these results provide some scope for predicting future impacts on the snapper fishery. Given that snapper is a species where the response to climate change has been specifically investigated, increasing uncertainty in a future where climate change and other stressors interact in complex and unpredictable ways is likely to be an important consideration for the management of nearly all fish populations.

Optimum yield of demersal fisheries in Japan's coastal and offshore waters

Optimum yield of demersal fisheries in Japan's coastal and offshore waters

Shifting trophic control of fishery-ecosystem dynamics following biological invasions.

Increasing human population size and mobility have accelerated the translocation of nonnative species globally, which has become a major threat to conservation of biodiversity and ecosystem services. Introduced species can disrupt species interactions of the recipient ecosystem, triggering system-wide events, and amplify or dampen effects of existing pressures. We show how two pervasive intercontinental invasive consumers in North American lakes, dreissenids (filter-feeding mussels) and Bythotrephes (carnivorous zooplankton), nonlinearly modify consumer-resource dynamics and undermine management interventions to rebuild cold-water predatory fish biomass. Synthesizing 30yr (1986-2015) of lake-wide monitoring data with a dynamic mass-balance food-web model (consisting of 61 species and trophic groups), we reconstructed historical food-web dynamics of Lake Simcoe, a large, temperate lake in Ontario, Canada that has shifted from a turbid to clear-water state. We then analyzed patterns of biomass fluctuations of three recreationally harvested, ecologically connected populations; lake trout (Salvelinus namaycush, a piscivore), lake whitefish (Coregonus clupeaformis, a benthivore), and cisco (C.artedi, a planktivore) before and after the invasions by testing hypotheses on their delayed recoveries under management interventions-predator manipulations (fishery removal and stocking) and nutrient (phosphorus)load reduction. Analyses suggest that fishery harvest primarily regulated early recovery trajectories of the piscivore and planktivore, weakening top-down control prior to the establishment of the invasive consumers. By contrast, the benthivore biomass patterns were shaped, in part, by the invasive mussels (via diet shift), independently of management actions. Although improved water quality (with reduced hypoxia in deeper water) and, in turn, higher macrophyte production are projected to expand the predation refuge for young fish, intensified planktivory (by Bythotrephes) and herbivory (by dreissenids) have triggered shifts in community composition (from pelagic to demersal dominance). These system-wide shifts, in turn, have substantially diminished ecosystem productivity, thereby shrinking fishery yields. Novel consumers can rewire food webs, disrupt energy flows, and suppress predator recoveries, underscoring the need to account for altered ecological reality when sustainably managing fishery resources in invaded ecosystems.

Impact of water development on river flows and the catch of a commercial marine fishery

AbstractThe growing demand for freshwater resources has led to dam construction and water diversions in a majority of the world's large rivers. With an increasing demand for freshwater, trade‐offs between water allocations and the preservation of ecological connections between terrestrial and marine ecosystems are inevitable. The ecological links formed by rivers flowing into the ocean benefit many commercially fished species. The degree to which different species and the livelihoods of fishers are negatively impacted by changes in river flows due to water extraction or diversion is important for management across terrestrial and marine boundaries. Our objective was to predict how changes in freshwater flows from three wet–dry tropical rivers in northern Australia, that is, the Mitchell, Gilbert, and Flinders rivers, affect the commercial banana prawn (Penaeus merguiensis) catch. We used a novel spatiotemporal Bayesian approach to model the effects of river flows and key climate drivers on banana prawn catch. We then predicted how the loss of flow due to water extraction or diversion affected prawn catch. Our analyses of three water development scenarios found that catch was most impacted by water extraction during low flows. The impact of water extraction was greatest for a scenario with dams on the Mitchell River, where we predicted catch would decline by 53% during a year with low flow. Overall, our results imply that maintenance of low‐level flows is a crucial requirement for sustained fishery yields. We suggest that water managers must balance agricultural demand for water during drier years against the impact of water extraction on prawn fisheries during low‐flow years. Protecting low‐level flows during drier years is a priority for maintaining terrestrial–marine linkages for adjacent marine fisheries.

