Fish Length Distributions Research Articles

BIOLOGI REPRODUKSI IKAN BALOBO (Hyporhamphus quoyi) HASIL TANGKAPAN JARING BALOBO DI PERAIRAN DESA APARA KABUPATEN KEPULAUAN ARU

Garfish is a small pelagic species that has long been used as a raw material for dry fish production from Maluku called balobo dried fish. Many species of Garfish have been exploited but the species Hyporhamphus quoyi has not much been informed. This study aims to understand the reproductive aspects of Garfish consisting of measuring the sex ratio, changes in the gonad maturity stages (GMS) and counting the size of the first size gonad maturity. Located at the waters of Apara village, Aru Archipelago Regency, this study was conducted using a balobo net from November to December 2023. The catches were identified, measured its fork length (FL cm) and dissected to examine its reproductive organ. The Chi-squire heterogeneity test was occupied to measure sex ratio at different sizes. GMS was accessed based on the morphology of testis and ovary. First size maturity was calculated using Spearman-Karber method. The target fish captured by the balobo net consists of the Hemirhamphus far and Hyporhamphus quoyi. The ratio of male and female Hyporhamphus quoyi is unbalanced (c2=8.36; df=1; P=0.0038) but the sex ratio based on the length distribution of fish is not significantly different ( c2=6.92; df=6; P =0.328). Changes in GMS during the observation period indicate the occurrence of spawning in November. Balobo fish reach gonad maturity at FL = 24.9cm for females and FL = 26.8cm for males. Since the optimum size of the fish Hyporhamphus quoyi caught by balobo net is 27cm, this net produced legal sized of fishes.

Length frequency distribution and length-weight relationships of Euthynnus sp. in North Sumatera, Indonesia

North Sumatra is one of the provinces that has a large fishery potential. The total catch of in North Sumatra reached 380,349 tons in 2016. This research to determine the growth pattern of Euthynnus sp. that caught in the waters of Nias Island, North Sumatra. Sampling was carried out in July 2020. The study was conducted by following fishing operations on purse seine vessels start from Sibolga City. Sample of 59 fish were taken randomly during the operation of the fishing gear in one trip. Length of fish was measured using a ruler (nearest: 1 mm) and weight of fish was measured using a digital scale (nearest: 1 g). The result of this research was the total length of the fish about 350–530 mm. There were 7 classes Length Distribution of fish that caught in July 2020. The highest frequency of total length was 401-427 mm. The growth pattern of Euthynnus sp. was positive allometric growth (b > 3). The Formula for Length-Weight Relationships is W = 0.06L3.2611 (r = 0.97). The length-weight relationship can describe the condition of fish population growth and the symptoms of fishing in nature. This is necessary to support the management of fishery resources.

Evaluating the fish aggregation effect of wind turbine facilities by using scientific echo sounder in Nanlong wind farm area, western Taiwan

During the stages of construction and operation of the wind power facilities, fishery and fishery resources in the wind farm areas will certainly be changed greatly. One of the major concern is the aggregation effect of wind turbines facility. We use scientific echo sounder together with scuba diving to survey fish aggregations in the wind farm areas. In order to obtain echoes very near the facility, we use tilt beam angle instead of traditional vertical one. Variation of target strength varies while using tilted beam angle were discussed both by ex-situ and in-situ experiment. In ex-situ experiment, we measured TS of sample fish in different attacking beam angle in three different rotation planes, and conducted by setting four different beam angles to detect free-swimming fishes in a cage. We found that fish length estimated by different title angle varied greatly, but maintained linear relationship with target strength at tilt angle of 30o and 60o. In in-situ experiment, we developed a special trackline for acoustic survey using 60o tilt beam angle together with scuba diving observation to evaluate fish aggregation effect among two wind turbines, a wind tower and a neighboring artificial reefs in the Nanlong wind farm. The results showed that in the core area (< 20 m) near the facilities the target strength distribution patterns and values were consistent with the fish length distribution from scuba diving data. In the joint surveys, we observed that the wind turbines had relatively better fish aggregation effect than nearby neighboring wind towers and artificial reefs.

Estimating reef fish size distributions with a mini remotely operated vehicle-integrated stereo camera system.

