Human interaction with whales in most parts of the world is limited to snorkelling or simply watching from a boat-deck to avoid undue disturbance of the mammals, though many scuba divers build one or other activity into their diving holidays.
But according to a new scientific study, it seems that the boats that bring people out for whale encounters can still present a problem, in the form of unwanted noise.
Whale-encounter operators tend to position their boats as close to the whales as they can within local legal limits, which can vary from simply staying behind them to keeping at least 100m away. However, even with the stricter distance rules it’s known that whales can still exhibit signs of disturbance.
These changes in behaviour might include diving, changing course, swimming faster, breathing more often, dispersing and emitting sounds outside normal patterns, says Australian biologist Kate Sprogis, who led the team from Aarhus University in Denmark.
“Unlike humans, the dominant sense in whales is not sight – it is hearing,” she says. “While whales might be unable to see a boat 100m away they are likely to hear it, so it makes sense to consider this when stipulating whale-watching guidelines.”
Previous research into the long-term consequences of disturbing whale mothers has established that the energy they expend in response reduces the amount available for evading sharks, orcas or unwanted males, undertaking long migrations and in particular feeding their offspring. The calves need to take on a lot of milk in a short time to be strong enough to migrate without falling victim to predators.
The researchers carried out experiments in Exmouth Gulf on Australia’s west coast, a resting area for the world’s largest population of humpback whales. The whales winter there, not feeding but suckling their calves ready to migrate to cooler feeding grounds in summer.
On 42 occasions the researchers drove their boat to within 100m of a mother and her calf and then used underwater speakers to emit different levels of engine noise, monitoring the whales’ response from above using a drone-mounted camera.
The loudest boat noise of 172 decibels caused the whale mothers’ resting time to drop by 30%, doubled their breathing rate and increased their swimming speed by 37%, though they would often return to a state of rest as the noise receded.
Mawasiliano ya binadamu na nyangumi katika sehemu nyingi za ulimwengu ni mdogo kwa snorkeling au tu kuangalia kutoka boti-deck ili kuepuka usumbufu usiofaa wa mamalia, ingawa wengi scuba divers kujenga moja au nyingine shughuli katika likizo yao diving. Lakini kulingana na utafiti mpya wa kisayansi, inaonekana kwamba mashua ambazo huleta watu nje kwa kukutana na nyangumi bado zinaweza kuwasilisha tatizo, kwa namna ya kelele zisizohitajika. Wenyeji wa whale-encounter wanaelekea kuweka mashua zao karibu na nyangumi kama wanavyoweza ndani ya mipaka ya kisheria ya mahali hapo, ambayo inaweza kutofautiana kutoka kwa kukaa tu nyuma yao hadi kuweka angalau mita 100 mbali. Hata hivyo, hata na sheria kali zaidi za umbali inajulikana kwamba nyangumi bado wanaweza kuonyesha dalili za usumbufu. "Mabadiliko hayo ya tabia yanaweza kujumuisha kupiga mbizi, kubadilisha mwelekeo, kuogelea kwa kasi zaidi, kupumua mara nyingi zaidi, kuenea na kutoa sauti nje ya mifumo ya kawaida, ""alisema mwanabiolojia wa Australia Kate Sprothes, ambaye aliongoza timu kutoka Chuo Kikuu cha Aarhus nchini Denmark." "Tofauti na wanadamu, hisi kuu katika nyangumi si kuona - ni kusikia", anasema. """Wakati nyangumi wanaweza kuwa na uwezo wa kuona mashua 100m mbali, wao ni uwezekano wa kusikia, hivyo ni busara kuzingatia hii wakati wa kuamua nyangumi-kuangalia miongozo.""Utafiti wa awali katika matokeo ya muda mrefu ya kusumbua nyangumi mama imethibitisha kwamba nishati wao kutumia katika majibu hupunguza kiasi inapatikana kwa kuepuka papa, orcas au wanaume zisizohitajika, kufanya uhamiaji mrefu na hasa kulisha watoto wao." Watoto hao wanahitaji maziwa mengi kwa muda mfupi ili wawe na nguvu za kutosha kuhamia bila kuathiriwa na wanyama wa kuwinda. Watafiti hao walifanya majaribio katika Ghuba ya Exmouth, pwani ya magharibi ya Australia, eneo la kupumzika kwa idadi kubwa zaidi ya nyangumi aina ya humpback duniani. Nyangumi hao hutumia majira ya baridi kali huko, si kulisha bali kunyonyesha ndama zao zilizo tayari kuhamia maeneo baridi zaidi ya kulisha wakati wa kiangazi. Katika matukio 42, watafiti waliendesha mashua yao hadi mita 100 kutoka kwa mama na ndama yake na kisha walitumia wasemaji wa chini ya maji kutoa viwango tofauti vya kelele za injini, wakifuatilia majibu ya nyangumi kutoka juu kwa kutumia kamera iliyowekwa kwenye drone. Sauti ya mashua ya 172 decibels ilifanya muda wa kupumzika wa mama wa nyangumi kupungua kwa 30%, kuongeza kasi ya kupumua kwa mara mbili na kuongeza kasi ya kuogelea kwa 37%, ingawa mara nyingi walirudi katika hali ya kupumzika wakati kelele ilipopungua.