4 North Sea Horse Mackerel: Divisions IVa (Q1 and Q2 ... Reports/Expert Group Report/aco… · VIIe...

ICES WGWIDE REPORT 2015 227

4 North Sea Horse Mackerel: Divisions IVa (Q1 and Q2), IIIa (exclud-ing Western Skagerrak Q3 and Q4), IVb, IVc and VIId

4.1 ICES Advice Applicable to 2015

In 2012, based on ICES approach to data-limited stocks (category 5), ICES advised for 2013 that catches of horse mackerel in Divisions IIIa and IVa first and second quarter, IVb,c, and VIId (North Sea stock) should be no more than 25 500 tonnes, which repre-sented a 20% precautionary reduction to then recent catch levels. In 2013, new data on survey indices available for this stock were considered to not change the perception of the stock and therefore the advice for the fishery in 2014 was the same as the advice for 2013: no more than 25 500 tonnes. Exploratory assessments and improve index anal-yses in 2014, though not conclusive, showed the stock to be in a poor condition. A con-siderable reduction in catches was felt necessary to reduce pressure on the stock. Hence the advise for 2015 was set less than 15 200 tonnes, almost half that of 2014. Discards are known to take place but cannot be quantified; therefore total catches could not be calculated.

The TAC for IVbc and VIId in 2015 was 15 200 tonnes.

4.2 The Fishery in 2014 on the North Sea horse mackerel stock

Based on historical catches taken by the Danish industrial fleet for reduction into fish-meal and fish oil 1970s and 1980s approximately 48% of the EU North Sea horse macke-rel TAC is Danish. Catches were taken in the fourth quarter mainly in Divisions IVb and VIId. The 1990s saw a drop in the value of industrial fish, limited fishing opportu-nities and steep increases in fuel costs, both with influenced the Danish quota uptake.

In 2001, individual quota scheme for a number of species, but not North Sea horse mackerel, was introduced in Denmark. This lead to a rapid restructuring and lower capacity of the Danish fleet, and this combined with decreasing prises of industrial fish led to that the Danish North Sea horse mackerel catches have diminished. Since the 1990’s, a larger portion of catches has been taken in a directed horse mackerel fishery for human consumption by the Dutch freezer-trawler fleet. This is possible because Denmark has traded parts of its quota with the Netherlands for fishing opportunities for other species, however due to the structure of the Danish quota management set-up only a limited amount of quota can be made available for swaps with other coun-tries. These practical implications of the management scheme largely explain the con-sistent underutilisation of the TAC (approximately 50% in 2010—2013) in recent years. However, following the sharp reduction in TAC in 2014, uptake has increased signifi-cantly to above 80% (see Figure 4.2.1).

Catches taken in Divisions IVa and IIIa during the two first quarters and all year in Divisions IVb, IVc and VIId are regarded North Sea horse mackerel (Section 3, Table 3.3.1). In Section 3, Table 3.3.3 shows the reported national catches of this stock from 1997—2014. The catches were relatively low during the period 1982—1997 (not shown) with an average of 18 000 tonnes. The catches increased between 1998 (30 500 tonnes) and 2000 (48 425 tonnes). Between 2000 and 2010, the catches varied between 23 379 and 48 425 tonnes. In 2014 the catch was 13 388 tonnes, with a total of 80% being caught in VIId. Catches by ICES Division are illustrated in Figure 4.2.2 for the period 1982—2014.

228 ICES WGWIDE REPORT 2015

4.3 Biological Data

Catch in Numbers at Age

In 2014, 63% of the landings were sampled. These samples were taken by Netherlands and Dutch observers on UK (England) vessels in all quarters except Q2 (only 8% of the landings occur in this quarter). A total of 19 samples were collected (Section 1.3.1). Sampling coverage in 2014 has decreased compared to 2013. The catch at age data re-mains questionable and, if an analytical assessment is to be carried out in the future, methods for distinguishing landings from the Western stock and the North Sea horse mackerel stock need to be developed.

Table 4.3.1 shows catch numbers by quarter (and annual totals) by area in 2014. Annual catch numbers at age for the whole stock for 1995—2014 are given in Table 4.3.2. Age compositions for the period 1987—1995 are also available and are plotted together with the estimates from 1995—2014 in Figure 4.3.1. However, these are based on samples taken from low numbers of Dutch commercial catches and catches from research ves-sels. These samples cover only a small proportion of the total catch and therefore only give a rough indication of the age composition of the stock. After 1998 catch at age data by area are available (Figure 4.3.3). Since the mid-2000s the majority of the catch has come from VIId.

Cohort structure is generally not clearly detectible in the data. This may partly be due to the shifts in distribution of the fishery. In addition, it may partly be due to age read-ing difficulties, which are a known to be encountered (e.g. Bolle et al., 2011). Most clearly detectable is the relatively large 2001 year class, although it is not clearly present in the catch in all years. There are indications that environmental circumstance may be an important factor (possibly stronger than stock size) contributing to spawning suc-cess in horse mackerel. This is for example illustrated by the largest year classes (1982 and 2001) observed in the Western stock which incidentally were produced at the low-est observed stock sizes. Since 2001 is considered to have been a relatively strong year class in the Western stock as well, it is plausible that circumstances in the North Sea were similar to those in Western areas and also allowed for relatively high spawning success in the North Sea.

Lastly, potential mixing of fish from the Western and North Sea stock in area VIId and VIIe in winter may also confuse the cohort signals. For example, the large recruitment in the Western stock may have led to more of these fish being located in the North Sea stock area as age 1 fish in 2002. In 2015, a research project has been started by IMARES and the Pelagic Freezer-trawler Association (PFA) that aims to clarify the mixing of horse mackerel of the Western and North Sea stocks in the Channel area.

Mean weight at age and mean length at age

Tables 4.3.3 and 4.3.4 show mean weight and length at age by quarter and by area in 2014. The annual average values are also shown in those same tables.

Maturity at age

There is no information available about the maturity at age of the North Sea Horse mackerel stock. Peak spawning in the North Sea falls in May and June (Macer, 1974), and spawning occurs in the coastal regions of the southern North Sea along the coasts of Belgium, the Netherlands, Germany, and Denmark.

