Survey trends of fish species in Shetland coastal waters Macdonald, P., Napier, I.

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1 Survey trends of fish species in Shetland coastal waters Macdonald, P., Napier, I. Introduction NAFC Marine Centre undertakes an annual fish survey of the inshore waters around the Shetland Isles, up to 12 nautical miles offshore. The survey was initiated in 2011 with the intention of providing an independent index of the relative abundance of fish species in the waters around Shetland. The survey also aims to determine the extent of inter-annual variability in the local distribution of commercially important species. Each year the survey is resourced from core NAFC funds, with the costs partially defrayed through the sale of marketable fish. The aim of this report is to provide a summary of the data collected during the most recent year of the study (2014) and, where possible, to provide an analysis of inter-annual variability in the size structure and abundance of a number of commercially important fish species. Material and Methods Data collection The survey was carried out using the NAFC Marine Centre s fishing vessel Atlantia II (LK 502). The survey gear used was a standard four-panel box trawl with a headline length of 23 metres (75 ), a fishing circle of 400 meshes (of 160 mm) and a small-mesh (~22 mm) cod-end (Figure 1). The trawl doors were Bison No. 6½ (Edwin Ashworth Ltd., York) and the sweeps were 92 metres long (50 fathoms) with 37 metres of doubles and 55 metres of singles. Door spread and trawl headline height were continuously recorded using a Notus net monitoring system throughout the duration of each tow. All tows were undertaken during August and September. A total of 25 pre-defined stations across 5 survey areas were sampled (Figure 2). Each tow typically lasted for one hour. The duration of the tow was recorded from the time the doors and net were steady and open on the seabed, until the trawl winch was engaged to haul the gear. Tows of less than 1 hour were undertaken at a small number of stations where there was not enough ground available to tow for an hour. The fish caught in each tow were sorted by species and weighed. Selected species - generally those of commercial importance - were measured (Table 1). Sub-samples were weighed and/or measured where necessary. Due to resource constraints no otoliths were collected in Data analysis Catch rates were calculated for each species in each tow as the total live weight caught per hour of fishing (kg/hr). Average catch rates and the standard errors of the mean were then

2 calculated for each species in each survey area and overall. For haddock and whiting, catch rates were calculated separately for small fish where there was a distinct gap between length classes, i.e. in 2014 there were a large number of haddock at lengths cm and no fish at lengths cm. Weights were calculated from the numbers at length using established parameters for the growth equation (W = al b ) 1. Figure 1 Net plan of NAFC survey box trawl used in inshore fish survey. Comparison of length frequency distributions Numbers at length were raised to the total catch for species where subsampling took place. Annual length frequency distributions were compared using the two sample Kolmogorov- Smirnov (K-S) test. Due to the nature of survey data collection, basic K-S test assumptions that 1 Parameters were taken from the weight-length calculator spreadsheet used by Marine Scotland Science s Marine Laboratory.

3 observations are collected at random and independent of each other are violated because individuals are collected in clusters (hauls). To account for this, a randomization test using hauls rather than individual fish as the primary sampling unit was used to derive the null probability distribution using the Fishmethods package in R (Nelson, 2014). Trends in relative abundance Relative abundance of individual species were determined using the Fishmethods package in R (Nelson, 2014). Pennington (1985) noted that the expected value of an abundance index is assumed to be proportional to the actual population. However, in many surveys this index is highly variable and is often a combination of an unobservable signal component, reflecting actual changes in the population, and a noise component resulting from within-survey sampling variability and other long term factors. In order to reduce the variance within the index of abundance, the underlying signal generated by the population is calculated by estimating parameters for a first difference, moving average model of order 1 from time series of mean catch per tow data for each species, following the time series method described by Pennington (1986). Fitted values are calculated from the model residuals and the estimate of theta. This methodology presently has limited use due to the relatively short length of the time series. It is included here to present the basis for assessing trends in relative abundance as the time series increases. Comparison of annual catch rates Catch rates of individual species were compared between years using the one-way repeated measures ANOVA with rank transformation using the nlme package in R (Pinhero et al., 2015). Catch rates were rank transformed prior to analysis to account for potential violations of ANOVA assumptions. Where appropriate, the post hoc Tukey test was used to determine which years differed significantly using the Multcomp package (Hothorn et al., 2010). Table 1 Summary of sampling protocol for fish species caught during the Shetland Inshore Fish Survey. Species Cod Haddock Saithe Whiting Hake Lemon Sole Ling Megrim Monkfish Plaice Witch Skates & Rays Sampling Protocol Total catch weight Lengths Other Species - Total catch weight

4 mile limt North West Fetlar Firth 60.5 The Bay Burra Haaf Lerwick-South Figure 2 Positions of individual tows made during the Shetland Inshore Fish Survey (blue lines), in relation to the survey areas (shaded).