Comparative fishery yields of African Large Marine Ecosystems

Fisheries around Africa have historically suffered from the erroneous perception that there is little to no data on or knowledge about these activities, beyond the sometimes questionable or sparse official reported capture statistics. However, concerted efforts by scientists in and associated with Africa have changed this over the last decades. This includes the decade long efforts of the global Sea Around Us initiative to reconstruct comprehensive estimates of total fisheries catches in the waters of each African country, and create indicators using these data. Here, we build on these and other efforts, and review the main catch features, and landed values over the last 65 years generated by the fisheries in the seven Large Marine Ecosystems (LMEs) that surround the African continent, i.e., Canary Current, Guinea Current, Benguela Current, Agulhas Current, Somali Coastal Current, Red Sea, and Mediterranean Sea LMEs. Note that the small African coastal area (north coast of Somalia and Djibouti) covered by the Arabian Sea LME is excluded here due to its negligible contribution to the Arabian Sea LME. We illustrate which countries or geographic regions extract catches in each LME, with focus on African versus non-African fishing countries; examine the potential for fishing down the food web in each LME; as well as the time trends in the status of stocks. Finally, we present comprehensive economic data describing the fisheries around Africa. Jointly, these data and indicators suggest that the fisheries around Africa have reached their peak, and in many cases, moved beyond peak catches to a declining trend. Indeed, these fisheries mostly rely on overfished resources in all LMEs. Thus, better management, monitoring, compliance and policy efforts are needed around Africa, with a strong emphasis on regional cooperation, to help rebuild their stocks. Clearly, this is a challenging prospect, but seems to be the only rational way to maintain what is, for Africa, a crucial economic resource as well as food security base.

Artisanal fisher perceptions on ghost nets in a tropical South Atlantic marine biodiversity hotspot: Challenges to traditional fishing culture and implications for conservation strategies

Ghost fishing, the ability of fishing equipment to continue to capture organisms even after it is no longer controlled, leads to serious marine impacts, including bycatch, which contributes to biodiversity loss. Insistent complaints from artisanal fisher in the state of Bahia, Brazil, concerning the impacts of nets lost or abandoned by fisher from other regions that operate in their traditional fishing territory were brought to the attention of our research group. Therefore, this study aims to describe the knowledge and classify fisher perceptions in south Bahia regarding ghost fisheries in the region, as well as the resulting impacts and fisher ideas for solving this problem in a coastal coral reef region. Semi-structured interviews were conducted between August 2015 and September 2017 with 60 fishers, 59 men and one woman, that fish with hand lines and hooks in the studied area. A total of 90% of respondents (n = 54) reported having found ghost nets in their ancestral fishing territories, while 93% (n = 56) associated ghost nets with financial losses and marine environment impacts. Most respondents (n = 56; 93%) also indicated lower fishery yields due to ghost nets and indicated (n = 55; 91.9%) that most ghost nets found in the area are used for lobster fishing, which is banned in Brazil. Fishers revealed an active interest in solving this socio-environmental problem, demonstrating detailed knowledge related to the loss of fishing nets in the local marine environment, as they have been finding and removing ghost nets from the local sea. Fisher's ideas to solve this problem included the implementation of fines for fishers caught in breach of regional and national fisheries regulations, and management actions, such as ghost net removal from the sea. Establishing partnerships between fisher and the federal government in curbing ghost fisheries is crucial.

Exploring synergies in the water-food-energy nexus by using an integrated hydro-economic optimization model for the Lancang-Mekong River basin

The Water-Food-Energy nexus study identifies developmental challenges and trade-offs present along the transboundary river basins. Intensive reservoir development for hydropower production impacts existing actors in the Lancang-Mekong River Basin. Concerns from these stakeholders highlight three major trade-offs that occur between hydropower and irrigation (HP-AG), hydropower and fisheries (HP-F), and irrigation and fisheries (AG-F). Dam construction has an impact not only on power production but also on ecosystems and ultimately the livelihood of people. In this study, we quantify the effects of reservoir operation on hydropower generation, irrigated crop production and fisheries yield in the Tonle Sap lake through a novel hydro-economic model at the whole basin scale. Our main finding is that trade-offs can be turned into synergetic opportunities. First, the dam operation can increase water availability for irrigation without severely harming hydropower production, raising irrigated crop revenue by 49% and reducing crop losses during droughts by 30%. Second, eco-friendly management increases fisheries yield by up to 75%, but decreases both irrigated crop production (−48%) and power production (−17%). Reservoirs can, therefore, benefit the whole basin by releasing more water in months with high irrigation demand (April and December) and by minimizing the adverse effects of flow fluctuations on the livelihood of farmers and fishers living downstream. Our results also reveal the overlooked trade-off between irrigated agriculture and fisheries. Cross-sectoral and transboundary partnerships should strengthen stakeholder participation in decision-making. Local solutions such as enhanced reservoir operation can respond to the broader global issue of natural resource trade-offs and sharing. Our alternative narrative enhances the dialogue about fair and efficient water use among Mekong riparian countries.

