This study was carried out throughout 10 fishing seasons between 2002 and 2018 to monitor the population and stock variations of Engraulis encrasicolus (L., 1758) on the south-eastern Black Sea coast of Turkey. Asymptotic length (L∞), growth constant (K) and growth performance indexes (φ) were calculated to be between 12.86 and 15.79 cm, 0.69 and 0.99, 2.10 and 2.29, respectively. Theoretical birth ages were determined to range between (to) −0.15 and −0.27, the maximum ages (tmax) ranged between 3.03 and 4.35, total mortality rates (Z) between 2.19 and 2.66, natural mortality rates (M) between 0.93 and 1.26, the fishing mortality rate (F) between 0.93 and 1.47, and the optimum fishing mortality rate (Fopt.) between 0.37 and 0.62. Fishing mortality rates (F) were estimated to be higher than the optimum fishing mortality rates (Fopt). Z/K ratios were determined to range between 1.91 and 3.43. Current exploitation rates (Ecurr.) were calculated to range between 0.42 and 0.62. The first recruit lengths (Lr) and first capture lengths (Lc50) were estimated to range between from 5.25–7.75 and from 7.66–8.74 cm, respectively. The first maturity lengths (Lm50) of E. encrasicolus ranged between 8.57 and 10.53 cm. The maximum sustainable exploitation levels (Emax) were determined to range between 0.72 and 0.83. These data indicate that if current levels of fishing pressure continue, anchovy stocks will collapse in the near future.

Quantifying and comparing stocks of oysters (Crassostrea virginica) within and among estuaries across the Gulf of Mexico is difficult because the sampling equipment used is either inconsistent among studies, or inefficient. In Texas, USA, stock assessments of oyster populations are made using an oyster dredge, which is an inefficient sampling tool. We compared sampling densities estimated by oyster dredges with more accurate estimates taken by diver-quadrat samples to determine a dredge efficiency rate. Our calculated efficiency rate (0.125) was negatively affected by the number of dead oysters, and the number and volume of total oysters in an area, but not affected by sediment grain size, water quality, and other oyster metrics. The dredge efficiency rate calculated in this study can be applied to past and future dredge-collected oyster quantity data to provide more realistic estimates of oyster densities and allow more accurate stock assessments and comparisons among studies and regions.

The purple sea urchin P. lividus is a marine resource greatly valued for its highly nutritious roe. The objective of this work is to analyse the spatial distribution pattern and population structure of this species in the region of Cantabria (Bay of Biscay) in order to identify the most appropriate zones for sustainable harvesting and for the establishment of adequate management strategies. Two depth ranges were studied (<5 and 5–10 m) in five coastal areas. The available stock of commercial individuals (size >55 mm) was estimated based on the density of individuals and biometric parameters. Significant differences were found among areas but not among depth ranges. Three areas showed low densities with large individuals, whereas two areas showed high densities with small individuals. Despite the average smaller size of the individuals, these high-density areas accumulated 76% of the commercial stock, making these the most suitable zones for the sustainable harvesting of P. lividus in the region. The high variability of the observed density values resulted in elevated uncertainty in the estimation of stocks. However, the high sea urchin densities together with the high percentages of commercial individuals suggest that the resource is currently underexploited. Further studies should be carried out, and precautionary measures should be adopted before opening the fishery. The suitability of many of these measures is discussed in the present work, as a necessary step in the management of the P. lividus fishery in Cantabria.

The grooved carpet shell Venerupis decussata (=Ruditapes decussatus) (Linnaeus, 1758) is a Mediterranean autochthonous species that in Tunisia is heavily harvested from natural populations. It represents one of the important economic issues, especially in terms of employment and the trade balances of the country via its exportation. Despite its economic value, no studies have been carried out about the spread of this mollusc. Thus the status of this species is still poorly known and there is a knowledge gap about its stocks assessment. This study aimed to investigate the distribution, abundance and population structure of the carpet shell clam in Sfax coastal areas. In terms of geographic occupation, maps of the population distribution were drawn. The results showed a scattered distribution pattern of the species according to location ranging between 0 and 152 ind m−2. The consequence was a remarkable biomass which represented 891 tonnes of total fresh weight and high abundance levels reaching over 261.7 ± 84.2 million individuals estimated in the area of 4182 hectares. The distribution of the species has also been investigated in consideration with the size which varied markedly according to location, the shell length ranged between 2 and 41 mm. The overall sex ratio (F:M) was 1:1.17, which was significantly different from parity (1:1). The size at which 50% of the population reached maturity was 24.08 and 24.76 mm shell length for males and females, respectively. Findings of the current study suggest that V. decussata proliferates along southern Tunisian coasts.

