Domoic acid (DA), the toxin responsible for amnesic shellfish poisoning (ASP) can accumulate in k... more Domoic acid (DA), the toxin responsible for amnesic shellfish poisoning (ASP) can accumulate in king scallop Pecten maximus leading to extensive fishery closures. Approximately 59% of the total value of all fish and shellfish landed in the Isle of Man in 2004 comprised king scallop, hence the economy of the Manx marine sector is particularly susceptible to impacts from this biotoxin. Scallop from fishing grounds around the Isle of Man were sampled in to determine levels of inter-animal and spatial variability in DA concentration and factors that might influence toxin concentration such as scallop size and water depth. Mean DA concentrations in hepatopancreas ranged from 296.3 mg g À1 to below the detection limit, in gonad from 27.8 mg g À1 to below the limit of detection and in adductor muscle from 7.3 mg g À1 to below the limit of detection. High levels of inter-animal variability of DA concentration in hepatopancreas were recorded; CVs ranging from 16.1% to 70.0%. DA concentrations above 20 mg g À1 were recorded in gonads on all three sampling dates. Scallops from fishing grounds on the east of the Isle of Man were significantly less contaminated than those from the west and southwest. A significant positive correlation between DA concentration and shell length was recorded in some sites, but there was no relationship with water depth. The high inter-animal, spatial and seasonal variability in toxin concentration highlighted the importance of understanding field variability for the development of reliable sampling and management protocols. # 2006 Published by Elsevier B.V.
Age composition and growth rates of queen scallops Aequipecten opercularis (L.) around the Isle o... more Age composition and growth rates of queen scallops Aequipecten opercularis (L.) around the Isle of Man.
Despite the current interest in using closed areas for fisheries management, few studies have act... more Despite the current interest in using closed areas for fisheries management, few studies have actually examined the benefits for invertebrate fisheries such as scallops. This study details the dynamics of a population of great scallops Pecten maximus (L.), within a closed area and an adjacent fished area off the Isle of Man, over a 14 yr period (1989 to 2003). Scallop densities were very low in both areas when the closed area was set up, but increased at an accelerated rate over time within the closed area. Scallop densities also increased on the adjacent fishing ground, but not to the same extent. Consequently, the density of scallops above the minimum legal landing size (110 mm SL) was more than 7 times higher in the closed area than in the fished area by 2003. There was also a shift towards much older and larger scallops in the closed area and, correspondingly, lower estimates of total mortality. Experimental dredging of 2 plots within the closed area confirmed that fishing drove these differences in population dynamics and structure. These patterns of scallop density, age and size structure resulted in the exploitable biomass (adductor muscle and gonad) of scallops being nearly 11 times higher in the closed area than in the fished area by 2003, and the reproductive biomass was 12.5 times higher. This is significant for fisheries management because the build up of high densities of large P. maximus individuals enhanced local reproductive potential and therefore the likelihood of export of larvae to the surrounding fishing grounds. Along with these direct benefits of closed area protection, juvenile scallops had higher survival and individual growth rates in the closed area, apparently in response to reduced fishing disturbance. Although juvenile scallops are not subject to direct removal by fishing, protection during this critical phase therefore appeared to assist the recovery of the closed area population. In summary, this study joins a growing number indicating that the use of closed areas offers a range of benefits over more traditional methods of managing fisheries. Fisheries for relatively sedentary and long-lived species such as P. maximus appear to be particularly suitable for this type of management.
2003. Population dynamics and predictions in the Isle of Man fishery for the great scallop (Pecte... more 2003. Population dynamics and predictions in the Isle of Man fishery for the great scallop (Pecten maximus, L.). -ICES Journal of Marine Science, 60: 224-242.
The annual success of the queen scallop fishery around the Isle of Man in the northern Irish Sea ... more The annual success of the queen scallop fishery around the Isle of Man in the northern Irish Sea is dependent on the strength of recruitment. We examined data from surveys and commercial logbooks on the annual density of spat, juvenile, and adult queen scallops in the fishery between 1982 and 2002. These were used to examine past population and fishery trends and the potential for formulating a predictive model for the fishery. The results were highly variable on both temporal and spatial scales, but there were some general trends. Density appeared to have been relatively stable during the 1980s, declined sharply from the early to mid-1990s, then recovered to produce relatively good catch rates thereafter. There was no relationship between spat settlement and the subsequent density of juveniles or adults in stock surveys or with commercial catch rates. However, within the stock surveys, there were three different significant relationships between cohort densities over time. Addition...
