Whale science and how (not) to use it

Transcription

1 Whale science and how (not) to use it Few creatures carry more emotion on their broad backs than whales; and few issues arouse as much passion as whaling. Each year around this time the International Whaling Commission comes under pressure to allow the resumption of commercial catching and killing of whales and the Save the Whale lobbyists protest. But how many whales are there? Can the scientists and statisticians tell us and how much influence do they wield in the real world of whale-politik? Philip Hammond, a former Chairman of the Scientific Committee of the IWC, explains. One Blue Whale Unit was equal to one blue whale killed, or 2.5 humpback whales, or 6 sei whales The IWC s annual meeting is often held in some exotic corner of the world. Last year s was in Korea, and this June it will be in St Kitts. These meetings usually make the headlines because of the clash between countries whose policy is to maintain the existing moratorium on whaling and those who seek to resume whaling. Whaling is an emotive issue for many people, but science should be able to play a role by providing information to assist the debate. The IWC was set up in 1946 to administer the International Convention for the Regulation of Whaling, which was established to try to put a brake on the decimation of whale populations in the Southern Ocean. At that time, management of whaling was based on the Blue Whale Unit (BWU), where one BWU was equal to 1 blue whale, 2 fin whales, 2.5 humpback whales or 6 sei whales. Whalers could take any combination of species up to the BWU limit. Management failed completely and this period of so-called modern whaling only came to a close when these populations of whales became commercially extinct that is, when it was no longer profitable to hunt them. The IWC is a relatively new organisation but commercial whaling has existed for centuries. It began in the 16th century in the North Atlantic and spread into the Pacific in Successive populations of right, bowhead, grey and sperm whales were systematically reduced to very low numbers. Modern whaling began in 1863 when Norwegian Svend Foyn industrialised an explosive-tipped harpoon based on the design by Erik Eriksen, and in 1864 mounted it on the first steampowered whaling vessel. It was now possible to catch the faster-swimming species of blue, fin, sei and humpback whales. During a period of about 40 years populations of these species were almost wiped out, first in the North and then in the South Atlantic. In 1906 the whalers reached South Georgia and the vast whale resources of the Southern Ocean were within reach. In 1926 the first factory ship steamed south towards Antarctica and by 1930 most of the world s whaling was concentrated there. Between 1928 and 1968 at least a million whales were taken from the Southern Ocean. It took the 1972 Conference on the Human Environment in Stockholm to galvanise the IWC to pursue 54 june2006

