Arctica Islandica Research Articles

Validated age, growth, and mortality estimates of the ocean quahog (Arctica islandica) in the western Atlantic

Abstract Kilada, R. W., Campana S. E., and Roddick, D. 2007. Validated age, growth, and mortality estimates of the ocean quahog (Arctica islandica) in the western Atlantic. ICES Journal of Marine Science, 64: 31–38. The age structure of offshore (Sable Bank) and inshore (St Mary's Bay) populations of eastern Canadian ocean quahogs (Arctica islandica), and of a northwestern Iceland population, is investigated. Age estimates for eastern Canadian ocean quahogs were validated through analysis of bomb-produced 14C in quahog shell growth increments deposited before, during, and after the atmospheric atomic bomb testing periods of the 1950s and 1960s. Delta 14C from shells with presumed birthdates between the late 1950s and 1970s clearly reflects the sharp increase in oceanic radiocarbon attributable to nuclear testing. The results validate our age interpretations of Sable Bank quahogs to an age of 45 y, and support longevity estimates of more than 200 y for the same population. Longevity calculations for the other populations exceeded 60 y. Von Bertalanffy growth parameters were estimated for the three populations; the growth rate of all three was relatively rapid for the first 20–30 y of life, but thereafter was very slow. The instantaneous rate of natural mortality (M), calculated using the age–frequency distribution of the unexploited populations, was estimated to be 0.03 and 0.10 for the Sable Bank and St Mary's Bay populations, respectively.

Compound response of marine and terrestrial ecosystems to varying climate: Pre-anthropogenic perspective from bivalve shell growth increments and tree-rings

Annual growth increments were examined from shells of the ocean quahog (Arctica islandica L.) from northwest Norway and from tree-ring samples of the Scots pine (Pinus sylvestris L.) from nearby coastal areas. The reconstructed annual growth increments were used to compare growth variability in marine and terrestrial ecosystems. Spatiotemporal comparison of the growth records showed statistically significant correlation during the 19th century A.D., indicative of ecosystem-independent response to pre-anthropogenic climate variations. Geographical correlation between marine and terrestrial records was only observed at the local scale. Years with particularly low winter or high summer North Atlantic Oscillation (NAO) indices showed the best synchronization of marine and terrestrial growth. Despite strong correlation during historical time, our palaeoecological evidence suggests that marine and terrestrial ecosystems may show dissimilar growth reaction to recently observed positive winter-NAO phases.

Sclerochronological records of Arctica islandica from the inner German Bight

Sclerochronological records of interannual shell growth variability were established for eight modern shells (26 to 163 years of age) of the bivalve Arctica islandica, which were sampled at one site in the inner German Bight. The records indicate generally low synchrony between individuals. Spectral analysis of the whole 163-yr masterchronology indicated a cyclic pattern with a period of 5 and 7 years. The masterchronology correlated poorly to time series of environmental parameters over the last 90 years. High environmental variability in time and space of the dynamic and complex German Bight hydrographic system results in an extraordinarily high ‘noise’ level in the shell growth pattern of Arctica islandica.

In vitro transformation of PSP toxins by different shellfish tissues

Many in vivo shellfish feeding experiments have been carried out in order to investigate the fate of PSP toxins in the marine food chain. A focal point of these studies concerns the species- and tissue-specific differences in toxin metabolism. However, tissue specific effects are often overlapped by selective toxin retention as well as transfer between individual compartiments. In in vitro experiments presented here digestive tissue and adductor homogenates of 10 shellfish species (bivalvia: Mytilus edulis, Crassostrea gigas, Cardium edule, Arctica islandica, Ensis ensis, Modiolus modiolus, Mactra stultorum, Pecten maximus as well as two snails: Littorina littorea and Buccinum undatum) were incubated with an extract of the toxic strain Alexandrium fundyense CCMP 1719. After incubation, changes in the toxin pattern could be observed in all samples with significant differences occuring between both the species and tissues. The greatest metabolic activity was found in digestive tissue samples. Among the organisms, the species with a non-filtering lifestyle, L. littorea and B. undatum, showed the highest conversion rates. Interestingly, the high metabolic transformation rate of the PSP toxins was accompanied with a fast reduction (up to 73%) of toxicity in the homogenates.

