Oversight probability in presence–absence sampling for detection of fish eggs

ABSTRACT:   Presence–absence sampling (PAS) is a sampling technique that observes only the presence or absence of objects, such as eggs, in sampling units. The purpose of the present paper was to study the oversight probability in a PAS study for detecting fish eggs in connection with the spatial distribution of eggs. It was shown that the oversight probability of presence of eggs under no-eggs observation is a monotone decreasing function of the parameter of the degree of contagion.     

Performance comparison of traditional sampling designs and adaptive sampling designs for fishery-independent surveys: A simulation study

We compared the performance of two traditional sampling designs with three adaptive sampling designs using simulated data based on fishery-independent surveys for yellow perch in Lake Erie. Traditionally, the fishery-independent survey has been conducted with a stratified random sampling design based on basin and depth strata; however, adaptive sampling designs are thought to be more suitable for surveying heterogeneous populations. A simulation study was conducted to compare these designs by examining the accuracy and precision of the estimators. Initially in the simulation study, we used bias, variance of the mean, and mean squared error (MSE) of the estimators to compare simple random sampling (SRS), stratified random sampling (StRS), and adaptive two-phase sampling (ATS). ATS was the best design according to these measurements. We then compared ATS, adaptive cluster sampling (ACS), adaptive two-stage sequential sampling (ATSS), and the currently used stratified random sampling design. ATS performed better than the other two approaches and the current stratified random sampling design. We concluded that ATS is preferable for yellow perch fishery-independent surveys in Lake Erie. Simulation study is a preferred approach when we seek an appropriate sampling design or evaluate the current sampling design.     

Spawning habitat of the Atlantic menhaden in Onslow Bay, North Carolina

The Continuous, Underway Fish Egg Sampler (CUFES) was used to sample pelagic eggs of the Atlantic menhaden ( Brevoortia tyrannus ) from 3-m depth off North Carolina in winter 1993–94 and 1994–95. Simultaneous measurements were made of temperature, salinity, and the concentration of chlorophyll a . The maximal concentration of eggs was 346 eggs m⁻³. Eggs were highly aggregated in patches which occurred between the Gulf Stream and mid-shelf fronts (17–23°C, 36.0–36.4‰). Unexpectedly, eggs were found almost exclusively in water of 20–60 m (mode 20 m) bottom depth. Thus, spawning appears related to bathymetry as well as hydrography. Variograms for egg concentration indicated a mean (± SE) patch scale of 3.6 ± 1.7 km and a high degree of spatial variance explained by CUFES sampling. Lagrangian modelling of particles moving in response to tides, winds, and a prescribed flow from the north indicated that the region of observed, maximal occurrence of eggs is favourable for the retention of eggs and larvae on the shelf adjacent to inlets used to enter nursery areas.     

Optimizing sampling effort within a systematic design for estimating abundant escapement of sockeye salmon (Oncorhynchus nerka) in their natal river

The upstream migration of adult sockeye salmon (Oncorhynchus nerka) in the Horsefly River was monitored by a DIDSON imaging sonar during the dominant stock-cycle year 2005 using a systematic 20-min h⁻¹ sampling scheme. We used a subset of these data collected between 16 and 29 September to investigate whether this sampling protocol was justified based on temporal variation in the salmon migration data. During post-processing, the 20-min sequence was split into two 10-min periods and the number of migrating salmon was counted separately. Cross- and autocorrelation analysis showed that estimates from the first and second 10-min samples were similar (r = 0.65) and variation between them (i.e., within the hour) was random, supporting the conclusion that systematic-hourly sampling is a defensible sampling design for acoustic enumeration when temporal variation in fish migration is unknown a priori. Using a simple benefit–cost model (statistical reliability of point estimates of salmon escapement–sampling effort), we recommend a minimum sampling effort of 10-min h⁻¹ and a maximum effort of 20-min h⁻¹ for projects using a systematic sampling scheme in which the goal is to estimate total upstream salmon escapement. An alternative sampling approach targets high-passage events such as diurnal peaks or periods when total daily upstream escapement exceeds 25 000 fish d⁻¹, for increased sampling effort while reducing sampling effort during low-passage periods. This design will improve the statistical reliability of the resulting point estimates of upstream escapement relative to that achievable with a systematic effort with no overall change in total sampling effort over the course of the migration period.     

