Orkney Shellfish Research Project Orkney Brown Crab (Cancer pagurus) Tagging Project

Transcription

1 Orkney Sustainable Fisheries Ltd. Report No. 19 Orkney Shellfish Research Project Orkney Brown Crab (Cancer pagurus) Tagging Project Matthew T. Coleman & Elisabete Rodrigues Coleman M., Rodrigues E., (2017). Orkney Brown Crab (Cancer pagurus) Tagging Project. Orkney Shellfish Research Project. Orkney Sustainable Fisheries Ltd. No.19, Pp 21.

2 Executive Summary This report outlines the results of the crab tagging work undertaken by Orkney Sustainable Fisheries Ltd (OSF) as part of the Orkney Shellfish Research Project (OSRP) from This report contains data collected from this project and pre-existing crab tagging data collected previously from OSF research. This report draws comparisons from previous tagging working undertaken by Marine Scotland Science with results collected by OSF. This project outlines differences in stock migratory behaviours presenting new findings previously unseen within Scottish brown crab stocks. OSF in partnership with the Orkney inshore fishery sector undertook crab tagging from Crab tagging involved attaching unique numbered cable tie tags to soft shelled or recently moulted individuals. Biological information relating to an individual s size, sex and mating success was recorded with individuals released and subsequent recaptures reported by Orkney fishermen and beyond. A broad size-range of individuals were tagged over the duration of the project, looking to identify differences in stock movement behaviour relating to size. Differences in crab tagging objectives between years resulted in differences in observed tagged sex ratios, with a far greater number of male brown crab tagged in the first year of the project (2013) compared to the final years of the project. At the conclusion of the OSRP a total 6,954 brown crab were tagged, of these 27% were male and 73% female. The size of tagged male brown crab released ranged from mm carapace width (CW) with an average of 150mm CW. Tagged female brown crab ranged from mm CW with an average CW of 160mm. As of March 2017, of all females released 4.25% (n=66) were recaptured, with 6.8% (n=77) of males recaptured. Days at liberty ranged from days, with distances travelled seen to vary between sexes. Of those females recaptured distances travelled from point of releases and recapture ranged from km. Whilst in the case of males, distances travelled ranged from km. Preliminary interpretation of the results indicated that a number of long distance migrations were recorded with a number of individuals moving in a westward direction, with two cases of individuals travelling a minimum distance 236 and 258km respectively, with other individuals equally travelling km prior to recapture. The interpretation of these results indicates the occurrence of a number of differing behavioural patterns exhibited by brown crab tagged within Orkney. Two behavioural patterns were exhibited within females with both localised movement patterns and long distance migratory behaviours observed. In the case of male brown crabs, observed movement patterns and associated behaviours coincide with existing literature, with males being predominantly inshore, undertaking little movement. The identified behaviours provide further insight into potential brooding behaviours and locations within the Orkney fishery. The results of this study indicates the occurrence of movement of Scottish crabs stock around the west coast transcending numerous stock assessment boundaries and both inshore and offshore fisheries. This is the first study to of long distance movements within Scottish brown crab stocks. Recommendations surrounding future work are discussed with the implementation of a Scottish-wide tagging study, designed to capture inter-stock movements all around Scotland s coasts. Additional research priorities are highlighted, including the use of data storage tags to identify brown crab brooding location. I

3 Contents Executive Summary... I 1. Project Background Overview Rational Methodology Data... 4 Distribution of tagging activity Results Size Frequency & Sex Ratios Annual Size frequency Overall Sex Composition Regional Sex Composition Sperm Plugs Recapture Rates and Timing / Tagging Results Marine Scotland Tagging Study Marine Scotland & OSF Comparison Female Movements Inshore Comparison Offshore Comparison Male Movement Inshore Comparison Discussion Migration Routes Brooding regions Conclusion References: Appendix... 1 II

4 List of Tables Table 1 Total number of Brown crab individuals tagged per Year per sex from OSF tagging exercises ( )... 2 Table 2 Average size per sex per year of tagged individuals released ( )... 5 Table 3 Percentage and Number of tagged crab recaptured per year of those released List of Figures Figure 1 Procedure of Sexing brown crab, location of carapace measurements and position of cable tie tag on a tagged individual prior to release... 3 Figure 2 Identification of visible sperm plugs within a female brown crab (Edwards, 1979)... 3 Figure 3 Distribution of OSF tagging release sites around Orkney ( )... 4 Figure 4 Overall size frequency of all tagged individuals by OSF ( )... 5 Figure 5 Annual size frequency of tagged individuals ( )... 6 Figure 7 Overall sex composition of tagged crab per ICES rectangle ( )... 7 Figure 8 Size frequency of tagged females recorded with sperm plug (2016)... 8 Figure 10 Long distance female brown crab movements from initial release points and recaptures from around North West Scottish Coast ( ) Figure 9 Inshore movements of tagged female crabs from initial release and subsequent recapture ( ) Figure 11 Inshore movements of tagged male brown crab from initial release site and subsequent recapture ( ) Figure 12 A) Offshore movement and recaptures of tagged female brown crab within the windsock tagging area. B) Movement of tagged female brown crab by Orkney inshore fleet (Jones et al, 2010) Figure 13 A) Offshore movement and recaptures of tagged male brown crab within the windsock tagging area. B) Movement of tagged male brown crab by Orkney inshore fleet (Jones et al, 2010) Figure 14Comparison of recorded movements of tagged female brown crab recaptures within the Orkney inshore fishery Figure 15 Comparison of recorded movements of tagged female brown crab within both Marine Scotland offshore tagging recaptures and Orkney Sustainable Fisheries long distance recaptures Figure 16 Comparison of inshore tagged male brown crab from Marine Scotland and Orkney Sustainable fisheries tagging experiments III

