Fish Stocks Research Articles

Provisions for nullification of conservation and management measures in RFMO objection procedures

In order to successfully exercise their mandate to adopt binding conservation and management measures (CMMs) for straddling and highly migratory fish stocks, regional fisheries management organizations (RFMOs) and arrangements (RFMAs) need effective decision-making procedures. The constitutive instruments of a considerable number of such bodies contain objection procedures which allow individual members to unilaterally opt-out of an adopted CMM. Most scholars and RFMO performance review panels consider that unconstrained unilateral objection procedures undermine the decision-making procedures of both RFMOs and RFMAs. This article examines the phenomenon of CMM nullification provisions, which are present in five RFMOs. Such provisions deprive adopted CMMs of their binding force for all members if a certain number of members of the RFMO object to the CMM. This article argues that there is a case for a phase-out of CMM nullification provisions together with the unilateral objection procedures to which they are closely tied. Compared to unilateral objections more generally, CMM nullification provisions raise additional legitimacy questions given that they result in the nullification of CMMs that have been democratically adopted in conformity with the legitimate decision-making procedures of the respective RFMO. This article first provides a brief overview of the rationale for objection procedures by placing the concept of objections in the broader context of RFMO decision-making. Thereafter, this article briefly examines the requirements and legal effects of individual objections of RFMO members to CMMs. The final substantive section analyzes and compares existing CMM nullification provisions, focusing on the requirements for their activation, the nature of their legal effects and the legitimacy of such procedures considering the broader decision-making procedures of individual RFMOs.

Disappearing fish: Grey seal depredation in a Baltic net fishery

Grey seals (Halichoerus grypus) in the Baltic Sea commonly attempt to steal fish captured in net fisheries. Seal depredation reduces economic yields for small-scale net fishers in a region already highly impacted by the collapse of important fish stocks. Visible damages in looted nets consist of injured fish with bite marks, or holes in the gear, but additional losses from seals eating entire fish without leaving a trace can often remain unnoticed. In this study, we estimated the daily rates of injured and of stolen fish in a commercial gillnet fishery operating off coast of Bornholm in the Central Baltic Sea in 2021–2022. Our results show that the Atlantic cod (Gadus morhua) is generally preferred over other target species [here, European plaice (Pleuronectes platessa), European flounder (Platichthys flesus), and turbot (Scophthalmus maximus)]. Although the observed ratio of 5.65 cods disappearing for each cod retrieved with seal bite marks is similar to a study from the 2000’s, we show that average daily cod disappearance rates are linked to the duration a gear is left soaking in the same location.

Improving access: Multi-analytical survey of the Norwegian Sea trade archive to establish storage conditions, digitisation priorities and conservation treatments

The Norwegian Sea Trade Archive (NST Archive) from the University of Bergen Library, Norway, is part of the UNESCO documentary heritage and contains unique documentation of the activity of companies that traded in stock fish in Norway and Europe (16th-20th century). The archive consists primarily of bound paper manuscripts written mostly in brown ink. We have surveyed this collection using a multi-analytical approach focused on the material characterization and condition of the paper carrier and inks. Our main aim was to support decision-making on establishing storage conditions, digitisation priorities, and type and extent of conservation treatments necessary to make the collection accessible.After a first visual examination to detect and quantify damages, for the paper support analysis we measured surface pH, paper thickness and water absorbency. Additionally, on a quarter of all tested materials, we performed a SurveNIR analysis, providing information regarding paper pulp type, lignin, protein and rosin content, degree of polymerization, and mechanical properties. The archival material was grouped into three periods characterising the three milestones in paper production: handmade gelatine-sized rag papers, machine-made rag papers with gelatine and rosin sizing, and papers made from processed wood pulp.Regarding the manuscripts’ inks, we used iron and copper tests to determine the presence of Fe2, Cu2+ and Cu+ions, respectively. For the visual characterization and condition rating of the inks, we used the protocols described by the Netherlands Institute for Cultural Heritage. The variety of ink colours and thickness of the inked lines encountered in each document was noted down. Thus specific tendencies present in each historical period became apparent. Results of the solubility of ink in water and alcohol significantly narrowed treatment options.General tendencies of paper and ink degradation based on differences in papermaking were observed. Surface pH measurement, SurveNIR pH, rosin and protein concentration data showed that most rag papers were of poor to fair quality (pH ≤ 6.0 and low protein content (< 5 %)). Rosin-sized papers dated after 1840 had a lower pH (from 3.3 ± 0.2 to 5.0 ± 0.2) compared to gelatine-sized ones. Based on the obtained results, the overall condition of all the papers is good – slightly damaged but stable. The inks are not severely corroded, and there is no loss of text, although 20 % of the collection does show signs of iron-gall ink (IGI) corrosion. A limited number of documents, mostly before 1800, would require local antioxidative treatment. Due to the low pH of all the papers and the detection of ink corrosion, the collection should be stored in a cool environment, with low relative humidity.After the survey, digitisation priorities were also established.