Natural mortality

There is no specific information available about natural mortality of this stock.


4.4 Data Exploration

Catch curves

The log-catch numbers were plotted by cohort to estimate the negative gradient of the slope and get an estimate of total mortality (Z). Fully selected ages 3—11 from the 1997—2014 period (when catch at age estimates are considered more representative of the whole fishery) provide complete data for the 1994 to 2003 cohorts (Figure 4.4.1). The estimated negative gradients by cohort (Figure 4.4.2) indicate a high mortality, de-clining towards 2000, before increasing to the previous high level. Recruiting year clas-ses around the turn of the century are thought to be strong, which may explain this reduction in F over those cohorts. However the poor quality of the cohort signals in the data likely make these Z estimates highly uncertain.

Alternative methods to estimate the biomass

In 2002, Ruckert et al. estimated the North Sea horse mackerel biomass based on a ratio estimate that related CPUE data from the IBTS to CPUE data of whiting (Merlangius merlangus). The applied method assumes that length specific catchability of whiting and horse mackerel are the same for the IBTS gear. Subsequently, they use the total biomass of whiting derived from an analytical stock assessment (MSVPA) to estimate the relationship between CPUE and biomass.

Other methods to use information from data-rich stocks to assess the biomass of data poor stocks have recently been suggested by Punt et al. (2011). WGWIDE suggests that these methods should be further investigated to enable stock estimates of the North Sea horse mackerel.

Survey Data

4.4.3.1 IBTS Survey in area IV

Many pelagic species are frequently found close to the bottom during daytime (which is when the IBTS survey operates) and migrate upwards predominantly during the night they are susceptible to semi-pelagic fishing gear and to bottom trawls (Barange et al., 1998). Eaton et al. (1983) argued that horse mackerel of 2 years and older are pre-dominantly demersal in habit. Therefore, in the absence of a targeted survey for this stock, the IBTS is considered a reasonable alternative. IBTS data are also used in the assessment of the southern horse mackerel stock.

IBTS data from quarter 3 were obtained from DATRAS and analysed. Based on a com-parison of IBTS data from 4 quarters in the period 1991—1996, Ruckert et al. (2002) showed that horse mackerel catches in the IBTS were most abundant in the third quar-ter of the year. In contrast to previous years, when during WGWIDE meetings, three indices were derived: (a) for fish < 14 cm, (b) for fish >= 14 cm and < 23 cm and (c) for fish >= 23 cm, the working group in 2013 considered that using an ‘exploitable biomass index’ is most appropriate for the purpose of interpreting trend in the stock.

Commercial catch data show that 2-year old fish and older make up 96% of the land-ings, which roughly coincides with fish of >= 20 cm (see Figure 4.4.3 in WGWIDE, 2014). Index including fish of 20 cm and larger (roughly corresponding to age 2 and older) were therefore derived for the interpretation of stock trend.

To create indices, a subset of ICES rectangles was selected. Rectangles that were not covered by the survey more than once during the period 1991—2012 were excluded from the index area. In 2012, WGWIDE expressed concern that the previously selected index area did not sufficiently cover the distribution area of the stock, especially in


years that the stock would be relatively more abundant and spread out more. Ruckert et al. (2002) also identified a larger distribution area of the North Sea stock. Based on the above, 61 rectangles were identified to be included in the index area as shown in Figure 4.4.4 (in WGWIDE, 2014).

In 2015, using the same methods, an index of the < 20 cm fish in the IBTS survey area was calculated.

All IBTS data were downloaded from DATRAS in July 20151.

4.4.3.2 The French Channel Groundfish Survey (CGFS) in Q4

In order to improve data basis for the North Sea horse mackerel assessment, alternative survey indices have been explored. Previous indices used had only cover the North Sea distribution of the stock, while the majority of catches in recent years have come from the eastern English Channel (VIId). We evaluated the potential contribution of the French Channel Groundfish Survey in VIId (CGFS) in Quarter 4. The CGFS is car-ried out since 1990 and has frequent captures of horse mackerel. Though this survey is conducted in a different quarter to the North Sea IBTS, the observed seasonal migration patterns of horse mackerel indicate that fish move into the channel following quarter 3, so the timing is considered appropriate.

The survey data was downloaded from the IFREMER website2 on 28 August 2015 after contacting the relevant survey coordinator (Franck Coppin). We selected only the horse mackerel data and used the catches by length per half hour tow. We also computed the number of hauls where no horse mackerel was caught.

4.4.3.3 UK Beamtrawl Survey in VIIe (WBEAM) in Q1

The UK Beamtrawl survey in VIIe is carried out in the first quarter. The start of the time series is 2006. It is aimed primarily at flatfish, but catches also some horse macke-rel. However, the catches of horse mackerel are low and infrequent. Overall, only 10% of the hauls had horse mackerel in them. We found that the survey indices for horse mackerel were very different from the trends observed in the IBTS and CGFS. Alt-hough this could be due to the WBEAM survey being held in VIIe (and hence pur-ported to be part of the Western Stock), we believe that the low number of positive hauls also makes this survey less useable as an index of abundance for horse mackerel. This survey has therefore not been included in the analyses below.

Survey analyses: General Linear Modelling approach

Even though survey trawl hauls in the IBTS are supposed to be directly comparable, there still may exist differences in catchability between vessels, especially with species for which the survey was not designed. If the proportion or the geographical distribu-tion of the data collected by the different vessels varies among years, then the vessel effect needs to be accounted for in the computation of the abundance index.

A generalized linear model (GLM) approach accounts for the above mentioned issue in establishing the index. Catches from the survey can be modelled as a linear function of explanatory variables, which may be continuous (depth) or factors (year, vessel, gear

1 http://www.ices.dk/marine-data/data-portals/Pages/DATRAS.aspx 2http://www.ifremer.fr/SIH-indices-campagnes/source/source.action?facade=mancheorientale&zone=ciem7d


type) and offer the possibility to specify a distribution different from the normal distri-bution. The abundance index (corrected for the other potential effects such as vessel effects) can then be obtained from the estimated year effects. Sensitivity tests suggested that the index is robust to the inclusion of new years of data.

