Management Of Fish Stocks Research Articles

Fishing event detection and species classification using computer vision and artificial intelligence for electronic monitoring

Fisheries regulations require detailed catch reporting on commercial fishing vessels. Vital components for the sustainable management of fish stocks include a robust estimate of the number of fish caught and the species composition. Catch recording is often done manually by human observers on fishing vessels. Human observers are costly, and consistent data streams can be subject to observer availability and the weather. On-vessel cameras (electronic monitoring, EM) are a growing alternative to human observers. However, on-land human auditors are required to review hundreds of hours of videos recorded during fishing trips that can last for weeks. In this paper, a framework is presented to automatically detect fish in EM videos, count the total fishing events, and classify the fish species. For this purpose, a deep learning and computer vision-based model is developed to efficiently detect fish and fishers onboard a vessel. Secondly, a vision-based tracking pipeline tracks the detected fish and counts the total fishing events in the videos. Thirdly, the extracted fishing events are classified through a deep learning-based fish species classifier, to provide the distribution of different fish species caught for a fishing trip. For our experiments, the datasets were prepared using the electronic monitoring data of multiple fishing trips of a fishing vessel. The videos were recorded on Australian longline vessels targeting tunas and billfish. For the fish detection task, video frames were extracted and labelled manually to provide a digital ground-truth. For the fish species classification task, hundreds of fish images of multiple species were cropped to provide a training dataset for the fish classifier. For the fish counting task, manual counts for the fishing events of individual fish species were generated for the test fishing trips. The developed fish and fisher detector achieves a mean Average Precision of 87.0 % for fish and 94.0 % for fishers on test video frames. The fishing event detection pipeline achieves an Average Precision of 81.0 % and an Average Recall of 74.5 % on test videos. The fish species classifier achieves an Accuracy (Top-1) of 91.11 % for the classification of cropped fish images and 89.05 % for the classification of extracted fishing events from the videos. Experimental results show that our proposed computer vision and artificial intelligence-based solution for video analysis has great potential to automate the auditing process from electronic monitoring footage and contribute to the sustainable management of fish stocks.

Stock assessment of rosy barb, Pethia conchonius (Hamilton, 1822) in Dal Lake of Kashmir Himalayas

For management of fish stocks, assessing the various parameters of population dynamics are regarded as being extremely important. Under this backdrop the population dynamics parameters viz. growth, mortality and recruitment of Pethia conchonius, inhabiting the Dal Lake of Kashmir Himalayas were analysed using FiSAT II software. The analysed specimens were collected from five different sites within the lake and exhibited a total weight range of 0.3 to 6.4 g and a total length range of 3.1 to 7.8 cm. The relative condition factor for the fish was reported to be 1.11. The growth parameter i.e., asymptotic length, age at zero length, growth performance index and growth constant were reported to be 10.0 cm, –0.75 years, 1.48 and 0.30 year–1 respectively. The total mortality of 1.49 year–1, consisting of natural mortality of 0.88 year–1 and fishing mortality of 0.61 year–1 was reported. An exploitation rate of 0.41 is suggestive of a less exploited state of the fish. The length at first maturity was found to be higher than the length at first capture, a condition that can disturb the stock, as such the utility of a net with relatively larger mesh size is advisable. The current research on the population dynamics of P. conchonius can be used as the baseline data for its management practices.

Mismanagement and poor transparency in the European processed seafood supply revealed by DNA metabarcoding

In the global processed seafood industry, disparate actors play different roles along the supply chain, creating multiple opportunities for mistakes, malpractice, and fraud. As a consequence, consumers may be exposed to non-authentic products, which hinder informed purchasing decisions and broader efforts to improve trade transparency and sustainability. Here, we characterised the taxonomic composition of 62 processed seafood products in Italian, British and Albanian retailers, purposefully obtained from different supply routes, using multiple DNA metabarcoding markers. By combining molecular results with metadata reported on labels, we revealed patterns of mislabelling in 24 products (39%) across sampling regions, denoting lack of transparency of processed seafood products based on resources sourced from either Europe or globally. We show that the accuracy of label claims and the mis-represented and underestimated levels of traded biodiversity are largely determined by the management of raw material by global processors. Our study shows that DNA metabarcoding is a powerful and novel authentication tool that is mature for application at different stages of the seafood supply chain to protect consumers and improve the sustainable management of fish stocks.