We tested the efficacy of a stereo camera (SC) system adapted for use with a remotely operated vehicle (ROV) to estimate fish length distributions at reef sites in the northern Gulf of Mexico. A pool experiment was conducted to test the effect of distance (1, 2, 3 or 5 m), angle of incidence (AOI; 0° to 40° at 5° increments), and SC baseline distance (BD; BD1 = 406, BD2 = 610, and BD3 = 762 mm camera separation) on the accuracy and precision of fish model length (288, 552, or 890 mm fork length) estimates compared to a red laser scaler (RLS). A field experiment was then conducted at 20 reef sites with SCs positioned at BD1 to compare fish length distribution estimates between the SC and RLS systems under in situ conditions. In the pool experiment, mean percent errors were consistently within the a priori selected threshold of ±5% at AOIs ≤10° at all distances with all four systems. However, SCs produced accurate estimates at AOIs up to 30° at all distances tested; 2–3 m was optimal. During reef site surveys, SCs collected 10.4 times as many length estimates from 4.3 times as many species compared to the RLS. Study results demonstrate that, compared to laser scalers, ROV-based SC systems can substantially increase the number of available fish length estimates by producing accurate length estimates at a wider range of target orientations while also enabling measurements from a greater portion of the cameras’ field of view.

Image-based, unsupervised estimation of fish size from commercial landings using deep learning

Abstract The dynamics of fish length distribution is a key input for understanding the fish population dynamics and taking informed management decisions on exploited stocks. Nevertheless, in most fisheries, the length of landed fish is still made by hand. As a result, length estimation is precise at fish level, but due to the inherent high costs of manual sampling, the sample size tends to be small. Accordingly, the precision of population-level estimates is often suboptimal and prone to bias when properly stratified sampling programmes are not affordable. Recent applications of artificial intelligence to fisheries science are opening a promising opportunity for the massive sampling of fish catches. Here, we present the results obtained using a deep convolutional network (Mask R-CNN) for unsupervised (i.e. fully automatic) European hake length estimation from images of fish boxes automatically collected at the auction centre. The estimated mean of fish lengths at the box level is accurate; for average lengths ranging 20–40 cm, the root-mean-square deviation was 1.9 cm, and maximum deviation between the estimated and the measured mean body length was 4.0 cm. We discuss the challenges and opportunities that arise with the use of this technology to improve data acquisition in fisheries.

Estimating the Size Selectivity of Fishing Trawls for a Short-Lived Fish Species

Long-term fish survey monitoring programs use a variety of fishing gears to catch fish, and the resulting catches are the basis for status and trends reports on the condition of different fish stocks. These catches can also be part of the data used to set stock assessment models, which establish harvest regulations, and to fit population dynamics models, which are used to analyze population viability. However, most fishing gears are size-selective, and fish size — among other possible covariates, such as environmental conditions — affects the probability that a fish will be caught in the path the gear sweeps. Failing to properly account for selectivity can adversely affect the ability to interpret and use status and trends measures, stock-assessment models, and population-dynamics models. Our side-by-side gear comparison study evaluated the selectivity of multiple open-water trawl surveys that have provided decades worth of information on the imperiled fish species Delta Smelt (Hypomesus transpacificus). We used data from the study to estimate gear selectivity curves for multiple trawls using two methods. The first method examines the total number of fish-at-length caught across all gears, and does not directly use or estimate fish length distribution in the population. The second method examines the total number of fish caught by each gear separately, and explicitly estimates fish length distribution in the population. The results from the two methods were similar, and we found that one trawl was highly efficient at catching larger Delta Smelt. This is the first formal multi-gear evaluation of the relative selectivity of how well survey gear used to monitor Delta Smelt in the San Francisco Estuary selects fish by size, and we plan to incorporate the results into Delta Smelt population models.

