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Anthropic exploitation of soil, forests, and water bodies contributes to the modification of river flow regimes and sediment transport dynamics, thus affecting fish habitats and water quality. In the last decades, the increasing awareness of the consequences of such modifications on natural contexts has stimulated researchers and practitioners to provide more innovative solutions aiming at enhancing river biodiversity. Recently developed eco-friendly approaches for river restoration evidenced the necessity of more careful planning and management of natural resources, including the maintenance and enhancement of fish species' habitats. The present study aims at assessing the interaction of different types of wood- and rock-made instream structures with river flow regimes and habitat requirements of many freshwater fish species, accounting for the influence of downstream scour potholes to facilitate fish species migration and spawning. Experimental tests showed that instream structures cause deep scour holes characterized by low flow velocity zones, thus decreasing the required fish swimming power and potentially providing suitable conditions for the migration of freshwater fish species. Using dimensional analysis, empirical relationships were derived to optimize the longitudinal distance between subsequent instream structures, accounting for the effects of various structure geometries and fish biological characteristics. Nevertheless, further investigation is needed to validate the proposed relationships at prototype scale. This study ultimately contributes at providing tools to design river instream structures favorable to fish migration. • The effects of different types of instream structures on fish swimming hydrodynamics have been investigated. • The analysis was conducted at model scale under identical fish Froude numbers F f. • Results showed that instream structures facilitate the migration of freshwater fish species. • Fish white muscles weight increases with the fish weight resulting in an increase of the available fish power. [ABSTRACT FROM AUTHOR]

Many commercially important groupers (Epinephelidae) form fish spawning aggregations (FSA) at specific sites where the spawning stock is concentrated to spawn within a couple of months each year. The concentrated nature and short duration of these FSAs render these species susceptible to fishing pressure leading to their disappearance or decrease in the number of spawning fish. As a result of directed fishing during FSAs many large-bodied groupers are now International Union for Conservation of Nature (IUCN) Red-listed. Puerto Rico within the US Caribbean is where protective measures have been designated for the recovery of grouper species that aggregate to spawn, in particular the threatened (Endangered Species Act) Nassau grouper (Epinephelus striatus) and sustainability of the red hind (Epinephelus guttatus). The regulations at three marine managed areas (MMAs) off the west coast of Puerto Rico, have been focused on reproductive seasons, through seasonal closures. However, these management zone boundaries may fail to fully encompass fish migration paths and temporal variability in FSAs, exposing threatened species like the Nassau grouper to incidental fishing and poaching. In addition to traditional methods used to study FSAs, passive acoustics represent a relatively new approach to assess the presence and spatio-temporal distribution of aggregating species. Sound production is common among many fishes, including the Nassau and red hind groupers, and is most often associated with courtship and spawning behavior. In this study, we present the results from the deployment of an autonomous surface vehicle equipped with a passive acoustic monitoring system along the insular shelf break that surveyed the MMAs during their peak spawning season. Our observations suggest that known FSA sites are critical habitat for both species and the existence of potential, previously unknown FSAs for multiple grouper species as well, highlighting the importance of spatial and temporal expansion of existing regulations. [ABSTRACT FROM AUTHOR]

A marine reserve’s effectiveness for sustaining transient spawning reef fish populations is dependent on inclusion of fish spawning aggregations and consideration of the natural spatial boundaries of the populations themselves. Seasonal migrations of Mutton Snapper Lutjanus analis between protected nearshore areas and spawning grounds on Riley’s Hump in Dry Tortugas, Florida, were assessed from 2008 to 2012 by acoustic telemetry. Individual fish showed synchronized reproductive migrations (up to 5 trips fish −1  yr −1 ) from resident habitats to spawning grounds swimming at an estimated 63 ± 18 cm s −1 (mean ± SD) over minimum linear distances up to 35.2 km. Migrations occurred from April to August, corresponding with the lunar cycle and an increase in water temperature from 25 to 30 °C. Fish arrived on spawning grounds on the full moon and stayed for 7 ± 2 d (mean ± SD). Observations of multiple spawning events made one to five days after the full moon in the late afternoon confirm these movements as spawning migrations. Functional migration areas (109.59 ± 61.01 km 2 ; mean ± SD), which included estimates of staging/courtship/spawning area (4.51 ± 1.84 km 2 [mean ± SD]) and home site area (2.50 ± 1.31 km 2 [mean ± SD]), were combined to estimate the minimum catchment area of the population studied (291.3 km 2 ). Although this study focuses on movements and habitat use of a single fish species in the Tortugas, the results are relevant to the design of marine reserve networks intended to protect and manage fishes that undergo transient spawning migrations in other locations as well. [ABSTRACT FROM AUTHOR]