In zero inflated GLMs, the zeros (absence of the species) are assumed to result of two different causes: i) the false zeros, corresponding to sampling errors (such as sampling in wrong areas, i.e. outside the distribution area of the species, or using an inadequate technique) and ii) the real zeros, corresponding to sampling in low abundance areas. The zero inflated GLM is then a combination of two models: a model for the probability of occurrence of a false zero multiplied by a model of the count data conditional to not having a false zero.

Where is the expected catch for the trawl haul i, and is the associated var-

iance, is the probability of having a false zero, is the expected catch, conditional to not having a false zero, and k is the dispersion parameter from the negative binomial distribution.

The probability of having a false zero is modelled by a logistic regression, where

The expected number of fish, conditional to not having a false zero is modelled as neg-ative binomial regression :

Using as an offset is a common way of standardizing samples taken by trawl haul of different length and it comes down to modelling the CPUE of the horse mackerel in fish per hour.

Due to changes in vessels conducting the the IBTS, the GLM analysis is only conducted using data since 1998. The year effect from this model fit then represents an index of the relative changes in stock abundance in the index area over time. The GLM analysis was only applied to the 20+ fish in the IBTS survey, and has not yet been applied to the CGFS data. The 20+ cm IBTS GLM index is shown in Table 4.4.1 and Figure 4.4.3.

Survey Analyses: Delta Log-Normal computation of index

As an alternative simple approach to deal with the skewed nature of the data together with its relatively large number of zeros, the mean annual cpue was computed assum-ing a lognormal distribution for the positive values only, together with an additional probability mass at zero. This type of distribution is commonly referred to as the delta-lognormal distribution, and was first discussed by Aitchison (1957). It has been used in various applications since then, and is commonly used in fisheries research (e.g. Pennington, 1996; Fletcher, 2008).

The expected annual index values are computed as the product of the proportion of positive (non-zero) hauls and the mean and variance of the cpue of the positive hauls:

Where: π = the proportion of positive hauls in each year

μ , σ = the mean and variance of the cpue from the positive hauls each year


The proportion of positive hauls, the cpue in the positive hauls and the resultant index values are shown in Table 4.4.1 and the standardised index values for 0—19cm and > 20 cm fish (compared to the mean from 2006—2014) are shown for the IBTS in Figure 4.4.4 and the CGFS in Figure 4.4.4. IBTS values are used from 1992 onwards (following improved standardisation of gears used in the survey) and from 1990 onwards for the CGFS.

Summary of index trends

20+ cm indices

IBTS GLM Index for 20+ horse mackerel decreased steadily over the 2000s. Since 2010 there are some signs of a slight increase in abundance/biomass, however the relative increase in the index is small in comparison to the uncertainty range and the most re-cent value (2014) is among the lowest of the time series.

The IBTS DLN index for 20+ cm fish in the North Sea shows a roughly similar pattern as the GLM index. In the DLN index the reduction is mainly due to the proportion of hauls in which horse mackerel are found decreasing steadily over time, from 74% in 1998 to the lowest observed value of 28% in 2013. 2014 saw a slight increase in non-zero hauls, but the low cpue of non-zero values keeps the index low. From 2008—2013, cpue in the positive hauls increased, but 2014 was the low.

The CGFS DLN index for 20+ cm horse mackerel in the eastern channel shows a strong decline from the early 1990s to the mid-2000s. Since then the index has fluctuated at a relatively low level. In contrast to the IBTS, the 2014 index value shows an increase, and is the highest value since 2006. The proportion of non-zero hauls from this survey is generally very high, though the last four years have been at a slightly lower level than previous years.

0—19cm indices

The IBTS DLN index for 0—19 cm fish indicates high numbers in 2002 and 2003 and more or less fluctuating numbers for the other years. The 2013 and 2014 values are slightly higher indicating a potential increase in recruits in this area.

The CGFS DLN index for 0—19 cm fish does not show the high index values from the early 2000s as observed in the IBTS index in the North Sea. Following higher values in the early 1990s, index values have been fluctuating at a lower level. The last two values are amongst the highest in the last ten years.

Conclusions on survey indices

Although the IBTS and CGFS survey indices for horse mackerel, roughly indicate a similar trend (higher values at the beginning of the time series, lower value towards the end of the time series), there are noticeable differences in the timing and the scale of the decline.

Preliminary examinations of how the juvenile (0—19cm) indices relate to subsequent exploitable abundance (20+ cm) do not indicate strong linkages. The very high juvenile indices in the early 2000s in the IBTS were not subsequently picked up in the exploita-ble component. Hence while increases in the juvenile indices are encouraging, whether these lead to increases in the exploitable component of the stock need to be confirmed in the future with observations in the 20+ cm indices.

Further work is needed to better explore the consistency of the surveys in dealing with recommendations for horse mackerel catches.


Ongoing work

To improve the knowledge base for North Sea horse mackerel, a project has been initi-ated in 2015 by the Pelagic Freezer-trawler Association (PFA) together with IMARES and University College Dublin. The project aims to 1) provide additional information on stock boundaries and mixing between North Sea and Western horse mackerel, and 2) explore or develop potential new abundance indices for North Sea horse mackerel.

To address stock boundaries and mixing, the project will explore the potential of uti-lizing skippers’ catch information (with a very high spatial resolution and detailed in-formation on size composition) to enhance the understanding on the mixing of stocks in the areas VIIe, VIId and the Southern North Sea. In addition, horse mackerel samples will be taken when the horse mackerel are separated in the summer spawning season (in the North Sea and Western waters) and when they are feeding in the winter season (in the Channel area). Genetic and chemical techniques will be used to detect the con-tribution of the different spawning components to the catches in winter.

To improve the abundance indicators, the project will explore additional (existing) sur-vey data, like the CGFS that has been reported to WGWIDE in the section above. We also want to explore the potential application of a commercial fishery search-time in-dex. Horse mackerel is fished while it is very close to the bottom in relatively dispersed, small schools. The fishery is mostly executed using long hauls and there may be exten-sive search time involved. Handled in an appropriate statistical framework, taking into account the nature of the fishery and other factors such as seasonality and alternative fishing opportunities, the search time and catch rates could provide for an indication of changes in stock size over time. Catch rates in areas VIIe, VIId and southern North Sea will be analysed from skippers’ private logbooks.

