Search

Understanding the factors that drive spatial synchrony among populations or species is important for management and recovery of populations. The range‐wide declines in Atlantic salmon (Salmo salar) populations may be the result of broad‐scale changes in the marine environment. Salmon undergo rapid growth in the ocean; therefore changing marine conditions may affect body size and fecundity estimates used to evaluate whether stock reference points are met. Using a dataset that spanned five decades, 172,268 individuals, and 19 rivers throughout Eastern Canada, we investigated the occurrence of spatial synchrony in changes in the body size of returning wild adult Atlantic salmon. Body size was then related to conditions in the marine environment (i.e., climate indices, thermal habitat availability, food availability, density‐dependence, and fisheries exploitation rates) that may act on all populations during the ocean feeding phase of their life cycle. Body size increased during the 1980s and 1990s for salmon that returned to rivers after one (1SW) or two winters at sea (2SW); however, significant changes were only observed for 1SW and/or 2SW in some mid‐latitude and northern rivers (10/13 rivers with 10 of more years of data during these decades) and not in southern rivers (0/2), suggesting weak spatial synchrony across Eastern Canada. For 1SW salmon in nine rivers, body size was longer when fisheries exploitation rates were lower. For 2SW salmon, body size was longer when suitable thermal habitat was more abundant (significant for 3/8 rivers) and the Atlantic Multidecadal Oscillation was higher (i.e., warmer sea surface temperatures; significant for 4/8 rivers). Overall, the weak spatial synchrony and variable effects of covariates on body size across rivers suggest that changes in Atlantic salmon body size may not be solely driven by shared conditions in the marine environment. Regardless, body size changes may have consequences for population management and recovery through the relationship between size and fecundity. [ABSTRACT FROM AUTHOR]

Gizzard shads are facing a continual decline in population, necessitating the implementation of selective gear design for effective resource management. This study aims to prevent the bycatch of young gizzard shads, a non-target fish species, and to derive mesh sizes appropriate for fishery management. Experimental fishing (n = 11) was conducted by manufacturing gillnet fishing gear with different mesh sizes (50.5, 55.1, 60.6, and 67.3 mm) in the coastal waters of the southern Gyeongsang Province. Two methods were employed to estimate the appropriate mesh size of the shad gillnet as follows: firstly, by analyzing the selectivity curve based on body length data; secondly, by developing a complex machine learning model considering biological and economic factors. Model 1 was constructed using mesh variables to classify the score groups. As a result of this study, the total length with a 0.5 gillnet selection ratio. which was estimated to be 179.3, 195.6, 215.1, and 238.9 mm for the 50.5, 55.1, 60.6, and 67.3 mm mesh sizes, respectively. In Model 1, a mesh size of 57.85 mm or less was determined as the most appropriate mesh size. Therefore, considering both biological and economic aspects, shad gillnets should have a mesh size in the 50.5 to 55.1 mm range. [ABSTRACT FROM AUTHOR]

Simple Summary: Poor quality of biological information, such as the relationship between length and weight parameters, could be a source of variability with a significant impact on stock assessment results. This relationship between the length and weight of individuals could differ between males and females as well as two separated islands and/or linked to the reproduction period according the studied species. In total, 109 fish species (24,996 individuals) were sampled around Guadeloupe and Martinique Islands from October 2021 to September 2022 to estimate the morphometric relationships between total length and weight (Length Weight Relationship: LWR) of each fish species according to potential spatial, temporal and sex differences. Of these species, this is the first time that the LWR was estimated in the Atlantic Ocean for 16 species. There is a significant relationship between length and weight for all tested species. For 83 tested species, the sex effect on the LWR showed significant sexual dimorphism for 24 species. Additionally, a link between the temporal effect and the reproduction period was tested for 68 species, of which 35 presented significant differences relative to the annual quarter of sampling. Finally, the geographical effect (i.e., the difference between samples from around Guadeloupe Island and those from Martinique Island) was significant for 60 species. This island effect was significant for 25 species. [ABSTRACT FROM AUTHOR]

A tag-recapture study was undertaken on the Natal seacatfish Galeichthys troworum in the Pondoland Marine Protected Area (PMPA) on the east coast of South Africa. A total of 473 fish were tagged over a period of 8 years, and 136 individuals (28.8%) were recaptured over a period of 16 years, some of them on multiple occasions. Most recaptures (82%) were caught within 200 m of their release site, with movements ranging between 0 and 617 m, and time-at-liberty ranging between 0 and 3 407 days (9.3 years). Data analysis showed that all recaptured fish remained in relatively small home ranges (of ∼360 m linear distance) and none of them abandoned their home range and moved out of the 2-km2 sampling blocks. While the no-take area of the PMPA provided effective protection for these fish, their relative abundance was similar in an adjacent exploited area. This is likely because G. troworum is not a desired linefish species, with most individuals caught being released, coupled with high post-release survival. [ABSTRACT FROM AUTHOR]

