Mussel Stocks Research Articles

Recovery and recruitment of the brown mussel, Perna perna (L.), in Transkei: implications for management

The brown mussel Perna perna, has been an important food resource for indigenous inhabitants of the Transkei coast for centuries. The impoverished state of mussel stocks in this region and major differences in low-shore community structure between exploited and protected areas, have been ascribed to the ever-increasing exploitation of this species. In spite of this there has been no effective management of this resource owing to political and logistical problems related to law-enforcement, and misconceptions concerning the resilience of P. perna and the interspecific interactions which govern its recovery. Our present understanding of the ecological impacts of exploitation, and of the potential for recovery, is based on a series of studies and observations made over the last 15 years. These studies have shown that algae usually replace mussels following disturbance and that recovery may take more than eight years. As mussels tend to recruit preferentially into existing mussel beds, exploitation not only a...

Predation by birds on blue mussel Mytilus edulis beds of the tidal flats of Spiekeroog (southern North Sea)

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 146:61-72 (1997) - doi:10.3354/meps146061 Predation by birds on blue mussel Mytilus edulis beds of the tidal flats of Spiekeroog (southern North Sea) Hilgerloh G Predation by birds on mussel beds was evaluated in the tidal flats of the East Frisian island Spiekeroog (Lower Saxony, Germany) based on measurements in 1991 and 1994. In May 1991, 32 locations with blue mussels Mytilus edulis covered an area of 5.2 km<+k-15>2<+k0>, 311 t AFDW blue mussels being available in the whole study area. Areal extent decreased thereafter. In May 1994, there were 20 locations covering an area of only 2.3 km2, a total biomass of 48 t AFDW being available. After the strong spatfalls in the summers of both years, 1290 t biomass were available in the study area in 1991, and 550 t in 1994. Herring gulls Larus argentatus, oystercatchers Haematopus ostralegus and eiders Somateria mollissima are the main predators on blue mussels. During one year (1992), oystercatchers were present on 3.7 million bird days, eiders on 1.1 million bird days and herring gulls on 0.7 million bird days. The annual consumption of blue mussels by birds in the intertidal flats was estimated at 165 t AFDW. The highest proportion of total consumption was by oystercatchers (54%), while eiders consumed 39% and herring gulls 7%. Consumption by all 3 species amounted to 32 g AFDW per m2 of mussel bed in 1991 and to 71 g AFDW per m2 in 1994. Predation could be compensated by 12% of production in 1991 and by 29% in 1994. In order to evaluate the relevance of predation for the mussel stocks, the share of the total biomass eliminated annually by predation was assessed on the basis of standing stock and annual production. Predation was responsible for 7% of total elimination in 1991 and for 15% in 1994. Thus, factors other than predation were responsible for 85 to 93% of elimination of mussel biomass. Predation · Tidal flats · Lower Saxony · Blue mussels Mytilus edulis · Oystercatchers · Haematopus ostralegus · Eiders Somateria mollissima · Herring gulls Larus argentatus Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 146. Publication date: January 30, 1997 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1997 Inter-Research.

Effects of season, stock, and laboratory protocols on survival of zebra mussels (Dreissena polymorpha) in bioassays

A series of experiments were conducted to determine the effects of maintenance method (fed or starved), stock location, season, mussel size, and rate of acclimation to temperature on the responses (mortality) of zebra mussels in bioassays. Mussels maintained on a diet of crushed Chlorella are more tolerant to Bayer 73® and more sensitive to sodium hypochlorite than starved mussels. Variability in LC50s of zebra mussels is high during the first ≈60 days in the laboratory, after which the resistance of mussels to both hypochlorite and Bayer 73® declines with reductions in body condition. Zebra mussels collected during the early summer and late fall are more tolerant to both hypochlorite and Bayer 73®. There is significant variation in tolerances to biocides depending on the stock, such that stocks from locations with more degraded water quality have increased tolerances. Acclimating mussels from 4 to 20°C at rates of 2 and 10°C d−1 does not significantly affect tolerance to biocides. In general, LC50s of mussels vary by only 2–3×, suggesting that mussels from any location, any season, and maintained under any maintenance protocol can be used in “range-finding” tests. Comparisons of results among studies requires knowledge of mussel stock, collection season, and laboratory maintenance protocols.

