scholarly journals Nursery areas and recruitment variation of Northeast Atlantic mackerel (Scomber scombrus)

2014 ◽  
Vol 72 (6) ◽  
pp. 1779-1789 ◽  
Author(s):  
Teunis Jansen ◽  
Kasper Kristensen ◽  
Jeroen van der Kooij ◽  
Søren Post ◽  
Andrew Campbell ◽  
...  
Keyword(s):  
Stock Assessment ◽  
Bottom Trawl ◽  
Supporting Evidence ◽  
Geostatistical Model ◽  
Nursery Areas ◽  
Northeast Atlantic ◽  
Scomber Scombrus ◽  
Temporal Correlations ◽  
Catch Rates ◽  
Trawl Surveys

Abstract There are currently no dedicated recruitment survey data available in support of the assessment of the abundance and distribution of Northeast Atlantic (NEA) mackerel (Scomber scombrus), one of the most widespread and commercially important fish stocks in the North Atlantic. This is despite the fact that an estimate of recruitment is an important requirement for the provision of advice to fishery managers. The work here addresses this by compiling catch rates of juvenile mackerel from bottom-trawl surveys conducted between October and March during 1998–2012 and applying a log Gaussian Cox (LGC) process geostatistical model incorporating spatio-temporal correlations. A statistically significant correlation between the modelled catch rates in adjacent quarters 4 and 1 (Q4 and Q1) demonstrates that bottom-trawl surveys in winter are an appropriate platform for sampling juvenile mackerel, and that the LCG model is successful in extracting a population abundance signal from the data. In this regard, the model performed appreciably better than a more commonly used raising algorithm based on survey swept-area estimates. Therefore, the LCG model was expanded to include data from the entire survey time-series, and a recruitment index was developed for use in the annual ICES stock assessment. We hypothesize that catchability is positively density-dependant and provides supporting evidence from acoustic observations. Various density-dependant transformations of the modelled catch rates were furthermore found to improve the correlation between the derived annual recruitment index and recruitment estimated by backcalculation of adult mackerel data. Square root transformation led to the strongest correlation, so this is recommended for further analysis of mackerel abundance. Finally, we provide maps of spatial distributions, showing that the most important nursery areas are around Ireland, north and west of Scotland, in the northern North Sea north of 59°N and, to some extent, also in the Bay of Biscay.

scholarly journals Development of a stock–recruit model for simulating stock dynamics for uncertain situations: the example of Northeast Atlantic mackerel (Scomber scombrus)

2011 ◽  
Vol 68 (5) ◽  
pp. 848-859 ◽  
Author(s):  
E. John Simmonds ◽  
Andrew Campbell ◽  
Dankert Skagen ◽  
Beatriz A. Roel ◽  
Ciaran Kelly
Keyword(s):  
Stock Assessment ◽  
Management Plan ◽  
Maximum Sustainable Yield ◽  
Fish Stock ◽  
Northeast Atlantic ◽  
Atlantic Mackerel ◽  
Scomber Scombrus ◽  
Stock Biomass ◽  
Spawning Stock ◽  
Functional Forms

Abstract Simmonds, E. J., Campbell, A., Skagen, D., Roel, B. A., and Kelly, C. 2011. Development of a stock–recruit model for simulating stock dynamics for uncertain situations: the example of Northeast Atlantic mackerel (Scomber scombrus). – ICES Journal of Marine Science, 68: 848–859. The assumption of a relationship between recruitment and a spawning stock is the cornerstone of the precautionary approach and may constrain the use of a maximum sustainable yield (MSY) target for fisheries management, because the failure to include such a relationship suggests that providing a measure of stock protection is unnecessary. The implications of fitting different functional forms and stochastic distributions to stock-and-recruit data are investigated. The importance of these considerations is shown by taking a practical example from management: the management plan for Northeast Atlantic mackerel (Scomber scombrus), a fish stock with an average annual catch of 600 000 t. The historical range of spawning-stock biomass is narrow, and historical data from a stock assessment explain only a small proportion of the recruitment variability. We investigate how best to reflect the uncertainty in the stock–recruit relationship. Selecting a single model based on simple statistical criteria can have major consequences for advice and is problematic. Selecting a distribution of models with derived probabilities gives a more complete perception of uncertainty in dynamics. Differences in functional form, distribution of deviations, and variability of coefficients are allowed. The approach appropriately incorporates uncertainty in the stock–recruit relationship for FMSY estimation.