Applying the Catch-MSY model to the stock assessment of the northwestern Pacific saury Cololabis Saira

The Pacific saury (Cololabis saira) is one of the major harvested species in the temperate waters of the northwestern Pacific Ocean (NPO). The Catch-MSY model uses catch data and basic life history information to estimate the Maximum Sustainable Yield (MSY) for data-limited fisheries. Since there is considerable uncertainty in the current status of the Pacific saury stock in the NPO, the Catch-MSY model was used in this study to estimate MSY on the basis of catch data and life history information from the North Pacific Fisheries Commission (NPFC). During the process, 17 scenarios, according to different prior distributions of the intrinsic rate of increase (r) and carrying capacity (K), were set for sensitivity analysis. Moreover, the influence of different catch time series and different process errors were taken into account. The results show the following: (1) there was a strong negative correlation relationship between ln(r) and ln(K); the MSY increases with an increase in the lower limit of r; (2) The time series of catch data had a limited impact on the assessment results, whereas the results of the model were sensitive to the annual catch in the first and last years; (3) The estimated MSYs of the Pacific saury were 47.37×104 t (41.57×104 t to 53.17×104 t) in scenario S1A and 47.53×104 t (41.79×104 t to 53.27×104 t) in scenario S1B. Given the uncertainty of the Catch-MSY model, maintaining a management target between 50×104 t and 70×104 t was a better management regulation. This study shows that the Catch-MSY model is a useful choice for estimating the MSY of data-limited species such as the Pacific saury.

Size‐selective fishing leads to trade‐offs between fishery productivity and reproductive capacity

AbstractMost fishing is inherently size‐selective, in that fishers preferentially select a subset of the population for harvest based on economic incentives associated with different‐sized fish. Size‐selective fishing influences the targeted population and fishery performance in multiple ways, including changing the reproductive capacity of the target population and altering fishery yield. Understanding how social–ecological variability, including size selectivity, affects target species populations is critical for fisheries management to optimize the benefits of fisheries and the ecological impacts on target populations. In this study, we used yield per recruit, spawning stock biomass per recruit, and length‐based spawning potential ratio models to explore how a range of size selectivity scenarios affect fishery and population productivity for Mexican chocolate clams, Megapitaria squalida, in Loreto, Baja California Sur, Mexico. We found that alternate slot limits result in trade‐offs between fishery yield and reproductive productivity of the target population. A more restrictive slot limit reduced the proportion of the population available to harvest, resulting in higher reproductive capacity of the population, compared to a less restrictive slot limit, conditional on the rate of fishing mortality. In the long run, a more restrictive slot limit will likely lead to a higher number of recruits, larger stock size, and higher long‐term fishery yield relative to a less restrictive scenario. Our findings highlight that how people fish matters, perhaps as much as the quantity of fish harvested; size‐selective fishing that aligns with the life history of target populations and stakeholders’ goals is critical to sustaining fisheries and the valuable food and livelihoods they provide.

Strategically designed marine reserve networks are robust to climate change driven shifts in population connectivity

Marine reserves can be effective conservation and fishery management tools, particularly when their design accounts for spatial population connectivity. Yet climate change is expected to significantly alter larval connectivity of many marine species, questioning whether marine reserves designed today will still be effective in the future. Here we predict how alternative marine reserve designs will affect fishery yields. We apply a range of empirically-grounded scenarios for future larval dispersal to fishery models of seven species currently managed through marine reserves in the nearshore waters in Southern California, USA. We show that networks of reserves optimized for future climate conditions differ substantially from networks designed for today’s conditions. However, the benefits of redesign are modest: a set of reserves designed for current conditions commonly produces outcomes within 10% of the best redesigned network, and far outperforms haphazardly designed networks. Thus, investing in the strategic design of marine reserves networks today may pay dividends even if the networks are not modified to keep up with environmental change.

