Growth, growth modelling and age determination of Pandalus borealis

Abstract

A growth model for pandalid shrimps accounting for seasonal variations in growth is presented based on successive additions of sigmoid functions along a basic von Bertalanffy growth (VBG) equation. Results obtained with this new model are compared with results from the VBG equation and from a VBG model modified by the addition of a sine function. Results show that growth of Pandalus borealis (Krsyer) from Gullmarsfjorden on the Swedish west coast is best described by the seasonal models. Of the 2 seasonal models, the new model gave a slightly better fit. Seasonal variations in growth are discussed in relation to the reproductive cycle of P. borealis. Differences in growth pattern between sexes were also found in a 4 yr series of data from the fjord. The main difference was that male growth declined earlier in the year (late summer-autumn) than female growth which declined later (autumn-winter) and for a longer period. Differences in growth rate between sexes are also discussed. Since Gullmarsfjorden contained 4 different periodically isolated P. borealis populations during the study period (1984 to 1987), the relationship between growth rate and mean ambient temperature could be investigated in the temperature interval of 4 to 6 "C. No correlation between these 2 factors was found. Results also indicated that recurring immigrations of adult shrimp during late winter-early spring from the Skagerrak population did not significantly affect growth-rate estimates. Finally, sizes by age of P. borealis in the fjord did not dlffer s~gnificantly from reported sizes by age In other boreal populations.

Growth Pattern of Pandalus gracilis (Decapoda: Pandalidae) in the Southern Coastal Waters of Korea

“…Similar results were found in Pandalus borealis and Pandalus jordani (Allen, 1959;Hopkins and Nilssen, 1990;Bergström, 1992). Because of the sex-differentiated growth pattern, Bergström (1992) suggested that growth in sequential hermaphrodites may be best described by either separate models for each sex, or perhaps for detailed growth analysis, by a model that combines the growth of each sex in relation to their proportional occurrence in the population. Mean size and age at sex transition were 7.07-mm (± 0.27) CL and 1.05 (± 0.21) years, respectively, suggesting that P. gracilis reached a transitional stage at 1 year of age.…”

Factors affecting the occurrence of early maturing males in the protandrous pandalid shrimp Pandalus latirostris

“…In our experiment, the growth of juvenile Pandalus latirostris was affected more by environmental conditions after hatching than by differences in hatching date. The age/size at sexchange in some pandalid shrimp is chiefly governed by genetic factors (Bergström 1992, Marliave et al 1993. Based on our results from Expt 1, which showed that variation of AMP among individuals increased with increasing body size, genetic factors may affect the occurrence of EMMs.…”

“…For example, Butler (1964) and Charnov (1979) suggested that populations at lower latitudes have a higher proportion of EMFs because those individuals grow more rapidly (Rasmussen 1953). There are few conclusive reports showing which factors govern growth in pandalid shrimps, and the effect of water-temperature fluctuations in any one area is not clear (Shumway et al 1985, Apollonio et al 1986, Parsons et al 1989, Bergström 1992. In shallow water, water temperature and/or the availability of food is much more variable among localities than in the deep sea.…”

“…Moreover, Bergström (1992Bergström ( , 1997 and Marliave et al (1993) have suggested that the varying frequencies of genotypes programming for sex-change at different ages/sizes in populations may affect the occurrence of EMFs in pandalid shrimps. Although the possible relationship between EMMs and EMFs still remains undescribed, juveniles that become EMFs need to grow more rapidly than other individuals of the same age group because EMFs have to pass through a size range in which they are not large enough to pro-duce eggs.…”

“…The age/size at which the sex-change occurs varies among latitudes and by year, even in the same species (Rasmassen 1953, Butler 1964, Haynes & Wigley 1969, Charnov 1979, Bergström 1992. Almost all populations have early maturing females (EMFs) that mature younger (smaller) than normal females (Charnov 1979).…”