Разработка мер по сохранению биологического разнообразия рыб, предложений по организации системы мониторинга состояния популяций редких видов рыб западного региона Республики Казахстан

The purpose of the work is to develop measures to ensure the development of fisheries, the conservation of fish resources and the biological diversity of the ichthyofauna of Western Kazakhstan (Mangystau, Atyrau, Aktobe and West Kazakhstan regions), improving the principles and methods of management and protection of fish stocks. The research was carried out both according to the methods generally accepted in the post-Soviet space, and according to the methods developed by the authors (a temporary method of accounting for the number of fish, withdrawal coefficients for populations of fish with undermined stocks) and methods of foresight research. The monitoring system for rare and endangered fish species should include both in-life research methods and the capture of a minimum necessary number of individuals in order to further domesticate and form breeding herds, artificially reproduce and release the resulting juveniles into those reservoirs. The continued decline in populations of rare and endangered fish species indicates the low effectiveness of the measures taken to preserve them. In order to prevent the loss of the gene pool, it is necessary to select sexual products for cryopreservation during the monitoring process. In addition to monitoring the condition of rare species of fish and other animals conducted by scientific organizations, it is necessary to create a geoinformation system for monitoring rare species, which any resident can replenish by sending experts photos of samples of flora or fauna with observation coordinates. The results of the work are supposed to be used to determine further ways of developing reservoirs in the context of “green growth”.

Non-model method for the stock status assessing and catch forecasting of the Flounder 26+28 subdivisions ICES in the Baltic Sea

The aim of this article: to assess the flounder stock state in the 26+28 ICES subdivisions of the Baltic Sea and forecast its catch in the Russian part of the 26th ICES subdivision using non-model methods.Methods used: The qualitative condition of the stock was assessed by length (LBI method — Length Based Indicators). To develop catch recommendations for flounder stock in 26+28 ICES subdivision, as well as in the Russian sea area, was used an approach for a stock category 3 (ICES classification), based on a combined biomass index for fish from bottom trawl surveys. The assessment was based on the ratio of the average values of population indices of the last two years to the previous values for three years. All methods have been successfully tested at the international level within the framework of seminars and Working Groups of the International Council for the Exploration of the Seas (ICES), in which Russian specialists took part.Novelty: In conditions of insufficient completeness and quality of available information to justification the flounder catch, using models of the exploited stock, for the Russian water area of the 26th ICES subdivision of the Baltic Sea, non-model methods for assessing the state and predicting its catch were used for the first time. Result: to solve problems of rational management and conservation of fish stocks, the LBI method, as a non-model assessment tool, allows timely identification of qualitative changes occurring in the stock. The flounder stock is within biologically safe limits. The fishery is aimed at preserving small and large fish (conservation option), the stock is exploited optimally. It is possible to maintain the species’ production level at least at the current level.Practical significance: In modern conditions the current level of information support for forecasting the flounder stock state and catch in the Baltic Sea will make it possible to solve problems related to the management of this resource in the near future.

Mesopelagic Mysteries: Regulating an Emerging Resource Amid Uncertainty

Mesopelagic species, which inhabit depths between 200 to 1000 m, have regained attention as potential new resources to replace and supplement the use of traditionally overfished species. Research and exploratory fishing are ongoing, yet much on the nature of mesopelagic organisms and their roles within ecosystems and the carbon cycle remains to be understood. Building on recent reports and reflecting on fisheries developments, this article examines some of the unique characteristics of the mesopelagic zone and the existing international legal framework to stimulate legal debate on the sustainable management of mesopelagic fish stocks in the high seas.

