Whale-watching tourism, currently worth $1 billion p.a. worldwide, depends upon the continued presence of whale, dolphin and porpoise species (collectively called cetaceans) within a specific area. Current evidence suggests that the distribution and/or abundance of cetaceans is likely to alter in response to continued changes in sea surface temperature with global climate change (GCC). This paper reviews how such changes may affect the sustainability of whale-watching operators from a resilience perspective. Potential implications include changes to the presence and frequency of cetacean species targeted and changes to lengths of tourism seasons to coincide with shifts in migration patterns. The review presents an interdisciplinary framework for evaluating the resilience of whale watching to changes in species occurrence, whereby resilience is the degree of change in cetacean occurrence experienced before tourist numbers fall below a critical threshold. The framework combines likelihood of observing a cetacean, trip type and tourist type, which when quantified could identify which operators are likely to experience a change in tourist numbers given a specific scenario of changing cetacean occurrence. In doing so, a step is taken towards providing a means by which resilience to GCC effects on cetacean species could potentially be provided.
The feeding ecology of striped dolphin, Stenella coeruleoalba , in the north-western Mediterranean Sea was studied using stable isotope analyses. Carbon and nitrogen stable isotope ratios were measured in skin and muscle tissues of stranded and by-caught dolphins from six geographical areas in the Mediterranean Sea and Atlantic Ocean. Variation in δ 15 N in relation to dolphin size is attributed to changes in diet. Nursing calves have a higher trophic level than weaned animals and their δ 15 N values decrease progressively until weaning, estimated to be at a body length of around 155 cm. δ 15 N values then increased for larger individuals which suggests changes in diet for mature dolphins. Geographical differences in diet were apparent between the Atlantic and the Mediterranean, although no clear differences were apparent between the five Mediterranean areas. Comparisons of the nitrogen isotope ratios of skin and muscle highlighted a higher fractionation in skin compared to the muscle tissue. Values of δ 13 C also increased with body length although it appears that this is not only driven by trophic level enrichment. δ 13 C increases before weaning and the difference in trophic level between newly-weaned and mature dolphins was twice as high for carbon as for nitrogen. Ontogenetic changes in carbon isotope composition may therefore be driven by feeding on deep water prey and dolphin movements outside the coastal feeding grounds. Indeed, seasonal variations in δ 13 C are suspected to be driven by migration within the Mediterranean basin.
The white-beaked dolphin ( Lagenorhynchus albirostris ) and short-beaked common dolphin ( Delphinus delphis ) are two of the most abundant delphinid species in shelf waters around the United Kingdom (UK) and Republic of Ireland (ROI) in the summer season (May–October). As these two species have similar habitat preferences and diets, it might be expected that they would partition their otherwise shared niche to reduce the potential for competition at this time of year. This study used 569 sightings of the two species, collected from shelf waters (<200 m water depth) in the summer season between 1983 and 1998, to investigate whether there is evidence of widespread niche partitioning based on water temperature in this area. Below 13°C, white-beaked dolphins were dominant with 96% of sightings comprising this species. In contrast, above 14°C, 86% of sightings comprised common dolphins. A classification tree analysis found that of the four eco-geographical variables analysed (water depth, seabed slope, seabed aspect and sea surface temperature), temperature was the most important variable for separating the occurrence of the two species. These results are consistent with widespread temperature-based niche partitioning between white-beaked and common dolphins in shelf waters around the UK and ROI. As temperature is important in determining the relative distribution of these species, the range of the white-beaked dolphin might be expected to contract in response to increasing sea temperature resulting from global climate change, while that of the common dolphin may expand.
There is a paucity of data on the family Ziphiidae (the beaked whales) and even basic information, such as body length, is not available for some species. This review examines published records of body length for 20 of the 21 currently recognised species of beaked whale. It considers maximum, median and modal body lengths, where possible by sex. For Cuvier’s, Blainville’s and Gray’s beaked whales, modal and median lengths were much shorter than the maximum reported lengths; this may reflect misidentification of the largest animals. Although males of some species reached a greater maximum size, there was only a significant difference in median body length for three species: True’s beaked whale; the strap-toothed whale; and Gervais’ beaked whale. In all three cases, females had a significantly larger median length. The apparent lack of consistent sexual dimorphism in body length suggests that, while male beaked whales use their tusks as weapons to compete aggressively for access to receptive females, large size does not give a competitive advantage. This may be a result of the way the sexually dimorphic tusks are used during combat. The only exception to this rule appears to be the northern bottlenose whale, for which males consistently reach greater body lengths than the largest females. Male-male combat appears to take a different form in this species.