Several recent papers have criticized the scientific robustness of the fisheries management system used by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), including that for Ross Sea toothfish. Here we present a response from the wider CCAMLR community to address concerns and to correct some apparent misconceptions about how CCAMLR acts to promote conservation whilst allowing safe exploitation in all of its fisheries. A key aspect of CCAMLR’s approach is its adaptive feedback nature; regular monitoring and analysis allows for adjustments to be made, as necessary, to provide a robust management system despite the statistical uncertainties inherent in any single assessment. Within the Ross Sea, application of CCAMLR’s precautionary approach has allowed the toothfish fishery to develop in a steady fashion with an associated accumulation of data and greater scientific understanding. Regular stock assessments of the fishery have been carried out since 2005, and the 2013 stock assessment estimated current spawning stock biomass to be at 75% of the pre-exploitation level. There will always be additional uncertainties which need to be addressed, but where information is lacking the CCAMLR approach to management ensures exploitation rates are at a level commensurate with a precautionary approach.

There is growing interest in bio-economic models as tools for understanding pathways of fishery behaviour, in order to assess the impact on natural resources. Based on ‘FishRent’, a modelling approach is presented that integrates economics of the fleet, the impact of fishing on stock development and their spatio-temporal interplay. The simulation of species seasonal movements in combination with both observed values and stochastic recruitment allowed analysing the economic response of fleet segments to changes in stock distribution and development. Optimisation of net profits determines the effort adjustment and spatial allocation of fleet segments, which in turn affects the level of catch rates. Effort tended to concentrate where fish abundance was high, but also where fishing costs were low. In simulations with the current management plan spawning stock of North Sea saithe (Pollachius virens) declined below its precautionary reference point. In response fishing far from home ports became expensive and 40% of the initial effort was shifted to areas closer to home ports, but as areas of high fish concentrations were located by the modelled fleet segments catch rates remained high. Changes in seasonal/annual stock distribution, the stock decline and costs influenced the change in fishing effort distributions leading to overestimated catch per unit of effort values that masked the decline of stock abundance.

The chub mackerel (Scomber japonicus) has been one of the important commercial pelagic species in the East China Sea since the decline of traditional demersal economic species. Although chub mackerel resources are suffering over-exploitation with the increase of fishing effort, their response to fishing and changing trends have not been analysed because of a shortage of data. In this paper we separated sample catches of chub mackerel from the central East China Sea during 2009 and 2010 into three age groups based on the age–fork length key. We then estimated the maximum sustainable yield (MSY) and built a spawner–recruitment relationship based on the fishery statistics of purse seine vessels, lighting purse seine vessels and deep-water purse seine vessels from 2006 to 2012. We predicted the biomass, spawning biomass, catches and the length compositions of catches when fishing at the current intensity (fishing mortality (F) = 0.7). The results showed that the MSY of chub mackerel is about 18.8 × 104t, and the fishing effort at MSY (EMSY) is about 72 standard purse seine vessels (both the lighting purse seine vessels and deep-water purse seine vessels were standardized to purse seine vessels), which is equivalent to F = 0.4. If F remains at the current level, the biomass of chub mackerel will remain at 45.3 × 104t. At the same time, more than 40% in the catch will be the individuals smaller than 200 mm, and only about 8% will be larger than 300 mm. Therefore, there is little potential for further exploitation of the chub mackerel resources in the central East China Sea, and it is better to reduce F to less than 0.4 for sustainable utilization.

Virtual population analysis requires information on the fishing mortality rate (orabundance) for one age group from each cohort. In many cases available data areinsufficient to estimate these rates for every age group and structural assumptions mustbe imposed to reduce the number of effective parameters. Past assessments of westernAtlantic bluefin tuna (Thunnus thynnus) have reduced the number ofparameters by assuming pre-specified values for the ratios of the fishing mortality rateson adjacent age groups. More recent bluefin tuna assessments have estimated terminalfishing mortality rates (F) on each age with a constraint that restrictschange from one year to the next. We explore the implications of these methods ofestimating terminal-year F through retrospective analyses of the 2006bluefin tuna assessment and through stochastic simulations. The use of pre-specifiedratios for F created strong retrospective biases and may have led tooverly optimistic projections. Constraining annual changes in the terminal-yearF appeared to mute retrospective patterns and resulted in abundanceprojections less prone to spurious initial leaps. Simulation results indicate that theconstraint improves estimation, particularly with moderate to low interannual changes inselectivity.

