Catch Levels Research Articles

‘It’s how you catch the fish’: debates on ecolabelling, yield thinking, and care in Denmark

Since the second half of the 20th century, Maximum Sustainable Yield (MSY) has been the guiding principle of fisheries management, focused on reaching sustainability through bioeconomic modelling and harvest regulations. MSY has allowed managers to set Total Allowable Catch levels for target species with further implications for various forms of catch share programs. In this article, we employ a feminist ethic of care approach and literature on local environmental stewardship to analyze the case of a Danish environmental organization trying to introduce another dimension to fisheries management grounded on the concept of care and collective responsibility. The case includes two related attempts of establishing ecolabelling schemes for small-scale fisheries focused on a concept of careful/gentle fishing. Through the case study, we trace how a management focus on yield hinders the care perspective but also engenders forms of local and national resistance.

Is inland aquaculture the panacea for Sierra Leone’s decline in marine fish stocks?

The literature on fisheries for developing countries often cites inland aquaculture as a promising source of wealth creation for a nation in terms of revenue generation from export products. However, in this paper we argue that inland aquaculture has a greater prospect of success if it focuses on social welfare – i.e. alleviating food insecurity and poverty in coastal fishing communities, particularly those that are experiencing increased and unsustainable fishing pressure on marine fish. Nevertheless, promoting inland aquaculture in coastal areas faces many challenges, including financial, legal, political, environmental, logistical, educational, and attitudinal obstacles. Our study investigates these challenges in two coastal communities in Sierra Leone – Tombo and Goderich – where declining levels of marine fish catches are intensifying efforts to provide alternative or supplementary forms of employment for artisanal fishers, but where knowledge and experience of, and enthusiasm and funding for, inland aquaculture are limited. The research is based on the perceptions of 51 key informant interviewees and 199 survey questionnaire respondents. The main findings of the fieldwork are as follows. (1) Few local fishers were familiar with inland aquaculture and its potential benefits. (2) There were land tenure problems (for example, women were excluded from ownership of land). (3) There was little funding to buy/rent land and equipment. (4) Despite declining fish stocks, respondents were reluctant to take up full-time fish farming because of the easier option of fishing. Our findings suggest that greater uptake of inland aquaculture is more likely if presented to local fishers as a supplementary livelihood activity rather than an alternative occupation to marine capture fishing. Our study reinforces the importance of understanding local fishers’ cultures, values, and preferences before introducing a new livelihood activity.

Моделирование динамики промысловой популяции, в условиях недостаточности информационного обеспечения, моделью CMSY на примере Черноморского шпрота в водах России

This study performs approbation of trend CMSY model on the example of Black sea sprat fishing unit, localized in Russian waters. Data sources has been reduced to the level of data limited modeling for indicator and trend models approach. CMSY population model results were compared with previously performed estimations by more powerful cohort model - XSA. CMSY results shows no significant deviations from the XSA results. Forecast scenarios and conclusions based on CMSY model fitting leads to the same statements with previously published results by XSA. CMSY model shows next results: stock biomass in 2019 B2019 = 63,9 ths. t, fishing mortality – F2019 = 0,29. Stock biomass in 2019 was significant below the target reference point BMSY = 105 ths. t and higher then limit reference point Blim = 52,7 ths. t. Some uncertain overexploitation in 2019 was underlined, F2019/FMSY = 1,12. Investigation of forecast scenarios with different total allowed catch levels indicates that there are no features for increasing the catch capacity in short-term projection. CMSY model fitting have passed the necessary stability tests and confirm previously founded results. In summary of this study, we can recommend to use CMSY model for stock assessment procedure in terms of data-limited information background.

The role of motorized boats in fishers’ productivity in marine protected versus non-protected areas in Davao Gulf, Philippines

