Interpol
Simon Thomas and Dave Uren
26 February, 2025
1 FISP pollack introduction
Pollack represents an economically and socially important fishery across the UK. Recreational and commercial fishers have highlighted a decline in Pollack (Pollachius pollachius) across the English channel. ICES stock assessments have similarly indicated there is insufficient evidence to identify exploitation and population trends, however have highlighted a decline of 72% in commercial landings since 1968. Data collection is required on life history parameters, abundance and spatial ecology to ensure sustainability in commercial and recreational fisheries.
2 Data summary
2.1 Catch, size and effort data
The pollack FISP project is a collaboration between charter skippers and scientists to address ongoing concerns of both the recreational and commercial fleet regarding the stock status for the species.15 skippers have already collected length data on 16207 pollack from 816 trips, this will allow the assessment of stock abundance, composition and recruitment. 18.58 % of pollack were returned alive.
The total catch during this time period was 32.89 tonnes of which 2.73 tonnes was returned alive.
The mean size of P. pollachius captured was 56.19 cm, equating to 3.36 years of age. The size distribution is shown in Figure 1) .
In 2023 there were 6278 pollack captured from 334 trips.This equates to 11.7 tonnes of fish. The mean size of P. pollachius captured during 2023 was 53.8 cm, equating to 3.12 years of age.
During the 2023 spawning period (January to the end of April) there were 1146 pollack captured from 64 trips.There were 2.29 tonnes of pollack caught during this period with a mean size of 54.13 cm, equating to 3.26 years of age.
From the first of May until June 30th there were 3654 pollack captured from 153 trips.There were 7.03 tonnes of pollack caught during this period with a mean size of 54.49 cm, equating to 3.19 years of age.There were 49 otoliths collected from 24 fish.
From the first of July until September 30th there were 905 pollack captured from 74 trips.There were 1.58 tonnes of pollack caught during this period with a mean size of 53.8 cm, equating to 3.04 years of age.There were 67 otoliths collected from 34 fish.There were 9 sampling trips. The direct value of the P. pollachius fishery to the 15 skippers, during this period is £59200 equating to £40/ kg.
From the first of October until 31st of December 2023 there were 573 pollack captured from 43 trips.There were 0.8 tonnes of pollack caught during this period with a mean size of 48.79 cm, equating to 2.52 years of age.There were 92 otoliths collected from 46 fish.There were 7 sampling trips. The direct value of the P. pollachius fishery to the 15 skippers, during this period is £34400 equating to £45/ kg.
From the first of January until 31st of March 2024 there were 400 pollack captured from 22 trips.There were 0.95 tonnes of pollack caught during this period with a mean size of 60.4 cm, equating to 3.84 years of age.There were 0 otoliths collected from 0 fish.There were 0 sampling trips. The direct value of the P. pollachius fishery to the 15 skippers, during this period is £18700 equating to £20/ kg.
From the first of April 2024 until 30/6/2024 there were 4468 pollack captured from 171 trips.There were 10.3 tonnes of pollack caught during this period with a mean size of 59.46 cm, equating to 3.74 years of age.There were 144 otoliths collected from 72 fish.There were 13 sampling trips. The direct value of the P. pollachius fishery to the 15 skippers, during this period is £145350 equating to £14/ kg.
From the first of June 2024 until 30 September 2024 there were 1033 pollack captured from 50 trips.There were 2.05 tonnes of pollack caught during this period with a mean size of 56.99 cm, equating to 3.35 years of age.There were 6 otoliths collected from 3 fish.There were 1 sampling trips. The direct value of the P. pollachius fishery to the 15 skippers, during this period is £42500 equating to £21/ kg.
From the first of October 2024 until 2025-02-26 there were 473 pollack captured from 25 trips.There were 1.04 tonnes of pollack caught during this period with a mean size of 58.38 cm, equating to 3.6 years of age.There were 6 otoliths collected from 1419 fish.There were 0 sampling trips. The direct value of the P. pollachius fishery to the 15 skippers, during this period is £21250 equating to £20/ kg.
The percentage of male fish found from 15864 fish sexed was 85.9 %
There have been 358 otoliths collected from 179 fish as of 2025-02-26.