Uncertainty about reporting rates of tags returned by fishermen has often prevented tagging data from being used in stock assessments. In this study we conduct a meta-analysis to estimate tag reporting rates of commercial tuna fleets by comparing their tag return data with those of the USA longline pelagic observer program. The longline fleets of Venezuela and the USA are estimated to report about 0.8% of tags caught, compared with less than 0.1% for Canadian, Spanish and Japanese longline fleets. For some fleets with sparse return data or for those that do not overlap often with the observer fleet, reporting rate estimates are sensitive to changes in the spatio-temporal resolution over which comparisons are made. Regardless of these sensitivities, the estimated reporting rates are low and there are likely to be large differences in reporting rate between different combinations of flag and gear.

The number of eggs produced by a parental stock is central to fisheries advice on recruitment potential. However, stock based estimates of egg production may give a misleading index of recruitment potential in stocks containing several reproductively isolated populations. This paper examines the ability of length, condition and oocyte developmental stage to predict levels of potential fecundity in the sandeel, Ammodytes marinus, in three important fished areas in the North Sea. Our results indicate that regional variation in this relationship exists, with fecundity in central areas of the North Sea being higher than those found just off the north-east UK. Oocyte diameter was also found to have a significant effect on potential fecundity, suggesting a down-regulation of oocyte numbers arising from pre-ovulatory atresia, however, this effect was not apparent in every model tested. Our findings have relevance to the local sustainability of spawning components and thus the regional management of the North Sea sandeel stock.

In the Northeast Atlantic fishery for roundnose grenadier Coryphaenoides rupestris, discards account for about 30% of the catch in weight. Data on discards are scarce; however, length distributions and discard rates appear to be relatively stable from year to year. In contrast, landings data available since 1990 show that the average pre-anal fin length has decreased from 20.7 cm in 1990 to 15.2 cm in 2008, resulting in a 58% reduction of the mean individual weight (850 g in 2008) and an increasing occurrence of overlapping class sizes between landings and discards in recent years. For stock assessment, the method of separable virtual population analysis (SVPA) was used. However, because of the lack of discard data for many of the years covered by the study, the catch data used as input to the assessment model had to be reconstructed from the available information (landings, discards, fishing effort and bathymetric distribution of the stock) using two methods. The first method relied on the assumption that the recent length distributions of discards were applicable to the earlier years (1990-1997). It resulted in unrealistic bimodal length distributions, suggesting a change in discarding practices through time, with larger individuals being discarded in the early days. The second method, based on the fishing effort and length distribution by depth strata, produced unimodal distributions for the whole period and confirmed that the average length of discarded fish was higher in the early days of the fishery. In both cases, the estimates of biomass follow parallel trends, suggesting a strong decline in the population. The available information and methods are discussed.

A statistical approach is proposed to utilize the information contained both in scientific surveys and commercial fishing logbooks, in order to determine spatial and temporal distributions of recruiting and spawning fish of exploited populations. The approach is based on multivariate descriptive methods including ordination methods and classification techniques. A typology involving a principal component analysis (PCA), followed by a hierarchical ascending classification (HAC), is applied to both scientific and commercial data. PCA that accounts for spatial and temporal contiguities were performed. These analyses allow to compare structures observed at global and local scales, with those observed without focusing on a particular scale. The method is applied to the whiting population in the Celtic Sea. The analyses performed on both scientific and commercial CPUE show that most age groups are found north of 50°N. The analysis of commercial CPUE indicates four periods in the year associated with particular areas. High abundances of adults (age >2 years) are observed during spawning season (January–April) in inshore areas (south of Ireland and off Cornwall). Intermediate abundances of adults are observed in the same area in May and June. Between July and September, all age groups are observed in the Smalls area, where particularly high abundance of recruiting group 1 are found. During the last quarter, the distribution of adults is more widespread, mainly ranging between 51°N and 52°N.

