Short-term mortality in post-emergent arval capelin Mallotus villosus. II. Importance of food and predator density, and density-dependence

Advection, diffusion, total mortality and starvation mortality were measured for 2 cohorts of Pacific herring larvae Clupea harengus pallas1 in Bamfield Inlet, British Columbia, in order to determine the roles of offshore dispersal, population density and starvation in the dynamics of populations. The most strilung differences between the 2 cohorts were in initial density, total mortality, and diffusion: the initial density of the cohort that hatched in 1981 (Cohort 2) was 78 times lower than the density of the cohort that hatched in 1982 (Cohort 6); total mortality was 8 times lower in Cohort 2, 0.02 d-l, than in Cohort 6, 0.16 d-l; and Fickian diffusion was 3 to 6 times lower in Cohort 2, 0.08 km2 d-l, than in Cohort 6, 0.31 to 0.48 km2 d-' Starving larvae, identified with a morphometric index, were found in the 1 to 26 d age group of both cohorts and starvation mortality followed the same trajectory in both cohorts: an increase in magnitude from 0 d-' at hatch to a maximum of 1.0 d 1 at ages 5 to 7 d and then a decline to 0 d-' at age 20 d. That the average magnitude of starvation mortality did not vary with total mortality, as did initial density and the rates of diffusion, suggests that starvation was only one of several agents of mortality and that density-dependent predation and offshore dispersal were equally important factors.

Section: Discussionmentioning

confidence: 99%

Advection, diffusion and mortality of Pacific herring larvae Clupea harengus pallasi in Bamfield Inlet, British Columbia

McGurk¹

1989

“…Density-dependent competition for food is thought to reduce growth and increase the duration of the period during which the larvae are vulnerable to predators, thus leading to density-dependent mortality (Cushing 1974, Ware 1975. However, direct evidence for the existence of density-dependent competition for food in fish larvae is lacking (Ware 1975, Sissenwine 1984, Rothschild 1986, Taggart & Leggett 1987. Further, estimates of the biomass consumed by fish larvae in the field indicate that individual species have little impact by themselves on the abundance of their prey (Cushing 1983, Dagg et al 1984, Peterson & Ausubel 1984, Monteleone & Peterson 1986, Jenkins 1987.…”

Section: Other Hypothesesmentioning

confidence: 99%

Optimal foraging and density-dependent competition in marine fish larvae

Fortier¹,

Harris²

1989

113

ABSTRACT. Ontogenetic migrations of fish larvae were studied in relation to vertical distribution of their prey and their predators at a single, unstratified, 60 m deep, station off Plymouth, UK. The vertical distribution of fish larvae was highly stratified. Die1 migrations were weak. Marked ontogenetic migrations reflected a size-related shlft in the equilibrium between predation and starvation risks. Yolksac larvae concentrated in the top half of the water column where planktonic predators were the least abundant. As size increased, the overlap between the vertical distribution of the postlarvae and that of potential predators increased. Postlarval stages of species feeding on copepods were distributed in direct proportion to resource availability. This suggested an optimization of postlarval foraging behaviour in response to density-dependent competition for food. Calculations showed that the larvae themselves had little impact on their resource, but indications were found that the abundance of larval fish food was affected by other planktivorous predators. We conclude that the density-dependent competition for food suggested by the observed patterns of postlarval distribution could only be generated at the level of the entire assemblage of planktonic predators.

“…These environments are often characterized by high availability of food organisms (Frank & Leggett 1982, 52 1983, Taggart & Leggett 1987, Doyle & Ryan 1989, low abundance of larval predators (Frank & Leggett 1982, 1983, and may be characterized by circulation fea-…”

Section: Introductionmentioning

confidence: 99%

“…Conception Bay is a fjord approximately 50 km long and 25 km wide with a maximum depth exceeding 300 m and a total surface area of about 1000 km2. Previous studies of ichthyoplankton in this region have either been limited to offshore waters >20 km (Frost 1938, Serebryakov 1965 or to small embayments <l000 m (Frank & Leggett 1981, 1983, Taggart & Leggett 1987. While most commercial species of fish are believed to reproduce mainly on the shelf, the presence of eggs, larvae and juveniles inshore (Frank & Leggett 1981, 1983, Taggart & Leggett 1987, Keats 1990 suggests that large bays bordering the shelf may contribute to the early-life history of fishes inhabiting the area.…”

mentioning

confidence: 99%

Factors influencing the spatio-temporal occurrence of fish eggs and larvae in a northern, physically dynamic coastal environment

Laprise¹,

Pepin²

1995

Distribution patterns, abundance and species composition of the assemblages of fish eggs and larvae in Conception Bay, Newfoundland. Canada. during the early summers of 1990 and 1991 are described. Several species appear to use Conception Bay as a spawning ground. lnterannual and seasonal differences in both species composition and abundance in the bay appear to be associated with differences in environmental conditions, particularly with temperature. Both egg and larval abundances were lower by an order of magnitude in 1991 corresponding to the coldest and less saline waters. Temperature and wind were the environmental factors most associated with the spatial distribution of eggs. In both years, highest abundances of all species were usually found at the head and the eastern side of the bay, corresponding to the warmest waters under dominant westerly winds. On one occasion, greatest abundances and warmer waters were found on the western side of the bay, concomitant with a southerly wind episode. Clustering samples by their relative species composition revealed well-defined assemblages of fish larvae. The variability in relative species composition was strongly associated with the physico-chemical conditions of the surface layer and was consistent with patterns of seasonal successions observed in other ecosystems. We propose that temperature is the principal factor controlling spatio-temporal occurrence of fish eggs and larvae in Conception Bay and, most probably, in coastal waters of Newfoundland and Labrador, Canada. This association may be critical in ecosystems characterized by an extremely short growing season. Conception Bay may play an important role in the early-life history of fish inhabiting the northeast Newfoundland/Labrador shelf. Even if a smaller proportion of fish reproduced in the coastal reglon, their offspring may contribute signiflcantly to the number of individuals recruiting to the population if growth and survival are considerably higher in coastal areas than in offshore areas due to the presence of more favourable habitats for early-life stages of fish.