Climate oscillations exert direct control over the environment in which they occur and may influence the physical condition of migratory marine species, such as tuna, as reported by several authors. The main aim of this study was to explore the association between the potential effects of the North Atlantic Oscillation (NAO) on the fitness condition of bullet tuna ( Auxis rochei ) migrating to the Spanish Mediterranean Sea. A total of 2357 length-weight pairs of data obtained from individuals collected on the Spanish Mediterranean coast were analysed. A non-parametric Spearman test was used to investigate correlations between the atmospheric oscillation indexes and two physical condition indexes. The results suggest that, in general, positive phases of the NAO index improve the physical condition of fish migrating to spawning grounds in the Mediterranean Sea. These results could be explained by changes in the dominant winds, which could favour pre-spawning migration, and by nutrients availability, which guarantees their recovery after the spawning period. [ABSTRACT FROM AUTHOR]

The conservation and management of heavily exploited fish stocks require reliable data on various aspects of reproduction. In particular, information about spawning migration and spawning period of both sexes is essential for protecting important spawning habitats. However, studies that focus on male spawning ecology are very limited. We elucidated the male spawning migration, core duration of reproduction, and seasonal changes in the maturity of the barfin flounder Verasper moseri , an important target flatfish for stock enhancement programs in Japan. We conducted histological observations of the testes and utilized the sperm duct volume index to facilitate accurate determination of the male spawning period. Fish before spermiation were mainly observed off Hokkaido and partially off northern Tohoku (40.2–43.4°N) during August–December. However, fish undergoing spermiation and sperm release were not found near these areas and were observed only off southernmost Tohoku (35.8–37.5°N approximately 300 m deep) from late January to April. Very few spent fish were caught off southern Tohoku, but were frequently observed off Hokkaido during May–June. These results demonstrate that male V. moseri repeat widespread spawning migrations over 700 km between feeding grounds off Hokkaido and spawning grounds off southern Tohoku. Moreover, a combined analysis related to seasonal variations in the sperm duct volume and the proportion of spawning adults identified that the core duration of male reproduction was during March. Until now, reproduction of the next generation in the wild has not been confirmed, despite the continual release of seedlings and local fishery restrictions around Hokkaido. Our results underscore the necessity of a more widespread fishery management plan for V. moseri that encompasses the waters off Hokkaido and Tohoku to more effectively enhance reproduction. [ABSTRACT FROM AUTHOR]

From late April until mid-June Atlantic bluefin tuna, Thunnus thynnus (Linnaeus, 1758), migrates along the western coast of Sardinia to reach spawning grounds of the Mediterranean. Despite the substantial information on the reproductive biology of the species, the tracking of its reproductive parameters along the migratory pathways is far to be completed. This study provides some reproductive parameters for adult bluefin tuna collected from the last trap fishery Tonnara of the Mediterranean. The following points summarize our results: (i) gonadosomatic index (GI) was positively correlated with fork length (FL) and varied significantly between sexes, having higher values in males; (ii) ovaries contained a mixture of oocyte stages with primary growth oocytes representing 72%, cortical alveoli 16%, primary and secondary vitellogenic stages 4.6% and 6% respectively, only a small proportion of late vitellogenic oocytes and atretic follicles; (iii) batch fecundity was 95–125 oocytes per gram of body mass and varied from 1.6 million for a female of 105 cm FL, to 29.5 million eggs for a 233 cm FL specimen; (iv) sex ratio differed significantly from 1:1, with males being predominant both for the size classes and years analyzed. These findings suggest that bluefin tuna from western Sardinia exhibits intermediate reproductive characteristics between specimens migrating through the Strait of Gibraltar and those from the spawning grounds of the Balearic Islands. [ABSTRACT FROM AUTHOR]