Genetic diversity and population structure of black sea bream (Acanthopagrus schlegelii) based on mitochondrial control region sequences: the genetic effect of stock enhancement

The black sea bream, Acanthopagrus schlegelii (Bleeker, 1854), has a great commercial value and a long history of stock enhancement in most coastal cities in China. The stock enhancement programs made significant achievements and contributions in increasing fishery yield, but few information was reported regarding the genetic effects on the wild population resulting from the releasing. In order to elucidate the potential genetic effects associated with stock enhancement releases, sequence variation based on the mitochondrial control region was investigated to characterize the genetic resources of black sea bream in Pearl River Estuary. The results showed that the broodfish and hatchery-released fish were characterized by lower genetic diversity indices compared with wild populations. In addition, after releasing, the genetic diversity was lower in the samples of Pearl River Estuary than other wild populations. The results of pair-wise FST value and AMOVA revealed low genetic differentiation among hatchery populations, samples in Pearl River Estuary and wide populations nearby the stock areas, which was consistent with the previous study. Hence, the black sea bream stock enhancement may have affected the genetic diversity of wild populations in Pearl River Estuary. In further stock enhancement of A. schlegelii, it is necessary to routinely monitor the genetic effects of stock releasing and improve the genetic management.

Underestimated Microplastic Pollution Derived from Fishery Activities and "Hidden" in Deep Sediment.

Fishery activities are an important source of microplastic pollution in coastal areas but have received little attention. The Beibu Gulf, a traditional fishing ground of China and the China-Indo Peninsula, was selected in this study, and the focus was on the impacts of fishery activities on the horizontal distribution of microplastics in sediment. The results showed that the dominant contaminants (polypropylene fibers and polyethylene fibers) might originate from the abrasion of fishing gear and contributed to 61.6% of the total abundance of microplastics in surface sediment. The abundance of polypropylene fibers and polyethylene fibers exhibited a strong correlation (R2 = 0.8586, p = 0.015) with values of fishery yields of different districts, which highlighted the effects of different fishery activities on microplastic contamination in marine sediment. Microplastics could be "hidden" in deep sediment to a depth of 60 cm. The estimated storage of microplastics in deep sediment (185 tons) was 5 times that in surface sediment. The assessment of microplastic storage worldwide might be underestimated because most previous studies only examined surface sediment. The abundance distribution and size distribution of microplastics in the sediment core suggested long-term burial of microplastics in deep sediment. Bioturbation might be responsible for the vertical transport of microplastics, leading to "fresh microplastics" preservation in "old sediment".

The interplay between fishery yield and top predator culling in a multispecies fishery context.

In food webs, fishery can play the role of top predator, competing thus with other top predators for valuable food resources. In this view, it has been claimed in fisheries management that culling of top predators can be a means to improve fishery yield. To investigate this hypothesis, we use theoretical population models to assess in a multispecies context how fishery yield from target species harvest responds to top predator cull. Defying crisp summary, the four analysed food web models show that this response may be either positive or negative or both, indicating that in terms of multispecies fishery management the harvest yield may not accrue as a consequence of predator removal. In addition, this multitude of behaviours points also to the fact that the response of fishery yield to top predator cull may be difficult to assess.

Maximum Sustainable Yield, Maximum Economic Yield and Sustainability in Fisheries

A brief review of the concept of Maximum Sustainable Yield (MSY) used in fisheries management is discussed. The convenience of assessing the exploited stocks with the aid of simulation is advised, because implies the possibility to analyze the age structure of the fishery in more detail, as compared to the traditional methods of fish stock assessment. Emphasis is given to the use of the MSY as limit reference point because as long as the Fishing Mortality or fishing effort required for that point is kept at lower values, the fishery will have a good chance to be sustainable. A mention of the Maximum Economic Yield is made, proposing its use a target for the management, because it is reached in general with lower F values that for the MSY, and this way keeping the fishery in a healthy condition.

Maximum sustainable yield, maximum economic yield and sustainability in fisheries

A brief review of the concept of Maximum Sustainable Yield (MSY) used in fisheries management is discussed. The convenience of assessing the exploited stocks with the aid of simulation is advised, because implies the possibility to analyze the age structure of the fishery in more detail, as compared to the traditional methods of fish stock assessment. Emphasis is given to the use of the MSY as limit reference point because as long as the Fishing Mortality or fishing effort required for that point is kept at lower values, the fishery will have a good chance to be sustainable. A mention of the Maximum Economic Yield is made, proposing its use a target for the management, because it is reached in general with lower F values then that for the MSY, and this way keeping the fishery in a healthy condition.