5 Orkney Shellfish Research Project Orkney Brown Crab (Cancer pagurus) Tagging Project 1. Project Background The Orkney shellfish research project (OSRP) has come to the end a four year project ( ). The project encompassed a number of objectives aimed to address the needs of two important sectors: Inshore fisheries and marine renewables. Specific objectives of the project relating to the fishing sector were: To assess the status of Orkney crustacean stocks in relation to sustainability criteria; To provide monitoring data and biological understanding to support the development and implementation of a harvest strategy and management systems for sustainable fishing in the context of marine spatial planning for renewable energy and other activities in Pentland Firth and Orkney waters; To satisfy shellfish consumers of Orkney s commitment to sustainable fishing. Objectives relating to the marine renewable energy industry: To determine key areas providing value to the Orkney creel fishery in terms of catch rates and the magnitude, composition and quality of catches; To describe spatial patterns of space-use by the Orkney creel fishery in terms of fishing effort, navigation, relocation of gear during bad weather and seasonal and inter-annual patterns of variability; To determine locations of critical habitat for crustacean species targeted by the Orkney creel fishery, particularly in terms of spawning areas and movement and migration patterns of brown crab. This report outlines the results collected over the past 4 years specifically relating to brown crab tagging activities within the Orkney inshore fishery and the outputs associated with the analysis of data collected. This programme was instigated to determine locations of critical habitat for crustacean species targeted by the Orkney creel fishery, particularly in terms of spawning areas and movement and migration patterns of brown crab. 2. Overview Extensive knowledge gaps relating to key biological processes and traits still exist within a number of commercial important species, brown crab Cancer pagurus being one of them. This species receives national management advice relating to current and historical trends in its exploitation (Marine Scotland Science, 2016) however is still listed as a data limited stock. Under current EU directives member states are required to manage all fish stocks at maximum sustainable yield (MSY) or equivalent by 2020, however to move toward successful sustainable management, further information is required surrounding key biological processes such as reproductive cycle and stock movements. Extensive research was conducted in the early 1900s (Pearson, 1908) and late 1970 (Bennet & Brown, 1976; Edwards, 1979) 1

6 investigating movement and reproductive behaviour of brown crab around the British Isles. This research has underpinned the understanding of brown crab within UK waters and northern Europe as a whole for the past century. Recent research however has started to shed further light onto biological processes such as reproduction (Ungfors, 2007; Hunter et al, 2013; Haig et al 2016), stock genetics (Ungfors et al, 2009; Moran, 2009) and migratory behaviour within this species (Ungfors & Nilsson, 2007). Even with this research however extensive knowledge gaps still exist within this species and fishery. 3. Rational The role of this project was to gather information on the movement patterns of crabs within the Orkney inshore fishery and beyond. The brown crab fishery is an important keystone specie of Orkney s inshore fishery with value at first sale of 3.6million in 2015 (Scottish Government, 2016). It is therefore very important to understand the biological characteristics of this socio-economic important stock. Previous tagging experiments have been conducted in Orkney in (Jones et al, 2010). This study investigated the overlap between the inshore and emerging offshore fishery, with results indicating possible stock movements between inshore and offshore areas through annual migration events. To build upon the findings of this project Orkney Sustainable Fisheries Ltd. undertook a series of tagging projects investigating the interaction between inshore and offshore fishery. Brown crab tagging was conducted by OSF from with participation of the Orkney inshore fleet as a component of the OSRP. Over the duration of the OSRP a total of 6,954 crabs were tagged (Table 1). An additional 747 individuals were tagged under a previous OSF crab tagging project (Lamb, 2012), totalling 7,294 tagged individuals (Table 1). No tagging was undertaken within 2014 due to staff limitations. Table 1 Total number of brown crab individuals tagged per year per sex from OSF tagging projects ( ) 2010/ Male Female Sub Total ,355* 543 1,056 Total 7,924 *See Section 2013 Data 4. Methodology Crabs were caught using baited creel deployed by commercial inshore fishers operating within the Orkney assessment area. Creels were typically hauled within and out to the 12 nautical mile limit, with gear deployment ranging from 15 80m depths. Tagging was conducted typically from August December, coinciding with the peak moulting period. A total of 9 vessels participated in the tagging project, either through the OSRP observer programme or undertaking tagging activities independently. 2