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3 rational management of whaling. This led to more research, to obtain better information, and to the separate management of each species, based on stock assessments similar to those used for fish populations. Despite being a big step forward, this management still did not work very well. At the same time the grassroots environmental movement was rapidly gathering pace and calls for a complete ban on whaling the Save the Whale campaign were growing. In 1982 the IWC voted for a pause in all commercial whaling and a moratorium came into effect in Part of its purpose was to allow time for a programme of assessment of the status of species that were or had been subject to whaling in other words, to find out how many whales were left. Another reason was to develop a new way to manage whaling safely that would actually work. That job was down to the Scientific Committee of the IWC. Prior to the political meeting of the IWC, the Scientific Committee meets for almost 2 weeks with the task of producing a report that could be used by the IWC to help it reach decisions. The Scientific Committee has a broad agenda, covering topics from the management of aboriginal subsistence whaling to consideration of the effects on whale populations of human activities other than whaling. Much of its time in recent years has been taken up with considering estimates of whale population abundance and how those estimates should be used. The minke whale is a small baleen whale that is still hunted in the North Atlantic, North Pacific and Southern Oceans by small we mean 8 to 10 metres long and weighing 8 to 13 tonnes at adulthood. On its website (www. iwcoffice.org) the IWC states that there are approximately minke whales in the North Atlantic. But where does this number come from? How do you determine how many whales there are in a particular population? It is not possible simply to go out and count the number of whales in a population. Although some populations are small, most number in the thousands or tens of thousands and range over wide areas of ocean. To make it more difficult, they spend a large proportion of their time underwater, unable to be observed. Not the best starting point for a count. Consequently, the number of whales in an area or a population needs to be estimated by collecting a sample of data and then extrapolating it using a statistical model. The primary method for doing this is line transect sampling. The idea behind line transect sampling is to estimate the density of the target species in 56 3(2)_03 Hammond_Whaling.indd 56 Abandoned whale-processing factory, Deception Island, Antarctica. Oil was extracted in the boilers to the right, and stored in the tanks whales were processed here before it was abandoned in Credit: Fiona McQuarrie. strips sampled by surveying along a series of transects, and to extrapolate this density to the entire survey area. The calculated statistic is therefore an estimate of the number of whales in a defined area at the particular time the survey took place. Because the probability of seeing a whale decreases the further away it is from the transect line, the distance to each detected whale is measured and the measurements are then used to estimate the effective width of the strip that has been searched. Measuring distance at sea is notoriously difficult, so these measurements are typically estimated and experiments conducted with inanimate objects to check for bias. Line transect surveys are currently all visual. Active sonar is not used because whales use sound as their main means of communication and are very sensitive to it. For some species passive acoustic methods are being developed but they cannot yet be used to estimate abundance. A fundamental assumption of line transect sampling is that all target subjects on the transect line itself are seen with certainty. This is clearly violated by whales because they are underwater most of the time. Consequently, the probability of detecting a whale on the transect line also needs to be estimated. A further complication is that whales often travel in schools and the size of each of these needs to be measured. Line transect sampling is the method used to estimate the number of minke whales in the North Atlantic. It has also been used to estimate minke whale populations in the western North Pacific and the Southern Ocean ( and , respectively, up to 1988/89). The Scientific Committee is currently in the process of reviewing this estimate for the Southern Ocean because analysis of recent data suggests a smaller population. It is unclear whether this is due to a real decline in population abundance or to changes in the survey methodology. Results from this review should be available later this year. Line transect sampling was first developed for estimating the number of flushing birds like grouse. Applying it in the marine environment to estimate numbers of whales has been a challenge. But whale biologists and statisticians working together over the last 25 years have made significant theoretical and practical developments that now allow the accurate and precise estimation of whale populations. These developments have also been of great benefit to scientists working on other animals. The primary software used to implement line transect sampling is DISTANCE ( st-and.ac.uk/distance), which is used by hundreds of wildlife biologists all over the world. Another way of estimating the size of whale populations that has developed during the last 20 years is a novel application of the capture-mark-recapture (CMR) method. Some species of whale have natural markings on their dorsal fins, tail flukes and bodies that allow individual animals to be permanently identified. These markings can be photo- june /05/ :04:22

4 Figure 1. A humpback whale identifies itself, and waves goodbye. Credit: Peter Stevick. graphed and matched over multiple sampling occasions a process known as photo-identification generating capture histories suitable for CMR analysis. These methods were originally developed for studies in which individual number of individuals animals are captured and marked in some way (painting, branding, tagging, etc.), released and then recaptured. Indeed, the initial application to whales was to mark them by firing so-called discovery tags (metal bolts about 30 cm long) Figure 2. Increase in numbers of humpback whales between 1978 and into the blubber and recapturing them when the animal was butchered after being harpooned in harvesting operations. Photo-identification has some advantages over traditional sources of mark-recapture data, the most obvious being that the animal does not have to be physically captured or marked, which means that marking does not affect the probability of the animal being recaptured. Another advantage is that appropriate natural marks are permanent and cannot be lost, as artificial marks can be. On the negative side, natural markings are more difficult and take more time to recognise than, say, a number on a brand or a tag, and not all species have adequate markings for the methods to be applied. Other assumptions of the CMR method are that marked animals must mix fully with the rest of the population between sampling occasions and that every animal in the population should have the same probability of being captured within any one sampling occasion. Violation of this last assumption is known as heterogeneity of capture probabilities and it leads to an underestimation of population size. This is a ubiquitous problem in CMR studies but the problems can be minimised by careful design of data collection and application of more complex models. These models are available in the widely used program MARK ( ~gwhite/mark/mark.htm), which was june

