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The Short-Beaked Common Dolphin (Delphinus Delphis) in the North-East Atlantic: Distribution, Ecology, Management and Conservation Status

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The Short-Beaked Common Dolphin (Delphinus Delphis) in the North-East Atlantic: Distribution, Ecology, Management and Conservation Status 21st ASCOBANS Advisory Committee Meeting AC21/Inf.4.1.b (O) Gothenburg, Sweden, 29 September - 1 October 2014 Dist. 26 August 2013 Agenda Item 4.1 Review of New Information on other Matters Relevant for Small Cetacean Conservation Population Size, Distribution, Structure and Causes of Any Changes Information Document 4.1.b The short-beaked common dolphin (Delphinus delphis) in the north-east Atlantic: distribution, ecology, management and conservation status Action Requested Take note Submitted by Zoological Society of London NOTE: DELEGATES ARE KINDLY REMINDED TO BRING THEIR OWN COPIES OF DOCUMENTS TO THE MEETING Oceanography and Marine Biology: An Annual Review, 2013, 51, 193-280 © Roger N. Hughes, David Hughes, and I. Philip Smith, Editors Taylor & Francis The ­short- bEaked commoN Dolphin (Delphinus Delphis) in the ­north-­east Atlantic: distributioN, Ecology, maNagEment and conservatioN staTuS SinéaD murphy1,2, EunicE H. Pinn3 & Paul D. JepsoN1 1institute of Zoology, Zoological society of london, Regent’s park, london, nW1 4RY, united Kingdom 2 C- MRG, institute of natural sciences, Massey university, private Bag 102 904, Auckland 0745, new Zealand E- mail: [email protected] (corresponding author) 3Joint nature Conservation Committee, inverdee house, Baxter street, Aberdeen, AB11 9QA, united Kingdom The common dolphin is the second most abundant cetacean species in the North- east atlantic, with a wide- ranging distribution and is, potentially, impacted by a wide variety of pressures and threats. To assess the conservation status of common dolphins in this region, it is essential to understand population structure, key drivers of population dynamics, key resources and the effects of stressors. In recent years, a number of studies have assessed population structure, distribution and abundance, life- history parameters, dietary requirements and the effect of stressors—especially those caused by anthropogenic interactions, such as incidental capture (i.e., by- catch) and pollutants. a full review of this work is presented, with particular focus on current and potential pressures and threats. Notwithstanding the recent research, due to the lack of baseline data (i.e., prior to human influence) on abundance and pregnancy rate and on historical direct and incidental capture rates, the actual conservation status of the North- east atlantic common dolphin population is unknown. current assessments of conservation status of the species are therefore reliant on recent data. However, these assessments are hindered by the lack of data on contemporary incidental capture rates in some fish- eries and limited sampling in other fisheries, as well as large data gaps for other stressors. In addi- tion, the numerous potential ways in which multiple and diverse stressors can interact remain poorly understood. This chapter provides an outline of a management framework and describes methods for future evaluation of conservation status through development of indicators focusing on not only population size and distribution but also mortality and condition. Recommendations for research and conservation actions are described. Introduction common dolphins (Delphinus delphis) are one of the most abundant cetaceans in the North- east (NE) atlantic and are potentially impacted by a wide variety of threats and pressures. a large number of studies since the year 2000 have focused on their biology, ecology, population struc- ture, abundance, health status, foraging behaviour, interactions with fisheries, and pollutant levels, 193 SINÉAD MURPHy, EuNIcE H. PINN & PAUL D. JEPSoN among other aspects. No baseline data (prior to anthropogenic impacts) are available for this spe- cies in the region, making comparisons to the modern situation impossible. current assessments of conservation status of the species therefore rely on recent data. Such assessments require informa- tion on genetic diversity, evidence of density- dependent compensatory responses in reproductive parameters, and, most importantly, trend analysis of abundance estimates—though for the last only primary (preliminary) survey data are available for most of the NE atlantic. as these parameters respond to a change after it has occurred, most likely years later, monitoring of anthropogenic (and environmental) impacts is extremely important to limit their effects. under European union leg- islation, member States now have a legal obligation to undertake such monitoring in their national waters. The present review encompasses a comprehensive assessment of knowledge on the common dolphin in the NE atlantic, with the aim