7 The selection of crabs was restricted to those that have recently moulted or white crabs 1 and those that would otherwise be discarded by the fishery. The selection of these individuals meant that fishermen were not required to sacrifice a proportion of their landed catch, nor was additional payment required to secure individuals. Selective grading of suitable individuals to a particular criterion occurred prior to tagging; this criterion restricted tagging to individuals that displayed no signs of damage, either through handling or through damage resulting from other crustaceans within creels. Grading was done to ensure only healthy crabs were selected. Crabs were tagged using uniquely numbered claw tags (coloured plastic cable tie) attached to either claw (Fig 1). Each tag in addition to its unique identifier was printed with a telephone number to enable fishers to report subsequent recaptures. At the time of initial capture individuals were sexed, sized (Fig 1) and sperm plug presence was recorded (Fig 2) allowing potential differences in migratory behaviour to be monitored. Due to the nature of tags and morphological differences in cheplids, females <150mm were not tagged due to the tag number becoming illegible, males were tagged from 130mm. Figure 1 Procedure of Sexing brown crab, location of carapace measurements and position of cable tie tag on a tagged individual prior to release Tagging preference during 2015/16 was directed towards tagging predominantly female crabs. Male brown crabs undertake limited inshore movements (<6km) and migratory behaviours, this behavioural pattern being extensively documented throughout its natural range (Ungfors & Nilsson, 2007; Jones et al, 2008; Edwards. 1979). Small quantities of male brown crab however were still tagged to provide a relative example of annual movement patterns within this inshore population. Figure 2 Identification of visible sperm plugs within a female brown crab (Edwards, 1979) 1 White crab describes a crba that has recently moulted, when the shell is soft and the underside is white instead of cream in colour. 3

8 2013 Data Access and use of 2013 data was severely limited due to data corruption. This has limited the inclusion of this year s data within the final reports analysis and subsequent interpretation of results. In some cases fragments of data was extracted from previous OSF reports through the use of GIS georeferencing and data mining. Subsequent safe guards relating to data security have now been in place within OSF since 2014 to ensure future data security. Distribution of tagging activity Distribution of tagging events over the duration of the project illustrates key areas in which large amounts of tagging occurred (Fig 3). Primary tagging areas throughout all years are highlighted as being off the West Mainland and Northern Hoy. In comparison small amounts of tagging occurred within and around the Northern Isles, predominantly within 2010, 2015 and Limited tagging occurred along the East Mainland, with tagging activities only occurring within this area in Figure 3 Distribution of OSF tagging release sites around Orkney ( ) 4

9 5. Results 5.1.Size Frequency & Sex Ratios Overall size frequency of tagged male crabs ranged from mm CW, with an average CW of 150 ±16mm (Fig 4), female crabs ranged from mm with an average CW of 160 ±16mm (Fig 4). Annually male crab average size remained constant, predominately between mm CW (Table 2), in comparison average tagged females were predominantly between mm CW range (Table 2). Figure 4 Overall size frequency of all tagged individuals by OSF ( ) 5.2.Annual Size frequency Annual size frequency was indicative of the tagging priorities of each year and the types of vessel from which tagging occurred. In earlier years ( ) the majority of tagged crabs were male, with peak frequency occurring typically around the MLS (140mm CW; Fig 5). In subsequent years (2015/2016) a broad size range of individuals were tagged (Fig 5, Fig 6), with the largest average size for both males and females tagged during this time period (Table 2) Table 2 Average size per sex per year of tagged individuals released ( ) Male Female Combined 150 ± (±16) (±15) 164 (±11) (±15) 158 (±15)

10 Figure 5 Annual size frequency of tagged individuals ( ) 5.3.Overall Sex Composition Sex composition was seen to fluctuate between years and ICES rectangles. In earlier years of the project ( ) far greater numbers of male crab were tagged in relation to females, in the case of 2010 male brown crab made up 62% of total crab tagged whilst females represented only 38% (Table 1). These differences in tagging behaviour can be attributed to differing OSF staff tagging priorities at the time. These differing methodologies over years present contrasting behavioural patterns within the stock. To adjust for these differences in tagging strategy, greater onus was placed upon tagging female crabs in 2015/2016, resulting in females making up 72% of total tagged crab in both years. The results of this present a holistic image of the movements of both female and brown crab around and further afield from the Orkney Islands and its inshore fishery. 5.4.Regional Sex Composition Regional sex ratios were investigated by combing all years per ICES rectangle in which releases occurred (Fig 7). West coast releases (ICES 46E6 & 47E6) were dominated by female brown crab, comprising 66% of tagging releases, whilst males in both cases represented 34% respectively. In contrast, east coast male crab represent a greater proportion (47E6: 41%) or dominate compositions entirely (46E7: 71%). Differences in catch compositions can be attributed to a combination of environmental conditions and fishery targeting behaviours and therefore shouldn t be interpreted as representative of the sex ratio for each of these regions. 6

