A linked separable–ADAPT VPA assessment model for western horse mackerel (Trachurus trachurus), accounting for realized fecundity as a function of fish weight

Abstract De Oliveira, J. A. A., Darby, C. D., and Roel, B. A. 2010. A linked separable–ADAPT VPA assessment model for western horse mackerel (Trachurus trachurus), accounting for realized fecundity as a function of fish weight. – ICES Journal of Marine Science, 67: 916–930. The western horse mackerel stock covers a large area of the Northeast Atlantic and is characterized by the sporadic occurrence of strong year classes. The only fishery-independent data available for its assessments are the estimates of total annual egg production from triennial egg surveys. Horse mackerel are indeterminate spawners, so a direct conversion of total annual egg production to spawning-stock biomass using prespawning-season estimates of fecundity is not viable. There is also evidence that potential fecundity per kg spawning female increases with fish weight. A linked separable–ADAPT VPA (SAD) model was developed that combines data on total catch, catch-at-age, and total annual egg production with data on potential and realized fecundity to provide population estimates for western horse mackerel. The model accounts for potential fecundity as a function of fish weight and for the development of a targeted fishery on the strong 1982 year class. Simulations confirm that the SAD model is able to reproduce population estimates without bias under a range of scenarios, except where there is a trend in realized fecundity. This underscores the need for improved information on realized fecundity, or alternatively the need to develop management plans that are robust to this source of uncertainty.

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Estimates of batch fecundity and spawning fraction for the southern stock of horse mackerel (Trachurus trachurus) in ICES Division IXa

ICES Journal of Marine Science ◽

10.1093/icesjms/fsp066 ◽

2009 ◽

Vol 66 (4) ◽

pp. 617-622 ◽

Cited By ~ 13

Author(s):

Patrícia Gonçalves ◽

Ana Maria Costa ◽

Alberto G. Murta

Keyword(s):

Egg Production ◽

Production Method ◽

Horse Mackerel ◽

Batch Fecundity ◽

Trachurus Trachurus ◽

Absolute Abundance ◽

Female Total ◽

Stock Biomass ◽

Spawning Stock ◽

Ovulatory Follicles

Abstract Gonçalves, P., Costa, A. M., and Murta, A. G. 2009. Estimates of batch fecundity, and spawning fraction for the southern stock of horse mackerel (Trachurus trachurus) in ICES Division IXa. – ICES Journal of Marine Science, 66: 617–622. Since 1995 the annual egg production method has been applied triennially to the southern stock of horse mackerel (Trachurus trachurus) in the Northeast Atlantic (ICES Division IXa). This method assumes that fecundity is determinate, but increasing evidence indicates that horse mackerel are indeterminate spawners. The daily egg production method (DEPM) does not rely on the assumption of determinate fecundity, making it the appropriate method for this species. Therefore, we reanalysed samples collected from previous surveys (2002, 2004, 2005, and 2007) to obtain estimates for batch fecundity and spawning fraction, which are important DEPM parameters. The estimates of batch fecundity are around 200 oocytes g−1 of female (total ovary-free weight). Several criteria were used to estimate spawning fraction (migratory nucleus stage, hydrated oocytes, and post-ovulatory follicles) and all showed the same trend among years, varying between 0.10 and 0.30 d−1. The estimates were significantly different among methods, but those differences were similar across surveys, indicating that a consistent bias would be reflected in the final spawning-stock biomass (SSB) estimates obtained from the DEPM. Until further information is available regarding the accuracy of the criteria used to estimate spawning fraction, the southern horse mackerel SSB estimates from the DEPM should only be taken as indicative of trends rather than measures of absolute abundance.