This study is the first to record Pacific saury's length–length relationships for converting various body length measurements from various fishing countries in the North Pacific Fisheries Commission. Also, we determined the length–weight relationship of the 2021 saury to compare with historical data. Neither age nor sex has a significant effect on the length–length and length–weight relationships. The length–length relationships were: fork length = 0.292 + 0.998 knob length (R2 = 0.999) and standard length = – 0.464 + 0.970 knob length (R2 = 0.986). The length–weight relationship was: body weight = 3.020 × 10–4 knob length3.788 (R2 = 0.894). The length–weight relationship comparison results indicate that saury has gotten thinner from 2004 to 2021. [ABSTRACT FROM AUTHOR]

Gizzard shads are facing a continual decline in population, necessitating the implementation of selective gear design for effective resource management. This study aims to prevent the bycatch of young gizzard shads, a non-target fish species, and to derive mesh sizes appropriate for fishery management. Experimental fishing (n = 11) was conducted by manufacturing gillnet fishing gear with different mesh sizes (50.5, 55.1, 60.6, and 67.3 mm) in the coastal waters of the southern Gyeongsang Province. Two methods were employed to estimate the appropriate mesh size of the shad gillnet as follows: firstly, by analyzing the selectivity curve based on body length data; secondly, by developing a complex machine learning model considering biological and economic factors. Model 1 was constructed using mesh variables to classify the score groups. As a result of this study, the total length with a 0.5 gillnet selection ratio. which was estimated to be 179.3, 195.6, 215.1, and 238.9 mm for the 50.5, 55.1, 60.6, and 67.3 mm mesh sizes, respectively. In Model 1, a mesh size of 57.85 mm or less was determined as the most appropriate mesh size. Therefore, considering both biological and economic aspects, shad gillnets should have a mesh size in the 50.5 to 55.1 mm range.

Highlight Research • Morphoregression and reproduction aspect of bonylip barb was analyzed • Fork length more accurately to estimate the body weight • Lm50 of bonylip barb in Tamblingan Lake was 116 mmTL • Growth pattern is isometric • Good reproduction aspect Abstract Bonylip barb (Osteochilus vitattus Valenciennes, 1842) is one of many native fish inhabiting Tamblingan Lake. The information about this species in Tamblingan Lake is rare which requires fulfilment in information gaps for the management of bonylip barb. The aims of this research were to find out the length-length relationship, length-weight relationship, length at first maturity, sex ratio, gonadal maturity stage, gonadosomatic index (GSI), fecundity, as well as spawning period and location in Tamblingan Lake. The fish sample was captured with experimental gillnet that was set in the afternoon and hauled in the next morning. Length and weight of every sample were taken. All samples were dissected to observe the sex and gonad. Fork length was the type of length with higher accuracy to estimate the body weight than the other length character. Growth pattern of this species was isometric. Lm50 of bonylip barb in Tamblingan Lake was 116 mmTL. Sex ratio of bonylip barb was imbalanced (1.00:0.82). Gonad maturity stage I-V was found during the research with GSI between 0.16-15.50 for male fish and 0.43-32.82 for female fish. The highest GSI was found in March, 15.50 for male fish and 32.73 for female fish. Mature fish were discovered in all stations in every month of sampling. The fecundity of bonylip barb ranged between 2,792-279,326 eggs. The length-length and the length-weight showed a strong relationship. The fish was isometric. Based on the growth pattern and the reproductive aspects, the population of bonylip barb in Tamblingan Lake was in good condition.