11 Figure 6 Overall sex composition of tagged crab per ICES rectangle ( ) 5.5.Sperm Plugs The reproductive stage of females was recorded during 2016 tagging. This involved recording the presence or absences of sperm plugs within the oviducts (Fig 2). Sperm plugs are clearly visible making their presence easily detectable. The presence or absence of sperm plug relates to potential behavioural difference between individuals that have or haven t successfully copulated. Such differences could be demonstrated with mated/unmated individuals undertaking differing migratory behaviours. Existing hypothesized brooding behavioural activities hinge upon individuals that have successfully copulated and subsequently remain inshore within unknown brood locations, with non-reproducing individuals undertaking large migrations. It is therefore essential that any future tagging studies undertaken record the copulatory state (sperm plug presence/absence) of individuals. Of those females tagged 16%were recorded as having sperm plugs present and ranged from mm CW with the mean size being 177mm CW (Fig 8). In relation to previous studies undertaken by OSF which also documented sperm plug presence, individuals recorded within 2016 tagging were far larger than those recorded previously (83-148mm CW: Haig et al, 2016). However the failure to detect individuals with sperm plugs at smaller size can be attributed to the discarding of these individuals due to them being morphometrically unsuitable for tagging. 7

12 Figure 7 Size frequency of tagged females recorded with sperm plug (2016) 5.6.Recapture Rates and Timing As of end of March % (n=66) of female brown crab have been recaptured and 6.8% (n=77) male crabs from Recapture rates varied between years (Table 3). The reasons behind this variability is unclear, however timing of tagging activities would have a significant effect on the recapture rates of tagged individuals and tagging composition for each year on the subsequent recaptures. Table 3 Percentage and number of tagged crab recaptured per year of those released. 2010/ Male 3.5% (15) 22.4% (40) 6% (9) 2% (7) Female 4.3% (14) 4.4% (2) 11.1% (44) 0.6% (5) /11 Recapture rates within 2010/11 demonstrate a relative, even recapture rate between sexes, with 99% recaptures occurring within 30 days of initial release, with one individual at liberty for 56 days (Appendix 2). Average distance travelled for all individuals was <1km from initial release site including the individuals at liberty for 56 days. One individual however was recorded moving a linear distance of 28km in 24 days at liberty. This movement however remained within inshore Orkney waters Recapture rates within 2012 were more variable, with 38% recaptures occurring within 30days of initial release (Appendix 3). During this time-period distance travelled ranged from km, with an average of 1.7km. In the case of those individuals with times at liberty >30days limited movements were 8

13 documented, with distance ranging from 0.12 = 4.8km, and an average of 3km. Low average distances travelled by individuals at liberty >30 days can be attributed to the greater number of male crabs recaptured, with limited stock movements known to occur. Of the two females recaptured, recapture occurred within 30 days, providing limited opportunity for individuals to undertake any large behavioural movements Recapture rates within 2015 differed from previous years with 75% (n=33) of recaptures occurring within the initial 30 days post release (Appendix 4). Of these recaptured during this period 91% (n=30) were female with 9% (n=3) male. Distance travelled ranged from 0.1km 16km, with an average of 2.7km. Of the remaining individuals at liberty >30days, 29% (n=5) were male and 71% (n=12) were female. Marked differences are observed in the movement patterns of the two sexes over these larger times at liberty. Male time at liberty ranged from days, with corresponding movements ranging from km, with an average of 18km (Appendix 4). In contrast female time at liberty ranged from days, with an average of 178 days. Distance travelled ranged from km, with an average of 97km (Appendix 4). Of those females at liberty >30days, two were recaptured twice with subsequent re-releases. Two individuals demonstrated contrasting movement patterns. Tag No undertook significant offshore movements from its initial inshore release sites, moving 53km in a westerly direction. In contrast Tag No moved in a north easterly direction, moving into inshore waters Recapture rates as of March 2017, record 25% (n=3) of recaptures occurred within the first 30 days post release (Appendix 5). Of these 75% (n=2) were male and 25% (n=1) were female. Distance travelled for males was 8.7 and 9.7km, whilst the female moved a distance of 22.2km. Those recaptured 30 days post release comprised 75% (n=9) of those recaptured in % (n=4) were female and 56% (n=5) male. Females at liberty ranged from days, with an average of 94 days. Distance travelled ranged from km, with an average of 50.9km. Male s days at liberty ranged days, with distances travelled ranging from km, an average of 10.7km. 5.7.Tagging Results Of those individuals tagged over the course of the project clear differences in behavioural pattern emerged between that of male and female proportions of the stock. Female crab movements were seen to vary considerably between individuals, with some undertaking predominantly inshore limited movements between recaptures (Appendix 1; Fig 10). These limited inshore movements are exhibited by Tag number 24103, measuring 158mm CW, moving a minimum distance of 8.9km within 98 days at liberty. Similar behaviours are exhibited by other individuals; tag number 1154 measuring 176mm CW travelled 9.254km during 91 days a liberty; tag number 8514 travelling a minimum distance of 7lkm during 651 days at liberty (fig 10). However, some females travelled considerable distances > 150km from initial release (fig 9). With recaptured long ranging individuals accounting for18% (n=12) of all recaptured females. Of these, two females were recorded moving >200km minimum linear distance from first release. Tag number measuring 175mm CW travelled a minimum distance of236km in 336 days. Tag Number measuring 186mm CW travelled a minimum distance of 258km in 378 days. These two individuals correspond with existing literature on large movements undertaken by brown crab, similar distances 9

