Netherlands Journal of Sea Research最新文献

Growth of temporarily isolated subpopulations of tidally migrating 0-group plaice was registered during summer 1991 in two adjacent Wadden Sea areas separated by a high tidal watershed. One area had tidal sand flats with extremely poor food conditions for juvenile flatfish, as frequently occurring in the Wadden Sea. In contrast, the other area had mixed sediments which provide rich benthos conditions for the fish. By otolith microstructure analysis we demonstrated that individual fish grew faster in this rich area than in the other. Differences in growth between the two sites could be attributed to differences in food quality and quantity. Along the transect rich in benthos, individual growth equalled maximum growth calculated from a currently used, but not yet published, growth model for the early bottom-dwelling stages, which was thereby validated in the field.

To study recruitment of Barents Sea plaice, we used a series of annual data obtained during the 1972–1990 period on the abundance of eggs and larvae and strength of year classes entering the fishery. We calculated annual values for population fecundity and survival. To show the most important factors determining plaice recruitment, a multifactorial regression analysis was used. Year-to-year variations in plaice recruitment were significantly correlated with fluctuations in population fecundity and larval abundance. This suggests that year-class strength of Barents Sea plaice is determined before the end of the pelagic phase.

Sagittal otoliths from two bothid flatfish species (Citharichthys arenaceus and C. spilopterus) collected in Puerto Rico were microstructurally examined and periodic increments counted. C. arenaceus length-at-age (33 to 246 days) data were best fitted by a Gompertz growth model whose parameters were estimated to be SL_∞ = 170 mm and K = 0.0166. Adult size is reached in less than one year. The peak period of hatching occurred in late spring, and settlement took place 39 days later. Due to a smaller age range (71 to 150 days), growth of C. spilopterus was described by a linear relationship with slope = 0.693 and intercept = −15.1 days. Hatching occurred in winter and spring. These two species showed no significant difference in age at settlement. After settlement, growth of C. spilopterus (0.69 mm·d⁻¹ at 71 to 113 days old) was significantly slower than that of C. arenaceus (1.00 mm·d⁻¹ at 71 to 113 days) possibly due to poorer environmental (abiotic or food-related) conditions during the dry, cool season (December–April). C. spilopterus from North Carolina, hatched in the same period, settled about two weeks older than in Puerto Rico. Growth after settlement was significantly slower in North Carolina (0.44 mm·d⁻¹ at 71 to 113 days) than in Puerto Rico. Environmental conditions (including temperature), distance between spawning areas and settlement grounds, and/or food availability, might explain the dissimilarity in growth observed between the two geographic areas. We recommend absolute field growth to be compared by using growth rates obtained by deriving the growth curve formula.

Juvenile turbot (5–125 g) were reared under two experimental temperatures: 10°C and 16°C, and three experimental photoperiods: LDN (natural photoperiod), LD 16:8 (16 h light: 8 h darkness), LD24:0 (continuous light), to study effects of temperature and photoperiod on growth, activity and oxygen consumption. Growth was strongly affected by temperature and was higher at 16°C than at 10°C. Continuous light had a growth-promoting effect at 10°C from mid-December to late March, while at 16°C this effect was restricted to December and January. A seasonal change in the condition index was found. The groups reared in continuous light had higher condition indices in winter. The experimental groups held at 16°C had higher O₂ consumption than those at 10°C. The LD24:0 groups invariably had a higher overall O₂ consumption than did the LDN and LD16:8 groups, the differences being caused by reduced O₂ consumption in the latter groups during darkness. The LD24:0 groups displayed higher activity than the LDN groups, in which activity was very low at night.