Search

ABSTRACT Despite the global importance of inland fisheries, data available for stock assessment is often limited. Data‐limited methods that use length composition data offer a potential approach to assessing more inland fisheries. We assessed the population status of three fish species in Lake Hovsgol, Mongolia through length‐based spawning potential ratio (LBSPR) analysis and evaluation of trends in eight length‐based indicators of population status, catch‐per‐unit‐effort (CPUE), and body size. Hovsgol grayling (Thymallus nigrescens) were not yet overfished, but CPUE and body size declined due to targeting of large, mature fish. Lenok (Brachymystax lenok) were experiencing overfishing, especially of small, immature fish, which contributed to size–structure truncation. The burbot (Lota lota) population was healthy according to most indicators, but the lack of local life history information exacerbated already large uncertainties. Continued monitoring and improved coordination among fishers, managers, and scientists will be critical to enhancing the sustainability of these fisheries. [ABSTRACT FROM AUTHOR]

Inland fisheries are important for food security in communities around the world, especially in developing countries. In North Rupununi, Guyana, the state of exploited stocks is poorly understood, and fishery monitoring and assessment are challenging because diverse fishing gears and target species are distributed across a heterogeneous landscape. This complexity created an opportunity for community‐based monitoring (CBM) to support data‐limited assessment. Standardised CBM was established for the North Rupununi as part of a new inland fisheries management plan initiated by indigenous community groups with support from the government. Quantitative length‐based assessments undertaken for target stocks suggested moderate levels of exploitation consistent with local perception. Our study highlights that local experts and community participants with different levels of training can collect accurate biodiversity data. Further development of CBM is important in North Rupununi. We recommend using local ecological knowledge indicators to track spatial and temporal patterns in exploitation and fish stock status. [ABSTRACT FROM AUTHOR]

The black pomfret (Parastromateus niger) is one of the high-income-generating carangid fish species and the only known member of its genus. This study aims to identify existing gaps in stock status and population demography of this species and provide viable management recommendations to enhance the sustainability of this fishery. Therefore, three methodological approaches have been used in this study; TropFishR to present the current exploitation status, the length-based spawning potential ratio (LB-SPR) to quantify stock spawning biomass, and Froese's sustainability indicators (LBI) to establish a basic standard for sustainable management of the fishery. In the length-weight relationship of black pomfret, an allometric growth pattern (b = 2.19) was found. The VBGF life history parameters for black pomfret were L∞ = 55.25 cm, K = 0.54 year−1, and based on LCCC analysis, the total mortality (Z = 1.61 year−1), natural mortality (M = 0.69 year−1) and fishing mortality (F = 0.91 year−1) are calculated. The result reveals that this fishery is currently suffering from overexploitation and the stock's spawning biomass (SPR = 13%) is below the limit reference point because most of the catch (82%) was found to be under the maturity level. Based on the results, this study recommended strictly maintaining the mesh size of the net to ensure not to catch immature fish with a length smaller than 30.63 cm, recommended the length to catch be between 29 and 35 cm, and reducing fishing pressure by one-third to ensure the sustainability of the black pomfret fishery. [ABSTRACT FROM AUTHOR]

The black pomfret (Parastromateus niger) is one of the high-income-generating carangid fish species and the only known member of its genus. This study aims to identify existing gaps in stock status and population demography of this species and provide viable management recommendations to enhance the sustainability of this fishery. Therefore, three methodological approaches have been used in this study; TropFishR to present the current exploitation status, the length-based spawning potential ratio (LB-SPR) to quantify stock spawning biomass, and Froese’s sustainability indicators (LBI) to establish a basic standard for sustainable management of the fishery. In the length-weight relationship of black pomfret, an allometric growth pattern (b = 2.19) was found. The VBGF life history parameters for black pomfret were L∞ = 55.25 cm, K = 0.54 year−1, and based on LCCC analysis, the total mortality (Z = 1.61 year−1), natural mortality (M = 0.69 year−1) and fishing mortality (F = 0.91 year−1) are calculated. The result reveals that this fishery is currently suffering from overexploitation and the stock’s spawning biomass (SPR = 13%) is below the limit reference point because most of the catch (82%) was found to be under the maturity level. Based on the results, this study recommended strictly maintaining the mesh size of the net to ensure not to catch immature fish with a length smaller than 30.63 cm, recommended the length to catch be between 29 and 35 cm, and reducing fishing pressure by one-third to ensure the sustainability of the black pomfret fishery.