Jackknife method for estimating the variance of the age composition using two-phase sampling with an application to commercial catches of swordfish (Xiphias gladius)

An estimate of the age composition of a commercial swordfish catch and its variance was obtained using the replicate full jackknife estimator for two-phase sampling where the sampling units in the first phase are clusters (vessel-trips) and the units of the second phase are individual fishes. The jackknife variance estimator was compared with an analytical estimator of variance commonly used in fisheries studies which ignores the clustering, and assumes simple random sampling of individual fish. The application of these naïve estimators to the Chilean South Pacific swordfish fishery results in an underestimation of the variance. This is a consequence of using an inappropriate primary sampling unit of analysis in the first-phase sample where the vessel-trip unit is replaced by an individual fish unit, thus ignoring the intra-cluster correlation in age samples. The jackknife estimator of variance is an alternative useful for complex two-phase sampling designs.     

Lipid characterization of both wild and cultured eggs of cuttlefish (Sepia officinalis L.) throughout the embryonic development

The present work reports a characterization of mean wet weight and moisture, the lipid class and fatty acid (FA) composition from the total lipids (TL), of both culture and wild eggs of the cuttlefish, Sepia officinalis , throughout the embryonic development. Additionally, reproductive data, such as the number of spawnings, number and mean weight of eggs and duration of spawning period of cultured cuttlefish is provided. Both types of eggs were similar in mean wet weight, moisture content, TL content and lipid composition throughout embryonic development. Females from the cultured group spawned 13 times and laid 8654 eggs in 64 days, with a mean weight of 0.607 ± 0.179 g. A sex ratio of 1.57 (11♀ for 7♂) promoted an individual fecundity of 787 eggs/♀ (the biggest until now on our culture facilities), which might be related to increased bottom areas. The TL increased with day/stage of embryonic development ( P  < 0.05) only in the cultured egg group. However, no differences were found on TL between culture and wild eggs at the same day/stage ( P  > 0.05). Eggs displayed predominant levels of phosphatidylcholine, phosphatidylethanolamine (PE), cholesterol and triacylglycerol at the end of embryonic development. Polar and neutral lipids of both eggs groups remained consistently proportional (∼50% for each lipid fraction) and a significant increase ( P  < 0.05) was observed in phosphatidylserine, PE and free FA throughout the embryonic development. In either egg type and day, 16:0, 18:0, 20:5n-3 and 22:6n-3 accounted for approximately 70 g Kg⁻¹ of all FA and saturated and n-3 totals seemed to have the same proportion in the cuttlefish eggs. The present results suggest that lipids are not used as energetic substrate but as structural components in cuttlefish egg.     

Reproductive biology of whitespotted bamboo shark Chiloscyllium plagiosum in northern waters off Taiwan

ABSTRACT:   In total, 491 whitespotted bamboo sharks were collected from northern Taiwanese waters from February 2002 to February 2003. The sex ratio of the specimens was 0.65, total length (TL) ranged from 35.3–85 cm, and weight ranged 124–2580 g. The mean size at first maturity was estimated to be 64.9 and 65.6 cm TL for females and males, respectively, based on the relationship between mature percentage and TL. The ovulation season was estimated as March to May based on gonadosomatic index (GSI) variations and captive observation. The monthly changes in GSI of males suggested that the mating season was from December to January. The inconsistency between mating and ovulation seasons suggested that females have sperm storage and delayed fertilization. One or two eggs were deposited every 6 or 7 days on average. Deposition of eggs extended for 2 months, and fecundity was 8 ± 3.8 eggs. Thirteen of 48 eggs deposited in 2003 were hatched and the hatching rate was 0.27. The hatching period was 107 ± 9.3 days with accumulated water temperature ranging from 2372–2835°C.     