The direct value of the P. pollachius fishery to the 15 skippers, as of 2025-02-26 is £652800 equating to £23/ kg. This is an approximate direct value and does not account for indirect value such as accommodation, tackle, fuel and food for the anglers.
So far 202 pollack have been recorded from historical recreational angling data dating back to 1972-03-03 until 2023-09-15. This data came from 14 angling clubs and logbooks.
Figure 1: Size distribution of P. pollachius captured in ICES sea area viie Normal distributions are indicated by red lines.
Size distribution of P. pollachius varied across ICES sub-rectangles, with larger fish seen more commonly in areas to the west and the south of ICES sea area viie ( Figure 2).
The median size of P. pollachius captured was 58 cm (SD =14.63), equating to 3.3 years of age (SD =1.69). There was a significant difference in size of P. pollachius captured between wreck and reef marks (Table 1.)
Figure 2: Size distribution of P. pollachius captured in ICES sea area viie Normal distributions are indicated by red lines.
Figure 3: Age distribution of P. pollachius captured in ICES sea area viie from April 2022 to May 2023. Normal distributions are indicated by red lines.
Figure 4: Figure 4. Age distribution of P. pollachius captured in ICES sea area viie from April 2022 to may 2023 by ICES sub-rectangle. Normal distributions are indicated by red lines.
| Df | Sum Sq | Mean Sq | F value | Pr(>F) |
|---|---|---|---|---|
| 1 | 92808.5 | 92808.501 | 445.521 | 0 |
| 16205 | 3375733.7 | 208.314 | NA | NA |
P. pollachius sizes followed a normal distribution ( Figure 1). The lack of evidence for knife edge selection suggest a degree of non-specificity of the gear used. The maximum sized fish captured during the study period was 114 cm and the the minimum size was 1 cm.
Figure 5: Q-Q plot for P. pollachius size distribution. Solid red line indicates theoretical normal distribution.
P. pollachius age distribution does not follow a normal distribution (Figure 4.) and is positively skewed. The mean age is 3.36 years (Stdev 1.69 years) with the median age of 3.3 years.The positive skew in age distribution is more obvious in fish captured from wrecks (Figure 2.). However as the age is calculated from a rearrangement of the von Bertalanffy equation,
\(Age=ln(1-Length/ Linf))/-K +T0\)
this result may be an artifact and needs to be validated by otolith analysis.
Table. 2. Catch Per Unit Effort (CPUE (Kg/Trip)) per month| Month | Median | SD_dev | Mean | Max | Min |
|---|---|---|---|---|---|
| 1 | 19.62 | 23.18 | 26.90 | 73.84 | 0.88 |
| 2 | 15.41 | 25.76 | 26.26 | 88.74 | 0.00 |
| 3 | 37.60 | 61.67 | 57.55 | 234.07 | 0.00 |
| 4 | 32.71 | 53.23 | 46.25 | 275.05 | 0.00 |
| 5 | 36.94 | 35.37 | 46.46 | 167.14 | 0.00 |
| 6 | 44.27 | 51.71 | 52.75 | 374.92 | 0.00 |
| 7 | 24.57 | 27.14 | 29.87 | 156.22 | 0.28 |
| 8 | 17.44 | 26.93 | 25.41 | 134.53 | 0.21 |
| 9 | 16.30 | 29.27 | 22.92 | 190.10 | 0.00 |
| 10 | 23.94 | 46.35 | 33.49 | 216.77 | 1.94 |
| 11 | 9.84 | 26.06 | 20.36 | 94.55 | 0.19 |
| 12 | 11.99 | 23.23 | 19.58 | 103.27 | 0.03 |
2.1.1 Catch Per Unit Effort
Raw Catch Per Unit Effort (median Kg/ Trip) showed an increasing trend during February, which was sustained until June when catches decreased during the summer months. The raw median CPUE per trip peaked in March with a nadir in August (Figure 5.). The adjusted CPUE (Kg/trip/time spent targeting P. pollachius) peaked in March, with a nadir in September (Figure 6.).Correcting for numbers of anglers produced confusing results, as the relationship between angler numbers and catches is non-linear, due to disturbance of the shoal by additional fishing gear.