The Philippine fisheries sector continues to play a critical role in the livelihood of coastal households; however, the country’s fisheries production level has been declining at the municipal level. To reverse this trend, marine protected areas are established in critical geographic areas to ensure that management and conservation follow sustainable fishing practices. Mabini, Davao de Oro, and San Isidro, Davao Oriental are coastal municipalities located in the southern Philippines. Mabini is a declared National Integrated Protected Area System (NIPAS) while San Isidro is a non-NIPAS fishing area. This paper aimed to identify the determinants of coastal fish catches among 406 fisherfolks in both Mabini and San Isidro during the Northeast Monsoon season during 2018–2019. The study utilized power analysis to calculate the sample size for two independent groups. Stratified random sampling was used to determine the respondents in each village. Further, quantile regression was used to estimate the Cobb–Douglas production function model in determining the impact of the drivers across varying fish catch levels. Effort time, boat length, input costs, other costs, distance, and boat type are significant drivers of catch output in Mabini, while for San Isidro, effort time, input costs, other costs, and distance variables are positively associated with fish output. Compared with San Isidro, fishers in Mabini using motorized boats have relatively higher fish catch levels, which is more pronounced in upper catch quantiles. Thus, access to motorized boats is crucial in addressing the impact of regulatory restrictions on fishers’ livelihood in marine protected areas.

Assessing ocean temperature’s role in fishery production

Ocean temperatures are increasing. Little work has been done to examine the effects that these changes will have on fishery production. The study at hand seeks to incorporate the influence of climate change into an established static bioeconomic fishery model. Stock biomass is approximated to be a function of sea surface temperature. Following a feasible generalized least squares regression using data from the Western and Central Pacific, the interaction between fishery effort and temperature is found to be statistically significant. From this model, various functional forms relating effort, catch, profit, and temperature are specified. In particular, a function that returns an effort requirement given a target catch level and temperature forecast is generated.The importance of these tools for fishery management is explored through application to Western and Central Pacific tuna fisheries. Recommendations for extensions into future research are made and the foundation for a model of efficient effort allocation across time and the entirety of a management area, given changing temperatures, is specified. The study has succeeded in establishing the statistically significant role that temperature plays in the fishery production function.

Enhancing single-species stock assessments with diverse ecosystem perspectives: a case study for Gulf of Mexico red grouper (Epinephelus morio) and red tides

Impacts of Karenia brevis red tide blooms have been an increasing cause of concern for fisheries management in the Gulf of Mexico (Gulf). The 2019 Gulf red grouper (Epinephelus morio) stock assessment was confronted with the challenges of quantifying and parameterizing red tides during both historical and projection time periods. Red tide mortality was estimated for each age class in the model solely in 2005 and 2014 during severe events. Given the considerable uncertainty surrounding the 2018 red tide and its substantial implications on the status of the population, several projection scenarios were evaluated. Under the assumption of no 2018 red tide mortality, near-term catches were projected to nearly double, a predicted outcome that appeared to be in contrast with recent record low catches and fishing industry perceptions of major stock depletion. In the event that the 2018 red tide caused mortality, but was not accounted for in projections, the recommended catch levels would lead to high probabilities of overfishing and potentially stock collapse. Collectively, these results highlight how consideration of uncertainty in projections can help avoid unintended consequences.

Temporal variability in the reproductive parameters of deepwater rockfishes in the Gulf of Alaska

Reproductive parameters directly influence estimates of stock biomass and therefore affect the determination of catch levels of many federally managed fish species. These parameters can vary over different temporal scales and a better understanding of how and why reproductive traits change will aid in the management of these species. We examined the reproductive parameters of rougheye rockfish, Sebastes aleutianus, and shortraker rockfish, S. borealis, captured in December 2015 and compared them with parameters from an earlier published study. Maturity values in the earlier study were derived from samples collected in from 2008 to 2014 with a concentration of fish collected in the winter of 2009 and 2010. Rougheye rockfish had a smaller length and age at maturity during 2015 (447 mm, 17.7 years) compared to the earlier sampling period (450 mm, 19.6 years), but neither the interaction of length and time period (P = 0.507) nor the interaction of age and time period (P = 0.270) was significant. Shortraker rockfish also had a smaller length at maturity during 2015 (467 mm) compared to the earlier period of time (499 mm) and the interaction of length and time period was not significant (P = 0.830). Relative fecundity for rougheye rockfish was not significantly different between the two time periods (P = 0.444) and this was also true for shortraker rockfish (P = 0.341). Skipped spawning rates were significantly lower in 2015 for both rougheye rockfish (2010 = 37.4 %, 2016 = 21.8 %, P < 0.001) and shortraker rockfish (2010 = 60.0 %, 2016 = 47.0 %, P < 0.001). This study was a first step in examining how reproductive parameters for these species may change over time. A comprehensive approach to examining temporal trends in reproductive parameters will aid in the understanding of how changing environmental conditions are affecting the productivity of commercially important species.

