Question 15

Removing the largest fish from each generation may weaken the ichthyologist's argument.

The argument presented by the ichthyologist could be weakened by the information that the fish removed during the experiment were not representative of those caught by commercial fishers. Since commercial fishers typically target the largest and most mature fish, this discrepancy casts doubt on the validity of the experiment's findings regarding fish stock health.

A) Adult fish of species frequently caught by commercial fishers are smaller now, on average, than were adult fish of the same species several decades ago.

This option does not weaken the ichthyologist's argument. Instead, it could support the argument by indicating a trend of declining size in adult fish, suggesting that fishing practices may have contributed to diminishing fish sizes over time.

B) Excessive commercial fishing generally harms fish stocks even when the smaller fish are not released.

While this option indicates that excessive fishing has negative impacts, it does not directly address the specific argument about the implications of releasing smaller fish. Therefore, it does not effectively weaken the ichthyologist's argument regarding the effects on fish populations due to the removal of larger fish.

C) The experiment did not thoroughly examine every species of fish frequently caught by commercial fishers.

This option suggests a limitation in the experiment's scope, but it does not specifically counter the argument about the consequences of removing larger fish. While it is a valid critique, it does not directly weaken the central claim about fish stunting and predation.

D) In each phase of the experiment, the fish removed were the largest of a single generation, whereas the fish selected for marketing by commercial fishers are the largest and most mature fish from each catch.

This option directly undermines the ichthyologist's argument by highlighting a crucial difference in the selection of fish between the experiment and commercial fishing practices. Since the fish removed in the study were not representative of the fish that commercial fishers typically target, the validity of the experimental conclusions about population dynamics is called into question.

E) In the wild, some smaller fish species are just as able to forage for food and outwit predators as are some larger fish species.

This option does not weaken the ichthyologist's argument. It may suggest that some small fish can thrive, but it does not address the overall impact of removing larger fish on the population dynamics and survival of fish stocks as a whole.

Conclusion

The correct answer, D, highlights a fundamental discrepancy between the experimental conditions and real-world fishing practices, thereby weakening the ichthyologist's argument regarding fish population health. Other options either reinforce the argument or diverge from the critical comparison needed to challenge the findings of the experiment. Thus, D is the most effective in undermining the validity of the ichthyologist's conclusions.