14 recorded by individuals originally released off the coast of Ireland being recaptured within the French fishery (Fahy & Carroll, 2008). In comparison male crab movements are considerably different from those of female. The majority of male crab recaptures occurred within 6km of the original release site and predominantly within the 6nm inshore Orkney limit (Fig 11). However a number of individuals remained at liberty for large periods of time. These individuals undertook limited movements from point of releases, opposite to that of the behaviour exhibited by a number of females over similar time-frames (Appendix 1). This behaviour is exhibited within tag number 22886, a male measuring 137mm who was at liberty for 344 days moving a minimum distance of 3.8km from first release. Tag number measured 168mm CW and was at liberty for 445 days, moving a minimum of 12km from initial release point, remaining inshore and moving solely across rocky/hard reef substrate. Similar examples were seen with tag number and tag These two male crabs measured 170mm CW and 157mm CW and travelled a minimum distance of 4km and 2.8km over a total of 243 and 251 days. Conversely a small number of males undertook large scale movements prior to recapture, accounting for 3% (n=2) of males recaptured. Of these males, tag number 10189was at liberty for 98 days in which it travelled a minimum distance of 36.9km. Tag number was at liberty for 47 days and travelled a linear distance of 67.5km (Appendix 1; Fig 11). Figure 8 Long distance female brown crab movements from initial release points and recaptures from around North West Scottish Coast ( ) 10

15 Figure 9 Inshore movements of tagged female crabs from initial release and subsequent recapture ( ) Figure 10 Inshore movements of tagged male brown crab from initial release site and subsequent recapture ( ) 11

16 5.8. Marine Scotland Tagging Study 2010 Previous tagging experiments have been conducted by Marine Scotland Science (MS; Jones et al, 2010) within Orkney waters and further offshore within the neighbouring Sule stock assessment area also referred to as the Windsock. This study aimed to investigate the migratory behaviours and stock movement patterns between the emerging offshore brown crab fisheries and localised inshore fishery. Of the results presented, proportions of the offshore female stock appear to move inshore indicating possible immigration from offshore areas into the inshore fishery (Fig 12A), whilst female inshore stock indicated the possibility of emigration in a westward direction (fig 12B). Conversely male movement patterns within both tagging offshore (fig 13A) and inshore areas movement patterns are limited (Fig 13B), with individuals exhibiting localised movement patterns. A B Figure 11 A) Offshore movement and recaptures of tagged female brown crab within the windsock tagging area. B) Movement of tagged female brown crab by Orkney inshore fleet (Jones et al, 2010) 12

17 A B Figure 12 A) Offshore movement and recaptures of tagged male brown crab within the windsock tagging area. B) Movement of tagged male brown crab by Orkney inshore fleet (Jones et al, 2010) 13

18 5.9. Marine Scotland & OSF Comparison Aggregated data from both OSF tagging activities and MS (Jones et al, 2010) provide the opportunity to compare the results of both studies simultaneously, allowing difference in behaviours to be investigated between the different components of the Orkney brown crab stock. In the case of MS data, raw data points relating to crab releases and recaptures were unavailable, resulting in data being extracted through the use of ArcGIS georeferencing. Georeferencing allowed the merging of the two different published data sets through the use of spatial configuration In this case MS maps contained spatial qualifiers in the form of GPS grids Female Movements Inshore Comparison Inshore movements of brown crab were similar within both studies (fig 14). Of those individuals recaptured a small number demonstrated large inshore movements in westward direction, whilst a high proportion demonstrated smaller localised movements between recapture and release. A high concentration of capture and release events is located off the North West coast of Hoy, highlighting its potential importance as a mating or lekking region within Orkney. Similar observations are highlighted within identified commercial species hotspots and succorfish data (See report: Succorfish Report, 2016), demonstrating the importance of this area for commercial fishers also. Figure 13Comparison of recorded movements of tagged female brown crab recaptures within the Orkney inshore fishery. 14