The present study was conducted to investigate the impact of different percentages of animal and plant origin dietary lipids level on growth performance and body composition of major carps. Four plant and animal origin fats supplemented experimental diets of different levels of lipids viz. 0%, 3%, 6% and 9% were made. Twenty-one treatments were made with different levels of animal, plant and combination of animal and plant dietary lipids, where twenty fingerlings were stock in each experimental tank. Animalbased saturated (ABS), unsaturated (ABUS), plant-based monounsaturated (PBMU), polyunsaturated (PBPU) and the combination diets were prepared using different percentages of animal and plant based dietary lipids. Growth performance (weight gain, total length and fork length)and food conversion ratio was recorded monthly. The body composition in terms of crude protein, crude ash, crude fat and moisture were determined. Results showed that weight gain, total length and fork length in cirrhinus mrigalawas significantly higher as compared to other two carp species. Significant (p < 0.05) increase in both parameters at 6% and 9%dietary lipid levels as compared to the fish fed on 0% and 3%. The Cirrhinus mrigala showed significantly higher crude protein in 6% ABS dietary lipids followed by Labeo rohita and Catla catla. The significant higher moisture content and crude ash were recorded in L. rohita in 3% ABUS and 9% animal and 6% plant dietary lipids, whereas, C. catla showed the significant higher crude fat contents in 9% ABUSdietary lipids. In conclusion, C. mrigala shows significant improvement in growth performance. Similarly, fishes fed on animal-based dietsand in combination diet, showed consistently significant (p < 0.05) increase in crude protein, crude fat, moisture and crude ash with the increasing levels of dietary lipids from 0 to 9%. [ABSTRACT FROM AUTHOR]

Bonylip barb (Osteochilus vitattus Valenciennes, 1842) is one of many native fish inhabiting Tamblingan Lake. The information about this species in Tamblingan Lake is rare which requires fulfilment in information gaps for the management of bonylip barb. The aims of this research were to find out the length-length relationship, length-weight relationship, length at first maturity, sex ratio, gonadal maturity stage, gonadosomatic index (GSI), fecundity, as well as spawning period and location in Tamblingan Lake. The fish sample was captured with experimental gillnet that was set in the afternoon and hauled in the next morning. Length and weight of every sample were taken. All samples were dissected to observe the sex and gonad. Fork length was the type of length with higher accuracy to estimate the body weight than the other length character. Growth pattern of this species was isometric. Lm50 of bonylip barb in Tamblingan Lake was 116 mmTL. Sex ratio of bonylip barb was imbalanced (1.00:0.82). Gonad maturity stage I-V was found during the research with GSI between 0.16-15.50 for male fish and 0.43-32.82 for female fish. The highest GSI was found in March, 15.50 for male fish and 32.73 for female fish. Mature fish were discovered in all stations in every month of sampling. The fecundity of bonylip barb ranged between 2,792-279,326 eggs. The length-length and the length-weight showed a strong relationship. The fish was isometric. Based on the growth pattern and the reproductive aspects, the population of bonylip barb in Tamblingan Lake was in good condition. [ABSTRACT FROM AUTHOR]

Selectivity is a fishing gear characteristic capable of catching fish of a specific size and species from the existing population distribution. Mesh size is one of the important factors that influence gillnets’ selectivity, because different length-classes of fish are caught by them. This report focuses on the selectivity of two mesh sizes of gillnets (8.89 cm and 10.16 cm) on mackerel's catch and constructing a gillnet in Sungailiat waters. Experimental fishing methods and selectivity analysis were used for the fishing gear’s more selective preparation, if the largest fishing ratio's value at the fork length (L) is high and the standard deviation value (S) is closer to 1. It is concluded that to be more selective a largest S (L) value of 0.999267194 at fork length (L=54.95 cm), and with a larger value of S (L) 0.997096071 and with (L=66.55 cm) for mesh Sizes 8.89 cm and 10.16 cm, respectively.

Abstract Determining which factors are most effective for mitigative strategies in conservation management can be difficult for species with complex life cycles. Salmon (Oncorhynchus spp.) migrating through a hydroelectric power system experience conditions that can affect their survival directly within a life stage and indirectly in subsequent life stages through carryover effects. We quantified the association of covariates with survival across life stages of Chinook salmon (O. tshawytscha): juveniles migrating downstream, juveniles in the estuary, subadults in the ocean, and adults migrating upstream. We applied a hierarchical Bayesian mark–recapture model to ~400,000 wild Snake River Chinook salmon (Pacific Northwest, USA). Modeled covariates of survival included migration timing, river temperature, flow, percent of water spilled over dams, snow water equivalent, juvenile fish transportation, juvenile fish length, dam powerhouse passage, sea surface temperature, and the North Pacific Gyre Oscillation. By analyzing these covariates in a unified model, we evaluated their relationships to survival within and across life stages in a common currency. Among direct effects, the negative relationship of sea surface temperature to ocean survival had the largest marginal effect size. Carryover effects also had substantial marginal effect sizes. Ocean survival was associated positively with juvenile length and snow water equivalent and negatively with river temperature. In comparison, direct effects on juvenile and adult survival generally showed smaller marginal effect sizes. Both juvenile and adult survival were negatively associated with river temperature. Juvenile survival increased with fish length, while adult survival was positively related to flow and negatively to percent water spilled at dams. The greatest variability in survival, however, was in the ocean stage. Thus, as the ocean continues to warm and as the human population exerts more pressure on the ecosystem, carryover effects will be increasingly important for recovering salmon and other migratory species.

