![]() If only top predator fish are caught, the effect can be a trophic cascade as shown in the first figure below (low top predators, high medium predators, low bottom fish). Here the prey are released from predation and so may actually increase in numbers with more fishing.įinally, the following two graphs show a top-down ecosystem depending on which trophic levels are fished. Note that a TL of 1 corresponds to primary production and microbial biomass recycling, while TL 2 corresponds to herbivores and detritivores.įishing has the most impact on top predators because they're caught directly and face lower prey populations.Īnd here's a "top-down ecosystem" where the model specifies that prey abundance decreases as predators increase: Following is a " bottom-up ecosystem", where the biomass distribution is based only on energy transfer up trophic levels. Pages 28-29 of this paper show simulation results for the effect of fishing. For example, the decline of sharks in the north Atlantic allowed for an increase in cownose rays, which then ate many more scallops. There are many examples of this trend in fish food chains. Sunlight + nutrients <‑‑ phytoplankton <‑‑ zooplankton <‑‑ herring <‑‑ tuna <‑‑ sharks.įollowing the logic of "the enemy of my enemy is my friend", the idea of trophic cascades posits that "the predator of my predator is my friend". For example, one potential pathway up the food chain is the following, where "<‑‑" means "is eaten by": Marine ecosystems have many layers of predation. One of the reasons it's fiendishly difficult to evaluate the overall impact of fishing on wild-animal suffering is that most of the fish that people catch are predators. ![]() For a more detailed examination of suffering by trophic level (TL), see " Which Marine Trophic Level Contains the Most Total Suffering?". ![]() If we think the sentience of a fish scales linearly in its mass, then the total biomass of a fish population is a reasonable approximation to the total amount of suffering it contains, ignoring the fact that smaller fish probably suffer more per year due to higher infant mortality and shorter lifespans per individual. This piece discusses how the distribution of populations and biomass of fish change in response to human fishing. Are lower populations due to predation good or bad?.Increase in sardines and other small fish. ![]()
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