Argentine shortfin squid Illex argentinus (Ommastrephidae) is one of the most abundant cephalopods in the Southwest Atlantic, with total annual catch exceeding 1 mln t in some years. During its annual life cycle, I. argentinus perform long distance migrations, from their subtropical spawning grounds in Uruguay and southern Brazil to temperate feeding grounds on the Patagonian Shelf and back. Oceanography and squid distribution were studied during a research survey carried out in the south-eastern part of the Patagonian Shelf to reveal environmental cues that determine pathways of shelf to continental slope pre-spawning migrations. It was found that the outflows of less dense Patagonian Shelf Waters (PSW) over the slope may act as proxies determining the locations of I. argentinus migrations from the shelf to the slope. During maturation I. argentinus did not significantly change their buoyancy with females becoming slightly more buoyant with depth. Subsequent movement of mature I. argentinus to denser Sub-Antarctic Superficial waters (SASW) located at deeper depths (600–700 m) enable them to approach near-neutral buoyancy and therefore facilitate the distant pre-spawning migrations. [ABSTRACT FROM AUTHOR]

Body condition and reproduction data are broadly used to assess the health status of fish because of its implications for recruitment and ecosystem structure. Sardina pilchardus is a small pelagic distributed throughout both Mediterranean and Eastern Atlantic. Seasonal trend analysis of energy storage and reproduction was carried out in sardines from two areas along the Atlantic-Mediterranean transition: Southern Portugal-Gulf of Cádiz (POR-GC) (Atlantic Ocean) and Alboran Sea (Alb) (Mediterranean Sea) from 2019 to 2021. Energetic condition was estimated using tissue and mesenteric fat content, hepatosomatic index (HSI), and the relative condition factor (Kn). Sex, reproductive developmental stage, and gonadosomatic index (GSI) were also obtained. In addition, the oceanographic and meteorological characteristics of the areas were analysed. Results showed that seasonal Kn, tissue and mesenteric fat content, and HSI values of POR-GC specimens exceeded Alb's with summer arrival, period in which sardine acquires reserves to allocate them to reproduction. These differences could be associated to greater productivity of the former area mainly due to rivers discharges and trade winds intensification during summer (from July to September). Furthermore, gonad maturation of POR-GC stock occurred before the Alb. However, no spawning capable individuals were identified until February in POR-GC. In contrast, in Alb it was observed a remarkable fraction of spawning capable and active spawner individuals in October. We hypothesized the migration of mature individuals from POR-GC to the spawning areas located in the Alb. Seasonal genetic population studies are required to untangle it and reliably evaluate the environmental effect on the stocks. • Atlantic sardines show better somatic condition than Alboran individuals at storage period. • Productivity in the Atlantic area is greater than in the Alboran Sea. • Rivers discharges and summer's trade winds intensification could be its main cause. • Results suggest the migration of mature fish from the Atlantic towards the Alboran. • Seasonal genetic population studies are required. [ABSTRACT FROM AUTHOR]

Temporal movement patterns and spawning behaviour of the dusky grouper Epinephelus marginatus were investigated using depth and temperature sensors combined to acoustic telemetry. Results showed that these fish are year-round resident, remaining inside the fully protected area of the marine reserve of Cerbère-Banyuls (65 ha) and display a diurnal activity pattern. Records from depth sensors revealed that groupers range inside small, distinct, and individual territories. Individual variations in habitat depth are only visible on a seasonal scale, i.e., between the spawning season and the rest of the year. In fact, during summer months when the seawater temperature exceeded 20 °C, tagged groupers made vertical spawning migrations of 4–8 m in amplitude. These vertical migrations are characteristic of the reproductive behaviour of dusky groupers, during which they release their gametes. The results are notable for the implementation of management rules in marine protected areas, such as reduced navigation speed, boating or attendance during spawning season. [ABSTRACT FROM AUTHOR]

Abstract: European eel (Anguilla anguilla) larvae achieve one of the longest larval migrations of the marine realm, i.e., more than 6000km from their spawning grounds in the Sargasso Sea to European continental shelves. The duration of this migration remains debated, between 7 months and 3 years. This information is, however, crucial since it determines the period over which larvae are affected by environmental conditions and hence the subsequent recruitment success. We investigate the pathways and duration of trans-Atlantic connections using 3 years of high-resolution (daily, 1/12°) velocity fields available from a Mercator-Océan model configuration without data assimilation. We study specifically the effect of spatial and temporal resolutions on our estimates by applying various filters in time (from daily to 12-day averages) and space (from 1/12° to 1° gridcell aggregation) to the nominal model outputs. Numerical particles are released in the presumed European eel spawning area and considered as passive tracers at three specific depths (around 0, 50, and 200m). We diagnose particularly the intensity of the water transfer between suitable control sections that encompass the eel larva distribution. Transit ages are also investigated, with a particular focus on the pathways that minimize the connection times between the western and eastern North Atlantic. We show that small-scale structures (eddies and filaments) contribute to faster connections though they also correspond to additional complexity in trajectories. The shortest pathways mostly follow the Gulf Stream and the North Atlantic Drift, whereas interior connections require longer transfers that prove less compatible with biological observations. [Copyright &y& Elsevier]