Table. 3 Adjusted CPUE (Kg/Trip/Angler) per month
| Month | CPUE | Confint | Upper | Lower |
|---|---|---|---|---|
| 1 | 2.97 | 2.29 | 5.25 | 0.68 |
| 2 | 4.16 | 2.91 | 7.07 | 1.24 |
| 3 | 5.79 | 3.34 | 9.13 | 2.45 |
| 4 | 6.09 | 2.61 | 8.70 | 3.49 |
| 5 | 5.89 | 1.90 | 7.79 | 3.99 |
| 6 | 6.49 | 1.50 | 7.99 | 4.99 |
| 7 | 5.19 | 1.43 | 6.62 | 3.76 |
| 8 | 4.45 | 1.40 | 5.85 | 3.05 |
| 9 | 3.01 | 1.13 | 4.14 | 1.88 |
| 10 | 3.32 | 3.07 | 6.40 | 0.25 |
| 11 | 1.80 | 1.65 | 3.45 | 0.15 |
| 12 | 2.53 | 1.74 | 4.27 | 0.79 |
Figure 6: Q-Q plot for P. pollachius age distribution. Solid red line indicates theoretical normal distribution.
Figure 7: Raw median monthly CPUE (Kg/Trips). Ribbon indicates 95% confidence intervals.
Figure 8: Figure 8. Median CPUE (Kg/ trip) adjusted for fishing time spent targeting P. pollachius . Ribbon indicates 95% confidence intervals
2.1.2 Yearly Catch Per Unit Effort
Figure 9: Histogram of Catch Per Unit Effort per trip between years.Red line indicates theoretical normal distribution
Figure 10: Box plot comparison of mean CPUE (Kg/ trip) between years. Text indicate mean CPUE values
2.1.3 Standardised Catch Per Unit Effort
2.1.4 Von Bertalanffy growth parameters through ELEFAN
Von Bertalanffy growth parameters were obtained using ELEFAN for a subgroup of fish captured from May 2022 and May 2023. 95% confidence intervals were obtained by using the Jack knife procedure The results are shown is Table 4. The mean values for Linf (88.57 cm), K (0.168 year\(^{-1}\)) and PhiL (3.105) are similar to values from Southern Ireland in Fishbase. Natural mortality (M) was calculated as 0.25 year\(^{-1}\) (+/- 0.014).Total mortality (Z) was 0.616 year\(^{-1}\) giving a fishing mortality of 0.361 year\(^{-1}\) (+/- 0.014).
Table 4. Von Bertalanffy constants for P. pollachius from ICES sea area viie from May 2022 and May 2023.| Five | Mean | Ninety_five | |
|---|---|---|---|
| Linf | 84.610 | 88.570 | 92.510 |
| K | 0.150 | 0.168 | 0.180 |
| t_anchor | 0.260 | 0.614 | 0.970 |
| PhiL | 3.070 | 3.105 | 3.140 |
| M | 0.241 | 0.255 | 0.269 |
| Z | 0.616 | 0.616 | 0.616 |
| F | 0.375 | 0.361 | 0.347 |
Figure 11: Size distribution of P. pollachius by mark from April 2022 to 22/6/2023. Horizontal red lines show the mean size for wreck (Black) and reef (Red) caught fish.
The size distribution of through the study period is shown in figure 7. The largest fish are associated with the deeper wreck marks and the size of fish captured from wrecks decreased from April to July 2022 before increasing during January 2023. A boat from Penzance started providing data in January 2023 and much of the increase in sizes of wreck caught fish can be attributed to this new skipper fishing the far west of ICES sea area viie.
In both 2022 and 2023, the peak size and numbers of reef-caught fish peaked during May, which coincides with the arrival of large amounts of prey species on these reef systems, mainly Ammodytes and Hyperoplus sp. especially the sand launce Hyperoplus lanceolatus.
2.1.5 Hierarchical Generalised Additive Models (HGAM)
In order to determine differences in P. pollachius catches across ICES sea area viie, Hierarchical Generalised Additive Models (HGAM) were used to test five hypothesis.