EVIDENCE OF RECENT RECRUITMENT IN THE OCEAN QUAHOG ARCTICA ISLANDICA IN THE MID-ATLANTIC BIGHT

Abstract We report results of a survey explicitly focused on ocean quahog recruitment in the Mid-Atlantic Bight. The recruitment survey resampled all NMFS survey sites south of Hudson Canyon and a selection of sites north and east of Hudson Canyon off the Long Island coast over the entire depth range of this species with the exception of the most inshore reaches off Long Island. More ocean quahogs were encountered, on a per tow basis, in the vicinity of and north of Hudson Canyon. The proportion of recruits in the size-frequency distribution was higher in the south and the most recent recruitment events were concentrated there. Analysis of the 104 size-frequency distributions delineated regions of recent recruitment, areas that have not seen significant recruitment for many decades and areas that received heavy recruitment some decades previously but not recently. Overall, the survey suggests that three regionally distinctive processes determine the size-frequency distributions of ocean quahog assemblages...

Fishery biology and biological reference points for management of ocean quahogs (Arctica islandica) off Iceland

Abstract Ocean quahogs off Iceland are large, slow growing clams distributed on the continental shelf around the north Atlantic. The Icelandic stock is most northern and found in the shallowest water. Maximum age may exceed 200 y. Commercial fishing and biological research for ocean quahogs started in 1995 but relatively little biological information is available. We used published information, estimated key parameters, and calculated biological reference points for the Icelandic stock based on per recruit models. Commercial catches varied during 1995–2000 and increased to 14,200 t in 2003. The growth model was L = 99.9(1−e −0.0223( a +22.5) ), where L is shell length (SL, mm) and a is age (y). Fifty-percent of ocean quahogs reach sexual maturity by 64 mm SL (23 y) and 50% are fully selected by commercial fishing dredges by 72 mm SL (55 y). Based on a length-based per recruit model, F MAX = 0.0694, F 0.1 = 0.0312 and F 50% = 0.032 y −1 . Managers should consider precautionary management approaches in view of ocean quahog life history, uncertainties about recruitment, and likely low stock productivity. The current 2.5% harvest rate approach seems reasonable in the near term because 2.5% is less than F 50% and F 0.1 from a per recruit model. However, based on simulation analyses in the literature, approaches that maintain high levels of spawning biomass (e.g., 60–80% of virgin) might perform better in the long term. More accurate approaches to measuring stock size, simulation studies to determine optimum harvest strategies, estimation of current (near virgin) stock size, recruitment studies, and biological parameters are key areas for future research.

A seasonally resolved bottom‐water temperature record for the period AD 1866–2002 based on shells of Arctica islandica (Mollusca, North Sea)

AbstractExisting studies on recent global warming are almost exclusively based on environmental data from the Earth's surface. Seasonal information on the effects of climate change on subsurface settings of mid to high latitudes is extremely scarce. Here, we present the first temperature proxy record from bottom (c. 50 m) water settings of the North Sea employing the oxygen isotope composition of ocean quahog shells. Results indicate that δ18Oaragonite measured across shells of Arctica islandica can provide reliable estimates (±0.25 to ±0.4 °C) of the ambient bottom water temperatures. Over the period AD 1880–2001, warming trends in bottom waters are of the order of 0.042 to 0.138 °C/decade. Apparently, the annual maximum‐temperature trend shows a twofold increase over the past four decades (0.236 °C/decade) while the minimum‐temperature trend has remained relatively stable (0.042 °C/decade). During the same time interval, however, annual maximum temperatures at the sea surface quadrupled. Shell oxygen‐isotope‐derived winter temperatures also provide a proxy for the winter North Atlantic oscillation index (WNAO). Some 28 to 50% of the variability in minimum temperatures below the thermocline can be explained by changes of the WNAO. Our new tool enables testing and verification of climate models prior to the 20th century greenhouse forcing. Copyright © 2005 Royal Meteorological Society