Abstract: Salmon utilize olfactory cues to guide natal stream homing during spawning migrations. Both inorganic and biogenic chemicals have been proposed as odorants that might be used by salmon during homing. In this study, we used genomic DNA sequence data from nine salmonid species to compare nucleotide identities for orthologous main olfactory receptor (mOR) genes with nucleotide identities for orthologous vomeronasal type 1-like (ora) receptor genes. We found that orthologs for both classes of olfactory receptor genes (mORs and Oras) appear to be highly conserved among species. Our findings do not support the differential tuning hypothesis in Salmonidae, which predicts higher sequence conservation for mORs than ora. We did, however, find convincing evidence for site-specific positive selection acting on paralogous main olfactory receptor genes. [Copyright &y& Elsevier]

Abstract: Climate change accentuates the need for knowing how temperature impacts the life history and productivity of economically and ecologically important species of fish. We examine the influence of temperature on the timing of the spawning and migrations of North Sea Mackerel using data from larvae CPR surveys, egg surveys and commercial landings from Danish coastal fisheries in the North Sea, Skagerrak, Kattegat and inner Danish waters. The three independent sources of data all show that there is a significant relationship between the timing of spawning and sea surface temperature. Large mackerel are shown to arrive at the feeding areas before and leave later than small mackerel and the sequential appearance of mackerel in each of the feeding areas studied supports the anecdotal evidence for an eastward post-spawning migration. Occasional commercial catches taken in winter in the Sound N, Kattegat and Skagerrak together with catches in the first quarter IBTS survey furthermore indicate some overwintering here. Significant relationships between temperature and North Sea mackerel spawning and migration have not been documented before. The results have implications for mackerel resource management and monitoring. An increase in temperature is likely to affect the timing and magnitude of the growth, recruitment and migration of North Sea mackerel with subsequent impacts on its sustainable exploitation. [Copyright &y& Elsevier]

Abstract: Parasites were inventoried on and in 470 Atlantic cod (Gadus morhua) collected from the southern Gulf of St. Lawrence, NAFO (North Atlantic Fisheries Organization) division 4T, and Cape Breton Shelf (NAFO subdivision 4Vn) in September of 2004 and 2005, and August 2006, respectively. Forward stepwise discriminant function analysis (DFA) of the 4T samples indicated that the nematodes, Hysterothylacium aduncum, and Pseudoterranova decipiens and the acanthocephalans Echinorhynchus gadi and Corynosoma strumosum were significant in the classification of cod to eastern or western 4T. Cross-validation yielded a classification efficiency of 74% overall, thereby supporting the findings of earlier mark-recapture studies which have indicated that 4T cod are comprised of discrete eastern and western spawning groups. Further analyses indicated that western 4T cod was distinct not only from eastern 4T cod, but also differed from cod from the Smokey Channel and Cape Breton Shelf slopewaters (4Vn), with rates of misclassification ranging from 6% to 9%. Hence, “parasite tags” may prove useful for monitoring the exploitation of cod from western 4T during their annual migration through the Cabot Strait and while over-wintering along the edge of the Cape Breton Shelf where mixing with eastern 4T and 4Vn cod may occur. Similar results could be achieved with migrant cod from eastern 4T through analyses of parasite markers together with host meristic or morphometric parameters. [ABSTRACT FROM AUTHOR]

Abstract: In the present study we utilize tag recapture data to estimate year class abundance and spawning stock biomass of mackerel (Scomber scombrus L.) in the Northeast Atlantic for the period 1986–2008. On average 20,000 jigged mackerel have been tagged annually with internal steel tags in the spawning area west of Ireland and the British Isles, and the tags have been recaptured in commercial catches screened through metal detectors. The spawning stock biomass estimates derived from two different tag-based models were highly variable but were on average 2 and 2.3 times higher than the ICES official estimate. The official estimate is considered uncertain and most likely an underestimate of the actual biomass, due to unregistered mortality in the fisheries and lack of fishery-independent, age-disaggregated data. Hence, tag-based estimates could potentially improve the current assessment if included in the ICES stock assessment on a regular basis. These estimates also involve some uncertainty that needs consideration, especially related to variable tagging mortality, detector efficiency and migrations of the stock. [ABSTRACT FROM AUTHOR]