Maternal effects on recruitment of five gadoid species

AbstractCommercial fishing is almost always non‐random and generally removes large and old individuals from fish stocks, thereby reducing age diversity among spawners. Reduced age diversity may result in less stable recruitment. Here, we explore the influence of age diversity (H), mean age of the spawning stock (MA) and sea surface temperature (SST) on recruitment‐per‐spawning biomass (RSSB) for five commercial gadoid species (Atlantic cod, haddock, ling, saithe and tusk) by using data from analytical stock assessment spanning 4–7 decades. In the past 10–20 years, spawning stock biomass of these species (except for tusk) has increased due to lower fishing pressure. Concurrently, H and MA increased, especially for cod. However, our results did not indicate long term either positive or negative correlation between the maternal factors (H and MA) and RSSB for four of the studied species. Cod was the only species that showed significant positive correlation between H and RSSB, but the correlation did not hold during the most recent period of high SST. The conflicting outcomes underscore the difficulty in identifying a constant and direct maternal and/or environmental influence on RSSB.

Fish stocks as phosphorus sources or sinks: Influenced by nutritional and metabolic variations, not solely by dietary content and stoichiometry

The study provides a descriptive understanding of when fish (Cyprinus carpio model) are the source or sink of phosphorus. Dissolved reactive phosphorus (DRP; PO4-P) losses (51.1 ± 5.9 % of intake-P) increase at excess of bioavailable P (>0.83 g 100 g−1 dry matter, DM fed) or when food (digestible) N:P mass ratio (≤4.4:1) approaches organismal storage threshold (~4:1). This is known, however, even at a sub-threshold food P content (0.57 g 100 g−1 DM) and food N:P mass ratio (7.3:1), DRP losses (57.8 ± 4.5 % of intake-P) may be extraordinary if two indispensable amino acids are biologically insufficient (lysine ≤1.43 g, methionine ≤0.39 g 100 g−1 DM fed). Given that methionine and lysine are sufficient, DRP losses cease (≈0 %) and even some P from water is absorbed, given there is support from non-protein energy (NPE). Insufficient NPE (<180 kcal 100 g−1 DM fed) may drive DRP losses (81.6 ± 4.3 % of intake-P) beyond expected levels (46–59 % of intake-P) at a given food P content (0.91 g 100 g−1 DM). Natural food seldom fulfills low P, high lysine + methionine, and high NPE contents simultaneously, thus keeping fish in a perpetual P recycling for algae (scaleless carp > scaly carp). Such P recycling ceases only during basal metabolism. During feeding state, the richness of lysine + methionine bound N and lipid + carbohydrate bound C in the food base may enhance the fishes' threshold of P storage. P storage can be diminished when they are insufficient. We show that for fish, the decision of P recycling or not recycling (for algae) may change based on the supply of specific fractions of N or C from the food web or metabolic variations (basal metabolism, presence of scales). Novelty statementThe ecological stoichiometry theory is better connected to fish nutritional bioenergetics for better understanding and biomanipulation of eutrophication processes.

