Did the pile driving during the construction of the Offshore Wind Farm Egmond aan Zee, the Netherlands, impact porpoises?

The Dutch consortium "NoordzeeWind" has built the first offshore wind farm in Dutch North Sea waters, known as "Offshore Wind farm Egmond aan Zee" (OWEZ) Part of the construction works consisted of driving 36 monopiles into the sea floor, during April-June 2006. The noise levels that attended this activity may have been detrimental to marine life forms. Cetaceans in particular are sensitive to very high noise levels and a possible impact on the most abundant cetacean living off the Dutch coast, the harbour porpoise was therefore studied. Direct observations were hard to conduct, given the low (summer) densities of porpoises around the construction site. Pathological observations on stranded specimen failed to produce clear results. Inner ears of freshly stranded porpoises were examined for possible damage, but before necropsies could be conducted the animals had been stored frozen and this had destroyed any visible signs of noise-induced damage to the inner ear. Thus, the spatiotemporal pattern of porpoise strandings was examined. Porpoises did not strand in higher numbers on the coastal stretch directly east of the construction site, or to the north-east of this location (downstream) compared to other parts of the country. Porpoises also did not strand in higher than expected numbers near the construction site, at the time of construction. It was therefore concluded that the construction did not lead to visibly increased mortality of harbour porpoises. In retrospect this might have been expected, given that densities of porpoises are normally very low in summer at the site, that the building process is noisy anyway, scaring porpoises off (to safe distances) before the actual pile driving commences. A ramp-up procedure and usage of a pinger further helped to ward off porpoises from the site, before full-power pile driving started. These factors combined (timing and high before-pile driving noise levels) made it very unlikely that porpoises got in harm’s way during the construction of OWEZ

The <i>Tricolor</i> oil spill: characteristics of seabirds found oiled in The Netherlands

Between 28 January and 9 February 2003, c. 4000 heavily oiled seabirds washed ashore in The Netherlands, representing 21% of c. 20,000 casualties of the Tricolor oil spill recovered in northern France, Belgium and The Netherlands. Common Guillemot Uria aalge, Razorbill Alca torda and Black-legged Kittiwake Rissa tridactyla together represented 91% of the birds found and collected. Nearly 600 Common Guillemots and 267 Razorbills were examined in more detail and a large part of these birds were dissected. Autopsies revealed that the auks were in excellent condition when they died, indicating instant death through suffocation in oil. Of 440 Guillemots that could be aged, 76% were mature birds, with a sex ratio significantly different from equal (65% males). Of 262 Razorbills, 77% were adults and 62% were males. Biometrics suggested that the Guillemots belonged to the nominate subspecies, whereas the Razorbills were classified as A.t. islandica. Using the European cline in wing length, the Guillemots possibly originated from Scottish colonies (57°N), a finding that was supported by ringing recoveries (Scottish east coast). The total mortality caused by the Tricolor spill, 2-5 times the number of casualties recovered, may be estimated at 40 000-100 000 seabirds (25 000-62 500 Guillemots, 8000-20 000 Razorbills). With such a high proportion of mature birds in excellent pre-breeding condition being killed, an immediate effect on the breeding population is foreseen, rather than a diffuse and delayed effect if more immatures would have been killed. It is argued that effect of the Tricolor on seabirds would have been considerably less, had the salvage operation be postponed till summer. The Channel area is of the highest vulnerability to oil pollution only in winter (Dec-Mar)

Bruinvisstrandingen in Nederland in 2006: achtergronden, leeftijdsverdeling, sexratio, voedselkeuze en mogelijke oorzaken

Bruinvissen komen in steeds grotere aantallen voor in de Nederlandse (kust)wateren. In de periode 1960␂ 1985 was de bruinvis vrijwel uitgestorven in Nederland, maar de soort heeft een spectaculaire comeback gemaakt. Terwijl het aantal waarnemingen sterk toenam werd er ook een toename gevonden in het aantal dieren dat dood op de kust aanspoelde. In september 2006 werden 64 bruinvissen onderzocht die eerder dat jaar dood op de Nederlandse kust waren aangespoel

Did the pile driving during the construction of the Offshore Wind Farm Egmond aan Zee, the Netherlands, imapct local seabirds?

In this study, possible effects on sensitive seabirds are considered. Bird species most likely to be vulnerable to underwater sound are those that forage by diving after fish of shellfish. Diving birds that may occur in relatively high densities at the OWEZ location include auks, and possibly divers and seaduck. Terns, that feed by shallow dives are considered less vulnerable and mostly occur closer to the mainland coast. Several gull species may occur in the area in high densities, but they feed at the surface only, and are considered the least vulnerable. Pile driving took place from 17 April to 28 July 2007. The potentially vulnerable divers, seaduck and auks had largely left the area by the time the pile driving started. Migration commenced early in 2006 and any birds still left in the area by mid-April would have been scared away by the shipping activities long before actual pile driving started. Further mitigation of possible effects on sensitive seabirds included a ramp-up procedure that ensured that full hamming power was only administered after a period of low-energy blows that were unlikely to cause lethal effects on any birds still present. Furthermore, an underwater pinger, aimed at scaring off marine mammals, was put into operation 3-4 hours before pile driving started. Visual observations before and during three pile driving sessions failed to detect any of the seabirds deemed sensitive to pile driving noise in the vicinity of the construction work. Birds that did fly by the construction site (mainly gulls and terns) did not show a noticeable reaction to the activities. It is therefore concluded that effects of underwater noise on seabirds, though potentially detrimental, were negligible during construction of OWEZ. This was due to fortunate timing of the work and to appropriate mitigation measures