The catch characteristics and population structure of the brown crab (Cancer pagurus) fishery in the Isle of Man, Irish Sea

Abstract

Brown crab contributes to small-scale fisheries in the Isle of Man and landings (495 t) were worth in excess of £0.5 million in 2012. The present study sought to fill evidence gaps needed to improve the scientific understanding of this fishery. Observer data were collected to examine the spatial and temporal variations in the size distribution and sex ratio of crabs around the Isle of Man. This study also aimed to evaluate the catch characteristics of brown crab using logbook data (2007–2012), observer data (2012–2013) and questionnaire survey data (2013). The sex ratio is highly variable in different areas across seasons and was perhaps indicative of migration patterns in relation to mating. This change was most notable with a strong increase in the proportion of females to the south and west of the Isle of Man in the autumn months. The depth and pot volume were important factors that influenced the catch per unit effort (CPUE). Future survey designs would need to ensure adequate spatial coverage of the east and west coast of the Isle of Man together with a seasonal sampling regime that captures the spatial change in the distribution and abundance of male and female crabs.

Assessing the stability and mobilisation of crab-pot-strings anchored with Bruce anchors under different marine conditions

“…Apparently there is a strong regional aspect to behaviour and catchability. Of course one can expect seasonal influences as well but these are not strong in the short period the measurements of present study have been performed (Bennet, 1974, Tully et al, 2006, Öndes et al, 2019.…”

“…Catchability of an individual animal depends on size, sex, moult status, and rhythms (like day : night, seasonality) and environmental factors such as location, light, water temperature and currents, and also factors such as vessel and crew characteristics (Miller, 1990, Skerrit, 2014, Öndes et al, 2019.…”

Population, Reproductive and Fishery Dynamics of Spotted Box Crab (Calappa philargius), a New Claw-Only Fishery Species, in the Southern Taiwan Strait, China

“…female-biased in terms of sexual size dimorphism whereas Cancer pagurus, P. sanguinolentus, and P. trituberculatus (Oh, 2011;Yang et al, 2014;Öndes et al, 2017) are male-biased. Meanwhile, sexual size dimorphism could also exhibit spatial variation within the same species.…”

Ecology of the brown crab (Cancer pagurus) : and production potential for passive fisheries in Dutch offshore wind farms

“…During this period while female crabs carry the eggs (berried females), they do not feed, remaining in pits dug in the sediment or under rocks and are therefore unlikely to be caught in a baited pot (Howard, 1982). In fact, in a survey determining catch characteristics in the Irish sea a total of 5795 commercial pots were hauled and only 16 ovigerous females were found in the pots (Ondes et al, 2019). C. pagurus appears to use a "capitalist" reproductive strategy 1 , relying on previously accumulated energy to use throughout the reproductive season (Haig et al, 2016).…”

“…Female crabs with eggs that bury themselves in the sand are less susceptible to be caught in crabbing pots during the berried (oviparous) stage (Ondes et al, 2019), which poses an advantage in terms of keeping stock above recommended levels. The proposed function of monopiles acting as larvae collectors may also benefit local population densities however little is known about the early settlement of juvenile brown crabs and how this interaction takes place.…”