5 Results Total survey catch overview Ten days of surveying were carried out between 21st August and 16th September Twenty six tows were made, of which one was excluded as the net was badly torn. Of the remaining 25 valid tows, which totalled almost 25 hours in duration, six tows each were made in the Burra Haaf and The Bay areas, five each in the Fetlar Firth and Lerwick South areas, and three in the North West (Figure 2). A total of 9.5 tonnes of fish composed of 40 different species were caught, of which 10,471 fish of 17 species were measured (Table 2). The overall catch rate of commercial whitefish species in 2014 was higher than in any previous year, and almost double that in 2012 (84% greater) (Figure 3). The catch rates were similar between the different areas surveyed (Figure 4); the variability in catch rates between tows within the same area were generally greater than the differences between the areas. Results for individual species (where adequate data exists) are summarised below. Figure 3 Overall catch rate of principal commercial species in 2014 compared with previous survey years. Nb. species included are cod, haddock, hake, lemon sole, ling, megrim, monkfish, plaice, saithe, skates & rays, whiting & witch. +/- s.e. bars are also shown.

6 Table 2 Species recorded, measured and weighed during the 2014 survey. Common name Scientific name Total wt. (kg) No. of fish measured Cod Gadus morhua 1, Plaice Pleuronectes platessa 1, ,717* Dogfish - Lesser-Spotted Scyliorhinus canicula 1, Haddock Melanogrammus aeglefinus ,489* Whiting Merlangius merlangus ,225* Pout - Norway Trispoterus esmarkii Gurnard - Grey Eutrigla gurnardus Ray - Cuckoo Raja naevus Argentine Argentina sphyraena Monkfish Lophius spp Lemon Sole Microstomus kitt Dab - Common Limanda limanda Ray - Thornback Raja clavata Squid Loligo spp Gurnard - Red Chelidonichthys cuculus Skate - Common Dipturus batis Hake Merluccius merluccius Queen Scallops Aequipecten opercularis Ray - Spotted Raja montagui Poor Cod Trisopterus minutus Megrim Lepidorhombus whiffiagonis Dab - Long Rough Hipploglossoides platessoides Herring Clupea harengus Horse Mackerel Trachurus trachurus Mackerel Scomber scombrus Saithe Pollachius virens Ling Molva molva Witch Glyptocephalus cynoglossus Crabs Brown Cancer pagurus Dogfish Spur Squalus acanthias John Dory Zeus faber Sandeel Ammodytes spp Ray Shagreen Leucoraja fullonica Ray Sandy Leucoraja circularis Nephrops Nephrops norvegicus Blue Whiting Micromesistius poutassou Dragonet Callionymus lyra Solenette Buglossidium luteum Sprat Sprattus sprattus Redfish Sebastes spp Totals 9,424 10,471 * indicates catches that were sub-sampled.

7 Figure 4 Average catch rates of the principal commercial whitefish species during the 2014 survey. Nb. species included are cod, haddock, hake, lemon sole, ling, megrim, monkfish, plaice, saithe, skates & rays, whiting & witch. +/- s.e. bars are also shown. Cod Annual numbers at length for cod are shown in Figure 5. There was a significant difference in length frequency distributions between 2013 vs 2011 and 2014 (p<0.05) (Table 3). In 2014 there was a significant difference (p<0.05) in length frequency distributions between Fetlar and the North West survey areas. There was no significant difference between any other areas (Table 4). Relative abundance plots for cod are shown for all areas combined and each area individually (Figure 6). Annual catch rates of cod are shown in Figure 7. There was no significant difference in catch rates of cod between years (F (3, 72) = 1.54, p>0.05). There was a considerable amount of variation in cod cpue across the survey areas in 2014 (Figure 7).

8 Figure 5 Annual numbers at length for cod, combined for all survey areas.

9 Table 3 Annual comparison of total length frequency distributions for the main commercial species. Species Years Cod Haddock Whiting Saithe Plaice L. Sole Megrim Monkfish Hake 2011 vs *** vs * 0.363*** *** *** *** vs *** 0.495*** ** *** vs *** * * * 2012 vs *** 0.378* *** vs * 0.725*** 0.411* * 0.248*** 0.389* D values from Kolmogorov-Smirnoff test shown. Significance levels: * p<0.05, ** p<0.01, *** p<0.001.

