A tuna isn’t like a lion that’s eating large herbivores , It’s going to go after smaller predators that are going after smaller predators… until we get to copepods and such. Except all those animals would die of something without predators, so the relevant question is about impacts on population sizes of all relevant species.
Lets pretend the number of calories available is constant and all consumers are animals. All of those calories will be eaten by some life form, due to small body size/ fast reproduction of algae, ocean trophic pyramids are inverted compared to terrestrial ones, with more biomass at higher trophic levels. And unlike in terrestrial ecosystems with many large herbivores, ocean megafauna are mainly predators. Any calories consumed by sharks/tuna/marine-mammals etc aren’t being put to use making more small scavengers.
Now There are mamy complications with this simple model
-some of those calories being eaten by the large predators might be used by insentient consumers like bacteria in There absence instead of small scavenging animals
-bony fish often have very small offspring, and total-population-biomass/ adult-size might be a really bad proxy for relative population size of marine species
-through diving deep/ defecating near the surface/ trapping nutrients in There bodies they keep nutrients at the surface , which has two big effects
fertilizes surface waters and allows for more production of calories by algae
means those calories in There waste are available to the surface ecosystems instead of sinking to the deep, where the animals they would feed are long lived and have slow metabolisms due to the cold water and food scarcity.
Either way its more complicated than hunting big fish to save little fish and probably bad?
A tuna isn’t like a lion that’s eating large herbivores , It’s going to go after smaller predators that are going after smaller predators… until we get to copepods and such. Except all those animals would die of something without predators, so the relevant question is about impacts on population sizes of all relevant species.
Lets pretend the number of calories available is constant and all consumers are animals. All of those calories will be eaten by some life form, due to small body size/ fast reproduction of algae, ocean trophic pyramids are inverted compared to terrestrial ones, with more biomass at higher trophic levels. And unlike in terrestrial ecosystems with many large herbivores, ocean megafauna are mainly predators. Any calories consumed by sharks/tuna/marine-mammals etc aren’t being put to use making more small scavengers.
Now There are mamy complications with this simple model
-some of those calories being eaten by the large predators might be used by insentient consumers like bacteria in There absence instead of small scavenging animals
-bony fish often have very small offspring, and total-population-biomass/ adult-size might be a really bad proxy for relative population size of marine species
-through diving deep/ defecating near the surface/ trapping nutrients in There bodies they keep nutrients at the surface , which has two big effects
fertilizes surface waters and allows for more production of calories by algae
means those calories in There waste are available to the surface ecosystems instead of sinking to the deep, where the animals they would feed are long lived and have slow metabolisms due to the cold water and food scarcity.
Either way its more complicated than hunting big fish to save little fish and probably bad?