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No Safe Harbour For Cape Fur Seals

Canada's government has a long history of funding and promoting the commercial seal 'hunt'. The government agency responsible for managing the seal 'hunt', the Department of Fisheries and Oceans, has a history of using seals as scapegoats when they failed to manage fisheries well. Read more about the government's role in sealing.

No safe harbour for Cape fur seals

Atlantic Canadian off-season fishermen choose to go off seasonal unemployment insurance early to kill harp seal pups for their fur. But there's more to it than this. Politics and scapegoating seals are factors, too. Read more about the Canadian seal 'hunt' here.

Harbour seals (Phoca vitulina) and grey seals share habitats in the North Sea and there is evidence of direct competition between the two apex predators for certain resources26,27. Harbour seals tend to inhabit coastal waters more exclusively28, whereas grey seals also forage offshore to a large extent29. Haul-out sites and foraging areas can overlap with regional differences27,30. Whereas the number of grey seals in German waters is still increasing through recolonisation after local declines in the past (6,538 counted in 2019)31,32, the number of harbour seals remains stable (27,763 counted in 2019)32,33. Mass mortalities caused by phocine morbillivirus and avian influenza virus (H10N7) had detrimental effects on the harbour seal population34,35,36. The grey seal population seemed to be less affected, although it may have functioned as a vector for these pathogens37,38. Septicaemia with β-haemolytic streptococci and/ or E. coli is an important cause of death of adult harbour seals from German waters, which in many cases is the result of major pathologies such as gastritis, intestinal volvulus or mastitis. Active cannibalism among grey seals, also in the North Sea, has been previously reported39,40,41,42. Predation on other marine mammals, including harbour seals, adds to this aggressive behaviour and might represent a feeding strategy43,44,45.

Forced mating attempts and even successful copulations between male grey seals and harbour seals have been observed, albeit it is not reported whether or not the affected victims suffered from injuries or even died21,46. Young adult male grey seals have been witnessed to engage in interspecific mating attempts on the Island of Helgoland in the German North Sea, but related genital injuries or abortion were not documented43. This case series from the Wadden Sea for the first time describes morphological and molecular findings in pregnant female harbour seals after copulation with a male grey seal with subsequent fatal septicaemia, likely due to genital lacerations.

DNA-extraction and PCR of five formalin-fixed, paraffin-embedded (FFPE) genital tract specimens of the three animals with histologically visible spermatozoa (nos. 8, 9, 11) revealed grey seal DNA in all samples (Fig. 5). All control samples of harbour seals, including non-reproductive tract organ samples of harassed animals, as well as the reference samples of the seals, were negative for grey seal DNA.

The presented fatal cases of 11 adult, female harbour seals could be traced back to interspecific copulation with a grey seal bull via detection of spermatozoal structures in the female reproductive tracts as well as grey seal DNA verification. Pathological changes seen in the genital tracts included haemorrhagic or suppurative vaginal discharge, genital lacerations and abortion. Death occurred due to septicaemia with β-haemolytic streptococci. The narrow period, within which the strandings happened, coincided with the breeding season of grey seals in the North Sea. As such incidences have not been reported before in the Wadden Sea area, they provide new insights into interspecific interactions between the two native seal species.

Furthermore, it is exceptional that only females were affected that were either pregnant or at least demonstrated a recent pregnancy. This fact also doubles the death toll to potentially 22 animals in the context of this event. In contrast to the winter breeding season of grey seals, the pupping season of harbour seals in the Wadden Sea starts in June48. Both, the pregnancy as well as the season allows the assumption that the female harbour seals themselves were not interested in mating at this point.

Along the coastline of Dithmarschen, there are several sandbanks close to the shore, where harbour seals haul out routinely and grey seals are known to visit these occasionally. Seals are generally polygamous and depending on the group size, the sex ratio and the social system, different aggressive mating strategies can develop53,56,57,58,59. Injuries during interspecific interactions become more likely if there is great disparity in size and weight52. This is also reported for the here involved species, as a juvenile or young adult grey seal bull can easily over-power and subdue a female harbour seal25,26,60. The behavioural response of the female during mating is important for the stimulation of the male. If the female is incompatible, juvenile, seriously injured, or dead, the response may be inadequate and could result in multiple mountings and/ or longer mating attempts11,19. In the presented cases, vaginal discharge and a swelling of the vulva in some cases were the only external lesions.