It is expected that the results of the research project can be presented to WGWIDE in 2016.

4.5 Basis for 2015 Advice

The new index data for the IBTS and the additional indices from the CGFS do not change the perception that the adult North Sea horse mackerel stock remains at a low level. There are some potential signs of improved recruitment, but additional years of data are necessary to confirm that these will lead to an increased exploitable biomass in future.

There was a large reduction in advised catches in 2014, and ICES considered that this advice should remain valid for at least 2 years since any potential changes in stock status are highly uncertain. As a result no change in advice is proposed for 2015: catches should not exceed 15 200 tonnes.

4.6 Management considerations

In the past, Division VIId was included in the management area for Western horse mackerel together with Divisions IIa, VIIa–c, VIIe–k, VIIIa, VIIIb, VIIId, VIIIe, Subarea VI, EU and international waters of Division Vb, and international waters of Subareas XII and XIV. ICES considers Division VIId to be part of the North Sea horse mackerel distribution area. Since 2010, the EU TAC for the North Sea area has included Divisions IVb,c and VIId. Considering that a majority of the catches are taken in Division VIId, the total of North Sea horse mackerel catches are effectively constrained by the TAC since the realignment of the management areas in 2010.

Catches in Divisions IIIa (Western Skagerrak) and IVa in quarters 3 and 4 are consid-ered to be from the Western horse mackerel stock, while catches in quarters 1 and 2 are considered to be from the North Sea horse mackerel stock. Catches in area IVa and IIIa


are variable. In recent years only Norway has had significant catches in this area, but these are only taken in some years (see Figure 4.2.1).

4.7 References

Aitchison, J. 1955. On the distribution of a positive random variable having a discrete probability mass at the origin. J Am Sta Assoc 50:901–908.

Barange, M., Pillar, S. C., and Hampton, I. 1998. Distribution patterns, stock size and life-history strategies of Cape horse mackerel Trachurus trachurus capensis, based on bottom trawl and acoustic surveys. South African Journal of Marine Science, 19: 433–447.

Bolle, L.J., Abaunza, P., Albrecht, C., Dijkman-Dulkes, A., Dueñas, C., Gentschouw, G., Gill, H., Holst, G., Moreira, A., Mullins, E., Rico, I., Rijs, S., Smith, T., Thaarup, A., Ulleweit, J. 2011 . Report of the Horse Mackerel Exchange and Workshop 2006. CVO report: 11.007.Eaton, D. R. 1983. Scad in the North-East Atlantic. Laboratory Leaflet, Ministry of Agriculture, Fish-eries and Food, Directorate of Fisheries Research, Lowestoft, 56: 20 pp.

Eaton, D. R. 1983. Scad in the North-East Atlantic. Lab. Leafl., MAFF Direct. Fish. Res., Lowestoft (56): 20pp.

Fletcher, D., 2008. Confidence intervals for the mean of the delta-lognormal distribution. Environ Ecol Stat (2008) 15:175–189.

Macer, C.T. 1974. The reproductive biology of the horse mackerel Trachurus trachurus (L.) in the North Sea and English Channel. J. Fish Biol., 6(4): 415-438.

Pennington, M., 1996. Estimating the mean and variance from highly skewed marine data. Fish-ery Bulletin 94:498-505.

Punt, A. E., Smith, D. C., and Smith, A. D. M. 2011. Among-stock comparisons for improving stock assessments of data-poor stocks: the “Robin Hood” approach. – ICES Journal of Ma-rine Science, 68: 972–981.

Rückert, C., Floeter, J., A. Temming. 2002: An estimate of horse mackerel biomass in the North Sea, 1991-1997. - ICES Journal of Marine Science, 59: 120-130.


Table 4.3.1. North Sea Horse Mackerel stock. Catch in numbers (1000) by quarter and area in 2014.