The Bombay duck (Harpadon nehereus) forms the second-largest single-species marine fishery in Bangladesh and therefore has a significant impact on the local economy, providing employment, food, and nutrition to thousands of people. Despite the immense importance, this fishery has never been a priority for the relevant regulatory authorities. To enhance the sustainability of this fishery, an effective management policy based on the scientific evaluation of the current stock’s status is urgently required. Therefore, this study used three methodological approaches (traditional size structure-based stock assessment to reveal current exploitation status; the length-based spawning potential ratio (LB-SPR) to evaluate the stock’s spawning biomass; and Froese’s sustainability indicators for sustainable fishing) to conduct a thorough assessment of the Bombay duck stock to establish basic standards for the sustainable management of this fishery. The results revealed that this fishery is presently suffering from overexploitation and the stock’s spawning biomass (SPR = 8%) is below the limit reference point because of the juvenile-oriented fishing behavior of the fishery. Based on the outputs, this study recommended the mesh size regulation of the set bag nets (SBNs) (5 cm mesh size for the codend) to ensure not to catch immature fishes with a length equal to or smaller than 17.95 cm; and reduce the existing number of SBNs by half to reduce fishing pressure on the stock to ensure the sustainability of this fishery.

Managing coastal fisheries is challenging as the status of many fish stocks caught in these fisheries remains unknown. In the South African linefishery, regular comprehensive assessments of the status of most linefish stocks are unattainable owing to a scarcity of reliable long-term data. Length-based analysis remains the only option to determine stock status in the form of spawning potential ratio (SPR), as life-history information and representative length samples are available for many linefish species. Although per-recruit models are susceptible to bias due to violation of the steady-state assumption, the SPR has been shown to be robust for long-lived species under reasonably consistent fishing mortality. In this study we used observer-collected length-frequency data from two time-periods 20 years apart (1988–1990 and 2008–2010), before and after management regulations were implemented, in combination with life-history information, to estimate the SPRs for 17 linefish species. We then correlated the recent stock-status estimates to species-specific life-history traits to identify length-based indicators of susceptibility to exploitation. Most species showed improvements in SPR between the periods, caused mainly by decreases in fishing mortality (F) and also increases in length-at-first-capture (Lc). The ratio between Lc and asymptotic length (Lc/L∞), and the ratio between Lc and optimum length (Lc/Lopt), had significant relationships with SPR. We suggest that length-based indicators could be used to classify risk to overfishing in data-poor fisheries for medium- to long-lived species when time-series data are not attainable, but where representative size samples and adequate life-history information exist. [ABSTRACT FROM AUTHOR]

