A penguin walks into a bar and asks the bartender, ‘‘Hey, have you seen my brother?’’
The bartender replies, ‘‘I don’t know. What’s he look like?’’
Penguins are notoriously samey, to our eyes that is. They can certainly tell each other apart, as evidenced by the 75% of breeding pairs of hoiho that stay together each breeding season. Mind you, in any year about 13% of hoiho pairs divorce each other, puncturing the myth that penguins mate for life.
The other misconception is that saving one particular penguin is as good as saving any other for the conservation of the species. This was the calculation implied in Tom Clark’s thoughtful recent article (Opinion ODT 11.3.26) where he totted up the hoiho deaths due to various causes in the 2022-23 season and determined that drowning in fishing gear was a relatively minor cause of death compared to starvation, disease, and predation.
Tom’s sad conclusion was that closing fishing areas to avoid further hoiho deaths was not going to save these birds.
The problem with this rationale is that it treats all hoiho as being the same, but demographically they are not the same in their potential to grow and sustain the northern population.
A large proportion of hoiho deaths each year involve chicks, particularly deaths due to diseases that have increased in prevalence in the last 30 years. In any population many young will die before reaching maturity and will never be able to contribute to future generations.
Many hoiho die while still in the nest, but even those which manage to fledge (become independent) face tough times at sea. In some years virtually no fledglings survive and overall, only about 17% of fledged chicks which enter the sea are seen as juveniles a year later.
But adult hoiho play the numbers game, able to produce two chicks each year and with a breeding lifetime that could be over a decade. In good conditions this could be enough for population growth.
That is why demographic models track the fate and performance of adult birds. However, such models usually assume one breeding female is as good as another, and all are equally likely to produce chicks which become breeders which produce chicks ... etc.
An ambitious research project headed by Aviva Stein and Mel Young at the University of Otago tracked the fates of over 2000 hoiho over 23 years to determine their individual lifetime reproductive success — that is, how many offspring they produced that survived not only the first dangerous year of their lives, but also survived to when they were breeding themselves, which might be between two and four years of age, depending on whether they are males or females, and other factors.
They also figured out how many of those offspring produced their own offspring, that survived to become breeders. What an individual difference in performance they uncovered.
Surprisingly, less than 5% of breeding adults successfully fledge young that in turn go on to breed and fledge their own chicks. This means that a massive majority of breeding hoiho do not contribute to future generations, and that the population is sustained by a small number of what Stein and Young referred to as ‘‘super-breeders’’ — birds with a disproportionately important impact on population persistence.
So, of those 2147 hoiho that were followed over 23 years, only about 100 super-breeder birds were found to be largely sustaining the population. But which birds are they? Is it possible to tell, without tracking their reproductive performance and the survival and reproductive performance of their surviving offspring over many years?
The answer is no. We have no way of identifying which hoiho are super-breeders and which are reproductive duds (they all look the ‘‘same’’), so how do we manage the dwindling northern population?
Well, by doing everything we can to protect breeding adults because losing even one super-breeder a year could have huge population-level impacts. Tom Clark indicates that of the 320 hoiho deaths recorded in 2022-23, some 300 were due to non-fishing related causes.
However, most of those 300 will have been chicks, whereas the 20 birds that died in fishing gear would have to have been foraging in the sea, since chicks don’t go near fishing nets. And, worryingly, some proportion of that annual harvest would have been breeding adults that could include super-breeders.
In his Sand County Almanac the naturalist Aldo Leopold made the point that the first rule of intelligent tinkering is to keep all the pieces. We can’t know by looking which hoiho is going to be a super-breeder, but we do know that very few chicks become breeding adults, so our focus must be on eliminating unnecessary deaths.
Drowning in a fishing net is an unnecessary death. A drowned hoiho in a net is a tragedy. A drowned super-breeder hoiho in a net is a disaster.
Tom Clark is right that we need to find ways to help northern hoiho. It is not feasible currently to address climate-related changes to penguin prey species, but it is definitely feasible to prevent all further fisheries-related mortality.
Hoiho are not for captivity, they are for the wild. Let’s do all we can to allow those super-breeders to do some super breeding.
- Philip Seddon is an Emeritus Professor of Zoology, University of Otago; Yolanda van Heezik is a Professor of Zoology, University of Otago.