1Q Ages IIIa IVa IVb IVc VIId Total 0

1 0.00 0.00 0.00 0.00 1262.54 1262.54

2 0.19 0.17 36.68 37.82 682.71 757.57

3 1.52 1.35 286.87 295.80 1443.56 2029.11

4 2.10 1.86 395.60 407.91 2485.20 3292.66

5 1.54 1.37 290.80 299.85 1333.90 1927.47

6 1.90 1.69 358.92 370.09 1340.34 2072.94

7 0.38 0.33 70.74 72.94 712.63 857.01

8 0.76 0.68 144.09 148.58 605.53 899.64

9 0.19 0.17 36.68 37.82 221.00 295.87

10 0.58 0.51 108.72 112.11 507.95 729.87

11 0.38 0.34 72.05 74.29 424.20 571.25

12 0.00 0.00 0.00 0.00 157.82 157.82

13 0.00 0.00 0.00 0.00 0.00 0.00

14 0.00 0.00 0.00 0.00 122.42 122.42

15+ 0.00 0.00 0.00 0.00 59.23 59.23

Sum 9.55 8.46 1801.15 1857.20 11359.04 15035.40


1 0.0 0.0 0.0 0.0 332.3 332.3

2 0.0 0.0 0.0 48.9 188.4 237.3

3 0.0 0.0 0.0 382.3 375.1 757.5

4 0.0 0.2 2.2 527.3 641.1 1170.8

5 0.2 0.8 11.0 387.6 342.2 741.8

6 0.3 1.1 15.4 478.4 343.8 839.1

7 0.1 0.5 6.6 94.3 182.8 284.3

8 0.2 0.6 8.8 192.0 155.3 357.0

9 0.0 0.0 0.0 48.9 56.7 105.6

10 0.0 0.2 2.2 144.9 130.3 277.6

11 0.0 0.2 2.2 96.0 108.8 207.3

12 0.0 0.2 2.2 0.0 40.5 42.9

13 0.1 0.3 4.4 0.0 0.0 4.8

14 0.0 0.0 0.0 0.0 31.4 31.4

15+ 0.0 0.0 0.0 0.0 15.2 15.2

Sum 1.2 4.0 55.2 2400.6 2944.0 5404.9


3Q Ages IIIa IVa IVb IVc VIId Total

0

1 0.0 101.2 1480.5 1581.7

2 0.0 159.0 2326.5 2485.5 3 0.0 57.8 846.0 903.8

4 3.5 53.2 634.5 691.1

5 17.4 49.0 0.0 66.4

6 24.3 68.6 0.0 92.9

7 10.4 29.4 0.0 39.8

8 13.9 39.2 0.0 53.1

9 0.0 0.0 0.0 0.0

10 3.5 9.8 0.0 13.3

11 3.5 9.8 0.0 13.3

12 3.5 9.8 0.0 13.3

13 6.9 19.6 0.0 26.5

14 0.0 0.0 0.0 0.0

15+ 0.0 0.0 0.0 0.0

Sum 86.8 606.3 5287.6 5980.7


1 8.1 2110.0 10144.8 12263.0

2 6.5 1688.0 10084.8 11779.3

3 0.3 90.1 4943.1 5033.6

4 14.0 3646.3 21413.0 25073.3

5 10.9 2830.7 8222.7 11064.3

6 6.4 1654.8 2407.4 4068.5

7 0.7 180.2 1367.5 1548.4

8 1.6 422.0 1655.4 2079.1

9 0.7 180.2 357.5 538.4

10 0.0 0.0 0.0 0.0

11 0.0 0.0 537.0 537.0

12 0.0 0.0 195.2 195.2

13 0.0 0.0 0.0 0.0

14 0.0 0.0 0.0 0.0

15+ 0.0 0.0 0.0 0.0

Sum 49.1 12802.3 61328.5 74180.0


1-4Q Ages IIIa IVa IVb IVc VIId Total 0 1 0.0 0.0 8.1 2211.2 13220.2 15439.5

2 0.2 0.2 43.2 1933.7 13282.5 15259.7

3 1.5 1.3 287.2 826.0 7607.8 8724.0

4 2.1 2.0 415.3 4634.6 25173.9 30227.9

5 1.8 2.2 330.1 3567.2 9898.7 13799.9

6 2.2 2.8 405.0 2571.9 4091.5 7073.5

7 0.5 0.8 88.5 376.8 2262.9 2729.5

8 1.0 1.3 168.4 801.8 2416.3 3388.8

9 0.2 0.2 37.4 266.9 635.2 939.9

10 0.6 0.7 114.4 266.8 638.3 1020.8

11 0.4 0.5 77.7 180.1 1070.0 1328.8

12 0.0 0.2 5.7 9.8 393.5 409.1

13 0.1 0.3 11.4 19.6 0.0 31.4

14 0.0 0.0 0.0 0.0 153.8 153.8

15+ 0.0 0.0 0.0 0.0 74.4 74.4

Sum 10.8 12.4 1992.2 17666.4 80919.1 100601.0


Table 4.3.2. Catch in numbers at age (millions), weight at age (kg) and length at age (cm) for the North Sea horse mackerel 1995-2014.

millions Catch number

Age 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

1 1.8 4.6 12.6 2.3 12.4 70.2 12.8 60.4 13.8 15.7 52.4 5.0 3.4 1.7 34.1 3.3 8.1 9.5 7.6 15.4

2 3.1 13.8 27.2 22.1 31.5 78.0 36.4 16.8 56.2 17.5 29.8 23.7 15.5 8.8 13.9 22.5 23.3 24.3 10.0 15.3

3 7.2 11.0 14.1 36.7 23.1 28.4 174.3 19.3 23.4 34.4 27.8 61.5 22.8 36.1 28.4 10.7 76.5 20.4 21.3 8.7

4 10.3 11.9 14.9 38.8 17.6 21.4 87.8 11.9 33.2 14.5 12.6 40.9 82.6 16.7 22.1 15.7 37.3 40.2 22.2 30.2

5 12.1 9.6 14.6 20.8 23.1 31.3 18.5 5.6 26.9 27.8 16.7 73.0 71.2 36.4 17.3 23.7 14.6 25.8 27.1 13.8

6 13.2 12.5 12.4 12.1 26.2 19.6 11.5 5.8 10.6 20.2 5.2 23.4 30.5 36.1 16.3 15.9 9.9 20.8 6.0 7.1

7 11.4 8.0 10.1 14.0 20.6 19.5 18.3 5.5 6.3 10.6 2.9 13.7 23.9 27.3 21.5 27.6 5.8 3.1 7.2 2.7

8 12.6 6.6 8.6 10.8 21.8 9.0 14.7 10.5 9.6 3.8 2.4 5.9 17.3 21.9 47.1 5.6 6.0 5.0 4.3 3.4

9 7.3 1.5 2.5 8.3 12.9 11.5 10.2 6.3 10.9 5.4 3.8 1.6 7.9 10.2 11.2 6.3 3.4 4.6 4.0 0.9

10 5.9 5.3 0.8 4.0 8.2 9.0 10.0 6.8 1.5 11.0 5.8 1.4 1.7 7.5 9.3 8.3 10.1 1.5 5.4 1.0

11 0.0 0.3 0.3 2.7 2.1 7.0 9.6 5.1 3.4 6.2 2.3 0.2 0.6 1.9 7.2 2.9 6.9 0.5 3.7 1.3

12 8.8 1.3 0.3 0.7 0.4 3.1 5.4 3.0 3.3 4.5 4.1 1.7 0.2 2.1 3.7 0.3 3.6 0.1 1.0 0.4

13 0.2 8.9 1.8 1.4 1.6 3.7 2.2 2.3 6.2 2.5 0.6 0.7 0.4 0.3 0.3 0.8 0.6 0.0

14 4.4 8.0 1.4 0.3 3.8 2.0 1.3 3.4 2.3 9.9 1.0 0.7 2.4 0.9 0.2 0.3 0.2 0.0 0.2

15+ 5.1 4.0 12.2 5.8 2.7 4.7 8.5 9.6 0.8 1.0 6.1 1.1 0.5 0.1 0.1


kg weight

Age 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

1 0.076 0.107 0.063 0.063 0.063 0.075 0.055 0.066 0.073 0.076 0.079 0.069 0.073 0.063 0.063 0.077 0.06 0.069 0.08 0.078

