Lobster and Brown crab have been important local fishery species for centuries, but unlike the more recent scallop fisheries they have not received as much research attention. The method of capture (static-gear baited traps, known as ‘pots’ or ‘creels’) is considered environmentally benign compared to other methods of fishing; however, we know much less about the early life-history, reproductive biology and population movements of these species and how fishing effort may be affecting these biological characteristics. The Isle of Man government has been collecting catch and effort data since 2007, which provides valuable insight to this spatially and temporally variable fishery. Bangor University scientists have begun developing a long-term monitoring programme for lobster and crab, which involves the cooperation of local creel fishermen and utilisation of novel techniques, enabling us to monitor catches and better understand the population parameters of lobster and crab.
Baie ny Carrickey Closed Area
One of the challenges in managing lobster and crab fisheries is understanding how these species use (or are restricted by) habitat structure. The relationship is complex; however, by using equipment such as the flying array underwater video system and drop-down cameras, then combining the data with fishery-dependent catch samples, we can identify key habitats for these species at certain stages of their life cycle. The movie below is an example of our footage captured from our flying array trials.
By working closely with members of the Baie Ny Carrickey Crustacea Fishery Management Association (BNC-CFMA), Bangor University MSc student Lucy May was able to provide valuable insight into the influence of habitat and her thesis is available here. The team's research, together with the help of from members of the BNC-CFMA, has triggered a long-term capture-mark-recapture study within the BNC closed area which will commence in the near future. Understanding crustacean movements plugs a knowledge-gap which currently inhibits their management at appropriate spatial scales. This experiment was conducted in close collaboration with the fishing industry.
A summary report on the scientific monitoring program to July 2016 is available here.
Electronic Data Collection with Onboard Cameras
Image: Natalie Hold – onboard cameras undergoing sea-trials.
Data collection has traditionally relied upon scientific observers having to spend time onboard commercial fishing vessels, which are typically <10 m day boats. The high costs and inherent challenges associated with this method of data collection means that scientists and managers assess these fisheries using only snapshots of data (in both a spatial and temporal sense). Very few datasets exist where fine-scale patterns in fishing effort, catchability, sex-ratio, reproductive status, disease and population structure of target species can be directly compared between multiple local fishing grounds over a long-term period.
Preliminary work by Natalie Hold and other Fisheries and Conservation team members showed that onboard-cameras can capture this data at reduced costs. Researchers based on the Isle of Man, in collaboration with colleagues based in Wales, are working to increase the usability of this data collection method for scientists and fishermen. We are integrating hardware components to increase data quality and will conduct trials in the near future. Our aim is to develop image-recognition software to identify and measure target species from the video footage. Automated processing will further reduce project time and costs, ultimately increasing the volume of data which can be collected and analysed. The Isle of Man provides a unique opportunity to have this method of data collection implemented at a national level and create a comprehensive evidence base for management.
Lobster (Homarus gammarus)
Image: Jack Emmerson – juvenile lobster
DEFA have collected catch return data from fishermen for many years, but these only record the animals landed for sale, i.e. above the minimum landing size. Our research programme provides information on undersize lobsters, and those returned to the sea because they are egg-carrying females or are unsuitable for commercial sale (e.g. missing claws).
Creels are designed to catch marketable size lobsters, rather than juveniles, and now legally require escape gaps to allow juveniles to get out. As a result we use a different method to monitor the number of juvenile lobsters on the lobster grounds. We use Roscoff style pots with a smaller mesh size (10mm), smaller entrance holes and no escape gaps to capture the juveniles. This gives us a rare insight and valuable data on the little known early life stages of these lobsters. These juvenile samples provide a unique and critical element to datasets that are helping us to understand sexual maturity of the species.
Understanding the reproductive biology of a species is essential in protecting a population against recruitment overfishing. For many years, scientists have experimented with various methods with which to assess the size-at-maturity of the European lobster; however, unlike in the case of the North-east American/Canadian lobster fishery, there is no consensus or standard protocol to undertake routine assessments. Bangor University scientists, in collaboration with colleagues throughout Europe, are currently working towards a standard protocol for routine assessment by cross-validating the maturity estimates of various methodological techniques.
Unlike throughout much of the UK, the landing of egg-bearing or berried females is prohibited in the Isle of Man. Since female recruits (87 mm) are able to carry eggs for over 9 months of the year, they are afforded a considerable level of protection even in the absence of data on their reproductive biology. This is why Bangor University scientist based on the Isle of Man are focussing initially on methods to assess male size-at-maturity.
Bangor University scientists have provided small snips of tails and a small sample of eggs from berried females around the island in a larger project looking at the connectivity of shellfish resources in the Irish Sea. By collaborating with other fisheries scientists to compare the genetic structure of Manx lobsters with that of populations elsewhere in the Irish Sea, we will gain insight into the connectivity and recruitment of these populations. This allows decisions to be made about the necessity, or benefits, of local fishery management plans.
Previous work by the Fisheries and Conservation Team provided data on the efficiency of various escape panel designs and sizes (Report 9). This led to the legal introduction of these panels in all Manx creels from September 2011. Escape panels can significantly reduce catch sorting and handling time for fishermen, as well as protecting smaller lobsters from cannibalism or damage when trapped in creels with larger, more aggressive lobsters. Indeed, they have been so effective that some creel fishermen have increased their escape panels beyond the minimum requirement.
Edible Crabs (Cancer pagurus)
Image: Edible crab tag-placement analysis (left). Dr Fikret Ondes (alumni) onboard a commercial boat (right).