Directional selection, not the direction of selection, affects telomere length and copy number at ribosomal RNA loci

Many fisheries exert directional selection on traits such as body size and growth rate. Whether directional selection impacts regions of the genome associated with traits related to growth is unknown. To address this issue, we characterised copy number variation in three regions of the genome associated with cell division, (1) telomeric DNA, (2) loci transcribed as ribosomal RNA (rDNA), and (3) mitochondrial DNA (mtDNA), in three selection lines of zebrafish reared at three temperatures (22 °C, 28 °C, and 34 °C). Selection lines differed in (1) the direction of selection (two lines experienced directional selection for large or small body size) and (2) whether they experienced any directional selection itself. Lines that had experienced directional selection were smaller, had lower growth rate, shorter telomeres, and lower rDNA copy number than the line that experiencing no directional selection. Neither telomere length nor rDNA copy number were affected by temperature. In contrast, mtDNA content increased at elevated temperature but did not differ among selection lines. Though directional selection impacts rDNA and telomere length, direction of such selection did not matter, whereas mtDNA acts as a stress marker for temperature. Future work should examine the consequences of these genomic changes in natural fish stocks.

Changes in artisanal fishing as a driver of the shifting baseline syndrome: from the perspective of local ecological knowledge

This study aims to analyze changes in artisanal fishing perceived by fishers based on their local ecological knowledge, highlighting changes in species availability over time on the coast of Paraíba, in Northeast Brazil. Through data collection from fishers, it was observed that 78.88 % of them noticed changes in fishing activity over time, with a greater perception of changes among groups of more experienced fishers, reaching 93.42 %. The regression analysis applied to the study revealed that the increase in fishing experience is related to the perception of changes that have occurred, suggesting an increase of 5.5 % in the perception of changes for each additional year of experience. The main factors cited for these changes include over-exploitation and environmental degradation. The following most affected species stand out: Mutton snapper (Lutjanus analis), Serra Spanish mackerel (Scomberomorus spp), Quenn triggerfish (Balistes spp) and groupers (Mycteroperca spp), indicating a significant reduction in their catches over the years. Therefore, this study highlights the importance of integrating local ecological knowledge into public policies, not only aiming at the management and conservation of fish fauna, but also at maintaining communities which depend on fishing for their subsistence. This would include more adaptive fishing regulations and fish stock recovery initiatives which are culturally acceptable and ecologically sustainable.

Evaluation of Algal Control Measures in Eutrophic Reservoirs Based on Aquatic Ecosystem Models

The frequency of freshwater cyanobacterial blooms is increasing globally due to climate change and eutrophication, particularly in reservoirs. Reservoir ecosystems exhibit unique characteristics, and there is a complex relationship between factors such as light, temperature, nutrient salts, hydrology, and algal growth. The impact of the other factors on algal growth varies significantly among different reservoirs. Thus, it is crucial to assess the effectiveness of various algal control measures implemented in different reservoirs. This study conducted a comprehensive assessment by establishing a eutrophication model for the Shanzi Reservoir in Fuzhou City. The model incorporated meteorology, hydrology, carbon dynamics, nutrient cycling, and biological communities. The effectiveness of diverse management measures was systematically evaluated. The findings demonstrate that increasing the water level, reducing nutrient salts in sediments, and implementing ecological fish stocking effectively suppressed algal growth to varying degrees and improved nitrogen and phosphorus levels. Lower water levels and ecological fish stocking had a significant impact on algal reproduction, while sediment reduction had a minimal effect. Conversely, lower water levels and ecological fish stocking did not significantly improve nitrogen and phosphorus concentrations in the reservoir, whereas sediment reduction had a noticeable effect. Consequently, the management strategies for the Shanzi Reservoir should prioritize external control measures and the implementation of ecological fish stocking.

