Integrating multiple data sources to assess the distribution and abundance of bottlenose dolphins Tursiops truncatus in Scottish waters

Abstract

The distribution, movements and abundance of highly mobile marine species such as bottlenose dolphins Tursiops truncatus are best studied at large spatial scales, but previous research effort has generally been focused on relatively small areas, occupied by populations with high site fidelity. We aimed to characterize the distribution, movements and abundance of bottlenose dolphins around the coasts of Scotland, exploring how data from multiple sources could be integrated to build a broader‐scale picture of their ecology. We reviewed existing historical data, integrated data from ongoing studies and developed new collaborative studies to describe distribution patterns. We adopted a Bayesian multi‐site mark‐recapture model to estimate abundance of bottlenose dolphins throughout Scottish coastal waters and quantified movements of individuals between study areas. The majority of sightings of bottlenose dolphins around the Scottish coastline are concentrated on the east and west coasts, but records are rare before the 1990s. Dedicated photo‐identification studies in 2006 and 2007 were used to estimate the size of two resident populations: one on the east coast from the Moray Firth to Fife, population estimate 195 [95% highest posterior density intervals (HPDI): 162–253] and the second in the Hebrides, population estimate 45 (95% HPDI: 33–66). Interaction parameters demonstrated that the dolphins off the east coast of Scotland are highly mobile, whereas those off the west coast form two discrete communities. We provide the first comprehensive assessment of the abundance of bottlenose dolphins in the inshore waters of Scotland. The combination of dedicated photo‐identification studies and opportunistic sightings suggest that a relatively small number of bottlenose dolphins (200–300 individuals) occur regularly in Scottish coastal waters. On both east and west coasts, re‐sightings of identifiable individuals indicate that the animals have been using these coastal areas since studies began.

Predicting the effects of human developments on individual dolphins to understand potential long-term population consequences

“…The trajectory of this bottlenose dolphin population is currently stable [26,27] and, despite the biases deriving from the small sample size, the simulation study suggested that the proposed developments are unlikely to cause a substantial disruption of calf survival (or, at least, the effect cannot be distinguished from natural individual heterogeneity). In the light of these results, the condition of individuals should now be monitored, so that any deterioration following increased exposure to disturbance can be rapidly detected, before it translates into longer-term changes in the population's trend.…”

“…We focused on the sighting history of calves that were consistently associated with the same female [39], because we anticipated that disturbance was more likely to affect calf survival rather than female pregnancy rate [40,41]. Details of the photo-identification data collection are provided in [26,27,37]. We developed a multi-stage model of calf history, where each calf could transition between four different stages: -stage 1: newborn (age 0, born in that same year); -stage 2: age 1 or 2 years; -stage 3: age 3 or more; or -stage 4: dead.…”

Can citizen science contribute to the evidence-base that underpins marine policy?

“…Frequency relates to the abundance of marine citizen science programmes in these areas categorised as high, medium and low using expert judgement by the authors. sharks [51], rays [52], dolphins [53], seabirds [54], fish [55,56], crabs [57] sponges [58], coral [59], plankton [60], seagrass [61,62], rocky reefs [63,64], coral reefs [65,66], invasive species [67], subtidal habitats [68], fisheries [69], nutrients [70], pollution [21], litter [71,72], oceanographic data [73], marine protected areas [74], beach profiling [75], and coastal protection [76]. The number of citizen science projects [15] and the numbers of publications including volunteer data in the marine field have increased rapidly over the past 30 years (see Fig.…”

New Approaches to Marine Conservation Through the Scaling Up of Ecological Data

“…Replicate attempts to capture tagged animals yields an estimate of capture probability (Cheney et al 2013) Multiple observer Estimate detection error by observing how well two independent observations of occurrence overlap (Spear et al 2004) Line-transect methods…”