Intense local fishing pressure is likely to induce significant local decreases in both resource biomass and fishing yields. This is what we term ‘local overfishing’. Such a phenomenon and its consequences for stock assessment are investigated with the fisheries simulator SHADYS (Simulateur halieutique de dynamiques spatiales: spatialized simulator of fisheries dynamics). In SHADYS, resource dynamic is based on an advection–diffusion–reaction equation. After a brief presentation, the simulator is used to characterize the ‘local overfishing’ phenomenon as a ‘wound’ of the population. The latter is subsequently able to ‘heal’ and to recover its initial distribution. We show that, associated with cooperation tactics of the fishing fleets, local overfishing may induce non-linear relationships between catches per unit of effort (CPUE) and fishing effort calculated locally. In particular, it is shown that there is a strictly decreasing relationship between catchability and effort when fishing vessels apply intense local fishing pressure but do not cooperate; that the relationship may increase when vessels cooperate but do not apply intense local fishing pressures; and finally, that it may go through a maximum when, simultaneously, ships cooperate and have high local exploitation rates. These three main types of theoretical relationships correspond well with those observed in reality. The existence of such relationships could be an important source of biases in stock assessment.

Even when fishing effort data are not available in a developing fishery, it is often still possible to develop a simple fishery indicator to obtain information about the status of the stock. Using catch data only, Grainger and Garcia, (FAO Fish. Tech. Pap. 359, 1996) showed that the changes over time in the relative rate of catch increase (RRCI) can be used to detect when a stock reaches its over-fishing level, i.e., the year when RRCI falls to zero. The method presupposes that fishing effort increased steadily over the period concerned. We propose a generalization of this method that consists in obtaining a crude estimate of the maximum sustainable yield (MSY) by plotting the trend in catches against the smoothed RRCI. The yellowfin tuna (Thunnus albacares) fishery in the Eastern Atlantic was used to show the bold relationship between MSY estimates obtained from standard equilibrium production models and from this method. Given that it is very difficult to estimate effective fishing effort for skipjack tuna (Katsuwonus pelamis), we show how this simple fishery indicator can be used to obtain proxies of MSY for skipjack fisheries located in the Eastern Atlantic Ocean and in the Indian Ocean.

Fish stocks found on lagoon bottoms and near reefs are characterized by a high diversity and heterogeneous habitat which make stock estimation difficult. In particular, it is necessary to combine several methods in order to evaluate the major components of these stocks. The present study aimed at estimating reef fish stocks in the Northern Province of New Caledonia, a region where they represent a major target for the local fishermen. These estimates were based on experimental fishing with handlines and bottom longlines. Handlines were used to assess the stocks near reefs, and longlines for those in areas away from reefs and on lagoon soft bottoms. Handline stations (363) were sampled in three different regions (west, north and east lagoons) and three biotopes (nearshore, middle lagoon and barrier reef). A total of 104 species were caught, the major families being Lethrinidae, Lutjanidae and Serranidae. Species composition and catch per unit of effort (CPUE) varied among regions and biotopes. In particular, the north zone showed characteristics of an unexploited area with very high yields. An increase in CPUE and fish size from the coast towards the barrier reef and with increasing depth was observed in all regions. Correlations between CPUE from handlines and the numerical density and biomass estimates from underwater visual censuses (UVC) performed on nearby reefs were significant. A total of 206 longline stations were sampled in the west and east regions. A total of 80 species were caught, the major families being the same as those caught in stations with handlines with the addition of Carangidae. The CPUE of longlines was significantly correlated with numerical density and biomass estimates made by UVC along the longlines. Stock estimates based on the correlations between CPUE from handlines or longlines and UVC estimates indicate that 90 % of the lagoon stock were found on soft bottoms and near reefs. Reefs, despite biomasses that were five times larger than soft-bottom and near-reef areas, made only a small contribution to total stock. The ratio between density and CPUE was highest for the lowest densities, thus indicating that fishing efficiency increased with density. Comparison of handline catch performed around reefs and UVC data from nearby reefs suggests that there were bold relationships between the fish assemblages of these two biotopes.

