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.

Complex effects of acidification, habitat properties and fish stock on littoral macroinvertebrate assemblages in montane standing waters

Littoral macroinvertebrates in acidified waterbodies are affected by the interaction of acidification and local environmental conditions. Understanding the interplay of these factors in the structuring of communities is essential for interpreting responses to and/or recovery from acidification. Here, we analyse the species composition and richness of littoral macroinvertebrates in a range of acidified montane standing waters in relation to water chemistry, littoral characteristics and fish stock. The main species composition gradients were related to pH and conductivity; however, considerable variation along these gradients was associated with local habitat characteristics (changing water levels and littoral structure) and concentration of ionic aluminium and dissolved organic carbon. Although fish stock effects were confounded by correlated acidity, we observed a significant decline in abundance of macroinvertebrates vulnerable to fish predation at sites with fish stock. Overall, littoral macroinvertebrates of acidic waterbodies were diverse due to the heterogeneity of local habitat properties, despite they were dominated by acid-tolerant species. Acidic humic sites with dense, heterogeneous littoral vegetation were species-rich, hosting numerous habitat specialists and rare species, while chronically acidified lakes with high aluminium concentrations and sparse littoral vegetation had species-poor assemblages, characteristic of strong acid-stress. Water level manipulation resulted in serious assemblage impoverishment, overriding the effects of more favourable water chemistry. This study shows that the littoral fauna of acidic waterbodies is structured by complex effects induced by local factors in addition to acidity, resulting in acid-stressed assemblages with relatively high variability, emphasising a need to analyse local habitat factors when evaluating the impact of acidification on macroinvertebrates.

A Lab-on-a-Chip Based Automatic Platform for Continuous Nitrites Sensing in Aquaculture

In aquaculture, the density of fish stock, use of feeding, and surrounding environmental conditions can easily result in an excessive concentration of harmful compounds that require continuous monitoring. Chemical sensors are available for most of these compounds, however, operative conditions and continuous monitoring in water make the development of sensors suitable for long and unattended deployments difficult. A possible solution is the development of engineered automatic labs where the uptake of sample and the contact with water is reduced and the use of a minimal quantity of reagents enables the implementation of reliable chemical assays. In this paper, a platform for automatic chemical assays is presented. The concept is demonstrated with the detection of nitrites based on the well-known colorimetric Griess reaction. The platform is centered around a lab-on-a-chip where reagents and water samples are mixed. The color of the reaction product is measured with low-cost optoelectronic components. Results show the feasibility of the approach with a minimum detectable concentration of about 0.1 mg/L which is below the tolerance level for aquaculture farms.

The sustainable utilization of skipjack tuna in Northern Aceh waters

In recent years, production of skipjack tuna in Aceh was fluctuative in decreased trend due to relatively smaller fish size production. This study was aimed to analyse the skipjack tuna utilization sustainability on actual, maximum sustainable yield (MSY), maximum economic yield (MEY), and open-access (OA) conditions in North Aceh Waters. This study used time series data in 2009-2018. The analysis method used was a Gordon-Schaefer bioeconomical model. The results that the utilization of skipjack tuna in North Aceh Waters were at economical and biological overfishing. In long-term condition, this will potentially cause a decreased fish stock that will finally disrupt the sustainability level. In actual condition, the average of skipjack tuna utilization level per year was 163.77% more than the allowed total catching product, namely 2,712.64 ton per year. To achieve sustainable point, the fishermen should decrease their effort at 19.32% of the actual condition effort. The highest biomass level was occurred in MEY regime, followed by MSY and OA regimes. This means that the management of skipjack tuna in MEY regime is more conservative than in other regimes due to not spending skipjack tuna resource maximumly, but proposing to an optimum production level, which results in a maximum profit.

Bioeconomic Approach for Assessing Status of Trawl Fishery in the Straits of Malacca

The Straits of Malacca provides half of Malaysia’s total marine fish and seafood supply. Due to depleted fish stock, the Malaysian Government has established a comprehensive legal framework to reduce overfishing in the Straits over the last five decades. However, there are limited scientific studies on the current status of stock recovery. This paper aims to use bioeconomic approach to determine the current trawl fishery status in the Straits. Various statistical tests showed that the Clarke-Yoshimoto-Pooley model was better than the Schnute model in predicting and thus used to estimate the crucial bioeconomic parameters. The current yield and standardised effort of 239,692 tonnes and 931,692 standard fishing days were very close to the estimated biological maximum sustainable yield (239,915 tonnes) and above 18 % of the standardised effort (763,649 standard fishing days) to achieve it. The maximum economic yield was estimated at 201,542 tonnes while the corresponding standardised effort was 396,799 standard fishing days indicating serious economic overfishing in the Straits. If the current effort can be reduced by 57 %, fish biomass and economic rent will increase by 97 % and 835 %, respectively. A price sensitivity analysis predicted that demand-pull fish price inflation could exacerbate the overfishing problem, particularly under unrestrained environment. A 50 % increase in price could lead to a 132 % increase in fishing effort from the base case. The findings of this paper provide valuable insights for fishery managers to refine their existing fishery management program to achieve sustainable fishery for the future.

