Interesting questions there Tony, though I don't think that natural weather patterns should 'create a problem', in that periodic changes in weather and oceanic conditions associated with El Nino events have probably occured over the last 10,000-16,000 years, and the 'life time' of a species normally extends to millions of years. The time scales are overlapping and (theoretically) the species themselves have survived considerably more dramatic oceanic/climatic changes associated with glacial and interglacial periods.
It might be true that the species exist in suboptimal environmental conditions during El Nino conditions, but they'll bounce back (or at least they should, unless the species are commercially exploited, or their natural habitat is otherwise under threat - two [of more] factors, and that can stress a species above some (theoretical) critical threshold that could lead to a crash in population dynamics/the species viability).
It is true that the species range and population size could be affected by oceanic changes associated with an El Nino event, and consequently the species migratory path could be affected, but the same is true of the species range, population size and migratory pattern associated with a La Nina event. It is hard to know what the normal/natural distribution, population size and migratory pattern of a species is - it is rather dynamic and should actually be perceived as an average over space and time. Of course everything written above could be complete and utter nonsense! I'm just sitting here writing as I think the problem out aloud myself.
George Jackson may have looked at dietary changes in squid through different weather/oceanic conditions (I know he has looked at their size and age). I'll drop him a line and find out if he can answer the second part of your query. I'm not sure if any work has been done on octopus.
Cheers
Steve