Observed impact of climate change on abundance and distribution of Nile fish in Sudan during the period (2001-2020)

A reduction in species of Nile fish was observed during (2001-2020). Annual temperature revealed high levels (29 to 31 ˚C), with fluctuation between 2001 and 2008, decreased from 2009 to 2000. Rainfall fluctuated between 2001 and 2007, with highest peaks in 2019 and 2020. Positive correlation (r = 0.34402) was found between temperature and catch. Catch increased with decreased temperature. Negative correlation (r = -0.15869) was found between catch and rainfall, high level of catch was recorded with low rainfall. The results indicated changing in climate within Sudan over time. To tolerate climate change for the next twenty years, the Nile fish will either modify their body structure and function, or even stand the risk and extinct from the Nile. Future changes in the productive capacity of the Nile need effective and progressive responses to the urgent threat of climate change, through mitigation and adaptation measures and sustainable management practices.

Quantifying shark and ray discards in Western Australia’s shark fisheries

Commercial fisheries can discard a considerable volume of sharks and rays, which, as a group, are of high conservation concern. In Western Australia (WA), commercial shark fishing commenced in the 1940s; however, catch time series are not available for discarded species. The present study quantified catch (i.e. dead individuals) time series of discarded sharks and rays in WA’s shark fisheries using on-board observer information collected since 1993 and testing assumptions through sensitivity analysis. Overall, 18 shark and ray taxonomic groups were discarded, comprising ~20% of the observed catch by number. Port Jackson shark, southern eagle ray and spurdogs were the most commonly discarded elasmobranchs, followed by western wobbegong, angel sharks, stingrays, and guitarfish and shovelnose rays. For the base case scenario, the catch of these species was small, peaking at 12.6, 5.6, 1.3, 1.8, 4, 1.3 and 2.7 tonnes (Mg) respectively, given their low post-release mortality (PRM). Current catch levels were even lower (e.g. &lt;5 Mg for Port Jackson shark). Other discarded elasmobranchs were rarely caught. Assuming 100% PRM resulted in higher annual catches, highlighting the need for further research on the PRM of sharks and rays. The reconstructed catch series will be used in risk assessments to determine the sustainability of discarded species.

The Status of the Stock and the Current Fishery for the Atka Mackerel, Pleurogrammus monopterygius (Pallas, 1810), in the Olyutorsky–Navarin Area, Bering Sea

The dynamics of the Atka mackerel stock in the Olyutorsky–Navarin area in 1994–2019 is inferred from bottom-trawl surveys, fishery statistics, open-access NOAA data, and the results of simulation by the method of virtual population analysis. After the period of low stock in the mid-1990s, the abundance of the Atka mackerel group in the area increased sharply to a maximum in 2006–2008, when the spawning biomass was estimated at approximately 9500 t and the fishery biomass at 14 000 t. In 2008, the stock showed a tendency to decrease; by 2013, the spawning stock decreased to 3600 t and the fishery stock to 5600 t; subsequently, there was a period of stabilization at a low level with a slight tendency to further reduction. One of the possible causes of the sharp increase in the Atka mackerel stock in the 2000s could be the increased transport of juveniles of strong year-classes from the main spawning grounds off the Aleutian Islands with their subsequent settlement on available parts of the shelf off Cape Olyutorsky. The development of the Atka mackerel fishery in the Olyutorsky–Navarin area in 1994–2019 had a pattern similar in general to the stock dynamics. Until 1995, no more than an average of 100 t were caught per year; in 2006–2010, the average annual catch increased to 790 t; in 2011–2015, it increased to 1150 t; and in 2016–2019, the catch again decreased to 950 t. Due to the emerging trend of a general reduction in the stock of the Aleutian population, this low level of catches in the Olyutorsky–Navarin area is expected to continue in the coming years.