of providing both a current evaluation of conservation sta- tus and valuable information for the future development of a conservation management plan in these waters. Species identification The common dolphin was first identified bya rtedi in 1738 and later described by linnaeus in 1758. much confusion has arisen about whether the ‘common dolphin’ comprises one or more species due to the cosmopolitan distribution and high variability in morphological characters and pigmenta- tion patterns of otherwise- similar forms. almost two dozen nominal species have been described (Hershkovitz 1966, Heyning & Perrin 1994). During the 1990s, studies focused on clarifying taxonomic status and proposed that only two distinct species of common dolphin existed: the short- beaked common dolphin Delphinus delphis linnaeus, 1758 and the long- beaked common dolphin D. capensis gray, 1828 (Heyning & Perrin 1994, Rosel et al. 1994). contemporary taxonomic classifications further recognize an endemic sub- species of the short- beaked form, D. delphis ponticus (­Barabash- Nikiforov, 1935), which is restricted to the black Sea, and two endemic subspecies of the long- beaked form found in the Indo- Pacific region: D. capensis capensis gray, 1828, and the extremely long- beaked D. c. tropicalis (van bree, 1971) (amaha 1994, Heyning & Perrin 1994, Rosel et al. 1994, Jefferson & van Waerebeek 2002, Natoli et al. 2006, Perrin 2009). Delphinus delphis and D. capensis were differentiated on the basis of an assessment of morpho- logical data (including measurements of skeletal characters, such as overall body size, length of the rostrum, rostrum length/ zygomatic width ratio [Rl/ ZgW], and tooth counts) and colouration pat- terns in two sympatric populations inhabiting coastal waters off california, united States (Heyning & Perrin 1994). an assessment of samples and data from outside this region led the authors to pro- pose that D. delphis and D. capensis existed globally as two separate species. This view was further supported by a parallel genetic analysis of tissue samples from dolphins inhabiting californian waters and from D. delphis in the eastern tropical Pacific (ETP) and black Sea. No shared mito- chondrial DNa (mtDNa) haplotypes or cytochrome b sequences were observed between the two morphotypes, and both gene regions exhibited nucleotide frequency differences and fixed nucleo- tide substitutions between the two morphotypes (Rosel et al. 1994). The estimated genetic diver- gence in the mitochondrial DNa control region between the two forms was 1.1% (Rosel et al. 1994). However, the classification of individuals into the two species was not as clear cut as origi- nally perceived, and questions have arisen over the use of morphology- based taxonomy in com- mon dolphins. additional morphological studies have shown large variability in body and skull size and Rl/ ZgW ratio in D. delphis inhabiting the North atlantic and waters around New Zealand and southern australia compared with D. delphis off the coast of california (bell et al. 2002, murphy et al. 2006, Westgate 2007, Jordan 2012). Studies using mtDNa identified that D. del- phis and D. capensis do not show reciprocal monophyly (leDuc et al. 1999, amaral et al. 2007), and an assessment of nuclear divergence using amplified fragment length polymorphism markers 194 THE SHoRT-bEAKED COMMON DOLPHIN IN THE NoRTH-EaST aTLANTIc suggested that D. delphis and D. capensis diverged only recently (kingston & Rosel 2004). overall, the short- beaked form, despite having high morphological variability, exhibits low genetic differ- entiation between populations, with evidence of gene flow across oceans, reflecting high mobility and a fluid social structure in this species (Natoli et al. 2006; assessed nine microsatellite and 369 base pairs [bp] of the mtDNa control region). The opposite is true for the long- beaked form: populations are highly differentiated, suggesting that separate populations may have evolved from independent founder events, then converged on the same morphotype (Natoli et al. 2006). a more recent international collaborative genetics study, which analysed sequences of the mitochondrial DNa cytochrome b gene, further revealed that the distribution of mitochondrial lineages does not correspond to the geographical distribution of the long- beaked morphotype, thus suggesting some ambiguity in the phylogenetic relationships and taxonomy within this species (amaral et al. 2009, 2012a,b). Further analysis is required to clarify the species- level taxonomy of common dolphins (International Whaling commission [IWc] 2009). ­North- east Atlantic Ocean only the short- beaked form has been recorded in the North atlantic (murphy et al. 2006, Westgate 2007). based on tooth counts, absolute length of rostrum and Rl/­GZW ratio, murphy et al. (2006) proposed that common dolphins in the NE atlantic are most similar to Delphinus delphis described by Heyning
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