Preventive efficacy of sodium hypochlorite against water mold infection on eggs of chum salmon Oncorhynchus keta

ABSTRACT:   To protect chum salmon eggs from water mold infection during incubation, the eggs were treated daily with sodium hypochlorite solution (NaOCl) at 10 mg/L residual chlorine concentration for 15 min during their developmental period from fertilization to eyed stages. The number of infected eggs and number of eyed eggs were observed on day 23 of incubation. The percentage of infected eggs to total eggs was significantly lower with NaOCl treatment (1.8 : 33.4%) than in the control (11.3 : 59.3%, P  < 0.01). The percentage of eyed eggs to total eggs was significantly higher with NaOCl (85.9 : 98.6%) than in the control (66.1 : 97.5%, P  < 0.01). The antifungal activity of NaOCl resulted in improving egg survival. Accordingly, NaOCl is a useful antifungal agent against water mold infection on chum salmon eggs.     

An automatic counting system for transparent pelagic fish eggs based on computer vision

Alive eggs of marine species with pelagic eggs float, while dead eggs usually sink. A non-invasive method for counting the number of floating eggs therefore gives the possibility to track survival throughout experiments. In this paper we present an automatic image analysis method for counting live pelagic eggs of marine fish. Pelagic fish eggs are typically transparent and difficult to detect in images. Current image analysis methods for counting pelagic fish eggs are therefore done on eggs transfixed in a polymer to create contrast between the eggs and the background. This kills the eggs. The main advantage of the presented method is that it is non-invasive and only requires a minimum of handling of the eggs. As case studies we collected images of Atlantic haddock (Melanogrammus aeglefinus) and Atlantic cod (Gadus morhua) eggs. The eggs in the images were manually counted for verification of the methodology. The average counting error of false positives was 6% and the average counting error of false negatives was 2%. This demonstrates that the method is objective and accurate.     

Stocking effectiveness of hatchery-released kuruma prawns estimated by two-stage sampling of commercial catch in Ariake Sound, Japan

ABSTRACT:    To evaluate the stocking effectiveness of the kuruma prawn Penaeus japonicus , a two-stage sampling survey of Gensiki bottom-drift-netters was carried out in Ariake Sound, Saga Prefecture, Japan. A total of 471 000 hatchery-produced juveniles, marked by cutting off the right uropods, was released. Thirty-three fishing days were randomly drawn from four boats, which were selected from the 80 boats operating in the fishery. All prawns caught on the selected days were examined, and the hatchery-produced individuals were identified by their regenerated uropods. A telephone survey of all boats was also conducted, to determine the number of fishing days. A total of 286 marked prawns were caught on the survey days for the Saga area in Ariake Sound, from the last half of July to the first half of September 2002. The recapture rate and standard error were estimated at 0.76 ± 0.52%. Economic efficiency was estimated at 0.28 ± 0.02. Strategies for sampling schemes and stock recovery are also discussed.     

Foraging specialisms, prey size and life-history patterns: a test of predictions using sympatric polymorphic Arctic charr (Salvelinus alpinus)

Abstract –  We use arguments based on optimal foraging theory to predict body size constraints and the consequences of these on a range of life-history traits in three trophic specialist morphs of Arctic charr, Salvelinus alpinus , living in sympatry in Loch Rannoch, Scotland. As predicted, foraging specialists feeding on small prey items with a narrow size range showed evidence of deterministic growth; the ultimate body size of macrobenthos feeders being larger ( L _∞ = 238 mm) than that of planktivores ( L _∞ = 216 mm). In contrast, the piscivorous morph showed no evidence of reaching a maximal body size.
The two size-constrained morphs (benthivores and planktivores) matured earlier and died younger (living for up to 11 and 7 years, respectively, in this study) than did the piscivorous charr which showed continuous growth up to at least 17 years.
The pattern of annual reproductive investment in maturing individuals was complex. Planktivores invested in larger eggs than the other two forms, but benthivores produced a greater number of eggs than planktivores, which in turn produced more than piscivores. Planktivorous males had a greater investment in mean testis weight than the other two forms.
Lifetime reproductive output was the greatest in the benthivorous charr, intermediate in planktivorous and the lowest in the piscivorous charr when measured either as fecundity or as gonadal weight. We conclude that constraints imposed upon foraging specialists by foraging efficiency is a significant driver of body size and ultimately reproductive investment in gape-limited foraging salmonids.     

