Entanglement of Pinnipeds in Synthetic Materials at South-east Farallon Island, California, 1976–1998
Introduction
Entanglement in synthetic marine debris has been reported for many pinniped species (Bonner, 1982), and is thought to have contributed to population declines in the depleted Northern Fur Seal, Callorhinus ursinus (Fowler, 1987), as well as the endangered Hawaiian Monk Seal, Monachus shauinslandi (Henderson, 1990). In a survey for human-made debris at sea, Day et al. (1990) encountered thousands of items of debris, but few entangled marine mammals. Due to difficulties in monitoring marine mammal interactions with deployed fishing gear or entangled pinnipeds at sea, observational records of entangled marine mammals at haul out sites provides one of few insights into problems and threats to pinniped populations and sources of synthetic materials that entangle pinnipeds.
Stewart and Yochem, 1987, Stewart and Yochem, 1990 documented entanglement for pinnipeds hauled out at San Miguel and San Nicolas Islands in Southern California, 1983–1988. They noted an increase in the proportion of entangled California Sea Lions (Zalophus californianus) and Pacific Harbor Seals (Phoca vitulina richardsi), and a decline in entangled Northern Elephant Seals (Mirounga angustirostris). Heneman (1985) reported on 13 California Sea Lions and three Northern Elephant Seals observed entangled in synthetic material at South-east Farallon Island (SEFI), 1979–1983. Otherwise, there are no published reports of entanglement of free-ranging pinnipeds in Northern California.
This report summarizes trends of pinnipeds entangled in synthetic material and types of entangling material for 914 pinnipeds hauled out at SEFI, 1976–1998. Findings are compared to those of earlier studies and the potential impact of synthetic materials on pinniped populations in Northern California is considered.
Biologists of the Point Reyes Bird Observatory have surveyed and studied flora and fauna at SEFI (37°42′N and 123°00′W) year-round since 1969. Pinnipeds which routinely haul out on the island include California Sea Lions, Northern Elephant Seals, Steller Sea Lions (Eumetopias jubatus), and Pacific Harbor Seals (Sydeman and Allen, 1999). Small numbers of Northern Fur Seals and Guadalupe fur seals (Arctocephalus townsendi) have been observed hauling out more frequently in recent years Hanni et al., 1996, Pyle et al., in review. Data collection efforts were conducted in a standardized manner with generally consistent daily observation effort focusing on the vertebrate ecology (DeSante and Ainley, 1980). Efforts included weekly surveys of pinnipeds hauled out at SEFI, weather permitting. Species, age, and gender of animals surveyed were recorded when possible according to the criteria of Huber et al. (1985). Entanglement or evidence of entanglement based on typical open wounds or constrictions around an animal’s neck (Nakajima et al., 1990) were noted during surveys or daily routine biological work around the island. Information about each entangled animal was logged daily in the species journal by island biologists. When animals were accessible, and it would not disturb other hauled out animals, attempts were made to remove entangling material using a 3/4 in. thick 3 m long metal pole with a curved boat hook attached to the proximal end. One side of the hook was ground flat and two holes approximately 2 cm apart were drilled in the hook. A razor blade was affixed with small screws and bolts through the holes such that the blade spanned the inside curve of the hook. Species, date of observation, age, gender, entanglement type, and weekly census totals were collated from the SEFI species daily journal for analyses. Resighted animals were excluded from analyses.
Types of entanglement included: (i) monofilament – line, net, or unknown (type not specified or identified); (ii) trawl – a heavy, corded fishnet material; (iii) unknown fishnet material; (iv) salmon flasher (approximately 3 × 6 in. silver lure); (v) fish hook; (vi) packing strap; (vii) other – miscellaneous marine debris; and (viii) constriction (no material observed, but a circular indentation present around head, neck, or torso).
Entanglement type by year and total entangled by age-class were summarized for each species. Interannual trends in entangled pinnipeds at SEFI for the years 1981–1998 were analyzed using linear regression (Seber, 1977). To assess the trend of numbers of entangled animals in relation to the total number of pinnipeds hauled out at the island (as an index of population size), regression analyses for each species included annual means of the monthly counts for that species. Too few or no records of entanglement for Pacific Harbor Seals, Northern Fur Seals and Guadalupe fur seals existed for statistical analyses. Analyses were considered significant at p<0.05. Results are interpreted cautiously due to potential confounding by numerous factors, including observer bias, variation in pinniped haulout patterns, the variety of ways in which pinnipeds may become entangled in synthetic materials, and the possibility that some records were actually resights of the same animal over time.
Section snippets
Results and Discussion
From 1 January 1976 to 31 December 1998, a total of 914 pinnipeds were observed with evidence of present and past entanglement in a variety of debris (Table 1). Of these, 296 (32%) were entangled in observed material, while 618 (68%) had constrictions.