Habitat deterioration despite protection: long-term declines of littoral area of fishponds in Czech nature reserves

Fishponds play a key role in current pondscapes in many developed countries. Their littoral areas, supporting multiple ecosystem functions including the maintenance of aquatic and riparian biodiversity, have been adversely affected by the move shift towards more intensive aquaculture and widespread eutrophication in the middle 20th century. To counteract these changes, many fishponds received some protection, but its long-term efficiency has not been studied. Here we focus on the role of conservation status in protecting the area of littoral areas of fishponds in Czechia between the years 1950 and 2019. We found that the conservation status of these fishponds did not prevent habitat deterioration in most of the fishponds, especially during the second half of the 20th century. Moreover, we detected no significant effects of the reserve establishment year, fishpond area and conservation target on the littoral areas. This suggests that the conservation measures are insufficient across fishpond reserve types. We attribute the negative trends to persisting high fish stocks, especially of common carp, and eutrophication resulting from additional feeding, pond manuring, and ongoing nutrient inputs from the pond catchments. Sediment dredging and high grazing pressure by waterfowl in some reserves can further aggravate the situation. We conclude that effective protection of the littoral areas requires a paradigm shift towards less intensive fish stock management, more frequent summer drainage, and effective reduction of all nutrient inputs to increase the water quality. Such measures can help recover the littoral areas and the associated biota.

Variation in global distribution, population structures, and demographic history for four Trichiurus cutlassfishes

Background Species-specific information on distribution and demographic patterns provides important implications for conservation and fisheries management. However, such information is often lacking for morphologically-similar species, which may lead to biases in the assessments of these species and even decrease effort towards sustainable management. Here, we aimed to uncover the distribution range, population structure and demographic history for four exploited Trichiurus cutlassfishes using genetics. These cutlassfishes contribute substantial global fisheries catch, with a high proportion of catch harvested from the NW Pacific. Methods We chose the widely available mitochondrial 16S ribosomal RNA (16S) as the genetic marker for cutlassfishes. We compiled the 16S sequence data from both the GenBank and a survey of trawler catch samples along the NW Pacific coasts 22–39°N. Genealogical relationships within each species was visualized with haplotype networks and potential population differentiations were further evaluated with AMOVA. Demographic histories were estimated using neutrality test, mismatch analysis, and the Bayesian skyline plot. The reconstructed phylogenetic trees were used to delimit and estimate the divergence time of species and included populations. Results In each of two cosmopolitan species, T. lepturus and T. nanhaiensis, we observed distinct populations along the coasts of warm oceans; such population differentiation might result from historical geographic barriers in the Pleistocene. In the NW Pacific, four Trichiurus species vary in their distribution habitats, which reflect differential ecological niches among these species. The small-sized T. brevis are primarily found in nearshore habitats; the warm-affiliated T. nanhaiensis are present along the path of the Kuroshio Current; the cold-affiliated T. japonicus spatially diverged from the widely-distributed T. lepturus, with the latter mainly occupy in warmer regions. Despite these differences, a single well-mixing fish stock, thus one management unit, was identified in each of the four species, presumably due to expansion of their population sizes predated the Last Glacial Maximum and a lack of distribution barrier. The most dominant T. japonicus, which have at least one magnitude higher effective population size than the others, show a unique abrupt size expansion event at 75 to 50-kilo years ago when the low sea level occurred during the ice age. Main conclusions The demographic history revealed by our genetic analyses advances understanding of the current distribution and population structure for these congeneric species. Moreover, the uncovered population structure provides insight into the assessment and management of these species. Such information complements contemporary knowledge about these species and enables us to forecast their ability to resist future environmental and anthropogenic disturbances.

Optimization of a Marine Fish Release Strategy: A Case Study of Black Sea Bream Acanthopagrus schlegelii in the Zhanjiang Estuary, Northern South China Sea

