Manual declawing of Cancer pagurus before return to the sea and during storage aboard fishing vessels has been legal in Northern Ireland (NI) since the revocation in 2000 of the Crab Claws (Prohibition of Landing) Order (1986). However, the paucity of objective data on this fishery practice has raised concerns for the sustainability and welfare of C. pagurus. Feeding ability of edible crabs was examined by either inducing autotomy or manual declawing of a walking leg, one or both chelae, before crabs were offered prey items. Crabs were offered mussels, Mytilis edulis, to assess if having one or no chelae results in a reduced ability to feed on hard shelled prey for which its crushing chelae are adapted. Crabs that had a walking leg removed ate significantly more mussel mass than crabs that had one or two claws removed, with no difference between crabs that had one claw or two claws removed. This suggests that induced autotomy and manual declawing of C. pagurus has a detrimental effect on the ability of crabs to feed on readily available prey, and that other feeding opportunities must be found The physiological stress response to manual declawing of both claws, in males and females, was assessed by extracting lactate over 24 hours following claw removal. All manually declawed crabs died within 14 days, whereas all others survived for +23 days. Lactate concentrations in crabs that had both claws manually declawed increased significantly, compared to autotomized and intact crabs, and remained high for 24 hours. Thus, manual double declawing results in a prolonged stress response and high crab mortality, leading to the recommendation to cease this practice, or perhaps develop induced autotomy techniques as a more sustainable fishery practice. Fighting ability during contests for resources (female and a shelter) was investigated in crabs that had either 1 claw manually declawed, 1 claw autotomized or the crab remained intact. Contests involved an intact crab and an autotomized crab, or an intact crab and a manually declawed crab. Intact and autotomized crabs were motivated to fight for the female and won more contests than the manually declawed crabs. Manually declawed crabs displayed more submissive and defensive behaviour than the other crabs and were less motivated to fight for the female. More manually declawed crabs competed for and won the shelter than intact and autotomized crabs. The findings of these experiments provide an insight into realistic scenarios facing manually declawed crabs once returned to the sea, and raise serious concerns regarding sustainability and animal welfare.

The velvet swimming crab fishery is a relatively recent development in Ireland and the UK. The collapse of the traditional fishery in the Mediterranean in the 1980’s enabled this previous pest species to become a commercially significant sector in Northern Ireland. Now the second most important commercial fishery species in Northern Ireland, recent declines in catch have caused concern among local fishermen and industry. Limited information currently exists on current velvet crab populations and trends in fishery catch in Northern Ireland. To provide initial baseline information, studies of fishery catch detailed size discrepancies between Strangford Lough and the Irish Sea. Larger, heavier crabs were consistently landed in Strangford Lough. Berried crabs were mostly found in winter and spring, which is also the peak fishery season. Histological techniques were employed to adapt a newly published method to directly determine age in crustaceans. These studies have paved the way for future research in this area, suggesting that decalcifying eyestalks is an ineffective approach in preparing eyestalk sections, and recommends alternative methods. Known to be a species vulnerable to overfishing and sensitive to the stress of capture and transport, current measures made by fishermen to alleviate stress during capture were found to be ineffective. Crabs kept on a flow through system showed reduced signs of stress. Handling was found to cause a stress response in berried females, and it is suggested that handling of these animals is reduced as much as possible. Reducing stress and maximising survival of berried females will greatly enhance recruitment to populations. Overall, this investigation aimed to provide baseline information on velvet crab fishery catch and ensure sustainable practice in Northern Ireland. This study presents results which can be used to develop management policies and inform fisheries elsewhere.

No description available.

No description available.

Lake Victoria contributes more than 60% of the total fish yield in each of the respective riparian countries, Kenya, Uganda and Tanzania. Nile perch Lates niloticus contributed more than 60% to the total yield from the lake. Although accused of causing ecological instability of the ecosystem due to its predatory effects, the fishing industry became socially and economically dependable on the Nile perch. In the mid 1990s signs of overfishing were observed and concerns for the sustainability of the fishery were raised. To properly manage a fishery, knowledge of the factors that regulate the dynamics of the stock(s), their abundance and distribution is essential. Unfortunately data on the status of the Nile perch stocks are inadequate. This study was conducted on the Tanzanian part of Lake Victoria from 1997 to 2001 to address this problem. Reference is also made to the Kenyan and Ugandan national waters for comparison. Bottom trawl and catch assessment surveys were conducted to assess the status of the stocks. Abundance estimates and distribution patterns were determined. Current exploitation levels and practises were analysed and linked to growth and mortality, feeding and reproductive characteristics of the stock to determine status. Key environmental parameters were investigated and linked to the variations in the biological aspects and distribution patterns observed. There was an indication of reduced anoxic problems in the offshore deep waters and signs of improvement in the eutrophic state of the lake. Mean oxygen concentrations in the waters sampled varied from 8.02±0.73 mg L⁻¹ in the surface waters to 3.2±4.36 mg L⁻¹ in the bottom waters of 68 m deep, while Secchi disk readings at stations of 5-10 m depth ranged from 0.84±0.3 m in November to 1.9±1.02 m in August/September and in offshore waters of 50-6Om depth the readings were 3.08±0.62 m in February to 5.52±1.7 m in August/September. Distribution patterns of fish were highly aggregated but variable and were greatly influenced by seasonal patterns of oxygen and temperature, while reproduction and recruitment were related to rainfall patterns. Using the swept area method, biomass was estimated at 306,000 t for the Tanzanian waters and around 620,000 t for the whole lake, with a mean density of 9.87 t km⁻² and 10.56 t km⁻² respectively. Very high fishing mortality (1.55 yr⁻¹) and exploitation rates (0.84) were estimated using an L∞ of 218 em TL and a growth constant (K) of 0.16 estimated during the study. Excessively high fishing effort was observed in the 2000 frame survey while catch compositions reveal high dependence on juveniles for the Nile perch fishery. The size at first maturity was at 54.3 cm TL (1.6-yr.) and 76.7 em TL (2.5 yr.) for males and females respectively. About 83% of the catch survey data were below size at first maturity for males and 99% for females. Bottom trawl data (88% juveniles) suggested high recruitment in the stock. However the models indicated unsustainable exploitation of the fishery. A reduction of exploitation rate by 50% and increase of size at capture for optimum yield is recommended. The dominance of juveniles in the catch with the current yields (estimated at 138 323.85±6 229.14 t) higher than the sustainable yield (calculated at 108941.9 t yr⁻¹, using Cadima's formula) demands immediate management initiatives. Co-management is singled out as the most effective option for a functional system to implement control, monitoring and surveillance strategies within management process. With dynamic systems within the stocks, the environment as well as socioeconomic influences, and with continuous monitoring, adaptive and precautionary management strategies are recommended. Without reliable catch trend data it is difficult to confidently make predictions. The need to have a well-structured catch assessment survey system for reliable catch statistics is recommended. Priority areas to further research are also identified.

No description available.

No description available.

No description available.

No description available.

No description available.