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The shape of the length frequency distribution (LFD) is an important input for stock assessments and one of the most important features in studies of fish population dynamics, providing estimates of growth parameters. In practice, oversampling may occur when sampling commercially important species. At times of more and more limited resources, the length sample size can be optimized at some stages of national or regional sampling programmes, without reducing the quality of stock assessments. The main objective of this study is to demonstrate a general distribution-free methodological approach for an optimization of sample size developed as an alternative to both analytical and bootstrap approaches. A novel framework to identify the reduced but still informative sample and to quantify the (dis) similarity between reduced and original samples is proposed. The identification procedure is based on the concept of reference subsample, which represents a theoretical minimal representative subsample that despite smaller sample size still preserves a reasonably precise LFD for certain species. The difference between the original sample and the reference subsample called admissible dissimilarity value (ADV) serves as the upper threshold and can be used to quantify the reliability of derived subsamples. Monte Carlo simulations were conducted to validate the approach under various LFD shapes. We illustrate in case studies how ADV can support to evaluate adequate sampling effort. The case studies focus on length samples from the German commercial vessels fishing for North Sea cod ( Gadus morhua ).

Coastal trevally, Turrum coeruleopinnatum is one of the commercially important species caught from Terengganu waters, Malaysia. Lack of biological information available for this species inspire this study. The population parameters such as length-frequency distribution, length-weight relationships, and growth parameters of T. coeruleopinnatum were studied where fish sample were collected from the trawlers that landed at fishing port in Pulau Kambing, Terengganu from April 2019 to March 2020. Of 687 individuals examined, 362 were males (52.69%) and 325 were females (57.31%). The size of samples ranged from 6.3 to 26.6 cm L S (mean ± SD: 13.2 ± 3.84 cm) and body mass between 11.5 and 635.8 g (109.9 ± 93.5 g). This study found that T. coeruleopinnatum has negative allometric growth pattern with the growth coefficient (b) values were 2.7984, 2.7814, and 2.7937 for males, females, and pooled sexes respectively. The ages of fish was determined by counting the number of opaque rings in sectioned otolith where seven age groups were identified. Von Bertalanffy growth parameters of the males, females and pooled sexes were as followed: SL T =190.48 [1 – exp {-0.40(t-0.27)}], SL T = 57.91 [1 – exp {-0.71 (t – 0.21)}] and SL T = 153.55 [1 – exp {0.37 (t – 0.08)}] respectively, where SL T if standard length (cm) at age t. This study provides new references of T. coeruleopinnatum in Terengganu waters, South China Sea, Malaysia for the enrichment of fisheries database and relevant fishery management in the region.

The abundant pelagic tunicate Salpa thompsoni is a major grazer in the Southern Ocean (SO) with high ingestion rates, fast-sinking faecal pellets, and the potential to rapidly grow and form dense blooms. We investigated the length-frequency distribution, maturity stage composition, growth, development speed, and size-specific diel vertical abundance patterns at one of the northernmost habitats of S. thompsoni (Chatham Rise, east of New Zealand, ~ 44°S 178°E). By observing the in situ growth of distinct size cohorts and ex situ on-board experiments, relative growth was estimated for 6–10 mm blastozooids to be between 8.8–11.7% d−1 at ambient temperatures of 10 °C, with good agreement between our cohort-based field estimates and ex situ growth chambers. Transition times between development stages were estimated to be 3.8 ± 1.5 days, allowing for the succession from newly released aggregate chain to functional male blastozooid within 23 days. Integrative Bongo tows in the upper 200 m showed that S. thompsoni not only have daytime-dependent vertical abundance patterns, but also that these are size-specific, with medium-sized blastozooids and large oozooids contributing most to the elevated values during the night. The present study highlights the need for more in-depth biological studies of S. thompsoni at lower latitudes, which will help in understanding their increasingly structuring role in a gradually warming SO.

In 2001, the Pacific Fishery Management Council established 2 large (10 878 and 260 km²) Southern California Bight marine reserves called Cowcod Conservation Areas (CCAs) in response to declining abundance of west coast rockfishes, particularly overfished cowcod. Following closure, no fishery-independent monitoring took place for groundfishes within the CCAs through 2013. To assess the impact of the closures, we sampled multiple sites inside and outside CCAs from 2014 to 2016 via the Northwest Fisheries Science Center’s Hook and Line Survey. We investigated variations in catch per unit effort (CPUE), size, length frequency and percent of sites with positive catch for 14 abundant groundfishes (bank, bocaccio, chilipepper, copper, cowcod, greenspotted, lingcod, olive, rosy, speckled, squarespot, starry, swordspine and the vermilion-sunset complex). General linear models that included area, year, depth and distance from port revealed significantly greater CPUE inside CCAs for 11 species. CPUE for lingcod, copper rockfish and vermilion-sunset was significantly or near-significantly lower inside the CCAs. We saw significant or near-significant differences in size (12 species) and length-frequency distributions (10 species), with larger fish present inside CCAs. The percentage of sites positive for individual species tended to be greater inside CCAs (11 species). We also observed significantly elevated species richness (species per site) and total CPUE inside CCAs. Results indicate larger individuals and greater CPUE for multiple rockfishes inside CCAs either as a result of effective management or perhaps pre-existing conditions.