Evaluating the unexplored recreational fishing in the Turkish Black Sea: socio-economic significance and environmental impact

Marine recreational fishing, a globally popular outdoor activity, has deep cultural roots and ecological implications. This study, conducted between 2021-2022, explores marine recreational fishing practices along the Turkish Black Sea coast. It analyzes fisher numbers and demographics, fishing effort, fishing methods, and species caught and released. Furthermore, the research sheds light on the economic dimensions, emphasizing the substantial contributions of recreational fishing to local economies. Notably, responsible practices, such as catch-and-release initiatives, demonstrate anglers’ awareness of conservation efforts. Within the Turkish Black Sea region, an observed 18.5% participation rate among a population of 24.5 million implies the presence of approximately 4.5 million marine recreational fishers. Annually, this translates to nearly 30 million fishing days, accompanied by a total expenditure of 400 million Euros. However, it’s imperative to handle these figures cautiously as the timing of the screening survey during the COVID-19 pandemic may have influenced the high participation rate, introducing a potential bias. A detailed examination of a Turkish marine recreational fisher engaged in Black Sea fishing reveals an average annual catch of 16.5 kg of retained fish and 1.2 kg of released fish biomass. When extrapolated to the larger population of 4.5 million fishers, this culminates in a noteworthy landing biomass approaching 74,000 tons. The study unveils that marine recreational fishers in the Turkish Black Sea predominantly target commercially important species, resulting in a retained biomass surpassing commercial landings in 2021. This prompts concerns about potential impacts on crucial commercial fish stocks, underscoring the imperative inclusion of recreational fisheries in stock assessments. The research, providing essential insights into the intricate dynamics of recreational fishing, lays a foundation for well-informed policies and practices that concurrently promote environmental conservation and the continuation of this valued leisure activity.

Recreational fisheries selectively capture and harvest large predators

AbstractSize‐ and species‐selective harvest inevitably alters the composition of targeted populations and communities. This can potentially harm fish stocks, ecosystem functionality, and related services, as evidenced in numerous commercial fisheries. The high popularity of rod‐and‐reel recreational fishing, practiced by hundreds of millions globally, raises concerns about similar deteriorating effects. Despite its prevalence, the species and size selectivity of recreational fisheries remain largely unquantified due to a lack of combined catch data and fisheries‐independent surveys. This study addresses this gap by using standardised monitoring data and over 60,000 digital angling catch reports from 62 distinct fisheries. The findings demonstrate a pronounced selectivity in recreational fisheries, targeting top predators and large individuals. Catch‐and‐release practices reduced the overall harvest by 60% but did not substantially alter this selectivity. The strong species‐ and size‐specific selectivity mirror patterns observed in other fisheries, emphasising the importance of managing the potential adverse effects of recreational fisheries selective mortality and overfishing.

Identification of Konosirus punctatus (Temminic and Schlegel, 1846) stocks in Korean waters via otolith shape analysis and comparison of growth parameters

Accurate identification of fish stocks is essential for the successful management of fishery resources. In this study, the populations of dotted gizzard shad, Konosirus punctatus, which is listed on the International Union for Conservation of Nature red list of the threatened species, were identified by combining two phenotypic methods: otolith shape analysis and comparison of growth parameters. Otolith shape analysis revealed two types of otoliths, pointing to the presence of two gizzard shad stocks in two areas along the Korean coast: the East Sea and the Yellow Sea + western Korean Strait. It is also supported by the result that the two stocks are significantly different in the shape indices (SI), and asymptotic fork length (FL∞). These results may be due to the influence of several environmental factors, such as temperature, salinity, and food availability. Overall, our findings suggest that there are two phenotypic stocks of K. punctatus in the Korean coastal waters and they should be managed differently.

