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Steep Decline in Harbour Porpoise numbers in Blasket Islands SAC

Harbour Porpoise [Phocoena phocoena]

Harbour porpoise

Graph of Decline in Harbour Porpoise Population in Blasket Islands SAC

Graph of Harbour Porpoise population decline in Blasket islands SAC


Alarming decline in Harbour porpoise [Phocoena phocoena] population in Blasket Islands S.A.C. [Special Area of Conservation]. The reasons for the decline may be - prey redistribution; insufficient size of SAC for foraging ecology of harbour porpoises; inconsistent base survey transect lines from one survey period to another; competition from grey seals; fishing effort; excess marine traffic and speed throughout Blasket Islands SAC.

First, the flock of approx. 200 over-wintering Greenland White-fronted geese stopped coming to Beginish Island [now part of the Blasket Islands SPA [Special Protected Area for birds] in the late 1990's due to over-grazing by sheep - mainly lambs gathered from the Great Blasket island flock at the end of the summer put there to be fattened prior to transportation to the mainland for sale. This year, 2020, for the first time since the author can remember since 1975, none of the once 200 strong flock of Arctic terns came to breed on Beginish during the summer. again possibly due to interference by sheep and / or dogs and people. Now the once plentiful population of harbour porpoises in the Blasket Islands SAC, whose representative range of habitat is supposed to be protected by the European Habitats Directive, looks to be on the brink of collapse due to unsupervised activities in Blasket Islands SAC and SPA and lack of a Management Plan by the Irish designated authority - NPWS [National Parks and Wildlife Service] - again contrary to the Directive.

When we started our eco marine tours in Dingle Bay and around the Blaskets way back in 2001, Harbour porpoises were probably the species that we saw most, followed by common dolphins, bottlenose dolphins, basking shark [honorary cetaceans (!)], Minke whales, Risso's dolphins and one humpback whale, which was reflected in the statement made then that "The harbour porpoise is the most widespread and abundant cetacean species found in Irish waters" (Berrow 2001). Sadly, this is no longer the case as can be seen from the results of surveys below, undertaken on behalf of the NPWS, and the marine ecology of the Blasket Islands has totally changed with more humpback whales seen than harbour porpoises by a large factor and in all our eco tours of 2020 only a few regular harbour porpoise individuals were (rarely) seen and then they were outside the boundaries of the SAC and with no calves or juveniles or no large family groupings evident. This compares to humpback whale sightings when in August / September 2020 period we spotted  humpback whales on over 30 consecutive trips,- just outside the Blasket islands SAC - and no sightings of harbour porpoises within the SAC. Sighting frequency for cetaceans and basking shark for 2020 in order of most sighted species were - common dolphins, bottlenose dolphins, Minke whales, humpback whales, Risso's dolphins, basking shark, harbour porpoises and fin whales.

Our worry is that the harbour porpoise may follow the fate of the Greenland White-fronted geese and the Arctic terns in the Blasket Islands SPA and may soon be followed by the puffin in the outer Blasket islands SPA unless a Management Plan is put in place and NPWS Rangers deployed on a permanent basis (not sporadically as at present) to make sure that all users comply with guidelines to protect this unique but fragile marine ecosystem for the benefit of all and the protection of the marine wildlife in particular.

 Some Statistics from the Harbour Porpoise Surveys undertaken to date [ 2007 - 2018 NPWS]

From a brief study on the internet of available unpublished material by the NPWS harbour porpoise surveys in the Blasket Islands SAC from 2007 to 2018 it is evident that there is a  steady and steep decline in numbers from an estimated number of 372  ± 105 in 2008 to an estimated 60  ± 13 in 2018 and. as per calculations by the author from continuing the line on the graph of the survey results on the left-hand side of this article, an estimated projected total population number of 10  ± 3 by the time the next survey is due in 2022 or hopefully sooner!