Dreissenid bivalves (Dreissena polymorpha and D. rostriformis bugensis) are considered the most aggressive freshwater invaders inflicting profound ecological and economic impacts on the waterbodies that they colonize. Severity of these impacts depends on dreissenid population sizes which vary dramatically across space and time. We developed a novel method that analyzes video recorded using a Benthic Imaging System (BIS) in near real-time to assess dreissenid distribution and density across large waterbodies and tested it on Lake Erie. Lake Erie basins differ dramatically in morphometry, turbidity, and productivity, as well as in Dreissena distribution, density, and length-frequency distribution, providing an excellent model to test the applicability of our method across large and dynamic environmental gradients. Results of rapid assessment were subsequently compared with dreissenid density obtained from Ponar grab samples collected at the same sites. In the eastern and central basins, the differences in basin-wide density estimations from BIS and Ponar were 3% and 23%, respectively. In the western basin, this method had limited application due to high turbidity and abundance of small (< 10 mm length) mussels. By substantially reducing the time required to assess dreissenids across large areas, rapid assessment could be a useful and cost-effective addition for monitoring their populations.

Life history parameters are indicators of stock structure and the dynamics of populations. In this work, we examine multiple life-history parameters (size distribution, growth, mortality, and longevity) of Palaemon longirostris H. Milne Edwards, 1837 inhabiting the estuarine temperate waters of the Guadalquivir estuary through size-frequency distribution data obtained from June 1997 to May 1999. Sexual dimorphism in size was evident, as females displayed a larger body size with a maximum size of 19.1 mm CL compared to males’ 11.7 mm. The carapace length–weight relationship indicated an allometric growth pattern in both sexes. Additionally, the growth performance index was 2.50 for females compared to 2.33 for males. The recruitment pattern analysis of P. longirostris indicated that females experienced a recruitment rate distributed throughout the warm period between March and August, while males exhibited a higher concentration of recruitment from late spring to early summer. Our study found that natural and fishing mortality rates were similar among male P. longirostris , whereas fishing mortality had a smaller effect on the overall mortality of females. The exploitation rates for both male and female stocks were optimally balanced.

An assessment on the fluctuations in abundance of the striped venus clam (Chamelea gallina) in the southern Adriatic Sea (Central Mediterranean Sea), and the northern Gargano area, has been conducted through both historical information and recent data from monitoring surveys during the period 1997–2019. Production trends, conditions of the commercial stock biomass, and depth distribution pattern of juveniles and commercial sizes were analysed testing temporal differences. Moreover, the exploitation of the clam beds and recruitment events were investigated in 2018–2019. Changes in abundance were analysed using non-parametric tests for both juvenile (length class, LC < 22 mm) and commercial (LC ≥ 22 mm) fractions. Hydrodynamic changes, temperature and salinity variations were explored using a 3D hydrodynamic numerical model (MIKE 3 FM-HD) and statistical analysis, as well as changes in benthic assemblages impacted by hydraulic dredges were investigated through PERMANOVA and other multivariate analysis.The results showed a temporal decline of production and biomass of C. gallina during the 1997–2019 period, and a regression of the depth limit in the clams’ distribution towards shallower waters. A significant reduction in juveniles was observed during 2018–2019 with a very limited recruitment. The fishing exploitation showed high impacts on the commercial stock and benthic assemblages in the summer of 2018. Overall, water currents were predominantly directed offshore in 2018, during the C. gallina spawning period. This could affect the larval dispersal and settlement on unsuitable bottoms. Anomalies in temperature (high peaks in August 2018, > 28 °C) and salinity (low values in spring 2018, < 37 PSU) could have induced stress and mortality events on the entire clam bed in the study area. This first study highlights the need to integrate environmental information in the assessment of commercial stocks of clams in the Adriatic Sea, to better understand climate change effects on the fluctuations and to support effective ecosystem-based fishery management.