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Estimation of mackerel (Scomber scombrus L., 1758) and horse mackerel (Trachurus trachurus L., 1758) daily egg production outside the standard ICES survey area

ICES Journal of Marine Science ◽

10.1016/j.icesjms.2005.05.013 ◽

2005 ◽

Vol 62 (8) ◽

pp. 1705-1710 ◽

Cited By ~ 8

Author(s):

Leonie Dransfeld ◽

Oonagh Dwane ◽

John Molloy ◽

Sarah Gallagher ◽

Dave G. Reid

Keyword(s):

Egg Production ◽

Horse Mackerel ◽

Survey Area ◽

Trachurus Trachurus ◽

Spawning Activity ◽

International Standard ◽

Scomber Scombrus ◽

Rockall Trough

Abstract An experimental egg survey was carried out to assess whether there was significant spawning of mackerel and horse mackerel outside the area surveyed triennially by the international mackerel and horse mackerel standard egg survey. In all, 170 stations were sampled in May 2002 on the Porcupine, Rockall, and Hatton Banks, over the Rockall Trough, and in Faroese waters, with 38 control stations inside and 132 stations outside the standard survey area. There was some spawning of mackerel south and east of the Rockall Bank and southeast of the Faroe Bank, extending to west of the Scottish Shelf. Limited horse mackerel egg production was found west of the Rockall Bank and south of the Faroe Bank. The total mackerel and horse mackerel daily egg production estimated from samples collected in 2002 outside the standard survey area was low compared with the egg production estimated in adjacent waters just inside the standard area in the same year and during the international standard surveys in May and June of 2001. The results suggest that including the spawning activity of both species outside the standard survey area would not significantly contribute to the total estimated egg production.

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Investigating the use of proxies for fecundity to improve management advice for western horse mackerel Trachurus trachurus

ICES Journal of Marine Science ◽

10.1016/j.icesjms.2005.07.006 ◽

2006 ◽

Vol 63 (1) ◽

pp. 25-35 ◽

Cited By ~ 21

Author(s):

J.A.A. De Oliveira ◽

B.A. Roel ◽

M. Dickey-Collas

Keyword(s):

Egg Production ◽

Stock Assessment ◽

Biological Indicators ◽

Horse Mackerel ◽

Feeding Intensity ◽

Short Time Series ◽

Stock Biomass ◽

Spawning Stock ◽

Management Advice ◽

Short Time

Abstract Observations of fecundity from the 2001 western horse mackerel spawning-stock biomass survey suggest that the species is an indeterminate spawner. Therefore, estimates of fecundity based on biological analyses and until recently used in the calibration of the stock assessment are now questioned. The stock is assessed by fitting a linked Separable and ADAPT VPA-based model to the catch-at-age data and to the egg production estimates. Currently, the assumption is that egg production and spawning-stock biomass are linked by a constant but unknown fecundity parameter, estimated within the model. In this study, the effects of introducing relationships linking biological indicators of fecundity, such as lipid content or feeding intensity during the spawning season, to actual fecundity are examined within a simulation framework. Simulations suggest that when the underlying relationships between fecundity and the proxy are poorly described, weak, or based on a relatively short time-series of data, the assumption of constant fecundity will result in better management advice than using the proxy.

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Harvest control rules for the Western horse mackerel (Trachurus trachurus) stock given paucity of fishery-independent data

ICES Journal of Marine Science ◽

10.1093/icesjms/fsm016 ◽

2007 ◽

Vol 64 (4) ◽

pp. 661-670 ◽

Cited By ~ 12

Author(s):

Beatriz A. Roel ◽

José A. A. De Oliveira

Keyword(s):