Below is a  more detailed summary where 95% CI is 95% Confidence Interval and CV is the Coefficient of Variation

Surveys   Population Abundance Estimate in Blasket islands SAC    Publication

2007 (6)         303  ± 76  [95% CI: 186 - 494; CV = 0.25]                             Berrow et al. 2007  
2008 (3)         372  ±105 [95% CI: 216 - 647; CV = 0.28]                             Berrow et al. 2008
2014 (6)         146  ± 53  [95% CI:   41 - 516; CV = 0.36]                      O'Brien & Berrow 2014
2018 (6)           60  ± 3     [95% CI:    39 - 93;  CV = 0.22]                      O'Brien & Berrow 2018

Projected Harbour Porpoise abundance for year 2022 in Blasket Islands SAC based on predicted line on graph on left hand side of page:

2022                 10  ± 3   ( !!!)

This projected decline based on the previous data from the 4 previous surveys shows a projected decline in harbour porpoise numbers in the Blasket Islands SAC of 97% on 2008 surveyed population estimates, with the critical period of loss being in the period 2008 - 2014 with the numbers declining on a steady trajectory but at a lower rate (because of lower population densities?) since 2014

Suggested Reasons (5) for the decline of the Harbour Porpoise Population in the Blasket Islands SAC

1. In the Executive Summary of the Harbour Porpoise Survey Report 2018 carried out by O'Brien & Berrow 2018 for the NPWS the possible reason for the decline is suggested as being "a shift in the distribution of harbour porpoise this summer, probably associated with the distribution of their prey. The site is small in relation to the likely daily movements of these highly mobile marine mammals and even a small change in prey distribution could result in most prey occurring outside the boundaries of the SAC, resulting in low densities of harbour porpoises within the SAC. A better understanding of the ecology of harbour porpoises, including diet and foraging ecology, is required in order to interpret this decline in abundance".

The prey species of the Harbour porpoises may have spatially disappeared due to ecosystem and habitat degradation or being caught (the same effect) due to continuous unmanaged and unsupervised fishing effort in the SAC and its surrounds mainly for pollack (gill netting and "jigging machines") and pair trawling for sprat in the SAC and the surrounding Dingle Bay. This makes the case for the formation of a Management Plan for the SAC which includes the fishing effort and the enlargement of the SAC to MPA [Marine Protected Area] status, to include known Harbour porpoise "hotspots" outside the existing SAC area and which could also include the foraging grounds of humpback whales [recent welcome visitors since 2000] and Minke whales along the 100 meter depth contour from Ballydavid Head, north, west and south of the Blasket Islands and as far east as Parkmore Point, Ventry.

Until this further research into the foraging ecology of the harbour porpoises is carried out the Precautionary Principle should be applied to fishing efforts within the SAC and particularly pair-trawling by large trawlers for sprat which are unprotected as a no-quota species. Marine fish (apart from salmon and silver eels) and marine invertebrates are not protected by the Irish Wildlife Acts and the only protection that can be afforded to this valuable prey species (especially for seabirds and cetaceans) is by the creation of MPA's in up to 25%of Irish waters as is required by EU legislation.

2. The 2018 harbour porpoise survey carried out for the NPWS had different transect lines to the previous surveys carried out in the Blasket islands SAC and therefore it is difficult to draw a satisfactory statistical conclusion based on the results, as it is not comparing like with like, and the new transect lines of the 2018 survey missed known harbour porpoise "hotspots" within the SAC. The scientific reason for changing the transect lines for the 2018 survey is unknown to the author but one would hope that the next scheduled survey [2021, 2022 (?)] would revert back to the transect lines of the 2007, 2008, 2014 surveys in order to make valid statistical population estimates of decline in the harbour porpoise population in the SAC.