The impact of scallop dredging on benthic megafauna was assessed by direct observation of damage,... more The impact of scallop dredging on benthic megafauna was assessed by direct observation of damage, both in the bycatch and in organisms encountering dredges but not captured. Damage was assessed using a simple 4-point scale adapted for different taxonomic groups. Experimental dredging was undertaken on a scallop fishing ground in the north Irish Sea, off the Isle of Man. Divers were deployed immediately after dredges had passed, to record levels of damage to megafauna left in the dredge tracks. Mean damage levels, and the proportions of the 4 damage scores in the bycatch and on the seabed, were the same in most species. Some common species did show differences. The edible crab Cancer pagurus was more severely damaged when not captured, while the starfish Asterias rubens and whelk Neptunea antiqua received greater damage within the bycatch. Capture efficiency for the megafauna was low, ranging from 2 to 25 % among species. The results indicate that the majority of damage to large bent...
The efficiency and selectivity of spring-toothed scallop dredges was assessed using a concurrent ... more The efficiency and selectivity of spring-toothed scallop dredges was assessed using a concurrent depletion experiment and diver survey of dredge tracks on a north Irish Sea fishing ground. Two size classes of the scallop, Pecten maximus (L. 1758), were examined: below minimum legal landing size (MLLS), (90-109 mm shell length (SL)) and above MLLS (> 109 mm SQ. Estimates of efficiency from the depletion experiment (24.3% and 29.5% respectively) were consistently lower than those from the diver surveys (38.0% and 40.7% respectively). This difference appeared to be due to inherent variation in the efficiency of scallop dredges rather than bias from either technique. This emphasizes the need for error terms to be built into estimates of dredge efficiency. The diver survey also found that dredges were highly selective toward scallops greater than 90 mm SL, catching only 3.0% or less of individuals below this size. Consequently, the diver survey provided a much more accurate assessment...
1. Dredging for marine bivalves can cause considerable damage to benthic invertebrates and habita... more 1. Dredging for marine bivalves can cause considerable damage to benthic invertebrates and habitats. However, it is largely unknown how dredging affects fish communities. In this study patterns and impacts of fish bycatch in scallop dredges around the Isle of Man, in the north Irish Sea, were investigated by analysing data from fisheries-independent surveys conducted between 1992 and 2005.
Domoic acid (DA), the toxin responsible for amnesic shellfish poisoning (ASP) can accumulate in k... more Domoic acid (DA), the toxin responsible for amnesic shellfish poisoning (ASP) can accumulate in king scallop Pecten maximus leading to extensive fishery closures. Approximately 59% of the total value of all fish and shellfish landed in the Isle of Man in 2004 comprised king scallop, hence the economy of the Manx marine sector is particularly susceptible to impacts from this biotoxin. Scallop from fishing grounds around the Isle of Man were sampled in to determine levels of inter-animal and spatial variability in DA concentration and factors that might influence toxin concentration such as scallop size and water depth. Mean DA concentrations in hepatopancreas ranged from 296.3 mg g À1 to below the detection limit, in gonad from 27.8 mg g À1 to below the limit of detection and in adductor muscle from 7.3 mg g À1 to below the limit of detection. High levels of inter-animal variability of DA concentration in hepatopancreas were recorded; CVs ranging from 16.1% to 70.0%. DA concentrations above 20 mg g À1 were recorded in gonads on all three sampling dates. Scallops from fishing grounds on the east of the Isle of Man were significantly less contaminated than those from the west and southwest. A significant positive correlation between DA concentration and shell length was recorded in some sites, but there was no relationship with water depth. The high inter-animal, spatial and seasonal variability in toxin concentration highlighted the importance of understanding field variability for the development of reliable sampling and management protocols. # 2006 Published by Elsevier B.V.
Age composition and growth rates of queen scallops Aequipecten opercularis (L.) around the Isle o... more Age composition and growth rates of queen scallops Aequipecten opercularis (L.) around the Isle of Man.
