Marine mammals
Sea Watch Foundation; SMRU; University of Aberdeen
| WHAT IS ALREADY HAPPENING | WHAT COULD HAPPEN |
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Executive summary- The impact of climate change on marine mammals remains poorly understood. As a result, there has been a great deal of speculation but without very much substantive evidence. That evidence for marine mammals is very difficult to obtain, particularly when there are often synergistic effects from anthropogenicA change within part of the climate system that can be attributed to human action, rather than natural causes. activities.
- The strongest predictions of effects involve loss of available habitat, especially ice cover to ice-breeding pinnipeds. This is already thought to affect ringed seals and their main predator, the polar bear, in the arctic.
- In UK waters, environmental changes will likely be reflected mainly in responses to changes in prey distribution and abundance as a result of warmer sea temperatures.
- Apparent range shifts have been observed in a number of odontoceteToothed cetaceans cetacean species and these could be associated with changes in water temperatures, but at present it is not possible to differentiate between short-term responses to regional resource variability and longer-term ones driven by climate change.
- A wide range of potential impacts of climate change can be listed, mainly operating through marine mammal prey (zooplanktonPlanktonic marine animals. Click for link to the SAHFOS Marine Climate Change Encyclopaedia, fish and cephalopod abundance and distribution changes). The relative importance of these and their likelihood of occurrence remains unknown.
| what is happening now | what could happen in the future | |
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| Amount of evidence | low | low |
| Level of agreement or consensus | moderate | moderate |
| Level of confidence | low | low |
Our knowledge of gross status changes is good for seals but moderate-poor for cetaceans, whilst our understanding of links between demography and climate for both groups is poor. We therefore can only have a low level of confidence in what is happening now in relation to climate. As for what may happen in the future, without any clear understanding of impacts on marine mammals, in most cases it is impossible to make confident predictions.
Some marine mammal scientists are more confident than others that we are witnessing ecological effects of climate change as opposed to responses of individuals and local populations to local environmental variability. The statistical power to discriminate between the two remains low. Although more could be done to improve the current level of confidence, there will always be an upper limit to our ability to link population changes to the physical or biological drivers associated with climate change, particularly for some of the less accessible cetacean species.
- A pre-requisite to assessing impacts of climate change on marine mammals at a population level is a long-term, wide-ranging, monitoring programme that can discriminate between regional population responses and those occurring on a wider geographical scale. This is presently lacking for all UK cetacean species, whilst for seals there remain regions (e.g. Irish Sea) with only patchy coverage.
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Our knowledge of trends in basic life history parameters (growth rates, age at sexual maturity, reproductive rates, and mortality) for all cetacean species with the possible exception of harbour porpoise is woefully inadequate, based upon small sample sizes from a restricted number of areas, and without long-term continuity of data. For the majority of species, we are unlikely to obtain adequate information in the foreseeable future given how difficult they are to study and the resources available to do so. However, certain species could be targeted for more intensive study with some likelihood of success. In UK waters, these include (in addition to harbour porpoise) bottlenose dolphin, short-beaked common dolphin, white-beaked dolphin, Risso's dolphin, and minke whale.
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Functional responses to environmental change through physiological and behavioural mechanisms are also poorly understood for most marine mammal species. For this, seals are rather better suited to experimental studies where variables can be controlled. Once individual responses are better understood, it may be possible to make predictions at the population level.
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Too little is known about how changes in fish, cephalopod and plankton dispersion, distribution and abundance may affect the foraging ecology of particular marine mammal species. Often, one of the major gaps in information lies in the lack of data for non-commercial fish and cephalopod species, although even for some commercial species, such information is lacking.
No marine mammal species in the UK is exploited directly, although changes in the status and distribution of marine mammals could potentially have commercial effects if species that are targeted by the ecotourism industry become scarce, or alternatively if there are changes in competitive relations (e.g. an increase in seal predation upon commercially important fish).
Peter G.H. Evans
Sea Watch Foundation (SWF), Cynifryn, Abershore, Llanfaglan, Caernarfon, Gwynedd LL54 5RA.
Ian L. Boyd
Sea Mammal Research Unit (SMRU), Gatty Marine Laboratory, University of St Andrews, St Andrews, Fife KY16 8LB.
University of Aberdeen, School of Biological Sciences (Zoology), Tillydrone Avenue, Aberdeen AB24 3JG.