There is a common pattern of catches across the area for the year.
There is a common pattern of catches across the area for the year, but with variations between ICES rectangles which share a common pattern.
There is a common pattern of catches across the area for the year, but with variations between ICES rectangles have different patterns.
There are no common patterns of catches across the area for the year.
To test these hypotheses the following models were used:
P0: NULL model: sqrt (CPUE)~s(ICES_Rectangle, bs=“re”)
P1: Square root (CPUE)~s(Day of Year, k=30)+s(ICES_Rectangle, bs=“re”)
P2: Square root (CPUE)~s(Day of Year, k=50,m=2)+s(Day of Year,ICES_Rectangle, bs=“fs” ,m=2)
P3: Square root (CPUE)~s(Day of Year, k=50)+s(Day of Year,ICES_Rectangle, k = 5, bs=“fs”,m=2)
P4: Square root (CPUE)~s(Day of Year, ICES_Rectangle, k=5, bs=“fs”, m=2)
nb. K= degree of “wiggliness, m=2 Marginal Thin Plate Regressive Spline basis for term is penalised on the squared second derivative.
Table 5. ANOVA of HGAM models for P. pollachius CPUE from ICES sea area viie.
## Analysis of Deviance Table
##
## Model 1: sqrt(Trip_CPUE) ~ s(ICES_Rec, bs = "re")
## Model 2: sqrt(Trip_CPUE) ~ s(DOY, k = 30) + s(ICES_Rec, bs = "re")
## Model 3: sqrt(Trip_CPUE) ~ s(DOY, k = 50, m = 2) + s(DOY, ICES_Rec, bs = "fs",
## m = 2)
## Model 4: sqrt(Trip_CPUE) ~ s(DOY, k = 50) + s(DOY, ICES_Rec, k = 5, bs = "fs",
## m = 2) + ICES_Rec
## Model 5: sqrt(Trip_CPUE) ~ s(DOY, ICES_Rec, k = 5, bs = "fs", m = 2)
## Resid. Df Resid. Dev Df Deviance F Pr(>F)
## 1 851.93 8883.0
## 2 847.04 8104.0 4.88997 778.98 17.9849 < 2.2e-16 ***
## 3 815.26 7293.0 31.78741 811.04 2.8806 3.164e-07 ***
## 4 828.24 7549.9 -12.98321 -256.89 2.2338 0.007184 **
## 5 828.68 7575.9 -0.43733 -26.00 6.7111 0.029769 *
## ---
## Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1Table 5. indicates that the HGAM models are significantly different from the Null model (P<0.05) and model P2 has the best fit to the data (Table 6.) and that the residuals for this data are (square root) normally distributed (Figure 8.), with some positive skew. A summary of the model is shown in Table 7.
This suggests that catches of P. pollachius share a common pattern across ICES sea area viie but there are different some variations in catches present between ICES rectangles.This is suggestive of a common stock which disperses differently in geographical areas (Hypothesis 3.). However, the data are still sparse in some areas and the errors large, so these findings should be treated with caution.
Table 6. Comparison of GAM models for P. pollachius CPUE from ICES sea area viie.
##
## Pollack CPUE models
## ================================================================
## Dependent variable:
## -------------------------------------------------
## sqrt(Trip_CPUE)
## GAM
## (continuous)
## Null P1 P2 P3 P4
## (1) (2) (3) (4) (5)
## ----------------------------------------------------------------
## ICES_Rec28_E5
##
##
## ----------------------------------------------------------------
## AIC 4471 4399.7 4360.3 4371.6 4373.1
## Observations 861 861 861 861 861
## Adjusted R2 0.09 0.16 0.22 0.21 0.20
## Log Likelihood -2,235.52 -2,199.84 -2,180.13 -2,185.82 -2,186.54
## UBRE 10.51 9.68 9.26 9.38 9.39
## ================================================================
Figure 12: QQ plot of pearson residuals from GAM model P2 for P. pollachius CPUE from ICES sea area viie.
Figure 13: HGAM model P2 left: Day of Year; Right: Day of Year by ICES rectangle for P. pollachius CPUE from ICES sea area viie.