The lacerations of the uterus in two of the presented cases, as well as the dislocation of the foetus into the abdomen could not be explained by penile penetration alone, although the vaginal anatomy of harbour seals indicates that the depth of penetration depends only on the length of the penis22. In the case of a male elephant seal (Mirounga leonina) mounting female cape fur seals (Arctocephalus pusillus), it was observed that the weight of the male forced out the females intestines through the anogenital region20. Even a juvenile male grey seal can outweigh a female harbour seal28,29, but it remains unclear whether the mounting of pregnant females alone can lead to lacerations in the reproductive tract. Rupture of the gravid uterus is reported to be a rare event, and is often associated with severe abdominal trauma or fragility of the uterine wall due to infections or previous operations59. In the reported cases, it cannot be excluded that ascending infections or sepsis led to structural weakness of the uterus with secondary rupture. Since there were no observations of the encounters in the described cases, the extent of violence during the mating attempts and their possible contribution to the genital trauma, as seen in other cases11,19, cannot be assessed.

Grey seals are known to engage in inter- and intraspecific interactions, including predation43, cannibalism39,40,41,42 and forced sexual intercourse21 with harbour seals in the wild. The present study is the first one reporting fatal interspecific mating attempts of at least one male grey seal with pregnant harbour seals in the German Wadden Sea. It remains unclear if the described cases are an exception caused by one individual on a local scale. Therefore, future post-mortem investigations should always include a precise examination of genital tracts of harbour seals especially during the grey seal mating season.

Besides predation, sexual coercion appears to be another phenomenon by which grey seals negatively impact harbour seals. Apparently, especially juvenile males without access to fertile females display such behaviour. Due to missing or failing defensive behaviour, disparity in size and aggressive mating strategies, these encounters can be fatal for female harbour seals. The presented cases show that pathological indicators of sexual coercion in harbour seals may be haemorrhagic or suppurative vaginal discharge, genital lacerations and abortion. Spermatozoa may not always be detectable, but can serve as a valuable indicator of lesion genesis and can help in identifying interspecific encounters.

A little further on, I saw the sign Ship Wreck South West Seal and so I turned off in the direction of the coast. The first road seemed impassable and when I looked closer I saw that the road curved to the right. There I drove on until I thought I got stuck in the beach. Then I turned to go back inland a little, and parked the car where it seemed safe to do so. I started to walk, the weather was quite good at the time and the atmosphere is special on the Skeleton Coast. I saw some dead fur seals lying around and parts of ships sticking out of the beach. Also in the surf you could see something sticking out of the waves, more stranded ships.

During a seal watching tour off the coast of Walvis Bay, Namibia, kayakers on vacation were treated to a passing group of cape fur seals frolicking in the water. Video taken by Mikhail Samon and his wife show the animals jumping in and out of the water until one ill-fated frolic results in a seal colliding with the kayak.

The behavior that led to the collision is known as seal "porpoising," in which they jump in and out of the water while moving at high speeds. Curious and playful by nature, the seals were likely trying to get a better look at the kayakers moving through their natural surroundings. Seals can be wary of humans on land, but in the water, where they are more adept at making quick escapes, they commonly approach people and boats.

Seabird populations experience predation that can impact their breeding density and breeding success. The Cape gannet Morus capensis is endemic to the Benguela upwelling ecosystem and is classified as Endangered by the IUCN. They are affected by several threats, including predation by the Cape fur seal Arctocephalus pusillus pusillus. Many fledglings succumb to predation during their maiden flight across waters around the island. To curb predation, the selective culling of individual predatory seals was implemented in 2014, 2015, and 2018. Our first study objective was to determine if selective culling of Cape fur seals significantly reduced predation probability on Cape gannets. We tested whether predation probability in 2014, 2015, and 2018 was affected by fish biomass, gannet fledgling numbers, and/or the presence/absence of selective culling. Our second objective was to determine what led to fluctuations in Cape fur seal predation on Cape gannet fledglings between 2007 and 2018. We tested whether fish biomass and the amount of Cape gannet fledglings in the water affected predation probability on the fledglings. Results indicated that selective culling reduced predation within years. We found that with both increased fledgling numbers and increased fish biomass, seal predation probability was reduced. This suggests that a sustainable way to promote the conservation of Cape gannets would be to increase food availability for both the Cape fur seals and Cape gannets. Our findings, collectively with the global trend of the declining Cape gannet population and their endemism, provide reasons advocating for the conservation of the food resources of both the Cape fur seal and the Cape gannet in the Benguela system. 350c69d7ab


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