Shrimp egg counting with fully convolutional regression network and generative adversarial network

Accurate egg counting is the basic demand in the hatcheries of the aquaculture. However, the time-consuming, fallible manual counting is now still adopted in most situations. Also, many traditional automatic egg counting methods cannot provide enough high efficiency and accuracy, especially in densely-distributed cases. In this paper, we propose a novel convolutional neural network (CNN) based method for shrimp egg counting. Compared to traditional methods mainly based on contour detection or image segmentation, the proposed method exploits the density map regression and is more efficient in densely-distributed case even with severe occlusion. Firstly, a new dataset of the redclaw crayfish Cherax quadricarinatus eggs is collected, which includes 450 images with about 272,000 eggs annotated accurately. Also, a synthetic dataset generation method based on generative adversarial network (GAN) is proposed to avoid the onerous manual labeling, and has potential applications in the supervised learning for the densely-distributed eggs or larvae counting. Then, considering the advantages of no manual preprocessing and fine-grained feature extraction in CNNs, a shrimp egg counting network (SECNet) based on fully convolutional regression network (FCRN) is proposed to realize the counting through regressing the input image into its density map. The test results show the average counting accuracy of the proposed SECNet can be up to 99.2 % when the SECNet is pre-trained on the synthetic dataset and finetuned on the collected dataset. Finally, a simple and cheap computer vision based counting setup is built by using three off-the-shelf devices and a convenient operation program integrated with the SECNet is developed for a person computer, which provides an accurate, real-time, and highly-efficient egg counting way.     

Effects of sampling errors on abundance estimates from virtual population analysis for walleye pollock in northern waters of Sea of Japan

ABSTRACT:   Effects of sampling errors on abundance estimates from virtual population analysis (VPA) were quantified with the bootstrap method for stock of walleye pollock in the the Sea of Japan. In the bootstrap method, individual fish measurements were resampled. A total of 1000 bootstrap samples were produced for each year from 1991 to 2001. The coefficients of variation (CV) of catch at age in 2001 ranged 6.1–33.1%. The CV of an abundance estimate in 2001 ranged 9.0–35.7%. Abundance estimates of the oldest age and the latest year, which had larger CVs than the other estimates, were sensitive to sampling errors. Effects of sampling errors became smaller when the catch at age had been accumulated over a few years. Although VPA includes various types of errors, only the sampling errors have room for improvement in reality. Quantifying the effect of sampling error on VPA estimates is essential for sound and efficient stock management, and is emphasized in this study.     

Assessing the abundance and distribution of eggs of sardine, Sardinops sagax, and round herring, Etrumeus whiteheadi, on the western Agulhas Bank, South Africa, using a continuous, underway fish egg sampler

A continuous, underway fish egg sampler (CUFES) was employed to assess the abundance and distribution of eggs of both sardine, Sardinops sagax , and round herring, Etrumeus whiteheadi , on the Western Agulhas Bank, South Africa, during September 1996. Samples were collected while underway along six inshore/offshore transects, and at stations along the transects. Volumetric estimates of egg density (eggs m⁻³) from on-station CUFES samples were highly correlated with both volumetric and areal (eggs m⁻²) estimates of egg density from samples collected from CalVET net hauls at these stations, demonstrating the validity of this novel sampling technique. Sardine and round herring eggs were encountered in a band running parallel to the coast and extending from 10 to 30 nautical miles offshore to the shelf edge, and highest egg densities were associated with strong north-west-flowing currents in the region of the shelf edge. Collecting samples while underway increased the precision of the estimate of mean egg density for sardine eggs but not for round herring eggs. The use of CUFES in obtaining a fine-scale resolution of sardine egg distribution, and as a tool for stock assessment, are discussed.     