3. The Blasket islands marine SAC was designated with harbour porpoises and grey seals as qualifying interests in 2000 and since then the grey seal population has exploded and the harbour porpoise population has proportionally imploded as shown on the graph which is based on survey reports by the NPWS.
These two different marine mammal species are sympatric and frequently compete for the same food resource in the same marine habitat [Hernández-Milián 2014] with perhaps the harbour porpoises competing at a lower trophic level and targeting smaller individuals of the same fish species e.g. pollack or coley (black pollack or "blackjack"), haddock, whiting. Harbour porpoises specialise more in pelagic fish like herring, small mackerel, sprat and sand eels and grey seals specialise more in demersal species and flatfish and also sand eels.. But with the huge explosion in the grey seal population in the Blasket islands SAC, combined with an unmanaged fishery within the SAC and its immediate surrounds and the uncontrolled fishing of non-quota sprat by pair-trawling in Dingle Bay by large trawlers, competition for food resources in the Blasket islands SAC between harbour porpoises and grey seals must be intense with diminishing quantity and variety of prey species and on the law of averages the species that is higher up the trophic chain and also that outnumbers the "lower" species by a large factor would appear to be the winner in what has become an unbalanced marine ecological system. Grey seals have no natural predators like Killer whales or Great white shark in the Blasket Islands SAC [at the moment] and where formerly they were hunted and killed by islanders and fishermen, they are now a protected species. But this kilter in the local marine ecological balance may be having a detrimental effect on the harbour porpoise population which apart from showing a steep population decline corresponding to the increase in the grey seal population, is also showing a decline in sightings of family groups and very few, if any, sightings of juveniles or calves which is worrying as mature female harbour porpoises only have one calf per year.

It may not have happened yet in the Blasket islands SAC, but in the North Sea due to excess seal population growth and diminishing food resources due to over fishing - mainly sand eels -  grey seals have been reported as attacking and killing harbour porpoises, probably for the nutritional value of their blubber, in the south east area of the North Sea [Bouveroux et al. 2014; Haelters et al. 2012] so competition from grey seals for the same diminishing food resources (pollack, haddock, whiting, sand eels, sprat) must be seen as a factor in the decline of the harbour porpoise population in the Blasket islands SAC.

4. Fishing effort in and close to the SAC must also be taken into account both in respect of elimination or diminishing of harbour porpoise prey species  and also adverse interaction with various fishing methods often leading to death by strangulation, suffocation and drowning (Yes, harbour porpoises need to breath fresh air just like us!). The period of steepest decline in the population appears to have been the period from 2008 - 2014 and this may have been due to excessive gill netting and the use of "jigging machines" for catching pollack during that period. The uncontrolled and ongoing pair trawling for sprat was mentioned above already. The various fishing methods used may have a more detrimental effect on the harbour porpoise morbidity than the actual effect of diminishing the food resource.. Harbour porpoises and dolphins are a known bycatch of pair trawling methods for herring, mackerel and sprat but perhaps the most detrimental type of fishing method is the deployment of static bottom fishing gear - tangle nets for crayfish - often 7" mesh, multi monofilament nets, two fathoms deep, left on seamounts for days and sometimes over  a week and entangling all marine life in the vicinity including harbour porpoises who like to frequent this type of underwater marine habitat which is plentiful around the Blaskets.

An inclusive Management Plan for the Blasket islands SAC, including fisheries, should be able to address this issue but fishermen must be fairly compensated for any loss in fishing incomes as a result of complying with conservation measures in SACs and MPAs or it will never work properly and no stakeholder involved in preserving an SAC or MPA should be put at a loss financially. Farmers would not put up with it so why should the fishermen? The future for fishing in Ireland is an ecologically based fishery with the fisherman and the conservationist working together to create a richer more diverse and more plentiful marine ecosystem.