Approaches for modelling the distribution of animals in relation to their environment can be divided into two basic types, those which use records of absence as well as records of presence and those which use only presence records. For terrestrial species, presence–absence approaches have been found to produce models with greater predictive ability than presence-only approaches. This study compared the predictive ability of both approaches for a marine animal, the harbour porpoise (Phoceoena phocoena). Using data on the occurrence of harbour porpoises in the Sea of Hebrides, Scotland, the predictive abilities of one presence–absence approach (generalised linear modelling—GLM) and three presence-only approaches (Principal component analysis—PCA, ecological niche factor analysis—ENFA and genetic algorithm for rule-set prediction—GARP) were compared. When the predictive ability of the models was assessed using receiver operating characteristic (ROC) plots, the presence–absence approach (GLM) was found to have the greatest predictive ability. However, all approaches were found to produce models that predicted occurrence significantly better than a random model and the GLM model did not perform significantly better than ENFA and GARP. The PCA had a significantly lower predictive ability than GLM but not the other approaches. In addition, all models predicted a similar spatial distribution. Therefore, while models constructed using presence–absence approaches are likely to provide the best understanding of species distribution within a surveyed area, presence-only models can perform almost as well. However, careful consideration of the potential limitations and biases in the data, especially with regards to representativeness, is needed if the results of presence-only models are to be used for conservation and/or management purposes.
Little is known about cetacean communities in the tropical and sub-tropical Atlantic. This paper describes the cetacean community found east of Great Abaco in the northern Bahamas (26·5°N) during summer months between 1998 and 2001. Nine species of cetaceans were recorded, which could be divided into two distinct groupings: firstly, ‘permanent’ species, which had relative sightings rates between 0·026–0·084 sightings per hour and which were recorded on many occasions in all years and most months; secondly, ‘sporadic’ species, which had relative sightings rates an order of magnitude lower (0·004–0·008 sightings per hour) and which were recorded on very few occasions. The ‘permanent’ species were the Stenella frontalis (Atlantic spotted dolphin), Kogia simus (the dwarf sperm whale), Mesoplodon densirostris (Blainville's beaked whale) and Ziphius cavirostris (Cuvier's beaked whale). These four species differed significantly in the depth of grid squares utilized (χ=20·25, df=9, P <0·01) suggesting that these species occupied four separate niches. Stenella frontalis dominated the surface feeding niche, while the remaining three deep-diving species segregated into different depth ranges. Kogia simus was the dominant species in water depths of less than 200 m, M. densirostris in water depths of 200 to 1000 m and Z. cavirostris in water depths of greater than 1000 m. The overall relative density (2·533 individuals per hour of effort) and diversity of species in the study area was relatively low and may relate to low levels of local productivity. It is hypothesized that the four ‘permanent’ species may competitively exclude ecologically similar species, resulting in a reduced number of species and that ‘sporadic’ species may only enter the study area during times of higher than usual productivity when the ‘permanent’ species are no longer able to dominate their individual niches.
Little is known about the ecology and behaviour of species within the family Ziphiidae. In this paper, five aspects of beaked whale ecology and behaviour are reviewed in relation to possible anthropogenic impacts upon them: social structure; life history; foraging/diving ecology; form and function of beaked whale sounds; and habitat characteristics. Differences in social structure within and between species may affect how anthropogenic activities affect local populations. Life history parameters may likewise vary within and between species and may influence the extent of and ability to recovery from population level impacts. Foraging and diving ecology determine where beaked whales spend most of their time and therefore, where in the water column they are most likely to encounter anthropogenic activities. The form and function of beaked whale sounds may be important in determining whether and how beaked whales are affected by anthropogenic noise. Finally, habitat characteristics determine whether beaked whales are likely to occur in a specific area where anthropogenic activities are to be undertaken and may also determine exactly how beaked whales are affected by it within a local area. To help fill the gaps in our knowledge of beaked whale behaviour and ecology, available opportunities for data collection must be maximised. This includes greater levels of co-operation between research groups to build up large datasets, the use of platforms of opportunity to study beaked whales in areas where little research has previously been undertaken and maximising the amount of information that can be learned from each possible source of data, such as stranded animals, through co-ordinated national and international research programmes.
Fear of predation produces large effects on prey population dynamics through indirect risk effects that can cause even greater impacts than direct predation mortality. As yet, there is no general theoretical framework for predicting when and how these population risk effects will arise in specific prey populations, meaning that there is often little consideration given to the key role predator risk effects can play in understanding conservation and wildlife management challenges. Here, we propose that population predator risk effects can be predicted through an extension of individual risk trade-off theory and show for the first time that this is the case in a wild vertebrate system. Specifically, we demonstrate that the timing (in specific months of the year), occurrence (at low food availability), cause (reduction in individual energy reserves), and type (starvation mortality) of a population-level predator risk effect can be successfully predicted from individual responses using a widely applicable theoretical framework (individual-based risk trade-off theory). Our results suggest that individual-based risk trade-off frameworks could allow a wide range of population-level predator risk effects to be predicted from existing ecological theory, which would enable risk effects to be more routinely integrated into consideration of population processes and in applied situations such as conservation.
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