Copyright of Revista Ambiente e Água is the property of Revista Ambiente e Agua and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Determining which factors are most effective for mitigative strategies in conservation management can be difficult for species with complex life cycles. Salmon (Oncorhynchus spp.) migrating through a hydroelectric power system experience conditions that can affect their survival directly within a life stage and indirectly in subsequent life stages through carryover effects. We quantified the association of covariates with survival across life stages of Chinook salmon (O. tshawytscha): juveniles migrating downstream, juveniles in the estuary, subadults in the ocean, and adults migrating upstream. We applied a hierarchical Bayesian mark–recapture model to ~400,000 wild Snake River Chinook salmon (Pacific Northwest, USA). Modeled covariates of survival included migration timing, river temperature, flow, percent of water spilled over dams, snow water equivalent, juvenile fish transportation, juvenile fish length, dam powerhouse passage, sea surface temperature, and the North Pacific Gyre Oscillation. By analyzing these covariates in a unified model, we evaluated their relationships to survival within and across life stages in a common currency. Among direct effects, the negative relationship of sea surface temperature to ocean survival had the largest marginal effect size. Carryover effects also had substantial marginal effect sizes. Ocean survival was associated positively with juvenile length and snow water equivalent and negatively with river temperature. In comparison, direct effects on juvenile and adult survival generally showed smaller marginal effect sizes. Both juvenile and adult survival were negatively associated with river temperature. Juvenile survival increased with fish length, while adult survival was positively related to flow and negatively to percent water spilled at dams. The greatest variability in survival, however, was in the ocean stage. Thus, as the ocean continues to warm and as the human population exerts more pressure on the ecosystem, carryover effects will be increasingly important for recovering salmon and other migratory species. [ABSTRACT FROM AUTHOR]

Copyright of South China Fisheries Science is the property of South China Fisheries Science Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Length of fish species with forked tails, such as the Lake Trout Salvelinus namaycush, can be measured as total (TL), fork (FL), or standard (SL) length, although individual studies of such species often rely on only one measurement, which hinders comparisons among studies. To determine if variation in the relationship between FL and TL among Lake Trout populations affected estimates of FL from TL, we compared length relationships within Lake Trout populations sampled in multiple years, among multiple locations within lakes, among lakes, and from all samples from across the species' range. Samples were from across the geographic range of the species and a wide range of lake sizes (1.31–82,100 km2) to represent the full range of variation in abiotic and biotic variables expected to influence the FL:TL relationship. The functional relationship for estimating FL (mm) from TL (mm) was FL = 0.91 × TL − 8.28 and TL from FL was TL = 1.09 × FL + 9.05. Error induced by length conversion was less when using a length relationship from a different year in the same lake than from a different area in the same lake or from a different lake. Estimation error was lowest when using an overall length conversion from across the species' range, which suggests the overall relationship could be used whenever a more accurate length conversion is not available for a population of interest. Our findings should be useful for providing a standardized model for converting FL to TL (and TL to FL) for Lake Trout, such as comparing published findings of different measurement units, converting measurement units by agencies or institutions that change sampling methods over time, or programs that use different sampling methods among areas. [ABSTRACT FROM AUTHOR]

International monitoring of Atlantic mackerel ( Scomber scombrus ) and Atlantic horse mackerel ( Trachurus trachurus ), two commercial and ecologically epipelagic fish species in the North Atlantic, is currently done inconsistently. Depending on the country and institute, the length of a specimen is measured as either ‘Fork Length’, ‘Pinched Tail Length’ or ‘Total Length’. This inconsistency increases the uncertainty of results from data analyses that are based on international data compilations. Here we provide conversion tables between all three methods for both species, based on field sampling in Greenlandic and Scottish waters. For both species, we recommend the use of ‘Fork Length’ or ‘Pinched Tail Length’ rather than ‘Total Length’. [ABSTRACT FROM AUTHOR]

