Fig 1.
Acoustic listening stations (blue dots), visual sightings of sperm whales (red dots) and study zones. The study zones (A, B, C, D) are delimited by black doted lines. The radius of the circles around the acoustic listening stations (overlapping pink circles) is 16.9 km, representing the estimated effective radius of detection for the mean sperm whale group size. The green triangle indicates the position of the fixed acoustic recording station Poseidon-Pylos. The cyan line indicates the limits of the Ionian Sea that we considered for estimating mean shipping density. The study zones are: Zakynthos Island and west Peloponnese (A), Cape Tainaron (B), Kythira Sea (C), Crete (D). Numbers indicate Greek locations mentioned in the text as follows. 1: Lefkada Island, 2: Pylos, 3: Kefallonia Island, 4: Zakynthos Island, 5: Strofades Islands, 6: Kythira Island, 7: Gavdos Island, 8: Cape Tainaron.
Table 1.
Summary of acoustic search effort and sperm whale detections.
Fig 2.
Data on year round presence of sperm whales along the Hellenic Trench.
Average number of days with sperm whales detected on the fixed PAL acoustic recorder. Values of n indicate the number of years with data for each month.
Fig 3.
Propeller marks on stranded and free ranging sperm whales along the Hellenic Trench.
(A) One of the recent cases of ship strike with a sperm whale that occurred along the Hellenic Trench on 15 February 2014, 25 km north of Pylos in SW Peloponnese. Three big cuts from a large propeller were apparent on this very freshly dead whale. (B) One of the live sperm whales photographed in 2004 along the Hellenic trench in SW Crete (catalogued with the name “Ifaistos”) bearing clear and deep marks from a ship propeller between the head and the dorsal fin. Photo credits (A): Filiatranet, (B): Chris Johnson.
Table 2.
Data on sperm whale strandings that occurred along the coasts neighboring the Hellenic Trench (HT) or other Greek coasts from 1992 to 2017 and had marks from a ship strike or could potentially be due to a ship strike.
Fig 4.
Average shipping density estimates against distance from terrestrial receiver on Zakynthos Island.
Fig 5.
Density of ship traffic reported through AIS transmissions and sperm whale sightings (red dots) from our surveys.
Opportunistic and independent survey sightings are not presented. (A) Density of all ship traffic, excluding fishing vessels. (B) Density of container ship traffic. Traffic to the SW of Crete north of Gavdos Island is mainly dominated by container ships heading to or from the eastern Mediterranean (ports to the east of Port Said and the Suez Canal) through the Strait of Otranto or Strait of Messina. (C) Density of Ro-Ro cargo traffic. The main route of concern for sperm whales is between the Strait of Otranto and the Aegean via Elafonisos Strait, north of Kythira Island. (D): Fishing vessel presence by time spent in each grid square. The scale for shipping density plots (A), (B) and (C) is in km-1year-1 and for plot (D) is in days.km-2.year-1. Numbers indicate Greek locations mentioned in the text as follows. 1: Lefkada Island, 2: Pylos, 3: Kefallonia Island, 4: Zakynthos Island, 5: Strofades Islands, 6: Kythira Island, 7: Gavdos Island, 8: Cape Tainaron.
Table 3.
Composition and statistics on traffic passing west of Kefallonia Island while heading to and from the Strait of Otranto.
Table 4.
Composition and statistics on traffic passing east of Strofades Islands before merging with traffic to pass west of Kefallonia Island while heading to and from the Strait of Otranto.
Fig 6.
Possible routing options to reduce risks to sperm whales.
Areas bounded by yellow lines would be avoided by vessels on the major routes. Density of ship traffic reported through AIS transmissions and sperm whale sightings (red dots) from our surveys as in Fig 5A. Areas bounded by green lines are the three legislated marine Natura2000 sites (Sites of Community Importance SCI) by the Greek Authorities in 2018 in order to protect cetacean habitat mainly. Numbers indicate Greek locations mentioned in the text as follows. 1: Lefkada Island, 2: Pylos, 3: Kefallonia Island, 4: Zakynthos Island, 5: Strofades Islands, 6: Kythira Island, 7: Gavdos Island, 8: Cape Tainaron.
Table 5.
Risk indices with the current and alternative (proposed) routing options that will avoid the two areas of sperm whale habitat as shown in Fig 6, together with the effort and data for each zone examined.
The four zones are shown in Fig 1.
Table 6.
Differences in distances for major routes with proposed new routeing options (nm stands for nautical miles).