2 0.126 0.123 0.102 0.102 0.102 0.101 0.072 0.095 0.105 0.104 0.077 0.095 0.082 0.096 0.096 0.101 0.092 0.09 0.1 0.110

3 0.125 0.143 0.126 0.126 0.126 0.136 0.071 0.129 0.123 0.12 0.103 0.116 0.105 0.109 0.109 0.115 0.098 0.118 0.11 0.113

4 0.133 0.156 0.142 0.142 0.142 0.152 0.082 0.154 0.137 0.147 0.132 0.124 0.115 0.125 0.125 0.138 0.116 0.142 0.14 0.135

5 0.146 0.177 0.16 0.16 0.16 0.166 0.12 0.172 0.166 0.174 0.158 0.141 0.13 0.145 0.145 0.154 0.146 0.152 0.17 0.144

6 0.164 0.187 0.175 0.175 0.175 0.194 0.183 0.195 0.181 0.198 0.196 0.177 0.164 0.161 0.161 0.18 0.167 0.172 0.18 0.177

7 0.161 0.203 0.199 0.199 0.199 0.198 0.197 0.216 0.195 0.225 0.251 0.21 0.191 0.194 0.194 0.207 0.188 0.183 0.2 0.184

8 0.178 0.195 0.231 0.231 0.231 0.213 0.201 0.227 0.212 0.229 0.27 0.244 0.197 0.221 0.221 0.195 0.206 0.188 0.22 0.201

9 0.165 0.218 0.25 0.25 0.25 0.247 0.235 0.228 0.238 0.256 0.28 0.231 0.256 0.286 0.286 0.241 0.3 0.212 0.22 0.222

10 0.173 0.241 0.259 0.259 0.259 0.28 0.246 0.251 0.259 0.291 0.291 0.284 0.258 0.296 0.296 0.225 0.324 0.204 0.23 0.220

11 0.317 0.307 0.3 0.3 0.3 0.279 0.26 0.302 0.245 0.301 0.344 0.237 0.517 0.273 0.273 0.286 0.341 0.274 0.24 0.264

12 0.233 0.211 0.329 0.329 0.329 0.342 0.286 0.292 0.295 0.3 0.361 0.257 0.279 0.309 0.309 0.227 0.402 0.195 0.26 0.287

13 0.241 0.258 0.367 0.367 0.367 0.318 0.287 0.318 0.356 0.302 0.332 0.268 0.338 0.375 0.375 0.288 0.405 0.26 0.252

14 0.348 0.277 0.299 0.299 0.299 0.325 0.295 0.319 0.319 0.338 0.376 0.291 0.414 0.277 0.277 0.315 0.415 0.187 0.56 0.408

15+ 0.348 0.277 0.36 0.36 0.36 0.332 0.336 0.39 0.38 0.401 0.367 0.402 0.389 0.389 0.358 0.473 0.34 0.273


cm length

Age 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

1 19.2 19.2 19.2 19.2 19.2 19.0 18.7 17.1 20.2 19.8 20.5 19.9 20.1 20.0 20.0 20.8 19.2 19.9 20.9 20.4

2 22.0 22.0 22.0 22.0 22.0 21.5 20.4 21.4 22.4 22.2 21.5 21.9 20.8 21.6 21.6 22.6 21.7 21.7 22.4 22.9

3 23.5 23.5 23.5 23.5 23.5 23.9 20.6 22.9 23.8 23.6 23.0 23.4 22.6 23.2 23.2 23.8 23.1 23.5 23.5 23.5

4 24.8 24.8 24.8 24.8 24.8 24.9 21.3 24.9 24.6 25.2 24.7 24.1 23.6 24.1 24.1 25.0 24.5 25.0 25.3 24.8

5 25.5 25.5 25.5 25.5 25.5 26.0 25.0 26.2 26.2 26.6 25.5 25.4 24.4 25.6 25.6 25.7 25.9 25.7 27.0 25.4

6 26.4 26.4 26.4 26.4 26.4 27.8 27.4 26.6 27.3 27.5 27.8 27.0 26.6 26.3 26.3 27.0 27.5 27.0 27.1 27.3

7 27.2 27.2 27.2 27.2 27.2 28.3 28.0 27.4 28.2 28.9 30.4 28.5 27.8 28.1 28.1 28.2 28.0 27.1 28.3 27.5

8 29.2 29.2 29.2 29.2 29.2 28.6 28.4 28.2 29.0 29.2 31.2 29.8 28.1 28.8 28.8 28.2 27.7 27.1 28.9 28.0

9 29.5 29.5 29.5 29.5 29.5 30.0 29.7 29.2 29.9 30.5 31.8 30.6 30.1 31.2 31.2 30.2 31.9 28.6 29.2 28.8

10 29.5 29.5 29.5 29.5 29.5 31.3 30.2 30.8 30.8 31.5 32.3 31.6 31.2 31.8 31.8 29.9 32.5 28.0 29.5 29.2

11 30.6 30.6 30.6 30.6 30.6 31.4 30.7 32.5 30.8 32.0 34.4 31.2 39.5 31.6 31.6 32.1 33.3 30.1 30.0 30.7

12 32.1 32.1 32.1 32.1 32.1 33.7 32.0 33.8 31.9 31.8 36.2 30.8 31.5 32.2 32.2 29.6 34.5 27.5 30.4 30.6

13 33.3 33.3 33.3 33.3 33.3 33.5 31.7 33.8 32.9 32.0 34.2 32.1 33.4 33.9 33.9 31.8 35.2 32.1 30.0

14 31.1 31.1 31.1 31.1 31.1 33.4 32.1 32.4 32.7 33.0 34.9 32.2 34.5 32.3 32.3 33.0 36.0 27.5 38.5 36.0

15+ 32.5 32.5 32.5 32.5 32.5 33.4 33.4 34.4 34.6 34.8 35.4 35.4 35.1 35.1 34.7 37.0 34.2 32.5


Table 4.3.3. North Sea Horse Mackerel stock. Mean weight at age (kg) in the catch by quarter and area in 2014.