Different growth patterns reveal the potential origins of two Pacific saury (Cololabis saira) groups in the northwest Pacific Ocean

Identification of stock composition is essential for fish stock assessment and management. Previous studies have suggested that a mixed stock composition of Pacific saury Cololabis saira exists in the northwest Pacific Ocean, but the origins of the stock’s components are poorly understood. We analyze the otolith microstructure of Pacific saury collected in high-seas fishing grounds from June–November, 2016–2019, and estimate hatch date and reconstruct otolith growth trajectory before hyaline zone formation. Results confirm that Pacific saury recruiting to the high-seas fishing ground are mainly from a winter-spawned cohort, secondarily from an autumn-spawned cohort, but also with a small proportion from a spring-spawned cohort. Ages of medium (knob length 240–280 mm) and large (knob length > 280 mm) individuals are mainly 8–12 and 18–21 months, respectively. Two growth patterns are reported for individuals with different otolith growth axes in their early life stages. Each year, unsupervised random forest clustering analysis of otolith daily increment widths reveals two Pacific saury groups. One group, with younger age and a later hatching period, shows a consistently higher growth rate than the other, suggesting that the two groups have different hatch dates and locations. These findings permit more accurate prediction of Pacific saury recruitment, and improve the understanding of short-term stock fluctuations to enable more sustainable management of fisheries.

Genetic investigation of population structure in Atlantic chub mackerel, Scomber colias Gmelin, 1789 along the West African coast.

Sustainable management of transboundary fish stocks hinges on accurate delineation of population structure. Genetic analysis offers a powerful tool to identify potential subpopulations within a seemingly homogenous stock, facilitating the development of effective, coordinated management strategies across international borders. Along the West African coast, the Atlantic chub mackerel (Scomber colias) is a commercially important and ecologically significant species, yet little is known about its genetic population structure and connectivity. Currently, the stock is managed as a single unit in West African waters despite new research suggesting morphological and adaptive differences. Here, eight microsatellite loci were genotyped on 1,169 individuals distributed across 33 sampling sites from Morocco (27.39°N) to Namibia (22.21°S). Bayesian clustering analysis depicts one homogeneous population across the studied area with null overall differentiation (F ST = 0.0001ns), which suggests panmixia and aligns with the migratory potential of this species. This finding has significant implications for the effective conservation and management of S. colias within a wide scope of its distribution across West African waters from the South of Morocco to the North-Centre of Namibia and underscores the need for increased regional cooperation in fisheries management and conservation.

Use of otolith microchemical and morphological analyses for stock discrimination of Sarpa salpa on two Tunisian islands, Djerba and Kerkennah

Abstract Otolith morphological and microchemical analyses are relatively new scientific research methods used in fish stock evaluation and management. However, in Tunisia, only morphological methods have been used. The objective of this study was the Sarpa salpa stock discrimination of Djerba and Kerkennah by the otoliths morphological and microchemical analysis, while carrying out a fluctuating asymmetry analysis and a stock comparison of males and females for each population. The results revealed significant differences between the Djerba and Kerkennah populations, significant differences between the stocks of males and females in each population, and a highly significant fluctuating asymmetry for both populations. The results of the otolith morphological analysis were similar to those of the microchemical analysis. This result proves that both morphological and microchemical analyses are powerful tools for fish stock discrimination.

Length‐Weight and Length‐Length Relations of 14 Freshwater Fish Species from the Qiantang River, China

The Qiantang River, located in Zhejiang Province, China, is a crucial water resource with significant ecological and economic importance. This study aimed to evaluate fishery resources in the Qiantang River Basin by analyzing the length‐weight relationships (LWRs) and length‐length relationships (LLRs) of 14 fish species. Fish samples were collected between July 2021 and November 2023 using multipanel nylon gillnets and cage nets. Each specimen was measured for total length (TL) and standard length (SL), as well as weighed. Linear regression models were employed to estimate LWRs and LLRs, with statistical tests revealing significant relationships (P < 0.05) and high R2 values above 0.91. The study contributed new LWRs for two species and LLRs for three, deepening our understanding of their biology. These findings enriched FishBase and offered valuable data for fish stock assessments and management strategies in the Qiantang River Basin. Future research can utilize this foundation to explore population dynamics and promote sustainable management practices.