To provide scientific advice on the design of a successful sustainable fishery for the edible crab, Fikret Ondes (PhD alumni) collected baseline information on growth and reproduction of the crabs and has conducted shore surveys in the Isle of Man to look at juvenile crab nursery areas. His work is also investigated feeding, distribution and prevalence of shell disease. Fikret’s baseline study assessed the stock structure of the edible through fishery-dependent data. This is information on catch, effort and costs provided from fisheries statistics, fisher’s logbooks and the Department of Environment, Food and Agriculture (DEFA). It was also assessed through fishery-independent data, which was collected through field studies. This provided information on sex and size distributions, by-catch and catch per unit effort (CPUE).
Bangor University researchers based in Wales recently led a collaborative study to examine regional variation in the size-at-maturity of brown crab (Haig et al., in press), to which the Isle of Man based colleagues provided data. The ICES WGCRAB Report 2015 is an excellent source of information on the biology and life histories of crab species. The work supported initial findings by Fikret, that the brown crab population is functionally mature at the point of recruitment into the fishery (i.e the current minimum landing size afford a biologically appropriate level of protection).
An intriguing find from Fikret’s research was that females appear to undertake a spawning migration towards grounds to the southwest of the Isle of Man in the autumn, where ovigerous (egg-bearing) females seek out deeper water. Researchers based on the Isle of Man are seeking to investigate this further with a multi-annual tag-recapture experiment.
Image: Fikret Ondes - Lobster crab pots (left). A rare electic-blue lobster (right).
In 2015 the lobster fishery landed 57 tonnes worth £410,277 and the edible crab fishery landed 464 tonnes worth £494,653 (Source: DEFA Economic Fisheries Digest accessed on 22/01/16). Lobster and crab are targeted using the same gear, the traditional creel and parlour pots. These are baited using finfish. The size and number of traps deployed varies depending on the capacity of the vessel, which can range from <6 m to >12 m. The species fished for is prioritised depending on fishing location and bait type, for example, lobsters are typically found on rocky reefs within the 3 nautical mile (nm) limit, whereas edible crabs are found across the territorial sea all the way to the 12 nm limit.
The number of potting licences has been increasing, with some of these licences belonging to UK – registered vessels who do not always fish in the Manx territorial sea. The latent capacity within the fishery is a concern for sustainable management.
There are strict limits on the number of pots that are allowed to be set and animals must reach a certain size before they can be retained and landed (i.e a minimum landing size). Other measures in place to improve the sustainability of the fishery include fitting escape hatches to pots and a prohibition on the landing of berried animals. These measures reduce the capture of undersized and berried individuals.
The Brown Crab or Edible Crab (Cancer pagurus)
The edible “brown crab” has an oval, reddish brown carapace with a distinctive “pie crust” edge and black tipped pincers. Adults can grow to 25 cm wide, weigh up to 3kg and live as long as 30 years.
Habitat & Distribution
Brown crabs are abundant throughout British and Irish coastal waters; they can be found as far north as Norway and as far south as Africa. Brown crabs use a variety of coastal habitats during different stages in their life history, from intertidal algae beds to mixed coarse sediments and offshore in muddy sands in water as deep as 100m.
Male crabs will grab a female and guard her until she moults, which is when her carapace becomes soft, and she can be fertilised. After mating the female will retreat to soft sediments to brood her millions of eggs for anywhere up to nine months. The number of eggs will depend on the size of the mother and the development time is temperature dependant. Tiny larvae (1 mm) called zoea will hatch and go through several moults themselves before metaphorphising into a postlarval form called a megalopa. This megalopa stage will settle out of the water column and into juvenile habitats inshore. Juveniles will stay in the intertidal zone until they reach 60-70 mm at which point they will migrate to deeper waters. Size at sexual maturity appears to vary with region and a range of sizes has been reported for both males (101-117mm carapace width) and females (108-134 mm carapace width).
The European Lobster (Homarus gammarus)
The European lobster, Homarus gammarus, is a large lobster that can grow up to 1 m in length, but is more often is 60 cm. This lobster is blue on top and yellow below, with a large asymmetrical set of claws.
Habitat & Distribution
The European lobster can be found on rocky bottoms living in holes and excavated tunnels from the lower shore to depths of 60 m. These species are distributed from the eastern Atlantic Ocean, Mediterranean Sea and parts of the Black Sea. Although the European lobster is not known to migrate, they will roam to find food and typically have a home range of 2 km. Some individuals, however, have been found to move 10 km or more from their burrows. European lobsters have a varied diet which consists of crabs, molluscs, sea urchins, sea stars and polychaete worms.
Female European lobsters reach sexual maturity between the ages of 5 and 7 and mating takes place between a soft-shelled female and a hard-shelled male. Spawning usually takes place in summer and the female carries the eggs on her abdomen for 9-12 months. These females are called “berried.” Once the larvae hatch and are released into the water column, they float in the surface layers and are at the mercy of the ocean currents. This period last 5-10 weeks and they feed on microorganisms. After three moults, the body shape changes and the larvae look more like adult lobsters and adopt a life on the seabed. Once settled, the juveniles burrow in the seabed for approximately 2 years and move very little. At a carapace length of approximately 15 mm they leave their burrows and begin life as an adult.
- Report 9 - Lobster escape gap trials – 2009
- ICES WGCRAB Report 2015 - Report of the Working Group on the biology and life history of crabs
- Report 32 - The Baie ny Carrickey closed area- scientific trial (2013 - 2016): Scientific monitoring plan