10 Table 4 Comparison of length frequency distributions across the survey area for Species Area Cod Haddock Whiting Plaice L. Sole Monkfish Bay vs Fetlar Bay vs Haaf Bay vs Lerwick Bay vs NW * Fetlar vs Haaf *** Fetlar vs Lerwick * Fetlar vs NW 0.628* Haaf vs Lerwick * Haaf vs NW Lerwick vs NW D values from Kolmogorov-Smirnoff test shown. Significance levels: * p<0.05, ** p<0.01, *** p< Figure 6 Relative abundance plots for cod for all areas combined and for each individual survey area. Nb. Log-transformed average catch per tow index (o) and fitted values (-) are shown.

11 Figure 7 Annual catch rates of cod across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown). Haddock Annual numbers at length for haddock are shown in Figure 8. There was a significant difference in length frequency distributions between all years (p<0.001) (Table 3). There was also evidence of a strong year class (<20 cm) in 2014 compared to previous years. In 2014 there was a significant difference (p<0.05) in length frequency distributions between Fetlar and the Haaf and Lerwick survey areas (Table 4). There was no significant difference between any other areas. Relative abundance plots for haddock are shown for all areas combined and each survey area individually (Figure 9). Annual catch rates of haddock are shown in Figure 10. There was a significant difference in catch rates of haddock between years (F (3, 72) = 5.82, p<0.01). A post hoc Tukey test showed that 2011 was significantly higher from all other years at p<0.01. There was no significant difference between other years. There was a considerable amount of variation in haddock cpue across the survey areas (Figure 10).

12 Figure 8 Annual numbers at length for haddock, combined for all survey areas. Nb. Different scales are used on the y axes to adequately display numbers at length.

13 Figure 9 Relative abundance plots for haddock for all areas combined and for each individual survey area. Nb. Log-transformed average catch per tow index (o) and fitted values (-) are shown. Figure 10 Annual catch rates of haddock across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown).

14 Whiting Annual numbers at length for whiting are shown in Figure 11. There was a significant difference in length frequency distributions between 2014 and all other years (Table 3). There was also evidence of a strong year class (<20 cm) in 2014 compared to previous years. In 2014 there was no significant difference (p>0.05) in length frequency distributions between any survey areas (Table 4). Relative abundance plots for whiting are shown for all areas combined and each survey area individually (Figure 12). Annual catch rates of whiting are shown in Figure 13. There was a significant difference in catch rates of whiting between years (F (3, 72) = 2.93, p<0.05). A post hoc Tukey test showed that 2011 and 2014 were significantly different at p<0.05. There was no significant difference between other years. There was a considerable amount of variation in whiting cpue across the survey areas (Figure 13).

15 Figure 11 Annual numbers at length for whiting, combined for all survey areas.

16 Figure 12 Relative abundance plots for whiting for all areas combined and for each individual survey area. Nb. There was insufficient data available for North West. Log-transformed average catch per tow index (o) and fitted values (-) are shown. Figure 13 Annual catch rates of whiting across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown).

17 Plaice Annual numbers at length for plaice are shown in Figure 14. There was no significant difference in length frequency distributions between years (Table 3). In 2014 there was no significant difference (p>0.05) in length frequency distributions between any survey areas (Table 4). Relative abundance plots for plaice are shown for all areas combined and each survey area individually (Figure 15). Annual catch rates of plaice are shown in Figure 16. There was no significant difference in catch rates of plaice between years (F (3, 72) = 1.73, p>0.05). There was a considerable amount of variation in plaice cpue across the survey areas (Figure 16).

18 Figure 14 Annual numbers at length for plaice, combined for all survey areas.

19 Figure 15 Relative abundance plots for plaice for all areas combined and for each individual survey area. Nb. Log-transformed average catch per tow index (o) and fitted values (-) are shown. Figure 16 Annual catch rates of plaice across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown).

20 Lemon sole Annual numbers at length for lemon sole are shown in Figure 17. There was a significant difference in length frequency distributions between years (Table 3). In 2014 there was a significant difference in length frequency distribution (p<0.05) between The Bay and North West survey areas (Table 4). Relative abundance plots for lemon sole are shown for all areas combined and each survey area individually (Figure 18). Annual catch rates of lemon sole are shown in Figure 19. There was a significant difference in catch rates of lemon sole between years (F (3, 72) = 6.01, p=0.001). A post hoc Tukey test showed that 2011 was significantly different from 2013 and 2014 at p<0.01. There was no significant difference between other years. Catch rates of lemon sole in 2014 were higher on the west side of Shetland than on the east side (Figure 19).