Including close-kin mark-recapture data in statistical catch-at-age stock assessments and management strategies

Close-kin mark-recapture (CKMR) data can be used on their own to provide estimates of fish spawning stock biomass, adult mortality rate and fecundity-at-age. However, CKMR data can also be integrated directly into a stock assessment. We present a simplified example of integrating CKMR data within the Stock Synthesis assessment framework, and use simulation to evaluate management strategies based on the harvest control rule used to set catch limits for fish stocks off southeast Australia. The simulations are tailored to jackass morwong, Nemadactylus macropterus, a moderately-long lived (up to 46 years) fish species that is believed to have exhibited a regime-shift reduction in recruitment. We identify the sample sizes needed for a CKMR-based management strategy to achieve similar performance to an (optimistically parameterized) catch-per-unit-effort (CPUE)-based approach for this species. A CKMR-based management strategy can perform at least as well as a CPUE-based approach and CKMR data provide information to better estimate parameters such as adult natural mortality. Moreover, CKMR-based management strategies are not subject to the risk associated with CPUE-based approaches related to trends in catchability. The performances of CKMR-based assessment methods and management strategies are likely case-specific, but this paper shows the viability of including CKMR data in next generation stock assessments and harvest control rules.

Sustainability of Fish-Hydropower Dam Interaction: A Case Study of River Nyamugasani ecosystem, Albertine Graben

This study examined the River Nyamugasani ecosystem in western Uganda, evaluating fish diversity status before and after construction of a hydropower dam between 2015 - 2019 and 2021 - 2022. Using both electro fisher and minnow traps as the main fishing gears at ten preselected sites within the hydropower project areas, the study sampled 1,866 fishes from twenty-four (24) species, including the endemic Varicorhinus Ruwenzori, Pellegrin 1909. Nyamu II PH areas registered higher diversity (Simpson index of 0.8862) potentially attributed by hydrological alterations from hydropower dams. The findings emphasize the need for hydropower management need to consider fish stock controls, restorations and conservation measures, especially for theendemic Varicorhinus Ruwenzori species.

STATUS PEMANFAATAN IKAN KAKAP (Lutjanus spp.) BERBASIS DATA PANJANG IKAN DI PERAIRAN TAMAN NASIONAL TAKA BONERATE

Snappers (Lutjanus spp.) are the most common reef fish caught in Taka Bonerate National Park due to its high economic value and primarily targeted species. Without proper management measures, intensive fishing activities might result in unsustainable fish stocks. Therefore, in order to maintain sustainable utilization, it is important to understand the stock status of snapper fisheries. This study aimed to analyze the snappers' stock status in Taka Bonerate National Park's waters. Data were collected from January to December 2022 at three small-scale fisheries landing sites. The results showed that snappers are classified as slow-growing species with growth rates for species L. bohar, L. quinquelineatus, L. gibbus respectively 0,12, 0,39, and 0,35 per year to reach their respective asymptotic lengths of 83,41 cm, 29,5 cm, and 46,80 cm. The stock status of L. gibbus and L. bohar were indicated at overfished status where the exploitation rate (E) was &gt; 0.5 and the SPR was &lt; 0.3, hence a proper management measures is required. Furthermore, the species of L. quinquelineatus has a value of E is 0.5 and SPR is at 0.3, indicating that the utilization level of this species was at an optimal level. Keywords: Snapper, Taka Bonerate, Fisheries Management.

Implementasi Kebijakan Penanganan dan Penanggulangan Kegiatan Penangkapan Ikan yang Merusak (Destructive Fishing) di Indonesia