For the first time, we investigate the aspect of bio-ecological of chub (Squalius cephalus L., 1758) in upper Akcay River (Buyuk Menderes Basin) including the age, growth, length-weight relationship and reproduction. The study was conducted in upper Akcay River between June 2012 and May 2013. Monthly data showed that native fish chub were aboundantly with other native fish (Acanthobrama mirabilis) in upper Akcay River. The age distribution for both females and males of S. cephalus population was between I-VII, and the second age group was found at maximum rate of 30.60%. Their fork lengths and weights ranged between 6.0-22.8 cm and 3.7-134.62 g for females; 6.1-22.1 cm and 2.7-110 g for males, respectively. The growth parameters of the von Bertalanffy equation were found as Lt=34.71 [1-e-0.116(t+0.867)] for females and Lt=32.87 [1-e-0.127(t+0.717)] for males. The length-weight relationships were estimated to be WT= 0.0269 FL2.720 (R2=0.981) for females and WT= 0.0251 FL2.7535 (R2=0.983) for males. Weight increased negatively allometrical with the fork length for both sex. The average condition factor for females was calculated as 1.37 while 1.32 for males. The sexual maturity age of females and males was determined to be II age group and first sexual maturity. The total length was found as 11.33 cm for female and 10.89 cm for male. According to the trends of GSI values, it was assumed that their season of reproductivity was between March and May. [ABSTRACT FROM AUTHOR]

Predation after release is one of the major concerns of hatchery fish propagation. However, size-specific interaction between predator and prey on the survival of hatchery-released salmonid fish is largely unknown. To understand the size-selective predation risk, 24-h predation experiments were conducted on masu salmon Oncorhynchus masou in tanks. Four ranges of fork length (FL) were examined for masu salmon as a prey, in combination with three ranges of FL for white-spotted charr Salvelinus leucomaenis as a predator. The results show that not only predator and prey sizes, but also interaction between prey size and predator size, strongly affected the survival rate of masu salmon. Predation on masu salmon with the FL exceeding 40% of the FL of white-spotted charr was rare in the experiment. A logistic regression suggests that 37% relative FL of masu salmon to white-spotted charr results in the 50% survival of masu salmon. Our results suggest that adjusting relative size of hatchery fish to the size of local fish predators at the time of hatchery release will have a significant impact on the survival of hatchery fish in the wild. From this perspective, site-specific, adaptive management might be important to improve the effectiveness of hatchery fish propagation. [ABSTRACT FROM AUTHOR]

The body size of juvenile fish is often used as an index of growth rate, which in turn is influenced by local habitat conditions. We evaluated the size and origin of juvenile Chum salmon Oncorhynchus keta in the coastal areas of three regions (Atsuta, Shari, and Konbumori) of Hokkaido, northern Japan. The origin of the individuals in these communities differed between Konbumori and the other two regions. The former contained juveniles that originated from both the nearest stocked river and other rivers that were outside the area of interest. Conversely, the communities in Atsuta and Shari consisted exclusively of fish from the nearest stocked river. Moreover, the juveniles in Konbumori were larger than those in Atsuta and Shari. The results of our otolith analysis suggest that the larger size of the fish in Konbumori was due to the immigration of large individuals from natal rivers at distant locations. Thus, immigrants were likely to enlarge their body size composition in the area of interest. In summary, if the distance from a natal river is adjusted and daily growth is taken into account, body size can be used as an indicator of growth performance in coastal juvenile chum salmon. [ABSTRACT FROM AUTHOR]

A total of 453 Trachurus japonicus specimens with a fork length (FL) of 46-250 mm were sampled in the seasonal light seine net surveys in the East China Sea in May, August, and November, 2008 and in February, 2009. The stomach contents of the specimens were analyzed, and the seasonal and ontogenetic variations in the feeding habits of the T. japonicus were examined by the Kruskal-Wallis test, chi-squared test, and cluster analysis. There were 124 prey species (including not identified) ingested by the T. japonicus, among which, planktonic crustaceans and small-scale marine fish made up the dominant prey groups. According to the percentage index of relative importance (IRI%), Bregmaceros macclellandi was the most dominant prey, accounting for 39.2%, followed by Macrura mysis larva (18.4%), brachyura zoea larva (7.6%), and Euphausia pacifica (6.6%). The feeding intensity of the T. japonicus varied significantly with its FL and season, being the highest for the T. japonicus with a FL of 140-159 mm, higher for the T. japonicus juveniles with a FL of 45-99 mm, while lower for the T. japonicus of other size classes, and the highest in spring and the lowest in winter. Cluster analysis revealed there was an abrupt change in the diet composition for the T. japonicus with a FL of about 100 mm FL. The average trophic level of the T. japonicus in four seasons was 3.51, indicating that the T. japonicus in the East China Sea was of low-level carnivores feeding on plankton and nekton. [ABSTRACT FROM AUTHOR]