Abobi SM, Mildenberger TK, Kolding J, Wolff M. 2019. Assessing the exploitation status of main fisheries resources in Ghana's reservoirs based on reconstructed catches and a length-based bootstrapping stock assessment method. Lake Reserv Manage. 35:415–434. The cichlid species Oreochromis niloticus, Sarotherondon galilaeus, and Coptodon zillii, which are among the most exploited resources in the small-scale fisheries of the Tono, Bontanga, and Golinga reservoirs in northern Ghana, were assessed based on length frequency samples. Growth, mortality, exploitation status, stock size, and relative yield per recruit reference points were determined using bootstrapping fish stock assessment (BFSA), a novel framework that allows for the estimation of uncertainties around the life-history parameters and reference levels (e.g., L∞, K, and F0.1). The results suggest that the 3 species studied are heavily exploited in all 3 reservoirs, but with no alarming signs of overexploitation. The fishing effort at Golinga is comparatively low as a result of insignificant fishing during the agriculture season, which relates to low exploitation rates. Sarotherondon galilaeus and C. zillii have the highest and lowest biomass (t/km2) respectively in all the 3 reservoirs. The small shallow reservoir (Golinga) has the highest biomass of the target resources per unit area. According to a second assessment approach, based on length-based indicators, all species at Bontanga and O. niloticus and S. galilaeus populations at Golinga have spawning stock biomasses below 40% of the unfished biomass. This points to a situation of a possible ongoing recruitment overfishing of those species in the 2 reservoirs and suggests that a further increase in fishing effort should be prevented. Further monitoring of these fisheries will be needed for the improvement of assessments and thus management advice. [ABSTRACT FROM AUTHOR]

Decreasing abundance of many traditionally exploited fish stocks in the Baltic Sea force small-scale fisheries to find new ways to make a living. In line with Swedish national strategies on food supply there is an interest to develop commercial cyprinid fisheries. In the Bothnian Bay in the northern part of the Baltic Sea, annual catches have increased from zero-catches 2018–30 tonnes 2021. To aid a sustainable development of these cyprinid fisheries that target mainly bream (Abramis brama) and ide (Leuciscus idus), we study catch efficiency of target species and bycatch in different gears and seasons using logbook data from the Bothnian Bay. Using cameras, we also assessed bycatch rates. To assist the sustainability of the fishery we develop potential stock indicators. Our results suggests that larger gear (pound-nets) are more effective in catching bream, and that the proportion of bycatch decreased with gear size, being < 10% in the largest gear, which is similar or lower than many other Baltic Sea fisheries. By-catches of salmon is of concern in the Bothnian Bay, but the camera study indicates that salmon bycatches are sporadic. Catch per unit effort (CPUE) of bream was highest in spring and fall, and we conclude that site specific median CPUE is the most suitable stock abundance indicator. The size indicator L90 , the 90th percentile of the length distribution, was similar among areas and we propose it as a suitable indicator of the demographic structure of the targeted bream stocks. Our results provide reference points for relatively unfished conditions, but as the study was based on mainly fishery dependent data, it is important to also include fishery independent data to assess ecosystem effects of a future and intensified cyprinid fishery. • Cyprinids could diversify fisheries in the Baltic Sea but sustainability is unknown. • Bycatches in Baltic Sea cyprinid fishery was generally lower than 10%. • There are substantial spatiotemporal variation in catch per unit of effort. • Stock indicators of abundance must be site and time specific. • It may be possible to apply size based indicator at a regional scale. [ABSTRACT FROM AUTHOR]

The stomach contents of the giraffe catfish, Auchenoglanis occidentalis, populations from Lake Bontanga and Lake Tono, two artificial lakes, were analysed, together with length frequency data collected from July 2016 to June 2017, to gain knowledge of the stock bioecology and exploitation status. The feeding characteristics of the giraffe catfish did not differ significantly between the lakes, as revealed by a Wilcoxon rank-sum test (p > 0.05). Insect larvae and algae dominated stomach content, with proportionate contributions of 43.8% and 14.2% in Lake Bontanga and 49.3% and 10.6% in Lake Tono, respectively. In the larger Lake Tono, the growth coefficient (K = 0.34 year) and asymptotic length (L∞ = 38.3 cm) were higher than in Lake Bontanga and the exploitation rate was comparatively low (E = 0.24). This lower exploitation level in Lake Tono agrees with a higher mean catch size of 27.6 cm and a high spawning stock biomass >0.4 of the unfished biomass, as well as a higher spawning stock biomass of 3.12 tonnes km−2, suggesting that there is scope for an intensification of the fishery. In the smaller Lake Bontanga, the species growth was lower (K = 0.31 yr−1 and L∞ = 28.9 cm) and the stock is fully exploited (E = 0.48). The mean catch size and spawning stock biomass were critically low; 17.2 cm and <0.4 of the unfished biomass, respectively. Accordingly, this stock requires close monitoring to prevent resource depletion. [ABSTRACT FROM AUTHOR]