Size Selectivity of Sampling Gears Used to Sample Kokanee

AbstractKokanee Oncorhynchus nerka provide valued recreational fisheries and also serve as a prey resource for economically, socially, and ecologically important fishes. As such, management of kokanee is a major focus of natural resource agencies. Kokanee are typically monitored using midwater trawls, but the interpretation of data collected using midwater trawls is difficult due to the unknown size selectivity of the gear. We sought to assess the length selectivity of midwater trawls by comparing estimates obtained from midwater trawls with estimates obtained from gill nets adjusted for size selectivity. Experimental curtain gill nets and midwater trawls were used in conjunction to sample kokanee in seven lentic systems in Idaho. The size selectivity of gill nets was estimated by accounting for the probability of encounter and the probability of retention. Estimates of size selectivity were then used to adjust the length distribution of fish sampled in gill nets. The adjusted length distribution of fish sampled in gill nets was compared with estimates obtained from midwater trawls to identify potential size selectivity of midwater trawls. A pattern of size selectivity was apparent for both sampling techniques. The average length of kokanee sampled with midwater trawls was 111 mm; whereas, kokanee sampled with gill nets had a mean length of 235 mm. Our results suggest experimental gill nets are useful for common sampling of kokanee (e.g., trend monitoring) because the gear is less size selective than midwater trawls and is adjustable for size selectivity. However, midwater trawls are likely the best gear for addressing questions associated with early life history. Overall, our results provide a better understanding of gill‐net and midwater trawl selectivity and ultimately improve the ability to sample and manage the species.

Assessing Caribbean Shallow and Mesophotic Reef Fish Communities Using Baited-Remote Underwater Video (BRUV) and Diver-Operated Video (DOV) Survey Techniques.

Fish surveys form the backbone of reef monitoring and management initiatives throughout the tropics, and understanding patterns in biases between techniques is crucial if outputs are to address key objectives optimally. Often biases are not consistent across natural environmental gradients such as depth, leading to uncertainty in interpretation of results. Recently there has been much interest in mesophotic reefs (reefs from 30–150 m depth) as refuge habitats from fishing pressure, leading to many comparisons of reef fish communities over depth gradients. Here we compare fish communities using stereo-video footage recorded via baited remote underwater video (BRUV) and diver-operated video (DOV) systems on shallow and mesophotic reefs in the Mesoamerican Barrier Reef, Caribbean. We show inconsistent responses across families, species and trophic groups between methods across the depth gradient. Fish species and family richness were higher using BRUV at both depth ranges, suggesting that BRUV is more appropriate for recording all components of the fish community. Fish length distributions were not different between methods on shallow reefs, yet BRUV recorded more small fish on mesophotic reefs. However, DOV consistently recorded greater relative fish community biomass of herbivores, suggesting that studies focusing on herbivores should consider using DOV. Our results highlight the importance of considering what component of reef fish community researchers and managers are most interested in surveying when deciding which survey technique to use across natural gradients such as depth.

Development of Fishway Assessment Model based on the Fishway Structure, Hydrology and Biological Characteristics in Lotic Ecosystem

The main goal of this study is to develop a multi-metric fishway assessment model (M m-FA) and evaluate the efficiency of fishway. The M m-FA model has three major fishway components with nine metrics: structural characteristics, hydraulic/ hydrologic features, and biological attributes. The model was developed for diagnosing and assessing fishway efficiency and tested to Juksan Weir at the Yeongsan River Watershed. Structural characteristics of fishway included slope of the fishway (M 1), ratios of fishway width to stream width (M 2), and the proportion of orifice clogging and orifice size (M 3). Hydraulic/hydrologic characteristics included depth of fishway entrance head (M 4), depth of exit tail (M5), and current velocity of inner fishway (M 6). Biological characteristics included fish species ratio of inner fishway to upper-lower weir (M7), fish length distribution (M 8), and the proportion of migratory fish species to the total number of species (M 9). Overall, the assessment of fishway efficiency showed the total score of the M m-FA model was 25 in the Juksan Weir, indicating “good condition” by the criteria of the five-level classification system. The M m-FA model may be used as a key tool for the assessment of fishway efficiency, especially on the 16 weirs constructed for the “Four Rivers Restoration Project” after a partial calibration of Mm-FA model.