Juvenile Fish ◽

Management Plan ◽

Horse Mackerel ◽

Independent Data ◽

Trachurus Trachurus ◽

Total Allowable Catch ◽

Control Rules ◽

Constant Proportion ◽

Spawning Stock ◽

Harvest Control Rules

Abstract Roel, B. A., and De Oliveira, J. A. A. 2007. Harvest control rules for the Western horse mackerel (Trachurus trachurus) stock given paucity of fishery-independent data. – ICES Journal of Marine Science, 64: 661–670. The Western horse mackerel stock, widely distributed in EU waters, is characterized by spasmodic recruitment. Currently, the strength of a year class cannot be confirmed before it is fully recruited to the fishery and has reached the age of 5 years. The only fishery-independent information available is an estimate of egg abundance made every third year. The state of the stock is considered uncertain, and there is no agreed management plan. Following EU requests, a set of harvest control rules (HCRs) that allows for the increased proportion of juvenile fish taken by the fishery in recent years was tested by simulation. The proposed HCRs are based either on the results of a full assessment (Constant-proportion strategy) or simply on the egg estimate used as an indicator of stock status (Slope strategy). Biological risk is compared for scenarios where: (i) uncertainty regarding stock dynamics and in the relationship between egg data and spawning-stock biomass is high (current situation); (ii) variable fractions of the total allowable catch (TAC) are taken in the areas occupied by juveniles and adults; and (iii) there is an implementation error. Results suggest that taking a larger portion of the TAC in the area occupied by juveniles increases the risk of impaired recruitment. Comparison of the Constant-proportion and Slope strategies suggests that the former is more conservative, if the assessment is unbiased or if bias is low. Given the paucity of fishery-independent data, a strategy resulting in an approximately constant catch may be appropriate for this stock.

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Macroscopic vs. microscopic identification of the maturity stages of female horse mackerel

ICES Journal of Marine Science ◽

10.1093/icesjms/fsn216 ◽

2009 ◽

Vol 66 (3) ◽

pp. 509-516 ◽

Cited By ~ 21

Author(s):

Ana Maria Costa

Keyword(s):

Horse Mackerel ◽

Percentage Error ◽

Maturity Stage ◽

Trachurus Trachurus ◽

Microscopic Identification ◽

Maturity Stages ◽

Stock Biomass ◽

Spawning Stock ◽

Macroscopic Identification

Abstract Costa, A. M. 2009. Macroscopic vs. microscopic identification of the maturity stages of female horse mackerel. – ICES Journal of Marine Science, 66: 509–516. The consequences to fisheries management of erroneous macroscopic identification of maturity stages are evaluated. The percentage error in macroscopic identification of maturity stages of female horse mackerel (Trachurus trachurus) from the Portuguese coast was determined and analysed by maturity stage, between the periods January–June and July–December, between research surveys and commercial landings, and between per year and month and by length class, to assess its implications in determination of spawning season, maturity ogives, and spawning-stock biomass. The highest percentage errors in macroscopic identification were between late ripening and partly spent stages, in fish >30 cm, and for all fish collected in 1998 and 2005. Late ripening was generally macroscopically underestimated, and the partly spent stage overestimated. The implications for the information provided to the ICES assessment working group are analysed.

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Fecundity variation in Icelandic summer-spawning herring and implications for reproductive potential

ICES Journal of Marine Science ◽

10.1016/j.icesjms.2005.10.002 ◽

2006 ◽

Vol 63 (3) ◽

pp. 493-503 ◽

Cited By ~ 33

Author(s):

Guðmundur J. Óskarsson ◽

Christopher T. Taggart

Keyword(s):

Egg Production ◽

Reproductive Potential ◽

Clupea Harengus ◽

Maturation Stage ◽

Oocyte Diameter ◽

Potential Fecundity ◽

Residual Variation ◽

Stock Biomass ◽

Spawning Stock ◽

Spawning Time

Abstract An exploration of fish fecundity aimed at estimating the reproductive potential of a stock requires comprehensive and quantitative examinations of the influencing factors. Here, Icelandic summer-spawning herring (Clupea harengus) are used to quantify potential fecundity (FP, number of eggs) and relative fecundity [RFP = FP (body weight − ovary weight)−1] as functions of length (L) and weight (W) in mature prespawning herring. Using a coupled examination of atresia (oocyte degeneration in the ovary) and the maturation stage of oocytes as characterized by size, we show that atresia has no meaningful effect on fecundity estimates if determined near the spawning time. Among prespawning herring, FP is a strong function of L or W (r2 = 0.84 in either case). Fulton's condition factor K (=100WL−3) explains a trivial (1.5%) but significant (p < 0.0001) amount of the residual variation in FP, and appears to have the greatest effect among smaller length classes. RFP is also a function of L (r2 = 0.56), and oocyte diameter explains 36% of the residual variation (p < 0.001). Therefore, stock-specific total egg production in herring can diverge from the assumed proportionality between total egg production and spawning-stock biomass through variations in the length structure of the stock, and to a lesser extent through the condition of prespawning herring.

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