5 The minke whale is the most abundant species of baleen whale, with a world population of hundreds of thousands, maybe as much as a million. In recent years most whales killed for commercial purposes have been minkes. In the North Atlantic about 600 a year have been taken by Norway under objection to the moratorium and about 30 to 40 by Iceland under special permit. Japan annually takes about 450 minke whales in the Southern Ocean and about 150 in the North Pacific under special permit. These catches are small relative to the estimated numbers of whales and are unlikely to have an adverse impact on populations. The number of blue whales in the world, however, is only a few thousand. In the Southern Ocean an estimated 400 to 1400 remain from a population that probably once numbered about Blue whales have been protected since the 1960s but they have very low rates of increase and it will be a long time before we know whether or not they will recover from the devastating exploitation of the 20th century. primarily developed to estimate survival rates but is also the best software for estimating population size using CMR data. Analysis of photo-identification data to estimate whale numbers has been applied most successfully to humpback whales, which can be marked by photographing the black and white markings and the pattern of notches on the trailing edge of their tail fluke (see Figure 1). For example, a population size of greater than animals and an annual increase in population size of about 3% over the last 25 years has been documented in the North Atlantic (see Figure 2). A third way in which whale abundance can be estimated is by counting animals as they migrate past a suitable point on shore and then using a suitable model to account for animals that have been missed because, for example, they were out of range or passed during the night. The method has been used to estimate that in the eastern North Pacific there are grey whales and that that population has been increasing at about 3% annually in recent decades. A novel application of this method has been used for bowhead whales in Arctic waters of the North Pacific. Counts from the ice edge have been combined with data from underwater recordings of whale vocalisations in a CMR model to estimate a population size of 8000 and an annual increase of a similar 3%. The estimated numbers of these and other species of whales have been used to assess the status of populations and to monitor their recovery (or otherwise) from exploitation. Estimates for some species are used to ensure that safe catch limits can be set for populations that are still subject to whaling. This latter process occurs through one of the IWC s two management procedures. One is for aboriginal subsistence whaling, which is undertaken by native communities mainly in Arctic regions to provide meat for local consumption. The other applies to commercial whaling, currently under the moratorium adopted in 1982 (and effective from 1986). One reason for the IWC taking the moratorium decision was that scientific uncertainty precluded calculation of safe catch limits using available methods. The moratorium was to allow the science and the statistics to catch up. To deal with this the Scientific Committee spent 8 years developing a Revised Management Procedure (RMP) for baleen whales, a description of which can be found on the IWC website. The RMP was based on the principle of explicitly taking into account the considerable scientific uncertainty. Before this development many scientists doubted that whaling could ever be prosecuted safely. But extensive testing through computer simulation to ensure robustness to a wide range of uncertainties about population dynamics errors in catch and abundance data, population structure, etc. has shown that it can be done, at least in theory. At that time it was by far the most rigorously tested management procedure for a natural resource yet developed and it paved the way for the development of similar procedures for managing fishing all over the world. The RMP was adopted by the IWC in 1994 and could be used to manage commercial whaling on those populations for which the detailed preparatory scientific work had been completed currently minke whales in the North Atlantic, western North Pacific and Southern Ocean. But the RMP has never been formally implemented because the moratorium is still in place. There has been a continuing push from some countries to lift it, but IWC rules require a 75% majority to take this decision, and there are more than enough member countries opposed to whaling to stop that happening. However, commercial whaling has continued through two loopholes, both of which are somewhat anomalous. First, IWC rules allow any member state that formally objects to a decision to ignore it. Norway still maintains an objection to the original moratorium decision and catches whales under objection. Secondly, IWC rules allow any member state to issue special permits to its whalers to take whales for scientific research. There is an ongoing debate, both political and scientific, about the validity and necessity of such research. The bottom line is that commercial whaling continues because it remains legal, even under the moratorium, and because some countries continue to exercise their rights while the moratorium is in place. Although the IWC is required under the Convention to take decisions based on science (which is why it has a Scientific Committee), in practice science is only one type of information used by the member states, and not always the one taken most notice of. The IWC also uses technical/ethical advice on such things as whale killing methods, and financial and administrative advice on, for example, the feasibility and cost of ensuring that rules are followed. Most importantly, it takes account of opinion in its constituencies back home. For many countries, science is probably the least important aspect to consider when debating whaling issues. There is no doubt that the scientific advances (many of them statistical) made in the last 20 years or so have greatly increased our knowledge of how well whale populations are recovering (or not) from previous over-exploitation. Science can also tell us under what circumstances, if any, whaling can take place without endangering populations. But the debate here is primarily about whether whales should be hunted at all, and this is first and foremost a political issue that involves beliefs, principles and opinions. There are widely disparate views around the world about the acceptability of whaling. In some countries it is viewed as a perfectly reasonable activity to harvest food resources from the sea. In other countries killing whales is believed by many to be a cruel and unnecessary practice that should be banned forever. Governments broadly represent the views of the people they govern, so IWC member states have very different policies, which have become highly polarised. When it comes to whaling, people are either in favour of it or against it the science is largely irrelevant. Philip Hammond of the Sea Mammal Research Unit, St Andrew s University, is a former Chairman of the Scientific Committee of the IWC. He is a biologist with interests in statistical and mathematical modelling of marine mammal populations and interactions between marine mammals and man. 58 june2006