Migration, Size, and Age Structure of Brook Trout (Salvelinus fontinalis) from Two Lake Superior Tributaries

Abstract Brook trout (Salvelinus fontinalis) from Lake Superior and its tributaries exhibit a variety of life histories and different growth characteristics; however, life history-specific effects on population dynamics are not well understood. The goal of this study was to characterize the movement patterns of brook trout in two streams with access to Lake Superior and compare age and growth metrics between fish that moved into Lake Superior (coasters) and resident brook trout that remained within the streams (residents). There were no significant differences in length, condition factor, or relative weight between coasters and residents from a given stream. Less than 5% of PIT tagged fish were detected emigrating from the study streams, although there was a peak in migration during the fall. The length distribution of fish differed among years for both streams. The data demonstrate that migratory brook trout are likely present, though rare, in the study streams and multiple life histories are present in ...

A nonparametric model of empirical length distributions to inform stratification of fishing effort for integrated assessments

Length frequency data (LFD) are an important input to integrated stock assessments, and statistical tests for variables that significantly influence the length distribution of fish can assist in the definition of effort strata, typically denoted as fisheries or sub-fisheries, in order to account for important systematic differences due to availability and/or gear-specific selectivity of size classes. Here, a nonparametric model of the probability density function of lengths is described which, instead of fitting to LFD directly, is fitted to the set of length quantiles for a pre-determined set of corresponding probabilities p (in this instance 0.05, 0.1–0.9 in 0.1 increments, and 0.95). These length quantile data (LQD) can be constructed with individual hauls as sampling units or after pooling hauls to sampling units defined by combinations of covariates such as gear type, spatial block, depth strata, or the sex of sampled fish. The length quantiles are modelled as a Gaussian response variable using a Generalised Additive Mixed Model (GAMM) with smoothing splines fitted for each combination of the covariates (i.e. gear type, depth strata and sex). Graphical presentation of the fitted splines along with standard error of difference bounds were used to investigate where differences were significant in order to assist in the optimal definition of sub-fisheries. The model has the advantage of greater generality and sensitivity in detecting differences compared to modelling a single quantile such as the median. In addition, fitting splines allows flexible and parsimonious modelling of length distributions of any shape. The model is demonstrated using LQD from commercial fishing for Patagonian toothfish at Heard Island.

Bioacoustic absorption spectroscopy measurements at the shelf beak off Oregon

This paper describes the results of a Bioacoustic Absorption Spectroscopy (BAS) experiment, which was conducted at a biological hot spot at the shelf break off Oregon in August 2012. The location of the hot spot was identified by a NW Fisheries Science Center survey. This experiment included coincident measurements of transmission loss (TL), fish layer depths, fish length distributions, and continuous temperature profiles. The objective was to derive the bioacoustic parameters of hake (a physoclist), the dominant species in this region and other species from measurements of TL vs. range (0–10 km), frequency (0.3–5 kHz), depth (0–260 m), and time of day, and demonstrate consistency with trawl and echo sounder data. TL measurements were conducted between a moving, ship-deployed, broadband source and a 24 element, water column-spanning vertical array, which were provided by the Naval Research Laboratory. This was the first BAS experiment that targeted a physoclist. Previous BAS experiments targeted physostomes. The TL data exhibited absorption lines that were as high as 2 dB/km. Absorption lines at relatively high frequencies, which were observed on near-surface and mid-ocean hydrophones, are attributed to myctophids. Absorption lines, which were observed at relatively low frequencies on near-bottom hydrophones, are attributed to hake.

A Simple General Approach to Codend-Selectivity Estimation When the Mesh Opening of the Reference Codend is Not Sufficiently Small

The selection properties of gears are mainly determined by the selection properties of the codend, frequently described by the logistic function. This function reflects the retention probability of fish in the gear as a function of length caught from the length distribution of fish in that area. Certain conditions must be met for the measurements of the selection properties of trawls. According to the approach of Millar and Walsh (1992) the selection properties for the reference-trawl codend have to be chosen in a way that the frequencies of fish caught by the reference gear have a retention probability pr =1 for the length range within the test gear catches fish. We need small meshes in the reference codend. But small meshes in the reference trawl can reduce dramatically the flow rate in the codend (Thiele et al., 1997). This may change the fish behavior and may lead to measurement errors. A compromise must be found. In order to devastate not too much young fish, in practice the meshes of the reference-trawl codend are usually chosen as large as possible. Here, errors may occur, especially since the requirements for the selection properties of the reference-trawl codend depend on the results of the measurements which are obtained later. Applying the traditional approach but using too large meshes in reference-trawl codend can cause measurement errors. In the chosen example we get the largest measuring error for the selection-range factor SR with 36 % but for all other parameters lower errors. The new approach addresses this issue and avoids the occurrence of these errors.