Destructive fishing activities are a threat to the sustainability of fishery resources and harm fish stocks as well as environmental ecosystems. Comprehensive regulations are needed to cope with destructive fishing and ensure the regulations will be implemented well and appropriately. Using a qualitative approach, this study aims to scrutinize the implementation of policies issued by the central government in the regions, including laws and other national regulations related to coping with destructive fishing. North Maluku Province is the focus of the study to identify the implementation of national regulations in the region. In addition, this study also identifies the roles of maritime law enforcement agencies involved in efforts to supervise and implement national policies related to overcoming and preventing destructive fishing. The results reveal that existing laws are insufficient to cope with the destructive fishing criminal act. So far, eight actors have roles in the prevention and coping of destructive fishing activities, consisting of elements of maritime law enforcement agencies such as the Police, Indonesian Navy, Indonesian Coast Guard, and Directorate General of PSDKP, as well as civil or community elements such as the PWP3K Special Police, Forestry Police, Department of Marine Affairs and Fisheries, and Monitoring Community Supervisory Groups (Pokmaswas). Keywords: destructive fishing, Law, Maritime Law Agency, Gap

Deep genetic divergence among bluefish (Pomatomus saltatrix) of the Southwestern Atlantic

AbstractNeglected cryptic diversity can lead to the permanent loss of locally adapted alleles, which can reduce resilience to rapid environmental change. It can also result in overestimation of fisheries stock sizes that can result from treating different species as if they belonged to one. Bluefish (Pomatomus saltatrix) is considered a circumtropical and subtropical species and an important fishery resource all over the world. Differences in ecologically relevant traits are observed among isolated populations. Also, in the Southwestern Atlantic, molecular data suggest multiple populations, but these are treated as a single fish stock by regulatory agencies due to a lack of definitive information. We used whole mitogenome sequences, nuclear (rho) and mitochondrial (coxI and cytb) genes, as well as microsatellites to investigate historical and current genetic population structure and parameters of bluefish in the Western Atlantic. A total of 263 samples were collected along the Brazilian coast and in the USA (New Jersey, Northwest Atlantic). Data revealed the existence of two evolutionarily significant units (ESU) of bluefish along the South American coast, later confirmed by whole mitogenome sequencing of both haplogroups. These two ESUs have a mostly parapatric distribution, with some areas of overlap, which vary along the year. We also conducted seasonal sampling in Brazil to investigate migration patterns. ESUs occur mostly north and south of parallel 23° 40′ S, with an overlap area that varied seasonally. The level of differentiation between those two ESUs in the SW Atlantic, even in sympatry, is as high as that found between them and those from the NW Atlantic and Europe. Parapatric distribution and restricted gene flow suggest the existence of ecological barriers and local adaptation. The splitting of an ancient population from the Southwestern Atlantic into two putative species is important to understand bluefish evolutionary diversification and has implications for fishery regulatory measures in Brazil.

Northeast Atlantic fish stock productivity hindcasts and forecasts from a Bayesian framework reveal pronounced climate‐induced dynamics

AbstractClimate change continues to exert pressure on ocean ecosystems. The fisheries‐related responses, such as altered body growth, recruitment and spatial distribution of the targeted stock(s), have generally been reasonably well investigated. Nevertheless, there are still important knowledge gaps in how biophysical drivers impact stock productivity and thereby sustainable harvest levels. Considering this, we investigated 26 fish stocks in the Northeast Atlantic, a region characterized by accelerated climate change effects and a diverse set of fisheries. A novel, stepwise, Bayesian framework to quantify stock productivity was established to identify shared trends and project future patterns, aiming at determining essential baselines for adaptive fishery management in the face of climate change. Despite variation among large marine ecosystems and stocks, an overall declining trend in productivity over the past four decades was observed, especially in high‐latitude areas. These hindcast results were mainly attributed to higher temperatures posing negative effects on productivity, which was dependent on the stock's thermal preference. Contrastingly, the proxy for food availability – gross secondary production – exhibited less consistent impacts. In the forecast, the applied Shared Socio‐economic Pathways (SSPs) indicated that most stocks are likely to encounter adverse effects, with the worst cases expected to occur under SSP2‐4.5 in the 2050s, and under SSP5‐8.5 in the 2090s. Thus, this study generally not only supports earlier climate vulnerability assessments (‘scorings’) of experts but also provides evidence for revised directional effects under climate change, underlining the complexity of processes affecting stock productivity.

