CETACEAN STRANDINGS INVESTIGATION: ENGLAND AND WALES AND POSEIDON DATABASE Final Report on Contract CR0177 Conducted for the Department of the Environment, Transport and the Regions by the Institute of Zoology The Zoological Society of London Regent’s Park London NW1 4RY England Report compiled by: Peter M. Bennett, PhD Paul Jepson, MRCVS Rob Deaville, BSc Contract start date: 12 June 1995 Contract end date: 31 March 2000 CONTENTS Executive summary …………………………………………………………………. 4 1. Introduction …………………………………………………………………… 6 1.1 Aim 1.2 Policy background 1.3 Achievement of project objectives 2 Methodology …………………………………………………………………… 9 2.1 Management and personnel 2.2 Protocols for reporting of strandings and post-mortem investigation Reporting of marine mammal strandings Reporting of live cetacean strandings Pathology laboratories Standard protocols for post-mortem examination, tissue sampling and data recording 2.3 Collaboration with other organisations 2.4 Tissue archive and Poseidon central database 2.5 Reporting of data 2.6 Training 3 Results …………………………………………………………………………. 17 3.1 Causes of mortality in cetaceans (1995-1999) Entanglement in fishing gear (by-catch) Physical trauma Infectious disease Starvation Live stranding Dystocia and stillborn Neoplasia Other causes of death 3.2 Causes of mortality in grey seals 4 Results of analyses of pooled data …………………………………………….. 23 4.1 Patterns of harbour porpoise mortality (1990-1999) 4.2 Studies of the pathology and epidemiology of cetacean diseases Investigations into the epidemiology of morbillivirus in cetaceans in UK waters The pulmonary pathology of harbour porpoises (1990-1996) 4.3 Relationships between contaminants and infectious disease in harbour porpoises Polychlorinated biphenyls and infectious disease mortality Heavy metals and infectious disease mortality 4.4 Other analyses of contaminants Metals and organochlorines in other species Butyltins Radionuclides 4.5 Other ongoing research of pooled data on harbour porpoises Molecular genetic analysis of population structure Relationships between lungworm abundance and immunosuppressive contaminants Possible combined effect of organochlorines and heavy metals on health status Reproductive system pathology 5 Conclusions…………………………………………………………………….. 31 6 Recommendations for future research ………………………………………. 33 7 List of publications directly resulting from this project 1995-2000…………. 34 Appendices…………………………………………………………………………… 37 1 Details of postmortem examinations conducted during the period of this report 2 The standardised post-mortem examination guidelines and report forms for cetaceans 3 The standardised post-mortem examination guidelines and report forms for seals List of plates………………………………………………………………………….. 77 Executive summary During the period of this contract, 359 postmortem examinations of marine mammals stranded or by-caught in commercial fisheries in England and Wales were conducted, comprising 326 cetaceans of 14 different species and 33 grey seals Halichoerus grypus. The most frequently examined cetacean species were the harbour porpoise Phocoena phocoena (215 carcases), common dolphin Delphinus delphis (75) and striped dolphin Stenella coeruleoalba (15) respectively. A cause of mortality was established in 264 of the 326 cetaceans examined (81%). Entanglement in fishing gear (by-catch) was the most frequent cause of mortality in cetacean species representing 45% of all cases where the cause of mortality could be established. This comprised 64 stranded harbour porpoises, 32 common dolphins, one striped dolphin, one white beaked dolphin Lagenorhynchus albirostris and one pilot whale Globicephala melas. In addition, 21 by-caught harbour porpoises were retrieved for postmortem examination from commercial fishing vessels. Many of these known by-catches were reported through the EU-funded BYCARE research programme. Infectious diseases were frequent causes of mortality in harbour porpoises, accounting for the death of 26 harbour porpoises during the period of this report. The most common causes of infectious disease mortality in harbour porpoises were pneumonias (parasitic and bacterial) and generalised bacterial infections. In collaboration with CEFAS (Burnham Laboratory), we found that contamination by toxic pollutants may be implicated in these cases. Statistical analyses showed that tissue concentrations of PCBs and mercury were significantly higher in porpoises that died of infectious disease compared to healthy porpoises that were accidentally trapped in fishing nets. These results are in the direction predicted by the hypothesis that these industrial pollutants impair immune function in marine top predators. These associations demonstrate the importance of continued monitoring for the possible effects