Growth, mortality and shell morphology of cultivated mussel (Mytilus edulis) stocks cross-planted between two Scottish sea lochs

One-year-old rope-grown blue mussels (Mytilus edulis L.) were held in experimental lantern nets and cross-transplanted between two sea lochs (Lochs Etive and Leven) on the west coast of Scotland. Growth and mortality were monitored from May 1991 to May 1992, as well as shell morphology in native and transplanted mussels. There were highly significant differences (P≤0.001) in growth rates between lochs; both native and transplanted mussels performed better in all shell and tissue growth-parameters in Loch Etive than in Loch Leven. Stock also had a significant (P≤0.05) influence on shell length and live weight, but its contribution to total variance was considerable only in the latter case. Wet and ash-free dry meat weights were governed mainly by site and to some extent by site x stock interaction. Mortality rates were quite low (6 to 7% yr-1) and did not show any significant variation either between sites or stocks. There were significant morphological differences (ratios of shell length, height and width) between the Loch Etive and Loch Leven populations (P≤0.001) which persisted for one year after transfer. Stock appeared to be the main factor affecting shell morphology, as opposed to site. Linear regressions of shell height and width on length were significantly different between the native stocks, but became indistinguishable from those of the recipient populations one year after reciprocal transfer. This did not, however, conceal the effect of stock origin on dimensional ratios. It is concluded that site differences related to environmental factors, notably chlorophyll a levels and currents, and also possible stress caused by high levels of Zn and Cu, are major determinants of growth, which are of main interest to aquaculture, while morphological differences most probably result from genotypic variation.

Increased mortality in alternative bivalve prey during a period when the tidal flats of the Dutch Wadden Sea were devoid of mussels

In the course of 1990, stocks of mussels ( Mytilus edulis) declined to unprecedentedly low levels in the Dutch Wadden Sea. Hardly a wild mussel bed was left on the tidal flats as a consequence of three years (1988, 1989, and 1990) with failing recruitment and intensive fishing for seed mussels. During these three years, recruitment of cockles ( Cerastoderma edule) also failed, whereas fishing was continued. Bird species taking these bivalves as staple food, the oystercatcher ( Haematopus ostralegus) and the eider ( Somateria mollissima), experienced food shortage. Significant numbers of eiders left the Dutch Wadden Sea area or died, whereas oystercatchers remained abundant trhoughout the winter in most of the Dutch Wadden Sea. Alternative prey species of oystercatchers experienced unsually high mortality rates in the appropriate size classes. This was so in all other common species of bivalves, viz. first-year and older cockles, adult Macoma balthica, and juvenile Mya arenaria. This led to minimal stocks of food for oystercatchers in the late winter of 1991. In March 1991, cockles were depleted and the combined stocks Mya and Macoma would soon have run out of food supply to the overwintering oystercatcher population. Apparently, oystercatchers are able to reduce the stocks of their various bivalve prey species to very low levels.

Is there evidence of over-exploitation of mussel stocks on the Transkei coast?

Reductions in the proportion and the size of brown mussels Perna perna found in shell middens, coupled with a marked decline in the density of natural populations in Transkei, have previously been cited as evidence of over-exploitation. Data from a more intensive and regular sampling programme reported here, however, show that significant differences in size composition can be detected in samples taken as frequently as one month apart. These results indicate that the comparisons made after an interval of six years, as described by previous workers, should be treated with caution.

The prevalence ofProctoeces(Trematoda: Fellodistomidae) metacercarial infections in the brown musselPerna perna(Bivalvia: Mytilidae) around the southern African coast

Unencysted trematode metacercariae of the genus Proctoeces were found embedded in the mantle tissue and visceral mass of the intertidal mussel Pema pema. Data on the prevalence and intensity of infection in southern African populations of Pema are presented. Results from a geographic survey indicated that Proctoeces infections were more prevalent in the region Port Elizabeth to Isilaka. At the majority of sites both prevalence and intensity of infection increased in conjunction with host size. Detailed studies of mussels from Dwesa failed to show seasonal changes in metacercarial infection. A strong relationship, however, was found between sex of host and parasitic infection, with female mussels harbouring the most metacercariae. The most heavily infected mussels examined came, ironically, from two nature reserves situated on a stretch of coastline where otherwise unprotected mussel stocks are subjected to intense exploitation by man. The possible pathogenic effects of Proctoeces on such highly stressed m...