Abstract: In the present work we used a particle-tracking model coupled to a 3D hydrodynamic model to study the combined effect of hydrodynamic variability and active vertical movements on the transport of sole larvae in the southern North Sea. Larval transport from the 6 main spawning grounds was simulated during 40day periods starting on 2 plausible spawning dates, the 15/04 and the 01/05, during 2years, 1995 and 1996. In addition to a “passive” behaviour, 3 types of active vertical movements inspired from previous studies have been tested: (1) Eggs and early larvae float in the surface waters, late larvae migrate toward the bottom and stay there until the end of the simulation; (2 and 3) Eggs float in the surface waters, early larvae perform diel vertical migrations in the surface waters, and (2) Late larvae perform diel vertical migrations in the bottom waters until the end of the simulation; or (3) Late larvae perform tidally synchronised vertical migrations in the bottom waters until the end of the simulation. These behaviours have been implemented in the model with vertical migration rates, positive or negative, which can account for buoyancy or real swimming activity. Variations in larval transport were analysed in terms of mean trajectories, final larvae distribution, larval retention above nurseries, and connectivity. Results suggest that the variations in larval retention above nurseries due to the varying hydrodynamic conditions are not consistent in space i.e. not the same for all the spawning sites. The effect of active vertical movements on larval transport is also not consistent in space: Effects of active vertical movements include decreased retention above nurseries, decreased transport and/or decreased horizontal dispersion of larvae through reduced vertical shear (depending on the zone). The variability in larval retention due to hydrodynamic variability is higher than variability due to differences in the behaviour of larvae. In terms of connectivity, exchanges of larvae between the 6 areas considered are moderate: 10 connections happened out of the 30 possible, and the amount of larvae exchanged is much lower than the amount of larvae retained except in a few cases. This is not incompatible with the possible existence of subpopulations of sole in the Eastern Channel and southern North Sea. [Copyright &y& Elsevier]

Since the construction of the Gezhouba Dam in the 1980s, the number of Chinese sturgeon in the Yangtze River has been rapidly declining. The Gezhouba Dam has cutoff the migration path of these sturgeon, resulting in an overall reduction of suitable sturgeon habitat. This paper describes a habitat suitability index model that is used to evaluate the impacts of the Gezhouba Dam and Three Gorges Project on Chinese sturgeon spawning sites. Based on research concerning the reproduction characteristics of Chinese sturgeon, ten major ecological factors that influence reproduction were analyzed, including: water temperature, velocity, water depth, substrate, suspended sediment concentration, and the amount of egg predatory fish. The suitability index (SI) curves based on these ten ecological factors were obtained, and a habitat suitability function was developed. A two-dimensional mathematical model was also created to simulate and predict physical habitat situation (such as hydraulic, sediment, and substrate) of the Chinese sturgeon. By coupling the habitat suitability function and a two-dimensional mathematical model, a habitat suitability index model for Chinese sturgeon was established. The habitat suitability index model was validated by comparing measured data with predictions from the model. These comparisons showed that the computed results agreed well with the measured results, and the high calculated habitat suitability index (HSI) corresponded to high measured quantity of eggs per unit (1000m3) discharge (CPUEd). The calculated habitat suitability index for Chinese sturgeon also showed that the habitat suitability index was better in 1999, before the impoundment of the Three Gorges Project, compared with the habitat suitability in 2003. Simulation results of different discharges from Gezhouba Dam predicted that flow discharges between 10,000 and 30,000m3/s were most suitable for sturgeon spawning. [Copyright &y& Elsevier]

Abstract: Tagging of more than 2000 turbot in the eastern Gotland basin in the central Baltic Sea revealed strong spawning site fidelity. Only 4 out of 653 recaptures were made outside the Gotland area and 95% of recaptures, 1–4 years after tagging, were found less than 30km from the original tagging site. Within the summer spawning season turbot were almost stationary and 95% of them were recaptured less than 16km from the tagging site. During the spawning they dwelled close to shore at a mean depth of only 5m while migration to deeper areas was evident in the feeding season. Indications of differences in the spawning behavior between sexes were found together with a positive correlation between recapture probability and body length. The revealed spawning site fidelity has implications for management practices of turbot in the Baltic Sea. [Copyright &y& Elsevier]