5. Like the explosion in the grey seal population around the Blasket islands, there is also an explosion in the numbers, type and speed of marine traffic around the Blasket Islands SAC and SPA in recent years and noticeably during the 2020 season. Fishing boats going at an average speed of approx. 8 / 10 kts. comprised most of the traffic until recently, with similar types of vessels and speed for the vessels bringing passengers to and from the Great Blasket Island from Dún Chaoin, Ventry and Dingle and on eco tours around the Blasket islands. However, a vessel steaming at 8 / 10 kts. at the moment would be left feeling almost stationary by speed boats travelling at 20 / 25 kts. to and fro all day long through the Blasket Islands SAC. This must be having a very detrimental effect on the harbour porpoise population also as these are characteristically shy, retiring creatures and the remaining "hotspots" for these shy marine mammals are along the land, east of the SAC from Ventry Harbour to Slea Head. A Management Plan, in consultation with all stakeholders, is urgently required as most of these vessels are eco tourism vessels and there is a danger of over-exploitation of the resource and the possibility of "killing the goose that lays the golden egg" in this case the "goose" being the wonderful but very fragile marine ecosystem. 

Just as there is a limit set on the number and frequency of boats allowed visit the Skellig rock UNESCO site in order to preserve the built heritage there it is time to do the same with the Blasket islands SAC in order to preserve the natural heritage there with all eco tours boats required to obtain a licence from the legislative authority to operate within the marine SAC [from NPWS]; a restriction on the number of boats allowed with restricted speed limits within the Blasket islands SAC [ 8 / 10 kts.] and further speed limits [ 6 kts.] and distance off [ 200 meters] at known hotspots of harbour porpoises [ Dunbeg fort to Slea Head and off Gob an Oileáin]; haul out locations foGrey seals [ An Trá Bán and Carraig Fhada]; and in the vicinity of the Puffin colonies at Inishvickillaun and Inish na Bró, and including the rafts of puffins on the water where young birds and unattached adult birds socialise and the non-breeding birds form juvenile relationships which are necessary for future breeding success as adults and also for adults who may have lost their mates.

Summary: Immediate need for Management Plan for Blasket Islands SAC & SPA

A conversation needs to start immediately between all the above stakeholders and the NPWS on how best to preserve the ecology of the Blasket islands SAC and SPA for future generations (including future generations of seabirds and marine mammals); possibly expand the area of the present marine SAC to an MPA and locate Wildlife Rangers and research personnel in a building on the Great Blasket Island to supervise all activities in the SAC as is normal in other jurisdictions with such a wealth of fragile and varied wildlife, and urgently publish and implement a Management Plan as is required by the EU legislation. With an increased (but still Insufficient) NPWS budget* for 2021 there is no reason why the Blasket Islands SAC and SPA could not support a world class multi-disciplinary marine research station, create more jobs in the green / blue economy and by implementing a strict but fair boat quota and speed regime for eco tours boat operators ensure a long term future and a sustainable model rather than the "boom and bust" (fishing model) and "free for all" type of activity that is presently putting the fragile marine ecosystems at risk, in particular for harbour porpoise numbers and potentially interfering with the breeding patterns and success of the puffin colonies on Inishvickillaun and Inish na Bró.

* [The NPWS budget for 2020 at €19 million was the same amount as that dedicated for Irish Greyhound Racing for 2021 and although the NPWS budget was increased to €29 million for 2021 is still very far short of the approx. €100 million  required to adequately protect, conserve and enhance Ireland's biodiversity and wildlife habitats. By contrast in the October 2020 budget by a Fianna Fáil / Fíne Gael / Green Party coalition government €96 million was given to the Horse and Greyhound Racing Fund and €52 million to Bord Bia to market the beef and dairy industry internationally which industries are largely responsible for Ireland's continuing loss of biodiversity and wildlife habitats and increasing greenhouse gases.]

The first step on this journey should be the drawing up of a Management Plan by the NPWS for the Blasket Islands SAC and SPA and consultation with all relevant stakeholders, and the implementation of the protective measures for wildlife in the Plan by a dedicated Wildlife Ranger team as is normal in other jurisdictions which may not even enjoy a fraction of the rich variety of marine, terrestrial and avian wildlife that we have here in the wonderful Blasket islands SAC and SPA but which is already showing visible signs of over-exploitation and deterioration due to lack of protective measures and the implementation of a Management Plan.

Log of the whale watching tour boat M.V. "Blasket Princess"      01.01. 2021

Captain Whales Galore   (still in lockdown obviously)

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