scholarly journals Recruitment indices of European hake, Merluccius merluccius (Linnaeus 1758), in the Northwest Mediterranean based on landings from bottom-trawl multispecies fisheries

2004 ◽  
Vol 61 (5) ◽  
pp. 760-773 ◽  
Author(s):  
Raquel Goñi ◽  
Sara Adlerstein ◽  
Federico Alvarez ◽  
Mariano García ◽  
Pilar Sánchez ◽  
...  
Keyword(s):  
Linear Models ◽  
Stock Assessment ◽  
Late Summer ◽  
Bottom Trawl ◽  
Multivariate Techniques ◽  
Merluccius Merluccius ◽  
Commercial Catch ◽  
Size Category ◽  
Catch Rates ◽  
Species Proportions

Abstract Temporal and spatial variation in Merluccius merluccius recruitment in the Northwest Mediterranean is examined, and recruitment indices are derived from monthly M. merluccius catch rates of four bottom-trawl fleets operating in Spanish and Italian waters during the period 1991–1999. Where M. merluccius catches were not recorded by size category, multivariate techniques were applied to species proportions in order to identify catch records most representative of recruit abundance. Selected catch rates were analysed by generalized linear models (GLMs) to estimate recruitment indices. The GLMs explain large proportions of the variation in recruit abundance (50–84%) and indicate significant annual and seasonal variation in recruitment strength. Vessel was by far the most important factor affecting catch rates of recruits, stressing the need to account for vessel characteristics when analysing commercial catch data for stock assessment. Seasonal patterns of recruitment reveal similarities among the study areas and interannual variations within areas. One major recruitment peak was identified in each area during either spring/summer or late summer/winter. In most areas, recruitment between 1991 and 1999 seemed to decline, but this could not be confirmed owing to high interannual variability. The coherence of annual fluctuations in recruitment indices with those of MEDITS surveys supports the present results.

Calculation of untrawlable areas within the boundaries of a bottom trawl survey

2003 ◽  
Vol 60 (6) ◽  
pp. 657-669 ◽  
Author(s):  
Mark Zimmermann
Keyword(s):  
Relative Abundance ◽  
Species Group ◽  
Bottom Trawl ◽  
Trawl Survey ◽  
Gis Analysis ◽  
Target Species ◽  
Abundance Estimates ◽  
Original Target ◽  
Catch Rates ◽  
Trawl Surveys

A geographic information system (GIS) analysis of 5039 bottom trawl events from U.S. west coast bottom trawl surveys (1977–1998) estimated that the survey area was about 77% trawlable but five of the 30 strata were less than 50% trawlable. Untrawlable areas, by definition, cannot be surveyed with the bottom trawl; however, there has never been a means of identifying and excluding these areas from relative abundance estimates, which are calculated only from hauls completed in the trawlable portions of each stratum. Unknown amounts of untrawlable habitat are a problem for relative abundance estimation in many bottom trawl surveys. This manuscript describes one method of using the bottom trawling events of a survey, such as ripped-up hauls and abandoned stations, to calculate the amount of area that is untrawlable. A comparison of catch rates between undamaged tows and a limited number of damaged tows, which are normally discarded as faulty samples, showed that Sebastes catch rates were generally higher in damaged tows. Thus untrawlable areas may have substantial importance on relative abundance estimates of Sebastes, the original target species group for this survey.

scholarly journals Anglerfish discard estimates and patterns in Spanish Northeast Atlantic trawl fisheries

2008 ◽  
Vol 65 (7) ◽  
pp. 1350-1361 ◽  
Author(s):  
Paz Díaz ◽  
Juan Santos ◽  
Francisco Velasco ◽  
Alberto Serrano ◽  
Nélida Pérez
Keyword(s):  
Atlantic Ocean ◽  
Length Distribution ◽  
Bottom Trawl ◽  
Trawl Survey ◽  
Marine Science ◽  
Target Species ◽  
Northeast Atlantic ◽  
Northeast Atlantic Ocean ◽  
Trawl Fisheries ◽  
Trawl Surveys