1Q Ages IIIa IVa IVb IVc VIId Total 0 1 0.000 0.000 0.000 0.000 0.094 0.094 2 0.053 0.053 0.053 0.053 0.077 0.074 3 0.094 0.094 0.094 0.094 0.096 0.095 4 0.106 0.106 0.106 0.106 0.117 0.114 5 0.140 0.140 0.140 0.140 0.145 0.143 6 0.166 0.166 0.166 0.166 0.162 0.163 7 0.148 0.148 0.148 0.148 0.164 0.161 8 0.215 0.215 0.215 0.215 0.211 0.212 9 0.186 0.186 0.186 0.186 0.208 0.203

10 0.201 0.201 0.201 0.201 0.230 0.221

11 0.287 0.287 0.287 0.287 0.300 0.296

12 0.000 0.000 0.000 0.000 0.246 0.246

13 0.000 0.000 0.000 0.000 0.000 -

14 0.000 0.000 0.000 0.000 0.408 0.408

15+ 0.000 0.000 0.000 0.000 0.273 0.273


10 0.285 0.285 0.285 0.201 0.230 0.215

11 0.282 0.282 0.282 0.287 0.300 0.294

12 0.391 0.391 0.391 0.000 0.246 0.254

13 0.252 0.252 0.252 0.000 0.000 0.252

14 0.000 0.000 0.000 0.000 0.408 0.408

15+ 0.000 0.000 0.000 0.000 0.273 0.273


3Q Ages IIIa IVa IVb IVc VIId Total 0 1 0.000 0.063 0.063 0.063 2 0.000 0.113 0.113 0.113 3 0.000 0.124 0.124 0.124 4 0.177 0.146 0.139 0.140 5 0.197 0.197 0.000 0.197 6 0.222 0.222 0.000 0.222 7 0.230 0.230 0.000 0.230 8 0.262 0.262 0.000 0.262 9 0.000 0.000 0.000

10 0.285 0.285 0.000 0.285

11 0.282 0.282 0.000 0.282

12 0.391 0.391 0.000 0.391

13 0.252 0.252 0.000 0.252

14 0.000 0.000 0.000

15+ 0.000 0.000 0.000

4Q Ages IIIa IVa IVb IVc VIId Total 0 0.062 0.062 0.082 0.078 1 0.102 0.102 0.114 0.112 2 0.141 0.141 0.120 0.121 3 0.127 0.127 0.141 0.139 4 0.135 0.135 0.147 0.144 5 0.170 0.170 0.195 0.185 6 0.215 0.215 0.199 0.200 7 0.166 0.166 0.199 0.192 8 0.209 0.209 0.252 0.238 9 0.000 0.000 0.000

10 0.000 0.000 0.218 0.218

11 0.000 0.000 0.321 0.321

12 0.000 0.000 0.000

13 0.000 0.000 0.000

14 0.000 0.000 0.000

15+ 0.062 0.062 0.082 0.078

0.101 0.082 0.175 0.174


1-4Q

Ages IIIa IVa IVb IVc VIId Total

0

1 0.000 0.000 0.062 0.062 0.081 0.078

2 0.053 0.053 0.060 0.101 0.112 0.110

3 0.094 0.094 0.094 0.101 0.115 0.113

4 0.108 0.112 0.108 0.123 0.138 0.135

5 0.148 0.161 0.145 0.137 0.147 0.144

6 0.175 0.188 0.172 0.170 0.181 0.177

7 0.171 0.196 0.164 0.186 0.185 0.184

8 0.225 0.238 0.221 0.192 0.203 0.201

9 0.186 0.186 0.186 0.202 0.233 0.222

10 0.208 0.221 0.205 0.204 0.230 0.220

11 0.287 0.286 0.287 0.287 0.259 0.264

12 0.391 0.391 0.391 0.391 0.283 0.287

13 0.252 0.252 0.252 0.252 0.000 0.252

14 0.000 0.000 0.000 0.000 0.408 0.408

15+ 0.000 0.000 0.000 0.000 0.273 0.273


Table 4.3.4. North Sea Horse Mackerel stock. Mean length (cm) at age in the catch by quarter and area in 2014.


10 28.8 28.8 28.8 28.8 29.4 29.2

11 32.0 32.0 32.0 32.0 31.9 31.9

12 0.0 0.0 0.0 0.0 29.5 29.5

13 0.0 0.0 0.0 0.0 0.0 NA

14 0.0 0.0 0.0 0.0 36.0 36.0

15+ 0.0 0.0 0.0 0.0 32.5 32.5

Mean


10 29.5 29.5 29.5 28.8 29.4 29.1

11 28.5 28.5 28.5 32.0 31.9 31.9

12 33.5 33.5 33.5 0.0 29.5 29.7

13 30.0 30.0 30.0 0.0 0.0 30.0

14 0.0 0.0 0.0 0.0 36.0 36.0

15+ 0.0 0.0 0.0 0.0 32.5 32.5


3Q


0

1 0.0 18.9 18.9 18.9

2 0.0 22.4 22.4 22.4

3 0.0 23.8 23.8 23.8

4 26.5 24.6 24.2 24.2

5 26.7 26.7 0.0 26.7

6 28.1 28.1 0.0 28.1

7 27.8 27.8 0.0 27.8

8 29.5 29.5 0.0 29.5

9 0.0 0.0 0.0 NA

10 29.5 29.5 0.0 29.5

11 28.5 28.5 0.0 28.5

12 33.5 33.5 0.0 33.5

13 30.0 30.0 0.0 30.0

14 0.0 0.0 0.0 NA

15+ 0.0 0.0 0.0 NA

4Q


0

1 19.9 19.9 20.5 20.4

2 23.3 23.3 23.2 23.2

3 25.5 25.5 23.9 23.9

4 24.5 24.5 25.1 25.0

5 25.3 25.3 25.3 25.3

6 27.2 27.2 28.0 27.7

7 28.0 28.0 28.1 28.1

8 27.5 27.5 27.5 27.5

9 28.5 28.5 30.1 29.5

10 0.0 0.0 0.0 NA

11 0.0 0.0 29.1 29.1

12 0.0 0.0 31.5 31.5

13 0.0 0.0 0.0 NA

14 0.0 0.0 0.0 NA

15+ 0.0 0.0 0.0 NA

Mean 17.67 13.07 24.85 26.26


1-4Q Ages IIIa IVa IVb IVc VIId Total 0 1 0.0 0.0 19.9 19.9 20.5 20.4 2 19.5 19.5 20.1 23.0 22.9 22.9 3 22.9 22.9 22.9 23.2 23.6 23.5 4 23.6 23.7 23.6 24.3 24.9 24.8 5 25.7 26.0 25.6 25.4 25.4 25.4 6 27.0 27.3 26.9 27.1 27.4 27.3 7 26.9 27.3 26.8 27.3 27.6 27.5 8 29.1 29.3 29.1 28.2 27.9 28.0 9 27.5 27.5 27.5 28.2 29.1 28.8