21 Figure 17 Annual numbers at length for lemon sole, combined for all survey areas.

22 Figure 18 Relative abundance plots for lemon sole for all areas combined and for each individual survey area. Nb. Log-transformed average catch per tow index (o) and fitted values (-) are shown. Figure 19 Annual catch rates of lemon sole across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown).

23 Monkfish Annual numbers at length for monkfish are shown in Figure 20. There was a significant difference in length frequency distributions between years (Table 3). Length frequency distributions were significantly different (p<0.001) between 2014 and previous years was also significantly different from 2011 (p<0.001). In 2014 there was a significant difference (p<0.05) in length frequency distribution between Fetlar and Lerwick-South survey areas (Table 4). Relative abundance plots for monkfish are shown for all areas combined and each survey area individually (Figure 21). Annual catch rates of monkfish are shown in Figure 22. There was no significant difference in catch rates of monkfish between years (F (3, 72) = 1.81, p>0.05). Catch rates were similar across all survey areas in 2014.

24 Figure 20 Annual numbers at length for monkfish, combined for all survey areas.

25 Combined Haaf Bay Loge(index): (o) observed, (-) predicted Loge(index): (o) observed, (-) predicted Loge(index): (o) observed, (-) predicted Year Year Year North West Fetlar Lerwick Loge(index): (o) observed, (-) predicted Loge(index): (o) observed, (-) predicted Loge(index): (o) observed, (-) predicted Year Year Year Figure 21 Relative abundance plots for monkfish for all areas combined and for each individual survey area. Nb. Log-transformed average catch per tow index (o) and fitted values (-) are shown. Figure 22 Annual catch rates of monkfish across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown).

26 Megrim Annual numbers at length for megrim are shown in Figure 23. There was a significant difference in length frequency distributions between 2013 and 2014 (Table 3). Relative abundance plots for megrim are shown for all areas combined and each survey area individually (Figure 24). Annual catch rates of megrim are shown in Figure 25. Catches were confined to four of the five survey areas in There was no significant difference in catch rates of megrim between years (F (3, 72) = 2.18, p>0.05).

27 Figure 23 Annual numbers at length for megrim, combined for all survey areas.

28 Combined Bay North West Loge(index): (o) observed, (-) predicted Loge(index): (o) observed, (-) predicted Loge(index): (o) observed, (-) predicted Year Year Year Fetlar Loge(index): (o) observed, (-) predicted Year Figure 24 Relative abundance plots for megrim for all areas combined and for each individual survey area. Nb. there was insufficient data available for Burra Haaf and Lerwick. Log-transformed average catch per tow index (o) and fitted values (-) are shown. Figure 25 Annual catch rates of megrim across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown).

29 Hake Annual numbers at length for hake are shown in Figure 26. There was a significant difference in length frequency distributions between years (Table 3). Length frequency distributions were significantly different (p<0.05) between 2013 vs 2014 and Relative abundance plots for hake are shown for all areas combined and each survey area individually (Figure 27). Annual catch rates of hake are shown in Figure 28. There was no significant difference in catch rates of hake between years (F (3, 72) = 0.21, p>0.05).

30 Figure 26 Annual numbers at length for hake, combined for all survey areas.

31 Figure 27 Relative abundance plots for hake for all areas combined and for each individual survey area. Nb. there was insufficient data available for North West and Lerwick areas. Log-transformed average catch per tow index (o) and fitted values (-) are shown. Figure 28 Annual catch rates of hake across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown).

32 Saithe Annual numbers at length for saithe are shown in Figure 29. There was a significant difference in length frequency distributions between years (Table 3). Length frequency distributions were significantly different (p<0.05) between 2013 and 2012 and between 2013 and 2011 (p<0.001). Relative abundance plots for saithe are shown for all areas combined and each survey area individually (Figure 30). Annual catch rates of saithe are shown in Figure 31. There was no significant difference in catch rates of hake between years (F (3, 72) = 0.21, p>0.05). Catches of saithe in 2014 were almost exclusively from Fetlar Firth with a small quantity also caught at Burra Haaf.