The ocean quahog Arctica islandica L.: a bioindicator for contaminated sediments

The use of benthic organisms as bioindicators in the aquatic environment is a suitable method for assessing the effects of contaminants in coastal waters. The accumulation of heavy metals in body tissues due to lifestyle and feeding mechanisms makes it possible to reveal contamination rates and recovery trends within polluted areas. Comparing a polluted historical dumping site in the inner Mecklenburg Bight (western Baltic Sea) with a less-contaminated reference site at the edge of the Mecklenburg Bight, representing the background contamination of the western Baltic Sea, the present study discusses the population structure and heavy metal exposure of the ocean quahog Arctica islandica L. (Mollusca, Bivalvia) and evaluates this organism as a bioindicator for contaminated sediments. The organism density was higher at the reference site in comparison to the dumping site. The absence of juvenile and adult individuals at the dumping site seems to be a sign that this ecological environment has not completely regenerated since the dumping event in the late 1950s to early 1960s. Heavy metal concentrations of copper, lead, and zinc in the soft body tissue of A. islandica were analysed using atomic absorption spectrometry (AAS). Shell measurements were carried out using laser ablation–inductively coupled plasma–mass spectrometry. Particularly the concentrations of copper and lead were significantly higher in the soft body tissue as well as in the shell from the dumping site than from the reference site. For pollutant biomonitoring research, the shells of the ocean quahog can be used as an indicator for heavy metal accumulation. They are more suitable for reflecting historical contamination events than the soft body tissue.

Meetings with Costly Participation: An Empirical Analysis

We analyse a firm’s decision to participate in public meetings which determine regulation. Using data from the Mid-Atlantic surf clam and ocean quahog fishery, we find that firms with a preference for extreme policies are much more likely to participate in public meetings than firms with a preference for moderate policies. We also find that participation rates are higher for larger, closer, and more influential firms. These results are of interest for several reasons. Voluntary meetings with costly participation are ubiquitous as an institution for resource allocation. Examples include: faculty meetings, parent teacher association meetings, and condominium association meetings. Moreover, the requirement that regulators allow and encourage public participation is an almost universal feature of the U.S. regulatory process. 1 Yet, despite their importance, meetings with costly participation are little studied, and basic questions about them are unanswered: Who goes? Does participation vary with observable characteristics? Do meeting participants represent the interested population? Our analysis of the Mid-Atlantic clam fishery answers these questions: large, nearby extremists participate in meetings with costly participation. It is clear that these findings improve our understanding of voluntary participation in costly meetings, and hence of most regulatory decisions taken in the U.S. However, they also suggest 1. The Administrative Procedure Act requires that all U.S. federal regulatory agencies “shall give interested persons an opportunity to participate in the rule making through submission of written data, views, or arguments with or without the opportunity for oral presentation” (Title 5 U.S. Code Section 553(c), 1988 edition). In Corrosion Proof Fittings v. Environmental Protection Agency (1991) the Supreme Court showed its willingness to require that public opinion be adequately consulted. (In this case, the court vacated proposed regulation because the Environmental Protection Agency prematurely ended public hearings and deprived the public of sufficient opportunity to “comment [on], analyse, and influence the [regulatory] proceedings”. In this case public participation is mandated by the Toxic Substances Control Act rather than the Administrative Procedure Act.)