Despite the current interest in using closed areas for fisheries management, few studies have act... more Despite the current interest in using closed areas for fisheries management, few studies have actually examined the benefits for invertebrate fisheries such as scallops. This study details the dynamics of a population of great scallops Pecten maximus (L.), within a closed area and an adjacent fished area off the Isle of Man, over a 14 yr period (1989 to 2003). Scallop densities were very low in both areas when the closed area was set up, but increased at an accelerated rate over time within the closed area. Scallop densities also increased on the adjacent fishing ground, but not to the same extent. Consequently, the density of scallops above the minimum legal landing size (110 mm SL) was more than 7 times higher in the closed area than in the fished area by 2003. There was also a shift towards much older and larger scallops in the closed area and, correspondingly, lower estimates of total mortality. Experimental dredging of 2 plots within the closed area confirmed that fishing drove these differences in population dynamics and structure. These patterns of scallop density, age and size structure resulted in the exploitable biomass (adductor muscle and gonad) of scallops being nearly 11 times higher in the closed area than in the fished area by 2003, and the reproductive biomass was 12.5 times higher. This is significant for fisheries management because the build up of high densities of large P. maximus individuals enhanced local reproductive potential and therefore the likelihood of export of larvae to the surrounding fishing grounds. Along with these direct benefits of closed area protection, juvenile scallops had higher survival and individual growth rates in the closed area, apparently in response to reduced fishing disturbance. Although juvenile scallops are not subject to direct removal by fishing, protection during this critical phase therefore appeared to assist the recovery of the closed area population. In summary, this study joins a growing number indicating that the use of closed areas offers a range of benefits over more traditional methods of managing fisheries. Fisheries for relatively sedentary and long-lived species such as P. maximus appear to be particularly suitable for this type of management.
2003. Population dynamics and predictions in the Isle of Man fishery for the great scallop (Pecte... more 2003. Population dynamics and predictions in the Isle of Man fishery for the great scallop (Pecten maximus, L.). -ICES Journal of Marine Science, 60: 224-242.
The annual success of the queen scallop fishery around the Isle of Man in the northern Irish Sea ... more The annual success of the queen scallop fishery around the Isle of Man in the northern Irish Sea is dependent on the strength of recruitment. We examined data from surveys and commercial logbooks on the annual density of spat, juvenile, and adult queen scallops in the fishery between 1982 and 2002. These were used to examine past population and fishery trends and the potential for formulating a predictive model for the fishery. The results were highly variable on both temporal and spatial scales, but there were some general trends. Density appeared to have been relatively stable during the 1980s, declined sharply from the early to mid-1990s, then recovered to produce relatively good catch rates thereafter. There was no relationship between spat settlement and the subsequent density of juveniles or adults in stock surveys or with commercial catch rates. However, within the stock surveys, there were three different significant relationships between cohort densities over time. Addition...
The impact of scallop dredging on benthic megafauna was assessed by direct observation of damage,... more The impact of scallop dredging on benthic megafauna was assessed by direct observation of damage, both in the bycatch and in organisms encountering dredges but not captured. Damage was assessed using a simple 4-point scale adapted for different taxonomic groups. Experimental dredging was undertaken on a scallop fishing ground in the north Irish Sea, off the Isle of Man. Divers were deployed immediately after dredges had passed, to record levels of damage to megafauna left in the dredge tracks. Mean damage levels, and the proportions of the 4 damage scores in the bycatch and on the seabed, were the same in most species. Some common species did show differences. The edible crab Cancer pagurus was more severely damaged when not captured, while the starfish Asterias rubens and whelk Neptunea antiqua received greater damage within the bycatch. Capture efficiency for the megafauna was low, ranging from 2 to 25 % among species. The results indicate that the majority of damage to large bent...
The efficiency and selectivity of spring-toothed scallop dredges was assessed using a concurrent ... more The efficiency and selectivity of spring-toothed scallop dredges was assessed using a concurrent depletion experiment and diver survey of dredge tracks on a north Irish Sea fishing ground. Two size classes of the scallop, Pecten maximus (L. 1758), were examined: below minimum legal landing size (MLLS), (90-109 mm shell length (SL)) and above MLLS (> 109 mm SQ. Estimates of efficiency from the depletion experiment (24.3% and 29.5% respectively) were consistently lower than those from the diver surveys (38.0% and 40.7% respectively). This difference appeared to be due to inherent variation in the efficiency of scallop dredges rather than bias from either technique. This emphasizes the need for error terms to be built into estimates of dredge efficiency. The diver survey also found that dredges were highly selective toward scallops greater than 90 mm SL, catching only 3.0% or less of individuals below this size. Consequently, the diver survey provided a much more accurate assessment...
1. Dredging for marine bivalves can cause considerable damage to benthic invertebrates and habita... more 1. Dredging for marine bivalves can cause considerable damage to benthic invertebrates and habitats. However, it is largely unknown how dredging affects fish communities. In this study patterns and impacts of fish bycatch in scallop dredges around the Isle of Man, in the north Irish Sea, were investigated by analysing data from fisheries-independent surveys conducted between 1992 and 2005.
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