The Risky Decrease of Fishing Reference Points Under Climate Change

In Europe, implementation of sustainable fisheries management has been reinforced in the latest common fisheries policy, and presently marine fish stocks are mostly managed through assessment of their exploitation and ecological status compared to reference points such as Maximum Sustainable Yield (MSY). However, MSY and its associated fishing mortality rate F-MSY are sensitive to both stock characteristics and environment conditions. In parallel, climate change impacts are increasingly affecting fish stocks directly and indirectly but might also change the exploitation reference points and the associated level of catch. Here we explored the variability of MSY reference points under climate change by using a multi-species model applied to the Eastern English Channel, a highly exploited semi-continental sea. The spatial individual-based OSMOSE explicitly represents the entire fish life cycle of 14 species interacting through size-based opportunistic predation. The model was first parameterized and run to fit the historical situation (2000-2009) and then used to assess the ecosystem state for the 2050-2059 period, using two contrasting climate change scenarios (RCP 4.5 and RCP 8.5). For each condition, a monospecific MSY estimation routine was performed by varying species fishing mortality independently and allowed estimation of reference points for each species. The F-MSY estimated with OSMOSE were mostly in accordance with available values derived from stock assessment and used for fishing advice. Evolution of reference points with climate change was compared across species and highlighted that overexploited cold-water species are likely to have both MSY and F-MSY declining with climate warming. Considering all species together, MSY under RCP scenarios was expected to be higher than historical MSY for half of them, with no clear link with species temperature preferences, exploitation status or trophic level, but in relation with expected change of species biomass under climate change. By contrast, for 80% of cases F-MSY projections showed consistent decreasing pattern as climate conditions changed from historical to RCP scenarios in the Eastern English Channel. This result constitutes a risk for fisheries management, and anticipation of climate change impacts on fish community would require targeting a smaller fishing mortality than F-MSY to ensure sustainable exploitation of marine stocks.

Optimal shape of the harvest control rule for different fishery management objectives

Abstract To determine the optimal shape of the harvest control rule (HCR) achieving common fisheries management objectives (maximizing the average catch, reducing the deviation of yields, and avoiding stock collapse) and ensure robustness to observation errors, we estimate the optimal values of biological reference points (BRPs) composing the HCR. While traditional HCRs usually consist of three BRPs based on the fishing mortality coefficient (F3-HCR), we introduce an alternative HCR defined by 21 BRPs based on the catch levels (C21-HCR) to cover various possible shapes of HCR including smooth ones. We compare the shape and the performance between the optimal C21-HCR and the optimal F3-HCR and conclude that the optimal HCR can be composed of the gradual combination of the basic strategies: the constant escapement strategy, the constant harvest rate (CHR) strategy, and the constant catch strategy. However, the current F3-HCR does not necessarily allow this combination and generally returns lower performance levels than the optimal C21-HCR (since the basic strategy is confined to CHR) excluding the range of low biomass. This result will provide a clear perspective to improve HCR according to the magnitude of assessment errors and to compromise multiple fisheries management objectives when various stakeholders are involved.

The Geographical Expansion of Fisheries conceals the decline in the Mean Trophic Level of Iran's catch

One of the most consistent impacts observed in the analysis of commercial catch globally is the phenomenon known as ‘fishing down marine food webs', wherein fisheries increasingly target small fish in low-trophic levels as a result of the depletion of large, high-trophic level fish. Detecting and mitigating fishing down effects are critical to avoid undermining the long-term sustainability of marine ecosystems; yet the widespread geographical expansion of fisheries in response to declining coastal catches has concealed these effects. Iran is the most important fishing country in the Persian Gulf and Oman Sea region, with ever-growing artisanal fisheries that provide food and employment. In this paper, using catch time series spanning over 66 years (1950–2016) and biological data for 67 marine species/groups, we estimate mean trophic level (MTL), fishing-in-balance (FiB) and region-based MTL (RMTL) indicators to examine the effects of fishing down marine food webs while considering the geographical expansion of Iran's fisheries in the Persian Gulf and Oman Sea. We demonstrated that when not accounting for the geographical expansion of fisheries, MTL did not change much, and primarily reflected the presence of large fish (trophic level > 3.5). However, the climbing trend of FiB suggested that the increasing pattern of Iran's catch is potentially driven by the spatial expansion of the fishing fleet, which is concealing the fishing down effects. By considering the nonstationary nature of fishing fleet and fish stocks over time and area, results from RMTL bolster those obtained by FiB: the actual (observed) catch exceeded the potential catch calculated from the observed trophic structure, indicating that fleets have likely moved from nearshore to deeper, offshore waters to gain access to new resources. Once this is accounted for, our study reveals a downward trajectory of the coastal RMTL, providing insights into the condition of the coastal ecosystem in the Persian Gulf and Oman Sea.