19 Offshore Comparison Comparison between the MS offshore tagging exercise and long distance migration patterns documented by the OSRP illustrates potential differences between stock movements (fig 15). In the case of the MS tagging results, offshore crab illustrates a predominately localised movement pattern within the tagging area. This behaviour could therefore be interpreted as representative of the crab stock movements occurring outside of 12nm limit. However a number of individuals tagged within that project exhibited movement pattern Figure 14 Comparison of recorded movements of tagged female brown crab within both Marine Scotland offshore tagging recaptures and Orkney Sustainable Fisheries long distance recaptures. towards inshore areas, demonstrate the potential role that the offshore stock has in the emigration of individuals to inshore stock and fishery. Conversely in the case of the OSF project, recently moulted individuals demonstrated little to no movement patterns towards offshore locations, remaining predominantly inshore and moving in a south west direction. The lack of movement from inshore areas 15

20 back to offshore areas presents numerous questions relating to the movement cycle of brown crab stocks, primarily the overall movement pattern between offshore and inshore areas. Offshore areas cannot be deemed to experience localised recruitment due to the lack of suitable larval settlement habitat within these areas therefore the necessity of inshore areas for recruitment still arises. Additional recruitment areas separate to the Scottish mainland and islands could occur, with settlement and recruitment of individuals from Sule Stack and North Rona. These two studies provide insight into the movement patterns of the female portion of the stock, however both studies provide a limited view of the movement pattern overall. Therefore the implementation of other tagging activities would provide further insight into emigration and immigration behaviour cycles of the species at a Scotland wide level Male Movement Inshore Comparison Inshore movements of male brown crabs from both MSS and OSRP tagging studies illustrate limited localised moment within inshore areas. These combined movement patterns mirror that of other behavioural movements exhibited by male brown crab in other regions in northern Europe (Edwards, 1979; Ungfors & Nilsson, 2007). In both the MSS and OSF studies two long distance migrations are documented, indicating that large localised movements within inshore areas do occur, with the movements potentially due to high crab density within localised areas or a behavioural responses of male crab following migrating females. 16

21 Figure 15 Comparison of inshore tagged male brown crab from Marine Scotland and Orkney Sustainable fisheries tagging experiments 4.5. Discussion Crab tagging results illustrate the occurrence of annual migratory behaviour within brown crab around the North West Scottish coast. Behavioural differences are observed between the sexes, with the potential indication of differing behavioural movements depending on the condition and/or reproductive stage of individuals. General trends in female s movement highlights a population that undertake long westerly migration moving between stock assessment areas and fisheries. In contrast males demonstrate a localised distribution pattern undertaking limited movements within inshore areas, however exceptions to this behavioural pattern have been recorded. Reasons relating to the movements of brown crab along the north west of Scotland are currently largely speculative, the condition of tagged females relating to sperm plug presence was recorded only in The addition of this information provides the opportunity to untangle the behavioural response of different tagged individuals and identify potential triggers causing these large scale migrations potentially associated with reproduction. This additional information would produce a valuable insight into the reproductive cycle of brown crab with key components of this process significantly under-researched and large biological knowledge gaps within its cycle. It is currently hypothesised that brown crab undertakes a broad iteroparous reproductive cycle (Haig et al, 2016); meaning that they can undertake multiple reproductive cycles over their life time. Loose annual reproductive cycles have been hypothesised (Pearson, 1908), with these based upon 17

22 early research conducted within the 1900s. Little progress into key biological progress has been established since then. The observations and movement documented here coincide within the behavioural patterns observed within newer studies conducted around the British coast with clear seasonal patterns with inshore and offshore migrations. Further insight into female brown crab brooding behaviour has been identified off the south west coast by Hunter et al ( 2013). In this case ovigerous female brown crab were fitted with data storage tags providing the capabilities to track direction and associated behavioural changes over the course of brooding, spawning and subsequent returning inshore emigrations. The extent and direction of tagged females can be indicative of localised environmental patterns, such as water temperature and primary tidal flow. Further understanding of reproductive biology could be inferred from existing reproductive strategies of other decapoda (H.americanus - Cobb & Phillips,2012), with the assumption of a biannual spawning cycle and decreases in reproductive frequency relating to size/age but compensated within increase in overall fecundity. This proposed reproductive strategy also ties into behavioural observation of brown crab, specifically the apparent differentiation between two components of stock, perhaps those that undertake large migrations and that of individuals that moult and subsequently remain inshore, abstaining from reproduction. This behaviour separation of the stocks has subsequently been captured through tag returns within this study but also within other regions within northern Europe (Ungfors et al, 2006; Fahy & Carrol, 2008) Migration Routes The roles of environmental drivers behind crab migration that occur in the north west of Scotland still remain unknown. Observed movement patterns within this study illustrate clear interaction occurring across multiple assessment areas and within different components of the Scottish creel fisheries (both inshore and offshore fisheries). These migrations tie into existing knowledge surrounding crab behaviour with migrations occurring against primary currents within the surrounding region. The uses of primary currents are hypothesised to be used within larvae transport (Sinclair, 1988), with larvae carried back on regional primary currents, providing the opportunity for both localised and long distance recruitment. Similar migratory behaviours and larval transport has been observed within other areas of the UK (Eaton et al, 2003), with female migrations documented along the Northumberland coast moving from a south to a northern orientation post moult (Edwards, 1979). Similar migrations were observed and documented within populations off the coast of Norway and Sweden (Ungfors et al, 2007). Brooding regions The area in which the brooding process occurs within Scottish brown crab or stocks is still unknown. The result from this study highlights the possible occurrence of these brooding sites based on the migratory behaviours observed. Of the currently reported recaptures a number of these have been in the water surrounding the Western Isles. Based on existing predictive habitat mapping and the observed migratory behaviours, the west coast of Lewis provides a potential area for a brooding site within the Scottish crab stock along the North West. This area provides large ideal habitat extents of sand/muddy sand and coarse sediment and is preferable burrowing and brooding habitat for brown crab surrounded by large expanses of hard reef substrate (Appendix 6). Ocean currents additionally provide ideal temperature conditions with average SST around the Western Isles 7.6 o c (NOAA), with 7-8 o c necessary for larval development and spawning (Eaton et al, 2003). 18