There is considerable uncertainty in the model P2 at both extremes of the year (Figure 9) which reflects the restricted data due to inclement weather conditions during this period. The deviance explained by model P2 is 0.3 with an adjusted R2 of 0.224
Table 7. Summary of HGAM model P2
2.2 Historical information
2.2.1 North Wales
There were 208 P. pollachius captured from ICES sea area viia during this study of which 85 were identified as female and 94 identified as males. The sex of fish was not ascertained for 29 fish.
The overal mean total length of fish sampled during the study was 51.88 cm and the median total length was 51.65 cm.
The total lengths (cm) by sex are shown in Table.8.
Table 8. Summary length data (cm) by sex of P. pollachius captured from ICES sea area viia during 1989| Sex | Mean | Median | StDev |
|---|---|---|---|
| Female | 51.68 | 52.69 | 9.99 |
| Male | 52.05 | 51.65 | 10.07 |
Figure 14: Weight distribution (kg) of P. pollachius from ICES sea area viia during 1989.
Figure 15: Maturity ogive for P. pollachius from ICES sea area viia during 1989. blue dotted line indicates length at 50% maturity and black dotted line at 90% maturity
The length which 50% of pollack were mature at was 45.49 cm and 90% maturity occurred at 50.04 cm (Figure 11.)
Figure 16: Maturity ogive for P. pollachius by sex from ICES sea area viia during 1989. blue dotted line indicates length at 50% maturity and black dotted line at 90% marturity.
Figure 17: Confidence intervals for growth from VB statistics from P. pollachius captured from ICES sea area viia during 1989. Grey shading indicate 95% confidence intervals. Points are otolith age data
The von Bertalanffy growth constants obtained from otolith-derived ages are shown in Table 9.
Table 9. Von Bertalanffy constants for P. pollachius from ICES sea area viia during 1989
## Nonlinear regression model
## model: tl ~ vb(age, Linf, K, t0)
## data: wf14T
## Linf K t0
## 97.3006 0.1679 -0.8444
## residual sum-of-squares: 3107
##
## Number of iterations to convergence: 5
## Achieved convergence tolerance: 1.833e-062.2.2 Commercial landings data
2.2.2.1 Plymouth
Between 2013 to 2025-02-26 the have been 1.8535^{4} tonnes of pollack landed commercially at Plymouth fish market. Of this, 46.29% of fish were landed during the spawning season (January until the end of March).
The weekly landings are from 2013 until 2025-02-26 are shown in figure 16 and a GAM model (sqrt(Catch~s(Month)+s(Year)+te(Month, Year))) illustrates that the landings peaked in the first three months of the year and that landings have declined during this time period (Figure 17 and 18)
Figure 18: Weekly Commercial landings of P. pollachius from the port of Plymouth from 2013 until 2023
Table 10 Summary of Plymouth landings data (kg) from 2013 until 2025-02-26
| Year | Landings | Median_Landings | SD_dev_Landings | mean_Landings | Max | Min |
|---|---|---|---|---|---|---|
| 2013 | 224318 | 2764.0 | 4366.495 | 4313.808 | 20578 | 5 |
| 2014 | 269637 | 2361.0 | 7103.199 | 5185.327 | 35038 | 148 |
| 2015 | 203025 | 2532.0 | 4444.819 | 4060.500 | 23743 | 98 |
| 2016 | 241277 | 3127.0 | 5374.556 | 4730.922 | 24270 | 435 |
| 2017 | 212363 | 3156.0 | 4528.336 | 4006.849 | 23670 | 120 |
| 2018 | 141751 | 1824.0 | 2656.790 | 2779.431 | 10925 | 179 |
| 2019 | 112927 | 1900.5 | 1524.737 | 2171.673 | 6017 | 152 |
| 2020 | 132183 | 1948.5 | 2671.949 | 2541.981 | 12042 | 33 |
| 2021 | 154434 | 1508.0 | 3693.129 | 2913.849 | 14834 | 0 |
| 2022 | 81503 | 1196.0 | 1814.586 | 1734.106 | 8615 | 0 |
| 2023 | 80077 | 699.0 | 2102.517 | 1404.860 | 12136 | 0 |
```
Figure 19: GAM model partial effect of year of landings of P. pollachius from Commercial landings from the port of Plymouth from 2013 until 2023
The GAM model explained 0.44 % of the deviance observed in the data with and pseudoR^2 value of 0.42. The P values for all smooths were less than 0.001.