Abstract: Trace elemental signatures of otolith nuclei and edges were analysed by LA-ICP-MS in 514 specimens of the highly migratory oceanic fish southern blue whiting, Micromesistius australis australis, that were caught in their two distant spawning grounds located in the Southwest Atlantic (Patagonian Shelf around the Falkland Islands) and Southeast Pacific (shelf and slope of the southern Chile). The elemental fingerprints in the otolith edges, accumulated during the adult life of M. a. australis were spawning-site specific. Using just four elements (Li, Mg, Sr and Ba), the correct allocation of fish to their sampling areas situated in either Chilean or Falkland spawning grounds was about 90%, meaning the adult fish have a close affinity to their respective spawning grounds. Despite this, chemical concentrations in their otolith cores revealed two clusters of signatures, with the majority of Chilean fish (more than 80%) grouped into Cluster 1, which is characterized by lower Sr concentrations, and about 80% of Patagonian fish grouped into Cluster 2, which is characterized by higher Sr concentration. This most likely indicates that the Chilean spawning population consists of about four fifths of the native fish plus about one fifth of migrants from the Atlantic, and vice versa. Possible ways of the population interchange and migrations of Chilean and Patagonian fish were discussed contributing to identification of their stock status. [Copyright &y& Elsevier]

• Timing and duration of herring coastal spawning migration differ by fish age and size. • Older fish spawn earlier and remain in frozen surface Akkeshi Lake waters. • Younger fish swim shallower than older fish through the day and night. • Different fish ages and length may lead to variable risk and cost in migration. Timing and duration of spawning migration of Pacific herring is known to vary by fish age and length. Older fish mature earlier, but there are few verified examples of differences in the pre-spawning migration of individuals varying in age or size. Here we use sonic tagging to examine the fluctuations in age, fish length and maturity throughout the migration of herring in Akkeshi, Japan. We tracked the horizontal and vertical movement of individual fish using acoustic telemetry and biologging methodology. In Akkeshi Lake, older, larger individuals migrated early, reached peak maturity and remained in the lake until early April, after spawning. The timing and duration of the stay in Akkeshi Lake coincided with the freezing and melting of the surface layer of the lake. Fish tracking indicated no differences in herring in different length classes migrated to and from Akkeshi Lake and offshore and stayed in Akkeshi Bay. For the vertical movement, larger, older herring occupied a wide depth range during diurnal vertical movements as they moved to Akkeshi Lake and to offshore. In contrast, the smaller group occurred frequently in depths shallower than 5 m throughout the day and night. Greater depth variation could result in beneficial effects in predator avoidance and increased prey encounter opportunities though vertical migration. In contrast, smaller herring that were more confined to surface waters could experience more frequent sensing of the environmental cues of spawning grounds such as low-salinity water and olfactory stimulation near the surface. Therefore, there are differences in the benefits and risks during migration for each fish length, which may result in superior spawning grounds and individual mortality in this area. [ABSTRACT FROM AUTHOR]

Abstract: A high variability in fish''s aspect, causing strong target-strength (TS) fluctuations, was observed in nase Chondrostoma nasus (L.) during upstream spawning migration through a horizontal, bottom-aligned beam in the Fischa River, a tributary of the Danube. Size estimates based on traditional mean target strength underestimated the total length of nase. Applying maximum TS from side-aspect detections overestimated size due to signal amplifications of up to 10dB in the single-echo detections of tracked fish. Based on Lilja''s simulations, the strong signal amplifications probably originated from flash-effects. Inhomogeneous sound-propagation due to cylindrical spreading and the maturity state of spawning nase probably contributed to signal amplification of up to 6dB. In order to find better size estimators than the mean and max size estimator, we tested percentile estimators, and we developed a new statistical method—the Maximum Excess Test and Maximum Isolation Test (MET–MIT). This method links information from catch data with the TS-distribution from tracked fish in order to exclude outliers. The results show that both the MET–MIT and the percentiles gave reasonably similar results and that both were better size estimators than the traditional mean-target-strength estimator. [Copyright &y& Elsevier]