Perspectives on lamprey management contrast between pest control in the US Great Lakes and species conservation in the Pacific Northwest, New Zealand, and Europe. Five lamprey species are listed in the European Union (EU) Habitats Directive (HD) as requiring conservation measures. Assessments of HD 'conservation status' for these lampreys mainly target the larval (ammocoete) stage.Larval lamprey populations can be assessed by evaluating presence or absence, density and demographic structure in riverine samples. Demographic structure has typically been described from length–frequency data using qualitative approaches and the statistical assignment of age classes. Length‐based indicators (LBIs) may provide a more rapid and flexible framework.The demographic structure of a fish population can be described by univariate length metrics: length range (LRANGE) and 90th percentile of length (L90). This study used a pooled data set from seven Irish catchments to estimate a reference point (RP) value for each metric corresponding to a healthy larval lamprey population. Two LBIs were then derived that can be estimated for an observed (OBS) population as LBIRANGE = LRANGE_OBS/LRANGE_RP and LBI90 = L90_OBS/L90_RP.Simulated lamprey population length structures, representing a range of status values, were used to develop a reference gradient (RG) to support population assessment using LBIs. The assessment framework was applied to each of the seven Irish catchments, and also to subcatchment and sampling‐site scales within the Barrow system. The LBIs and RG suggested that most catchments had favourable conservation status overall, whereas smaller assessment scales revealed a spread of status values.The proposed framework allows the rapid assessment of demographic structure and comparison across systems. There is potential to track states across sampling sites, events, and legislative reporting cycles, and to interpret change in relation to the local environment. The general approach may be adaptable for other fish species monitored during juvenile stages. [ABSTRACT FROM AUTHOR]

This paper reviews a selection of nine indicators for assessing the biological state of a fish population monitored only by using trawl surveys in which catchability is assumed constant from time to time and place to place. The intention is to inform or remind of the range of possibilities and of associated practical and statistical issues. The indicators, grouped according to relationships with abundance, length, age, weight, and reproduction, are documented in a standard format covering estimation, interpretability, sensitivity, considerations for reference points where possible, and an example of their application. Lastly, selected indicators together with year-class curves fitted to abundance indices-at-age are applied to the North Sea cod to demonstrate the feasibility of an assessment based on only one trawl survey. Results support findings of the International Council for the Exploration of the Sea (ICES) working group on the assessment of demersal stocks in the North Sea and Skagerrak. [ABSTRACT FROM AUTHOR]

The Bombay duck (Harpadon nehereus) forms the second-largest single-species marine fishery in Bangladesh and therefore has a significant impact on the local economy, providing employment, food, and nutrition to thousands of people. Despite the immense importance, this fishery has never been a priority for the relevant regulatory authorities. To enhance the sustainability of this fishery, an effective management policy based on the scientific evaluation of the current stock's status is urgently required. Therefore, this study used three methodological approaches (traditional size structure-based stock assessment to reveal current exploitation status; the length-based spawning potential ratio (LB-SPR) to evaluate the stock's spawning biomass; and Froese's sustainability indicators for sustainable fishing) to conduct a thorough assessment of the Bombay duck stock to establish basic standards for the sustainable management of this fishery. The results revealed that this fishery is presently suffering from overexploitation and the stock's spawning biomass (SPR = 8%) is below the limit reference point because of the juvenile-oriented fishing behavior of the fishery. Based on the outputs, this study recommended the mesh size regulation of the set bag nets (SBNs) (5 cm mesh size for the codend) to ensure not to catch immature fishes with a length equal to or smaller than 17.95 cm; and reduce the existing number of SBNs by half to reduce fishing pressure on the stock to ensure the sustainability of this fishery. [ABSTRACT FROM AUTHOR]