Selectivity of gillnets on the main fish species caught in the floodplains of the Madeira River (Rondônia, Brazil)

Small-scale fishing in the floodplains of the Amazon basin has intensified, with gillnets being one of the main types of tackle used. In this study, we evaluated the length structure of fish species in a floodplain lake of the Madeira River basin, emphasizing the selectivity of the nets in the main species caught. The fisheries were collected in periods of high water and low water, with nets of mesh sizes of 40, 60, 80, 100, 120 and 160 mm. Tests between the periods and also comparing the meshes were performed and the parameters of the selectivity curves estimated with the SELECT calculation code. Records of 17 new maximum lengths are presented. Of the 12 most abundant species, the selectivity of the nets in the modal lengths for Anchovia surinamensis were 13.3, 19.9, 26.6 and 33.2 cm in the nets with mesh sizes of 40, 60, 80 and 100 mm, respectively. In the three smallest mesh sizes, the values for Potamorhina altamazonica were 12.7, 19.0 and 25.3 cm and for Pellona flavipinnis values were 15.4, 23.2 and 30.9 cm. In the two smallest mesh sizes, the following values were presented for the species Potamorhina latior (12.9 and 19.4 cm), Potamorhina rutiloides (11.3 and 16.9 cm), Triportheus elongatus (19.7 and 29.5 cm), Triportheus flavus (14.1 and 21.1 cm) and Pimelodus blochii (15.5 and 23.0 cm). The estimates of selectivity of the nets, in addition to being basic information for fishery sciences, are also fundamental for the management of Amazonian fish stocks.

Annotating otoliths with a deep generative model

Abstract Otoliths are a central information source for fish ecology and stock management, conveying important data about age and other life history for individual fish. Traditionally, interpretation of otoliths has required skilled expert readers, but recently deep learning classification and regression models have been trained to extract fish age from images of otoliths from a variety of species. Despite high accuracy in many cases, the adoption of such models in fisheries management has been slow. One reason may be that the underlying mechanisms the model uses to derive its results from the data are opaque, and this lack of legibility makes it challenging to build sufficient trust in the results. Here, we implement a deep learning model that instead of age predicts the location of annotation marks for each of the annuli. This allows an expert to evaluate the model’s performance in detail. The quality of the annotations was judged by a panel of four expert otolith readers in a double-blinded randomized survey. Using a scale from 1 to 5, the generated marks received an average quality score of 4.22, whereas expert annotations received an average score of 4.33. By counting the marks to determine fish age, we obtained an agreement between expert and model annotations of 64% on our test set, which running the model stochastically increased to 69%. Stochastic sampling yields further benefits, including an explicit measure of the model’s uncertainty, the post hoc likelihood of the different age classes for each otolith, and a set of alternative annotation sequences that highlight the structure of the annuli.

An overview on hydro-biology and management of Kaptai Lake Fisheries, Bangladesh

Kaptai Lake is the largest artificial Lake in Bangladesh. This Lake provides most of the fish stock for the people of the Hill tract. Over the years, due to various anthropogenic and environmental reasons population of Indian Major Carp (IMCs) has declined, and some native species are on the way to extinction in this Lake. Considerable research has been conducted on different aspects of lake fishery with hydrology, culture technology, fish diversity, management, threats, and mitigations, but no such consolidated report on the overall overview is not available on this Lake. This review paper has been prepared to combine all the available information along the information gap, further study of which will be helpful to enhance the Indian major carp catch and sustainable management of fish stock.

Bio‐ecological studies on two cichlids in the Brimsu reservoir of Ghana

AbstractAlthough small‐scale fisheries and aquaculture provide opportunities to increase fish yield to supplement rural food and income, they remain undeveloped in Ghana. To contribute towards the development of the sectors, this study sought to assess the biology and ecology of Oreochromis niloticus and Sarotherodon melanotheron in the Brimsu reservoir to provide the requisite information for their management. From the results, mean temperature, dissolved oxygen, pH and transparency of the reservoir were 30.03 ± 0.27°C, 3.78 ± 0.38 mg/L, 8.30 ± 0.21 and 69.79 ± 1.76 cm, respectively. S. melanotheron had a sex ratio of 1:1.36; with mean condition factors of 2.177 ± 0.089 and 2.06 ± 0.029 (p = 0.08) for males and females, respectively. The sex ratio of O. niloticus was 1.45: 1; with mean condition factors of 2.208 ± 0.012 and 2.257 ± 0.014 (p = 0.07) for males and females, respectively. Both species exhibited positive allometric growth with no significant differences between the condition factors for males and females. In addition, there was no significant difference between the sex ratios for S. melanotheron but the number of males of O. niloticus was significantly higher than the females (p ˂ 0.05). Size at sexual maturity (Lm), form factor (a3.0), growth coefficient (K), asymptotic length (L∞) and natural mortality (M) of S. melanotheron were 18.00 cm, 0.020, 0.42 year−1, 30.32 cm and 0.64 year−1, respectively. For O. niloticus Lm, a3.0, K, L∞ and M were 18.57 cm, 0.0223, 0.26 year−1, 38.42 cm and 0.41 year−1, respectively. However, the catch per unit effort for O. niloticus was higher than that of S. melanotheron throughout the study period. The conditions of the reservoir were favourable for the growth of these cichlids. It is recommended that measures should be put in place for the sustainable management and exploitation of fish stocks.

