question archive Use the following information to answer the next two questions
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Use the following information to answer the next two questions. Pacific herring play a key role in the marine food web of Canada's West Coast. They are prey fish and comprise 30% to 70% of the summer diets of Chinook Salmon, Pacific cod, lingcod and harbour seals in the coastal waters of southern British Columbia. The eggs of Pacific herring are important to the diets of migrating sea birds, gray whales, and some invertebrates. Pacific herring are not mature enough to spawn until age three. Spawning takes place in coastal areas where algae beds are abundant and the water is uncontaminated.
Which of the following factors is an example of a density-independent factor that influences Pacific herring survival and growth?
A. Algae populations
B, Ocean temperatures
C. Population of grey whales
D. Imposition of fishing quotas
Answer:
Density-dependent limiting factors are those which causes growth rate of a population fall when its density increases. It includes biotic variable such as, competition, predation, disease and parasites.
Density-independent limiting factors affect growth rate regardless of the density of a population. It includes abiotic variables such as weather, climate, temperature, natural disasters and anthropogenic activities.
Looking at the question, option (a) algal population- Algae is the food of Pacific herring, so increased population of fishes would bring a competition among them for food thus causinv their numbers to decline. So, algae limiting the number of individuals in a population act as Density-dependent factor.
Option(b) Ocean temperatures- The temperature of ocean can vary regardless of the population density of fishes. So, it is Density-independent factor.
Option(c) Population of grey whales- The higher density of pacific herrings would make them more noticeable to predator whales, thus leading to more predation which ultimately lead to decrease in their numbers, So, it is Density-dependent factor.
Option(d) Imposition of fishing quota- Fishing quota could be imposed anywhere to collect more fishes, so fish density is not considered in this practices makinh it a Density-independent factor.
Now, option(a) and option(c) can be ruled out because they are density dependent factors.
Out of option (b) and (d), imposition of fishing quota would not influence the survival and growth of fish. A fish to be caught in fishing quota is a by-chance process, it could not influenc the growth of fish.
But, ocean temperatures can influence the growth and survival of fishes because fishes are ectotherms or cold-looded animals and they are unable to tolerate a wide range of temperatures. An increase in ocean temperature will cause increased metabolic activities and after a while fish would not be able to maintain increased respiration and cardial functions and die. While decrease in temperature would make them lethargic and inactive. Thus, correct answer is option(b)