Improving mesocosm data analysis through individual-based modelling of control population dynamics: a case study with mosquitofish (Gambusia holbrooki)

Experimental ecosystems such as mesocosms have been developed to improve the ecological relevance of ecotoxicity test. However, in mesocosm studies, the number of replicates is limited by practical and financial constraints. In addition, high levels of biological organization are characterized by a high variability of descriptive variables. This variability and the poor number of replicates have been recognized as a major drawback for detecting significant effects of chemicals in mesocosm studies. In this context, a tool able to predict precisely control mesocosms outputs, to which endpoints in mesocosms exposed to chemicals could be compared should constitute a substantial improvement. We evaluated here a solution which consists in stochastic modelling of the control fish populations to assess the probabilistic distributions of population endpoints. An individual-based approach was selected, because it generates realistic fish length distributions and accounts for both individual and environmental sources of variability. This strategy was applied to mosquitofish (Gambusia holbrooki) populations monitored in lentic mesocosms. We chose the number of founders as a so-called "stressor" because subsequent consequences at the population level could be expected. Using this strategy, we were able to detect more significant and biologically relevant perturbations than using classical methods. We conclude that designing an individual-based model is very promising for improving mesocosm data analysis. This methodology is currently being applied to ecotoxicological issues.

Changes in phytoplankton, benthic invertebrate and fish assemblages of boreal lakes following invasion by Gonyostomum semen

Summary 1. During recent decades, Gonyostomum semen populations have spread in northern temperate regions forming dense blooms that may dominate the phytoplankton assemblage for extended periods. In this study, we investigate the effects of G. semen blooms in boreal brown water lakes with special emphasis on phytoplankton, fish and benthic invertebrate assemblages using data from 10 boreal lakes sampled annually over a 10-year period. 2. Significant differences in phytoplankton and benthic invertebrate assemblages were found between lakes with high (3.01 mm3 L−1; >80% phytoplankton biomass) and lakes with low G. semen biomass (0.03 mm3 L−1; <5% phytoplankton biomass). In particular, high G. semen lakes had lower biomass of smaller, edible phytoplankton and a higher abundance and biomass of benthic invertebrates, especially Chaoborus flavicans, and perch than low G. semen lakes. 3. The length distribution of fish also suggested a tendency towards large and older fish and a lower recruitment success in high G. semen lakes, as denoted by lower abundances of fish shorter than 10 cm and higher biomass and abundance of fish longer than 15 cm in high G. semen lakes. 4. This study shows that high G. semen lakes are characterised by less edible phytoplankton, dominance by a few species and enhanced benthic secondary and fish production. Hence, the conjecture that high biomasses of G. semen create a bottleneck in the energy transfer to higher trophic levels seems less likely in boreal lakes.

IN SITU AND EX SITU TARGET STRENGTH MEASUREMENT OF MESOPELAGIC LANTERNFISH, DIAPHUS THETA (FAMILY MYCTOPHIDAE)

Acoustic target strengths (TS) of myctophid fish Diaphus theta were measured in situ at 70 kHz off the east coast of Hokkaido by tethering an acoustic-optical system (the Japanese Quantitative Echosounder and Stereo-video Camera System or J-QUESTχ) at a depth of 150 m from a research vessel. Fish length distributions were obtained from daytime hauls taken with a frame trawl after the TS measurement. Measured average TS (＜TS＞) and a standard length (SL) in cm gave the empirical length-average TS relationship,＜TS＞=20logSL-70.6, assuming that the linear TS is proportional to the square of the SL. A laboratory TS measurement and theoretical modeling of D. theta support the estimated length-average TS relationship.