The landings of P. pollachius to Plymouth fish market decreased after 2016, before levelling out in 2020 and falling further since (Figure 17.). Although most of the landings occurred during the spawning season (January until March, Figure 18), the reduction in landings was driven by a reduction in the quantity of landings during these months (Figure 19.). However, the catches during the summer months increased slightly, which probably was driven by an increase in commercial rod and line fishing for the species when present on the inshore reef systems off Plymouth.
It is noted that landings are a poor proxy for biomass as they are susceptible to market forces and targeting preferences as well as stock biomass
Figure 20: GAM model partial effect of month from Commercial landings from the port of Plymouth from 2013 until 2023
Figure 21: GAM model tensor product of month/ Year smooth from Commercial landings from the port of Plymouth from 2013 until 2023
2.2.2.2 Plymouth, Newlyn and Brixham 2008-2019
From 2008-2019 there were 7226.44 tonnes of P. pollachius landed in Newlyn, Brixham and Plymouth, worth £1.9085105^{7} at a mean Cost/kg of £2.64. The data is summarised in Table. 10.
Figure 22: Landings of P. pollachius from 2008-2019 by port
Figure 23: Landings of P. pollachius from 2008-2019 by gear type
Figure 24: Landings of P. pollachius from 2008-2019 by Vessel length
| Port | Year | Landings | Median_Landings | SD_dev_Landings | mean_Landings | Max | Min |
|---|---|---|---|---|---|---|---|
| Brixham | 2008 | 96.267 | 0.194 | 2.908 | 1.284 | 16.786 | 0.001 |
| Brixham | 2009 | 78.938 | 0.273 | 2.129 | 1.067 | 11.477 | 0.000 |
| Brixham | 2010 | 75.902 | 0.131 | 1.995 | 0.883 | 11.218 | 0.000 |
| Brixham | 2011 | 65.312 | 0.101 | 1.391 | 0.710 | 7.313 | 0.001 |
| Brixham | 2012 | 79.289 | 0.131 | 1.825 | 0.881 | 10.839 | 0.001 |
| Brixham | 2013 | 89.820 | 0.174 | 2.396 | 1.082 | 16.218 | 0.001 |
| Brixham | 2014 | 85.839 | 0.086 | 3.069 | 1.145 | 19.196 | 0.000 |
| Brixham | 2015 | 61.238 | 0.189 | 1.792 | 0.795 | 11.329 | 0.002 |
| Brixham | 2016 | 76.632 | 0.156 | 1.506 | 0.891 | 7.785 | 0.001 |
| Brixham | 2017 | 62.190 | 0.051 | 2.266 | 0.749 | 15.920 | 0.001 |
| Brixham | 2018 | 41.012 | 0.031 | 1.198 | 0.482 | 6.835 | 0.001 |
| Brixham | 2019 | 38.214 | 0.043 | 1.174 | 0.490 | 5.904 | 0.000 |
| Newlyn | 2008 | 582.561 | 0.525 | 19.278 | 6.774 | 104.121 | 0.003 |
| Newlyn | 2009 | 534.594 | 0.322 | 15.098 | 5.569 | 99.109 | 0.002 |
| Newlyn | 2010 | 441.058 | 0.391 | 14.485 | 5.012 | 103.938 | 0.001 |
| Newlyn | 2011 | 530.389 | 0.306 | 19.023 | 5.703 | 131.780 | 0.001 |
| Newlyn | 2012 | 470.951 | 0.604 | 13.392 | 5.292 | 92.430 | 0.002 |
| Newlyn | 2013 | 445.638 | 0.328 | 10.555 | 4.126 | 65.813 | 0.001 |
| Newlyn | 2014 | 545.796 | 0.591 | 15.489 | 5.998 | 95.884 | 0.001 |
| Newlyn | 2015 | 367.656 | 0.312 | 8.608 | 4.226 | 47.911 | 0.001 |
| Newlyn | 2016 | 579.425 | 0.525 | 15.424 | 5.737 | 98.663 | 0.002 |
| Newlyn | 2017 | 277.790 | 0.550 | 5.721 | 2.987 | 28.445 | 0.000 |