of exposure to persistent environmental contaminants on the health status of marine mammals in UK waters, both in the context of their population viability and also as potential biomarkers of contaminant-related damage to marine ecosystems. Infectious disease mortality was rarely recorded in strandings of other cetacean species. Since 1995, nine stranded harbour porpoises (8 juveniles, 1 adult) had fatal traumatic lesions that were consistent with those first described in stranded harbour porpoises from the Moray Firth, Scotland and which have been attributed to lethal attack by bottlenose dolphins Tursiops truncatus. All nine of these harbour porpoises stranded within Cardigan Bay, West Wales. Harbour porpoises have a sympatric distribution with a resident population of bottlenose dolphins within Cardigan Bay. These findings represent the first evidence for this intriguing behaviour in bottlenose dolphins outside Scottish waters. During the period of this contract no mass mortalities of cetaceans or seals were reported from England and Wales. In addition, no cases of morbillivirus were diagnosed in any species during the period of this report. The results of the serological investigation for morbillivirus-specific antibodies provided an interesting insight into the prevalence and epidemiology of morbillivirus in cetaceans in UK waters. There was a very low prevalence of seropositives in harbour porpoises and common dolphins suggesting that morbillivirus is not endemic in these species within UK waters. Apart from one seropositive juvenile pilot whale, all seropositive cetaceans were adults in which morbillivirus- specific antibodies could be the consequence of an infection contracted during 1988-1990 when the last cases of fatal morbillivirus infection were diagnosed in cetaceans in the NE Atlantic. There has been a low prevalence of neoplasia recorded in cetaceans both during the period of this report and since the beginning of strandings research in 1990. Neoplasia is an important biomarker for the potential effects of exposure to carcinogenic environmental compounds such as radionuclides and some polycyclic aromatic hydrocarbons such as benzo-a-pyrene. It is well known that investigating threats to rare species is difficult and this is especially true with sparsely distributed free-living cetaceans. Our approach to this problem has been to use systematic post-mortem investigations to establish the cause of death and disease status of animals that have stranded on the coastline. This method has obvious limitations, the most important being that it is impossible to be sure that our observations accurately measure the true impact of threats, such as entanglement in fishing gear, infectious disease or toxic pollutants upon cetacean populations. Nevertheless, careful statistical analyses of the aggregated data between 1990-1999 have allowed us to draw some important conclusions about the relative importance of these threats and the need for future research. Between 1990-1999, 737 cetacean carcases from England and Wales were examined at postmortem. A cause of mortality was established in 563 of these animals. By far the most frequent cause of mortality was entanglement in fishing gear representing nearly half (48%) of cases where a cause of mortality was established. Statistical analyses showed that a greater number of harbour porpoise by-catches were juveniles rather than adults or neonates. This may indicate that immature individuals are more vulnerable to by-catch related mortality, and that a degree of learning may be involved in the avoidance of entanglement in fishing gear. Common dolphins and harbour porpoises diagnosed as by-catches were also typically in good health and nutritional status. By-caught porpoises were most frequently recorded in Wales, South-west England (Cornwall and Devon) and along the North Sea coastline from Northumberland to Humberside. In contrast, by- caught common dolphins were mainly recorded in South-west England. By-catch was also markedly seasonal within Cornwall and Devon with more porpoises and common dolphins stranding between January to April. This seasonal pattern of high by-catch related mortality in both stranded common dolphins and harbour porpoises within Cornwall and Devon may be due to factors such as seasonal changes in the distribution of these species and their prey or changes in fisheries effort. Future research should include continued monitoring of cetacean mortality using standard procedures on a European scale, investigations into interactions between fisheries and cetacean populations, genetic studies of population structure, and investigations into the importance of toxic contaminants as causes of immunosuppression and endocrine disruption in cetaceans. 1.