Assessment and Management of Small Yellow Croaker (Larimichthys polyactis) Stocks in South Korea

We aimed to determine the appropriate annual total allowable catch (TAC) levels for the small yellow croaker (Larimichthys polyactis). A Bayesian state-space model was used to assess the species stock. This model has been widely used after research confirmed its reliability over other models. However, setting prior distributions for analyzing this model remains controversial. Therefore, a sensitivity analysis was conducted using the model with different prior distributions and biomass growth functions. Informative and non-informative prior distributions were compared using Schaefer and Fox growth functions. Considering the results of the sensitivity analysis, the assumption of inverse-gamma prior distribution of K, a non-informative distribution, with the Fox function could yield relatively superior estimates than those obtained from other assumptions. Moreover, changing the growth function could have a greater effect on the fitness of the model estimates than changing prior distribution. Therefore, future fishery stock analyses based on this model should consider the effectiveness of various growth functions in addition to the sensitivity analysis for prior distributions. Furthermore, the biomass of small yellow croaker will decrease if the catch increases by 10%. Therefore, the annual TAC levels should be set below the maximum sustainable yield (21,301 tons) for effective small yellow croaker stock management.

Assessing the perceived impact of exploration and production of hydrocarbons on households perspective of environmental regulation in Ghana.

This paper seeks to critically study the perceived impacts of the exploration of hydrocarbons in selected coastal communities in the Western region, the oil and gas industry benefits to local communities, and to determine whether hydrocarbon development is a means for sustainable development. The study uses both quantitative and qualitative approaches using a questionnaire survey, key informant interview, and focus group discussion tools to understand the impact of oil and gas exploration and production in selected affected communities along the coast of Ghana. The activities of oil production and exploration impact negatively on communities; it also leads to a sharp increase in food prices thereby increasing their costs of living. The activity has also caused a decline in fish catch levels which happens to be the main economic activity as a result of exclusion zones created by oil companies which limited the extent fishermen can go fishing. In terms of infrastructure, the three communities are lacking, 77% of respondents from Princess Town hold the view that there is no motorable road linking their community in the next town and 60% from Aketakyi also hold the same view. Infrastructure such as roads, schools, water provision, and clinics are woefully provided in these communities.

Field assessment on management of South American pin worm, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in tomato

Field trials were conducted for three years during kharif season of 2014, 2015 and 2016 to evaluate the integrated pest management (IPM) module against pinworm (Tuta Absoluta) in tomato in comparison with farmer’s practice. Seasonal incidence studies revealed that population increased gradually from September and touched its peak during December (28.00 adults/trap). The insect was found to be higher at the fruit maturity stage and infestation found decreased with increase in temperature. IPM module reduced the cost of cultivation by Rs. 9615.66 ha-1 and the net returns were increased by Rs. 53282.00 per hectare. The average benefit cost ratio was improved with 2.39 in treatment compared to farmers practice 1.92. The results based on pooled data showed that reduction in the fruit damage by Tuta absoluta and good yields is due to the integrated management strategy taken up by installing pheromone traps 2 weeks after transplanting by which awareness on timely spraying of Azadirachtin 1500ppm @ 5ml/lt or combination of Azadirachtin with Chlorantraniliprole 18.5% SC @ 0.3 ml or Flubendiamide 480 SC @0.3ml or Indoxacarb 14.5% SC @ 1.75ml carried in practicing farmers field based on ETL level of adult catches and burning of infested plants and remnants of the crop immediately after the fruits have been harvested also found effective in managing the pest.

