Answer:
-------> Herring---------> Tuna
/
Sand eels ⇒/
\
\
---------> Cod -----------> Seabirds
Explanation:
Food Web is the complex interplay of interconnection between food chains and a graphical representation of what-eats-what in an ecological community.
From the question, the herring population was reduced by fishermen and as a result the tuna which feed on the herring disappeared. This implies that the tuna depends solely on the herrings for feeding. without they wont survive.
As we proceed, we were being told that the sand eels which are eaten by herring, increased in number.
If we pay close attention, we will understand that due to the reduction of the herrings made the sand eels to increased in numbers. The point is that herrings also feed on the sand eels, but as the herrings is being reduced by some anthropogenic factors caused by the fishermen the sand eels increased.
Also, the fishermen overharvested the sand eel population and the aftermath effect shows reduction in Cod and Seabirds. This implies that Cod feeds on sand eels and Seabirds feeds on Cod, but as the food chain is being disrupted by overharvesting of the sand eels, the effect was shown by a decreased in the Cod and Seabirds.
Therefore, the best diagrammatic representation that could fit best for this explanation is:
-------> Herring---------> Tuna
/
Sand eels ⇒/
\
\
---------> Cod -----------> Seabirds