The release strategy (choice of the species and locations stocked, releasing mode, and stocking size and times) is an important part of quantitative evaluations of marine fish stock enhancement, while optimization of the release strategy can contribute to assess the stocking success intended to alleviate declining fishery resources and to increase the income of fishers. In this study, a typical fish species released in the northern South China Sea, black sea bream Acanthopagrus schlegelii, was taken as the research object. The biological characteristics of this sparid were determined from samples collected from waters in the Zhanjiang estuary during June, July, and September 2020 to April 2021, and the data were applied to estimate its length frequency and its growth parameters using the ELEFAN I run in FiSAT II. We then simulated and evaluated the stocking effects of five scenarios under different release strategies, while assuming a fixed total quantity of released fish and a constant of mortality rate at different life stages. The results showed that (1) the breeding season of black sea bream in this region is mainly from December to March of the next year, which is also the period when most significant sexual reversal in this species occurs, and (2) the relationship between standard length and weight in black sea bream is W = 5.092 × 10–5L2.906, L∞ = 54.39 cm, K = 0.15, and t0 = −0.967. (3) The recommended period to release black sea bream in Zhanjiang waters is from June to October. It appears more productive if the total quantity of fish released can be divided into two batches. The growth potential of released juvenile fish in this study was evaluated based on a density-dependent theory, and the stocking effect of released stocks was simulated with the consideration for biological parameters and field sampling technique. This study provides a reference for the optimization of fish release strategies in coastal waters.

Effective Governance and Policy Implementation in Governing High Seas Fisheries: A Comparative Study of Three Regional Fisheries Management Organizations

<p>Two-thirds of fish stocks commercially fished on the high seas are either depleted or overexploited. Regional Fisheries Management Organizations (RFMOs) are key international actors having the legal competence to establish fishery conservation and management measures to improve the optimal and sustainable utilization of high seas fisheries resources. The literature suggests that their effectiveness is varied. While some RFMOs are making progress towards more sustainable fisheries, some are facing fish stock depletion. The literature indicates that organizational governance design and quality of implementation are central to the disparities. Thus far, while most of the discussion has focused on the effectiveness, and how to enhance the transparency of RFMOs, very little research has explored the designs of governance arrangements and implementation of RFMOs. Accordingly, this study contributes to the literature on governance arrangements and policy implementation of the high seas by offering in-depth case studies of the selected RFMOs. It employs qualitative methods to analyze data collected from semi-structured interviews with 24 actors (i.e., officials, delegations, and fisheries experts), as well as a collection of published and unpublished documents regarding three selected RFMOs. The three selected RFMOs are the Commission for the Conservation of Southern Bluefin Tuna (CCSBT), the Western and Central Pacific Fisheries Commission (WCPFC), and the South Pacific Regional Fisheries Management Organization (SPRFMO). The findings show that it is possible to apply Ostrom’s (1990) design principles to uncover how RFMOs can be designed for higher performance in governing high seas fisheries. However, adjusted and additional design principles are necessary to have a better understanding of the factors that contribute to sustainable high seas fisheries. For example, the design principles should include policy learning and adaption, particularly in the regional and global contexts, so as to address complexities and uncertainties. Furthermore, the research reveals a number of critical factors of RFMO policy implementation, such as strong political will and commitment, the availability of proper resources and coalitions. This study concludes with recommendations for policymakers of the RFMOs to better achieve their overarching objectives.</p>

Effective Governance and Policy Implementation in Governing High Seas Fisheries: A Comparative Study of Three Regional Fisheries Management Organizations

<p>Two-thirds of fish stocks commercially fished on the high seas are either depleted or overexploited. Regional Fisheries Management Organizations (RFMOs) are key international actors having the legal competence to establish fishery conservation and management measures to improve the optimal and sustainable utilization of high seas fisheries resources. The literature suggests that their effectiveness is varied. While some RFMOs are making progress towards more sustainable fisheries, some are facing fish stock depletion. The literature indicates that organizational governance design and quality of implementation are central to the disparities. Thus far, while most of the discussion has focused on the effectiveness, and how to enhance the transparency of RFMOs, very little research has explored the designs of governance arrangements and implementation of RFMOs. Accordingly, this study contributes to the literature on governance arrangements and policy implementation of the high seas by offering in-depth case studies of the selected RFMOs. It employs qualitative methods to analyze data collected from semi-structured interviews with 24 actors (i.e., officials, delegations, and fisheries experts), as well as a collection of published and unpublished documents regarding three selected RFMOs. The three selected RFMOs are the Commission for the Conservation of Southern Bluefin Tuna (CCSBT), the Western and Central Pacific Fisheries Commission (WCPFC), and the South Pacific Regional Fisheries Management Organization (SPRFMO). The findings show that it is possible to apply Ostrom’s (1990) design principles to uncover how RFMOs can be designed for higher performance in governing high seas fisheries. However, adjusted and additional design principles are necessary to have a better understanding of the factors that contribute to sustainable high seas fisheries. For example, the design principles should include policy learning and adaption, particularly in the regional and global contexts, so as to address complexities and uncertainties. Furthermore, the research reveals a number of critical factors of RFMO policy implementation, such as strong political will and commitment, the availability of proper resources and coalitions. This study concludes with recommendations for policymakers of the RFMOs to better achieve their overarching objectives.</p>