Effect of salinity on reproductive performance of Acanthopagrus latus (Houttuyn) in spawning tanks

More than 250 male and female yellowfin seabream (Acanthopagrus latus) were caught in the creeks near the Mahshar area in the north‐west of Persian Gulf using fishhooks to study the effects of salinity on reproductive indices. The experiments were carried out using three salinity treatments (30 ± 1 g L^?1, 35 ± 1 g L^?1 and 40 ± 1 g L^?1) with three replications. A total of six males and three females were randomly introduced to each tank. The survival rate of the broodstock was estimated at more than 90% at different salinity levels and the maximum rate was observed at 30 g L^?1 of the experiment rate. The percentage of buoyant eggs was more than 90% at 40 g L^?1 and it was significantly different from other treatments. The average number of eggs per female (312 914 ± 65 085), and the average number of eggs per kilogram of female (649 460 ± 173 574) at 40 g L^?1 were more than those in the other treatments but no significant differences were observed (P ≤ 0.05). The average percentage of fertilized eggs (86.7%) and the average percentage of hatched larvae (67%) at 40 g L^?1 treatment was more than those at 30 g L^?1 and 35 g L^?1 treatments but no significant differences were observed (P ≤ 0.05). At 40 g L^?1 salinity, in all spawning cases, the released eggs were hatched. Overall, the present study has shown that better buoyant eggs of A. latus can be obtained at salinity 40 g L^?1. On the other hand, the percentage of fertilized eggs and hatched larvae were not affected by salinity.     

Multiple GnRHa injections to induce successful spawning of wild caught greater amberjack (Seriola dumerili) matured in captivity

Reliable reproduction and sufficient amounts of juveniles obtained in captivity constitute a main bottleneck for mass production of greater amberjack. The aim of the present study was to combine several aspects of broodstock management and hormonal induction, to obtain a large number of high quality spawns. Captured Seriola dumerili sub‐adults were kept for three years in 10 m³ tanks. When fish were larger than 75 cm, they were individually tagged, periodically explored to determine gonad maturation and injected with gonadotropin releasing hormone analogue from June to October. A total of 15 inductions to four males and two females produced 330 821 ± 219 519 eggs/induction and a total of 22 spawns. The number of spawns and female fecundity (2.48 millions eggs/female/spawning season) were similar to those of free wild populations and higher than those previously obtained in captivity for this species. Egg quality increased from an initial low in the first two spawns in June to give, during July to October, a mean of 96.01 ± 6.50% fertilized eggs, 92.58 ± 17.56% hatched eggs, 78.66 ± 12.60% larval survival at day 3 after. These results showed that intramuscular injections of 20 μg kg^?1 body weight GnRHa under natural temperature and photoperiod conditions in the Canary Islands produced a high induction efficiency.     

Morphological development of eggs, larvae and juveniles of laboratory-reared Ryukyu-ayu Plecoglossus altivelis ryukyuensis