Mortality Variations in Natural Populations of the Blue Mussel, Mytilus edulis

To investigate environmental and seasonal patterns of mortality among natural populations of the blue mussel, Mytilus edulis, we transplanted 11 stocks of juvenile mussels to nine sites along the coast of Nova Scotia, Canada. Stock, Stock by Site, and Stock by Season together accounted for 53% of the variance in mortality whereas Site and Season together explained less than 1% of the variance. Genetic variability among stocks was inferred from differences in their cumulative mortality averaged over all environments. Several stocks, however, exhibited similar levels of mortality over all sites and were apparently insensitive to the environmental gradient. This implies physiological flexibility or the ability to tolerate a wide range of environmental conditions. We conclude that the blue mussel adapts to variable environments by maintaining both physiologically flexible and genetically variable populations. In addition, we noted that stocks originating from more stressful environments tended to exhibit lower mortalities than those originating from less stressful environments.

Exploitation and Conservation of Brown Mussel Stocks by Coastal People of Transkei

The Brown Mussel (Perna perna) is an important fooditem for coastal people in the Republic of Transkei, providing some 16% of their annual protein requirements in 1978, though the energy benefit associated with the consumption of Mussels is relatively low. Uncontrolled heavy exploitation of the stocks of these Mussels resulted in reductions in both their density and size between 1978 and 1984. The reduced availability of Mussels to collectors led to increased exploitation-pressure on other, longer-lived, intertidal species: the proportion of limpets in the take of collectors rose from 7% in 1978 to 37% in 1984, while the proportion of Brown Mussels decreased from 92% to 57%.

Influences of Stock and Site on Growth and Mortality in the Blue Mussel (Mytilus edulis)

Reciprocal transfers of three blue mussel (Mytilus edulis) stocks among three rearing sites resulted in marked changes in growth, mortality, and maximum biomass. Results indicate that site differences were major determinants of the growth effects, while stock differences were chiefly responsible for the mortality effects. The overall effect on biomass and potential yield was approximately equally attributable to site and stock influences. The results have relevance to aquaculture and environmental assessment using mussels and illustrate genotypic responses that may be significant for fisheries management.

PEARL INCIDENCE IN Mytilus edulis L. AND ITS COMMERCIAL RAFT CULTIVATION IMPLICATIONS

AbstractThe presence of pearls in Mytilus edulis L. from Gulf of Maine waters may be the result of infection by a parasitic trematode (probably Gymnophallus bursicola) morphologically very similar to the pearl‐forming distome described by various European workers. Techniques have been devised for the removal and grading of pearls from individual specimens of Mytilus edulis and for quantifying differences between pearl incidence and age structure of studied populations. The relationship between number of pearls per mussel and age has been defined for one rafted and one shore population of mussels in South Bristol, Maine. No significant age‐independent differences were found between the 2 populations with regard to the quantity of pearls present. The harvesting of mussels from floating structures which have been in the water for less than 5 years (i.e., raft cultivation of Mytilus edulis) should provide a method of obtaining a quality product even in areas where the presence of pearls in natural stocks of mussels has proven a deterrent to the commercial utilization of this species.

Experiments on the survival, growth and yield of relaid seed mussels (Mytilus edulis L.) in the Menai Straits, North Wales