10 28.9 29.0 28.9 28.8 29.4 29.2

11 31.6 30.9 31.8 31.8 30.5 30.7

12 33.5 33.5 33.5 33.5 30.5 30.6

13 30.0 30.0 30.0 30.0 0.0 30.0

14 0.0 0.0 0.0 0.0 36.0 36.0

15+ 0.0 0.0 0.0 0.0 32.5 32.5


Table 4.4.1. North Sea horse mackerel. Relative indices of abundance derived from the IBTS Q3 data (North Sea only, no VIId included) and the French Channel Groundfish Survey in Q4 (CGFS, VIId). The GLM index uses a zero inflated negative binomial model to predict the trend in abundance of exploitable (≥ 20 cm) horse mackerel in the North Sea. The DLN indices is derived as the product of the CPUE in the positive (non-zero) hauls and the proportion of positive hauls.

IBTS Q3 IV CGFS Q4 VIId

Year GLM 20+ cm

GLM 5%

GLM 95%

DLN 0—19 cm

DLN 20+ cm

Proportion non-Zero

DLN 0—19 cm

DLN 20+ cm

Proportion non-Zero

1990 6.17 1.28 0.91

1991 3.39 5.03 1.00

1992 478 68823 0.78 12.88 3.53 0.98

1993 279 58569 0.77 4.71 0.98 0.98

1994 554 51375 0.76 5.20 3.66 0.98

1995 104 54688 0.65 8.64 2.07 0.94

1996 208 98715 0.73 2.85 1.87 0.94

1997 1184 28743 0.70 2.33 1.54 0.97

1998 1.89 0.94 3.83 245 24014 0.74 1.88 1.39 0.98

1999 3.99 1.85 8.62 774 8005 0.68 3.27 1.10 0.95

2000 9.15 3.99 20.99 241 38015 0.64 3.71 0.41 0.94

2001 1.51 0.69 3.32 420 31967 0.60 2.81 1.21 0.95

2002 3.47 1.61 7.48 2073 16119 0.64 2.63 0.46 0.96

2003 2.70 1.25 5.83 2396 6363 0.67 4.31 0.42 0.98

2004 1.68 0.78 3.66 283 5083 0.66 3.08 0.52 0.96

2005 2.70 1.17 6.21 450 7417 0.53 2.09 0.73 0.92

2006 2.15 0.97 4.77 288 10923 0.53 1.60 0.98 0.92

2007 0.38 0.17 0.88 193 2044 0.51 1.56 0.53 0.88

2008 1.22 0.50 2.99 257 789 0.51 0.72 0.24 0.86

2009 0.92 0.39 2.17 234 1500 0.50 1.86 0.20 0.92


2010 0.43 0.18 1.02 213 2361 0.49 4.43 0.23 0.90

2011 0.94 0.39 2.24 103 1554 0.39 0.79 0.32 0.80

2012 1.01 0.40 2.54 108 5562 0.32 0.79 0.14 0.87

2013 1.61 0.61 4.21 313 6301 0.28 3.48 0.28 0.86

2014 0.34 0.14 0.83 303 366 0.46 4.86 0.61 0.89


Figure 4.2.1. North Sea horse mackerel. Utilisation of quota by country.

Figure 4.2.2 North Sea horse mackerel. Catch by ICES Division for 1982—2014.

0

2000

4000

6000

8000

10000

12000

14000

16000

Quota versus catch in 2014

Quota 2014

Catch 2014


A

B

Figure 4.3.1 North Sea horse mackerel. A- Age distribution in the catch for 1995—2014. B- Bub-bleplot of age distribution in the catch in all areas for 1987—2014. Area of bubbles is proportional to the catch number. Note that age 15 is a plus group.


Figure 4.3.2. North Sea horse mackerel. Bubbleplot of age distribution in the catch in all areas for 1987—2014. The area of bubbles is proportional to the catch number. Note that age 15 is a plus group.



Figure 4.3.3. North Sea horse mackerel. Bubbleplots of age distribution in the catch by area for 1998—2014. The area of bubbles is proportional to the catch number. Note that age 15 is a plus group.

Figure 4.4.1. North Sea Horse Mackerel. Catch curves for the 1994 to 2003 cohorts, ages from 3 to 11. Values plotted are the log(catch) values for each cohort in each year. The negative slope of these curves estimates total mortality (Z) in the cohort.

Figure 4.4.2. North Sea Horse Mackerel. Cohort total mortality (Z), negative gradients of the 1994—2003 cohort catch curves.


Figure 4.4.3. North Sea horse mackerel. GLM abundance indices. Top: Abundance index, the shaded area indicates the 95% confidence intervals for the estimated index values. Bottom: The abundance index standardised to the 2006—2014 mean, with 3yr running mean trendline.


Figure 4.4.4. Delta-lornormal indices derived from the IBTS survey in the North Sea (IVbc). Top: Young fish (~ages 0 and 1); Bottom: older fish (~age 2+). The abundance index values are standard-ised to 2006—2014 mean, with 3yr running mean trendline.


Figure 4.4.5. Delta-lognormal indices derived from the CGFS survey in the eastern English Channel (VIId). Top: Young fish (~ages 0 and 1); Bottom: older fish (~age 2+). The abundance index values are standardised to the 2006-2014 mean, with 3yr running mean trendline.

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