| Newlyn | 2018 | 263.450 | 0.638 | 5.286 | 2.864 | 33.340 | 0.001 |
| Newlyn | 2019 | 263.020 | 0.440 | 5.091 | 2.579 | 29.781 | 0.001 |
| Plymouth | 2008 | 97.377 | 0.191 | 3.839 | 1.411 | 21.982 | 0.001 |
| Plymouth | 2009 | 98.199 | 0.135 | 4.858 | 1.309 | 39.770 | 0.001 |
| Plymouth | 2010 | 76.843 | 0.142 | 2.783 | 0.817 | 21.924 | 0.001 |
| Plymouth | 2011 | 87.022 | 0.201 | 3.130 | 1.102 | 19.374 | 0.000 |
| Plymouth | 2012 | 87.122 | 0.171 | 2.453 | 0.990 | 17.177 | 0.001 |
| Plymouth | 2013 | 85.910 | 0.205 | 1.989 | 0.914 | 15.039 | 0.001 |
| Plymouth | 2014 | 111.116 | 0.204 | 3.469 | 1.307 | 21.977 | 0.001 |
| Plymouth | 2015 | 72.562 | 0.081 | 2.353 | 0.854 | 18.644 | 0.001 |
| Plymouth | 2016 | 94.111 | 0.068 | 2.988 | 1.001 | 19.966 | 0.001 |
| Plymouth | 2017 | 117.476 | 0.048 | 4.273 | 1.566 | 31.242 | 0.001 |
| Plymouth | 2018 | 74.292 | 0.024 | 1.858 | 0.884 | 9.150 | 0.001 |
| Plymouth | 2019 | 71.432 | 0.027 | 2.356 | 0.882 | 13.885 | 0.001 |
To model the trends over time and to account for port, gear type and length group, the following GAM model was used: log10(weight+1)~s(Month)+s(Year)+te(Month, Year)+Gear type + Port+ boat length Group, where s is a Thin plate spline and te is the tensor product. Gear type, port and boat length group were factors. The model explained 0.48 % of the deviance with an R^2 of 0.48.
Figure 25: Year effect of GAM model for Landings of P. pollachius from 2008-2019 from Plymouth, Brixham and Newlyn
Figure 26: Month effect of GAM model for Landings of P. pollachius from 2008-2019 from Plymouth, Brixham and Newlyn
Figure 27: Month/ Year tensor product of GAM model for Landings of P. pollachius from 2008-2019 from Plymouth, Brixham and Newlyn
Figure 28: Landings by gear type from GAM model for Landings of P. pollachius from 2008-2019 from Plymouth, Brixham and Newlyn
Figure 29: Landings by Port from GAM model for Landings of P. pollachius from 2008-2019 from Plymouth, Brixham and Newlyn
Figure 30: Landings by vessel length from GAM model for Landings of P. pollachius from 2008-2019 from Plymouth, Brixham and Newlyn
2.2.3 Historical recreational angling data from club records and skipper logbooks.
There has been an apparent decline is sizes of P. pollachius captured in ICES sea area Viie in the last 10 years from both wreck and reef marks (Figure 31.). Fish of a maximum size of around 10 kg were found intermittently until 2015, since then only one fish of this weight has been recorded. This is inline with anecdotal information from both commercial and recreational fishermen.
It is noted that the British boat caught angling record for P. pollachius of 13.25 Kg was set in 1987, whilst the shore caught record of 8.27 Kg was captured in 1986.The heaviest specimen of P. pollachius recorded in this data set was 12.01 Kg was captured in 1986-08-23.
Figure 31: Largest P. pollachius landed since 1984 from wreck and reef marks from logbook and club data. Lines indicate trends obtained from GAM. Grey shaded areas are 95% confidence intervals