For the study period, 820 California Sea Lions showed evidence of entanglement in synthetic material, 105 (13%) were entangled in monofilament, 594 (72%) had neck constrictions, and 32 (4%) were entangled in a variety of other marine debris,
Acknowledgements
We thank D. G. Ainley for overseeing the initiation of data collection, the work of the many SEFI volunteers, and biologists R. P. Henderson, H. R. Huber, W. J. Sydeman, R. J. Boekelheide, H. R. Carter, and S. D. Emslie. Research was conducted at the Farallon Islands National Wildlife Refuge under permitting authority of the US Fish and Wildlife Service, Newark, California. This is PRBO contribution #926.
References (23)
- Bonner, W. N. (1982) Seals and Man: A Study of Impacts. University of Washington Press,...
- Bonner, W. N. and McCann, T. S. (1982) Neck collars on fur seals, Arctocephalus gazella, at south Georgia. British...
- Barlow, J., Baird, R. W., Heyning, J. E., Wynne, K., Manville II, A. M., Lowry, L. F., Hanan, D., Sease, J. and...
- Day, R. H., Shaw, D. J. and Ignell, S. E. (1990) The quantitative distribution and characteristics of marine debris in...
- DeSante, D. F. and Ainley, D. G. (1980) The avifauna of the South Farallon Islands, California. Studies in Avian...
- Fowler, C. W. (1987) Marine debris and fur seals: a case study. Marine Pollution Bulletin 18,...
- Hanni, K. D., Long, D. J., Jones, R. E., Pyle, P. and Morgan, L. E. (1996) Observations of range, diet, and causes of...
- Henderson, J. R. (1990) Recent entanglements of Hawaiian monk seals in marine debris. In Proceedings of the Second...
- Heneman, B. (1985) Records of pinniped entanglement in fishing gear at South-east Farallon Island. In Proceedings of...
- Huber, H. R., Beckham, C., Nisbet, J., Rovetta, A. and Nusbaum, J. (1985) Studies of marine mammals at the Farallon...
Cited by (62)
Entanglement of Steller sea lions (Eumetopias jubatus) in man-made marine debris on Tyuleniy Island, Sea of Okhotsk
2022, Marine Pollution BulletinCitation Excerpt :Very few studies addressed the issue of SSL entanglement in the western part (Russia, west of the Commander Islands) of the range, and the available information is extremely fragmentary (Kuzin, 2002; Altukhov et al., 2012; Ryazanov and Permyakov, 2021). This issue has been studied more in detail for the eastern part (east of the Commander Islands) of the range (Loughlin et al., 1986; Hanni and Pyle, 2000; Raum-Suryan et al., 2009; Allyn and Scordino, 2020). Data on injuries caused by man-made debris and their consequences can be used as an additional source of information to find the causes responsible for the decline in the number of SSL almost throughout the species' range.
Entanglement of Cape fur seals (Arctocephalus pusillus pusillus) at colonies in central Namibia
2021, Marine Pollution BulletinCitation Excerpt :The discrepancy between the overall proportion of packaging strap in the entangling records (10%) and that causing very severe entanglement (27%), indicates this material is likely to cause impact over a longer duration to the affected animal. Our results support the growing body of research demonstrating the impact of waste plastics (De Stephanis et al., 2013; Gall and Thompson, 2015) and most notably fishing gear on the wellbeing and health of wild animals (Hofmeyr et al., 2002; Campagna et al., 2007; Hanni and Pyle, 2000). At both colonies, fishing gear was the primary entangling material of Cape fur seals, and juveniles were most commonly affected.
Plastics in marine ecosystem: A review of their sources and pollution conduits
2021, Regional Studies in Marine SciencePrevalence of entanglements of seabirds in marine debris in the central Portuguese coast
2020, Marine Pollution BulletinSize-dependent elimination of ingested microplastics in the Mediterranean mussel Mytilus galloprovincialis
2019, Marine Pollution BulletinTools and constraints in monitoring interactions between marine litter and megafauna: Insights from case studies around the world
2019, Marine Pollution BulletinCitation Excerpt :The Marine Mammal Health and Stranding Response Program of NOAA have recently made available a human interaction form that does provide a check box for debris which should aid researchers in their assessments of marine debris occurrence. In seals, marine debris entanglement is expected to result in death of those affected because they cannot remove the entanglement themselves (Fowler, 1987; Hanni and Pyle, 2000; Campagna et al., 2007). Materials entangling Australian fur seals (AFS) Arctocephalus pusillus doriferus are varied but predominantly consist of commercial and recreational fishing material (Lawson et al., 2015; McIntosh et al., 2015).