Reproductive characteristics of the hermaphroditic four-finger threadfin, Eleutheronema tetradactylum (Shaw, 1804), in tropical coastal waters

This study investigated the reproductive traits of the hermaphroditic four-finger threadfin, Eleutheronema tetradactylum, along the coasts of Thailand during January to December 2021. Fish samples were collected from Pattani Bay, Thailand to assess the sex ratio, gonadosomatic index (GSI), maturity stage and fecundity. Additional fish samples were also collected from other areas to evaluate the length and weight at first sex change (Ls50 and Ws50) and length at first maturity (Lm50). The overall sex ratio for male and female was 1:0.69 with male being predominant throughout the year. Threadfin fish spawn the whole year round with peaks during moderate rainy and heavy rainy seasons. Histological examination confirmed its protandrous hermaphrodite posing multiple spawning habits. The average fecundity was 1.85 × 105 ± 1.05 × 105 eggs and positively related with standard length, body weight, gonad weight, and egg diameter (p < 0.05). The Ls50 and Ws50 were 27.58 cm and 419.39 g, and 29.71 cm and 457.28 g, for fish from Pattani Bay and Samut Prakan province, respectively. The Lm50 of male from Pattani Bay and Samut Prakan province were 25.78 cm and 25.56 cm, respectively, which were larger than those from Satun and Nakhon Sri Thammarat provinces. The Lm50 of females from Pattani Bay was smaller than that from Samut Prakan province. This study provided fundamental information on the reproductive characteristics of E. tetradactylum, which can be implemented to support management of natural fish stock and aquaculture development.

Spatial patterns of within-stock connectivity provide novel insights for fisheries management

While concepts of connectivity are increasingly used in determining locations for marine protected areas, they are much less applied in the management of fish stocks, which are assumed to be well-mixed populations. However, due to seascape structure and often asymmetrical dispersal, the stocks of many species are unlikely to be well mixed and there is potential to enhance management by utilising emerging ecological modelling approaches that incorporate functional connectivity. Here, we apply a new model, MerMADE, that couples biophysical modelling of dispersal with spatial population demography, to predict within-stock patterns of connectivity of sandeels in the North Sea. By deriving origin- and destination-centrality measures, we highlight a set of key origin sites within the area occupied by the stock that contribute immigrants to many other sites and also identify patches that are particularly isolated, unlikely to receive immigrants from elsewhere. We show that the connectivity characteristics of the stock have a strong impact on how rapidly it recovers following a major harvesting event that leads to a patch depletion. Furthermore, the recovery of a local population will depend on the demographic status of the sites from which it can obtain immigrants. Thus, sites that provide strong out-centrality (especially if they themselves have weak in-centrality) and sites that are especially isolated should be harvested less heavily. To reduce the potential for local or regional stock collapse, models incorporating both biophysical dispersal and local demography are needed to support spatially explicit management of commercial marine species.

Harassment and obstruction of observers in U.S. fisheries

Fishery observers play a crucial role in the management and conservation of fish stocks, but the treatment they receive aboard fishing vessels can affect their ability to perform their duties. Using law enforcement data from the Northeast and Alaska regions, home to the most important commercial fisheries in the United States, we explore the extent of observer harassment, assault, interference, and obstruction (OHAIO). We find that 16% of 10,346 fishery violations reported in the Northeast and Alaska regions from 2014-2018 are observer-related, and over 80% of those involve OHAIO. We trace how OHAIO incidents are reported and processed and propose steps to mitigate the issue.