Marine shrimp fisheries research—a mismatch on spatial and thematic needs

Marine shrimp fishing is an economic activity of global importance due to its high profitability, but it also presents several environmental and socioeconomic problems. In a context of increasing need for fishery sustainability, scientific basis supporting fishery resources management is essential. However, evidence-based information is frequently scarce or generated by developed countries, even when resources are most abundant in areas of developing economy. Here we present a bibliometric analysis to map each country’s scientific production in relation to its marine shrimp fishery yield, along with a hurdle model with socioeconomic factors that could influence publication of articles on this subject. We observed a geographic mismatch between research needs and the places that produce them, once tropical and subtropical regions account for most of fishery yield while knowledge is produced in temperate regions where the most developed countries are concentrated. Accordingly, our model reveled that GDP was the most influential factor in number of articles, while population density had a negative effect. Concurrently, key research interests about marine shrimp fisheries tend to be basic biology topics, despite the need for conservation solutions.

Two-stage mean-risk stochastic optimization model for port cold storage capacity under pelagic fishery yield uncertainty

The problem of the optimal capacity of cold storage for pelagic fisheries under uncertain harvesting/production is studied. We establish a two-stage mean-risk stochastic optimization model, by considering the uncertainty of pelagic fishery yield and the risk measure of the cold storage cost loss. Applying a Benders-type scenario decomposition method, a modified cutting decomposition algorithm is proposed to solve the two-stage mean-risk stochastic optimization model, yielding the optimal capacity and maximal expected return of cold storage simultaneously. Further, the effects of the refrigeration cost, storage fee, weight of the conditional value-at-risk, and the confidence level on the expected profit are analyzed. We compare the modified cutting decomposition algorithm with a multi-cutting decomposition algorithm, to validate the proposed algorithm based on the computational time and the number of iterations.

Neonicotinoids disrupt aquatic food webs and decrease fishery yields.

Invertebrate declines are widespread in terrestrial ecosystems, and pesticide use is often cited as a causal factor. Here, we report that aquatic systems are threatened by the high toxicity and persistence of neonicotinoid insecticides. These effects cascade to higher trophic levels by altering food web structure and dynamics, affecting higher-level consumers. Using data on zooplankton, water quality, and annual fishery yields of eel and smelt, we show that neonicotinoid application to watersheds since 1993 coincided with an 83% decrease in average zooplankton biomass in spring, causing the smelt harvest to collapse from 240 to 22 tons in Lake Shinji, Shimane Prefecture, Japan. This disruption likely also occurs elsewhere, as neonicotinoids are currently the most widely used class of insecticides globally.

The effect of anthropogenic and environmental factors in coupled human‐natural systems: Evidence from Lake Zürich

AbstractExploiting a rich data set including both individual fishing activities and ecology, we study how eutrophication and climate warming influence plankton biodiversity in Lake Zürich and the consequent effects on fishers’ behavior and fishery yield. Our analysis indicates that changes in the fishery of Lake Zürich were driven by complex dynamic interactions between fishing efforts, environmental conditions, and lake ecosystem ecology. Results show that nutrient levels and climate warming have both direct and indirect dynamic and nonlinear effects on both fishers’ behavior and lake productivity. Ecological factors such as plankton abundance and diversity affect the dynamics of the fish population, which, in turn, influences fishing effort. The analysis highlights the importance and the interdependence of ecological‐human linkages in aquatic ecosystems.Recommendations for Resource Managers This model estimates and simulates the effects of temperature and nutrients on the ecology and the management of a commercial lake fishery. Natural and anthropogenic factors have both direct and indirect effects on fishing intensity and the dynamics of lake productivity. In the long term, increasing phosphorus has negative impacts on the plankton of the lake; higher nitrogen has a positive impact on zoo‐abundance, but a negative impact on zoo‐richness; higher temperatures have positive effects on phytoplankton. Considerable heterogeneity exists in both in lake ecology at different habitats (top vs. bottom of the lake) and behavioral response (pelagic nets vs. demersal nets) to environmental fluctuations.