The survival, growth and yield of young mussels relaid on small plots, at densities of 8·75 and 13·25 kg/m2 live weight, were studied at low-water mark of spring tides in the Menai Straits, North Wales. Populations grew from mean lengths of 27 mm to minimum market size (50 mm) in 15–20 months, and to 55–58 mm in two years, but good growth was offset by high mortality so that no significant gains in live crop weight resulted. Heavy predation by shore-crabs (Carcinus maenas (L.)) upon mussels smaller than 45 mm shell length was the major factor restricting crop growth. During the first year, mortality of unprotected mussels was very high (70–85%), whereas losses within crab-proof cages were significantly less (17–41%). Second-year mortality on open plots fell significantly to 22–57%, most losses then being caused by storms and bird predators, but that in cages rose to 27–54% due to overcrowding and smothering in biodeposits (‘mussel-mud’). Dry-flesh biomass (ash-inclusive) of unprotected mussels amounted to 4–6% of live crop weight (shell inclusive) and fluctuated seasonally, attaining peak values in late summer and early autumn. Standing crops were usually between 0·4 kg/m2 and 0·8 kg/m2, with a maximum of 1·2 kg/m2. Total production of dry-flesh over the two year growing period was 0·75–1·43 kg/m2, most production (about 69%) occurring in spring and summer of the first year. For optimum utilisation of mussel stocks and cultivation grounds the relaid mussels should be harvested at peak biomass, in late summer and autumn, and at a smaller size (45–50 mm) than at present.

Seasonal changes in flesh weight and biochemical composition of mussels ( Mytilus edulis L.) in the Conwy Estuary, North Wales

Sublittoral Mytilus edulis L. from natural mussel beds of the Conwy Estuary fishery exhibited an annual cycle of dry flesh weight, biochemical composition, and caloric value during 1971–1974. Mean percentage values of the main components of dry flesh, with seasonal extremes in parentheses, were: protein 58.7 (46.4–73.1), carbohydrates 22.5 (4.1–36.7), lipids 7.0 (3.9–9.6), and ash 11.8 (8.8–17.2). The mean caloric values of dry flesh were 5.57 kcal/g ash-free and 4.92 kcal/g ashinclusive. Individual dry flesh weight was highest in summer and autumn, when protein and carbohydrate were maximal, and decreased through the winter to a post-spawning minimum in spring. Weight loss in winter resulted from rapid utilization of carbohydrate (glycogen) reserves and a depletion of both protein and lipid content. It is considered likely that mussels were then stressed by food shortage at the time when metabolic demands, due to gametogenesis, were highest. During the six main fishing months, October to March, the average weight of dry flesh fell by 30–50 % and caloric content by 35–45 %. The likelihood of similar losses in cultivated mussel stocks is indicated and the need for comparable information in fishery management is emphasized. The extent to which predators compensate for these seasonal changes in prey quality also requires examination.

Surveys of mussels (Mollusca: Lamellibranchia) in the firth of Thames, 1961–67

Summary Surveys are described which were made to determine distribution and relative density of stocks of mussels, Perna canaliculus Gmelin (Lamellibranchia: Anisomyaria; Mytilidae), in the Firth of Thames, North Island, New Zealand, during the late autumn‐early winter of each year 1961–63 and 1965–67. Two dredges available for sampling were tested against one another over similar ground. Both gave comparable results, but although the one chosen was never actually calibrated, it gave consistent results which allowed relative changes of abundance to be studied. In 1961, 206 stations were sampled on a grid of 1 square mile which covered most of the Firth. Early results showed that the densest beds were along the western shore line; there were only small patches of mussels off Coromandel and along the eastern shore. A well‐stocked and readily identifiable area of 2 square miles off Matingarahi Point was selected for more intensive sampling on a 1/16 square‐mile grid. Samples collected there annually showed a...

Peach Orchards in England

MR. JUSTIN BROOKE is an enthusiast with a sense of proportion. He grows fruit commercially on a considerable scale near Newmarket, has grown and marketed peaches since 1936, and outlines, in the present volume, details for a great expansion of the crop in Great Britain. The variety Peregrine yields heavy crops and is self-fertile; it is best grafted upon the Broad Leaf Mussel stock. The author considers that peach blossom is rather less sensitive to damage by spring frosts than Victoria plum blossom. Manuring should be directed towards the production of vigorous growth, and pruning should also be subordinated to the same end. Thinning of fruit to one every four inches of branch is necessary, and the would-be grower will find adequate detail of all cultural aspects, and of pest and disease control, in the text and in the twelve excellent halftone plates. Mr. Brooke points out that mechanized corn-growing and fruit production go well together, and it is greatly to be hoped that some of his readers will be stimulated to repeat his experiment in other parts of Britain. It would indeed be a national asset if peaches were within the economic reach of all members of the community.