The current study investigated the effects of different strength Electromagnetic Field (EMF) exposure (250 µT, 500 µT, 1000 µT) on the commercially important decapod, edible crab (Cancer pagurus, Linnaeus, 1758). Stress related parameters were measured (l-Lactate, d-Glucose, Total Haemocyte Count (THC)) in addition to behavioural and response parameters (shelter preference and time spent resting/roaming) over 24 h periods. EMF strengths of 250 µT were found to have limited physiological and behavioural impacts. Exposure to 500 µT and 1000 µT were found to disrupt the l-Lactate and d-Glucose circadian rhythm and alter THC. Crabs showed a clear attraction to EMF exposed (500 µT and 1000 µT) shelters with a significant reduction in time spent roaming. Consequently, EMF emitted from MREDs will likely affect crabs in a strength-dependent manner thus highlighting the need for reliable in-situ measurements. This information is essential for policy making, environmental assessments, and in understanding the impacts of increased anthropogenic EMF on marine organisms.

Proposed offshore windfarm sites could overlap with the brooding and spawning habitats of commercially important crustacea, including European lobster, Homarus gammarus and Edible crab, Cancer pagurus. Concerns have been raised on the biological effects of Electromagnetic Fields (EMFs) emitted from subsea power cables on the early life history of these species. In this study, ovigerous female H. gammarus and C. pagurus were exposed to static (Direct Current, DC) EMFs (2.8 mT) throughout embryonic development. Embryonic and larval parameters, deformities, and vertical swimming speed of freshly hatched stage I lobster and zoea I crab larvae were assessed. EMF did not alter embryonic development time, larval release time, or vertical swimming speed for either species. Chronic exposure to 2.8 mT EMF throughout embryonic development resulted in significant differences in stage-specific egg volume and resulted in stage I lobster and zoea I crab larvae exhibiting decreased carapace height, total length, and maximum eye diameter. An increased occurrence of larval deformities was observed in addition to reduced swimming test success rate amongst lobster larvae. These traits may ultimately affect larval mortality, recruitment and dispersal. This study increases our understanding on the effects of anthropogenic, static EMFs on crustacean developmental biology and suggests that EMF emissions from subsea power cables could have a measurable impact on the early life history and consequently the population dynamics of H. gammarus and C. pagurus.

The literature suggests regional variations in the size at which sexual maturity is reached for commercially important edible crab (Cancer pagurus), worth GBP 74.3 million annually, which could have implications for regional fisheries management. Berwickshire and Northumberland are geographically divided by the Scotland and England border and remain within the Berwickshire and North Northumberland Coast SAC (Special Area of Conservation). Each are managed by differing fisheries authorities and Minimum Conservation Reference Sizes (MCRS). Morphometric measurements were recorded for each C. pagurus individual to categorise morphometric maturity using segmented regression, with gonadal maturity categorised using visual gonad characteristics and general linear model regressions to compare onset in sexual maturity. Results showed regional variations for gonadal maturity with males reaching sexual onset at a carapace width size of 108.5 mm in Berwickshire and 109.9 mm in Northumberland; females at a size of 126.8 mm in Berwickshire and 120.8 mm in Northumberland. This was also true for morphometric maturity based on chelae height, that males (141.1 mm) and females (134.7 mm) from Berwickshire were morphometrically mature at greater sizes than males (130.1 mm) and females (120.8 mm) from Northumberland. This study shows that the respective MCRS in both regions are appropriate for the C. pagurus populations, but implications for fisheries management could be present.

C. pagurus and H. gammarus are deemed to be declining in abundance in the Berwickshire Marine Reserve from personal communications with local inshore fishers. Fisheries data in the form of catch per unit effort (CPUE) were collected for these two commercially important decapods. Other explanatory variables from fishing activity such as the creel and bait type used, the soak time of the fishing gear, and deployment depth were recorded to provide as much detail as possible to describe the effort applied to catch these decapod species. In this study, CPUE was higher for H. gammarus and C. pagurus outside the Berwickshire Marine Reserve. General additive models (GAMs) were used to describe the effects of the explanatory variables and showed that soak time (days) and depth (m) significantly affected CPUE for C. pagurus, not H. gammarus. Sea temperature (°C) showed a negative correlation with the CPUE of both H. gammarus and C. pagurus; however, a positive correlation was found with the number of C. pagurus caught. The data collected in this study provide a foundation in understanding the current abundance of C. pagurus and H. gammarus in a voluntary marine reserve on the east coast of Scotland, which can be used to inform future changes in fisheries management in Berwickshire.