33 Figure 29 Annual numbers at length for saithe, combined for all survey areas.

34 Figure 30 Relative abundance plots for saithe for all areas combined and for each individual survey area. Nb. there was insufficient data available for North West, Bay and Lerwick areas. Log-transformed average catch per tow index (o) and fitted values (-) are shown. Figure 31 Annual catch rates of saithe across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown). Additional commercial species A number of other commercial species were recorded in smaller numbers on the survey. Annual catch rates and a summary of the 2014 catch rates for each species are included below. There was no significant difference in catch rates of cuckoo ray (Figure 32) between years (F (3, 72) = 1.09, p>0.05). There was a significant difference in catch rates of spotted skate (Figure 33) between years (F (3, 72) = 5.01, p<0.01). A post hoc Tukey test showed that 2014 was significantly different from 2011 and 2012 at p< was also significantly different from 2013 at p<0.05. There was no significant difference between other years. There

35 was no significant difference in catch rates of thornback ray (Figure 34) between years (F (3, 72) = 0.36, p>0.05). Figure 32 Annual catch rates of cuckoo ray across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown). Figure 33 Annual catch rates of spotted ray across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown).

36 Figure 34 Annual catch rates of thornback ray across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown). Other species An overview of annual catch rates and a summary of the 2014 catch rates for a number of other species are included below. There was no significant difference in catch rates of argentine (Figure 35) (F (3, 72) = 2.00, p>0.05), common dab (Figure 36) (F (3, 72) = 0.38, p>0.05), long rough dab (Figure 37) (F (3, 72) = 0.45, p>0.05), lesser spotted dogfish (Figure 38) (F (3, 72) = 1.81, p>0.05), grey gurnard (Figure 39) (F (3, 72) = 44.92, p>0.05) and red gurnard (Figure 40) (F (3, 72) = 55.37, p>0.05) between years. There was a significant difference in catch rates of poor cod (Figure 41) between years (F (3, 72) = 3.85, p<0.05). A post hoc Tukey test showed that 2012 was significantly different from 2013 and 2014 at p<0.05. There was no significant difference between other years. There was also a significant difference in catch rates of Norway pout (Figure 42) between years (F (3, 72) = 4.13, p<0.01). A post hoc Tukey test showed that 2013 was significantly different from 2011 and 2012 at p<0.05. There was no significant difference between other years. Finally, there was no significant difference in catch rates of common skate (Figure 43) between years (F (3, 72) = 0.49, p>0.05).

37 Figure 35 Annual catch rates of argentine across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown). Figure 36 Annual catch rates of common dab across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown).

38 Figure 37 Annual catch rates of long rough dab across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown). Figure 38 Annual catch rates of lesser spotted dogfish across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown).

39 Figure 39 Annual catch rates of grey gurnard across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown). Nb. Grey and red gurnards were recorded collectively in Figure 40 Annual catch rates of red gurnard across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown). Nb. Grey and red gurnards were recorded collectively in 2011.

40 Figure 41 Annual catch rates of poor cod across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown). Figure 42 Annual catch rates of Norway pout across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown).

41 Figure 43 Annual catch rates of common skate across all survey areas (left) and average catch rates per survey area in 2014 (right) (+/- s.e. bars and number of hauls sampled are also shown). An additional number of species were captured in very small quantities: ling, witch, brill, catfish, spur dogfish, dragonet, flounder, forkbeard, John Dory, lythe, pouting, silvery pout, shagreen ray, redfish, solenette and turbot. There was not enough catch data for annual comparisons of these species. Conclusion The data collected during the survey provide an annual overview of the size structure and catch rates of commercially important species in Shetland waters. A particular feature of the 2014 survey was the relatively high catch rates of juvenile haddock and whiting, as well as monkfish <35cm, in comparison with previous years. This suggests the influx of new year classes of these species that can be monitored during subsequent surveys. The data collected during the 2014 survey adds to that collected since It is anticipated that further interpretation of annual variability in distribution and abundance of the species considered during this survey will be undertaken as the data series increases. While the survey has the potential to provide valuable long-term data, the lack of coverage (due to resource limitations) of the important fishing grounds north and north-east of Shetland remains a weakness of the current survey design.

42 References Pennington, M Estimating the relative abundance of fish from a series of trawl surveys. Biometrics 41, Pennington, M Some statistical techniques for estimating abundance indices from trawl surveys. Fishery Bulletin 84, Nelson, G. A fishmethods: Fishery science methods and models in R. R package version [accessed ]. Hothorn, T., Bretz, F., Westfall, P., Heiberger, R. M., Schuetzenmeister, A multcomp: Simultaneous Inference in General Parametric Models. R package version [accessed ]. Pinheiro, J., Bates, D., DebRoy, S., Sarkar, D., EISPACK, R-core nlme: Linear and nonlinear mixed effects models. R package version [accessed ].