Length-Weight Relationship and Condition Factor of Ethmalosa fimbriata (Bowdish, 1825) and Mugil cephalus (Linnaeus, 1758) in Coastal Waters of Ondo State

The study aimed at examining the Length-Weight Relationships (LWRs) and Condition factor of M. cephalus and E. fimbriata. 240 fish specimens were collected from November 2021 to April 2022 from Obi, Idiegbin, Okesiri and Araromi following standard methodologies subjected to length-weight relationship and condition factor analysis. The results showed that the mean total length of M. cephalus ranged from 30.96 ± 0.56cm (Araromi) to 23.80 ± 1.16cm (Okesiri) and weight ranged from 118.86 ± 9.36g (Araromi) to 71.32 ± 18.12g (Okesiri). E. fimbriata total length ranged from 21.04 ± 0.74cm (Araromi) to 13.96± 0.38cm (Okesiri) and weight ranged from 150.90 ± 1.14g (Araromi) to 70.54 ± 5.76g (Okesiri). The regression coefficient (b) revealed that both M. cephalus (2.19-1.97) and E. fimbriata (2.06-1.05) sampled in Araromi, Okesiri, Idiegbin and Obi respectively exhibited negative allometric growth. Condition factor range (2.41-1.50) recorded for E. fimbriata was higher than (0.50-0.45) range value recorded for M. cephalus. The study concluded that the two species exhibited negative allometric growth pattern and the environment was for conducive for E. fimbriata than for M. cephalus. The variations in growth of the species could be attributed to prevailing ecological conditions of the environment. Therefore, sustainable fish stock management should be carried out.

The rapid expansion of offshore wind farms challenges the reliability of ICES-coordinated fish surveys—insights from the Baltic Sea

Abstract Fish stock assessment and sustainable management requires that the whole distribution area of the managed fish stocks is representatively sampled. Along with an increasing demand for renewable energy in Europe, a growing number of areas are allocated for current and future offshore wind farms (OWF). Besides various unknown environmental effects, impacts on different stakeholder activities, such as fisheries, are considered during the implementation process. Scientific interests and tasks are, however, often marginalized. The current ban of commercial fisheries and fisheries monitoring in OWFs, in combination with an increase of OWF areas and habitat alteration within OWFs, might therefore bias the time series of scientific surveys and, thus, fisheries stock assessments. The expected increase in the overlap between OWFs and scientific fish surveys coordinated by the International Council for the Exploration of the Sea (ICES) in the Baltic Sea could result in, depending on the survey, up to 6.6–11.5% of the stations and transects being unavailable for sampling. We discuss the potential consequences for survey time series and stock assessments. Further, we aim to stimulate the discussion about the future of current standard surveys in the context of rapid expansions of OWFs, including the need for adaptations in survey design.

Widespread long-term declines of littoral areas in protected and unprotected Czech fishponds

Fishponds play a key role in current pondscapes in many developed countries. They provide multiple ecosystem services affected by trade-offs mediated by different types of fishpond management. Many fishponds were impacted by the shift towards more intensive aquaculture and widespread eutrophication in the 20th century. These changes can undermine various ecosystem functions including the maintenance of aquatic and riparian biodiversity in the littoral areas, but their extent is not well documented. Here we use aerial photographs to investigate the changes of littoral areas of 46 protected and 20 unprotected fishponds in the Czech Republic between the years 1950 and 2019. Protected fishponds had initially larger littoral areas than the unprotected ones, and the difference persisted over time. However, littoral areas decreased markedly in 38 protected (mean area decrease by 22.5%) and all unprotected (mean area decrease by 16%) fishpond categories, especially during the second half of the 20th century. Within protected fishponds, the trend was unaffected by the reserve establishment year, fishpond area and conservation target. Our results suggests that legal protection did not prevent the initial catastrophic loss of littoral areas and facilitated at most minor recovery in the last two decades, with negative implications for long-term maintenance of aquatic diversity. We attribute the losses of fishpond littoral areas to high fish stocks and eutrophication resulting from additional feeding, pond manuring, and ongoing nutrient inputs from the pond catchments. We conclude that littoral areas of fishponds urgently need effective protection. This would require 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 could help recover the littoral areas and the associated biota.