Overfishing of a small planktivorous freshwater fish, vendace (Coregonus albula), in the boreal lake Pyhäjärvi (SW Finland), and the recovery of the population

Vendace (Coregonus albula) is a small and rapidly reproducing planktivorous coregonid species that is known to endure very high fishing pressure. Catch levels of 10–25 kg ha−1 a−1 have been sustained for extended periods in several Finnish lakes without signs of fishery-related deterioration of recruitment or decline of spawning stocks. However, data from the lake Säkylän Pyhäjärvi (SW-Finland) in the 1990s indicate an episode of recruitment overfishing of the vendace population. The combination of unfavourable spring weather and unusually high abundance of piscivorous fish led to poor vendace recruitment in two successive years (1990, 1991). In spite of the reduced stock, fishing effort remained high, which resulted in excessively high premature mortality, a depressed spawning stock, and markedly reduced catches. Fishing mortality remained high until the mid-1990s. Then, because of the impaired profitability of the fishery, part of the winter seine crews ceased fishing altogether. The ensuing reduced fishing pressure immediately brought about lowered mortality of vendace, and the spawning stock gradually recovered during the late 1990s. In the 2000s the year-class size stabilized to an average level about half of that in the 1980s. Concurrently, the importance of winter seine fishing diminished due to weakening ice conditions in the warming climate, resulting in a reduced overall fishing pressure on the vendace stock. This study shows that even small, rapidly reproducing freshwater planktivores can be overfished. In the case of Pyhäjärvi, the fishery was self-regulating through economic forcing. A recovery from overfishing was possible because the biological features of vendace make it a highly resilient species.

Construction and Interpretation of Particle Size Distribution Spectra From 19 Ecopath Models of Chinese Coastal Ecosystems

To assess the changes that fisheries have imposed on the functioning of coastal marine ecosystems in China, nineteen published Ecopath models were used to construct particle size distribution (PSD) spectra. The results show that high biomass of jellyfish from ranching operation impacted almost all of the ecosystems studied here. As well, an increasing impact of fisheries was demonstrated, via steeper PSD slopes, for ecosystems with models covering two or more periods. Models of nearshore areas, i.e., bays and estuaries, exhibited steeper PSD slopes that models of offshore areas. The PSD slopes were also correlated with total catch (TC), with the mean trophic level of catch and with the Shannon-Wiener diversity index (H’) that can be computed from Ecopath models. A multiple regression predicting the PSD slopes from year and mean trophic level of the catch explained 38.5 % of the variance in the slopes. Overall, this study confirmed the status of depletion in China’s marine fisheries resources. Also, it established that including a PSD while constructing an Ecopath model, which is straightforward, will improve it, and allow more insights to be obtained from it regarding the impact of fishing on marine ecosystems.

An approximate assessment of the production levels of the Italian fishing fleet in the Mediterranean Sea during selected years in comparison with the analogous previous estimates

During the past two decades, the organization Sea Around Us (based at the Fisheries Centre in British Columbia, Canada) has been carrying out the relevant task of reconstructing national statistics on marine fisheries for almost all countries and territories to fill information gaps and correct the general trend of severe underestimation of the “true” level of catches, discards and landings.A recent reconstruction of this kind showed that the annual catches by the Italian fleet fishing in the Mediterranean Sea had been presumably underestimated during most of the 1950-2010; in the 1970-1995 sub-period, they would have ranged from 0.7-1.1 million metric tons per year. However, comparisons with the landings for the few years for which there are “independent” estimates (i.e., not based on official statistics) show that many more bivalve molluscs and fewer “small pelagics” were caught and that the highest annual outputs reported by Sea Around Us should be presumably cut by 25%-35%.

Loss of Mitochondrial Genetic Diversity in Overexploited Mediterranean Swordfish (Xiphias gladius, 1759) Population

Intense and prolonged mortality caused by over-exploitation could drive the decay of genetic diversity which may lead to decrease species’ resilience to environmental changes, thus increasing their extinction risk. Swordfish is a high commercial value species, especially in the Mediterranean Sea, where it is affected by high catch levels. Mediterranean swordfish consist of a population genetically and biologically distinct from Atlantic ones and therefore managed as a separate stock. The last Mediterranean swordfish stock assessment reported that in the last forty years Mediterranean swordfish has been overfished and, to date, it is still subject to overfishing. A comparison between an available mitochondrial sequence dataset and a homologous current sample was carried out to investigate temporal genetic variation in the Mediterranean swordfish population over near twenty years. Our study provides the first direct measure of reduced genetic diversity for Mediterranean swordfish during a short period, as measured both in the direct loss of mitochondrial haplotypes and reduction in haplotype diversity. A reduction of the relative females’ effective population size in the recent sample has been also detected. The possible relationship between fishery activities and the loss of genetic diversity in the Mediterranean swordfish population is discussed.