NEW threats to global whale numbers have been identified as Scottish researchers find a "significant" drop in breeding success in the wild.

It's understood that the fall in newborn sightings is linked to the availability of prey fish in the previous year – something itself is connected to ocean conditions.

Scientists say key cetacean species could be more vulnerable to climate change than has been assumed.

Experts from St Andrews University documented a major decline in calving rates amongst humpback whales.

The species can grow to measure 60feet in length and weigh 40 tonnes and is found in all of the world's oceans.

While major changes have been documented in these waters as a result of climate change, much remains unknown about the impact on populations of top marine predators, including whales.

The St Andrews team has now established that environmental shifts in the krill-rich Gulf of Lawrence in Canada – one of the world's top whale watching sites and an important summer feeding ground – is affecting the breeding of humpbacks.

The sea mammal specialists worked with colleagues from Canada's Department of Fisheries and Oceans to investigate using blubber biopsy samples to identify pregnant females and sightings records of individual females collected by the Mingan Island Cetacean Study, comparing the years from 2004 to 2018.

They found calving rates have fallen "significantly" over the period.

And the probability of sighting females with calves was found to be linked to the abundance of herring – a main prey species – the previous year.

Prior to the work, it had been thought that humpbacks and other baleen whales could show resilience to climate change because of their ability to change their migratory patterns or change their diet.

However, the results are said to show that these attributes may not be enough to prevent ecosystem change from harming their reproductive success.

The study – which has been published in the scientific journal Global Change Biology – was carried out by Dr Joanna Kershaw, Professor Patrick Miller and Professor Ailsa Hall of the Sea Mammal Research Unit (SMRU) at the Fife institution.

They're clear that more investigation now needs to be done.

Kershaw explained: “Long term monitoring efforts and inter-disciplinary collaborations like these are vital to assess how marine mammals, and other marine species, may be impacted by climate change now and into the future.”

Dr Carol Sparling, SMRU director, commented: “This is an important study that provides evidence that breeding success is linked to prey availability and that large whale species such as humpbacks may be more vulnerable to climate change than previously thought.”