23 Alternatively, brooding locations could be localised and far closer inshore, with the interpretation that localised female inshore movements in fact form the Orkney spawning stock. Such an interpretation is strengthened by the implausibility of larval transport from spawning locations situated off the Isle of Lewis reaching Orkney. Based on larval biology and known diurnal movement behaviours, tidal regimes and larval development time scales, such recruitment appears implausible. Similar stock differentiations are exhibited within crab populations along the north east English coast. With localised recruitment from brooding locations close inshore and restricted localised larval transport and settlement, long distance travel only occurs through emigration and immigration of adults from neighbouring regions (Eaton et al, 2003). This therefore presents the idea that large scale movements observed within this tagging experiment are in fact emigration behaviours, with individuals naturally emigrating between regions and assessment areas. However the identification of these brooding areas is purely speculative and further tagging studies, both national tagging studies and regional data storage tagging (DST) are recommended. The use of DST tagging experiments similar to that of Hunter et al (2013) would allow the possibility for geolocation of tagged individuals providing fine scale movements, something that is lost from typical A to B tagging studies. This could potentially identify the location of brood stock areas Conclusion The results of this study and that of Marine Scotland present the foundation of crab movements around the northern west coast of Scotland. It highlights a number of additional avenues of research including the development and implication of national tagging experiments to understand the regional and broad scale movement patterns of the brown crab stock around Scotland. Additionally it highlights key knowledge gaps surrounding this species, specifically spawning behaviour and how to address these knowledge gaps (potentially through use of DST). OSF is currently in the process of implementing and organising a national tagging project aiming to address some of these knowledge gaps and in partnership with Heriot Watt University is in the initial stages of developing a low cost open source DST. 19

24 References: Bennett, D. and Brown, C. (1976). The crab fishery of south-west England. Laboratory Leaflet., Fisheries Lab. Lowestoft, 33, p.11. Bruce, M. (2009). Population genetic structure of brown crab (Cancer pagurus) in Irish waters. Master of Science in Molecular Ecology. Galway-Mayo Institute of Technology. Cobb, J. and Phillips, B. (2012). Theœ Biology and Management of Lobsters. Burlington: Elsevier Science. Eaton, D., Brown, J., Addison, J., Milligan, S. and Fernand, L. (2003). Edible crab (Cancer pagurus) larvae surveys off the east coast of England: implications for stock structure. Fisheries Research, 65(1-3), pp Edwards, E. (1979). The edible crab and its fishery in british waters. Surrey: Fishing news books. Fahy, E., & Carroll, J. (2008). Two records of long migrations by Brown or Edible Crab (Cancer pagurus L.) from the Irish inshore of the Celtic Sea. The Irish Naturalists' Journal, 29, Haig, J., Bakke, S., Bell, M., Bloor, I., Cohen, M., Coleman, M., Dignan, S., Kaiser, M., Pantin, J., Roach, M., Salomonsen, H. and Tully, O. (2016). Reproductive traits and factors affecting the size at maturity of Cancer pagurus across Northern Europe. ICES Journal of Marine Science: Journal du Conseil, 73(10), pp Hunter E, Eaton D, Stewart C, Lawler A, Smith MT (2013) Edible Crabs Go West : Migrations and Incubation Cycle of Cancer pagurus Revealed by Electronic Tags. PLoS ONE 8(5): e doi: /journal.pone Jones G, Gibson P, Dobby H, McLay A, (2010). Brown Crab (Caner pagurus) Migrations off the Northern Scottish Coast. Scottish Industry Science Partnership Report 02/10. Marine Scotland Science. Pp19. Lamb, S. (2011). 2010/2011 Project Review. Orkney Sustainable Fisheries Ltd. Mesquita C, Dobby H, McLay A (2016) Crab and Lobster Fisheries in Scotland: Results of Stock Assessments Scottish Marine And Freshwater Science Vol 07 No. 09. Marine Scotland Science, ISSN: Pearson, J. (1908). Cancer (the edible crab). Liverpool Marine Biology Committee Memoirs, 16, p.263. Ungfors, A. (2006). Sexual maturity of the edible crab (Cancer pagurus) in the Skagerrak and the Kattegat, based on reproductive and morphometric characters. ICES Journal of Marine Science, 64(2), pp Ungfors, A., Hallbäck, H. and Nilsson, P. (2007). Movement of adult edible crab (Cancer pagurus L.) at the Swedish West Coast by mark-recapture and acoustic tracking. Fisheries Research, 84(3), pp Ungfors, A., McKeown, N., Shaw, P. and Andre, C. (2009). Lack of spatial genetic variation in the edible crab (Cancer pagurus) in the Kattegat-Skagerrak area. ICES Journal of Marine Science, 66(3), pp