Calibration of commercial fisheries echo sounders using seabed backscatter for the estimation of fishery resources.

Acoustic methods are often used for fisheries resource surveys to investigate fish stocks in a wide area. Commercial fisheries echo sounders, which are installed on most small fishing vessels, are used to record a large amount of data during fishing trips. Therefore, it can be used to collect the basic information necessary for stock assessment for a wide area and frequently. To carry out the quantification for the fisheries echo sounder, we devised a simple method using the backscattering strength of the seabed to perform calibration periodically and easily. In this study, seabed secondary reflections were used instead of primary reflection because the fisheries echo sounders were not equipped with a time-varied gain (TVG) function, and the primary backscattering strength of the seabed was saturated. It was also necessary to use standard values of seabed backscattering strength averaged over a certain area for calibration to eliminate some of the effects of differences in seabed sediment and vessel motions. By using standard values of the seabed secondary reflections, the fisheries echo sounder was calibrated accurately. Our study can provide a reliable framework to calibrate commercial fisheries echo sounders, to improve the estimation and management of fishery resources.

Impacts of locally managed periodic octopus fishery closures in Comoros and Madagascar: short-term benefits amidst long-term decline

Octopus fisheries face heightened demand driven by depleted fish stocks and escalating economic value, leading to overextraction of octopus populations and magnifying threats to coastal ecosystems and the livelihoods of fishers who depend on them. Implementation of management strategies such as periodic fishing closures can offer sanctuary for octopus, providing the necessary space and time for the growth and reproduction of this rapidly proliferating species. Despite evidence of positive management outcomes, the role of periodic closures in the long-term sustainability of octopus populations remains uncertain. Here, we examine trends in octopus landings over time and the effects of periodic closures along the Mozambique Channel from Comoros to Madagascar (12°-25°S). Long-term trends in octopus landings varied across three regions: generally stable over a 6-year period in Comoros, increasing over a 4-year period in the Barren Isles and declining over a 17-year period in Atsimo Andrefana, Madagascar. We observed a significant increase in mean catch per unit effort (CPUE, kilograms/fisher-day), and mean total catch (kilograms/day) following periodic closures across villages extracting octopus from closure areas. When evaluating each region independently, we observed this positive effect across Comoros and Atsimo Andrefana, Madagascar while trends in the Barren Isles showed no effect of octopus closures. We applied generalized linear mixed models to examine the influence of 10 covariates on mean daily total catch and CPUE within 7 days and 30 days post-closure. Baseline conditions (quantified by the pre-closure CPUE and daily total catch), closure duration and start month of closure had positive, statistically significant correlations with post-closure CPUE and daily total catch. Additionally, closure duration from 13 to 16 weeks and closure size of approximately 70 hectares were qualitatively associated with net gains in CPUE. Although periodic closures yield positive outcomes for octopus fisheries, the effects may be short-lived, as observed in Atsimo Andrefana, Madagascar, where catch declined over the long-term despite temporary improvements. Our findings underscore a need for a diverse portfolio of management strategies to restore and sustain populations over the long-term.

Dams trigger exponential population declines of migratory fish.

The impact of dams on global migratory fish stocks is a major challenge and remains seriously underestimated. China has initiated a dozen fish rescue programs for the dams on the Yangtze River, focusing on five flagship species-Chinese sturgeon, Chinese paddlefish, Yangtze sturgeon, Chinese sucker, and Coreius guichenoti. Despite 40 years of effort, these five fishes are on the verge of extinction. Here, we propose an analytical tool that includes a framework of fish migration taxonomy and six life cycle models, the concepts of invalid stock and the dam impact coefficient, and a simplified population model. We then clarify the migration patterns and life cycles of these fishes and show that the Yangtze dams have severely disrupted the life cycle integrity of these species, causing seven types of invalid stocks and their exponential population declines. Last, we discuss six scientific misjudgments underpinning the fish rescue programs and recommend reforms to China's fish rescue strategy.