ABSTRACT:   The development of embryos, larvae and juveniles of the Ryukyu-ayu, Plecoglossus altivelisryukyuensis are described based on laboratory-reared specimens.The eggs were spherical, 0.98–1.18 mm (mean 1.06 mm)in diameter with an adherent membrane. The incubation period after fertilizationwas approximately 155 h at a water temperature of 19.7–22.0°C(mean 20.7°C). Newly hatched larvae were 5.0–5.9 mm(mean 5.5 mm) in body length (BL) with 59–62 myotomes.Within 5 days after hatching, the larvae had attained 6.4–8.2 mm(mean 7.8 mm) BL and had completely consumed their yolk.Notochord flexion began at 13.7 mm BL and was completedby 16.3 mm BL. The rudimental dorsal, anal, pelvic andadipose fins appeared at 14.7, 16.3, 21.8 and 21.8 mm BL, respectively.All fin rays reached the same fixed number of adult fish at about28 mm BL. The comb-like teeth began to form at approximately30 mm BL and were fully developed at about 40–50 mm BL.The proportions of P. a. ryukyuensis specimens,which were consistent with adult fish, occurred at approximately40 mm BL.     

分层抽样误差分析及其在渔业统计中的应用

分层抽样是统计工作中最常采用的抽样方法之一.以全国海洋捕捞动态信息采集网络中南海区三省2009年10月采集的渔业信息为实际案例,分析研究了分层随机抽样和简单随机抽样方法的渔获量统计结果精度.结果表明:分层抽样方法的渔获量评估均值的方差明显小于简单随机抽样方法,后者的方差是前者的28.17倍;合理的分层和样本量分配,既可...     

Efficacy of formalin,iodine and sodium chloride in improvement of egg hatching rate and fry survival prior to the onset of exogenous feeding in yellow perch

Egg disinfection is considered the most important routine work in hatcheries to avoid fungal and/or bacterial infection of fish eggs. The aim of this study was to determine the effectiveness of three disinfectants: formalin, iodine and sodium chloride on the hatching success of yellow perch eggs. The disinfectants were tested in triplicate at different concentrations for 15 and 30 min bath treatments. Two experiments were conducted; formalin at five concentrations (25, 50, 100, 150 and 200 mg L^?1) and 25 mg L^?1 iodine were tested in the first experiment. The second experiment involved formalin at three concentrations (250, 500 and 1000 mg L^?1), iodine at three concentrations (50, 100 and 250 mg L^?1) and sodium chloride at three concentrations (500, 1000 and 3000 mg L^?1) were used. Iodine and sodium chloride‐treated eggs hatched earlier than formalin‐treated eggs. The highest mean percentage of eyed stage, hatching rate and survival to first feeding fry was observed at 200 mg L^?1 formalin for 30 min, 50 mg L^?1 iodine for 15 min and 500 mg L^?1 sodium chloride for 30 min. High concentrations of formalin (1000 mg L^?1), iodine (250 mg L^?1) and sodium chloride (1000 and 3000 mg L^?1) showed toxicity to yellow perch eggs, resulting in low hatching rate and survival to first feeding fry. We recommended formalin at a concentration of 150–200 mg L^?1 for 30 min as an effective, easily available and low‐cost disinfectant for routine use to improve yellow perch hatchability.     

Reproductive biology of bluefish (Pomatomus saltatrix) along the East Coast of the United States

The reproductive biology of bluefish (Pomatomus saltatrix) along the U.S. East Coast is examined from a collection 1437 females sampled from nearshore to the continental slope and from Florida to New York over a period of 3 years (2001–2003). In most years concurrent sampling along the coast was conducted over spring and summer months to resolve the initiation of spawning. We examined the spawning location, pattern and timing, and calculated the fecundity of fish from 600 to 840 mm in length. Based on macro- and microscopic analysis of female gonads, bluefish are multiple spawners with indeterminate fecundity. The presence of all stages of development in fully mature ovaries further indicates that bluefish have asynchronous oocyte development. Mean age at first maturity for female bluefish was 1.90 years and 480 mm total length. Mean batch fecundity was 402,247 eggs and ranged from 114,513 to 920,746 eggs, depending on age and weight. Direct observation of gonads showed imminent spawning in Florida and North Carolina during March to April, and from April to August from Virginia to New York. Given the progression of oocyte development over the range of space and time we sampled, we suggest that bluefish exhibit continuous spawning during their migration from the South Atlantic Bight (SAB) to Middle Atlantic Bight (MAB).