Length measurements of fishes are commonly used by fishery scientists because of their ease of collection and the profound insight into fish populations that they provide. Specifically, obtaining accurate fish lengths is imperative for obtaining accurate population demographics. Thus, reproducibility and consistency of measuring an individual fish over time can greatly influence population level metrics and ultimately management decisions. To investigate this, we recorded fork lengths of 526 shovelnose sturgeon Scaphirhynchus platorynchus captured, measured, and marked in the field and recaptured within six years. Secondarily, we evaluated 37 shovelnose sturgeon measured in a controlled laboratory setting. We found that in both our field and laboratory evaluation that experienced biologists (between 5 and 20 years experience as fishery biologists) inaccurately measured (greater than 15 mm reduction in length) shovelnose sturgeon in approximately 5% of all cases. Of the approximately 5% erroneous measurements, substantial negative growth (greater than 100 mm reduction in length) occurred in some situations. This suggests that errors in recorded fish lengths exist and because of this, we believe multiple steps should be taken to minimize measurement error. Individual fishery biologists performing measurements should strive to ensure every fish is measured properly (i.e., fish laid completely flat on measuring board) and is recorded accurately. To this end, fishery biologists must accept that measurement error occurs and perform periodic quality assurance/quality control measures to account for these inaccuracies. [ABSTRACT FROM AUTHOR]

To provide target strength (TS) information for estimating the body length of yellowfin tuna Thunnus albacares and its abundance around fish aggregating devices, TS was measured ex situ and in situ. In the ex situ TS measurements, two cameras synchronized with a 200 kHz echosounder were used to obtain the precise orientation of the yellowfin tuna under free swimming conditions. The ex situ TS (dB re 1 m)-fork length (FL, cm) regression was: TS = 27.06 log (FL) − 85.04. Ex situ TS was found to reach its maximum in the tilt angle range of −15° to −20° after excluding TS samples with insignificant correlation to the tilt angle. The angle between the vertebra and the swim bladder was approximately 25° according to X-ray images, supporting the above tilt range. The relationship between the swim bladder volume ( V, ml) and the fork length was: V = 0.000213 FL. The results from the in situ TS measurements indicated that the tilt angle was highly concentrated between −10° and 15°. The results from a calculation using the ex situ TS-FL equation with the fork length from biological sampling agreed strongly with the average in situ TS. [ABSTRACT FROM AUTHOR]

An experiment demonstrated that post-mortem shrinkage in fork length of juvenile pink snapper Pagrus auratus(179–262 mm) was the same in fish in which rigor mortis was surgically inhibited, as in intact fish, and averaged 5·5 ± 0·2 mm (mean ± s.e., range 2–9 mm) after 168 h. [ABSTRACT FROM AUTHOR]

Informed fishery management decisions require primary input data such as the fluctuations in the number of fish landed and fish length. Obtaining these data can be costly if conducted by hand, which is the case for length data in most fisheries. This cost often implies reduced sample sizes, which may introduce biases and lead to information loss at, for example, the boat level. The recent boost in artificial intelligence applied to fisheries provides a promising way to improve the assessment and management of stocks. We present an operational system using a deep convolutional network (Mask R-CNN) coupled with a statistical model that automatically estimates the number and the mean fork length of dolphinfish (Coryphaena hippurus) caught in a Mediterranean fishery with a resolution of each landed fish box from each boat. The system operates on images of fish boxes collected automatically at the centralized fish auction. The statistical model corrects for biases due to undetected fish using the convolutional network and estimates the mean fork length of the fish in a box from the number of fish and the box weight, allowing for high-resolution monitoring of fishery dynamics during the entire fishing season. The system predictions were empirically validated and showed good accuracy and precision. Our system could be readily incorporated into assessment schemes. We discuss how this type of monitoring system opens new opportunities for improving fishery management. • We developed a deep learning/statistical approach to obtain massive data on fish length and numbers from fishery landings. • The results showed good accuracy and precision. • We operationalized the system and showed its results over a fishing season of Coryphaena hippurus in Mallorca. • We estimated the length and numbers of fish at a resolution of each fish box disembarked by each boat. • We show the advantages of this high-resolution system to study fisheries. [ABSTRACT FROM AUTHOR]