Intelligence is a complex subject but let's get one thing straight, dolphins aren't dumb. The question about which species are the 'smartest' fascinates us. Our answers will always depend on human-derived value judgements associated with the merit of different attributes. Just as humans cannot agree on the diverse parameters for defining a 'successful' human existence, we also find it difficult to identify - even following IQ tests - which of our friends and colleagues are the smartest.
In truth, we struggle to pin down the exact nature of human aptitude with its component intelligence and emotional quotients. The fact is that all species are beautifully adapted for the ecological niche which they inhabit, with perhaps the one exception of humans. Darwin referred to a 'cognitive continuum', in other words a distribution of cognitive abilities across species; framing cognition as an evolutionary currency, where the ability to exploit a novel resource or environment potentially provides a potent selective advantage.
Bottlenose dolphins, for example, are well adapted in their intelligence for their environment and have evolved as a social species, many living in communities, using collaboration and intelligence to help find the resources that they need to survive. Like other social mammals this has implications for how we treat them. For example, a social dolphin isolated in captivity may suffer psychological stress and a dolphin driven ashore in a drive hunt may well be aware of what is happening to the other members of their social group nearby.
Recent media attention on dolphin aggression or mating activities, come heavily laden with human value judgements about how other species should behave, whilst somehow missing the wide diversity of behaviours characteristic of our own species. Intelligence and aggression are distinct and shouldn't be conflated. If we were to confuse them in human societies, prison inmates might be running the government. Some, pro-social behaviours may be just as important for evolutionary success as competitive behaviours.
I've also recently read suggestions that some scientists (and NGOs) believe that dolphins are the second smarted species on the planet - I have yet to meet a scientist or NGO that makes such an assertion. There is an often quoted statistic that dolphins have the second largest EQ (Encephalisation Quotient - not to be confused with 'Emotional Quotient') after humans. This is a simple representation of the relationship between body and brain size, but it is most certainly not equivalent to an intelligence rating, as many parrot species attest.
It is true that, as Justin Gregg notes, we have only scratched the surface in our understanding of the intelligence and cognitive abilities of other species. But I don't think any NGOs are trying to advocate for a strict hierarchy of species intellect, as this utterly misses the complexity of the incredible biodiversity of our planet. It isn't a race to write the complete works of Shakespeare, it is a struggle for survival and often in a rapidly changing environment. Intelligence, in all its different forms, is part of the species tool kit and the tool kit itself is not infallible.
Yes, many other species besides dolphins demonstrate amazing cognitive capacities and this should be celebrated. The arguments about dolphin intelligence are not intended to be exclusionary. The important point is that our growing understanding of the social and cognitive complexity of other species requires a readjustment of attitudes about our duties towards protecting these individuals and their habitats.
Perhaps a more important issue than ranking species intelligence is understanding how different species suffer, whether they are aware of their own suffering or even if they can suffer vicariously. This will ultimately guide us in our attempts to protect them as individuals, families, communities, populations and species.