We compare estimates of krill density derived from gliders to those from contemporaneous and previous ship-based surveys. Our comparisons cover several temporal and spatial scales within two strata around the northern Antarctic Peninsula (off Cape Shirreff on the north side of Livingston Island and in the Bransfield Strait). Our objective is to explore the feasibility of using gliders to supplement or replace vessel-based surveys of fishery resources. We deployed two long-duration Slocum G3 gliders manufactured by Teledyne Webb Research (TWR), each equipped with a suite of oceanographic sensors and a three-frequency (38, 67.5, and 125 kHz, each single-beam) Acoustic Zooplankton Fish Profiler. We used the acoustic data collected by these gliders to estimate biomass densities (g⋅m –2 ) of Antarctic krill ( Euphausia superba ). The two gliders were, respectively, deployed for 82 and 88 days from mid-December 2018 through mid-March 2019. Off Cape Shirreff, glider-based densities estimated from two repeat small-scale surveys during mid-December and January were 110.6 and 55.7 g⋅m –2 , respectively. In Bransfield Strait, the glider-based estimate of biomass density was 106.7 g⋅m –2 during December–January. Contemporaneous ship-based estimates of biomass density, from a multi-ship broad-scale krill survey ( Macaulay et al., 2019 ) restricted to the areas sampled by the gliders, were 84.6 g⋅m –2 off Cape Shirreff and 79.7 g⋅m –2 in Bransfield Strait during January. We compared two alternative krill-delineation algorithms (dB differencing and SHAPES); differences between biomass densities estimated by applying these algorithms were small and ranged between 4 and 7%. Alternative methods of sampling krill length-frequency distributions (LFDs) (nets or predator diets), which are required to convert acoustic energy to biomass density, also influenced the glider-based results. In Bransfield Strait, net-based estimates of biomass density were 6% less than those based on predator diets. Off Cape Shirreff the biomass density of krill estimated from a net-based LFD was 20% greater than that based on predator diets. Development of a variance estimator for glider-based biomass surveys is ongoing, but our results demonstrate that fisheries surveys using acoustically-equipped gliders are feasible, can provide density estimates to inform management, and may be conducted at lower cost than ship surveys in some cases.

Horse mackerel is a semi-pelagic fish widely distributed in the eastern Atlantic, where it represents a species of interest for fisheries and is subject to intense exploitation, leading to its global classification as a vulnerable species by IUCN. In the Northwestern (NW) Mediterranean Sea, the knowledge of their distribution, abundance and main biological parameters is fundamental to achieve their sustainable exploitation and contribute to the ecosystem approach to fisheries management. The time series (2009–2020) data set analyzed in this study came from two geographical subareas (GSAs) defined by the General Fisheries Commission for the Mediterranean (GFCM), Northern Spain (GSA06) and Northern Alboran Sea (GSA01) sampled in July during the MEDiterranean International Acoustic Survey (MEDIAS). Our results suggest that in summer, a higher concentration and aggregation of fish exists in GSA01, with a density ten times greater than in GSA06. Possible life history changes can be inferred through the analysis of the biological parameters of Trachurus trachurus in the NW Mediterranean Sea. In both GSAs, the annual decline of the size at first maturity ( L 50 ) and condition factor (Kn) was prominent. Moreover, the population structure lacked adult modes that could guarantee a successful recuperation of future stocks. Nonetheless, fish inhabiting GSA01 seem to have a better adaptive response to the events responsible for these alterations. In comparison, GSA01 is under less fishing pressure and the upwelling occurring in this area contributes to a higher availability of food, in addition to reducing the increases in sea surface temperature due to climate change during the study period.

The current work was conducted to investigate fisheries dynamics, rate of growth, and mortality, along with demographic features of Schizothorax niger using length-frequency data collected monthly from Manasbal Lake from August 2020 and July 2022. The length data for estimation was categorized into 13 bins, and population parameters were explored utilizing various options in ELEFAN I, with the best fit (Rn = 0.282) calculated by means of the FiSAT-II application. TW = 1.94 TL 2.94 , with a  =  − 1.94, b  = 2.94, and an attuned r 2  = 0.77 were derived for the weight and length association. The growing performance metric (ϕ) was calculated as 2.80. S. niger harvested stock in Manasbal Lake was prevalent in length categories of 20.5 to 25.4 and 25.5 to 30.4 cm. Different growth attributes were valued utilizing length frequency statistics as L ∞  = 46.05 cm, k  = 0.30/year, and t 0  =  − 0.493 years. Over all mortality ( Z ), natural mortality ( M ), and fishing mortality ( F ) coefficients were evaluated as 1.43 year −1 , 0.56 year −1 , and 0.87 year −1 , respectively. The fish’s average length was assessed at the culmination of the 1st, 2nd, 3rd, 4th, 5th, and 6th year as 15.42 cm, 22.78 cm, 28.09 cm, 32.61 cm, 36.03 cm, and 38.53 cm, respectively. Recruitment patterns in S. niger from Manasbal Lake indicate a singular annual recruitment occurrence, exclusively observed during the month of June. The current value of the exploitation (fish harvest) ratio ( E ) was 0.61 by the size-transformed catch curvature method, found to be marginally lower than the maximum value ( E max ) of 0.699 depicting that the species is on the brink of overexploitation, and caution is required to maintain sustainability. The seasonal analysis of water quality parameters revealed that except for pH and free carbon dioxide, the other parameters showed pronounced temporal variations. Total alkalinity values were reflective of hard water type of the lake, and dissolved oxygen and free carbon dioxide values were reported to be suitable for S. niger.