Investigation into Seasonal Growth of Branchiostoma lanceolatum off Heligoland, According to Data by Courtney (1975)

Values of length growth of Branchiostoma lanceolatum off Heligoland were gained in 1962–63 by COURTNEY (1975a, b) over six age groups comprising about 800 individuals. Growth, generally was found to stop when sea water temperatures fell below 10 °C. Stagnation for at least six months could be observed as a result. COURTNEY gave a graph for length development in consecutive age groups by connecting clusters of points by straight lines, for lack of more adequate methods not available at that time. In a review, tests are recalled for the mathematical representation of growth with seasonal variations. Initial work was done by URSIN (1963), followed by CLOERN and NICHOLS (1978). These authors tried to introduce temperature to the PÜTTER/BERTALANFFY function of length growth, in a direct or indirect way. SAGER (1982) extended this idea regardless of the growth function proper. In a first step, the modification holds for seasonally restricted growth just down to momentary stagnation (SAGER, 1983a, b). The second step (SAGER, 1984a) allows for stagnation over several months and is suitable for approximation of the COURTNEY values, which is performed by nonlinear regression. Results show fully satisfying coincidence, as manifested in numerical and graphical displays. Moreover, the growth rate or growth velocity has been calculated and is plotted graphically. Complete description of growth development, according to the COURTNEY samples, has been achieved by a function with only five parameters.