음향카메라시스템을 이용한 낙동강어도의 어류모니터링

This study investigated a method for monitoring fishes immigrating to upper streams from the sea in relation to water level with elapsed time, and measured fish behavior patterns and swimming speed in a fishing boat gateway using an acoustic camera system. This method was employed due to difficulties, linked to high turbidity, of using only underwater optical systems for monitoring fish migrating to brackish water. Results showed that fish length distribution showed high correlation between haul sampling and an automatic counting algorithm supported by the DIDSON software program. These results will help to maximize the effects of fish run management by increasing understanding of the amount of major fish species migrating in relation to durable water levels.

Selection due to nonretention mortality in gillnet fisheries for salmon.

Fisheries often exert selective pressures through elevated mortality on a nonrandom component of exploited stocks. Selective removal of individuals will alter the composition of a given population, with potential consequences for its size structure, stability and evolution. Gillnets are known to harvest fish according to size. It is not known, however, whether delayed mortality due to disentanglement from gillnets exerts selective pressures that reinforce or counteract harvest selection. We examined gillnet disentanglement in exploited populations of sockeye salmon (Oncorhynchus nerka) in Bristol Bay, Alaska, to characterize the length distribution of fish that disentangle from gillnets and determine whether nonretention mortality reinforces harvest selection and exerts common pressures according to sex and age. We also evaluated discrete spawning populations to determine whether nonretention affects populations with different morphologies in distinct ways. In aggregate, nonretention mortality in fish that disentangle from gillnets counters harvest selection but with different effects by sex and age. At the level of individual spawning populations, nonretention mortality may exert stabilizing, disruptive, or directional selection depending on the size distribution of a given population. Our analyses suggest nonretention mortality exerts significant selective pressures and should be explicitly included in analyses of fishery-induced selection.

Quality and status of fish stocks in lakes: gillnetting, seining, trawling and hydroacoustics as sampling methods

All sampling methods give selective or biased estimates of fish species abundance, distribution and size structure. This creates problems, e.g. in regard to the Water Framework Directive of the European Union, which demands evaluation of the quality and status of fish stocks in lakes. We compared fish sampling by means of Nordic multimesh gillnets, seining, trawling and hydroacoustics in two Finnish lakes in summer 2007 and 2008. Sampling methods were used ‘as such’, i.e. no special design was implemented for method comparison. In the shallow eutrophicated lake the species’ composition of gillnet sampling and seining were very different. The biomass-% of percids dropped from gillnet (61%) to seining (9%) and that of cyprinids grew from 39 to 90%, respectively. In the deep pelagic area of the oligotrophic lake, vendace and smelt predominated in trawl catches. The number of fish caught by gillnetting in that area was too small to make any conclusions about the species composition. In the eutrophicated lake, the combined length distribution for all fish species differed significantly between gillnetting and seining. In the oligotrophic lake, the gillnet catches were too small for any comparison of fish size. The difference in the length distribution of fish between trawl and echosounding was significant in most analysed depth layers. In upper depth layers acoustics sampled larger fish than trawling, and in deeper layers smaller fish. Using a combined acoustic-trawl method, the pelagic fish biomass was estimated to be approx. 17 kg ha−1 in the deep and oligotrophic lake. We conclude that in large and deep-water areas, the use of active gear is enough in fish sampling to evaluate the quality and status of fish stocks. Gillnetting together with seining is an appropriate method to work out the quality and status of fish stocks in shallow and littoral areas of large lakes. Variation in the catch selectivity of fish sampling gear requires a discrete ecological classification for each type of gear.

MODELING FISH LENGTH DISTRIBUTION USING A MIXTURE TECHNIQUE

In fisheries science, length and age are important aspects of fish life history. Length is a function of growth, which provides an integrated measure of the environmental and endogenous conditions, e.g. genetics, affecting individuals and populations. Length at age data can be used to assess quality and quantity of habitat, food availability, or the need for and influence of management activities. Statistical mixture techniques may be used as a means to effectively model fish length distribution. A three-component mixture model, based on normal variates, was employed to describe length distribution in mountain whitefish species. The resulting model provided parameter estimates with meaningful biological interpretations, which were in turn used for inferential and comparative purposes. The technique will be demonstrated with reference to seven years of bio-monitoring data collected from the Kootenai River in Northern Idaho prior to and post nutrient addition treatment.