Self-thinning dynamics in experimental scallop populations
- 249 Downloads
Self-thinning-related mortality has been encountered in extensively cultured scallop populations. Here we report an experiment aimed at studying actual population dynamics of scallops undergoing self-thinning and develop a model of the process. Scallops were kept in small tanks at various initial population densities. Growth and survival were monitored for 39 months. Two cohorts were monitored (cohorts 1 and 2 were 1 and 2 years old, respectively). Growth was density-dependent in cohort 2. Survivorship was high in cohort 1 during the first summer but mass mortality occurred during the second summer. Mortality in cohort 2 peaked during the first summer. In both cohorts, peak mortality occurred at age 2+ years and thus was uncoupled among cohorts. Therefore, negative environmental factors are ruled out as explanations of mortality. Instead, it appears as if self-thinning interacted with some ontogenetic factor. Although cohort 1 was undergoing self-thinning, trends in biomass–density curves were non-monotonous because of mass mortality. In contrast, self-thinning in cohort 2 followed a classical pattern. One possible mechanism for such contrasting differences was that 1+-year-old scallops produced byssal threads and attached to one another during the first year, forming multilayered clumps. This behaviour disappeared during the second year and mass mortality was experienced as scallops adopted a single-layered arrangement. Although details may differ among species, the process depicted above provides a potential trigger to the sequence of events leading to mass mortality in scallop culture. Our model suggests that self-thinning occurred in all density groups, with a common slope but with different elevations in the biomass–density space.
KeywordsPlacopecten magellanicus Scallop Self-thinning Stocking density
We thank L. Pagé, A. Aitken, N. Paille, J.-L. Beaulieu, A.-M. Cabana and L. Girard for invaluable assistance at various steps of this study. Scallops were supplied by J. C. Bonardelli.
- Aoyama S (1989) The Mutsu Bay scallop fisheries: scallop culture, stock enhancement, and resource management. In: Caddy JF (ed) Marine invertebrate fisheries: their assessment and management. J. Wiley, New York, pp 525–539Google Scholar
- Baba K, Miyazono A, Matsuyama K, Kohno S, Kubota S (2007) Occurrence and detrimental effects of the bivalve-inhabiting hydroid Eutima japonica on juveniles of the Japanese scallop Mizuhopecten yessoensis in Funka Bay, Japan: relationship to juvenile massive mortality in 2003. Mar Biol 151:1977–1987CrossRefGoogle Scholar
- Bi H (2001) The self-thinning surface. For Sci 47:361–370Google Scholar
- Cao QV, Dean TJ, Baldwin VCJ (2000) Modeling the size—density relationship in direct-seeded slash pine stands. For Sci 46:317–321Google Scholar
- Giguère M, Cliche G, Brulotte S (1994) Reproductive cycles of the sea scallop, Placopecten magellanicus (Gmelin), and the Iceland scallop, Chlamys islandica (O. F. Müller), in Îles-de-la-Madeleine, Canada. J Shellfish Res 13:31–36Google Scholar
- Guiñez R, Castilla JC (2001) An allometric tridimensional model of self-thinning for a gregarious tunicate. Ecology 82:2331–2341Google Scholar
- Mori K (1975) Seasonal variation in physiological activity of scallops under culture in the coastal waters of Sanriku district, Japan, and a physiological approach of a possible cause of their mass mortality. Bull Mar Biol Stn Asamushi 15:59–79Google Scholar
- Rincón PA, Lobón-Cerviá J (2002) Non-linear self-thinning in a stream-resident population of brown trout (Salmo trutta). Ecology 83:1808–1816Google Scholar
- Shinozaki K, Kira T (1956) Intraspecific competition among higher plants VII. Logistic theory of the C–D effect. J Biol Osaka City Univ 7:35–72Google Scholar
- Therriault J-C, Levasseur M (1985) Control of phytoplankton production in the lower St. Lawrence Estuary: light and freshwater runoff. Nat Can 112:77–96Google Scholar
- Yoda K, Kira T, Ogawa H, Hozumi K (1963) Self-thinning in overcrowded pure stands under cultivated and natural conditions (Intraspecific competition among higher plants XI). J Biol Osaka City Univ 14:107–129Google Scholar