Short-run Welfare Losses from Essential Fish Habitat Designations for the Surfclam and Ocean Quahog Fisheries

In this paper, we present a spatial model of fishing that can be used to assess some of the economic welfare losses to producers from setting aside essential fish habitat (EFH) areas. The paper demonstrates how spatially explicit behavioral models of fishing are estimated, how these models can be used to measure welfare losses to fishermen, and how these models can then, in turn, be used to simulate fishing behavior. In developing the spatial model of fishing behavior, the work incorporates ideas of congestion and information effects, and we show a modification of standard welfare measures that accounts for these spillover effects. Using this methodology, these effects are traced through to the policy simulations, where we demonstrate how these welfare and predicted shares need to be modified to account for spillover effects from fleet activity.

Copepods link quahog growth to climate

From samples collected in 1983, 1991 and 2000, a long-term growth record for the bivalve Arctica islandica from the northern North Sea was constructed with methods derived from dendrochronology. Subsequent response-function analyses demonstrated that shell growth was mainly influenced by the abundance of copepods as recorded by the CPR survey. In years with dense copepod populations a major part of the downward flux of food particles is intercepted by the copepods before it reaches the seafloor. This may lead to a shortage of food for A. islandica resulting in a depression of shell growth. Although the abundance of copepods in the northern North Sea is linked to climate there is only a weak statistical relation between shell growth and climate.

The distribution and population structure of the bivalve Arctica islandica L. in the North Sea: what possible factors are involved?

The present paper summarises observations on the distribution, abundance and population structure of the bivalve Arctica islandica in the North Sea between 1970 and 2000, and demonstrates that Arctica has a widespread distribution in the North Sea north of 53°30′N. Along its southern and eastern borders the distribution seems to be limited to depths beyond 30 m. A comparison between distribution patterns of Arctica in 1972–1994 and in 1996–2000 suggests slight changes along its southernmost border in the Oyster Ground. In the south-eastern North Sea, the average density of Arctica (>10 mm) was 7 individuals per 100 m 2 and the population was dominated by full-grown specimens exceeding 50 mm shell height. The highest abundance of spat, juveniles and adults was found in the deeper central section of the Oyster Ground that is stratified during summer. There, the mean density was 21 individuals (>10 mm) per 100 m 2. These densities were much lower than in the northern North Sea (Fladen Ground), where abundance was one to two orders of magnitude higher and peaked at 28 600 individuals per 100 m 2. In the Fladen Ground, the population structure was bimodally shaped and dominated by juveniles. In the Oyster Ground, the skewed size class distribution suggests that the recruitment to larger size classes is hampered. An insufficiently dense stock of reproducing adults generating less dense spatfalls, possibly in combination with limited survival of spat and juveniles, prevents successful recruitment. Although natural processes may contribute to the skewed population structure, intensive bottom trawling is thought to have a major effect as well. It is therefore questionable whether under present-day conditions the population of Arctica in the SE North Sea can be considered sustainable in the long term.

The cornucopia of chilly winters: Ocean quahog (Arctica islandica L., Mollusca) master chronology reveals bottom water nutrient enrichment during colder winters (North Sea)

We studied variations in annual shell growth rates of ten live-collectedArctica islandica specimens from three localities at the Dogger Bank in the central North Sea. Synchronous growth curves from contemporaneous specimens enabled the construction of a 65-year multi-locality master chronology. Stepwise multiple linear correlation analysis indicated a highly significant (p<0.01) negative relationship between annual shell growth and winter sea surface temperatures (SST) during the period of 1953 to 1995. Up to 27.5% of the variation in the annual shell growth is explained by winter temperature. We explain the higher growrh levels in colder winters by higher food supply. During warmer winters both the stratification and bottom water currents in the study area seem to be stronger and prevent downward-mixing of nutrients as well as settlement of food on the sea floor. During colder winters, however, the stratification weakens and phytoplankton produced in the cold surface layer reaches the sea floor. Long-term changes in shell growth rates are thus directly connected to hydrographic changes in the North Sea, which in turn are relared to fluctuations of the North Atlantic Oscillation (NAO).