25 Ungfors, A., McKeown, N.J., Shaw, P.W. and André, C., Lack of spatial genetic variation in the edible crab (Cancer pagurus) in the Kattegat Skagerrak area. ICES Journal of Marine Science: Journal du Conseil, 66(3), pp Walker, K. (2013). Orkney Research Project. End of Year Report Orkney Sustainable Fisheries Ltd. 21

26 Distance Travelled (Km) Appendix Female Male 50 0 Days at Liberty Appendix 1 Average distance travelled by recaptured brown crab individuals in relation to days at liberty ( Appendix 2 Details of recaptures, distance between release and recapture sites, bearing and day between releases and recapture of crabs tagged in 2010& Dashed lines separates days at liberty >30days Year Tag_Number Sex CW Sperm Plug Days at Liberty Distance Travelled (km) M 164 NA M 179 NA M 172 NA M 158 NA M 188 NA M 157 NA M 163 NA M 163 NA M 205 NA M 217 NA M 217 NA M 164 NA M 166 NA M 164 NA NA F 152 NO Direction 1

27 Appendix 3 Details of recaptures, distance between release and recapture sites, bearing and day between releases and recapture of crabs tagged in Dashed lines separates days at liberty >30days Year Tag_Number Sex CW Sperm Days at Distance Plug Liberty Travelled (km) Direction M 145 NA W M 140 NA NW M 136 NA N M 138 NA W M 133 NA NW M 130 NA N M 151 NA SW M 133 NA SW M 148 NA W M 133 NA S M 145 NA E M 154 NA N M 140 NA S M 139 NA W M 130 NA S M 135 NA NW M 137 NA S M 147 NA NW M 140 NA W M 145 NA SW M 140 NA W M 143 NA S M 150 NA S M 139 NA N M 154 NA N M 142 NA S M 151 NA S M 133 NA SW M 141 NA W M 140 NA N M 147 NA S M 154 NA SE M 166 NA SW M 160 NA S M 136 NA S M 134 NA SW M 142 NA NW M 137 NA E F 138 NA S F 161 NA W 2

28 Appendix 4 Details of recaptures, distance between release and recapture sites, bearing and day between releases and recapture of crabs tagged in Dashed lines separates days at liberty >30days Year Tag Sperm Days at Distance Travelled Sex CW Number Plug Liberty (km) Direction M 140 NA W M 142 NA W M 139 NA N M 147 NA SW M 170 NA E M 157 NA N M 137 NA SE M 168 NA S M 145 NA NA NE F 138 NA SW F 149 NA W F 150 NA SW F 152 NA S F 158 NA W F 175 NA W F 158 NA S F 163 NA NW F 154 NA NW F 148 NA W F 154 NA 9 10 S F 158 NA SW F 163 NA SW F 165 NA SW F 182 NA W F 188 NA W F 135 NA W F 146 NA SW F 147 NA W F 151 NA SW F 152 NA W F 161 NA SW F 167 NA SW F 170 NA SW F 183 NA W F 158 NA W F 161 NA NW F 170 NA NW F 193 NA NW F 158 NA NE 3

29 F 144 NA NW F 165 NA NW F 158 NA W F 129 NA SW F 168 NA W F 190 NA SW F 160 NA W F 147 NA SW F 168 NA SW F 158 NA NE F 175 NA SW F 172 NA SW F 159 NA SW F 186 NA SW F 147 NA NA SW F 154 NA NA 2.43 W Appendix 5. Details of recaptures, distance between release and recapture sites, bearing and day between releases and recapture of crabs tagged in Dashed lines separates days at liberty >30days Year Tag Number Sex CW Sperm Days at Distance Travelled Plug Liberty (km) Direction M 158 NA N M 164 NA W M 176 NA S M 172 NA SE M 172 NA N M 165 NA E M 160 NA S F 158 NA SW F 170 NA S F 176 NO N F 178 NO W F NA NA E F 173 NA SW 4

30 Appendix 6 Identification of potential brooding sites based on habitat predictive mapping and brown crab tag recaptures situated of the Isle of Lewis. Appendix 7. Identification of potential brooding sites based local bathymetry and brown crab tag recaptures situated of the Isle of Lewis. 5

31 6