An assessment of the state of the fisheries of hake, red mullet and Norway lobster was carried out by using trawl survey data from the MEDITS research programme. The assessment was performed by means of the application of a composite model utilising the total mortality rate Z as a direct index of fishing effort. The studied area covered the whole western Italian coast (Ligurian and Tyrrhenian seas) and the eastern coasts of Corsica. The area was divided into twelve sub-areas, considered to be of similar ecological characteristics with similar initial productivity but considered to experience different rates of exploitation. Available information on fishing fleets and their geographic distribution was used in creating sub-areas. For each one of these sub-areas, the total mortality rates and a mean catch per unit of effort were estimated. The estimation of Z was performed by analysing the size structure of the cumulated catch in each sub-area and for each year. Catch rates were estimated as the mean catch per one hour of tow. The positioning of the current values of Z for the different sub-areas relative to the Z at maximum biological production suggests that, in most of the sub-areas, hake is in general fully exploited and red mullet overexploited. In the case of Norway lobster, it was not possible to obtain a statistically acceptable result probably due to a lack of contrasting enough levels of fishing pressure among sub-areas. The results obtained for hake and red mullet are in good agreement with the available information on the consistency of the fleets operating in the different sub-areas.

Catch-per-unit effort (CPUE) has frequently been used as an index of abundance and more specifically to calibrate virtual population analysis (VPA). In multi-species fisheries, CPUE calculated from fishing trips targeting the species seems to be more effective for calibration than the classical ratio total landings/total effort. Target species are determined from an analysis of the composition of catches (landings) of each fishing trip, each trip being categorised as to whether it targets the given species or not. It is obvious that existing but not reported discards would affect these results. Classification of trips can be achieved on a single-species basis, each species being considered successively and each trip possibly being relevant for more than one species. Using a more general approach, classification can be achieved by métiers, each of these being determined by one or a group of target species and each trip being categorised into one and only one métier. This method of categorising trips is based on thresholds of target species contribution to the catch and on an overall explanatory level. For the main species of the French demersal fishery off the west coast of Scotland and in the Celtic Sea, CPUEs are calculated using different methods to define the trips used to calculate fishing effort and associated landings. Besides important differences in actual values, CPUEs may also differ in their trends depending on the definition of directed effort. Tuned VPA, carried out for some species, shows that large variations in population estimates, fishing mortality or short-term predictions could occur when using directed effort, while the catchability model fits the data better.

A split-beam hydroacoustic system with automatic tracking of individual fish is being used to estimate the number of upstream migrating adult Pacific salmon in the Fraser River in British Columbia, Canada. To determine the bias and variance of the estimates of migrating fish numbers produced by this system, we compare simultaneous acoustic and visual estimates. These data demonstrate that, as fish densities increased, both a 4° × 10° and an 8° transducer produced lower estimates than the visual count. However, in the region of fish densities typically observed for migrating salmon, the 4° × 10° transducer estimates did not differ significantly from the visual count. A detailed description of the experimental configuration is given, including how the acoustic and video data were synchronized. Analyses of the data indicate that the size and shape of the acoustic beam has a pronounced effect on the bias of the acoustic estimates. In addition, the performance of the tracking software deteriorates as fish densities become very high.

This paper presents a multispecific approach in order to assess the main demersal resources exploited off Senegal (West-Africa). In absence of reliable data on the actual fishing effort, two series of theoretical fishing effort are estimated, using available species abundance indices from 1971 to 1991. These two series correspond to different hypotheses concerning the trends of fleets' fishing power: an optimistic one and a pessimistic one. For each species or taxa, a surplus production model is calculated with landings statistics and effort. The combining of monospecific models provides a multispecific diagnosis. The analysis is completed by the calculation of diversity indices of catches at the equilibrium level, expressed as a function of fishing effort. While considering the uncertainty around this first assessment, we show that Senegalese groundfish resource is globally full or over-exploited, according to the considered hypothesis. Under the pessimistic hypothesis, 9 among the 11 taxa of Pisces were clcarly over-exploited, with fishing effort some-times as much as twice or three times the effort of maximisation (fMSY). The situation is very critical for Arius sp., Epinephelus aeneus, Pagellus bellottii and Pomadasys sp. Using the multispecific approach, pessimistic diagnosis indicates a fishing effort nearly twice fMSY, with a Maximum Sustainable Yield at about 53 000 t for the 11 taxa together. Conversely, in 1991, octopus and cuttlefish appeared under-exploited. The diversity analysis shows that an increase in fishing effort would lead to a decrease in catch diversity. This result is interpreted as a sign of fragility in the exploited ecosystem.