An empirical analysis of production distortions in the mid-Atlantic surf clam and ocean quahog fishery

This paper presents empirical evidence of production distortions under controlled access management in the Mid-Atlantic surf clam and ocean quahog fishery. Results indicate that vessels harvested multiple clam species even though the harvest technology exhibits diseconomies of scope. Vessels also operated in a region of the production surface where the marginal product of vessel capital services was negative. These distortions are explained by perverse regulations which restricted vessel capital replacement and severely limited fishing times.

Phenotypic and genotypic population differentiation in the bivalve mollusc Arctica islandica: results from RAPD analysis

The bivalve mollusc Arctica islandica is an important commercial species with a presumed panmictic dispersal strategy, and is widely distributed throughout much of the soft sediment benthos of the North Atlantic continental shelf. Previous studies have shown that there can be gross morphologi- cal differences between populations, which has led to the suggestion that this may be reflected in geno- type. So far, only one study has examined the population genetics of this species, revealing, depending upon location, that populations are only genetically distinct at a macroscale (>1000 km), thereby supporting the assumption of panmixia. Examination of the quantitative morphological traits between 5 different populations (4 North Sea and 1 Canadian) determined that all populations could be readily identified from their unique morphologies (shapes/growth patterns) derived from 2 factors resulting from a principal components analysis. Investigation, using random amplified polymorphic DNA (RAPD) analysis, into the genetics of the populations, to indirectly assess whether the observed phenotypic differences could be related to potential differences in genotype, revealed that all populations were genetically distinct (between populations overall phiST = 0.662) from each other even at a microscale (< 25 km) (phiST = 0.719). However, no correlation between genetic distance, morphological distance and/or geographical distance, whatever metric was applied, could be obtained. It is concluded that although phenotypic differences can be used to distinguish between populations of A. islandica, it should not and cannot be used to infer genetic differences in the absence of further studies. What is interesting is that the results from the genetic analysis dispute the presumption that the dispersal patterns of A. islandica is in any shape or form panmictic. This has very important consequences for the management of the species. The results are discussed with reference to the possible mechanisms responsible for maintaining a high degree of genetic diversity between the populations that were studied.

Post-glacial depositional environments in a mid-high latitude glacially-overdeepened sea loch, inner Loch Etive, western Scotland

A high-resolution seismic and gravity coring survey has been conducted on inner, and part of outer Loch Etive, a 30 km long, 150 m deep sea loch on the west coast of Scotland. The seismic reflection profiles reveal a 30–60 m thick sediment pile that has accumulated on the floor of the loch since the last (Younger Dryas stadial) glacial re-advance 11–10 ka BP. Four seismic facies have been identified grouped into two seismic sequences, A and B, which are separated by a distinct reflector termed ‘E1’. A highly reflective facies is interpreted as direct river input, an acoustically well-laminated, draped facies interpreted as fine-grained river sediments and a well-laminated to transparent facies interpreted as glaciomarine and glaciolacustrine. Throughout the loch, methane gas-rich sediments occur producing a chaotic seismic facies. The transition from glacially-influenced to river-dominated deposition is displayed by the seismic reflector E1. Core analysis identified eight lithofacies. The oldest sediments are grey muddy sands and olive sandy silts, overlain by younger laminated greeny-grey muddy sand and greeny-grey and greeny-black homogeneous watery sandy mud. Abundant shell material is present throughout, notably the bivalve Arctica islandica, from which a 14C age of 9490±90 yr BP was obtained from the laminated greeny-grey muddy sands. The sediments are interpreted as being of glaciomarine and glaciolacustrine (Younger Dryas to early-mid Holocene) and more modern riverine-derived origin (mid-latest Holocene).