Abstract Díaz, P., Santos, J., Velasco, F., Serrano, A., and Pérez, N. 2008. Anglerfish discard estimates and patterns in Spanish Northeast Atlantic trawl fisheries. – ICES Journal of Marine Science, 65: 1350–1361. Estimates of Spanish bottom trawl discards of anglerfish Lophius budegassa and Lophiuspiscatorius in the Northeast Atlantic Ocean are presented. Both species are commercially valuable in ICES Subareas VI and VII, and Divisions VIIIc and IXa. Information was obtained from observers on board during discard-monitoring programmes. Raising by effort, rather than by landings and target species, was used to determine the total annual discards by weight and number, the discard percentage, and the discard length distribution by stock throughout the dataseries. By weight and number, discards varied interannually, ranging from 4 to 600 t (∼28 000–7 000 000 fish) in northern stocks of anglerfish, and from 1 to 100 t (∼20 000–400 000 fish) in southern stocks. The discard percentage for both species and northern and southern stocks therefore ranged between 2 and 76% by number. Length distributions of the discarded anglerfish show that most were juveniles, although the pattern differed in years with high or with low rates of discarding. The number of juveniles caught apparently increased in most areas after 2000. Correlations between the quantities discarded and recruitment indices from French and Irish trawl surveys were found for northern stocks and with Spanish trawl survey indices for southern stocks.

scholarly journals Abundance and spatial distribution of brown crab (Cancer pagurus) from fishery-independent dredge and trawl surveys in the North Sea

2020 ◽  
Author(s):  
Carlos Mesquita ◽  
Helen Dobby ◽  
Graham J Pierce ◽  
Catherine S Jones ◽  
Paul G Fernandes
Keyword(s):  
Spatial Distribution ◽  
North Sea ◽  
Stock Assessment ◽  
Additive Models ◽  
Early Years ◽  
The North ◽  
Cancer Pagurus ◽  
The North Sea ◽  
Catch Rates ◽  
Trawl Surveys

Abstract Brown crab (Cancer pagurus) is a widely distributed crustacean that occurs around the British coastline supporting important commercial fisheries. The habitat preferences of brown crab around Scotland are poorly documented and for the purposes of stock assessment, the species is considered data-poor. Based on an analysis of dredge and trawl surveys taking place in the North Sea (2008–2018), we describe the spatial distribution of brown crab and for the first time, develop abundance and recruitment indices for the species. We make use of geostatistical methods and apply generalized additive models to model catch rates in relation to a number of explanatory variables (depth, distance to the coast, sediment type and year). The dredge and trawl abundance indices were correlated showing a similar trend of increasing catch rates in the early years of the time series up to 2016 and a subsequent reduction. The recruitment index showed a gradual increase in captured juvenile crabs up to 2014 followed by a steep decrease with 2018 being the lowest value estimated. The derivation of robust indicators of stock abundance will contribute to the stock assessment of this species and enable the provision of improved fisheries management advice for brown crab around Scotland.

Population structure, reproduction and exploitation of the greater forkbeard Phycis blennoides (Brünnich, 1768) from the Algerian basin

2020 ◽  
Vol 33 ◽  
pp. 20
Author(s):  
Zakia Alioua ◽  
Soumia Amira ◽  
Ghollame Ellah Yacine Khames ◽  
Ulla Fernandez-Arcaya ◽  
Beatriz Guijarro ◽  
...  
Keyword(s):  
Population Distribution ◽  
Stock Assessment ◽  
Bottom Trawl ◽  
Fish Stock ◽  
Commercial Fisheries ◽  
Trawl Survey ◽  
Bottom Trawl Survey ◽  
First Maturity ◽  
Density And Biomass ◽  
Trawl Surveys

The objective of this study was to determine the population distribution and some biological aspects for fish stock assessment of the greater forkbeard Phycis blennoides along the Algerian basin. The distribution of P. blennoides (3418 individuals) was studied using data collected between 170–779 m depth during two bottom trawl surveys developed on 2003 and 2004. Additionally, some biological parameters were obtained from 1050 individuals sampled from commercial fisheries in Algerian ports (i.e. Annaba, Azeffoun, Dellys, Cap Djinet, Zemmouri, Bouharoun, Algiers, La Madrague, Cherchell, Tenes and Mostaganem) during the period 2013–2017. P. blennoides sampled from bottom trawl surveys showed a depth related distribution with the largest individuals being found at 600–800 m depth and the smallest at shallower depths. Density and biomass varied with depth and density also with longitude, while biomass showed no pattern with longitude. Recruitment was recorded in the eastern sector of Algeria during winter, for individuals sampled by bottom trawl surveys. Young P. blennoides entered commercial fisheries in summer, with an overall sex ratio skewed towards males (1F:2.18M). The size at first maturity (L 50) was 24.30 cm and 30.39 cm for males and females, respectively. The age at 50% maturity was 2–3 years for specimens collected by a bottom trawl survey in 2003 and commercial fisheries, but 3–4 years for the bottom trawl survey in 2004.

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