Estimation of tow distance and spatial heterogeneity using data from inclinometer sensors: an example using a clam survey dredge

A major clam fishery in the USA is based on the Atlantic surfclam ( Spisula solidissima) and ocean quahog ( Arctica islandica). For stock assessment, the National Marine Fisheries Service (NMFS) has conducted surveys of these species with a standardized hydraulic clam dredge since 1980. The sampling procedure has been to tow the dredge for 5 min at 0.77 m/s (i.e., 1.5 kn), which gives a nominal tow distance of 232 m. This indirect calculation does not include any sampling that may take place when the dredge is being set out or retrieved. To get a direct estimate of distance sampled, we placed sensors and a camera on the dredge to monitor bottom contact and towing speed. A total of 70 tows was made in May 1997 across a range of depths, typical of those made during clam surveys, and at a range of tow speeds and scopes (i.e., ratio of tow line length to bottom depth). For each tow, we counted the number of clams captured and estimated the distance sampled based directly on the sensor data. Actual distance sampled per tow was often 1.5–3 times greater than the nominal distance (timed tow), and tow distance increased with water depth. This occurred because the dredge sampled the bottom when it was being set out and hauled back to the ship. Consideration of actual tow distance changed conclusions regarding the effect of scope on catch rate of surfclams. In addition, data on tow distance and catch per tow allowed us to examine the spatial heterogeneity of the two clam species using a negative binomial model. Our findings suggest that estimating tow distances directly can improve estimates of biomass in clam resource surveys.

Ontogenetic trends in aspartic acid racemization and amino acid composition within modern and fossil shells of the bivalve Arctica

Ontogenetic trends (umbo to growth edge of shell) in aspartic acid (Asp) racemization and amino acid composition and their evolution over time are examined in serial samples of annual growth bands from a time-series of three live-collected and two fossil (ca. 500 and 1000 y BP) shells of the long-lived bivalve Arctica islandica. The rate of Asp racemization is shown to be higher in the umbonal portion of the shells (laid down when the clams are young) but constant from a biological age of 10 to 20 y to more than 100 y. Corresponding changes are also seen in amino acid composition and concentration: with increasing biological age of the clam: total amino acid concentration increases substantially, the acidic amino acids Asp, glutamic acid, and alanine decrease in relative concentration (mole-percent) and more basic amino acids including tyrosine, phenylalanine, and lysine increase in relative concentration. These ontogenetic trends are generally retained in the fossil shells. These trends may reflect changing protein composition related to changes in growth rate. Clams grow considerably faster in their youth than when they are older, as indicated by changes in the annual growth increments. Production of more acidic proteins, which play a role in crystal growth, may be favored during the phase of faster growth, whereas more structural proteins, perhaps enhancing structural strength of the shell, may be favored during later growth. These ontogenetic differences in protein composition affect the observed rates of racemization of the protein pool. Some weak diagenetic trends in amino acid composition and abundance may be represented in the time series of shells. These results emphasize the importance of standardization of the location from which samples are taken from shells for dating by amino acid racemization analysis.

An analysis of the efficient production frontier in the fishery: implications for enhanced fisheries management

The transformation relationship between factor inputs and outputs-the efficient production frontier (EPF)-contains important information for fisheries managers. A directional technology distance function model of the harvesting technolgoy is used to measure changes in the EPF over time. Frontier shifts are summarized with input- and output-based frontier indicators that are interpreted as measures of bio-economic productivity change. The model is applied to the Mid-Atlantic surf clam and ocean quahog fishery.

An analysis of the efficient production frontier in the fishery: implications for enhanced fisheries management

The transformation relationship between factor inputs and outputs - the efficient production frontier (EPF)- contains important information for fisheries managers. A directional technology distance function model of the harvesting technology is used to measure changes in the EPF over time. Frontier shifts are summarized with input- and output-based frontier indicators that are interpreted as measures of bioeconomic productivity change. The model is applied to the Mid-Atlantic surf clam and ocean quahog fishery.